NWL Troubleshooting Guide

ESPControls & Electrical Systems

TroubleshootingGuide

ContentsIntroductionSection IConcepts and Terminology: Power Sources forElectrostatic Precipitators 1

Abstract 2Overview 2The Current Limiting Reactor

(CLR) 5The Transformer Rectifier (T/R) 9The T/R Controller 23

Section IITroubleshooting Tips 33

The “Lamp Test”—A Simple Means for Testing T/Rs 34

What Meter Readings Can Tell You When Troubleshooting Transformer Rectifiers (T/Rs) 40

Recommended Practice: Oil Integrity Testing 43Mineral Oil Filtering

Procedure for Transformer Rectifier (T/R) Sets 47

© 1998 NWL312 Rising Sun Road

Bordentown, NJ 08505 USA609-298-7300

All rights reserved under Pan-American Copyright Conventions.

Published in the United States by NWL

Bordentown, NJUnauthorized reproduction of this book

is forbidden by law.

Library of Congress Catalog Card Number98-091393

DISCLAIMER: The information in this booklet is for reference only. Neither NWL, nor any of its divisions,makes warranties, expressed or implied, concerning theapplication or use of this information.

IntroductionA Portable InformationalResource on ESP Controlsand Electrical Systems Competitive pressures on the utility industry man-date doing more with less—fewer (and younger)maintenance personnel, tighter budgets and less timeto effect solutions to electrostatic precipitator controlsystem problems. Yet, in the utility industry, pollu-tion control remains as critical as ever. While thereare a number of good resources available on the the-ory and operation of electrostatic precipitators(ESPs)—The Art of Electrostatic Precipitation, firstpublished November 1, 1979, immediately comes tomind—there has not been a good book that provideshelpful diagnostic sequences one can use to dealwith day-to-day ESP electrical control problems.

Until now.Welcome to NWL’s ESP Controls & Electrical

Systems Troubleshooting Guide. Organized into foursections, this handbook is designed to give mainte-nance essential, critical troubleshooting informationin an easy to read and understand format. Towardthat end it contains:

• Quick overviews of key terms and concepts

v

Contents (continued)

Section IIIEquipment Troubleshooting 51

Electrical Systems (overall) 52T/R Set 54T/R Controller 56Rapper Controller 58Meter Readings Low 60Back Corona 62Opacity Spikes 63

Section IVIndex 65

Glossary of Air Pollution Control and ESPTerminology 66

Clean Air Act Amendments 108Conversion Factors Metric

Equivalents 109Altitude-Pressure Temperature

Density Table of Air 111Title III

Hazardous Air Pollutants 113

iv ESP Troubleshooting Guide

Having designed and built more than 10,000 T/Rsover the past ten years, NWL can provide both fieldservice and shop repair of almost any ESP T/R. Ourrepair group—with dedicated facilities and invento-ry—is extraordinarily responsive to equipment-repair needs, providing one-to-four week turnaroundon most repairs.

Preventive maintenance is, of course, the mostcost-effective way to deal with problems—beforethey occur. In fact, many T/R failures are oftencaused by process and system changes that can onlybe truly evaluated on-site. Our trained techniciansand engineers may also be called upon to evaluateT/R and control-system performance under actualoperating conditions.

Finally, if you have questions you would likeanswered in future editions of this Guide, pleasecontact us. We stand ready to help meet your pollu-tion control equipment diagnostic and preventivemaintenance needs.

Introduction vii

along with descriptions of two critical compo-nents: the Current Limiting Reactor (CLR) andTransformer Rectifier (T/R).

• Practical, easy to use troubleshooting tips.• Equipment diagnostic “decision trees” for deter-

mining the cause of malfunctions among suchequipment as T/R Sets, T/R Controllers, andRapper Controllers and poor electrical perfor-mance indicated by low meter readings, backcorona and opacity spikes.

The troubleshooting decision trees follow a sim-ple “yes-no” question format to make getting to theroot causes of problems quickly. In short, whetheryou are new to the field or an old hand, the Trou-bleshooting Guide offers a wealth of informationright at your fingertips—including a helpful index.The index contains important ESP terminology,glossary of air-pollution control terms, listing ofClean Air Act Amendments as well as useful metricand altitude-pressure temperature density tables,along with a listing of Title III hazardous air pollutants.

As you can well imagine, it would be impossibleto cover every imaginable potential problem withinthe confines of a short pocket book such as this one.As a result, we have only focused on those ourexperience shows to be most common and critical.

Please feel free to call our technical staff if youhave troubleshooting issues not covered in the con-fines of this guide—whether the equipment wasmade by NWL or not. If required, we can also offerexpert field-service diagnostics, repair and replace-ment equipment.

vi ESP Troubleshooting Guide

CONCEPTS AND TERMINOLOGY:

Power Sources For Electrostatic Precipitators■ Abstract

■ Overview

■ The Current Limiting Reactor(CLR)

■ The Transformer Rectifier(T/R)

■ The T/R Controller

SECTION I

viii ESP Troubleshooting Guide

the Voltage Control System which is a major sub-assembly of the control cabinet. The term AutomaticVoltage Controller or AVC is commonly used whenreferring to the control electronics of the system.

The control cabinet accepts a line feed that is typ-ically 480AVC and provides an output that is aphase angle controlled power source for the system.Phase angle control is established through the use ofsilicon controlled rectifiers (SCRs). The level ofpower delivered to the system is a complex functionof set points and feedback signals.

The major components of a typical control cabi-net include the Automatic Voltage Control System,the SCR system, panel meters, illuminated indica-tors and a circuit breaker.

The current limiting reactor is an iron core induc-tor that serves to limit current surges in the systemand to provide “wave shaping” of the T/R primarycurrent. The electrical rating and physical size forthe CLR varies widely for different size systems and

Concepts and Terminology 3

AbstractThe purpose of this section is to provide a summaryof technical terms and concepts that are generallyemployed in the field of commercial electrostaticprecipitation. The descriptions provided are limitedto the components and concepts associated withproviding electrical energy to the precipitator. Thissystem of components shall be referred to as theESP Power Supply.

OverviewThe purpose of the power supply for an electrostaticprecipitator (ESP) is to provide a source of highvoltage for the discharge electrodes of the system.The power supply must accept incoming voltagethat is available from the plant; typically 380VAC to690VAC single phase and output voltage levelsfrom 45KVDC to over 100 KVDC. The amount ofelectrical current delivered by the power supply is afunction of the size and load of the ESP field. Cur-rent levels from 500 maDC to 1500 maDC are typi-cal for industrial applications.

The dynamic nature of the ESP load imposessevere stress on the power supply system due to therequisite sparking and arcing that occurs within theESP field. The power supply must be capable ofsensing these disruptions and then be capable ofaltering its output to clear these disruptions whilemaximizing the efficiency of the ESP field.

The four major components of the systeminclude: the Control Cabinet, the Current LimitingReactor (CLR), the Transformer Rectifier (T/R) and

2 ESP Troubleshooting Guide

Figure 1 ESP power supply main components

Line in Typical 480 VAC 1 Phase

Current LimitingReactor (CLR)

Control Cabinet Voltage Control System

To ESP DischargeElectrode Field

Transformer Rectifier (TR)

The Current Limiting Reactor (CLR)A. Physical LocationThe Current Limiting Reactor (CLR) is a largeinductor that is used in the primary circuit of theT/R. The purpose of the CLR is to limit the maxi-mum current in the T/R primary and to provide ameans of shaping the wave form of the Power Sup-ply output. The CLR can be physically locatedinside the T/R tank, inside the T/R junction box orin a separate free standing enclosure. The choicesfor locating the CLR are primarily economically dri-ven for systems below 200 amps. At currents above200 amps, the heat generated by the CLR usuallymakes the choice of a separate enclosure mandatory.

B. InductanceThe unit of measure for reactors is the henry. Theability of a reactor to impede the flow of AC currentis termed inductance. The inductance of CLRs isusually from 5 to 20 millihenries (.005H to .020H).The CLR value that is required is based upon thetotal system impedance that is desired for the powersupply. This system impedance limits the maximumamount of current that can flow in the primary cir-cuit and is usually specified as percent impedance.A value of from 30% to 50% is usually employed.The impedance of the reactor can be calculated by:

Zclr = L x (2 x π x f) = L x 377where Zclr = impedance in ohms

L = inductance in henriesπ = 3.1415


varied applications. For smaller systems, the CLRmay be either mounted inside the control cabinet, inan attached enclosure to the T/R, or inside the T/Roil tank. Large systems usually include a separatestand-alone enclosure for the CLR.

The Transformer Rectifier accepts a phase anglecontrol feed signal typically up to 575VAC anddelivers a high voltage Direct Current (DC) voltageto the ESP. Average output voltages for T/Rs rangefrom 55KVDC to over 100KVDC. T/Rs are oilfilled assemblies that house a step-up transformerand a high voltage rectifier system. In addition, theT/R provides feedback signals to the control elec-tronics (AVC) to permit spark detection, waveformanalysis and metering for operator readout. The T/Rassemblies are usually mounted on the top of theESP and use pipe and guard systems for distributingthe high voltage power to the emitter electrodes.

The Automatic Voltage Controller (AVC) mountsinside or on the door of the control cabinet. ModernAVCs are microprocessor based systems availablefrom a variety of vendors. The AVC accepts feed-back signals from the T/R as well as feedback sig-nals from components in the control cabinet. Theprimary output signal of the AVC is a signal that isused to control the firing angle for the SCRs withinthe control cabinet. The AVC continuously adjuststhe firing angle to achieve the desired performancefor the ESP field. Modern AVCs are usuallyequipped with digital readout, keypad operator entrysystem and a communication link for remote controland monitoring.


CLR nor the T/R can withstand such current for anylength of time before failing. The current limitingcharacteristic of the CLR that is most important isthe ability to limit the rate of rise of current over ahalf line cycle (8.3 milliseconds). When a severe arcoccurs in the ESP, the voltage at the point of the arcdrops to near zero. The amount of current that willflow through the arc is limited by impedance of thevarious feed components, including the transformer,CLR as well as the inductance of the ACR and HVbuss work.

In addition, the peak current through the arc isincreased by the capacitive discharge of the ESP. Asthe current through the arc increases, the CLR willbe subject to the full line voltage. A 50% impedancesystem will limit the peak current through the pri-mary to about two times the rated current. In addi-tion, the rate of rise in current through the primarycircuit and the SCR controller will be limited toremain within the rating of the SCR devices.

The peak current that accompanies arcs imposesa severe stress on the CLR. The CLR must be capa-ble of withstanding repeated arcing with the resul-tant two times rated current without adverse effect.To accomplish this, both conductor size and coresize must preclude magnetic saturation during peakcurrent conditions. If the core of the CLR were tosaturate, then the inductance would diminish to nearzero and the CLR would cease to contribute to lim-iting fault currents.


f = frequency in hertzThe percent impedance that the CLR provides iscalculated by:

%Z = L x 377 x I x 100V

where%Z = percent impedanceL = inductance in henriesI = rated primary currentV = system voltage (typically 480 or

575 VAC)The same formula can be used for calculating theinductance required for a desired % impedance by:

L = V x %Z I x 377 x 100

The system impedance also includes the reac-tance of the transformer which is typically 5% to10%. A system impedance of 50% limits the maxi-mum AC current to twice the rated current. At 33%the limit is three times the rated current. When spec-ifying the CLR, the inductance in henries, the pri-mary rated current, and the anticipated spark ratemust be given. Since the ESP will periodicallyspark, the actual average current that the CLR willneed to withstand is greater than the T/R rated current.

C. Limiting Peak CurrentThe term Current Limiting Reactor is somewhatmisleading. Although a system impedance of 50%will limit AC current to twice its rating, this is oflimited value in light of the fact that neither the


The Transformer Rectifier (T/R)The T/R is a critical component of the ESP powersupply. The purpose of the T/R is to accept an ACpower feed from the SCR/CLR control system andconvert the 0 to 480VAC (nominal) signal to therequired level of high voltage. Transformer Recti-fiers are oil filled tanks with a low voltage junctionbox and one or two high voltage bushings. Singlebushing T/Rs are referred to as full wave units anddual busing T/Rs are referred to as double half waveunits.

Figures 2 and 3 show the electrical configurationof a full wave and a double half wave unit. T/Rs areusually mounted on the roof of the ESP. Large ESPsmay require 50 or more T/Rs. The electrical compo-nents of a T/R include the high voltage transformer,the diode assembly, the air core reactor (ACR), thefeedback voltage divider and a ground switch whichmay be integral with the T/R or mounted in the busduct.

A critical component of the T/R, that is notshown in the electrical drawing, is the dielectricfluid that fills the T/R tank. This fluid provides ameans for electrically insulating the internal compo-nents as well as a means for dissipating internallygenerated heat.


D. CLR Wave ShapingThe second function of the CLR is to smooth outthe pulsating waveform to the ESP. The full waverectified signal that is supplied to the ESP is actuallya pulse train at 120 pulses per second. If the systemwas permitted to run at full conduction, then theoutput signal would tend to be a sinusoidal. In reali-ty, however, the waveform of the primary current aswell as the secondary voltage (KV) is affected bythe conduction angle of the controller, the systeminductance, the capacitance of the ESP and the sec-ondary current level.

The wave shape of the T/R primary current isaffected by the amount of reactance in the primarycircuit. This wave shaping results in several benefitsto the overall system. These benefits become partic-ularly important for systems that are running at con-duction angles of 90 degrees or less (50% conduc-tion or less). As the inductance of the primarycircuit is increased, the percent conductance at aparticular load level can be significantly increased.The benefit that is realized is the ability to increasethe average current to the ESP before sparkingoccurs. In many instances, this increased currentlevel results in better collection efficiency for theESP.


the fractional distillation of crude petroleum. Miner-al oil is the most commonly used dielectric fluid forT/Rs.2. Silicone Oil: a linear polymer liquid termed poly-dimethyl siloxane or PDMS. This fluid has a higherfire point than mineral oil. Silicone fluid is normallyused for indoor applications or when decreasedflammability is deemed necessary. Silicone fluidcosts considerably more than does mineral oil. Sili-cone fluid is slightly more viscous than mineral oilfor temperatures above 10 degrees Celsius andsometimes requires additional measures be taken tofacilitate heat transfer (additional radiator or biggertank). Usually, however, this is not a critical para-meter if tank size is conservatively designed.3. High Molecular Weight Hydrocarbon: Thisdielectric fluid is a less costly alternative to siliconefluid for installations needing reduced flammability.HTH fluid is a petroleum based product. Since HTHis significantly more viscous than both silicone andmineral oil at temperatures below 100 degrees Cel-sius, heat transfer characteristics at lower tempera-tures require extra consideration in the T/R tank andradiator sizing. The use of this dielectric could be aproblem when used in a cold environment whereT/Rs are allowed to cool off. This problem is over-come by gradually bringing the T/Rs up to fullpower to allow the fluid to heat up.

