Catterpillar Gens Set Requirment

8/3/2019 Catterpillar Gens Set Requirment

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Contents

Petroleum Applications ......................................................... 1Petroleum Equipment & Terminology................................... 2

Drilling Rig................................................................... 2Conventional or Compound Rig................................... 4Split Rigs................................................................. 5

Service Rigs................................................................. 6Workover Rig ...........................................................6Technical Well.......................................................... 6Additional Service Rig Terms...................................... 7

Mobile Rigs.................................................................. 8Carrier Designations.................................................. 8Mobile Rig Drivetrain Configurations.......................... 10

Production Pumping.................................................... 10Piston Pumps......................................................... 10Centrifugal Pumps .................................................. 10Horizontal Pumps.................................................... 10Rating Review for Pumps......................................... 11

Fire Pump.................................................................. 11Offshore Crane........................................................... 11Auxiliary Power.......................................................... 11

Electric Power Generation................................................ 12DC Generators ........................................................... 12


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AC Generators with SCR ............................................. 13Silicon Controlled Rectifier (SCR) Drives..................... 14

Variable Frequency Drive (VFD) Systems ....................... 14Other Petroleum Power Application Considerations ............. 16

Loading Considerations ............................................... 16Transient Response..................................................... 16

Sizing Criterion....................................................... 16ISO Classification ................................................... 17Equipment Selection................................................ 17

Off Shore Requirements .............................................. 18Island Mode............................................................... 18Motor Loads .............................................................. 18Motor Starting ........................................................... 19Regenerative Power .................................................... 20


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2006 Caterpillar

All rights reserved.

Information contained in this publication may be considered confidential.

Discretion is recommended when distributing. Materials and specificationsare subject to change without notice.

CAT, CATERPILLAR, their respective logos and Caterpillar Yellow, as well

as corporate and product identity used herein, are trademarks of Caterpillar

and may not be used without permission.

ForewordThis section of the Application and Installation Guide generally describes

Petroleum Applications for Caterpillar engines. Additional engine systems,

components and dynamics are addressed in other sections of this Application

and Installation Guide.Engine-specific information and data are available from a variety of

sources. Refer to the Introduction section of this guide for additional

references.


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Application and Installation Guide Petroleum Applications

2006 Caterpillar

All rights reserved. Page 1

Petroleum ApplicationsThe use of Caterpillar engines in petroleum applications requires specific

considerations for engine selection and installation to ensure dependable

performance and a long, trouble-free life.

Petroleum applications for diesel engines include drilling, well servicing,production power, offshore emergency or essential services power, and

pumping applications. Natural gas engines are often used in petroleum

applications for gas compression drive, production power and production

pumping.

The information presented in this guide will aid in planning, installation and

customer acceptance phases of a project. While this application and

installation guide summarizes many aspects of installation, Caterpillar dealers

stand ready to assist you.

It is the installers responsibility to consider and avoid possibly hazardous

conditions which could develop from the systems involved in the specificengine installation. The suggestions provided in this guide regarding

avoidance of hazardous conditions apply to all applications and are

necessarily of a general nature since only the installer is familiar with the

details of a particular installation. Consider the suggestions provided in this

guide as general examples only and are in no way intended to cover every

possible hazard in all installations.

SECTION CONTENTS

Petroleum Equipment &

Terminology........................ 2

Drilling Rigs Service Rigs Mobile Rigs Production Pump Fire Pump Offshore Crane Auxiliary PowerElectric Power Generation....12

DC Generator AC Generator with SCR

Variable Frequency Drive(VFD) Systems

Generator Set EngineRequirements

Other Petroleum Power

Application Considerations...16

Loading Considerations Transient Response Offshore Requirements Island Mode Motor Loads Motor Starting Regenerative Power


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Petroleum Applications Application and Installation Guide

2006 Caterpillar

Page 2 All rights reserved.

Petroleum Equipment & Terminology

Before selecting an engine, a

general understanding of the driven

equipment is necessary. Since

nomenclature in the petroleumindustry is not completely standard,

the terminology used in this guide

should be considered representative.

Below are the terms this guide uses

for equipment and systems used in

the petroleum industry.

