8.Shortcircuit_IEC

8/9/2019 8.Shortcircuit_IEC

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1996-2009 Operation Technology, Inc. Workshop Notes: Short-Circuit IEC

Short-Circuit AnalysisIEC Standard


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1996-2009 Operation Technology, Inc. Workshop Notes: Short-Circuit IEC Slide

CORTO CIRCUITO

Estndar de ANSI/IEEE & IEC.

Anlisis de fallas transitorias(IEC 61363).

Efecto de Arco (NFPA 70E-2000)

Integrado con coordinacin dedispositivos de proteccin.

Evaluacin automtica de

dispositivos.

Caractersticas principales:


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Purpose of Short-Circuit

Studies

A Short-Circuit Study can be used to determineany or all of the following:

Verify protective device close and latch capability

Verify protective device interrupting capability

Protect equipment from large mechanical forces

(maximum fault kA) I2t protection for equipment (thermal stress)

Selecting ratings or settings for relay coordination


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Types of Short-Circuit Faults



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Types of SC FaultsThree-Phase Ungrounded FaultThree-Phase Grounded FaultPhase to Phase Ungrounded FaultPhase to Phase Grounded FaultPhase to Ground Fault

Fault CurrentIL-G can range in utility systems from a few percent to

possibly 115 % ( if Xo < X1 ) of I3-phase (85% of all faults).

In industrial systems the situation IL-G > I3-phase is rare.Typically IL-G .87 * I3-phase

In an industrial system, the three-phase fault conditionis frequently the only one considered, since this type offault generally results in Maximum current.

Types of Short-Circuit Faults


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)tSin(Vmv(t) +=

i(t)v(t)

Short-Circuit Phenomenon


7/4531996-2009 Operation Technology, Inc. Workshop Notes: Short-Circuit IEC Slide

Offset)(DC

TransientStateSteady

t)-sin(ZVm)-tsin(

ZVmi(t)

(1))tSin(Vmdt

diLRiv(t)

L

R-

e++=

+=+=

expressionfollowingtheyields1equationSolving

i(t)v(t)


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DC Current

AC Current (Symmetrical) with

No AC Decay



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AC Fault Current Including theDC Offset (No AC Decay)



10/4531996-2009 Operation Technology, Inc. Workshop Notes: Short-Circuit IEC Slide 1

Machine Reactance ( = L I )

AC Decay Current



Fault Current Including AC & DC Decay



IEC Short-Circuit

Calculation (IEC 909)

Initial Symmetrical Short-Circuit Current (I"k)

Peak Short-Circuit Current (ip)

Symmetrical Short-Circuit Breaking Current(Ib)

Steady-State Short-Circuit Current (Ik)


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Transformer Z Adjustment

KT-- Network XFMR

KS,KSO Unit XFMR for faults on system side

KT,S,KT,SO Unit XFMR for faults in auxiliarysystem, not between Gen & XFMR

K=1 Unit XFMR for faults between Gen &XFMR



Syn Machine Z Adjustment

KG Synchronous machine w/o unit XFMR

KS,KSO With unit XFMR for faults on system

side

KG,S,KG,SO With unit XFMR for faults in

auxiliary system, including points betweenGen & XFMR



Types of Short-Circuits

Near-To-Generator Short-Circuit

This is a short-circuit condition to which at least

one synchronous machine contributes aprospective initial short-circuit current which ismore than twice the generators rated current, ora short-circuit condition to which synchronousand asynchronous motors contribute more than5% of the initial symmetrical short-circuit current( I"k) without motors.


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Near-To-Generator Short-Circuit

1996-2009 Operation Technology, Inc. Workshop Notes: Short-Circuit IEC Slide 1




Far-From-Generator Short-Circuit

This is a short-circuit condition during which the

magnitude of the symmetrical ac component of

available short-circuit current remains essentially

constant.


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Far-From-Generator Short-Circuit



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Factors Used in If Calc

calc ip based on Ik

calc ib for near-to-gen & not meshed network

q calc induction machine ib for near-to-gen & notmeshed network

Equation (75) of Std 60909-0, adjusting Ik fornear-to-gen & meshed network

min

& max calc ik


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IEC Short-Circuit Study Case


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Maximum voltage factor is used

Minimum impedance is used (all negative

tolerances are applied and minimumresistance temperature is considered)

When these optionsare selected


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Minimum voltage factor is used

Maximum impedance is used (all positive

tolerances are applied and maximumresistance temperature is considered)

When this option isselected


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Voltage Factor (c)

Ratio between equivalent voltage &nominal voltage

Required to account for:

Variations due to time & place

Transformer taps

Static loads & capacitances

Generator & motor subtransient


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Calculation Method

Breaking kA is moreconservative if the option

No Motor Decay isselected


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Device Duty Comparison


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L-G FaultsL-G Faults


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Symmetrical Components

L-G Faults


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Sequence Networks


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0

ZZZ

V3I

I3I

021

efaultPrf

af 0

=

++=

=

gZif

L-G Fault Sequence

Network Connections


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21

efaultPrf

aa

ZZ

V3I

II 12

+=

=

L-L Fault Sequence Network

Connections


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0

ZZ

ZZZ

VI

I0III

20

201

efaultPrf

aaaa 012

=

+

+=

==++

gZif

L-L-G Fault Sequence

Network Connections


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Transformer Zero Sequence Connections


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grounded.

solidlyareertransformConnectedY/

orGeneratorsifcasethebemayThis

I

:thentrueareconditionsthisIf

&

:ifgreater

becanfaultsG-Lcase.severemost

theisfaultphase-3aGenerally

1f3

1021

1.4


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Complete reports that include individualbranch contributions for:

L-G Faults

L-L-G Faults

L-L Faults

One-line diagram displayed results that

include:L-G/L-L-G/L-L fault currentcontributions

Sequence voltage and currents

Phase Voltages

Unbalanced Faults Display

& Reports


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Total Fault Current Waveform

Transient Fault Current



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Percent DC Current Waveform




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AC Component of Fault Current Waveform




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Top Envelope of Fault Current Waveform




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Top Envelope of Fault Current Waveform




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IEC Transient Fault Current

Calculation



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Complete reports that include individualbranch contributions for:

L-G Faults

L-L-G Faults

L-L Faults

One-line diagram displayed results that

include:L-G/L-L-G/L-L fault currentcontributions

Sequence voltage and currents

Phase Voltages

Unbalanced Faults Display

& Reports


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TEMA 2


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Protective Device Coordination

ETAP Star


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ETAP START PROTECCION Y COORDINACION

Curvas para ms de 75,000dispositivos.

Actualizacin automtica de

Corriente de Corto Circuito. Coordinacin tiempo-corriente de

dispositivos.

Auto-coordinacin de dispositivos.

Integrados a los diagramas

unifilares. Rastreo o clculos en diferentes

tiempos.



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A d


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Agenda

Concepts & Applications

Star Overview

Features & Capabilities

Protective Device Type

TCC Curves STAR Short-circuit

PD Sequence of Operation

Normalized TCC curves

Device Libraries

D fi iti


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Definition

Overcurrent Coordination A systematic study of current responsive

devices in an electrical power system.

Obj ti


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Objective

To determine the ratings and settings offuses, breakers, relay, etc.

To isolate the fault or overloads.

C it i


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Criteria

Economics

Available Measures of Fault

Operating Practices

Previous Experience

D i


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Design

Open only PD nearest (upstream) of the faultor overload

Provide satisfactory protection for overloads

Interrupt SC as rapidly (instantaneously) aspossible

Comply with all applicable standards and

codes

Plot the Time Current Characteristics ofdifferent PDs

Anal sis


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Analysis

When:

New electrical systems

Plant electrical system expansion/retrofits

Coordination failure in an existing plant

Spectrum Of Currents


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Spectrum Of Currents

Load Current

Up to 100% of full-load

115-125% (mild overload)

Overcurrent Abnormal loading condition (Locked-Rotor)

Fault Current

Fault condition

Ten times the full-load current and higher

Protection


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Protection

Prevent injury to personnel

Minimize damage to components

Quickly isolate the affected portion of the system Minimize the magnitude of available short-circuit

Coordination


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Coordination

Limit the extent and duration of serviceinterruption

Selective fault isolation

Provide alternate circuits

Coordination


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Coordination

t

I

C B A

C

D

D B

A

Protection vs Coordination


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Protection vs. Coordination

Coordination is not an exact science

Compromise between protection andcoordination

Reliability Speed

Performance

Economics

Simplicity

Required Data


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Required Data

One-line diagrams (Relay diagrams)

Power Grid Settings Generator Data

Transformer Data Transformer kVA, impedance, and connection

Motor Data

Load Data

Fault Currents

Cable / Conductor Data

Bus / Switchgear Data

Instrument Transformer Data (CT, PT)

Protective Device (PD) Data Manufacturer and type of protective devices (PDs) One-line diagrams (Relay diagrams)

Study Procedure


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Study Procedure

Prepare an accurate one-line diagram (relay diagrams)

Obtain the available system current spectrum (operatingload, overloads, fault kA)

Determine the equipment protection guidelines

Select the appropriate devices / settings

Plot the fixed points (damage curves, )

Obtain / plot the device characteristics curves

Analyze the results

Time Current Characteristics


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Time Current Characteristics

TCC Curve / Plot / Graphs

4.5 x 5-cycle log-log graph

X-axis: Current (0.5 10,000 amperes)

Y-axis: Time (.01 1000 seconds)

Current Scaling (x1, x10, x100, x100)

Voltage Scaling (plot kV reference)

Use ETAP Star Auto-Scale


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TCC Scaling Example


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TCC Scaling Example

Situation:

A scaling factor of 10 @ 4.16 kV is selected forTCC curve plots.

Question What are the scaling factors to plot the 0.48 kV

and 13.8 kV TCC curves?

TCC Scaling Example


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TCC Scaling Example

Solution

Fixed Points


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Fixed Points

Cable damage curves

Cable ampacities Transformer damage curves & inrush points

Motor starting curves

Generator damage curve / Decrement curve

SC maximum fault points

Points or curves which do not change regardlessof protective device settings:

Capability / Damage Curves


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Capability / Damage Curves

t

I

I22t

Gen

I2t

MotorXfmr

I2t

Cable

I2t

Cable Protection


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Cable Protection

Standards & References

IEEE Std 835-1994 IEEE Standard Power Cable AmpacityTables

IEEE Std 848-1996 IEEE Standard Procedure for theDetermination of the Ampacity Derating of Fire-ProtectedCables

IEEE Std 738-1993 IEEE Standard for Calculating theCurrent- Temperature Relationship of Bare OverheadConductors

The Okonite Company Engineering Data for Copper and

Aluminum Conductor Electrical Cables, Bulletin EHB-98

Cable Protection


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Cable Protection

2

2

1

t

A T 2340.0297log

T 234

= + +

The actual temperature rise of a cable when exposed toa short circuit current for a known time is calculated by:

Where:

A= Conductor area in circular-mils

I = Short circuit current in amps

t = Time of short circuit in seconds

T1= Initial operation temperature (750C)

T2=Maximum short circuit temperature

(1500C)

Cable Short-Circuit Heating Limits


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Cable Short Circuit Heating LimitsRecommended

temperature rise:

B) CU 75-200C

Shielded


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Shielded

Cable

The normal tape

width is 1

inches

NEC Section 110 14 C


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NEC Section 110 14 C

(c) Temperature limitations. The temperature rating associated with theampacity of a conductor shall be so selected and coordinated as to not exceed

the lowest temperature rating of anylowest temperature rating of any connected terminationconnected termination, conductor, ordevice. Conductors with temperature ratings higher than specified forterminations shall be permitted to be used for ampacity adjustment, correction,or both.