B. The TransformerThe step-up transformer is the major component ofthe T/R system. Transformers designed for ESP


A. T/R Dielectric FluidsThree types of fluid are presently used for T/Rdielectric fluid.1. Petroleum Based Oil: also known as “trans-former oil” or mineral oil. This oil is obtained from


Figure 2 Electrical drawing single bushing full wave transformer

Figure 3 Electrical drawing dual bushing (double half wave) transformerrectifier (TR)

ExternalBushing

Diode Bridge

Air Core Reactor

VoltageDivider

mA Resistor

Power Feed

mA Feedback

KV Feedback

Low VoltageJunction Box

Diode Bridge

Bushing 1 Bushing 2

Power Feed

mA 1Feedback

KV 1Feedback

mA 2Feedback

KV 2Feedback

Low Voltage Junction Box

mA Resistor

mA Resistor

Oil Filled Tank

Air Core Reactor 1

Air Core Reactor 2

Voltage Divider 1

Voltage Divider 2

determined by the feed voltage and the prima-ry reactance of the system.

7. The KVA rating of the system to determineconductor sizes as will as core size.

The transformer is typically the most reliablecomponent in the system. Failures of transformers,however, do occur and can often be placed in twogeneral categories. The first is degenerative failurethat is caused by the long term breakdown of a com-ponent part. If the transformer is used within itsrated parameters, then degenerative failure is mostlikely due to a defect of material or workmanship.the second failure category is overstress failure.Overstress failure is caused by subjecting the trans-former to either excessive voltage or excessive cur-rent. Overstress failure is usually the case for trans-formers that fail between five and twenty years ofoperation.

Degenerative FailureOf the components and materials used on T/Rs, thelayer insulation on the transformer winding deter-mines the life expectancy of the system. Moderndesigns use Kraft insulation. The life expectancy ofthe insulation is a function of stress level (voltageacross the insulation) and temperature of the insula-tion material. The operating temperature of the insu-lation is usually assumed to be 10˚ (C) higher thanthe overall temperature rise of the winding. The 10˚margin is based upon the assumption that heat trans-fer between the coils and the oil can never beabsolutely uniform. The expected life of the insula-


applications employ design techniques specificallydeveloped for this use. ESP transformer coils mustbe capable of withstanding repeated sparking andarcing of the load. Disruptions such as these, alongwith occasional shorted fields, cause current surgeswell above the system ratings. These surges causethe windings of the transformer to exert consider-able physical force on the system insulation andsupport mechanism. If not properly accounted for,these forces will eventually cause prematuredestruction of the insulation and system failure. Thetransformer design must integrate the many speci-fied requirements of the system. Included are

1. Turns ratio of the transformer (A 400 VAC to40 KVAC transformer requires a ratio of 400to 40,000 or 1 to 100).

2. The peak secondary voltage to determine theinternal insulation and clearances.

3. The average/peak secondary current required.4. The voltage and current “form factors” as

determined by the impedance of the load.These form factors define the relationshipbetween the average and RMS values of theoutput waveforms. There is a separate formfactor for the load voltage and load current.These form factors are used to size the trans-former to provide the desired average outputvoltage and current for a specific load impedance.

5. The maximum temperature rise allowed asdetermined by the ambient air temperatureextremes.

6. The maximum available primary voltage as


the T/R become greater when controls are not prop-erly calibrated and/or if the system feedback doesnot include the KV signal.

C. The Diode Assembly1. Function in T/RThe diode assembly of the T/R converts the highvoltage AC output of the transformer to a DC sig-nal. The diodes are configured as a full wave bridgewith the positive output of the bridge connected toearth ground. The negative output is routed throughan air core reactor and then to the high voltagebushing. The diode assembly is made up of a seriesstring of many diode junctions. This series string ofdiodes should be capable of blocking at least twicethe peak output voltage of the T/R. A typical 45 KVT/R will have a peak output voltage in excess of 75KV. The diode assembly must, therefore, have aneffective PIV (peak inverse voltage) of at least 150KV.

The use of a series string of diodes to obtain highblocking voltage requires that special measures beemployed to assure proper voltage sharing. Improp-er voltage sharing is caused by variation of thereverse leakage of individual diode junctions. Thisvariation results in an uneven distribution of the PIVamong the diodes. The wide tolerance that is charac-teristic of standard silicon diodes will cause thedevices with the lowest leakage to accept a dispro-portionate share of the total voltage. If this phenom-enon is permitted to occur, then the diodes will failin a “domino” fashion.


tion for modern designs is 34 years if the unit iscontinuously subjected to rated current and ratedvoltage (REF ANSI C57.91.1981). Degenerativeinsulation failure after less than 15 years, althoughpossible is statistically very unlikely, unless thereare other contributing factors.

Degenerative insulation failure can be caused byabrasion caused by excessive vibration and physicalmovement of the transformer windings. Vibration isinduced by the 60 cycle AC current while coil move-ment is induced by current surges. ESPs by naturepresent a harsh load for transformers due to thesparks and arcs that are expected. T/Rs designed forsuch applications must therefore employ extraordi-nary measures to tolerate such conditions. If suchmeasures are not employed or improperly employed,then the abrasion of the coils will occur.

Stress FailureStress failure of the T/R occurs when the unit issubjected to either overvoltage or overcurrent condi-tions. Operators should be suspicious of overstressfailure mode if a T/R failure was preceeded by somechange that effected operating levels. Commoncauses for such changes include change in the fuelin use and change out of the T/R controller. But achange in fuel and the resultant change in ESP oper-ating conditions should not cause overstress of theT/Rs. The task of operating the T/R within theirdesign limits is accomplished by the T/R controller.The controller should limit both the KV level andthe current level as well as the spark rate to safelimits. The potential for problems with overstress of


occur if the power supply is allowed to exceed itsrated current output for an extended period of time.Since most T/Rs in service have a source impedanceof about 50%, the T/R can actually deliver twice itsrated current.

In cases of disruptions such as severe arcs orshorted output, the system relies upon the controllerto maintain the output current to a safe level. Whensuch disruptions occur, the current may instantlyrise to twice rating but must be quickly reduced bythe controller to preclude damage to the T/R. If anovercurrent condition is permitted to continue,excessive heat is generated by the diodes. As thediode junctions heat to beyond their rated tempera-ture, the bridge will fail.

Heat Related Failures. In many cases of T/R over-current, the heat generated by the diodes cause thediode junctions to exceed their maximum operatingtemperature. When this occurs the diodes will fail.Occasionally the heat generated will be sufficient tocause the solder that fastens the diodes to the PCboard to melt away. As the solder melts and is dis-placed with dielectric fluid, arcing occurs betweenthe diode lead and the PC board. This arcing resultsin the breakdown of the dielectric fluid. Carbon andcyanide gas are two of the resultant components ofthis breakdown. If the internal arcing continues,then the generated carbon will eventually be attract-ed to the transformer windings and cause failure ofthe transformer. If excessive cyanide gas is generat-ed, then the air space between the tank lid and theoil will become explosive.


2. Types UsedPrior to 1980, T/R manufacturers employed the useof RC (Resistor-Capacitor) compensation to addressthe voltage sharing problem. This approach provideda means of using standard 1000 volt diodes in astring with each diode connected in parallel with aresistor and capacitor. The resistor serves to limit theDC reverse voltage to be shared, while the capacitordistributes high frequency AC voltages caused bysparking and/or “ringing” of the ESP system.

Since 1980, several T/R manufacturers haveemployed “controlled avalanche” diodes and elimi-nated the need for the RC compensation. Thesediodes are now available with ratings exceeding10,000 volts PIV for each device. Avalanche diodesare screened to insure closely matched reverse leak-age characteristics. Because of this, they can berelied upon to properly share the total reverse volt-age without the need for parallel RC compensators.

T/R bridge assemblies that use such diodes canusually be assembled on a single circuit board thatis mounted in the T/R tank. The RC compensatedtechnology required large assemblies that are popu-lated with many small circuit boards to make up thediode bridge network. Such assemblies consumeconsiderable space in the tank, are prone to mechan-ical failure and are difficult to replace in the eventof failure.

3. Failure ModesThe two common causes for diode failure are exces-sive electrical stress due to either overcurrent or toovervoltage. Diode failure from overcurrent may


the primary voltage in conjunction with the turnsratio to calculate the KV value. This calculatedvalue, however, can never be truly accurate becauseof the unknown load characteristics of the ESP.

When T/Rs are specified, the primary voltage rat-ing is usually 10% to 20% lower than the actualfeed voltage. This primary voltage rating (usually400 VAC for a 480 VAC feed) is specified so thatfull KV output can be supported under full currentconditions. A 480 VAC system with 50% impedancecan only deliver about 400 VAC to the transformerprimary under full current conditions because of thevoltage drop in the reactor (CLR). If, however, theT/R is under no load conditions (i.e. open circuited),then entire feed voltage of 480 VAC can beimpressed upon the primary. This 20% overvoltageon the primary results in a similar overvoltage onthe secondary. In addition, under open circuit condi-tions the output bushing will charge to the peakvoltage of the secondary voltage waveform. A 55KV, T/R will charge to approximately 92 KV.Bridge failure under such conditions depends uponthe bridge rating. Its ability to survive such stressdepends upon the amount of safety factor designedinto the T/R.

High Voltage “Ringing.” The second cause ofovervoltage condition is “ringing” of the secondarycircuit. This phenomenon is fairly unusual but doesoccur under some conditions. Ringing is a term thatdenotes resonant oscillation of the secondary circuit.An important element of the T/R secondary circuitis the ESP box itself. A resonant circuit is created


In some cases of overcurrent the diode junctionfails to an open condition prior to melting the sol-der. In such cases, the open circuit diode will besubjected to the entire output voltage of the T/R.This voltage is sufficient to permit arcing around thefailed diode creating carbon and cyanide. In addi-tion, the remaining diodes will be subject to exces-sive voltage and in turn fail. In some cases thisprocess may take place within a few minutes afterwhich the T/R will cease to perform. Such rapidfailure modes are less catastrophic because the oil isusually not severely contaminated and the T/R canbe repaired on-site. If the failure, however, takesdays, then the oil will be severely contaminated andthe T/R will require major rebuild in order to be putback in service.

Voltage Related Failures. The second cause of fail-ure of the diode bridge is an overvoltage condition.The diode bridge must be rated for a PIV of at leasttwice the peak output voltage of the T/R. Intuitivelyit could be assumed that such a condition could notoccur. There are, however, two ways that T/Rs aresubject to overvoltage. The most common cause ofovervoltage is a malfunctioning or misused con-troller. A less common cause of overvoltage is volt-age “ringing” of the T/R and the ESP.

The provision for KV limitation of the T/R outputis a standard feature of most controllers. To accom-plish this, a KV feedback is needed. This feedbacksignal is sometimes either not available because of alack of voltage dividers in the T/R system orbecause of a feedback failure. Some controllers use


ing to obtain KV feedback.The voltage divider is a resistor network connect-

ed to the high voltage bushing. This divider is madeup of a series string of many resistors. Divider val-ues of 50 megohm, 80 megohm and 120 megohmare typically used. The high resistance is used tocreate a current source that is typically a 0–1 mil-liamp that is proportionate to the full scale voltageof the T/R. A 50 meg divider provides 0–1 ma feed-back signal that corresponds to 0–50 KV output.The output of the voltage divider could be used todirectly drive a 1 ma meter with an appropriatescale or it could be converted to a voltage signal. A10 K ohm resistor is commonly used to provide a0–10 volt feedback signal. This approach permitsthe physical location of the resistor to be close tothe T/R and reduce the possibility of high voltagesignals in the control area. Many of the modern dig-ital controllers use a 0–5V or 0–10V signal for KVfeedback for metering and for spark detection. Thislow voltage feedback can be used to drive an analogvoltmeter with an appropriate scale that is wired inparallel with controller.

2. External Dividers: The external voltage dividernetwork is usually mounted in a protective insulat-ing tube of PVC or fiberglass. The divider must becapable of dissipating the heat that is caused by themaximum voltage (KV) output of the T/R. For a 50meg divider, the power at 50KV is 50 watts. Thephysical configuration of the external divider mustprovide a means of dissipating this energy (heat) ata rate sufficient to maintain the resistor temperature


whenever a capacitor and an inductor are connectedtogether. The plates and wires of an ESP have both aresistive and a capacitive component. Prior to theonset of corona, the ESP is essentially a capacitiveload to the T/R. As corona current increases, theresistive component of the ESP increases.

“Ringing” or resonant oscillation is more likelyto occur when sparking occurs under light load con-ditions. Under such conditions, a tank circuit ismade up of the ESP acting as a capacitor and a com-bination of the transformer, the ACR and the highvoltage bus work as an inductor. Oscillation willoccur at the resonant frequency of this system whichis typically a few KHz.

The existence of ringing can be observed throughuse of an oscilloscope on the secondary feedback.Ringing can be detected by monitoring KV feed-back using an ESP spark as a scope trigger. If aproblem exists, then a damped oscillation at 1–5KHz will be observed with peak voltages in excessof T/R ratings.

D. The Voltage Divider1. Function: The voltage divider provides a meansfor supplying a low voltage feedback signal that isproportionate to the KV output of the T/R. This sig-nal is used for both metering and for control purpos-es. Most modern T/Rs include a voltage divider thatis mounted under fluid within the T/R tank. Many ofthe older systems, however, did not use KV feed-back as a control or metering parameter. In manysuch installations, external voltage dividers may bemounted outside the T/R near the high voltage bush-


of T/Rs results in severe stress of ACRs. The Dou-ble Half Wave system provides a means of excitingtwo isolated electrode fields from one T/R. Eachfield is energized by half of the DC output to pro-vide a 60 Hz pulse train, with 8.3 milliseconds onand 8.3 milliseconds off. While seldom used today,this configuration was often employed during thelate 1960s. During that period, several installationsachieved increased efficiency through the use of thepulsing effect of the split output.

In addition, this approach provided the benefit ofisolating a faulty field through the use of the HVswitch that is provided. Potential problems for thepower supply of the DHW include: unbalanced loadfor the transformer, complex spark reaction for thecontroller and capacitor dumping and ringingthrough the ACR. The ACR problem occurs whenone of the fields sparks and discharges both fieldsthrough the ACRs and the switch. Many installa-tions that featured the DHW configuration now con-nect the two bushings together to avoid excessivestress of the T/R components.