Drilling RigDue to the fact that oil and gas are

often located far beneath the earth's

surface, it can take a lot of work to

tap into reservoirs containing these

resources.

A drilling rig creates a borehole, or

well, where oil and natural gas can

be extracted for the production of

fuels and other petroleum-based

products. An example of a land

based drilling rig is shown in Figure

1. While all drilling rigs move from

site to site, some rigs requireconsiderable effort and up to 70

semi trucks to change location,

while others can fit on just one

truck. These easily portable rigs will

be referred to as mobile rigs and are

discussed later in this section.

Drilling rigs may be described as

mechanical or electric. These terms

refer to the method in which power

is supplied to the larger equipmenton the rig.

On mechanical rigs, power from

the engine(s) drives the rig

equipment either directly, through a

clutch or through a torque converter.

Electric rigs use engine power to

drive one or more generators. The

generated electricity is then used to

operate motors for the largerequipment on the rig. There are

three types of electric rigs: DC, SCR,

and VFD. DC, or direct current

indicates that a DC generator

supplies power to DC motors. These

are the oldest type. SCR, or Silicon

Control Rectifier, indicates that AC

power from the generators is

changed to DC by switchgear to

power DC motors. This allows for

more power to be generated by

smaller generators and is the most

common type. VFD, or variable

frequency drive, is the newest kind

of rig which utilizes variable rpm AC

motors allowing for even more

power out of the same sized

equipment. The details of these

applications are discussed later in

this guide.

Typical rig equipment, for both

mechanical and electric, include a

drawworks, a rotary table and mud

pumps. These equipment items are

among the larger equipment on the

rig and will have the most significant

and important power requirements.

Some applications also run

compressors which can have any

variety of power requirements.

Drawworks

The drawworks is the cable reel

and controls that hoist the drilling

string into place.

The drawworks also has accessory

drives which assist the crew to


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make up and break out the

joints to and from the drill string.

The power rating of the rig refers

to the power rating of the

drawworks. However, the total

power on the rig will be more. Forexample, a rig referred to as a

3000 hp rig will be equipped with

more than 3000 hp (likely 4500 hp,)

but is equipped with a 3000 hp

drawworks.

Drilling String

A drilling string is a length of pipe

made from separate pieces on which

a drill bit or other borehole tools are

mounted. A portion of the rotarytable turns, which turns the drill

string, which turns the bit attached

to the bottom of the drill string.

Electric rigs might also use a top

drive instead of a rotary table. In this

case, an electric motor in a piece of

equipment attached to the traveling

block on the hoist connects to the

top of the drill string and serves to

turn the bit.

Rotary Table

The rotary table provides the rotary

movement to the drilling string. The

table clamps to the kelly, a special

length of rectangular pipe at the top

end of the drilling string and a

portion of the table turns, providing

a clockwise rotation to the drill

string.

Mud Pumps

Drilling fluid, or mud, is a slurry of

fluid, chemicals and suspended

solids. Mud pumps circulate the mud

down the drill string and up the

outside of the bore hole (also called

the annulus). Mud pumps are usually

piston style, high pressure pumps.

To meet industry demands, mud

pumps are being designed for deeper

wells, requiring higher horsepower.

Mud is absolutely crucial to a

successful drilling operation, makingreliable power to these pumps

equally crucial.

Various mud formulas serve as a

coolant for the drill bit, a medium for

removing drilled rock (or cuttings)

from the hole, and as weight to

stabilize drill-casing pressures and

reduce the possibility of blowouts.

Mud pumps also supply other

fluids and chemicals to the borehole

that stimulate well production.

Gas Compressors

Unlike crude oil, natural gas cannot

be easily pumped into tanks and

shipped. To achieve enough volume

for economical transportation,

natural gas must be compressed and

either loaded as a liquid into

specially designed tank vehicles, or

compressed into a pipeline. Enginedriven compressors are commonly

used for this purpose.

Compressor plants, consisting of

many individual compressors,

pressurize natural gas so it will flow

over long distances through

pipelines. The pipelines are used to

carry gas from the field, to auxiliary

treatment processes and to market.

AC Auxiliary Generators

Although mechanical rigs are

driven directly by engine power, AC

electricity is needed for lighting,

switches and smaller electric

equipment. AC auxiliary generators


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provide the electricity needed on

mechanical rigs.

