dr. ibrahim el-amin_power system protection

8/12/2019 Dr. Ibrahim El-Amin_Power System Protection

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Power System Protection

Dr. Ibrahim El-Amin


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Protective Device Coordination


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Definition

Overcurrent Coordination A systematic study of current responsive devices

in an electrical power system.


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Objective

To determine the ratings and settings of

fuses brea!ers relay etc.

To isolate the fault or overloads.


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Criteria

Economics

Available "easures of #ault

Operating $ractices

$revious E%perience


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Design

Open only $D upstream of the fault or overload $rovide satisfactory protection for overloads

Interrupt &C as rapidly 'instantaneously( as

possible Comply with all applicable standards and codes

$lot the Time Current Characteristics of

different $Ds


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Analysis

)hen*

+ew electrical systems

$lant electrical system e%pansion,retrofits

Coordination failure in an e%isting plant


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Protection vs. Coordination

Coordination is not an e%act science Compromise between protection and

coordination eliability

&peed

$erformance

Economics

&implicity


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Protection

$revent inury to personnel

"inimi/e damage to components

0uic!ly isolate the affected portion of the system

"inimi/e the magnitude of available short-circuit


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Spectrum Of Currents

1oad Current 2p to 3445 of full-load

336-3765 'mild overload(

Overcurrent Abnormal loading condition '1oc!ed-otor(

#ault Current #ault condition

Ten times the full-load current and higher


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Coordination

1imit the e%tend and duration of service

interruption

&elective fault isolation

$rovide alternate circuits


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Coordination

t

I

C B A

C

D

D B

A


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!uipment

"otor

Transformer

8enerator

Cable

9usway


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Capability " Damage Curves

t

I

I##t

$en

I

#

t

%otor&fmr

I#t

Cable

I#t


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'ransformer CategoryA(SI"I C)*+.,-


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Infrequent Fault Incidence Zones for Category II & III Transformers

/ S0ould be selected by reference to t0e fre!uent)fault)incidence protection curve or for

transformers serving industrial1 commercial and institutional power systems wit0 secondary)side

conductors enclosed in conduit1 bus duct1 etc.1 t0e feeder protective device may be selected by

reference to t0e infre!uent)fault)incidence protection curve.

Source2 I C*+

Source

'ransformer primary)side protective device

3fuses1 relayed circuit brea4ers1 etc.5 may be

selected by reference to t0e infre!uent)fault)incidence protection curve

Category II or III 'ransformer

6ault will be cleared by transformer

primary)side protective device

Optional main secondary 7side protective device.

%ay be selected by reference to t0e infre!uent)fault)

incidence protection curve

6eeder protective device

6ault will be cleared by transformer primary)side

protective device or by optional main secondary)

side protection device

6ault will be cleared by

feeder protective device

Infre!uent)6ault

Incidence 8one/

6eeders

6re!uent)6ault

Incidence 8one/


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'ransformer

t

3sec5

I 3pu5

'0ermal#--

#.*

I#t 9 ,#*-

#

#*Isc

%ec0anical

:93,"85#t

3D)D ;;5 -.


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'ransformer Protection

MAXIMUM RATING R !"TTING FR #"RCURR"NT $"#IC"P=I%A=> SCO(DA=>

Over ?-- @olts Over ?-- @olts ?-- @olts or Below

'ransformer

=ated

Impedance

Circuit

Brea4er

Setting

6use

=ating

Circuit

Brea4er

Setting

6use

=ating

Circuit Brea4er

Setting or 6use

=ating

(ot more t0an

?

?-- -- -- #*- ,#*

3#*- supervised5

%ore t0an ?

and not moret0an ,-

-- -- #*- ##* ,#*

3#*- supervised5

'able *-)3a5 source2 (C


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Protective Devices #use

elay '64,63 $ + 8 &8 63: ;