The T/R ControllerThe purpose of the T/R controller is to accept theincoming line voltage from the power source (typi-cally 480 VAC) and provide a variable voltage tothe T/R set. Modern day controllers utilize fast act-ing Silicon Controlled Rectifiers (SCRs) to phaseangle control the primary voltage. Older controllersutilized much slower saturable core reactors to varythe voltage. The exact voltage that the controller


within its rated maximum.Voltage dividers are simple devices and are easily

maintained. Failure of the divider is often caused bymechanical or thermal stress. The testing andreplacement of dividers is usually a task well withinthe skills of plant personnel. The testing of dividersfor proper resistance could be accomplished throughthe use of a general purpose digital meter althoughthe use of a “Megger” is preferred. If a general pur-pose multimeter is used, then the divider should bedisconnected from the T/R; connections should bemade through use of high voltage clip leads. Anystray charge or capacitance that may exist will affectreadings in the 50 meg+ range.

E. The Air Core Reactor (ACR)1. Function: The Air Core Reactor (ACR) providesa means for protecting the diode bridge from highvoltage “transients” that occur within the ESP.ACRs used in modern T/Rs are rated from 20 to 50millihenries. As the ESP sparks and arcs, the fullESP voltage will be impressed across the ACR.ACR design must provide sufficient layer insulationand clearance to accommodate such voltage. Typicalfailure mode for ACRs is a sparkover of the layerinsulation. Since the ACR is physically much small-er than the transformer secondary coil, it is subjectto extreme voltage stress. In the event of any conta-mination of the dielectric fluid, the ACR is often thefirst component to fail.

2. Double Halfwave: The “Double Half Wave” use


shunt trip circuit breaker instead of a contactor.

C. SCR AssemblyThe SCR assembly is the main device used to regu-late the primary voltage to the T/R set. The assem-bly is made up of two SCRs connected in a reversepolarity parallel configuration.

One SCR controls the positive half cycles while theother controls the negative. The SCRs are protectedfrom dv/dt damage by a resistor capacitor snubbernetwork and a metal oxide varistor. They are alsofused to protect against overcurrent conditions.

The SCR will turn on when two conditions aresimultaneously met. The SCR must be forwardbiased and the gate must be given a trigger signal.By varying the time delay between when these twoconditions occur, the amount of time that the SCR ison will also vary. The amount of time that an SCRis on is called the conduction time. It is more com-monly referred to as the conduction angle and


will output to the T/R is a function of a number ofvariables that are dependent upon the precipitatorload and the T/R set being used. The controller willtry to maintain the highest possible voltage on theprecipitator field for varying load conditions. Thehighest possible voltage is typically the sparkovervoltage of the field. The controller must also protectthe T/R set from sparks or arcs that occur in thefield. It must also make sure that the system is notoperating at any current or voltage levels thatexceed the design ratings of the T/R set.

Modern controllers utilize microprocessor circuitsto analyze feedbacks and operating setpoints todetermine the proper output levels. These micro-processors also provide data acquisition, graphicaltrending of metering values, graphical V-I curve ofthe precipitator field and an assortment of other fea-tures. Most control enclosures contain the followingmajor components.

A. Circuit BreakerThe circuit breaker is used to protect the systemfrom short circuits that occur primarily on the 480VAC line. It also acts as a lockable disconnectdevice for removing power from the controller formaintenance purposes.

B. ContactorThe contactor is the main device for energizing andde-energizing the primary power to the T/R set. Thecontrol circuits open the contactor to remove powerif an system alarm occurs. Some controllers use a


Output VoltageInput Voltage

SCR Assembly

core to saturate and draw a large amount of DC cur-rent. This type of alarm usually indicates a problemwith the SCRs or the triggering of the SCRs.

T/R Overtemperature—This monitors the tem-perature switch on the T/R set. If the oil gets too hot(typically 95˚ C) the unit will shutdown. This alarmindicates that the system may be operating at toohigh a current, or that there is a problem in the T/Rset.

T/R Liquid Level—This monitors the levelswitch on the T/R set. If the dielectric fluid gets toolow, the unit will shutdown. This alarm usually indi-cates a lead in the T/R set. Not all T/Rs have thisfeature.

SCR Overtemperature—This monitors the tem-perature switch on the SCR heatsink. If the heatsinkgets too hot, it indicates either a problem with theSCRs, or the ventilation system in the enclosure.Not all SCR assemblies have this feature.

F. Limit CircuitsThere are certain conditions that occur within thesystem that require some type of corrective action,but not necessarily turning the T/R off. With limitcircuits, the conduction angle of the SCRs will auto-matically change to try to correct the condition. Themost common limit circuits are:

Current Limit—If the current starts to exceed apreset level, the controller will reduce the conduc-tion angle of the SCRs to whatever is required tomaintain that level. Because of this, a T/R set canoperate a shorted precipitator field and never exceed


expressed in terms of degrees. Zero degrees conduc-tion means that the SCR is not gated on, and 180degrees conduction means the SCR is fully gatedon.

D. Metering CircuitsMost control enclosures also contain analog metersin addition to the digital metering displays of themicroprocessor circuits. The analog meters providea better visual trend of the readings under sparkingconditions of the precipitator.

E. Alarm CircuitsAlarm circuits are used to monitor the system andde-energize the T/R set if certain conditions occur.The common alarm conditions are:

Overcurrent—Protects the T/R and controllerfrom operating at current levels above the T/R ratings.

Undervoltage DC—This occurs if the outputvoltage of the T/R remains low (typically under 10KVDC) for more than a short period of time (typi-cally 30 seconds). Undervoltage alarms usually indi-cate a shorted field, a shorted T/R, or a malfunctionin the controller.

Overvoltage DC—This occurs if the output volt-age of the T/R set goes above the rating of the set.This alarm usually indicates a problem with thepower system or an open circuit in the precipitatorfield.

SCR Unbalance—If both SCRs are not operat-ing at the same conduction angle, a DC voltage willbe fed to the T/R primary. This can cause the T/R


that can be applied to a field, actually causes thefield to spark. The controller must also protect thesystem from the effects of this sparking. There aretwo different types of sparkovers that occur, a sparkand an arc. The controller should recognize wheneach type occurs and respond accordingly.

Spark—A spark is a relatively small dischargewithin the precipitator that self-extinguishes with noincrease in the base waveform current.

Since the spark is gone by next half cycle, thecontroller really doesn’t have to protect against anylarge fault currents. But if it takes no control action,

another spark will occur on the next half cycle. Eachtime a spark occurs the electrostatic field is dis-charged. If the field is rapidly sparking in this man-ner, it will never reach its optimum voltage. The


the current rating of the T/R.Voltage Limit—If the output voltage starts to

exceed a preset level, the controller will reduce theconduction angle of the SCRs to whatever isrequired to maintain that level. This is used to pro-tect a T/R set from operating at too high a KVDCoutput.

Conduction Angle Limit—This is used to placethe unit in manual operation or to limit the conduc-tion angle from exceeding a certain value.

G. Process ControlThe controller must perform certain process controlalso. The efficiency of the precipitator is directlyrelated to the voltage applied to it. The higher theaverage voltage on the fields, the better they willperform. The controller must find the optimum volt-age to operate at. The highest voltage that can beapplied to any field is the voltage at which that fieldsparks. The controller will continually increase theoutput of the T/R until one of the following condi-tions occurs:

a. A spark or arc occursb. Current limit is reachedc. Voltage limit is reachedd. Maximum conduction angle is reached

By continually searching for the highest possibleoperating voltage, the controller is able to optimizethe collection process for any load variations.

H. Spark/Arc ResponseThe controller’s search for the maximum voltage


Time Seconds

AC

SW

Vo

ltag

e

100% SB - 10% SB = 15%

RAMP= 1 Sec.

RAMP= 1 Sec.

0 5 10

are off is called the “quench time”. A “fast ramp”then quickly increases the voltage to the “spark set-back” level where the “slow ramp” then increases itback to the arc over voltage.

I. Intermittent EnergizationThis mode allows the primary voltage to the T/R tobe pulsed a variable number of half cycles on and avariable number of full cycles off. This pulsing maybe helpful for back corona conditions or for powersavings.

Care must be taken that the off time is alwaysconfigured in full cycles of voltage. If half cycles areused the voltage being applied to the transformerwhen it turns on would be the same polarity as thevoltage that was applied when it turned off. Thiscould possibly cause the transformer core to saturate.

J. Back CoronaBack corona is a condition that occurs primarilywith high resistivity ash loads and is usually associ-ated with low sulfur coals. The resistivity of the ashdetermines the voltage drop across the dust layer on


proper control response is to reduce the conductionangle of the SCRs a small amount on the next halfcycle. This “setback” will reduce the KVDC in theprecipitator so as to stop another spark from occur-ring. A “slow ramp” then increases the voltage backto the original sparkover point.

Arc—An arc is a large disruptive discharge with-in the precipitator that will not self-extinguish. Dur-ing an arc large levels of fault current continuallyflow. The level of that current is determined by thesystem impedance but is usually high enough todamage the SCRs or the T/R rectifiers.

To stop this from happening the controller turnsthe SCRs off during the next half cycle. They willstay off for a certain duration of time. This reducesthe KVDC to zero allowing the arc to extinguish or“quench” itself. The period of time that the SCRs


AC

SW

Vo

ltag

e

100%

Time (Seconds)

0 5

Quench =1 Cycle

Slow Ramp =1 Second

Fast Ramp =5 Cycles

SB = 25%

Pri

mar

y C

urr

ent

TroubleshootingTips■ The “Lamp Test”—A Simple

Means for Testing T/Rs

■ What Meter Readings Can Tell You When Troubleshooting Transformer Rectifiers (T/Rs)

RecommendedPractice:

■ Oil Integrity Testing

■ Mineral Oil Filtering Procedure forTransformer Rectifier (T/R) Sets

33

the collecting and electrode surfaces. If the resistivi-ty of the dust is high enough, the voltages will behigh enough to cause a back corona to be generatedin the dust layer. This back corona generates posi-tive ions that neutralize the negative charge from theelectrodes. The loss of the space charge also causesa loss in the precipitator efficiency. Back corona canbe diagnosed by performing a V-I curve. If the curvegoes vertical, meaning small changes in KV causelarge changes in mADC, back corona is present. Ifthe curve bends backwards, meaning the KV actual-ly decreases and the MADC increases, there is asevere back corona condition present.


SECTION II

■ Connected to 120VAC power source available as a standard wall plugA recommended lamp size of 60 to 100 watts will

limit the maximum current draw to about 1 ampereunder a short circuit condition. The test operator candraw various conclusions by simply observing thebrightness of the light bulb. In addition, if the testoperator has the skill to use other instruments suchas a volt/ammeter and/or an oscilloscope, significantadditional information can be assessed as well.

The basic indicator of the lamp test is the obser-vation of a dull glow of the light bulb. In general,this will indicate that the T/R is in operable condi-tion (a bright illumination or no illumination indi-cates an abnormal condition). If an abnormal condi-tion is suspected then this hookup can provide aconfiguration for further testing.

Test rig assembly1. Connect a wire of desired length between the

“hot side” of the wall plug and one terminal (orwire) of the lamp socket (the “hot side” is nor-mally the smaller prong).

2. Connect a wire to the return side of the wallplug long enough to reach the test connectionpoint. The loose end of this wire should be suit-ably dressed (lug or clip) to hook up to the T/Rconnection point. This is the “Return Wire.”

3. Connect a wire to the second terminal or wireof the lamp socket long enough to reach the con-nection point (same as wire in step 2). This is the“Hot” wire.

4. Install the light bulb.

Troubleshooting Tips 35

TROUBLESHOOTING TIP

The “Lamp Test”—A Simple Means For Testing T/RsOften, the functional “health” of a T/R needs to bedetermined. The “T/R Lamp Test” can be performedon T/Rs that are already installed as well as on T/Rsthat are disconnected.

When testing an installed T/R, the T/R Lamp Testcan be performed either at the T/R location or at theController location. While the Lamp Test should byno means be considered a complete T/R test, it doesprovide a means of ruling out many common failuremodes. In addition, the test provides a high confidencelevel that the T/R system is “safe” to energize with afully powered control system (typical 480 VAC).

But before you proceed with this test, severalwarnings are in order:

1. The tests described results in high-voltage out-put on the T/R high-voltage bushing as well asthe possibility of high voltage on feedbackconnection points.

2. This test should ONLY be performed by per-sons familiar with high-voltage systems.

SummaryThe lamp test uses an ordinary incandescent lightbulb to permit low level energization of a T/R. Thistechnique can provide excellent information aboutthe unit’s functionality. The test setup consists of:■ A light bulb that is wired in series with the T/R

primary winding


impact on the test indications since the currentdraw is so low.

4. If the system is equipped with a KV feedbackcapability the operator must be mindful of thehigh voltage that will be present on the high volt-age bushing as well as on the KV feedback sys-tem. Verify that the KV feedback signal has anappropriate resistance path to ground. This pathmay be through the KV indicator meter orthrough an external resistor. IF THE KV FEED-BACK WIRE IS OPEN CIRCUIT TO GROUNDTHEN HIGH VOLTAGE WILL BE PRESENTON THIS WIRE! IF THERE IS ANY DOUBTOF THIS THEN CONNECT THE KV FEED-BACK TERMINAL TO GROUND!

5. Connect the test fixture “Hot” wire (the wirefrom the lamp) to the “hot side” (the terminal thatconnects the SCRs to the CLR and then to theT/R). If the connection is to be made at the T/Rjunction box then the “hot side” of the system isthe connection point between the T/R and theCLR.

6. Connect the test fixture “Return Wire” (thewire from the plug) to the “Return Side” of thesystem under test.

7. Plug the fixture into a wall socket and observethe lamp. A dull glow indicates a basically“Healthy System”; a bright illumination or noillumination indicates trouble. The choice of lampsize, either 60 or 100 watt, should be a functionof the T/R size. For units under 700 ma thesmaller lamp is more effective.


5. Verify proper connections by connecting the“Hot” wire to a ground point, plugging in thewall plug and observing the lamp illuminatingbrightly.

Configuration for Installed T/R1. The hookup to the system may be either at the

T/R junction box or at the controller outputterminals. In all cases the circuit breaker feed tothe T/R must be opened.

2. The High Voltage connection (bushing) to theESP field may be open or connected at theoperators option. Upon conducting the test,High Voltage in excess of 20,000 volts will bepresent on the T/R output. All interlocks andsafety precautions for the ESP and High Voltageduct work MUST BE OBSERVED!

If the ESP field is connected, then a shortedfield will give the same results as will a shortedsecondary in the T/R.