(1) Termination provisions of equipment for circuits rated 100 amperes or less,or marked for Nos. 14 through 1 conductors, shall be used only for conductorsrated 600C (1400F).

Exception No. 1: Conductors with higher temperature ratings shall be permittedto be used, provided the ampacity of such conductors is determined based onthe 6O0C (1400F) ampacity of the conductor size used.

Exception No. 2: Equipment termination provisions shall be permitted to beused with higher rated conductors at the ampacity of the higher ratedconductors, provided the equipment is listed and identified for use with the

higher rated conductors. (2) Termination provisions of equipment for circuits rated over 100 amperes, or

marked for conductors larger than No. 1, shall be used only with conductorsrated 750C (1670F).

Transformer Protection


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Standards & References

National Electric Code 2002 Edition C37.91-2000; IEEE Guide for Protective Relay Applications to Power

Transformers

C57.12.59; IEEE Guide for Dry-Type Transformer Through-Fault CurrentDuration.

C57.109-1985; IEEE Guide for Liquid-Immersed Transformer Through-Fault-Current Duration

APPLIED PROCTIVE RELAYING; J.L. Blackburn; Westinghouse ElectricCorp; 1976

PROTECTIVE RELAYING, PRINCIPLES AND APPLICATIONS; J.L.Blackburn; Marcel Dekker, Inc; 1987

IEEE Std 242-1986; IEEE Recommended Practice for Protection andCoordination of Industrial and Commercial Power Systems

Transformer Category


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Transformer CategoryANSI/IEEE C-57.109

Transformer Categories I II


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Transformer Categories I, II

Transformer Categories III


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Transformer Categories III

Transformer


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Transformer

t

(sec)

I (pu)

Thermal200

2.5

I2t = 1250

2

25Isc

Mechanical

K=(1/Z)2t

(D-D LL) 0.87

(D-R LG)0.58

Frequent Fault

Infrequent Fault

Inrush

FLA


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Any Location Non-Supervised



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Turn on or inrush current

Internal transformer faults

External or through faults of majormagnitude

Repeated large motor starts on thetransformer. The motor represents amajor portion or the transformers KVArating.

Harmonics Over current protection Device 50/51

Ground current protection Device50/51G

Differential Device 87

Over or under excitation volts/ Hz Device 24

Sudden tank pressure Device 63

Dissolved gas detection

Oil Level

Fans

Oil Pumps Pilot wire Device 85

Fault withstand

Thermal protection hot spot, top of oiltemperature, winding temperature

Devices 26 & 49

Reverse over current Device 67

Gas accumulation Buckholz relay

Over voltage Device 59

Voltage or current balance Device 60

Tertiary Winding Protection if supplied

Relay Failure Scheme

Breaker Failure Scheme

Recommended Minimum


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Transformer ProtectionProtective system Winding and/or power system

grounded neutral groundedWinding and/or power system

neutral ungrounded

Up to 10 MVAAbove 10 MVA

Up to 10 MVA Above10 MVA

Differential - -

Time over current

Instantaneous restricted

ground fault - -

Time delayed groundfault

- -

Gas detection -

Over excitation - Overheating - -

Question


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Question

What is ANSI Shift Curve?

Answer


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Answer

For delta-delta connected transformers, withline-to-line faults on the secondary side, thecurve must be reduced to 87% (shift to theleft by a factor of 0.87)

For delta-wye connection, with single line-to-ground faults on the secondary side, thecurve values must be reduced to 58% (shiftto the left by a factor of 0.58)


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Motor Protection


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Standards & References IEEE Std 620-1996 IEEE Guide for the Presentation of

Thermal Limit Curves for Squirrel Cage InductionMachines.

IEEE Std 1255-2000 IEEE Guide for Evaluation ofTorque Pulsations During Starting of Synchronous Motors

ANSI/ IEEE C37.96-2000 Guide for AC Motor Protection

The Art of Protective Relaying General Electric

Motor Protection


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Motor Starting Curve

Thermal Protection

Locked Rotor Protection

Fault Protection

Motor Overload Protection


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(NEC Art 430-32 Continuous-Duty Motors)

Thermal O/L (Device 49) Motors with SF not less than 1.15

125% of FLA

Motors with temp. rise not over 40C

125% of FLA

All other motors 115% of FLA

Motor Protection Inst. Pickup


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p

LOCKEDROTOR S d

1I

X X "=

+

PICK UP

LOCKED ROTOR

IRELAY PICK UP 1.2 TO 1.2

I=

PICK UP

LOCKED ROTOR

IRELAY PICK UP 1.6 TO 2

I=

with a time delay of 0.10 s (six cycles at 60 Hz)

Recommended Instantaneous Setting:

If the recommended setting criteria cannot be met, or where more sensitive

protection is desired, the in-stantaneous relay (or a second relay) can be set more

sensitively if delayed by a timer. This permits the asymmetricalasymmetrical starting component

to decay out. A typical setting for this is:

Locked Rotor Protection


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Thermal Locked Rotor (Device 51)

Starting Time (TS < TLR)

LRA

LRA sym

LRA asym (1.5-1.6 x LRA sym) + 10% margin

Fault Protection


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(NEC Art / Table 430-52)