Conventional or Compound Rig

Conventional rigs use a mechanical

drive system, known as a

compound, to transmit engine power

to the rigs hoisting, drilling and mud

pump systems.

Various configurations of engines,

compounds and equipment are

possible; for instance, a compound

may be used along with additional

independent drives, as shown in

Figure 1 and Figure 2.

Clutches are used to transfer the

power from the engines to the

compound and the equipment.

Power transfer from the engines can

be direct drive (usually through an

air clutch from the flywheel) or

torque converter drive. Caterpillar

engines work well with both,

however a torque converter is more

forgiving, and acts as a shock

absorber which can reduce wear on

the engine and compound

components. The torque converter

does require cooling however

(usually a 30% increase in heat

rejection requirements) which must

be taken into consideration whensizing the radiator.

Other conventional rig details can

be seen in Figure 1.

The drawworks and rotarytable are on an elevated

structure to provide clearance

for drilling safety valves.

The engines are also elevatedto simplify power transmission

to the drawworks.

Engine outputs are connectedtogether with the compound.

A number of clutches control

power distribution. Normally,

engines operate in compound

while hoisting and separately

when running the rotary table

and mud pumps.

Conventional Rig

Figure 1


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Typical Conventional Rig

Figure 2

Typical Split Rig

Figure 3

Split Rigs

Split rigs utilize independent drivesto power the various pieces of

drilling machinery. Figure 3 shows

two engines driving the drawworks

and rotary table through a

compound and two independent

engines driving separate mud

pumps. Split rig applications allow

for numerous combinations ofequipment, compounds and drives.

This can include the use of electric

motors for a portion of the rigs

power requirement.


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Service RigsSimilar to drilling rigs, service rigs

can be mechanical or electric.

Service rigs perform well servicing

after the primary drilling is

completed. This broad categorygenerally includes oilfield activities

that provide underground repair or

alteration of an existing well. They

help prolong the useful life of the

well.

Service rigs that utilize large

engines are used to perform three

distinct services: cementing,

acidizing and fracturing.

Workover and technical well aretwo types of service rigs.

Workover Rig

Workover rigs provide maintenance

support for an existing well. This

can include the removal and

replacement of the drill-string, the

repair of casings and cementing. A

workover rig may be called a pulling

unit when there is no provision of

rotating the tubing string.

Cementing

Cementing is the process of

pumping cement down a well bore

to anchor the casing. Cementing can

be required several times during the

drilling and workover of a well.

Cementing units normally carry

mixing equipment not found on

acidizing/fracturing units.

Cementing a well requires less

power, 75-373 kW (100-500 hp)

than fracturing or acidizing [500-

10000 hp (373-7460 kW)].

Cementing is thus usually done with

trucks with two engines of

approximately 400 hp (300 kW)

each.

Additionally, some rigs include a

limited rotary table capacity for use

during well bore cleanout, while

drilling out plugs (packers), or limitedredrilling in an existing well.

Technical Well

Technical well service rigs are not

equipped to do mechanical work on

a well. Technical well services

provide support functions to improve

production. One capability is to

provide means to change

productivity of underground

formations. This is usually done byacidizing and fracturing. Multiple

mobile units are used for high power

acidizing and fracturing operations.

Acidizing

Acidizing is the process of

pumping an acid down the casing of

a completed well into the desired

producing formation. Certain types

of rock can be dissolved by acid,

and this dissolving process createschannels by which hydrocarbons can

more readily flow to the well bore.

Fracturing

Fracturing is the process of

applying an ultra-high pressure,

13783 to 103448 kPa (2,000 to

15,000 psi), down the casing of a

completed well to a desired

producing formation. This pressure

fractures the rock and createschannels by which hydrocarbons can

more readily flow to the well bore.

The same service rig may be used

to acidize or fracture. This does

however require changing the fluid


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end of the pump to match various

pressure and flow requirements.

An acidizing and fracturing unit

consists of an engine, transmission,

and piston-type pump. This

equipment is usually mounted on acommercial truck chassis or may be

trailer-mounted. Mobil rigs will be

discussed in more detail later in this

section. Figure 4 shows a mobile

acidizing/fracturing unit.