3. If the hookup is at the Controller output thenthe CLR will also be in the primary circuit.The impedance of the CLR will have negligible


Current Limiting Reactor

T/R SetTransformer

functionality. If you would like more informationon this and other tests you can use in T/R trou-bleshooting—let us know on the reply cardattached to this issue. Or better still, call 1-800-PICK NWL—and talk with one of our servicepeople who have long-term experience in per-forming on-site ESP equipment diagnostics.


Interpreting the resultsVERY DULL GLOWNormal indications from a very dull glow:■ The T/R does not have any shorted turns in

either the Primary or Secondary windings.■ There are no direct shorts in the “hot side” feed

to the T/R nor shorts to ground in the transformer winding.

■ There are no shorts to ground in the CLR if connected during test.

■ The T/R Rectifier bridge does not have a shorted leg.

■ The output, High Voltage feed system and ESPfield (if connected) are not shorted to ground.

BRIGHTER THAN DULL GLOW

A brighter than dull glow indicates potential for:■ Shorted turns in transformer■ Shorted High Voltage bushing or ESP field or HV

duct■ Shorted rectifier bridge■ Short in primary voltage feed system

NO GLOW

No glow from the bulb indicates an open circuit onthe 480 VAC system. The open circuit may be in theinterconnection wiring, in the CLR (if present), or inthe T/R primary winding or connections.

This T/R Lamp Test is an abbreviated versionof but one test that can be used to determine T/R


Problem: Short Circuit—DC SideTests1. Run T/R set with HV bushing disconnected from

the precipitator.a. If no current flows the short is in the precipitator.b. If current still flows the short is in the T/R set.

2. If precipitator is shorted, check electrodes andinsulators for shorts.

3. If T/R is shorted, check HV bushing and externalswitch (if applicable) for shorts.

Problem: Short Circuit T/R setTests1. Megger diodes for shorts.2. Run T/R without diodes. If AAC still high, trans-

former is bad.


TROUBLESHOOTING TIP

What Meter Readings Can TellYou When TroubleshootingTransformer Rectifiers (T/Rs)You pass by them dozens of times in the course of awork week—meters. They’re designed to give youinformation about the performance of specific com-ponents of your clean-air system.

Analyzed collectively, however, they can alsohelp perform an important diagnostic function. Thefollowing are four problems indicated by T/Rmeters—along with tests you may want to performin resolving those problems.

Probable Cause: No power to T/R setTests1. Check if controller is responding to sparking. If it

is, use a scope to verify that sparks/arcs areoccurring. Run T/R with precipitator disconnect-ed to verify that T/R is not sparking internally.

2. Check for open SCR fuses.3. Verify that SCRs are firing.4. Check for open CLR.5. Check for proper operation of controller power

components.a. circuit breakerb. contactor


VAC AAC KDVC mADC

VAC AAC KDVC mADC

VAC AAC KDVC mADC

RECOMMENDED PRACTICE

Oil Integrity TestingTo insure continued performance of your power sup-plies, the following ASTM tests should be performedannually on dielectric fluid sample extractions.

Test 1Neutralization Number (D664)—The neutral-ization number for service-aged transformers is, ingeneral, a measure of the acidic constituents of theoil. It may be pertinent, if compared to the value ofthe new product, in detecting contamination of theoil from substances which have come in contactwith the oil. It may also be important in revealing atendency toward chemical change or deterioration ofthe oil and its additives. It may be used as a generalguide for determining when oil should be replacedor reclaimed, provided suitable rejection limits havebeen established and confirmation is received fromother tests.

Test 2 Dielectric Breakdown Voltage (D877)—The dielectric breakdown voltage of an insulating liquidis of importance as a measure of its ability to with-stand electric stress without failure. It is the voltageat which breakdown occurs between two electrodesunder prescribed test conditions. It serves primarilyto indicate the presence of contaminating agentssuch as water, dirt or conducting particles in the liq-uid, one or more of which may be present when lowdielectric values are found by test. However, a high


Problem: Open circuitTests1. Run T/R set with HV bushing grounded externally.

a. If current flows, precipitator field is open.b. If no current flows, T/R is open.

2. If precipitator is open, check all HV connectionsto electrodes.

3. If T/R is open, megger unit. Check for opendiodes or connections in T/R tank.


VAC AAC KDVC mADC

Test 6Water in Insulating Oil, Karl Fisher Method (D1533)—Water contamination of insulating oilmay be present in several forms. The presence offree water may be disclosed by visual examinationin the form of separated droplets or as a cloud dis-persed throughout the oil. This type of water invari-ably results in decreased dielectric strength, whichmay be restored by filtration or other suitablemeans. Water in solution cannot be detected visual-ly and is normally determined by either physical orchemical means.

ASTM methods cited are suitable for the deter-mination of water in insulating oil and, dependingupon conditions of sample handling and method ofanalysis, can be used to estimate total water as wellas soluble water content of oil. The unit of measureof the water is in soluble water content of oil inparts per million. These tests are significant in thatthey will show the presence of water which may notbe evident from electrical tests.

The following typical control limits for oil areused for evaluating the conditions of dielectric fluid:

Neutralization NumberASTM D664 .4 mg XOH/gram Maximum

Dielectric Breakdown ASTM D877 22 KV Minimum

Interfacial Tension ASTM D971 18 dynes/DM Minimum

Power FactorASTM D924 1.0% (Doble limit)


dielectric breakdown voltage does not indicate theabsence of all contaminants.

Test 3Interfacial Tension (D971)—The interfacial tensionbetween an electrical insulating oil and water is ameasure of the molecular attractive force betweentheir unlike molecules at the interface. It isexpressed in dynes per centimeter (millinewtons permeter). This test provides a means of detecting solu-ble polar contaminants and products of deteriora-tion. Soluble contamination or oil-deteriorationproducts generally decrease the interfacial tensionvalue.

Test 4Power Factor (D924)—Power factor is the ratio of the power dissipated in the oil in watts tothe product of the effective voltage and current involtamperes, when tested with a sinusoidal fieldunder prescribed conditions. A high value is an indi-cation of the presence of contaminants or deteriora-tion products such as oxidation products, metalsoaps, charged colloids, etc.

Test 5 Color (D1500)—The color of an insulating oil is determined by means of transmitted light and isexpressed by a numerical value based on compari-son with a series of color standards. A rapidlyincreasing or high color number is an indication ofoil deterioration or contamination or both.


RECOMMENDED PRACTICE

Mineral Oil Filtering Procedure for TransformerRectifier (T/R) SetsOne of the best ways to insure continued operationof your T/R set is to insure the proper condition ofthe mineral oil in it. The mineral oil provides notonly a cooling medium but a dielectric medium tohandle the voltage stress within the unit. It’s notuncommon that as the operational age of the unitincreases, the dielectric strength of the oil willdecrease. One of the ways to remove any contami-nation, and restore the dielectric strength, is to filterthe mineral oil. Although the filtering processdescribed below will not remove moisture or degasi-fy the oil, it is very effective for particulate removal.

Equipment RequiredFiltering should be done with a two-stage filter. Thefirst stage should use a cellulose cartridge designedto remove particles 25 microns or larger. The secondstage filter should be designed for removal of parti-cles .5 microns or larger. A pump will also berequired to circulate the mineral oil through the fil-ters. The pump should be suitable for use with min-eral oil. The flow rate of the pump should not exceedthe maximum allowable flow through the filters.

Equipment HookupThe hookup of the equipment is relatively simple.First you should de-energize the T/R set and proper-ly ground the precipitator field for personnel safety.


ColorASTM D1500 4.0 Maximum

Moisture Content ASTM D1533 55 ppm Maximum


Let stand for 2–3 hours, then check for any decreasein the pressure level. The pressure test is performedto insure that the T/R is properly sealed and will notbreathe. After the pressure test is completed, bleedoff excess nitrogen to .5 psi. The process of apply-ing the nitrogen blanket then bleeding off excesspressure can be repeated several times. This willessentially purge the top air space of any moisture.

Routine MaintenanceThe T/R set mineral oil should be tested on a annualbasis to insure proper dielectric strength. Additionaltests as can also be performed on the oil. Theyinclude neutralization number, interfacial tension,power factor, color, and moisture content.


Next attach the intake side of the pump to the drainvalve located at the bottom of the T/R set. The out-let of the pump will be run through the filter.Remove the T/R set access cover and place the filteroutlet hose in a horizontal position just below the oillevel. This horizontal position will help eliminatethe formation of air bubbles as the oil is returned tothe T/R set. Once the hose is in position reinstall theaccess cover as tightly as possible to reduce any fur-ther contamination.

Filtering the OilOnce the equipment is properly connected the pumpshould be run for about 8 hours to remove the cont-aminants from the fluid. It may be necessary to havesome additional fluid available to prime the pump orserve as make up for the oil in the filtering system.It is very important that the high voltage coils arenot exposed to air during the filtering process.Exposure of the coils to air may result in a failureupon re-energization of the T/R set. After the filter-ing is complete, remove the access cover and visual-ly inspect the mineral oil. If particles can still beseen, continue filtering until all of the particles havebeen removed. Once completed, test the oil’s dielec-tric strength. The minimum level should be 28 KVusing ASTM test method D877.

Pressure TestOnce the filtering equipment has been disconnected,reinstall the T/R access cover. Next, pressurize thetop air space above the oil with dry nitrogen to 4 psi.


EQUIPMENT TROUBLESHOOTING

NWL EquipmentThe following decision trees will help you conduct more thoroughtroubleshooting for the following:

■ Electrical Systems (overall)■ T/R Set■ T/R Controller■ Rapper Controller■ Meter Readings Low■ Back Corona■ Opacity Spikes


SECTION III

Equipment Troubleshooting 5352 ESP Troubleshooting Guide

ELECTRICAL SYSTEMS

AreMeters

ReadingLow?

yes

yes yesno noAre AllFields

Energized?

yes no

no

Is OpacityHigh?

yes yes

Go to T/RSection

Is Problem inT/R Set?

Go to ControllerSection

Is Problem inController?

Go to MetersReading Low

Section

Are Rappers

Operating?

Go to Rapper

Controller Section

yes

Are There

OpacitySpikes?

Go to OpacitySpikes Section

yes

Is There Back

Corona?

Go to Back

CoronaSection

no


Is T/R open circuited?Are there high voltageand low current levels?

Is T/R short circuited?Are there high Currents,low voltage levels?

Are meter read-ings normal, butno KVDC?

1. Meggerdivider.2. Check lowend resistor.3. Check forshorted surgearrestor.4. Check foropen or shortedfeed back wiring.5. Check fordefectivemeters.

Are meter read-ings normal, butno MADC?

No metermovements.

T/R SET

1. Check MADCshunt.2. Check shorted surgearrestor.3. Check openor shorted feed-back wiring.4. Check fordefective meter.

Go to controllersection.

Ground HV bushing.Does current flow?

Open inprecip.

Open inT/R.

1. Check foropen jumpersin penthousesection.

1. Megger T/R.2. Check foropen connec-tions in T/Rtank.

Is there MADC current?

Disconnect T/R fromfield. Is there still current flowing?

1. Meggar diodes.2. Run T/R with nodiodes.

1. Check H.V.bushing.2. Check groundswitch for shorts.

1. Check for shortedelectrodes in precip.2. Check hopper level.

no no

no

no

yes

yes

yes

no

no no

yes yes yesyes

yes


Does display light up? Does contactor energize?

T/R CONTROLLER

Is there 120VAC on J1 pin 1& 2 of powersupply?

no

no no

yes

Is there +5VDCon regulator oncontrol module?

yes

Is there +5VDCon regulator ondisplay cable ofdisplay module?

yes

Clear memory—doesproblem continue?

yes

Replace display mod-ule. Does problem continue?

yes

Contact NWL.

Apply120VAC.

no Replacecable.

no Replacecontrolmodule.

Are thereany activealarms?

yes Clearalarms.

no

Is there120 VACon TB1-11(enableline)?

no Apply 120 VAC.

yes

Is there 120VAC onTB1-15(contactor)?

no Apply 120 VAC.

Is there120 VACon TB1-16?


yes

Is the con-tactor coilgood?

no Replacecontactor.

yes

Contact NWL.

Is there output?

Is there control?

Is spark indi-cator showingspark or arcs?

yes yes

no

no

no no

Is SCR fuseopen?

yes

Using an oscil-loscope, arethere firing puls-es coming fromcontrol module?

yes

Using an oscillo-scope, are theregate pulses atthe SCRs?

yes

Replace SCRs.

Verify ifsparks or arcsare real usingan oscillo-scope. Arethey real?

Go toMetersReadingLowsection.


no Replacetriggerboard.

yesReplacefuse.

UnplugSCRs fromtriggerboard. Doesoutput gofull on?

yes ReplaceSCRs.

no

ReconnectSCRs trig-ger boardandunplugtriggerboard fromcontrolmodule.Does out-put go fullon?

yes Replacetriggerboard.

no

Replacecontrolmodule.

Lower spark/arc sensitivity.

yes yes yes


Are all the rap-pers in ques-tion fired fromthe samepower module?

Does display lightup?

Is there garbageon the display?

RAPPER CONTROLLER

Is there 120 VACon J2-1, J2-2 ofpower supply?

no

no yes

yes

Is there 5VDCoutput from thepower supply; J1-3 to J1-4 andapprox. 13VDC onJ1-2 to J1-4?

yes

Is there 5 VDCoutput to J2-11 toJ2-12 of theCPU/crate controller?

yes

Is there 5 VDCoutput at the endof the 25 pin cablethat connects todisplay?

yes

Does clearing the mem-ory solve the problem?

no

Does replacing the dis-play solve the problem?

no

Does replacing CPU/crate controller solvethe problem?

Check circuitbreaker,checkfuses.

noReplaceCPU/cratecontrollerD20624.

no Replacecable.

no Replacepowersupply.

Is the voltageon J1-3 andJ1-4 of thepower supplyabove4.8VDC?

noDoesreplacingpowersupplysolveproblem?

yes

Does clear-ing the mem-ory solve theproblem?

Pull cardsfrom cageone at atime to seeif one cardis loadingthe 5VDCdown.

no

Does replac-ing theCPU/cratecontrollersolve theproblem?

no

Are allground connectionssecure?

yes

Contact NWL.

Are all of therappers firing?

Are fuses blowingon power module?

Check the coilresistance ofrappers inquestions. Arethey correct?

no yes

yes

yes

Are fuses onpower moduleopen?

no

Is power mod-ule in questionbeing selectedto fire? Is LEDflashing?

yes

Is the A/D cali-bration correct?

yes

Are all of therappers on thesame outputcard?

Replace outputcard and recali-brate A/D, doesproblem goaway?

yesReplacefuses.

noDoes replac-ing the powermodule solvethe problem?

no Put a rapper in repeatmode and calibrate.

yesReplace out-put card andrecalibrateA/D on powermodule.

