IEEE CTs and PTs 6-10.pdf

8/11/2019 IEEE CTs and PTs 6-10.pdf

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GE MultilinInstrument Transformers, Inc.

Are you using the right CT's and PT's

for your application?John Levine, P.E.

Levine Lectronics and LectricE-mail: [email protected]

GE Multilin / Instrument Transformers, Inc.


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Current & Voltage TransformerBasics (IEEE Standards)


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Agenda

Current TransformersVoltage TransformersRequired Information for Specifying CTs & VTsTake Home Rules for CTs & VTsApplications where used


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Why use Instrument Transformers?

Circuit Isolation

Reduce voltage and currents

to reasonable working levels.

Phasor combinations for

summing and measuringpower


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CURRENT TRANSFORMERS

TYPES OF C.T. CONSTRUCTION

The most common type of C.T. construction is the DOUGHNUTtype. It is constructed of an iron toroid, which forms the core of thetransformer, and is wound with secondary turns.

Secondary Winding Primary Conductor

Iron Core


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Transformer ratio (TR)

Primary Current(100 amps) Secondary Current(5 amps)

Primary Current

Secondary CurrentTransformer Ratio = _____________________

1005

___ = 100:5 or 20:1


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Polarity

Direction of Primary Current

Direction ofSecondary Current

H1

X1

Primary current into polarity =

Secondary current out of polarity

P1

IEEE

IEC

PrimaryPolarityMarks

IEEEIECS1

SecondaryPolarityMarks

Remember:


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Polarity

Direction of Primary Current

Direction ofSecondary Current

H1

X1

P1

IEEE

IEC

PrimaryPolarityMarks

IEEEIECS1

Secondary

PolarityMarks

Primary current into non polarity =Secondary current out of non polarity

Remember:


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Generator t !ical "irin#


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What is your application?

If your application is metering , how high do I

need to go in current? 2 times ?

If your application is protective relaying, howhigh do I need to go in current? 20 times ? 40times ?


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C! Ratin" #actor $R#% IEEERated current & $R#% =

Ma&imum continuous current carryin"capability:

'it(out e&ceedin" temperature limits'it(out loss of publis(ed accuracy class

!ypical ratin" factors for Meterin" C!s are:)*+, )*--, )*., /*+, -*+, 0*+


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+*-+

+*-+

+*1+

+*1+

Ratin" #actor

2 c c u r a c y C

l a s s 3

C! Ratin" #actor $R#% IEEE

)+3 )++3 /++3 -++3 0++3

)*+ /*+ -*+ 0*+

IEEE C.4*)- 2ccuracy+*-3 5 67*7 R# 0*+

+*-3 2ccuracyRe"ion

+*132ccuracy

Re"ion


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S(ort !ime !(ermal Current Ratin"

8ne $)% 9 second t(ermal ratin"E&pressed as alue of RMS primary current

Main influencin" factor:C! primary ; secondary e< 2mbient?>e< 2mbient

E&ample: C!


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C! Meterin" 2ccuracy

Actual secondarycurrent

Rated secondarycurrent=

Difference in 3 is kno


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IEEE C! Meterin" 2ccuracy2ccuracyClass $ B %

2pplication

+*).i"( 2ccuracy Meterin"

+*).S Special i"( 2ccuracyMeterin"

+*-Re enue Meterin"

+*1

B 2ll accuracy classes defined by IEEE C.4*)- or C.4*)-*1

B 2ccuracy classes include bot( ratio ; p(ase an"le error


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IEEE C! Meterin" 2ccuracy

6urdenoad connected to C! secondary

Includes de ices ; connectin" leads

E&pressed in o(ms

Standard alues = 6+*), 6+*/, 6+*., 6+*A, 6)*@E+*+0, E+*/

2ll burdens defined by IEEE C.4*)- or C.4*)-*1 for 1+ only


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Application BurdenDesignation

Impedance(Ohms)

VA @5 amps

PowerFactor

Metering B0.1 0.1 2.5 0.9B0.2 0.2 5 0.9B0.5 0.5 12.5 0.9B0.9 0.9 22.5 0.9

B1.8 1.8 45 0.9

Standard IEEE C! 6urdens $. 2mp%$Per IEEE Std* C.4*)- )AA- ; C.4*)-*1%


E0.2E0.04

0.20.04

51

1.01.0


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A current transformer for metering purposes maytypically have an accuracy of 0.3%. The C.T. mustmaintain this accuracy for normal load currents,

provided the rated burden on the C.T. is not exceeded.It is quite acceptable, and in fact desirable, for the C.T.to saturate when fault current flows. The accuracy for atypical metering C.T. is specified as:

0.3 M 0.9

O.3% METERING O.9 OHMS BURDEN

This metering C.T. has an accuracy of 0.3% when the

connected burden does not exceed 0.9 OHMS.

