153691706 Relay Coordination Guidelines

7/26/2019 153691706 Relay Coordination Guidelines

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Over current & Earth fault relay co-ordination

Over current fault relay co-ordination:

Let us consider one small section of Aditya cement plant,Sambhupura and let

us see how over current and earth relay co-ordination is done on it.

Over Current Relay Co-ordination Guidelines:


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1. Over current relays are co-ordinated from load end till the source. Generally

the operating time of relay at load end is assumed to be at .! seconds and

considering this assumption operating time of bac" up relays are calculated.

#. $iscrimination time for relays on series element is considered as .% and

for non-series elements discrimination time is considered as .&.

&. 'or calculation of ()S of upstream*bac"up relay, the downstream relay

having higher operating time is considered.

!. Generally it is preferable to have the plug setting +amperes of upstream

relays to be eual or little more than plug setting +amperes of downstream

relays.

%. nstantaneous settings for upstream relays are provided so as to provide

protection against the close in faults occurring at the respective buses

such that respective relays trip much before the ma/imum fault current flows

through them. nstantaneous settings should be provided such that they

should have a discrimination of about .& second with thermal curve of theirbac" up relay.

0. ut for transformer primary relays instantaneous setting should be set such

that the relays don2t trip for charging current but protect the transformer

against close in faults.

3. (ime grading is an important criterion for instantaneous protection. (he

relays should be time graded in such a way that bac" up relays trip

instantaneously with certain standard time delay, such that for any fault at

lower stream, the upstream relays don2t undergo cascaded tripping.


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4. As per the standard convention, instantaneous time delay of .% seconds

is provided for relays at e/treme load end and at transformer primary.

5. n case of phase overcurrent protection generally an instantaneous time

delay of .# seconds should e/ist between primary and it2s bac"up.

1.n case where condition of critical clearing time needs to be satisfied, there

the instantaneous time delay is "ept as .1% seconds between two relays

acting as primary and bac" up.

11. f there is a fault at one voltage level then the relay at that voltage level

should trip instantaneously and it2s bac" up at a different voltage level

should trip thermally.

1#.t is always advisable to run co-ordination 6 simulation in )i-power, to chec"

whether the relays operate in co-ordination with proper time discrimination.

7onsidering the above guidelines let us proceed to perform the overcurrentrelay co-ordination of the section considered above.

Relay.No.104:


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Let the operating time of relay.8o.1! be .! seconds

(he three-phase fault current viewed by relay no. 1! is &phf1! 9 #%05&.&3 A

:lug settingof relay.8o.1! in amperes 9 &0 A.

(herefore ()S of relay 1! is ()S 9 .!;*.1!9.11

Since the ()S range of ?@ %#1 relay is in range of .% = 1 in steps of .%

Bence above calculated ()S is appro/imated to .1%

8ow as per the appro/imated ()S, recalculated operating time is C

(op?1!2 9 .1%;.1!* 9 .%#&4 sec.

Relay.No.100:

Since relay.8o.1 is in the same series element as relay no. 1! hence

discrimination time between them is .% sec.

Bence remote operating time for relay no. 1 is (op?1remote9 .%#&4 D .% 9 .%3 sec.

?emote fault current viewed by relay no. 1 is remote9 53&.1# A

:lug setting of relay no.1 is 1! A

(herefore ()S of relay 1 9 .%3&4;*.1! 9 .10

ut as step value is .% hence appro/imated ()S of relay no.1 is .#

7lose in fault current viewed by relay no.1 is &phf19 &1104.%3 A

Bence close in operating time of relay no. 1 is

(op?19.#;.1!* 9 .!%&! sec.

Note:f )9 E #, then

) 9 # +eyond )9#, relay is considered to be saturated. Bence in the above

calculation as ) 9 +&1104.%3*1!E# hence )9# has been considered.

@/actly the calculations for relay no. 1% and ?elay.8o 11 are made and

results are same as above.


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Let the operating time of relay.8o.3 be .50% sec +7alculated similarly as

above.

And the operating time of relay.8o.00 be 1.55 sec. +7alculated similarly as

above.

Relay.No.6:

'or calculation of operating time for relay no.0, operating time of relay no.1

and relay no. 11 is considered and out of them whichever2s operating time is

higher that operating time is considered for calculation of ()S of the relay no.0.

but as relay.8o.00 has an higher operating time of 1.55 sec hence operating time ofrelay. 8o.00 is considered for ()S calculation of ?0.

Bence operating time of relay ?09operating time of relay.8o.00Ddiscrimination time.

Operating time of relay ?0, (op?0 9 1.55 D .& 9 #.#5 sec.

7lose in fault current viewed by relay no.0 is &phf09 %#0!.& A

:lug setting of relay ?0 in amperes 914 A

Bence ()S of relay ?0 9 #.#5;*.1! 9.&%%

Appro/imating the above result we get ()S 9.!So recalculating the operating time as per new ()S,

(op029.!;.1!* 9 #.%4 sec.