Replace CPUcard, does prob-lem go away?

Is the A/D cal-ibration cor-rect for thepower mod-ule?

no Adjustthe A/Dgain pot.

yes

Remove alloutput cards,except in slot1.Energize arapper in slot 1and see if fuseblows.

yesReplaceoutputcard.

yesReplacethat out-put card.

no

Repeat aboveprocedureafter addingthe output cardin the next slot.Does the fuseblow?

yes no no

no

Contact NWL.

yesAre two or morerappers on a singleoutput card firing?

Contact NWL.

no Does replacingCPU/cratecontroller solveproblem?

Contact NWL

no

Go tofuseblowingsection.

yes

no

no

no

Contact NWL.

no


Is controller indicatingsparks?

Use a scope to verify ifsparks/arcs are reallyoccurring. Are they?

Energize the T/R in man-ual mode with the precip.disconnected from the HVbushing. Can higher volt-

age level be reacted?

Is controller still indicatingspark/arcs are occurring?

Something internal to theT/R set is sparking or arcing, contact NWL.

METER READINGS LOW

Is the controller indicatinga current or voltage limit?

yes

yes

no

yes

Readjust thespark/arc

sensitivity pots.

no

Something inthe precip. islimiting the

voltage. Checkclearances,

electrode, align-ment, hopperlevels, insula-

tors, etc.

yes

Using external meters,make sure the digitalmeters are calibrated.

Are they?

yes

The limiting conditionsreally exist. Probably dueto the load in the precip.

yes

Calibrate themeters.

no

no


Do a VI curve. Does backcorona exist?

Place controllers in backcorona mode. Does opac-

ity improve?

Place the controller inintermittent energization

mode. Does opacityimprove?

Is sodium or sulfur injection system

operating properly?

Fix injection systems.

BACK CORONA

yes

no

no

no

Do the spikes occur on aperiodic basis?

Is the timing the same asthe timing of any of the

rapping groups?

Does lowering the intensi-ty of that rapping group

stop the spikes?

Does increasing the ACGtime stop the spikes?

Contact NWL.

yes

yes

no

no

yes

OPACITY SPIKES

Does opacityin the rip rapmode at the

original inten-sity stop the

spikes?

Index■ Glossary of Air Pollution

Control and ESP Terminology

■ Clean Air Act Amendments

■ Conversion Factors Metric Equivalents

■ Altitude-Pressure Temperature Density Table of Air

■ Title III Hazardous Air Pollutants


SECTION IV

collect gaseous pollutants. Used both for measure-ment and control.

Adsorption—The adhesion of a substance to thesurface of a solid or liquid.

Aerosol—Particle of solid or liquid matter that canremain suspended in the air because of its smallsize. Particulates under 1 micron in diameter aregenerally called aerosols.

Air Changes per Hour (ACH)—The movement ofa volume of air in a given period of time; if a build-ing has one air change per hour, it means that all ofthe air in the building will be replaced in a one-hourperiod.

Air Contaminant—An impurity emitted to the out-side air. It can be solid (dust, particulate matter), liq-uid (vapor/mist), or gas (carbon monoxide, sulfurdioxide).

Air Core Reactor (ACR)—Protects the T/R diodebridge from high voltage transients that occur withinthe ESP.

Air Horsepower—The theoretical horse powerrequired to drive a fan if there are no losses in thefan, that is, if its efficiency is 100%.

Air Leakage—Unwanted air intruding into anexhaust system (holes in ducts, missing and ineffec-tive seals, etc.).

Index 67

Glossary of Air-Pollution Control and ESP TerminologyThe terminology for electrostatic precipitators hasbeen standardized by the Institute of Clean AirCompanies, Inc. (ICAC). The terms most used aredefined below.

Abrasion-Flex—Where cloth has abraded in acreased area by excessive bending.

Absorber—A kind of scrubber.

Absorption—the penetration of a substance into orthrough another; distinct from adsorption.

ACFM—Actual Cubic Feet per Minute of gas vol-ume at the actual condition temperature, pressureand composition. See gas flow rate.

Acid Deposition—(Acid Rain) A complex chemicaland atmospheric phenomenon that occurs whenemissions of sulfur and nitrogen compounds andother substances are transformed by chemicalprocesses in the atmosphere, often far from the orig-inal sources, and then deposited on earth in either awet or dry form. The wet forms, popularly called“acid rain,” can fall as rain, snow or fog. The dryforms are acidic gases or particulates.

Adsorbent—In addition to the adjectival meaning,the term describes any of several substances that


Antisneakage baffles—Internal baffle elementswithin the precipitator to prevent the gas frombypassing the active field or causing hopper reen-trainment.

APC—Air Pollution Control.

Arc—A discharge of substantial magnitude of thehigh voltage system to the grounded system, of rela-tivity long duration and not tending to be immedi-ately self-extinguishing.

Area Source—Any small source of nonnatural airpollution which is not large enough to be classifiedas a major source or point source.

Aromatics—A type of hydrocarbon, such as ben-zene or toluene, added to gasoline in order toincrease octane. Some aromatics are toxic.

Aspect Ratio—The ratio obtained by dividingeffective length of the precipitator by the effectiveheight.

ASTM—American Society of Testing Materials.

Attainment Area—An area considered to have airquality as good as or better than the National Ambi-ent Air Quality Standards as defined by the CleanAir Act. An area may be an attainment area for onepollutant and a nonattainment area for others.

Attrition—Wearing or grinding down by friction.

Index 69

Air Monitoring—The continuous sampling for andmeasuring of pollutants present in the atmosphere.

Air Quality Criteria—As the Federal governmentuses the term, the varying amounts of pollution andlengths of exposure at which specific adverse effectsto health and welfare take place.

Air Quality Standards—The approximate concen-tration level of a selected pollutant that is permittedin the atmosphere to minimize detrimental effects.

Air Pollution—the presence in the atmosphere ofgases, fumes or particulate matter, alone or in com-bination with each other, in sufficient concentrationto disturb the ecological balance; cause objection-able effects, especially sensory offenses; cause transient or chronic illnesses; or impair or destroyproperty.

Air, Standard—Dry air at 70˚ and 29.92 inches(Hg) barometer. This is substantially equivalent to0.075 lb/ft3.

Air Toxics—Any air pollutant for which a nationalambient air quality standard (NAAQS) does notexist (i.e., excluding ozone, carbon monoxide, PM-10, sulfur dioxide, nitrogen oxides) that may reason-ably be anticipated to cause cancer, developmentaleffects, reproductive dysfunctions, neurological dis-orders, heritable gene mutations or other serious orirreversible chronic or acute health effects inhumans.


or liquid entering the filter media and not being dis-charged by the cleaning mechanism. Once enoughmaterial has built up, air flow is severely restrictedand the bags have to be cleaned or replaced.

Blow-pipe—See manifold.

Blue Smoke—A descriptive term for the gaseoushydrocarbons that escape from hot asphalt and othersources of VOC.

Bolted Plate—A cover provided with sufficientbolts to insure tight closure where occasional acces-sibility is required.

Brake Horsepower—The horsepower actuallyrequired to drive a fan. This includes the energylosses in the fan and can be determined only byactual tests of the fan (this does not include thedrive losses between motor and fan).

Bridge—Material building across an opening (suchas a screw conveyer) and blocking off that opening.

Bus Section—The smallest portion of the precipita-tor which can be independently de-energized (bysubdivision of the high voltage system and arrange-ment of support insulators).

CAAA—Clean Air Act Amendments of 1990.

Cable—Oil filled cable or dry cable for transmittinghigh voltages.

Index 71

One of the three basic contributing processes of airpollution, the others being vaporization and com-bustion.

Automatic Power Supply—Automatic regulationof high voltage power for changes in precipitatoroperating conditions utilizing feedback signal(s).Sometimes referred to as AVC (automatic voltagecontrol).

Auxiliary Control Equipment—Electrical compo-nents required to protect, monitor and control theoperation of precipitator rappers, heaters and otherassociated equipment.

BACM—(Best Available Control Measure) A termused in the CAAA referring to the “best” measures(according to EPA guidance) for controlling emis-sions.

BACT—(Best Available Control Technology) Anemission limitation based on the maximum degreeof emission reduction achievable. Under Title I ofthe CAAA, EPA will establish BACT standards forserious, severe and extreme nonattainment areas.

Back Corona—A phenomenon that occurs whenthe gas within a high resistivity dust layer becomesionized, which causes heavy positive ion backflow,which neutralizes negative ion current and reducesvoltage levels.

Blind—(Blinding) Blockage of bag by dust, fume


total number of bus sections.

Cellplate—See tubesheet.

CFM—Cubic Feet (of any gaseous matter) perMinute. See gas flow rate.

Chamber—A gastight longitudinal subdivision of aprecipitator. A precipitator with a single gastightdividing wall is referred to as a two chamber precipi-tator. NOTE: Very wide precipitator chambers arefrequently equipped with nongastight load bearingwalls for structural considerations. These precipita-tors by definition are single chamber precipitators.

Clean Coal Technology—Any technology not inwidespread use as of the date of enactment of theClean Air Act Amendments which will achieve sig-nificant reductions.

Clean Fuel—Blends and/or substitutes for gasolinefuels. These include compressed natural gas,methanol, ethanol and others.

COH—Abbreviation for coefficient of haze, unit ofmeasurement of visibility interference.

Coke Oven—An industrial process which convertscoal into coke, which is one of the basic materialsused in blast furnaces for the conversion of iron oreinto iron.

Collecting Surface Area—The total flat projected

Index 73

Capture Velocity—The air velocity at any point infront of a hood or at a hood opening necessary toovercome opposing air currents and to capture thecontaminated air at the point by causing it to flowinto the hood.

Carbon Monoxide—A colorless, odorless gaswhich is toxic because of its tendency to reduce theoxygen-carrying capacity of the blood.

Carrying Velocity—The gas velocity that is neces-sary to keep the dust airborne. Usually 3500 to 4599ft/min in ductwork depending upon the nature of thedust.

CAS (Chemical Abstracts Service)—RegistryNumber is a numeric designation assigned by theAmerican Chemical Society’s Chemical AbstractsService which uniquely identifies a specific chemi-cal compound.

Casing—Enveloping structure to enclose the inter-nal components of the precipitator. Rectangular orcylindrical configuration are used. The casingincludes the gas tight roof, side walls, and end wallsand hoppers and/or bottoms. A gastight dividingwall is used to separate chambers. A nongastightload bearing wall is used to separate bus sections.The casing is sometimes called the housing or shell.

Cell (In width)—A cell is an arrangement of bussections parallel to gas flow. NOTE: Number ofcells wide times number of fields deep equals the


ter such as carbon oxides, nitrogen, oxygen andwater vapor resulting from the combustion of fossilfuels. 2) In the context of emission control, thegaseous products resulting from the burning of anykind of material containing carbon in a free or com-bined state. Also referred to as “combustion contam-inants.”

Concentration—The amount of dust in gas. Usual-ly expressed in terms of grains per ft3, lbs per 1000lbs of gas, parts per million or milligrams per cubicmeter.

Conduction—The transfer of heat by physical con-tact between substances.

Control Damper—A device installed in a duct toregulate the gas flow by degree of closure. Exam-ples: Butterfly or Multilouver.

Conversion Factors—See page 109 and 110.

Convection—The transfer of heat through a liquidor gas by the actual movement of the molecules.

Corona Power (KW)—The product of secondarycurrent and secondary voltage. Power density isgenerally expressed in terms of: (1) watts per squarefoot of collecting surface, or (2) watts per 1000ACFM of gas flow.

Current Density—The amount of secondary cur-rent per unit of precipitator collecting surface. Com-

Index 75

area of collecting surface exposed to the active elec-trical field (effective length x effective height x 2 xnumber of gas passages).

Collecting Surface Rapper—A device for impart-ing vibration or shock to the collecting surface todislodge the deposited particles or dust.

Collecting Surfaces—The individual elementswhich make up the collecting system and which col-lectively provide the total surface area of the precip-itator for the deposition of dust particles.

Collecting System—The grounded portion of theprecipitator to which the charged dust particles aredriven and to which they adhere.

Collection efficiency—The weight of dust collectedper unit time divided by the weight of dust enteringthe precipitator during the same unit time expressedin percentage. The computation is as follows:

Efficiency = (Dust in) - (Dust out) x 100(Dust In)

Combustion—the production of heat and light ener-gy through a chemical process, usually oxidation.One of the three basic contributing processes of airpollution, the others being attrition and vaporization.

Combustion Air—Amount of air necessary to burnthe available fuel.

Combustion Products—1) Primarily gaseous mat-


humidity and pressure as the temperature is reduced.For flue gaining water vapor and SO it is the set ofconditions at which liquid sulfuric acid begins tocondense as the temperature is reduced.)

Dielectric Fluid—A substance used to keep thetransformer operating at moderate temperature lev-els, and as a dielectric where space is concerned.

Diode Assembly—Converts high voltage AC outputof the transformer to a DC signal.

Discharge Electrode—The part which is installedin the high voltage system to perform the functionof ionizing the gas and creating the electrical field.Typical configurations are

Rigid (RF)Weighted Wire (W/W)Rigid Discharge Electrode (RDE)

Discharge Electrode Rapper—A device forimparting vibration or shock to the discharge elec-trodes in order to dislodge dust accumulation.

Doors—A hinged or detached cover provided with ahand operated fastening device where accessibilityis required.

Dry Bulb Temperature—The actual temperature ofa gas, taken with a conventional thermometer.

DSCFMT—Dry Standard Cubic Feet per Minute.See gas flow rate.

Index 77

mon units are ma/ft.2 and mA/cm2.

Current Limiting Reactor (CLR)—An impedancedevice used to protect T/R diode bridge by limitingthe current flow during an arc or spark. It also pro-vides a means of wave shaping that voltage to pro-vide higher average valves.

CTG (Control Techniques Guideline)—Guidancedocuments issued by EPA which define ReasonablyAvailable Control Technology (RACT) to beapplied to existing facilities that emit certain thresh-old quantities of air pollutants; they contain infor-mation both on the economic and technological fea-sibility of available techniques.

Delta P (AP)—Change in pressure, or pressuredrop, that occurs across a piece of control equip-ment.

DNAPLS—Dense nonaqueous phased liquids.

Density Factor—The ratio of actual air density todensity of standard air. The product of the densityfactor and the density of standard air (0.075 lbs/ft3)will give the actual air density in pounds per cubicfoot.

Dew Point—the temperature at which the equilibri-um vapor pressure of a liquid is equal to the existingpartial pressure of the respective vapor. (For air con-taining water vapor, it is the temperature at whichliquid water begins to condense for a given state of


Effective Width—Total number of gas passagesmultiplied by spacing dimension of the collectingsurfaces.