Non-Time Delay Fuses 300% of FLA

Dual Element (Time-Delay Fuses)

175% of FLA Instantaneous Trip Breaker

800% - 1300% of FLA*

Inverse Time Breakers 250% of FLA

*can be set up to 1700% for Design B (energy efficient) Motor

Low Voltage Motor Protection


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Usually pre-engineered (selected fromCatalogs)

Typically, motors larger than 2 Hp are

protected by combination starters Overload / Short-circuit protection

Low-voltage Motor


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gRatings Range of ratingsContinuous amperes 9-250

Nominal voltage (V) 240-600

Horsepower 1.5-1000 Starter size (NEMA) 00-9

Types of protection Quantity NEMA designation

Overload: overload relayelements

3 OL

Short circuit:circuit breaker current

trip elements

3 CB

Fuses 3 FU

Undervoltage: inherentwith integral control

supply and three-wirecontrol circuit

Ground fault (whenspeci-fied): ground relaywith toroidal CT

Minimum Required Sizes of a NEMA

Combination Motor Starter System


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Combination Motor Starter System

R

HP

C

FLC

T

ER

EUM

Required Data - Protection of a


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Medium Voltage Motor Rated full load current

Service factor

Locked rotor current

Maximum locked rotor time (thermal limit curve) with the motor at ambient and/oroperating temperature

Minimum no load current

Starting power factor

Running power factor

Motor and connected load accelerating time

System phase rotation and nominal frequency

Type and location of resistance temperature devices (RTDs), if used Expected fault current magnitudes

First cycle current

Maximum motor starts per hour

Medium-Voltage Class E Motor ControllerRatings Class El Class E2 (with


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Ratings Class El(withoutfuses)

Class E2 (withfuses)

Nominal system voltage 2300-6900 2300-6900Horsepower 0-8000 0-8000

Symmetrical MVA interruptingcapacity at nominalsystem voltage

25-75 160-570

Types of Protective Devices Quantity NEMA Designation

Overload, or locked Rotor, orboth:

Thermal overload relay

TOC relayIOC relay plus time delay

3

33

OL OC TR/O

Thermal overload relay 3 OL

TOC relay 3 OC

IOC relay plus time delay 3 TR/OC

Short Circuit:

Fuses, Class E2 3 FU

IOC relay, Class E1 3 OC

Ground Fault

TOC residual relay 1 GP

Overcurrent relay withtoroidal CT

1 GP

NEMA Class E2 mediu

voltage starte

NEMA Class E1medium voltage starter

Phase Balance

Current balance relay 1 BCNegative-sequence voltagerelay (per bus), or both

1

Undervoltage:Inherent with integralcontrol supply and three-wire control circuit, whenvoltage falls suffi-ciently topermit the contractor to

open and break the seal-incircuit

UV

Temperature:Temperature relay,operating from resistancesensor or ther-mocouple instator winding

OL

Starting Current of a 4000Hp, 12 kV,

1800 rpm Motor


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1800 rpm Motor

First half cycle current showing

current offset.

Beginning of run up current

showing load torque pulsations.

Starting Current of a 4000Hp, 12 kV,

1800 rpm Motor O ill h


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1800 rpm Motor -

Motor pull in current showing motor

reaching synchronous speed

Oscillographs

Thermal Limit Curve


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Thermal Limit Curve


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TypicalCurve

(49)


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200 HP

MCP

O/L

Starting Curve

I2T

(49)

MCP (50)

(51)ts

tLR

LRAs LRAasym

Protective Devices


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Fuse

Overload Heater

Thermal Magnetic

Low Voltage Solid State Trip

Electro-Mechanical

Motor Circuit Protector (MCP)

Relay (50/51 P, N, G, SG, 51V, 67, 49, 46, 79, 21, )

Fuse (Power Fuse)


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Non Adjustable Device (unless electronic)

Continuous and Interrupting Rating

Voltage Levels (Max kV)

Interrupting Rating (sym, asym)

Characteristic Curves

Min. Melting

Total Clearing

Application (rating type: R, E, X, )

Fuse Types


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Expulsion Fuse (Non-CLF)

Current Limiting Fuse (CLF)

Electronic Fuse (S&C Fault Fiter)


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Minimum Melting

Time Curve

Total Clearing

Time Curve

Current Limiting Fuse


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(CLF)

Limits the peak current of short-circuit

Reduces magnetic stresses (mechanical

damage)

Reduces thermal energy

Current Limiting Action


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Curre

nt

(peakamps)

tm ta

Ip

Ip

tc

ta = tc tm

ta = Arcing Time

tm = Melting Time

tc = Clearing Time

Ip = Peak Current

Ip = Peak Let-thru Current

Time (cycles)


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1996-2009 Operation Technology, Inc. Workshop Notes: Short-Circuit IEC Slide 11 1996-2009 Operation Technology, Inc. Workshop Notes: Protective Device Coordination


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Fuse


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Generally:

CLF is a better short-circuit protection

Non-CLF (expulsion fuse) is a betterOverload protection

Electronic fuses are typically easier tocoordinate due to the electronic controladjustments

Selectivity Criteria


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Typically:

Non-CLF: 140% of full load

CLF: 150% of full load

Safety Margin: 10% applied to MinMelting (consult the fuse manufacturer)

Molded Case CB


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Thermal-Magnetic

Magnetic Only Motor Circuit Protector

(MCP)

Integrally Fused (Limiters)

Current Limiting High Interrupting Capacity

Non-Interchangeable Parts

Insulated Case (InterchangeParts)

Types

Frame Size Poles

Trip Rating

Interrupting Capability Voltage

MCCB


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MCCB with SST Device


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Thermal Minimum

Thermal Maximum

Magnetic

(instantaneous)

LVPCB


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Voltage and Frequency Ratings

Continuous Current / Frame Size / Sensor

Interrupting Rating

Short-Time Rating (30 cycle)

Fairly Simple to Coordinate

Phase / Ground Settings

Inst. Override

LT PU


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CB 2CB 1

IT

ST PU

ST Band

LT PU

LT Band

480 kV

CB 2

CB 1

If=30 kA


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Inst. Override

Overload Relay / Heater


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Motor overload protection is provided by a

device that models the temperature rise ofthe winding

When the temperature rise reaches a pointthat will damage the motor, the motor is de-energized

Overload relays are either bimetallic, meltingalloy or electronic

Overload Heater (Mfr. Data)


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Question


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What is Class 10 and Class 20 Thermal

OLR curves?