CT CLASSIFICATION for Metering


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2ccuracy Class$+*-, +*1, )*/% $B%

6urden $8(ms%$6+*), 6+*/, 6+*.,6+*A, 6)*@%

2ccuracy e&pressed as:

+*-6+*/+*16+*A

)*/6)*@+*).E+*/

=

!ypicalE&amples

B 2ccuracy class is stated at )++3 rated currentB 2t )+3 rated current, t


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+*-+

+*-+

+*1+

+*1+

Ratin" #actor

2 c c u r a c y C

l a s s 3

)+3 /++3 -++3

)*+ /*+ -*+ 0*+

IEEE C.4*)- 2ccuracy+*- 5 67*7G R# 0*+

+*-3 2ccuracyRe"ion

+*132ccuracy

Re"ion


)++3 0++3

>o accuracy "uaranteed atcurrent le els less t(an )+3


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IEEE C! Meterin" 2ccuracyC! Parallelo"ram 9 IEEE C.4*)-

8ut of +*-3 Class

+*- classparallelo"ram

+*1 class

parallelo"ram

)++3)+3

>ote:6urden mustbe specified


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Corrected to +*-3 Class

C! Parallelo"ram 9 IEEE C.4*)-+*- classparallelo"ram

+*1 class

parallelo"ram

)++3

)+3

>ote:6urden mustbe specified


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+*-+

+*-+

+*1+

+*1+

Ratin" #actor

2 c c u r a c y C

l a s s 3

.3 )++3 /++3 -++3 0++3

)*+ /*+ -*+ 0*+

IEEE C.4*)-*1 2ccuracy+*). 5 E0.04, E0.20$+*). 5 67*7G R#0*+

+*).3 2ccuracyRe"ion+*-3

2ccuracyRe"ion


+*).

+*).

>o accuracy "uaranteed

at current le els less t(an .3


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+*-+

+*-+

+*1+

+*1+

Ratin" #actor

2 c c u r a c y C

l a s s 3

.3 /++3 -++3

)*+ /*+ -*+ 0*+

IEEE C.4*)-*1 2ccuracy+*).S 5 E0.04, E0.20$+*).S 5 67*7, R#0*+

+*).3 2ccuracyRe"ion


+*).

+*).

>o accuracy "uaranteed

at current le els less t(an .3

0++3)++3


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IEEE C! Relay 2ccuracyProtection C!

Standard Relay 2ccuracy Classes

C or !)++

C or !/++C or !0++

C or !@++

'(at do t(ese meanH


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Instrument Transformers, Inc.

IEEE C! Relay 2ccuracy

Relay class $C or ! % desi"nates minimum

secondary terminal oltsJ2t /+ times rated current

'it(out e&ceedin" )+3 ratio error

Into a ma&imum specified burden

Now that everyone is totally confusedlets look at some simple examples


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T = Determined by test

CT CLASSIFICATION for RELAYING

10 C 400

Protection Class CTs - Must supply 20 times rated current

C = CalculatedK = CalculatedL = Low internal secondary impedanceH = High internal secondary impedance

Format

LetterAccuracy Voltage at 20 times CT


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Primary current/0,+++ amps$/+ & )/++ %


C!)/++:.

C or !)++

7)7/

6urden of De ices $ %

6urden of eads $ %

Secondary current)++ amps $/+ & .%

!otal E&t6urden)*+

C or !)++ e&ample

!erminal Kolts = $/+ times rated% $!otal e&ternal burden%)++ Kolts = $)++ amps% $)*+ %

! e r m

i n a l K o l t s =

) + +


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Primary current/0,+++ amps$/+ & )/++ %


C!)/++:.

