Transformer tripping the incoming transmission line

[adityalagudu]

Please see the attached one line.

We successfully charged T/F-1,2,3,4,5.

Whenever we try to charge T/F-6 with Tiebreaker CB2 open, it is tripping on the 132KV Transmission line -2. If a tiebreaker is closed, it is tripping both 132 KV transmission lines. All the transformers are new and there are no loads connected to them yet.

So the problem is with T/F-6. Relay settings are as per the design. Some saying the problem is because of the harmonics injected by the T/F-6 to the BUS. But we couldn't able to have a clear idea, why it is tripping both Transmission lines?

Please suggest if you have any insight.

 

[gadfly56]

I'm not a power engineering guy, but does this happen no matter what order you do this in? Or does it have to be done in a particular order?

 

[topgone]

First things first. Can you de-sensitize your relay pickups at 132kV side (a delay or something so they don't react as fast as the protections on the 69kV side)? We have encountered this type of tripping and we attributed the incident to high inrush of one transformer! Good luck!

 

[adityalagudu]

I'm not a power engineering guy, but does this happen no matter what order you do this in? Or does it have to be done in a particular order?

The problem is not with the order. We can do in any way. But while charging this transformer it is effecting the conditioning of whole power system.

 

[adityalagudu]

First things first. Can you de-sensitize your relay pickups at 132kV side (a delay or something so they don't react as fast as the protections on the 69kV side)? We have encountered this type of tripping and we attributed the incident to high inrush of one transformer! Good luck!

We will look into that. But the other three Transformers also have the same rating. The problem is occurring only with this one.

 

[mbrooke]

We will look into that. But the other three Transformers also have the same rating. The problem is occurring only with this one.

Have you verified that the CT wiring and polarities are all correct? Second, what targets come up when the transmission lines trip and what is initiating the trip? Ie, step distance, directional over current, Direct transfer trip, ect.

 

[adityalagudu]

Have you verified that the CT wiring and polarities are all correct? Second, what targets come up when the transmission lines trip and what is initiating the trip? Ie, step distance, directional over current, Direct transfer trip, ect.

CT wiring and polarities are good. T/F-2 Differential is initiating the trip whenever we try to charge the T/F-6. And the disconnect for the 132 KV Transmission line-2 is connected towards the end of the line. I mean no disconnect was there at the high voltage side of the T/F-2. So it was making to trip the whole line.

 

[Sahib]

Any test reports for T/F-6?

 

[adityalagudu]

Any test reports for T/F-6?

I don't have a report for the transformer right now. What data exactly you will be looking? The field testing reports are acceptable.

 

[mbrooke]

CT wiring and polarities are good. T/F-2 Differential is initiating the trip whenever we try to charge the T/F-6. And the disconnect for the 132 KV Transmission line-2 is connected towards the end of the line. I mean no disconnect was there at the high voltage side of the T/F-2. So it was making to trip the whole line.

Can you upload the syncrophaser data from the differential relay of the event?


And nothing to worry about- the setup you have is common about 50% of the time where there is no primary circuit breaker so any transformer or bus trip requires opening of remote breakers.

 

[Sahib]

I don't have a report for the transformer right now. What data exactly you will be looking? The field testing reports are acceptable.

The subject transformer commissioning test reports.

 

[mivey]

How about some relay data like what currents you were seeing, what flags were indicated showing pickups, what settings/scheme you are using etc.

Normally we block 2nd harmonic inrush so I assume that is done but why is #2 differential operating inside #6 zone?

What are the bus lengths and configurations? What are the transformer sizes and are they of similar impedance/design?

Sometimes if the differential is wrong, the higher the load current the more likely the trip so are you sure the CTs and diff relay settings are correct in the 138 kV stations? It is odd that it trips both stations with the tie closed so we go back to what currents were read during inrush.

Assuming the same transformer sizes and design, if you can't energize 6 with 5 offline then something is up at 6 or with the bus. How far is the 2 differential reaching? Is there a backup reaching 6 that causes the trip.

We really need some trip data to know where to focus.

 

[adityalagudu]

Can you upload the synchrophasor data from the differential relay of the event?


And nothing to worry about- the setup you have is common about 50% of the time where there is no primary circuit breaker so any transformer or bus trip requires the opening of remote breakers.

The event record shows the following. I could not able to attach the file.

1. The trip was from 87 restraint elements 1 and 2(87R1 and 87R2).

1. There is no significant change to these currents at the time of the trip.

1. The 87 restraint element 3 stays restrained (87HR3).

1. There are enough harmonics to keep harmonic block 3 active throughout the event (87BL3).

 

[mbrooke]

The event record shows the following. I could not able to attach the file.

1. The trip was from 87 restraint elements 1 and 2(87R1 and 87R2).

1. There is no significant change to these currents at the time of the trip.

1. The 87 restraint element 3 stays restrained (87HR3).

1. There are enough harmonics to keep harmonic block 3 active throughout the event (87BL3).

Wild guess, but a miswired CT can cause restraint values to be registered as operate values by a relay. Not saying thats it, but one real possibility.


Can you take screen pics of the waveforms, save them to the computer and then upload them one by one? If they will not upload on holts, tiny pic of photo bucket and then link them to this site.