Fracturing and acidizing are usually

performed by trucks that have a

1250-2250 hp (930-1575 kW)

engine.

A cement unit is similar but uses

smaller engines; cementing units are

not normally used for fracturing and

acidizing.

Figure 4

Nitrogen Pumping

Nitrogen pumpers can be used

with fracturing units. Nitrogen is

used for foam-fracturing in

formations that would be damagedby a large volume of fracturing fluid.

Nitrogen can also be used to remove

the fracturing fluid from a well after

the fracturing operation; the nitrogen

expands on removal of pump

pressure.

Additional Service Rig Terms

Coil Tubing

Coil tubing is a long, continuous

length of pipe wound on a spool.

The pipe is straightened prior to

pushing into a well bore and recoiled

to spool the pipe back onto the

transport and storage spool.

Depending on the pipe diameter,

typically 25.4 to 114.3 mm (1 to 4-

1/2 in.), and the spool size, coiled

tubing can range from 610 to 4570

m (2000 to 15,000 ft) or greater

length.

Well Workover and Intervention

Well workover and intervention is a

generic term relating to the use of a

coiled tubing string and associated

equipment. As a well-intervention

method, coiled tubing techniques

offer several key benefits over

alternative well-intervention

technologies. The ability to work

safely under live well conditions,

with a continuous string, enables

fluids to be pumped at any timeregardless of the position or

direction of travel. This is a

significant advantage in many

applications. Installing an electrical

conductor or hydraulic conduit

further enhances the capability of a

coiled tubing string and enables

relatively complex intervention

techniques to be applied safely.

BlendersBlenders are the equipment used to

prepare the slurries and gels

commonly used in stimulation

treatments. The blender should be

capable of providing a supply of

adequately mixed ingredients at the

desired treatment rate. Modern
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blenders are computer controlled,

enabling the flow of chemicals and

ingredients to be efficiently metered

and requiring a relatively small

residence volume to achieve good

control over the blend quality anddelivery rate.

Hydraulic Pump

The hydraulic pump is an artificial-

lift system that utilizes an

underground, or down-hole, pump. A

surface hydraulic pump pressurizes

crude oil called power oil, which

drives the down-hole pump. When a

single production string is used, the

power oil is pumped down thetubing and a mixture of the

formation crude oil and power oil are

produced in the space between the

casing and tubing; this space is also

known as the annulus. If two

production strings are used, the

power oil is pumped through one of

the pipes, and the mixture of

formation crude oil and power oil are

produced in the other parallel pipe.

Mobile RigsMobile units are defined as oil field

drilling or workover units that are

permanently mounted on wheels.

They are frequently called chassis or

carrier units, self-propelled or trailer

mounted. They are a version of the

split rig.

Carrier Designations

Figure 5 shows a back-in workoverrig. It is representative of the

workover rig carrier designation. A

drive-in carrier has the drivers cab

located at the hinge point of the

derrick.

These rigs may also be trailer-

mounted.

Figure 5

Mobile Drilling Rig

A truck or trailer-mounted unit

used to drill a well is known as a

mobile drill rig. The unit consists of

an engine, transmission, drawworks

and a rotary table. In regard to

mobile drilling rigs, mud pumps are

normally independent units.

A mobile drilling rig may even be

used for both drilling and workover,

or the basic unit can be sold into

either application. In such cases, the

major difference is depth capacity. Adrawworks and derrick used for

drilling (where heavy casing is

handled) has a smaller depth

capacity than when used for work-

over (where lighter tubing or rods

are handled).

Manufacturers sales specifications

will state both drilling and workover

depth capacities. Depending upon

power and derrick capacity, dual-purpose rigs (workover/drilling) can

drill to more than 12,000 ft. (3600

m) and workover to more than

20,000 ft. (6000 m).
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Mobil Workover Rig

A truck or trailer-mounted unit

used to pull rod and tubing from a

producing well describes a mobile

workover rig. The unit consists of an

engine, transmission anddrawworks. Occasionally, a mobile

workover rig includes a chassis-

mounted mud pump. This is required

to kill a flowing well, provide

circulation during cleanout and while

drilling out plugs, etc. Normally, a

mobile workover rig will use an

independent mud pump kill unit.

