GE489 for generator-transformer (block) diff prot 1

[validtech]

Hi there..

GE's 489 protection relay is supposed to be solely used for generator protection, and is therefore fitted with enough (7) current and (3) voltage sensing inputs to acheive this. I previously assumed that a so-called block (Gen-Transfo) differential protection scheme could be acheived as well with this same relay, possibly by using interposing CTs on the phases output to correct the angle shift due to the Dyn11 transformer (this is even handled by software on certain relays such as ABB's REG216). Now, I doubt...

I just realized that in the 489, there is only one setting provided for the phase primary current, so that all of the 6 CTs are supposed to have same ratio (well, it makes actually sense that CTs are supposed to be identical as far as possible, but here...).

Does anybody here have experience on having a SR489 used for generator-transformer block differential scheme? Please let us know !

 

[slavag]

Hi Validtech.
87G and 87T isn't same, yes it's diffirential protection,
but few very important points.
87T have:
1. 2-nd harmonic blocks
2. Vector group setting
3. HV/MV CT ratio setting.
Gen diff protection haven't it.
489 is generator protection only.
Best Regards.
Slava

 

[validtech]

Yes Slava, you're right, thanks for this.
I missed the 2-nd harmonics problem...

So I guess ther's no way through...

Phil.

 

[alehman]

If you are purchasing a relay, there are others that can provide the block protection function. SEL300G comes to mind.

 

[validtech]

Thanks Alehman,

489 is already there. I might purchase a second one for 87T and add some CTs at transformers on generator side. SEL300G looks good although it lacks ethernet capability, but is
overkilled for such small transformers (1MVA) we are using... perhaps SEG's XD1-T would be good enough.

 

[slavag]

Sorry Validtech.
If you go to SEG/Woodward please pay attention on this one:
ESDR4/4T

Seems as good relay and it's digital.
Good Luck.
Slava