C or !/++

7)7/


6urden of eads $ %

Secondary current)++ amps $/+ & .%

!otal E&t6urden/*+

C or !/++ e&ample

!erminal olts = $/+ times rated% $!otal e&ternal burden%/++ Kolts = $)++ amps% $/*+ %

! e r m

i n a l K o l t s =

/ + +


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Standard IEEE C! 6urdens $. 2mp%$Per IEEE Std* C.4*)- )AA-%


Application BurdenDesignation

Impedance(Ohms)

VA @5 amps

PowerFactor

Relaying B1 1 25 0.5 B2 2 50 0.5 B4 4 100 0.5 B8 8 200 0.5


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IEEE C! Relay 2ccuracyE&citation cur e includes

olta"e reLuired to o ercomeinternal resistance $DCR% of C!*2ppro&imately -/ olts*

)+3 ratio error = $/+ & .% $)+3%= $)++% $+*)+%= )+ amps

o< many terminal olts


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)+++:. C!

)+++ 2mps .amps

IE +*.amps

I6 N0*.amps

'it( )+3 error, I 6 is any


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C! 6urden Calculation

PrimaryCurrent

C!

7)7/


6urden of eads $ %

Secondary current

!otal6urden

!

o< do


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C! 6urden Calculation

2ssumption: - p(ase C!s are Q connected

! = RC! R 6

! = !otal burden in o(ms $ ector summation ofresistance and inductance components%

RC! = C! secondary resistance in o(ms 54. de" C $DCR%

R = Resistance of leads in o(ms $!otal loop distance%

6 = De ice impedance in o(ms


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GE Multilin Electronic %ela &ur'en

VA = VI. V= IR, So 0.2 = I*I*R.

.2/25 = .008 ohms


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100:5 C.T. Secondary Winding Resistance (DCR) = .062 ohm

Resistance of Cable from C.T. to Relay and back = .1 ohms

Resistance of Relay Coil = .02 ohms

Total Resistance = .182 ohms

If we have a fault of 2,000 amps and the C.T. ratio is 100:5 then the C.T.secondary current is 100 amps. Therefore we will produce a voltage of 100

amps x .182 ohms = 18.2 Volts. To prevent CT saturation, select a CT with aknee point above 18.2 Volts.

.062

.1

.02


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780-102 is a 1000 to 5 CT, Class C100

1000:5 C.T. Secondary Winding Resistance (DCR) = .32 ohm

Resistance of Cable from C.T. to Relay and back = .1 ohms

Resistance of Relay Coil = .008 ohms

Total Resistance = .428 ohms

If we have a fault of 20,000 amps and the C.T. ratio is 1000:5 then the C.T.secondary current is 100 amps. Therefore we will produce a voltage of 100amps x .428 ohms = 42.8 Volts. To prevent CT saturation, select a CT with a

knee point above 42.8 Volts.What happens if the fault current is 40,000 amps?

.32

.1

.008

# I fl i " C! 2


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#actors Influencin" C! 2ccuracy#reLuency

Current Ratio

6urden

o< freLuency and i"( accuracy are not friends

o< ratio and (i"( accuracy are not friends

i"( burden and i"( 2ccuracy are not friends


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(T )aturation

*+at is (T )aturation


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-o"er ) stems %ela (ommittee -)%(/

)aturation (alculator

ff f )


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actors ffectin# e#ree of )aturation

an' Time to )aturation( ffsetault Ma#nitu'e s mmetrical current/

100 to 5 (T 20 times 2000 am!s, at 20,000 am!s "e +a e 200 times (T

(T Turns %atio

)econ'ar &ur'en(T ccurac%emanence lu

(an occur if current interru!te' "+en core is saturate'If ( flo"s in "in'in#s 'urin# testin#

ee' a olta#e a:o e 60; of


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!ips for 2 oidin" C! Saturationse (i"(er ratio C!s

se separate set of (i"( ratio C!s for (i"( faultcurrent trippin"

Reduce secondary burden

Select lo< burden relays ; metersDistribute sin"le p(ase burdens amon" p(asesIncrease si e of secondary leads

Reduce len"t( of secondary leadsse step do


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-otential Transformers

f


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DefinitionsVoltage Transformer (VT)

An instrument transformer used to reflect a primaryvoltage into a secondary voltage through a magnetic medium.Always connected in parallel with primary conductor across acircuit load.