Mobile Rig Drivetrain Configurations

Figure 6


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Mobile Rig Drivetrain Configurations

Figure 6 shows a few mobile rig

drivetrain configurations. There are

many other possible combinations of

equipment and configurations.

If the unit is a trailer unit, the

power system drop-box (K) and drive

axle (J) are eliminated.

On the twin engine in-line setup,

the two engines may also be offset

or the rear engine elevated to

eliminate the dropbox (C).

Rigs using only a torque converter

behind the engine may have a

drawworks with either a two-or

three-speed transmission or high-low

drum clutches.

Production PumpingPetroleum applications require a

wide range of pumps to move fluid

(either crude oil, processed products,

or salt water brine) in and out of the

well, to and from processing plants,

and on and off transport vehicles.

Production pumps can be driven byelectric motors or mechanically by

direct engine power. In the case of

electric motor drive, an engine and

generator, or genset, is required to

provide power in remote locations.

This varies on a site-by-site basis

and could include anywhere from

one genset per pump site, to a large

centrally located power house for an

entire field.

Several types of pumps are used

for this application.

Piston Pumps

Piston pumps are low rpm,

reciprocating, positive displacement

pumps that are very similar to mud

pumps for drill rigs. These pumps

are typically used to gather fluids

from the wellheads as well as

loading and unloading fluids to and

from tanks and transportation. These

pumps have high pressure ratios,and will demand a variable speed

engine rating. Piston pumps will

almost always require a speed

reducer.

Centrifugal Pumps

Centrifugal pumps work best for

steady state type pumping

applications such as pipeline

transmission. These pumps in

constant flow applications will havemoderate pressure ratios and may or

may not have a speed increaser.

Horizontal Pumps

Horizontal pumps are an adaptation

of a down-hole pump to a surface

mechanical drive or VFD electric

drive. The electric versions consist

of three parts: a gas or diesel engine

and generator, variable frequency

control, and an electric variablefrequency down hole pump. Properly

configuring the generator to be

compatible with the VFDs is crucial,

because of the complex harmonics

produced by the VFD. They are used

primarily for gathering and waste

disposal. These can have very high

pressure ratios and are used in a

manner similar to piston pumps.

These are becoming more common

in the oil field because they require

less maintenance than traditional

piston pumps.

Note: Most mechanical drive pumps

require a speed increaser or reducer.

To eliminate the chance of torsional

resonance in the system a torsional


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vibration analysis (TVA) will be

required to properly select the

coupling between the engine and the

gearbox and/or load.

Rating Review for Pumps

Mainline transmission / Highhour steady load A rating

Gathering and processing anddisposal B rating

Unloading and loading pumpsC rating

Fire Pump

Another piece of equipment thatrequires power is the fire pump. Fire

pumps are used to pump water for

fire emergencies.

Fire pumps are usually driven by an

independent engine and are common

in locations where access to an

adequate supply or pressure of

municipal water is limited; this

includes offshore and remote

applications. Figure 7 shows a

Caterpillar 3126 engine configured

for a fire pump application.

Figure 7

Offshore CraneOffshore cranes are used for

moving supplies on, off and around

the platform. Electric and hydraulic

systems for these cranes are usually

driven by an independent engine.Figure 8 shows a typical offshore

crane and a 3406 engine configured

to power a crane or other auxiliary

marine application.

Figure 8

Auxiliary Power

In addition to the powerrequirements of the petroleum

equipment already mentioned, many

smaller systems and components

also require power. These include

mud mix pumps, supercharger

pumps and air compressors. These

must be considered when selecting

an engine for petroleum applications.

Mobile applications, especially

single engine configurations, haveadditional auxiliary power concerns

because the engine cooling fan,

alternator, steering pump, air

compressor and hydraulic pump can

represent a significant proportion of

total engine power available.


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Electric Power Generation

Many petroleum applications use

engine power to drive electric

generators instead of gears, belts

and chains associated withmechanical compounds. Electric

motors power the drawworks, rotary

table, pumps and other systems

with electricity from the generator.

These applications are called electric

drilling rigs or electric rigs.

The electric motors used for

hoisting, drilling and pumping require

high torque at zero rpm and variable

speed characteristics for efficientoperation. These characteristics are

possible using the following

methods.