125/453

Answer


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Overload Relay / Heater


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When the temperature at the combination motor starter is more than10 C (18 F) different than the temperature at the motor, ambient

temperature correction of the motor current is required. An adjustment is required because the output that a motor can safely

deliver varies with temperature.

The motor can deliver its full rated horsepower at an ambienttemperature specified by the motor manufacturers, normally + 40 C.At high temperatures (higher than + 40 C) less than 100% of thenormal rated current can be drawn from the motor without shorteningthe insulation life.

At lower temperatures (less than + 40 C) more than 100% of thenormal rated current could be drawn from the motor without shorteningthe insulation life.

Overcurrent Relay


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Time-Delay (51 I>)

Short-Time Instantaneous ( I>>)

Instantaneous (50 I>>>)

Electromagnetic (induction Disc) Solid State (Multi Function / Multi Level)

Application


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1996-2009 Operation Technology, Inc. Workshop Notes: Short-Circuit IEC Slide 12 1996-2009 Operation Technology, Inc. Workshop Notes: Protective Device Coordination

Time-Overcurrent Unit


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Ampere Tap Calculation

Ampere Pickup (P.U.) = CT Ratio x A.T. Setting

Relay Current (IR) = Actual Line Current (IL) / CTRatio

Multiples of A.T. = IR/A.T. Setting

= IL/(CT Ratio x A.T.

Setting)

IL

IR

CT

51

Instantaneous Unit


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Instantaneous Calculation

Ampere Pickup (P.U.) = CT Ratio x IT Setting

Relay Current (IR) = Actual Line Current (IL) / CTRatio

Multiples of IT = IR/IT Setting

= IL/(CT Ratio x IT Setting)IL

IR

CT

50

Relay Coordination


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Time margins should be maintained between T/C

curves Adjustment should be made for CB opening time

Shorter time intervals may be used for solid state

relays Upstream relay should have the same inverse T/C

characteristic as the downstream relay (CO-8 toCO-8) or be less inverse (CO-8 upstream to CO-6

downstream) Extremely inverse relays coordinates very well with

CLFs

Situation


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Calculate Relay Setting (Tap, Inst. Tap & Time Dial)For This System

4.16 kV

DS 5 MVA

Cable

1-3/C 500 kcmil

CU - EPR

CB

Isc = 30,000 A

6 %

50/51 Relay: IFC 53CT 800:5

Solution


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AInrsuh 328,869412I ==

A338.4800

5II LR ==

Transformer: A

kV

kVAL 694

16.43

000,5I =

=

IL

CTR

IR

Set Relay:

A551.52800

5328,8)50(

1

)38.1(6/4.3380.6

4.5338.4%125

= >==

==

==

AInst

TD

ATAP

A

Question


135/453


What T/C Coordination interval should be maintained between relays?

Answer


136/453


At

I

B

CB Opening Time

+

Induction Disc Overtravel (0.1 sec)

+

Safety margin (0.2 sec w/o Inst. & 0.1 sec w/ Inst.)

Recloser


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Recloser protects electrical transmission systems from temporaryvoltage surges and other unfavorable conditions.

Reclosers can automatically "reclose" the circuit and restore normalpower transmission once the problem is cleared.

Reclosers are usually designed with failsafe mechanisms that preventthem from reclosing if the same fault occurs several times insuccession over a short period. This insures that repetitive line faultsdon't cause power to switch on and off repeatedly, since this couldcause damage or accelerated wear to electrical equipment.

It also insures that temporary faults such as lightning strikes ortransmission switching don't cause lengthy interruptions in service.

Recloser Types


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Hydraulic

Electronic

Static Controller

Microprocessor Controller

Recloser Curves


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TEMA 3


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Transient Stability

Topics


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What is Transient Stability (TS)

What Causes System Unstable

Effects When System Is Instable

Transient Stability Definition Modeling and Data Preparation

ETAP TS Study Outputs

Power System TS Studies Solutions to Stability Problems

What is Transient Stability


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TS is also called Rotor Angle StabilitySomething between mechanical system and

electrical system energy conversion

It is a Electromechanical PhenomenonTime frame in milliseconds

All Synchronous Machines Must Remain inSynchronism with One AnotherSynchronous generators and motorsThis is what system stable or unstable means



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Torque Equation (generator case)

T = mechanical torqueP = number of poles

air = air-gap flux

Fr = rotor field MMF

= rotor angle



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Swing Equation

M = inertia constant

D = damping constant

Pmech = input mechanical powerPelec = output electrical power


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What Causes System Unstable


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In real operationShort-circuitLoss of excitationPrime mover failureLoss of utility connectionsLoss of a portion of in-plant generationStarting of a large motorSwitching operationsImpact loading on motorsSudden large change in load and generation



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Case 1: Steady-state stableCase 2: Transient stableCase 3: Small-signal unstableCase 4: First swing unstable

Swing in Rotor Angle (as well as in V, I, P,

Q and f)



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A 2-Machine

Example

At = -180(Out-of-Step,Slip the Pole)