Secondary (measuring) voltage is usually 115 or 120volts nominally. The secondary voltage level is selected for easeof measurement and safety.Control Power Transformer (CPT)

Designed to provide power for contractors, relays and

devices with high inrush currents, Regulation is not as critical.


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POTENTIAL TRANSFORMERS

VP

Vs

Relay

14,400/120 = 120/1

4200/120 = 35/1

2400/120 = 20/1

IEEE K! 2ccuracy Class


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IEEE K! 2ccuracy ClassMeterin" 2ccuracy

Classes $3 error%

+*-

+*1

)*/

+*).

Defined by IEEE C.4*)-

2pplicable from A+3 to ))+3rated olta"e

Defined by IEEE C.4*)-*1



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!(ese standard burden desi"nations (a e no si"nificanceat freLuencies ot(er t(an 1+ *

Burden VA PF

W 12.5 0.10X 25 0.70M 35 0.20Y 75 0.85Z 200 0.85

ZZ 400 0.85

Meterin" 2ccuracyClass 6urdens



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E&pressed as:

2ccuracy Class 6urden Code

+*- ',7,Q+*1

)*/

!(ese standard desi"nations (a e no si"nificanceat freLuencies ot(er t(an 1+ *


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K! Installation Tuidelines


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K! Installation TuidelinesCaution:

Rated olta"e: Do not operate abo e ))+3

ine to "round rated:Do not connect line to lineDo not use on un"rounded systems


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pK!

Troup>o* of

6us(in"Connection

Met(od

>eutralTroundin"

>otes

) / open

Q Q possible

2ny 'it(stand /.3 o er rated olta"e onan emer"ency basis

/ / open

Q Q possible

2ny 'it(stand )+3 o er rated olta"econtinuously* Primary rated for line toline olta"e*

- ) Q Q Q 2ny 8utdoor, t


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K! !ypical Connections

8pen Delta Connection$/% Double 6us(in" K!s

Q 9 Q Connection$-% Sin"le 6us(in" K!s

#erroresonance


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#erroresonancePossible


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#erroresonance

Recommended readin":

Ferroresonance of rounded !otential

Transformers on "ngrounded !ower #ystems$

2IEE Po


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p

Q 9 6roken Corner K! connection

Ferroresonance

damping resistor % F%

Kolta"e relay todetect "roundfault

>on effecti ely"rounded system

+ olts 5 normal condition

- times normal > p(aseolta"e 5 "round fault

Preferred met(od

#erroresonance Dampin"


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e o eso a ce Da p

Q Q?6roken Corner Connection

Double secondary K!$)% Relayin" ? Meterin"

$)% Tround fault detectionand ferroresonance damping

Preferred met(od

#erroresonance


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Dampin"#erroresonancedampin" resistor

R#R alue

6ased on / ariables:2ir core inductance of primary


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ReLuired Informationfor Specifyin" C!s ; K!s

Current !ransformer $C!% R#V SpecificationEn ironment: Indoor 8utdoor


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En ironment: Indoor 8utdoor

System Kolta"e $kK%+*1+*4/-*1.*+4*/

@*4)/)./0/.

-0*.-0*.

Po


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Indication 8nly: 3, K2 $Skip meterin" ; protection selections%

Meterin" Class:IEEE: +*- +*1 )*/ /*0 8t(erIEC: +*/ +*. )*+ 8t(er

Meterin" 6urden:

IEEE $8(ms%: 6+*) 6+*/ 6+*. 6+*A 6)*@ 8t(erIEC $K2%: /*. .*+ )+ ). -+ 8t(er

Protection Class: C $IEEE% K2, P $IEC%

8peratin" #reLuency: 1+ .+

Ratin" #actor: )*+ )*-- )*. /*+ 8t(er

Secondary Connections: !erminals /0 inc( leads

8uter Insulation: Standard Cotton tape ; arnis( Polyester tape

Insulation Class: )+. +C $Standard% 8t(er

8t(er Special ReLuirements $dimensional constraints, mountin" reLuirements, Jetc%:

Kolta"e !ransformer $K!% R#V SpecificationEn ironment: Indoor 8utdoor


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System Kolta"e $kK%+*1+*4/-*1.*+4*/

@*4)/)./0/.