Direct Current (DC)Generators

Alternating Current (AC)Generators with Silicon

Controlled Rectifiers (SCR)

AC Generators with VariableFrequency Drive (VFD) Motors

DC GeneratorsDC generators, shown in Figure 9,

supply electricity to DC motors. A

control panel regulates the power

and provides means to connect the

generators to various motors or a

motor assignment. Figure 9 also

shows that different motor

assignments are used when hoisting

or pumping and drilling.

Figure 9 is representative of diesel

engine power modules for DC

generators. It is common for these

rigs to have some AC generation

capability. The DC generator is at

the rear of the engine and utilizes a

blower, powered by a separate AC

generator, for forced ventilation of

the generator.

Many of the older DC rigs are

being converted to use the more

common AC generators.

Electric Rig with DC Generator

Figure 9


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Electric Rig with AC Generator & SCR

Figure 10

AC Generators with SCRDistribution of AC current is much

more efficient than DC current; this

makes AC generators an attractiveselection for power generation.

Unfortunately, the majority of

electric motors used in the

petroleum industry are DC-powered.

DC motors provide the high torque

at low rpm and variable speed

characteristics required for hoisting,

drilling and pumping. To take

advantage of AC power and DC

motors, Silicon Controlled Rectifiers(SCR) are used to convert AC power

to DC power.

The AC generators, as shown in

Figure 10, supply power to a

switchgear. The switchgear is

essentially a control panel that

regulates the AC power. The AC

power is then fed to SCR modules

where it is rectified to DC. An

integral DC control panel connects

the SCR modules to various DCmotors or a motor assignment.

Figure 10 also shows that different

motor assignments are used when

hoisting or pumping and drilling.

Figure 10 is representative of

diesel engine power modules for

SCR drives.

Auxiliary AC power, for smaller

equipment and services, is normally

supplied from the same generators;however, the 600V AC power must

be transformed to a lower voltage.

In many SCR applications, separate

main and spare AC generators are

also required for auxiliary power.


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Silicon Controlled Rectifier (SCR)

Drives

Most electric drilling rigs use SCR

systems to convert AC generator

power to DC. The rated generator

voltage is usually 600V AC for both50 and 60 Hz; when rectified, this

voltage provides an ideal 800V DC

to the motors.

SCR drives require special

generators to compensate for

varying Power Factor (PF) levels and

surges relating to SCR operation.

Operating DC motors at variable

speeds causes the generator Power

Factor (PF) to fluctuate. Forexample, the drawworks transition

from 0 PF to 1.0 PF every hoisting

cycle. This is expected but the

generator must work harder to

maintain an appropriate PF.

Operation of the mud pumps at low

strokes also causes a low PF. To

overcome these fluctuations, AC

generators in drilling applications are

oversized to 0.6 or 0.7 PF and ahigher KVA rating to provide more

generator ampere capacity. The

actual power output of a generator

set with an oversize generator is

limited to the engines rated power

capacity even if the oversized

generator has a higher KVA rating.

Actual power output capacity of the

generator set is given by the

equation:

EkW = (bhp - rad fan hp) x Gen eff x 0.746

Simply oversizing the generator

will not be enough. The generator

must be form wound to provide

additional mechanical bracing of the

generator winding. This bracing

resists the forces caused by current

surges resulting from operation of

the SCR controllers. The design limit

for the generator windingtemperature rise is also lowered to

compensate for additional heating

caused by the SCR load.

Undersized generators may cause

circuit breaker tripping, slower

drawworks acceleration and

unacceptably short generator life.

Variable Frequency Drive (VFD)

SystemsThe newest technology for electricdrill rig power utilizes variable

frequency drive or VFD. The same

engine and generator that are used

for the SCR system will suit the VFD

system perfectly. The VFD

applications generate at 600 or

690VAC to the rigs buss. A portion

of the 600VAC is transformed to

480 VAC for hotel loads and non-

variable speed loads. The majority ofthe power is rectified to 800VDC

and is made available to a VFD

control system for variable speed

750 and 1500 hp AC motors. New

technology has also improved the

efficiency of the VAC motors. VFDs

use of front end diode technology,

which smoothes the conversion from

AC to DC, removes much of the

stress that the older SCR systemsplaced on the generator, and creates

load characteristics similar to a large

UPS load. However, harmonics

remain a concern, and the need to

use the same type of generator as in

the SCR application still exists.