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Synchronous machine slip poles

generator tripping Power swing

Misoperation of protective devices

Interruption of critical loads

Low-voltage conditions motor drop-offs

Damage to equipment Area wide blackout

Transient Stability Definition


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Examine One Generator

Power Output Capability Curve

is limited to 180

Transient Stability Definition


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Transient and Dynamic Stability Limit

After a severe disturbance, the synchronousgenerator reaches a steady-state operatingcondition without a prolonged loss of

synchronism Limit: < 180during swing

Modeling and Data Preparation


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Synchronous Machine

Machine

Exciter and AVR Prime Mover and Governor / Load Torque Power System Stabilizer (PSS) (Generator)



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T i l h hi d t


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Typical synchronous machine data



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Induction Machine

Machine Load Torque



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Power Grid

Short-Circuit Capability Fixed internal voltage and infinite inertia



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Load

Voltage dependency Frequency dependency



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Load



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Events and Actions


Device Type Action


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Device Type Action

Bus 3-P Fault L-G Fault Clear Fault

Branch Fraction Fault Clear Fault

PD Trip Close

Generator Droop / Isoch Start Loss Exc. P Change V Change Delete

Grid P Change V Change DeleteMotor Accelerate Load

ChangeDelete

Lumped Load Load Change Delete

MOV StartWind Turbine Disturbance Gust Ramp

MG Set Emergency Main

Power System TS Studies

Fault


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Fault

3-phase and single phase faultClear faultCritical Fault Clearing Time (CFCT)Critical System Separation Time (CSST)

Bus TransferFast load transferring Load SheddingUnder-frequency

Under-voltage Motor Dynamic Acceleration Induction motorSynchronous motor


C iti l F lt Cl i Ti (CFCT)


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Critical Fault Clearing Time (CFCT)

Critical Separation Time (CSST)

unstable

unstable

Cycle

Clear faultClear fault

1 cycleunstable

stab

le

1 cycle

Clear faultClear fault

CFCT

Fault

unstable

unstable

Cycle

1 cycleunstable

stable

1 cycle

CSST

SeparationSeparationSeparationSeparationFault


F t B T f


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-1

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

1

-1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1

Vmotor

s

Fast Bus Transfer

Motor residual voltage

Fast Bus Transfer



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Fast Bus Transfer

Ttransfer 10 cycles

90 degreesER 1.33 per unit (133%)

ES = System equivalent per unitvolts per hertz

EM = Motor residual per unit perhertz

ER = Resultant vectorial voltagein per unit volts per hertz


Load Shedding


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Load Shedding


Motor Dynamic Acceleration


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Motor Dynamic Acceleration

Important for islanded system operationMotor starting impact

Generator AVR action

Reacceleration

I S t D i

Solution to Stability Problems


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Improve System Design Increase synchronizing power

Design and Selection of RotatingEquipment Use of induction machines Increase moment of inertia Reduce transient reactance Improve voltage regulator and exciter

characteristics

A li ti f P S t St bili

Solution to Stability Problems


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Application of Power System Stabilizer

(PSS) Add System Protections Fast fault clearance Load shedding System separationOut-Of-Step relay


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TEMA 4


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Harmonic Analysis

ARMONICAS



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Exploracin de frecuencia. Flujo Armnico de Carga.

Dimensionamiento y Diseo deFiltros.

Evaluacin Automtica del lmitede distorsin.

Factores de la influencia deltelfono (TIF & I*T)



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Types of Power Quality

Problems


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Waveform Distortion

Primary Types of Waveform Distortion


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Primary Types of Waveform Distortion

DC Offset

Harmonics

Interharmonics Notching

Noise

Harmonics

One special category of power quality


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One special category of power quality

problems

Harmonics are voltages and/or currents

present in an electrical system at somemultiple of the fundamental frequency.(IEEE Std 399, Brown Book)

Nonlinear Loads

Sinusoidal voltage


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Sinusoidal voltage

applied to a simplenonlinear resistor

Increasing thevoltage by a fewpercent may causecurrent to double

Fourier Representation

Any periodic waveform


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y pcan be expressed as asum of sinusoids

The sum of the sinusoidsis referred to as FourierSeries (6-pulse)

)cos(

13cos13

111cos

11

17cos

7

13cos

5

1(cos

32

1h

hh

dac

thI

tttttII

+

++=

=

Harmonic Sources

Utilities (Power Grid)


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Utilities (Power Grid)

Known as Background Harmonic Pollution from other irresponsible customers

SVC, HVDC, FACTS,

Usually a voltage source

Synchronous Generators

Due to Pitch (can be eliminated by fractional-pitch winding) and Saturation

Usually a voltage source

Harmonic Sources (contd)

Transformers


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Transformers

Due to magnetizing branch saturation Only at lightly loaded condition

Usually a current source

Power Electronic Devices Charger, Converter, Inverter, UPS, VFD, SVC, HVDC,

FACTS (Flexible alternating current transmission systems)

Due to switching actions Either a voltage source or a current source

Harmonic Sources (contd)

Other Non-Linear Loads


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Other Non Linear Loads

Arc furnaces, discharge lighting,

Due to unstable and non-linear process

Either a voltage source or a current source

In general, any load that is applied to a powersystem that requires other than a sinusoidalcurrent

Harmonic I and V


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Classification of Harmonics

H i b l ifi d


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Harmonics may be classified as:

Characteristic Harmonics

Generally produced by power converters

Non-Characteristic Harmonics

Typically produced by arc furnaces and discharge

lighting (from non-periodical waveforms)

Phase Angle Relationship

F d t l F


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Fundamental Frequency


Thi d O d


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Third Order


Fifth Order


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Fifth Order

Seventh Order

Order vs. Sequence


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Characteristic Harmonics


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Characteristic Harmonics(contd)


