Transformer Differential Protection feeding a aluminum smelter

[ballenden]

Hi,

We've had a few trips on our transformer differential relay that feeds an aluminum smelter. The differential relay is microprocessor-based, low impedance type.

Are there anyone who has seen any funnies with this load? What from the load side could affect the protection adversely?

The transformer is a 275/33kV, autotransformer. There are no paralleling of other transformers.

 

[jghrist]

Check CT wiring and connections.

 

[DiscoP]

I agree with jghrist - normally inadvertant differential trips are associated with CT connections.

or with modern relays incorrect settings for things that mimic what used to be done using CT connections)

Are you able to extract oscilography records from the relay, it usually provides some useful data.

 

[slavag]

Agree with Jghrist and DiscoP.
Few things:
1. Please search at the Forum, lot of threads on the issue.
2. Please send us DR file ( better in comtrade file) of fault.
3. Please try triggered DR by manual trigger and will send us too.
4. Please check on-line HMI diff and restraint currents per phase and angels too.
5. What is a setting of 87T diff protection?
Regards.
Slava

 

[slavag]

BTW, if possible, what is a type of relay?
It's more easier help.
Best Regards.
Slava

 

[NCTHAI]

It is said that it is auto transformer.

Check relay manual for specific application details with auto transformer.

 

[prc]

It is a very special application. I had seen differential tripping in such a case for external incoming side flash over.Look on such possibilities on 275 kV side.Can you post the connection diagram ?