Control of the engine and generator


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is usually left to the engine governor

and generator voltage regulator. The

VFD controller controls the load

application rate. Drilling contractors

should see significantly increased

generator life when comparing the

same generator in VFD rig service to

older SCR rig service.

Some drill rigs could have a

combination of both SCR and VFD

loads.


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Other Petroleum Power Application Considerations

This section describes some key

factors to consider when sizing

generator equipment for common

petroleum applications. Refer tothe Petroleum Diesel Engine

Selection, Ratings and

Configuration sections of this

Application & Installation Guide for

a detailed discussion of engine

sizing and selection. Additional

guidance can be found in the

Electric Power Applications &

Generator Sizing section of this

Application & Installation Guide.

Loading ConsiderationsLoad acceptance, stability and

response play a major role in

making an installation successful.

Before selecting equipment, the

load requirements and starting

characteristics of all the systems

to be powered by the generator

must be identified, and the stability

and response requirements mustbe specified.

Transient ResponseWhen a load is applied to or

removed from a generator set, the

engine speed, voltage and

frequency are temporarily changed

from its steady-state condition.

This temporary change is called

transient response.

When a significant load is

applied, the engine speed

temporarily reduces (generally

referred to as frequency or voltage

dip) and then returns to its steady

state condition. On removal of

load, the engine speed increases

momentarily (generally referred to

as overshoot), then returns to its

steady-state condition. The time

required for the generator set toreturn to its normal steady-state

speed is called recovery time. This

is illustrated in Figure 11.

Figure 11

The degree of voltage dip or

overshoot depends on:

The amount of active power(kW) and reactive power

(kVAR) changes

The voltage regulatorsettings

The total capacity anddynamic characteristics of

the generator set

The electrical inertia of theother loads in the system

Sizing Criterion

Three primary criteria need to beprovided to accurately size a

generator set:

The acceptable percent ofvoltage & frequency dip


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The acceptable duration ofthe voltage & frequency dip

recovery time

The percent of a load stepand type of load to be

connected

The larger the voltage dip a

generator set can tolerate, the

smaller and perhaps more

economical the generator set can

be. Typical permissible voltage dip

for oil field applications is 25%-

30%. By comparison, a sensitive

application, such as a hospital or a

hotel where loading is light and

equipment is sensitive or flickeringof lights would be highly

objectionable, the permissible

voltage dip might be only 2%.

ISO Classification

ISO Class 1 and 2 are

international standards for

generator set response criteria.

Note that there are two separate

and different sets of Class 1 and 2

standards for diesel engines andnatural gas engines. The ISO

requirements for gas engines are

not as stringent as they are for

diesel engines.

Equipment Selection

The transient response and

steady state stability of generator

set engines can vary with a

number of factors:

Engine Model Engine Speed Aspiration Power Factor Carburetion Governor

It is important to review the

response capability of the specific

generator set against the

application requirements.

Carburetion

To match changing load

requirements, the engine must

adjust is the amount of fuel

available for combustion. Due to

the differences in the fuel delivery

systems, natural gas and diesel

fuel engines will have very

different transient response

capability.

Diesel Engine Transient Response

Caterpillar diesel engines utilize

direct injectors for each cylinder

(unit injectors), which deliver a

precisely controlled amount of fuel

to each cylinder. These injectors

can be either mechanically

controlled (MUI) or electronically

controlled (EUI), however,

pertaining to transient response,

their basic operation is the same. A

certain amount of fuel is allowedinto the injector, and then at the

right time for combustion, a

plunger forces the fuel through

very small nozzles, and into the

combustion chamber. Each injector

acts as an exclusive fuel system

for each cylinder, which delivers

fuel directly to the cylinder. When

the governor or ECM signals to

change the amount of fuel needed

in the cylinder, the amount of fuel

available for combustion is

adjusted and available almost

instantly. This almost

instantaneous power adjustment

ability allows the diesel engine to


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respond to transient loads very

effectively.

Gas Engine Transient Response

Caterpillar gas engines have

either a carbureted fuel system or

a gas admission valve system.