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Harmonic Spectrum


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%

Harmonic-Related Problems

Motors and Generators


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Increased heating due to iron and copper losses

Reduced efficiency and torque

Higher audible noise

Cogging or crawling

Mechanical oscillations

Harmonic-Related Problems(contd)


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Transformers Parasitic heating

Increased copper, stray flux and iron losses

Capacitors (var compensators)

Possibility of system resonance

Increased heating and voltage stress

Shortened capacitor life

Harmonic-Related Problems(contd) Power Cables


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Power Cables

Involved in system resonance

Voltage stress and corona leading to dielectricfailure

Heating and derating

Neutrals of four-wire systems(480/277V; 120/208V) Overheating

Fuses

Blowing

Harmonic-Related Problems(contd) S itchgears


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Switchgears

Increased heating and losses

Reduced steady-state current carrying capability

Shortened insulation components life Relays

Possibility of misoperation

Metering Affected readings

Harmonic-Related Problems(contd)

C i ti S t


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Communication Systems

Interference by higher frequency electromagnetic field

Electronic Equipment (computers, PLC)

Misoperation System

Resonance (serial and parallel)

Poor power factor

Parallel Resonance

Total impedance at resonance frequency


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p q y

increases High circulating current will flow in thecapacitance-inductance loop

Parallel Resonance


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Capacitor Banks


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Capacitor Banks


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Capacitor Banks


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Say, Seventh Harmonic Current = 5% of 1100A = 55 A

Capacitor Banks


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Resistance = 1% including cable and transformer

CAF = X/R = 7*0.0069/0.0012 =40.25

Resonant Current = 55*40.25 = 2214 A

Parallel Resonance (contd)

Cause: Source inductance resonates with


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Impacts: 1. Excessive capacitor fuseoperation

2. Capacitor failures

3. Incorrect relay tripping4. Telephone interference5. Overheating of equipment

capacitor bank at a frequencyexcited by the facilities harmonicsources

Harmonic DistortionMeasurements

Total Harmonic Distortion (THD)


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Total Harmonic Distortion (THD)

Also known as Harmonic Distortion Factor (HDF), isthe most popular index to measure the level ofharmonic distortion to voltage and current

Ratio of the RMS of all harmonics to the fundamentalcomponent

For an ideal system THD = 0%

Potential heating value of the harmonics relative to

the fundamental

Harmonic DistortionMeasurements (contd)

Good indicator of additional losses due to


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1

2

2

F

F

THD

i

=

Where Fiis the amplitude of the ith harmonic,

and F1

is that for the fundamental component.

current flowing through a conductor Not a good indicator of voltage stress in a

capacitor (related to peak value of voltagewaveform, not its heating value)

Harmonic DistortionExample

Find THD for this waveform


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Find THD for this waveform

Harmonic Example

Find THD for this Harmonic Spectrum


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Adjustable Speed Drive Current Distortion


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Adjustable Speed Drive Voltage Distortion


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Harmonic DistortionMeasurements (contd) Individual Harmonic Distortion (IHD)


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-Ratio of a given harmonic to fundamental- To track magnitude of individual harmonic

1F

FIHD

i= Root Mean Square (RMS) - Total

-Root Mean Square of fundamental plus allharmonics

- Equal to fundamental RMS if Harmonics arezero =

1

2

iFRMS


Arithmetic Summation (ASUM)


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( )

Arithmetic summation of magnitudes of allcomponents (fundamental and all harmonics)

Directly adds magnitudes of all components toestimate crest value of voltage and current

Evaluation of the maximum withstanding ratingsof a device

=1

iFASUM


Telephone Influence Factor (TIF)


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p ( )

Weighted THD

Weights based on interference to an audiosignal in the same frequency range

Current TIF shows impact on adjacentcommunication systems

( )2

1

2

1

=i

ii

F

FWTIF


I*T Product (I*T)


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( )

A product current components (fundamentaland harmonics) and weighting factors

= H

h

hh TITI1

2

)(

where Ih

= current component

Th= weighting factorh = harmonic order (h=1 for fundamental)H= maximum harmonic order to account

Triplen Harmonics

Odd multiples of thethird harmonic


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third harmonic(h = 3, 9, 15, 21, )

Important issue forgrounded-wye systems

with neutral current Overloading and TIF problems

Misoperation of devices due to presence of

harmonics on the neutral

Triplen Harmonics


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Winding Connections

Delta winding provides ampere turn balance


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Triplen Harmonics cannot flow

When currents are balanced Triplensbehave as Zero Sequence currents

Used in Utility Distribution Substations

Delta winding connected to Transmission

Balanced Triplens can flow

Present in equal proportions on both sides

Many loads are served in this fashion

Implications

Neutral connections are susceptible to overheatingwhen serving single-phase loads on the Y side that


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when serving single phase loads on the Y side that

have high 3rd Harmonic Measuring current on delta side will not show the

triplens and therefore do not give a true idea of theheating the transformer is subjected to

The flow of triplens can be interrupted by appropriateisolation transformer connection

Removing the neutral connection in one or both Y

windings blocks the flow of Triplen harmonic current Three legged core transformers behave as if they have

a phantom delta tertiary winding

Modeling in HarmonicAnalysis


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Motors and Machines Represented by their equivalent negative

sequence reactance

Lines and Cables Series impedance for low frequencies

Long line correction including transposition anddistributed capacitance

Modeling in HarmonicAnalysis (contd)


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Transformers Leakage impedance

