Vinodh Pancha
Vinodh Pancha
Branch Unspecified
03 Feb 2012

Bus PT Feeder

Why there is no Circuit breaker in Bus PT feeder?? In our system, interlock is given such that if any fault in Bus PT, then it opens the Incoming Bus breaker...Why it is done???
Its 11kV busbar. Any economical problem in havng breaker for PT or its not necessary to have??? Kindly clarify.
neo23

neo23

Branch Unspecified
7 years ago
Can you upload a sld of your system....that would help a lot.
Vinodh Pancha

Vinodh Pancha

Branch Unspecified
7 years ago
Sorry if I have asked you in wrong manner. ie. I referred to 11kV Switchgear panels of Unit, Station Transformer.Kindly find below the snapshot of the part of feeder.Hope it is enough for you to rectify my doubt.
neo23

neo23

Branch Unspecified
7 years ago
it is very difficult to read . can you just simply explain clearly what you really want to know? are you referring to the coupler circuit breaker used in bus bar or what. please explain everything
Vinodh Pancha

Vinodh Pancha

Branch Unspecified
7 years ago
neo23
it is very difficult to read . can you just simply explain clearly what you really want to know? are you referring to the coupler circuit breaker used in bus bar or what. please explain everything
Simple!!!
In the fig, u can see two feeders...one is ID fan feeder and other is Bus PT feeder.U can see VD4 1250A- Breakerfor ID fan feeder whereas same is absent in Bus pt FEEDER.Y is it so??? Y no breaker is installed for Bus Pt feeder for its protection???This is ma doubt.
Can u get me ???
neo23

neo23

Branch Unspecified
7 years ago
Yeah i got you.
Now see clearly there is a PT with two cores on the Bus bar side.
One core is used for metering .
And the second core i think is used for protection . Read the digits in the box and do tell me ( i am unable to read them) . As far as i know these must be the protection scheme codes , resulting in the feeding of certain relays. and definitely these relays must be driving some breaker circuit or an alarm circuit.
Please confirm and revert. after that we shall continue our discussion
aarthivg

aarthivg

Branch Unspecified
7 years ago
the potential transformer from feeder should not have any circuit breaker, because pt is just a measuring equipment. just consider if there is a circuit breaker before pt, we can interrupt the supply and change the pt itself, or make the meter reading standstill, there is lot of such chances to misuse the supply. so there should not be any circuit breaker.

with respect to protection of pt, fuse will be provided. ground fault protection will be provided.
neo23

neo23

Branch Unspecified
7 years ago
What about the Bus Ground Protection? What breaker shall trip?
aarthivg

aarthivg

Branch Unspecified
7 years ago
from feeder, the supply will be given to bus that ht bus which has 3 runs. from ht bus only supply will be given to pt. there will be separate protection to bus
neo23

neo23

Branch Unspecified
7 years ago
Plus , this is an 11 kv busbar. What misuse of power can you do on an 11 kv busbar?
aarthivg

aarthivg

Branch Unspecified
7 years ago
PT is just a meter to measure voltage. if circuit breaker is there, we can isolate the pt. and we can even stop the rotation of meter reading. but the supply can be feed from the feeder
aarthivg

aarthivg

Branch Unspecified
7 years ago
circuit breaker helps to isolate the equipment
neo23

neo23

Branch Unspecified
7 years ago
aarthivg
pt is just a meter to measure voltage. if circuit breaker is there, we can isolate the pt. and we can even stop the rotation of meter reading. but the supply can be feed from the feeder
suppose a fault comes and the pt trips the breaker on other run of the bus bar as you are saying. In that case also the meter rotation stops , and it also stops if it is on the same run.
aarthivg

aarthivg

Branch Unspecified
7 years ago
how can a pt trip a cb? whats that other run which u have specified?
can u be clear please.
neo23

neo23

Branch Unspecified
7 years ago
I am sorry to be unclear, but i meant the fault is sensed by a relay which furthur trips the breaker. And the other run thing i said because i thought you were reffering to
from feeder, the supply will be given to bus that ht bus which has 3 runs. from ht bus only supply will be given to pt. there will be separate protection to bus
aarthivg

aarthivg

Branch Unspecified
7 years ago
neo23
I am sorry to be unclear, but i meant the fault is sensed by a relay which furthur trips the breaker. And the other run thing i said because i thought you were reffering to
runs are nothing bur R,Y,B. three runs. since you have mentioned it has a 11 kv feeder, most probably it will be in distribution side. so from the feeder, the supply is given to ht line which has three runs
Vinodh Pancha

Vinodh Pancha

Branch Unspecified
7 years ago
neo23
Yeah i got you.
Now see clearly there is a PT with two cores on the Bus bar side.
One core is used for metering .
And the second core i think is used for protection . Read the digits in the box and do tell me ( i am unable to read them) . As far as i know these must be the protection scheme codes , resulting in the feeding of certain relays. and definitely these relays must be driving some breaker circuit or an alarm circuit.
Please confirm and revert. after that we shall continue our discussion
Hi Neo,
as u said,
1st core for metering and 2nd core for protection.
Inside the box, its
ABB make REU610-VOLTAGE PROTECTION RELAY with 27(Undervoltage),27N(No volt),2(timer).

I found that as @aarthivg stated, CB is not provided for PT as its just a measuring device and just a MCB is provided to isolate the fault from transformer. Some said Since the output of pt is just 110V for measurement purposes, it doesnt have any effect.
But I think its not the right reason....
Also, as aarthivg stated, there is no chance of misuse in power????what you exactly mean to say
neo23

neo23

Branch Unspecified
7 years ago
Now can you tell me which circuit the voltage protection relay makes or breaks , by reading the drawing?
aarthivg

aarthivg

Branch Unspecified
7 years ago
Vinodh Pancha
Hi Neo,
as u said,
1st core for metering and 2nd core for protection.
Inside the box, its
ABB make REU610-VOLTAGE PROTECTION RELAY with 27(Undervoltage),27N(No volt),2(timer).

I found that as @aarthivg stated, CB is not provided for PT as its just a measuring device and just a MCB is provided to isolate the fault from transformer. Some said Since the output of pt is just 110V for measurement purposes, it doesnt have any effect.
But I think its not the right reason....
Also, as aarthivg stated, there is no chance of misuse in power????what you exactly mean to say
I am sorry, if it is wrong. but this explanation was given by my hod, who had more than 30 years of experience in transmission field. anyway i will get you a clear explanation soon.
Vinodh Pancha

Vinodh Pancha

Branch Unspecified
7 years ago
  1. neo23
    Now can you tell me which circuit the voltage protection relay makes or breaks , by reading the drawing?
neo23
Hi neo, as per the drawing,
As the relay gets activated on undervolt or no volt, it opens the MCB which protects the secondary of transformer where the voltage will be 110V. thereby transformer is protected from any fault.
Hope am right.
Hereby I have attached clear view of feeder again. Sorry for my previous unclear attachment.

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