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6use

+on Adustable Device Continuous and Interrupting ating

:oltage 1evels

Characteristic Curves

"in. "elting

Total Clearing

Application


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%inimum %elting'ime Curve

'otal Clearing

'ime Curve


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Current ;imiting 6use

3C;65 1imits the pea! current of short-circuit

educes magnetic stresses 'mechanical

damage(

educes thermal energy


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&ymmetrical "& Amperes

$ea!1et-Throug

hAmperes

344 A

;4 A

365 $# ', B ;.;(

37644

6744

74444

44 A

344444

;et)'0roug0 C0art


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6use

8enerally*

C1# is a better short-circuit protection

+on-C1# 'e%pulsion fuse( is a better Overload

protection


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Selectivity Criteria

Typically*

+on-C1#* 3=45 of full load

C1#* 3645 of full load


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%older Case CB

Thermal-"agnetic "agnetic Only

Integrally #used

Current 1imiting

@igh Interrupting

Capacity

Types

#rame &i/e

Trip ating

Interrupting Capability

:oltage


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'0ermal %inimum

'0ermal %aimum

%agnetic3instantaneous5


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;@PCB

:oltage and #reuency atings Continuous Current , #rame &i/e

Override '37 times cont. current(

Interrupting ating

&hort-Time ating '4 cycle(

#airly &imple to Coordinate


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480kV

CB #

CB ,

CB #CB ,

I'

S' PE

S' Band

;' PE

;' Band

If9- 4A


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%otor Protection

"otor &tarting Curve

Thermal $rotection

1oc!ed otor $rotection

#ault $rotection


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%otor Overload Protection3(C Art -)#5

Thermal O,1 'Device =>( "otors with not less than 3.36

3765 of #1A

"otors with temp. rise not over =4 3765 of #1A

All other motors

3365 of #1A


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;oc4ed =otor Protection

Thermal 1oc!ed otor 'Device 63(

&tarting Time 'T& T1(

1A 1A sym

1A asym '3.6-3.; % 1A sym( F 345 margin


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6ault Protection3(C Art -)*#5

+on-Time Delay #uses 445 of #1A

Dual Element 'Time-Delay #uses( 3


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200 HP

MCP

O";

Starting Curve

I#'

35

%CP 3*-5

3*,5ts

t;=

;=As ;=Aasym


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Overcurrent =elay

Time-Delay '63 IJ( &hort-Time Instantaneous ' IJJ( Instantaneous '64 IJJJ( Electromagnetic 'induction Disc( &olid &tate '"ulti #unction , "ulti 1evel(

Application


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'ime)Overcurrent Enit

Ampere Tap Calculation Ampere $ic!up '$.2.( B CT atio % A.T. &etting

elay Current 'I-( B Actual 1ine Current 'I

1( , CT

atio "ultiples of A.T. B I

-,A.T. &etting

B I1,'CT atio % A.T. &etting(I1

I

CT

63


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Instantaneous Enit

Instantaneous Calculation Ampere $ic!up '$.2.( B CT atio % IT &etting

elay Current 'I-( B Actual 1ine Current 'I

1( , CT

atio "ultiples of ITB I

-,IT &etting

B I1,'CT atio % IT &etting(I1

I

CT

64


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,

=elay Coordination Time margins should be maintained between T,C

curves Adustment should be made for C9 opening time &horter time intervals may be used for solid state

relays 2pstream relay should have the same inverse T,C

characteristic as the downstream relay 'CO-G to CO-G(or be less inverse 'CO-G upstream to CO-;downstream(

E%tremely inverse relays coordinates very well withC1#s


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6ied Points

"otor starting curves

Transformer damage curves K inrushpoints

Cable damage curves

&C ma%imum fault points Cable ampacities

$oints or curves which do not changeregardless of protective device settings*


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Situation

Calculate elay &etting 'Tap Inst. Tap K Time Dial(#or This &ystem

=.3; !:

D& 5 MVA

Cable

1-3/C 500 kcmilC2 - E$

C9

IscB 4444 A

6 %

64,63 elay* I#C 6CT G44*6


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Solution

AInrsuh B#


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Fuestion

)hat is A+&I &hift CurveL


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Answer

#or delta-delta connected transformers with

line-to-line faults on the secondary side the

curve must be reduced to G


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Fuestion

)hat is meant by #reuent and

Infreuent for transformersL


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Answer


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Fuestion

)hat T,C Coordination interval should bemaintained between relaysL


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Answer

At

I

B

CB Opening Time

+

Induction i!c O"e#t#$"el 0&1 !ec'

+

($)et* m$#gin 0& !ec ,/o In!t& 0&1 !ec ,/ In!t&'


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Fuestion

)hat is Class 34 and Class 74

Thermal O1 curvesL


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Answer

Class 34 for fast trip 34 seconds or less

Class 74 for 74 seconds or less

There is also a Class 4 for long trip time


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Answer

dr. ibrahim el-amin_power system protection

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