Relay.No.:

Operating time of relay.8o.% for remote fault is (op%remote9 #.%4D.% 9 #.0& sec

?emote fault current as viewed by relay no.% 9 %#0!.& A

:lug setting of relay no.% in amperes 9 14 A

()S of relay no. % 9 #.0&;*.1! 9 .!1

Appro/imating the ()S as per the step value of ?@ %#1 we get ()S9.!%

?emote operating time as per appro/imated ()S

(op%remote2 9 .!%;.1!* 9#.5 sec


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7lose in fault current &phf% 9 4410.4 A

7lose in operating time of relay no.% is given asC

(op?% 9 .!%;.1!* 91.5% sec.

!nstantaneous "ettin# :

Relay.No. 104: $%eeder

7lose in fault current viewed by relay.8o.1! is &phf1!9 #%35&.3 A

7( ?atio 9 !*1

(herefore pEE is set such that the relay trips instantaneously before the

ma/imum fault current and has a discrimination of .& with thermal curve of it2s

bac" up relay.

Bence if relay is set at &F then the relay trips at 1# A which is much

before the ma/imum fault current and discrimination of .& is maintained with

the thermal curve of it2s bac" up relay.

'actor to be entered in )i-power database 9 & +for relays at load end directly

the instantaneous factor is entered in database

nstantaneous time delay tpEE 9 .% sec

Relay.No. 100:$'ransfor(er )ri(ary

?ated current of relay.8o. 1 , rated 9 1&1.# A

?emote fault current 9 53&.1# A

7harging current 9 1;?ated current 9 1&1# A

ac" up current 91.&;?ated current 9 1#0%.0 A

Since !char#* !+ac,, hence charg is considered for instantaneous calculation

nstantaneous setting, pEE 9 charg*7( ratio 9 1&1#*#9 0.%0


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Appro/imating the above value to nearest whole number we get pEE 9 3 times

or 3F.(he factor to be entered in database 9 3 / 7( ratio*?emote fault

current 9 1.!!

nstantaneous phase time setting 9 .% sec.

nstantaneous setting for ?elay no. 1% is e/actly same as that of relay

no.1! 6 instantaneous setting for ?elay no. 11 is e/actly same as that of

relay no.1.

Relay.No.6:$%eeder

7lose in fault current viewed by relay no.1! is &phf1!9 %#0!.& A

7( ?atio 9 #*1

(herefore pEE is set such that the relay trips instantaneously before the

ma/imum fault current and has a discrimination of .& with thermal curve of it2s

bac" up relay.

Bence if relay is set at 1%F then the relay trips at & A which is much

before the ma/imum fault current and discrimination of .& is maintained with

the thermal curve of it2s bac" up relay.

'actor to be entered in )i- :ower database 9 &*%#0!.& 9 .%3. nstantaneous phase time setting for relay.8o.0 is done ta"ing the higher

instantaneous time setting of relays connected to its outgoing feeder and then

adding an instantaneous time delay of .1% sec to it.

Since the instantaneous phase time setting for relay. 8o 3 is .&% sec, hence

the instantaneous phase setting of relay.8o.0 is .% sec+.&% secD .1% sec.

Relay.No. :$'ransfor(er )ri(ary

?ated current of relay.8o.%% is rated 9 134!.% A

?emote fault current 9%#0!.& A

7harging current, charg9 1;?ated current 9 134!% A

ac" up current, ac" 91.&; ?emote fault current 9 04!&.%5 A


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Since charg E ac" , hence charg is considered for instantaneous

calculation

nstantaneous setting, pEE 9 charg*7( ratio 9 134!%*# 9 4.5

Appro/imating the above value to nearest whole number we get pEE 9 5

times or 5F.

(he factor to be entered in )i- :ower database 9 5 / 7( ratio*?emote fault

current 9 &.!1

nstantaneous phase time setting 9 .% sec

(he :hase co-ordination curves are given in the figure 1.1 below.


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%i#ure 1.1. )hase Co-ordination curves


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Earth %ault Relay Co-ordination :

Earth Relay Co-ordination Guidelines:


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1. n case of single line to ground fault the plug setting of the relay depends upon

the single line to ground fault current viewed by the relay and the setting range of

the relay used. Generally plug setting of 1F - #F is set for the relay, as an

unbalance of about 1F always e/ists in the system.

#. ?elay used should be sensitive enough to operate for an single line to ground

fault occurring in it2s one but should not trip for too low SLG current.

&. (he :lug setting should be provided such that the plug setting current+amperes

of upstream relays should be either eual to or greater than plug setting current

+amperes of the downstream relays.

!. 'or transformers having delta-star configuration or vice versa, the relay located

at transformer primary can2t be co-ordinated with relay located at transformer

secondary because delta windings isolate the fault current from the healthy side

and hence SLG fault current doesn2t find a path to flow to the other side. n such a

case relay located on star side should be set so as to only operate for close in fault

current.

%. n case of earth overcurrent protection generally an instantaneous time delay

of .# seconds should e/ist between primary and it2s bac"up.