Effluent—A discharge or emission of a fluid (liquidor gaseous).

Electrostatic Attraction—Mutual attraction, causedby static electricity, by which particles tend to drawtogether or adhere.

Electrostatic Precipitator—A kind of precipitatorthat first charges particulate (ESP), allowing electro-static forces to attract particles to a collection point.

Emission—Release of pollutants into the air from asource.

Emission Control Equipment—Machinery used toremove air contaminants from the discharge ofindustrial exhaust streams.

Emission Factor—The statistical average of theamount of a specific pollutant emitted from eachtype of polluting source in relation to a unit quantityof material handled, processed or burned. Eg. theemission factor of oxides in nitrogen in fuel oilcombustion is 119 lbs per 1,000 gallons of fuel oilused. By using the emission factor of a pollutantand specific data regarding quantities of materialused by a given source, it is possible to computeemissions for that source—information necessaryfor an emission inventory.

Index 79

Dust—A dispersion aerosol formed by the grindingor atomizing of a solid, or the transfer of a powderinto a state of suspension through the action of aircurrents or by vibration.

Dust Collector Efficiency—See collection efficiency.

Dust or Mist Concentration—The weight of dustor mist contained in a unit of gas, e.g. pounds perthousand: pounds of gas, grains per standard drycubic foot (the temperature and pressure of the gasmust be specified if given as volume).

Early Reduction/Early Compliance—A provisionin the CAAA which provides incentives to a compa-ny for complying with new standards before theyare required to by law.

Effective Cross-Sectional Area—Effective widthtimes effective height.

Effective Height—Total height of collecting surfacemeasured from top to bottom.

Effective Length—Total length of collecting sur-face measured in the direction of gas flow. Lengthbetween fields is to be excluded.

Effective Stack Height—The height at which aplume becomes essentially level. It is the actualstack height plus the plume rise.


the exhaust stack, usually measured in ACFM.

Federal Implementation Plan (FIP)—Under cur-rent law, a Federally implemented plan to achieveattainment of an air quality standard, used when aState is unable to develop an adequate plan. Underthe Senate bill, a plan containing control measuresdeveloped and promulgated by EPA in order to fillgaps in a State Implementation Plan (SIP).

Field (in depth)—A field is an arrangement of bussections perpendicular to gas flow that is energizedby one or more high voltage power supplies.

Fines—Fine particulate; aerosol.

Flexing—Bending, or contracting and expanding.

Fly Ash—The particulate impurities resulting fromthe burning of coal and other material.

Fog—The condensation of water vapor in air. Alsosee smog.

Forced Draft Burner—A burner which has its sec-ondary air supplied under pressure. This is normallydone by surrounding the dryer opening by a plenumor windbox and supplying the air with a low pres-sure fan.

Fossil Fuels—Coal, oil and natural gas; so-calledbecause they are the remains of ancient plant andanimal life.

Index 81

Emission Inventory—A list of primary air pollu-tants emitted into a given community’s atmosphere,in amounts (commonly tons) per day, by type ofsource. The emission inventory is basic to the estab-lishment of emission standards. Also see emissionfactor.

Emission Standard—The maximum amount of apollutant that is permitted to be discharged from asingle polluting source: e.g., the number of poundsof fly ash per cubic foot of gas that may be emittedfrom a coal-fired boiler. Rule or measurement estab-lished to regulate or control the amount of a givenpollutant that may be discharged to the outdooratmosphere from its source.

EPA—Environmental Protection Agency.

Evaporation—The physical transformation of a liq-uid to a gas at any temperature below its boilingpoint.

Excess Air—Air in excess of the amount necessaryto combust all the available fuel.

Exhaust Gas—The gases emitting from an industri-al process, generally a combustion process.

Exhaust Stack Temperature—The temperature ofthe exhaust gas, measured in the discharge stack.

Exhaust Volume—The amount of exhaust gas (air,products of combustion and water vapor) leaving


The volume of process gas at any point of the plantexhaust system measured in terms of minutes. Thereare several units of measurement:

ACFM—The actual gas flow measured (Actual Cubic Feet per Minute)SCFM—The gas flow volume reduced to 70˚F (standard temperature) by calculation (Standard Cubic Feet per Minute)DSCFM—The gas flow reduced to 70˚ (standard temperature) and without volume of steam or water vapor contained in the exhaust gas(Dry Standard Cubic Feet per Minute)

Gas Passage—Formed by two adjacent rows of col-lecting surfaces; measured from collecting surfacecenterline to collecting surface centerline.

Grain—A dust weight unit commonly used in airpollution control. Equal to one seven thousandth ofa pound. One grain = 1/7000 lb.

Grain Loading—The rate at which particles areemitted from a pollution source. Measurement ismade by the number of grains per cubic foot of gasemitted.

Halons—A family of compounds containingbromine, fluorine, iodine and chlorine used in fight-ing fires, that breakdown in the atmosphere deplet-ing stratospheric ozone.

HAPs (Hazardous Air Pollutants)—Any of the189 chemicals listed under Title III of the CAAA.

Index 83

Fugitive Emissions—Emissions not caught by acapture system.

Fume—solid particulates generated by condensationfrom the gaseous state, generally after volatilizationfrom molten metal, and often accompanied by achemical reaction, such as oxidation. Fumes floccu-late and sometimes coalesce.

GACT—(Generally Available Control Technology)Methods, practices and techniques which are com-mercially available and appropriate considering eco-nomic impacts and the technical capabilities of thefirms to operate and maintain the emissions controlsystems. Under Title III of the CAAA, EPA willestablish either GACT or MACT standards for eachsource of HAPs.

Gas Distribution Devices—Internal elements in thetransition or ductwork to produce the desired veloci-ty contour at the inlet and outlet of the precipitator.Example: turning vanes or perforated plates.

Gas Distribution Plate Rapper—A device used toprevent dust buildup on perforated plates.

Gases—Normally, formless fluids which occupy thespace of their enclosure and which can be changedto a liquid or solid state only by the combined effectof increased pressure and decreased temperature.Gases diffuse.

Gas Flow Rate, Cubic Feet per Minute (CFM)—


3. Silicon Controlled Rectifier (SCR)—Electronic switch for voltage regulation

High Voltage Structure—The structural elementsnecessary to support the discharge electrodes intheir relation to the collecting surface by means ofhigh voltage insulators.

High Voltage Systems—All parts of the precipitatorwhich are maintained at a high electrical potential.

High Voltage System—Support Insulator—Adevice to physically support and electrically isolatethe high voltage system from ground.

Hi-Volume Sampler—Also called a Hi-Vol. Adevice used in the measurement and analysis of sus-pended particulate pollution.

HON—Hazardous Organic NESHAPs.

Hopper Capacity—Total volumetric capacity ofhoppers measured from a plane 10" below high volt-age system or plates, whichever is lower.

Humidity, Absolute—The weight of water vaporper unit volume, pounds per cubic foot or grams percubic centimeter.

Humidity, Relative—The ratio of the actual partialpressure of water vapor in a space to the saturatedpressure of pure water vapor in a space to the satu-rated pressure of pure water at the same temperature.

Index 85

All HAP sources will have to comply with GACT orMACT standards.

HCFCs—Chlorofluorocarbons that have beenchemically altered by the addition of hydrogen, andwhich are significantly less damaging to stratospher-ic ozone than other CFCs.

HEPA Filter (High Efficiency Particulate Air Fil-ter)—Capable of removing at least 99.97% bycount of a standard 0.3 micron challenge particulate(DOP test).

High Voltage Conductors—Conductor to transmitthe high voltage from the transformer rectifier to theprecipitator high voltage system.

High Voltage Power Supply—The supply unit toproduce the high voltage required for precipitation,consisting of a transformer rectifier combination andassociated controls. Numerous bus sections can beindependently energized by one power supply.

High Voltage Power Supply ControlEquipment—Electrical components required toprotect, monitor and regulate the power supplied tothe precipitator high voltage system. Regulation ofthe primary voltage of the high voltage transformerrectifier is accomplished by one of the followingdevices:

1. Saturable Core Reactor—A variable impedance device

2. Variable “Auto-Transformer” control


Isolation Damper—A device installed in a duct toisolate a precipitator chamber from process gas.

Inversion—An atmospheric condition caused by alayer of warm air preventing the rise of cooling airtrapped beneath it. This prevents the rise of pollu-tants that might otherwise be dispersed and resultsin a concentration of the air pollution.

Impedance Devices—1. Linear inductor or current limiting reactor

required to work with SCR-type controllers2. A transformer with a specially designed high

impedance core and coils3. Saturable core reactor4. Resistors

LAER (Lowest Achievable Emission Rate)—Therate of emissions which reflects either the moststringent emission limit contained in the implemen-tation plan of any state (unless it is proved that suchlimitations are not achievable) or the most stringentemission limit achieved in practice, whichever ismost stringent.

Liquid Flowrate—The amount of water or “scrub-bing liquid” introduced into a wet collector.

Low NOx Burners—One of several combustiontechnologies used to reduce emission of NOx.

Lower Explosive Limit—The lower limit of flam-mability or explosibility of a gas or vapor at ordi-

Index 87

H.V. Bus—A conductor enclosed within a groundedduct.

Hydrocarbon—Any of the vast family of com-pounds containing carbon and hydrogen in variouscombinations: found especially in fossil fuels. Someof the hydrocarbon compounds are major air pollu-tants; they may be carcinogenic or active partici-pants in the photochemical smog process.

Inch of Water—A unit of pressure equal to thepressure exerted by a column of water one inch highat a standard temperature. (407" WC = 14.7 PSI)

Inches WG (Inches of Water Gauge)—See inch ofwater.

Incinerator—A device which burns household,industrial, pathological or hazardous solid, liquid orgaseous wastes under controlled conditions.

Inclined Manometer—A testing instrument using aliquid column, set at an incline to increase readingaccuracy, to measure pressure. Normally used toread velocity pressure.

Insulation—Any method which will retard the flowof heat through a wall.

Insulator Compartment—Enclosure for the insula-tor(s) supporting the high voltage system (may con-tain one or more insulators, but not enclosing theroof as a whole).


fall. The difference in the level of the water columnsis equivalent to the pressure differential.

Manual Power Supply—Manual regulation of highvoltage power based on precipitator operating con-ditions as observed by plant operators.

Mechanical Collector—Devices that are function-ally dependent on the laws of mechanics governingthe motion of bodies in space. Can be operated dryor wet. When operated wet, devices are generallycalled scrubbers. Examples of mechanical collectorsare cyclones, settling chambers and various types ofimpingement collectors.

Mega—A prefix meaning 1 million.

Micro—A prefix meaning 1/1,000,000 abbreviatedby the Greek letter u.

Micrometer—See micron.

Micron—Symbol um; a unit of length equal to onemillionth of a meter. An average human hair is 70microns in diameter. In general, particles down to 10microns can be seen without the aid of magnification.

Migration Velocity—A parameter in the Deutch-Anderson equation used to determine the requiredsize of an electrostatic precipitator to meet specifieddesign conditions. Other terminology used: W-valueand precipitation rate. Values are generally stated interms of ft/min or cm/sec.

Index 89

nary ambient temperature expressed in percent of agas or a vapor in air by volume.

Lower Weather Enclosure—A nongastight enclo-sure at base of precipitator to protect hoppers fromwind and/or detrimental weather conditions.

MACT (Maximum Achievable Control Technolo-gy)—the standard with which sources of HAPs willhave to comply; the CAAA defines MACT as “themaximum degree of reduction in emissions...achievable for new or existing sources... taking intoaccount the cost of achieving such reductions.”MACT standards for existing sources must be atleast as stringent as the average level of controlachieved at the best controlled 12 percent of facili-ties, and MACT for new sources will have to beeven stricter.

Major Source—A stationary source which emits alarge amount of pollution. In nonattainment areas,under Title I of the CAAA, a major source is onewhich emits more than 100, 50, 25 or 10 tons peryear depending on whether the area is classified asMarginal or Moderate, Serious, Severe or Extreme,respectively. For hazardous air pollutants, underTitle III of the CAAA, a major source is one whichcan emit more than 10 TPY of any one HAP or 25TPY of total HAPs.

Manometer—A u-shaped device for measuring thestatic pressure at a point relative to some otherpoint; the pressure difference causes water to rise or


New Source—A stationary source, the constructionor reconstruction of which is commenced after theproposal date of the standard. Also NSPS (NewSource Performance Standard).

NIOSH (National Institute for OccupationalSafety and Health)—Created by the OccupationalSafety and Health Act of 1970. NIOSH is part of theCenters for Disease Control under the Departmentof Health and Human Services. Its mandate includesconduction research in developing criteria and/orrecommendations to be used in setting occupationalexposure standards, identifying and evaluatingworkplace hazards, measurement techniques andcontrol technologies, and providing professionaleducation as well as health and safety information.

Nonattainment Area—An area which has notachieved air quality as good as the National Ambi-ent Air Quality Standards as defined by the CAAA.

NOx (Nitrogen Oxides)—Chemical compoundscontaining nitrogen and oxygen; react with volatileorganic compounds, in the presence of heat and sun-light, to form ozone. They are also a major precur-sor to acid rain. Nationwide, approximately 45% ofNOx emissions come from mobile sources, 35%from electric utilities and 15% from industrial fuelcombustion.

OCIS (OSHA Computerized Information Sys-tem)—A comprehensive data base that contains

Index 91

Milli—A prefix meaning 1/1,000.

Mist—Suspended liquid droplets generated by con-densation from the gaseous to the liquid state or bybreaking up a liquid into a dispersed state, such asby splashing, foaming and atomizing.

Modeling—An investigative technique using com-puter mathematical or physical representation of asystem that accounts for all or some of its knownproperties.

Montreal Protocol—An international environmen-tal agreement to control chemicals that deplete theozone layer. The protocol, which was renegotiatedin June 1990, calls for a phaseout of CFCs, halonsand carbon tetrachloride by the year 2000, a phase-out of chloroform by 2005, and provides financialassistance to help developing countries make thetransition from ozone-depleting substances.

MSDS (Material Safety Data Sheet)—Compila-tion of data and information on individual hazardouschemicals produced by the manufacturers andimporters of that chemical, as required by OSHA’sHazard Communication Standard, 29 CFR1910.1200.

NEDS—National Emission Data System.

NESHAP—National Emissions Standards for Haz-ardous Air Pollutants.


over the precipitator to contain the high voltageinsulators.

Permit—An authorization, license or equivalentcontrol document issued by EPA or an approvedstate agency to implement the requirements of anenvironmental regulation; e.g., a permit to operate afacility that may generate harmful emissions.