Magnetizing impedance

Loads

Static loads reduce peak resonant impedance

Motor loads shift resonant frequency due tomotor inductance

Reducing SystemHarmonics

Add Passive Filters


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Add Passive Filters

Shunt or Single Tuned Filters Broadband Filters or Band Pass Filters Provide low impedance path for harmonic

current Least expensive

Reducing SystemHarmonics (contd)


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Increase Pulse Numbers Increasing pulse number of convert circuits

Limited by practical control problems

Reducing SystemHarmonics (contd) Apply Transformer Phase Shifting


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pp y g

Using Phase Shifting Transformers

Achieve higher pulse operation of the totalconverter installation

In ETAP

Phase shift is specified in the tab page of thetransformer editor

Reducing SystemHarmonics (contd) Either standard phase shift or special phase


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Either standard phase shift or special phaseshift can be used

Reducing SystemHarmonics (contd) Add Active Filters


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Add Active Filters

Instantly adapts to changing source and loadconditions

Costly

MVA Limitation


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Current Distortion Limits

Recommended Practices for General


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Distribution Systems (IEEE 519):


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TEMA 5


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Motor Starting

Dynamic Acceleration

ARRANQUE DE MOTORES



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Aceleracin dinmica demotores.

Parpadeo (Flicker) de tensin.

Modelos dinmicos de motores.

Arranque esttico de motores.

Varios dispositivos de arranque.

Transicin de carga.


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Why to Do MS Studies?

Ensure that motor will start with voltage drop


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If Tst 80% Generation bus voltage > 93%

Why to Do MS Studies?

Ensure motor feeders sized adequately


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(Assuming 100% voltage at Switchboard or MCC) LV cable voltage drop at starting < 20%

LV cable voltage drop when running at full-load < 5%

HV cable voltage drop at starting < 15%

HV cable voltage drop when running at full-load < 3%

Maximum motor size that can be started across the line Motor kW < 1/6 kW rating of generator (islanded)

For 6 MW of islanded generation, largest motor size < 1 MW

Motor Sizing

Positive Displacement Pumps / Rotary Pumps


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p = Pressure in psi

Q = fluid flow in gpm

n = efficiency

Centrifugal Pumps

H = fluid head in feet

Motor Types

Synchronous


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Salient Pole Round Rotor

Induction Wound Rotor (slip-ring)

Single Cage CKT Model

Squirrel Cage (brushless) Double Cage CKT Model

Induction Motor Advantages

Squirrel Cage


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Slightly higher efficiency and power factor Explosive proof

Wound Rotor

Higher starting torque Lower starting current

Speed varied by using external resistances

Typical Rotor Construction


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Rotor slots are not parallel to the shaft butskewed

Wound Rotor


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Operation of InductionMotor


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AC applied to stator winding Creates a rotating stator magnetic field in air gap

Field induces currents (voltages) in rotor

Rotor currents create rotor magnetic field in air gap

Torque is produced by interaction of air gap fields

Slip Frequency

Slip represents the inability of the rotor to


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keep up with the stator magnetic field

Slip frequency

S = (s-n)/s where s= 120f/Pn = mech speed

Static Start - Example


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Static Start - Example


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Service Factor


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Inrush Current


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Resistance / Reactance

Torque Slip Curve is changed by altering


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resistance / reactance of rotor bars. Resistance by cross sectional area or

using higher resistivity material like brass.

Reactance by placing conductor deeper inthe rotor cylinder or by closing the slot at theair gap.

Rotor Bar Resistance

Increase Starting Torque


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Lower Starting Current Lower Full Load Speed

Lower Efficiency No Effect on Breakdown Torque

Rotor Bar Reactance

Lower Starting Torque


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Lower Starting Current Lower Breakdown Torque

No effect on Full Load Conditions

Motor Torque Curves


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Rotor Bar Design

Cross section Large (lowresistance) and positioned deep in


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the rotor (high reactance).(Starting Torque is normal andstarting current is low).

Double Deck with small conductorof high resistance. During starting,most current flows through theupper deck due to high reactanceof lower deck. (Starting Torque ishigh and starting current is low).

Rotor Bar Design

Bars are made of Brass or


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similar high resistancematerial. Bars are close tosurface to reduce leakagereactance. (Starting torque ishigh and starting current islow).

Load Torque ID Fan


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Load Torque FD Fan


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Load Torque C. Pump


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Motor Torque Speed Curve


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Double Cage Motor


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Motor Full Load Torque

For example, 30 HP 1765 RPM Motor


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Motor Efficiency

kW Saved = HP * 0.746 (1/Old 1/New)

$ S S * / * $/


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$ Savings = kW Saved * Hrs /Year * $/kWh

Acceleration Torque

Greater

A l i


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AccelerationTorque meanshigher inertiathat can behandled by themotor withoutapproaching

thermal limits

Acceleration Torque


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P

Operating Range Motor, Generator, or Brake


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)

Rated Conditions Constant Power


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0.8 1.0

kvar

Load(kva)

Terminal Voltage

TerminalCurrent

Terminal Voltage0.8 1.0

P = Tm Wm , As Vt ( terminal voltage ) changes from 0.8 to 1.1 pu, Wm

changes by a very small amount. There fore, P is approx constant since

Tm ( wm) is approx. constant

L1Ir

P

It

Starting Conditions Constant Impedance

Starting Conditions Constant Impedance


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0.9 1.0

Kva

LR

Terminal VoltageTerminal Voltage

0.9 1.0

.8 kva

LR

Vt (pu)Vt (pu)

.9 I LR

I LR

KVA LR= Loched - rotor KVA at rated voltage = 2HP

2 Code letter factor Locked rotor KVA HP

Z st = KVA B KVR

KVA LR KVB

Pu, Rst = Zst cos s

8.Shortcircuit_IEC

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Transcript of 8.Shortcircuit_IEC