?est all other guidelines are similar to that of over current fault co-ordination

8ow let us see how earth relay co-ordination is set using the above guidelines.

Relay.No. 104:


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(he single line to fault current viewed by relay.8o.1! is, slgf1! 9 #44&&.& A

(he plug setting 9 %F of 7( ratio 9 .%;!9 # A

Let the relay operating time be 9.! sec

(herefore ()S of relay.8o.1! 9 .!; 9 .130

Bere )9#

Appro/imating the ()S as per step value of ?@ %#1 is 9 .#

So new operating time as per the appro/imated ()S

(opSLG1!9 .#;.1!* 9.!%& sec

As relay. 8o 1 is on delta side of transformer hence no co-ordination is not

possible with relay.8o 1!.

Relay.No. 100:

(he single line to fault current viewed by relay.8o.1! is, slgf1! 9 !00.0 A

(he plug setting 9 1F of 7( ratio 9 .1;#9 # A

Let the relay operating time for close in fault be 9.% sec

(herefore ()S of relay.8o.1! 9 .%;*.1! 9 .#

Appro/imating the ()S as per step value of ?@ %#1 9 .%

8ew operating time as per appro/imated ()S is given as

(opSLG1 9 .%;.1!* 9.11& sec

(he operating time of relay.8o 3 is (opSLG3 9 .35 sec +calculated similarly as

above.

Similarly operating time of relay.8o 00 is (opSLG3 9 .!# sec +calculated similarly as

above.

Relay.No. 6:


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'or calculating the operating time of relay.8o.0 ,the highest operating time of the

relay, among the relays, connected to its outgoing feeder is considered. Bere the

operating time of relay.8o 3 is considered for calculation of ()S of relay.8o 0 is

considered.

(opSLG0 9 .35 D .& 9 1.5 sec

Single line to ground fault current at relay.8o 0,SLGf0 9 0!# A

:lug setting 9 1F of 7( ratio 9 # A

Bence ()S of relay.8o 0 is 9 1.5; * .1! 9 .14!

Appro/imating the ()S as per steps provided in ?@ %#1,we get ()S9.#

As per the new ()S, the operating time of relay.8o.0,

(opSLG0 9.#;.1! * 9 1.140 sec,

Relay.No.:

?elay.8o.% can2t be co-ordinated with real.8o.0 as relay.8o % is on delta side.

ut however it should operate for any close in fault.

Single line to ground fault current at relay.8o.%, SLGf%9 1 A

:lug setting 9 1F of 7( ratio 9.1;#9 # A

Let the operating time for the close in fault be (opSLG%

9 .% sec.

Bence ()S 9 .%;*.1! 9 .1

Appro/imating the ()S as per step value we get new ()S 9 .%

Operating time as per appro/imated ()S 9 .%;.1! * 9 .#1 sec.

!nstantaneous settin# :

Relay.No.104:$%eeder

SLG 'ault current viewed by relay.8o.1!, slgf1! 9 #44&&.& A nstantaneous earth setting, oEE 9 &F of 7( ratio 9 &;! 91# A

nstantaneous earth time setting, (oEE 9.% sec

nstantaneous 'actor to be entered in database 9& +load end and delta side of

transformer directly instantaneous factor is entered in )i-power database


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Relay.No.100:$'ransfor(er ri(ary

SLG 'ault current viewed by relay.8o.1!, slgf1 9 !00.0 A

nstantaneous earth setting, oEE 9 %F of 7( ratio 9 %;# 91 A

nstantaneous earth time setting, (oEE 9.% sec nstantaneous 'actor to be entered in database 9 % +load end and delta side of

transformer directly instantaneous factor is entered in )i-power database

Relay.No.6:$%eeder

SLG 'ault current viewed by relay.8o.1!, slgf0 9 0!# A

nstantaneous earth setting, oEE 9 1%F of 7( ratio 9 .1%;# 9& A

nstantaneous phase time setting for relay.8o.0 is done ta"ing the higher instantaneous time setting of relay connected to out going feeders and then adding a time delay of

.# seconds tom it.

nstantaneous earth time setting, (oEE 9 nstantaneous earth time setting of relay.8o.3

D .# sec 9.!% D .# 9 .0% sec

nstantaneous 'actor to be entered in database 9 &*0!# 9 .!03

Relay.No.:$'ransfor(er )ri(ary

SLG 'ault current viewed by relay.8o.1!, slgf% 9 1 A

As per the range of instantaneous earth setting provided by ?@) %!& + .1 = 1#

/ n , relay.8o.% is not sufficient to provide instantaneous earth protection. (he

lowest instantaneous current that can be set is .1;# 9 # A, but the fault

current is 1 A, hence relay is unable to operate instantaneously as relay would

only be able to sense current above # A.


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%i#ure 1.. Earth relay co-ordination curves


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%i#ure 1.4. Earth relay co-ordination curves

Documents

153691706 Relay Coordination Guidelines