Photochemical Process—The chemical changesbrought about by the radiant energy of the sun act-ing upon various polluting substances. The productsare known as photochemical smog.

Pitot Tube—A specially constructed probe for tak-ing velocity pressure readings in a duct.

Plenum—Pressure equalizing chamber.

Plenum Pulse—Type of pulsing collector whereentire sections of the clean air plenum are isolatedand pulsed with either compressed air or air from ahigh pressure blower.

PM10—A new standard for measuring the amount ofsolid or liquid matter suspended in the atmosphere(“particulate matter”). Refers to the amount of par-ticulate matter under 10 micrometers in diameter.The smaller PM10 particles penetrate to the deeperportions of the lung, affecting sensitive populationgroups such as children and people with respiratorydiseases.

Index 93

information and data on standards interpretation,chemical information, hazardous waste activity5(a)(1) citations, a health hazard evaluation index,training materials and other information compiledby OSHA on subjects related to occupational safetyand health.

Opacity—Refers to the amount of light that canpass through; normally refers to the degree of visi-bility of an exhaust plume. Normal measurementtechnique used is by EPA method 9.

Ozone—A compound consisting of three oxygenatoms, that is the primary constituent of smog. It isformed through chemical reactions in the atmos-phere involving volatile organic compounds, nitro-gen oxides and sunlight. Ozone can initiate damageto the lungs as well as damage to trees, crops andmaterials. There is a natural layer of ozone in theupper atmosphere which shields the earth fromharmful ultraviolet radiation.

Particulate—A particle of solid or liquid matter.

Particulate Matter—Any solid or liquid material inthe atmosphere.

PEL (Permissible Exposure Limits)—Limitsdeveloped by OSHA to indicate the maximum air-borne concentration of a contaminant to which anemployee may be exposed.

Penthouse—A weatherproof, gastight enclosure


Precipitator Voltage—The average DC voltagebetween the high voltage system and grounded sideof the precipitator.

Effective cross section is construed to be theeffective field height x width of gas passage x num-ber of passages.

Pressure, Atmospheric—The pressure due to theweight of the atmosphere. It is the pressure indicat-ed by a barometer; standard atmospheric pressure is29.92 inches of mercury.

Pressure Drop—The differential pressure betweentwo points in a system. The resistance to flowbetween the two points.

Pressure, Static—The potential pressure exerted inall directions by fluid at rest. For a fluid in motion itis measured in a direction normal (90˚) to the direc-tion of flow. Usually expressed in inches watergauge when dealing with air.

Pressure, Velocity—The kinetic pressure in thedirectional flow necessary to cause a fluid at rest toflow at a given velocity. Usually expressed in incheswater gauge.

Prevention of Significant Deterioration (PSD)—EPA program in which state and/or federal permitsare required that are intended to restrict emissionsfor new or modified sources in places where airquality is already better than required to meet pri-mary and secondary ambient air quality standards.

Index 95

Point Source—A stationary location or facilityfrom which pollutants are emitted. Also, any singleidentifiable source of pollution.

Polymerized—A chemical reaction in which twoore more small molecules combine to form largermolecules that contain repeating structural units ofthe original molecules.

Pounds per 100 Pounds of Gas—A common quan-titative definition of pollution concentration.

PPM (Parts per Million)—The number of parts ofa given pollutant in a million parts of air. Units areexpressed by weight or volume.

Precipitator Current—The rectified or unidirec-tional average current to the precipitator measuredby a milliammeter in the ground leg of the rectifier.

Precipitators—Any number of devices usingmechanical, electrical or chemical means to collectparticulates. Used for measurement, analysis or con-trol. See electrostatic precipitator.

Precipitator Gas Velocity—A figure obtained bydividing the volume rate of gas flow through theprecipitator by the effective cross sectional area ofthe precipitator. Gas velocity is generally expressedin terms of ft./sec. and is computed as follows:

Velocity = Gas Volume (CFM)Effective cross section area ft2


Measures)—A broadly defined term referring totechnologies and other measures that can be used tocontrol pollution; includes Reasonably AvailableControl Technology and other measures. In the caseof PM10, it refers to approaches for controlling smallor dispersed source categories such as road dust,wood stoves and open burning.

RACT (Reasonably Available Control Technolo-gy)—An emission limitation on existing sources innonattainment areas, defined by EPA in a ControlTechniques Guideline (CTG) and adopted andimplemented by states. Under Title I of the CAAA,EPA will establish RACT standards for marginal,moderate and serious nonattainment areas.

Radionuclide—Radioactive element which can beman-made or naturally occurring. They can have along life as pollutants, and are believed to havepotentially mutagenic effects on the human body.

Radon—A colorless, naturally occurring, radioac-tive, inert gaseous element formed by radioactivedecay of radium atoms in soil or rocks.

Rapper Insulator—A device to electrically isolatedischarge electrode rappers yet transmit mechanical-ly, forces necessary to create vibration or shock inthe high voltage system.

Reentrainment—The phenomenon whereby dust iscollected from the air stream and then is returned tothe air stream. Occurs when dust is pulsed from a bag

Index 97

Primary Collector—A dry or wet collector whichis followed by a secondary collector with greater fil-tering efficiency.

Primary Current—Current in the transformer pri-mary as measured by an AC ammeter.

Primary Voltage—The voltage as indicated by AC voltmeter across the primary windings of thetransformer.

Process Weight—The weight per hour that is runthrough the process. Commonly used in APC codesto determine the maximum allowable pollutionexhausted.

Promulgate—To make a new law known and put itinto effect. The EPA promulgates a rule when itissues the final version in the Federal Register.

PSI (Pounds per Square Inch)—A measure ofpressure. 1 psi equals 27.7" water gauge.

PSIA (Pounds per Square Inch Absolute)—Theabsolute pressure without reference to another point.Atmospheric pressure is 14.7 PSIA.

PSIG (Pounds per Square Inch Gauge)—Thepressure relative to atmospheric. For instance, 10PSIG equals 24.7 PSIA. This is the common pres-sure term.

RACM (Reasonably Available Control


cent black; a Ringelman No. 5, to 100 percent. Theyare used for measuring the opacity of smoke arisingfrom stacks and other sources, by matching with theactual effluent, the various numbers, or densities,indicated by the charts. Ringelman numbers weresometimes used in setting emission standards.

RTECS (Registry of Toxic Effects of ChemicalSubstances)—A data base that lists an identificationnumber, synonyms, Department of Transportation(DOT) hazard label information, EPA Toxic Sub-stances Control Act (TSCA) information, OSHAand Mine Safety and Health Administration(MSHA) air exposure limits, and animal and humantoxicologic data.

Sanctions—Actions taken against a state or localgovernment for failure to plan or to implement aSIP, e.g., a ban on construction of new sources.

Safety Grounding Device—A device for physicallygrounding the high voltage system prior to person-nel entering the precipitator. (The most commontype consists of a conductor, one end of which isgrounded to the casing, the other end attached to thehigh voltage system using an insulated operatinglever.)

SCFM (Standard Cubic Feet per Minute)—Thevolume that a gas would occupy at standard temper-ature and pressure conditions (70˚ F and 14.7PSIA). See gas flow rate.

Index 99

and then caught up by an upward moving air stream.

REL (Recommended Exposure Limits)—Issuedby NOISH to aid in controlling hazards in the work-place. These limits are generally expressed as 8- or10-hour TWAs for a 40-hour work week and/or ceil-ing levels with time limits ranging from instanta-neous to 120 minutes.

Repowering—The replacement of an existing coal-fired boiler with one or more clean coal technolo-gies, in order to achieve significantly greater emis-sion reduction relative to the performance oftechnology in widespread use as of the enactment ofthe Clean Air Act Amendments.

Residual Risk—The quantity of health risk remain-ing after application of the MACT (MaximumAchievable Control Technology).

Resistance—In air flow, it is caused by friction ofthe air against any surface, or by changing themomentum of the gas.

Ringelman—A measure of the opacity caused bypollution from a stack. Grades opacity from 0 to 5,where 0 is an invisible discharge and 5 is totallyopaque.

Ringleman Chart—Actually, a series of charts,numbered from 0 to 5, that simulate various smokedensities, by presenting different percentages ofblack. A Ringelman No. 1 is equivalent to 20 per-


taken by the State and its subdivisions to implementtheir responsibilities under the Clean Air Act.

Smog—The irritating haze resulting from the sun’seffect on certain pollutants in the air, notably thosefrom automobile exhaust; see photochemicalprocess. Also a mixture of fog and smoke.

Smoke—Carbon or soot particles, less than 0.1micrometers in size which result from the incom-plete combustion of carbonaceous materials such ascoal, oil, tar and tobacco.

SO2—Sulfur dioxide is an invisible, nonflammableacidic gas, formed during combustion of fuel con-taining sulfur.

SO3—Sulfur trioxide oxidized from SO2; combineswith atmospheric moisture to form sulfuric acid mist(H2SO4).

Soot—Very finely divided carbon particles clusteredtogether in long chains.

Source—Any place or object from which pollutantsare released.

Spark—A discharge from the high voltage systemto the ground system, self-extinguishing and ofshort duration.

Specific Collecting Area (SCA)—A figure obtainedby dividing total effective collecting surface of the

Index 101

Scrubber—A device that uses a liquid spray toremove aerosol and gaseous pollutants from an airstream. The gases are removed either by absorptionor chemical reaction. Solid and liquid particulatesare removed through contact with the spray. Scrub-bers are used for both the measurement and controlof pollution.

Scrubber, Gas—Any device in which a contami-nant, solid or gaseous, is removed from a gas streamby liquid droplets. (Types include spray towers,packed towers, cyclone scrubbers, jet scrubbers, ori-fice scrubbers, venturi scrubbers, impingementscrubbers and mechanical scrubbers).

Secondary Collector—A dust collector which ispreceded by primary collector(s). The secondary fil-ter normally has a higher filtering efficiency.

Settling Chamber—A dry collection device whichremoves particulate matter from the gas stream byslowing down the exhaust gas velocity.

Silicon Rectifier—A rectifier consisting of silicondiodes immersed in mineral oil or silicone oil.

Single Precipitator—An arrangement of collectingsurfaces and discharge electrodes contained withinone independent casing.

SIP (State Implementation Plan)—Documents pre-pared by states, and submitted to EPA for approval,which identifies actions and programs to be under-


air in excess of the stoichiometric ratio is usually pro-vided to encourage complete combustion of the fuel.

Sulfur Dioxide (SO2)—A heavy, pungent, colorlessair pollutant formed primarily by the combustion offossil fuels. It is a respiratory irritant, especially forasthmatics, and is the major precursor to the forma-tion of acid rain.

Sulfur Oxides—Pungent, colorless gases formedprimarily by the combustion of fossil fuels; consid-ered major air pollutants, sulfur oxides may damagethe respiratory tract as well as vegetation.

System Gas Volume—All gases flowing throughthe exhaust gas system (including excess air, scav-enger air, leakage air).

Tape Sampler—A device used in the measurementof both gases and fine particulates. It allows air sam-pling to be made automatically at predeterminedtimes.

Threshold Limit Values (TLV)—Represents the airconcentrations of chemical substances to which it isbelieved that workers may be exposed daily withoutadverse effect.

TLV® (Threshold Limit Value)—A registeredtrademark for an exposure limit developed by theAmerican Conference of Governmental IndustrialHygienists (ACGIH). A listing of TLVs may befound in the ACGIH’s “Documentation of the

Index 103

precipitator by gas volume, expressed in thousandsof actual cubic feet per minute.

Stack—A smokestack; a vertical pipe or fluedesigned to exhaust gases.

Stage II Controls—Systems placed on service sta-tion gasoline pumps to control and capture gasolinevapors during an automobile refueling.

Static Pressure (Cold)—The pressure caused bythe resistance to air flow through the system if thegas were at standard conditions or colder, if this is apossibility.

Static Pressure (Hot)—The pressure caused by theresistance to air flow through the system at actualconditions. Measured in inches of water (WG).

Streamline Flow—Fluid flow in which the velocitypressure and fluid density of a given particleremains constant with time.

STEL (Short Term Exposure Limit)—Theemployee’s 15 minute time weighted average expo-sure which cannot be exceeded at any time. STEL isset by OSHA for each pollutant and expressed interms of ppm or mg/m3.

Stoichiometric Air—The exact quantity of airrequired to combine with the given fuel so that theensuing combustion reaction is perfect and no freeoxygen or unburned constituents remain. In reality,


TSCA (Toxic Substances Control Act)—Adminis-tered by the Environmental Protection Agency(EPA), was passed by Congress to protect humanhealth and the environment by requiring testing andnecessary use restrictions to regulate the commerceof certain chemical substances.

TSD (Facility)—Treatment, Storage and Disposal.

Turbulent Flow—Fluid flow in which the velocityof a given particle changes constantly both in mag-nitude and direction—here, uneven gas flow in theexhaust system is caused by obstructions andchanges in direction.

Turning Vanes—Vanes in ductwork or transition toguide the gas and dust flow through the ductwork inorder to minimize pressure drop and to control thevelocity and dust concentration contours.

TWA (Time Weighted Average)—Employee’saverage airborne exposure which can not be exceed-ed in any 8-hour work shift. TWA is set by OSHAand expressed in mg/m3.

Upper Weather Enclosure—A nongastight enclo-sure on the roof of the precipitator to shelter equip-ment (T/R sets, rappers, purge air fans, etc.) andmaintenance personnel.

Vaporization—The change of a substance from theliquid to a gaseous state. One of the three basic con-tributing processes of air pollution: the others being

Index 105

Threshold Limit Values and Biological ExposureIndices for 1988-1989.”

TPY—Tons per year.

Transformer Rectifier—A unit comprised of atransformer for stepping up normal service voltagesto voltages in the kilovolt range, and a rectifier oper-ating at high voltage to convert AC to unidirectionalcurrent.

Transition—An aerodynamically designed inlet oroutlet duct connection to the precipitator. Transi-tions are normally included as part of the precipita-tor, sometimes referred to as inlet/outlet nozzles.

Transportation Control Measures (TCMs)—Stepstaken by a locality to adjust traffic patterns (e.g., buslanes, right turn on red) or reduce vehicle use(ridesharing, high-occupancy vehicle lanes) toreduce vehicular emissions of air pollutants.

Traverse—A method of sampling points in a ductwhere pressure readings will be taken to determinevelocity. A traverse divides the duct into equal,evenly distributed areas that are each tested, com-pensating for errors caused by uneven gas flow inthe duct.

Treatment Time—A figure, in seconds, obtained bydividing the effective length, in feet, of a precipita-tor by the precipitator gas velocity figure calculatedabove.