There are many variations of these

fuel systems, however for this

topic their basic operation is the

same. Similar to the diesel

system, a governor or ECM signals

to a valve to adjust the amount of

fuel allowed into the combustion

chamber, however this is the only

similarity. After the valve, the fuel

gas is not directly delivered to thecylinder, but is mixed in with the

inlet air. Regardless of how the

fuel system delivers this air fuel

mixture to the cylinder, the

distance (and volume) between the

fuel control valve and the

combustion chamber creates a lag

between when the cylinder needs

fuel and when it gets fuel. It is this

property of gas engines that

reduces their ability to respond to a

transient load relative to diesel

engines. Some regulations are

adjusted accordingly; however,

marine society regulations are not

as flexible.

Off Shore RequirementsGenerator sets on offshore rigs

have to meet the transient

response requirements of thevarious Marine Classification

Society (MCS) rules (e.g. ABS,

DNV, etc). This is true for the main

drilling units as well as emergency

or essential services gensets. MCS

requirements are demonstrated on

a resistive load bank with various

step load changes.

MCS transient response

requirements are typically more

stringent than can be met with a

natural gas engine. A solution thatmay be accepted is to use a load

management system to control the

loading of the genset.Island Mode

Many petroleum gas engine

generator sets operate in Island

Mode or independent of the utility

grid. It is especially important in

these applications to have athorough understanding of the

electrical load and transient

response demands and ensure that

the gas genset can meet the

requirements.

Motor LoadsMotors draw more than their

rated power during starting and

acceleration. Motors connected

directly to high inertia centrifugaldevices or loaded reciprocating

compressors cause severe

frequency excursions and lengthy

motor start up. Comparing starting

currents between loaded and

unloaded motors, Figure 12 shows

the extended time that loaded

motors demand high current.

Motors generally exhibit low power

factors (pf) of 0.3 to 0.4 when

starting. Engine load is calculated

by:

kW = Starting kVA x Starting pf


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Figure 12

As shown in Figure 12, the

starting kVA can be as much as 6

times the running kVA. This results

in an engine load of 1.8 to 2.4 times

the normal load required to run the

motor. This must be accounted for

in the load analysis if there are any

large motors that must be started

when the generator initially closes,especially if the motor is started

while loaded.

Jackup drill rigs can impose large

AC motor block loads with their leg

jacking systems. Typically, other AC

motors on land or offshore rigs do

not present significant transient

response challenges due to the size

of these motors in comparison to the

engine and generator capacity.The DC motors, powered through

the SCR control system, are

considered to be soft-start. The

severest transient DC load (but of

short duration) on a drill rig is

applied by the drawworks when

lifting empty blocks.

Motor StartingThe gensets ability to start large

motors without large frequency or

voltage dips depends on the entire

system. System factors include:

Available engine power Capacity of the generator Energy stored in the rotating

inertia of the genset

Acceleration of the motor andits load (motor characteristics)

Electrical componentsbetween the genset and

motor.

A properly sized generator willsupport the high starting kVA (skVA)

required and sustain adequate

output voltage for the motor so it

can produce the needed torque to

accelerate its load to rated speed.


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After the initial voltage dip, it is

important that the generator restore

voltage to at least 90% to develop

adequate torque to accelerate its

load to rated speed. Full voltage

starting causes the largest voltagedip.

Regenerative PowerSome motor applications, such as

hoisting, depend on motors for

braking. Motors then act as

generators and feed power back to

the generator set. The rating on the

motor is greater when used as a

brake, if no other loads are

connected to absorb thisregenerative energy, only engine

frictional horsepower is used for

braking. Exceeding frictional

horsepower causes generator set

overspeed.

Regenerative potential for a

common application, elevators, is

estimated by:

Regeneration kW = Hoist Motor hp x Full Load Brake Rating Factor x hp to kW Conversion x Motor Efficiency

Where:

Full Load Brake

Rating Factor = 1.8

hp to kW

Conversion = 0.746

Motor Efficiency = 0.9

Load banks activated by directionalpower relays must be installed to

prevent engine/generator damage

when combinations of connected

load and engine frictional

horsepower are not sufficient to

restrain regenerative energy.


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