-0*.-0*.

Po


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!(ermal Ratin": K2 $8ptional%

Primary Kolta"e: ) bus(in" K 2C P(ase to neutral

/ bus(in" K2C P(ase to p(ase

Secondary Kolta"e: )/+K )).K ))+K )++K )/+? - )).? - ))+? - )++? - 8t(er

Rated Kolta"e #actor $RK#% $) bus(in" only%: )*A for -+s

#uses:

Primary Secondary >one $1++ 9 4/+ K%

Primary i e parts only S


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C!s are intended to be proportionalcurrent de ices* Kery (i"( olta"es canresult from open circuitin" t(e secondary

circuit of an ener"i ed C!* E en ery smallprimary currents can cause dama"eJConsult t(e factory if you (a e Luestions*

>e er open circuit a current

transformer secondary


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>e er s(ort circuit t(esecondary of an ener"i ed K!

K!s are intended to be used as proportional olta"e

de ices* Dama"in" current


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Meterin" applicationsdo not reLuire a C class C!

C class ratin"s are specified for protection

purposes only* 'it( some e&ceptions meterin"class C!s are typically smaller and less e&pensi e*

!ake ome Rule W 0


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C! secondary leads must beadded to t(e C! burden

Electronic relays usually represent erylittle burden to t(e C! secondary circuit*

In many cases t(e maXor burden iscaused by t(e C! secondary leads*


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!ake ome Rule W 1


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E&ercise caution


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It is common practice to apply1++ Kolt C! to systems


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V ES!I8>SH


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=> )"itc+:oar's


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=> -anel:oar's

5 )eries

8)?T19%T

T !ical (T Mo'els

=> )"itc+:oar's


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=> -anel:oar's

T !ical >T Mo'els

460, 467, 475, 2>T460, 3>T460

=.>. M((@s


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8)?T

19%T

5 )eries

3-85

T !ical (T Mo'els

=.>. M((@s


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T !ical >T Mo'els

460, 467, 475, 2>T460, 3>T460

=.>. )"itc+#ear


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=.>. )"itc+#ear (urrent TransformersGE 2000 am! frameMo'el 560 Meterin#


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Mo el 560 Meterin#Mo'el 561 -rotection

(urrent TransformersGE 4000 am! frame=.>. )"itc+#ear


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Mo'el 562 Meterin#Mo'el 563 -rotection

=.>. )"itc+#ear


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o more room in t+e front

*e can recommen' a 'ifferentmo'el (T for t+e rear :us area.

=.>. )"itc+#ear


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T !ical 3 -+ase >TInstallation

3>T=4603 -+ase >T

M.>. )"itc+#ear


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84GE Multilin


T !ical =ine A!

*+ere are t+e (Ts,>Ts, an' (-Ts

M.>. )"itc+#ear


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(urrent Transformers

778 B 779680 B780 )eriesT !ical IEEE Meterin# C -rotection

M.>. )"itc+#ear (urrent TransformersMeterin# C -rotection


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Mo'el 780, 778

Mo'el 785

M.>. )"itc+#ear


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Mo'el 203 (Tsmounte' in rear:us com!artment

M.>. )"itc+#ear


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Dero )e uence (TMo'el 593, 594

Is this better than aResidual Connection?

M.>. )"itc+#earInstalle' in enclosure


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T !ical >T %ollout ra"er

*it+'ra"n fromenclosure

2/ -TG5@s in o!en 'elta

confi#uration


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M> M((@s


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=et@s o!en a 'ooran' see "+at@sinsi'e

M> M((@s


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T !ical (T Mo'els112113114115117

Generators


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&oar' Mounte' Generator (T

)tation (lass (ircuit &rea


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-ol ester Ta!e' &us+in# (T on

ut'oor (ircuit &rea


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ut'oor & 7 F%e!laces &(T@s in s+iel'e'aluminum +ousin#

Groun )+iel

-o"er Transformers)li! o er current transformer for installation o er


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ut'oor T !e & 7for %etrofit

)li! o er current transformer for installation o ere terior of out'oor :us+in#


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uestions

Documents

IEEE CTs and PTs 6-10.pdf