VOCs (Volatile Organic Compounds)—A groupof chemicals that react in the atmosphere with nitro-gen oxides in the presence of heat and sunlight toform ozone; does not include methane and othercompounds determined by EPA to have negligiblephotochemical reactivity. Examples of VOCsinclude gasoline fumes and oil-based paints.

Voltage Divider—A means for supplying a lowvoltage feedback signal that is proportional to theKV output of the T/R.

Water Gauge—Inches water is a pressure termdefined as a pressure equal to that exerted by a col-umn of water of the same height. 27.7" WG equals1 PSI.

Wet Bulb Temperature—The temperature of a gasstream taken with a wetted thermometer. It isapproximately equal to the adiabatic saturation tem-perature of the gas.

Wet Collector—Dust collector which uses water toremove particulate matter from the exhaust gas (wetwashers, venturis, wet fans).

Wrapper—Used in electrostatic precipitators, thelight gauge steel or aluminum covering put overinsulation.

Index 107

attrition and combustion.

Vapors—The gaseous form of substances which arenormally in the solid or liquid state and which canbe changed to these states, either by increasing thepressure or decreasing the temperature alone. Vaporsdiffuse.

Variance—Permission granted for a limited time,under stated conditions, for a person or company tooperate outside the limits prescribed in a regulation.Usually granted to allow time for engineering andfabrication of abatement equipment to bring theoperation into compliance.

Velometer—A simple instrument for determiningthe velocity of gas in a duct. Its operation is similarto an inclined manometer, except that it automatical-ly converts the reading to velocity.

Venturi—Device used to increase the efficiency ofa compressed air pulse. Designed with convergingcircular sides to a throat and then diverging sides.Designed such that when a pulse is introduced at thetop, a negative pressure zone is created outside thetop, and secondary air is induced into the venturi,compounding the pulse strength.

Venturi Scrubber—A wet type dust collector thatcan obtain very high efficiency, but requires largehorsepower to do so. The gas and dust particles areaccelerated in a throat, where finely atomized wateris introduced and water/dust collisions take place.


CONVERSION FACTORS METRIC EQUIVALENTSLengthcm = 0.3937 in in = 2.5400 cmmeter = 3.2808 ft ft = 0.3048 mmeter = 1.0936 yd yd = 0.9144 km

Volumecm3 = 0.0610 in3 in3 = 16.3872 cm3

m3 = 35.3145 ft3 ft3 = 0.0283 m3

m3 = 1.3079 yd3 yd3 = 0.7647 m3

Capacityliter = 2.2046 lb of liter = 0.2642 gal (US)pure water at 4C in3 = 0.0164 liter

liter = 61.0250 in3 ft3 = 28.3162 literliter = 0.0353 ft3 gal (US) = 3.7853 liter

Weightgram = 15.4324 grains grain = 1/7000 lbgram = 0.0353 oz grain = 0.0648 gkg = 2.2046 lb oz = 28.3495 g

lb = 0.4536 kg

Concentrationgrain/ft3 = 2288.1 mg/m3

lb/acre = 0.11208 g/m2lb/1000 ft3 = 16,017 mg/m3

lb/1000 ft2 = 4.8807 g/m2

ton/sq mile = 0.35026 g/m2

grain/ft2 = 0.69725 g/m2

Index 109

CLEAN AIR ACT AMENDMENTS1990Title I: Nonattainment: Ambient Air Quality

Title II: Motor Vehicles

Title III: Hazardous Air Pollutants

Title IV: Acid Rain

Title V: Permits

Title VI: Stratospheric Ozone

Title VII: Enforcement

Title VIII: Miscellaneous


ALTITUDE-PRESSURETEMPERATURE DENSITYTABLE OF AIRAltitude Pressure Temperature Density

(feet) (In Hg Abs) (Degrees F) (lbs/ft3)

0 29.92 70.0 .0750500 29.38 68.1 .0740

1000 28.85 66.1 .07301500 28.33 64.2 .07192000 27.82 62.3 .07092500 27.31 60.4 .06983000 26.81 58.4 .06873500 26.33 56.5 .06764000 25.84 54.6 .06664500 25.37 52.6 .06575000 24.89 50.7 .06485500 24.43 48.8 .06386000 23.98 46.9 .06286500 23.53 45.0 .06197000 23.09 43.0 .06107500 22.65 41.0 .06008000 22.12 39.0 .05908500 21.80 37.1 .05819000 21.38 35.2 .05739500 20.98 33.3 .0564

10000 20.57 31.3 .055511000 19.75 28.5 .053812000 19.03 23.6 .052113000 18.29 19.7 .050514000 17.57 15.8 .048815000 16.88 12.0 .047320000 13.70 -12.6 .0405

Index 111

Heat & Energy Units1 boiler HP = 33,475 Btu/hr1 ton (refrig) = 12,000 Btu/hrBtu = 0.2520 kg-cal

1 kw-hr= 1 hp-hr=1000 whr 0.7457 kw-hr1.3410 hp-hr 1,980,000 ft-lb3413 Btu 2545 Btu1 lb water evaporated from and at 212 F

Temperature EquivalentsFahrenheit, ˚F = ˚Ranking - 460 = (˚Cx9/5)+32Celsius, ˚C = ˚Kelvin - 273 = 5/9 = (˚F-32)x5/9

Pressure Equivalents1 atmosphere =14.696 lb/in2 = 2116.3 lb/ft2

33.96 ft of water = 407.52 in water29.92 in mercury = 760 mm mercury1.01296 bar

1 in water =0.0361 lb/in2 = 5.196 lb/ft2

0.0735 in mercury = 1.876 mm mercury0.002456 atmosphere = 0.08333 ft water

1 bar =0.9872 atmosphere14.5 lb/in2


TITLE IIIHazardous Air PollutantsCAS No. Chemical Name Category75070 Acetaldehyde OV60355 Acetamide OV75058 Acetonitrile OV96862 Acetophenone OV53963 2-Acetylaminofluorene OV107028 Acrolein OV79061 Acrylamide OV79107 Acrylic acid OV107131 Acrylonitrile OV107051 Allyl chloride HV92671 4-Aminodiphenyl OV62533 Aniline OV90040 o-Anisidline OV1332214 Asbestos N71432 Benzene OV

(including gasoline)92875 Benzidine OV98077 Benzotrichloride HV100447 Benzyl chloride HV92524 Biphenyl OV117817 Bls (2-ethylhexyl)phthalate OV

(DEHP)542881 Bls(chiromethyl)ether HV75252 Bromoform HV106990 1,3-Butadiene OV156627 Calcium cyanamide OV105602 Caprolactarn133062 Captan OV63252 Carbaryl OV

Index 113

Altitude-Pressure Temperature Density Tableof Air (continued)

Altitude Pressure Temperature Density(feet) (In Hg Abs) (Degrees F) (lbs/ft3)

25000 11.10 -30.1 .033730000 8.88 -47.5 .028135000 7.03 -65.6 .023340000 5.54 -69.8 .018545000 4.36 -69.8 .014550000 3.43 -69.8 .0114


Hazardous Air Pollutants (continued)

CAS No. Chemical Name Category542756 1,3-Dichloropropolene HV62737 Dichlorovos HV111422 Diethanolamine OV121697 N,N-Diethyl anilline OV

(N,N-Dimethylaniline)64675 Dimethyl sulfate OV119904 3,3-Dimethoxybenzidine OV60117 Dimethyl aminoazobenzene OV119937 3,3'-Dimethyl benzidine OV79447 Dimethyl Carbamoyl chloride OV68112 Dimethyl formamide57147 1,1-Dimethyl hydrazine OV131113 Dimethyl phthalate OV77781 Dimethyl sulfate OV534521 4,6-Dinitro-o-cresol, and Salts OV51285 2,4-Dinitrophenol OV121142 2,4-Dinitrotoluene OV123911 1,4-Dioxane OV

(1,4-Diethyleneoxide)122667 1,2-Diphenythydrazine OV106898 Ephichlorohydrin HV

(1-Chloro-2,3-epoxypropane)106887 1,2-Epoxybutane OV140885 Ethyl acrylate OV104414 Ethyl benzene OV51796 Ethyl carbonate (urethane) OV75003 Ethyl chloride (chloroethane) HV106934 Ethylene dibromide HV

(dibromoethane)

Index 115


CAS No. Chemical Name Category75150 Carbon disulfide OV56235 Carbon tetrachloride HV463581 Carbonyl sulfide OV120809 Catechol OV133904 Chloramben HV57749 Chlordane HV7782505 Chlorine N79118 Chloroscetic acid HV532274 2-Chloroacetophenone HV108907 Chlorobenzene HV510156 Chlorobenzilate HV67663 Chloroform HV107302 Chloromethyl methyl ether HV126998 Chloroprene HV1319773 Cresols/Cresylic acid OV

(isomers/mixer)95487 o-Cresol OV108394 m-Cresol OV106445 p-Cresol OV98828 Cumene OV94757 2,4-D, Salts and Esters HV3547044 DDE334883 Diazomethane OV132649 Dibenzofurans OV96128 1,2-Dibromo-3-chloropropane HV84742 Dibutylphthalate OV106467 1,4-Dichlorobenzene(p) HV91941 3,3-Dichlorobenzidene HV111444 Dichloroethyl ether HV

(Bls(2-chloroethyl) ether)



CAS No. Chemical Name Category71556 Methyl chloroform HV

(1,1,1-Trichloroethane)74884 Methyl iodide (Iodomethane) HV108101 Methyl isobutyl ketone OV

(Hexone)624839 Methyl isocyanate OV80626 Methyl methacrylate OV1634044 Methyl tert butyl ether OV101144 4,4'-Methylene bis

(2-chloroardiline) HV75092 Methylene chloride HV

(Dichloromethane)101688 Methylene diphenyl OV

diisocyanate (MDI)107779 4,4'-Methylenedlaniline OV91203 Naphthalene OV98953 Nitrobenzene OV92933 4-Nitrobiphenyl OV100027 4-Nitrophenol OV79469 2-Nitropropane OV684935 N-Nitroso-N-methylurea OV62759 N-Nitrosodimethylamine OV59892 N-Nitrosomorpholine OV56382 Parathion OV82688 Pentachloronitrobenzene OV87865 Pentachlorophenol HV108952 Phenol OV106503 P-Phenylenediamine OV75445 Phosgene HV7803512 Phosphine

Index 117


CAS No. Chemical Name Category107062 Ethylene dichloride HV

(1,2-dichloroethane)107211 Ethylene glycol OV151564 Ethylene imine (Aziridine) OV75218 Ethylene oxide OV96457 Ethylene thlourea OV75343 Ethylene dichloride OV

(1,1-Dichloroethane)50000 Formaldehyde OV76448 Heptachlor HV118741 Hexachlorobenzene HV87683 Hexachlorobutadlene HV77474 Hexachlorocyclopentadlene HV67721 Hexachloroethane HV822060 Hexamethylene-1,6-diisocyanate680319 Hexamethylphosphoramide OV100543 Hexane OV302012 Hydrazine N7647010 Hydrochloric acid A7664393 Hydrogen fluoride A

(Hydrofluoric acid)123319 Hydroquinone OV78591 Isophorone58899 Lindane (all isomers) HV108316 Maleic anhydride OV67561 Methanol OV72435 Methoxychlor HV74839 Methyl bromide (Bromethane) HV74873 Methyl chloride HV

(Chloromethane)



CAS No. Chemical Name Category95954 2,4,5-Trichlorophenol HV88062 2,4,6-Trichlorophenol HV121448 Triethylamine1582098 Trifluralin OV540841 2,2,4-Trimethylpentane108054 Vinyl acetate OV593602 Vinyl bromide HV75014 Vinyl chloride HV75354 Vinylidene chloride HV1330207 Xylenes (isomers/mixture) OV95476 o-Xylenes OV108383 m-Xylenes OV106423 p-Xylenes OV0 Antimony Compounds M0 Arsenic Compounds N0 Beryllium Compounds M0 Cadmium Compounds M0 Chromium Compounds M0 Cobalt Compounds M0 Coke Oven Emissions0 Cyanide Compounds1

0 Glycol Ethers2 OV0 Lead Compounds M0 Manganese Compounds M0 Mercury Compounds M0 Fine Mineral Fibers3

0 Nickel Compounds M0 Polycylic Organic Matter4 O0 Radionuclides (including Radon)5

0 Selenium Compounds N

Index 119


CAS No. Chemical Name Category7723140 Phosphorus N85449 Phthalic anhydride OV1336363 Polychlorinated biphenyls HV

(Alodors)1120714 1,3-Propane sultone OV57578 beta-Propiolactone OV123386 Proplonaldehyde OV114261 Propoxur (Baygon) OV78875 Propylene dichloride HV

(1,2-Dichloropropane) OV75569 Propylene oxide OV75558 1,2-Propylenimine OV

(2-methyl aziridine)91225 Quinoline OV106514 Quinone OV100425 Styrene OV96093 Styrene oxide OV1746016 2,3,7,8-Tetrachlorodibenzo-p-dioxin79345 1,1,2,2-Tetracholoethane HV127184 Tetrachloroethylene HV

(Perchloroethylene)7550450 Titanium tetrachloride M106883 Toulene OV95807 2,4-Toulene diamine OV584849 2,4-Toulene diisocyanate OV95534 o-Toluidine OV8001352 Toxaphene HV120821 1,2,4-Trichlorobenzene HV79005 1,1,2-Trichloroethane HV79016 Trichloroethylene HV


Index 121


V=VolatileN=Nonmetallic InorganicsO=OrganicM=Metals and Metal CompoundsA=Acids, Bases and Salts

NOTE: For all listings above which contain theword “compounds” and for glycol ethers, the fol-lowing applies: Unless otherwise specified, theselistings are defined as including any unique chemi-cal substance that contains the named chemical (i.e.,antimony, arsenic, etc.) as part of that chemical’sinfrastructure.

1 X'CN where X=H' or any other group where a for-mal dissociation may occur. For example KCN orCa(CN)2.

2 Includes mono- and di- ethers of ethylene glycol,diethylene glycol and triethylene glycol R-(OCH2CH)n - OR' wheren= 1, 2 or 3R= alkyl or aryl groupsR'= R, H or groups which, when removed, yield gly-col ethers with the structure: R-(OCH2CH)n - OH.Polymers are excluded from the glycol category.

3 Includes mineral fiber emissions from facilities man-ufacturing or processing glass, rock or slag fibers (orother mineral derived fibers) of average diameter 1micrometer or less.

4 Includes organic compounds with more than onebenzene ring, and which have a boiling point greaterthan or equal to 100˚ C.

5 A type of atom which spontaneously undergoesradioactive decay.


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