SEL-387, 487, 587 restraint elements

[collies99]

Does anyone have a procedure for testing the restraint differential elements using single phase test source while on the Y-D configuration ?

Relay manual suggest using identical winding cofiguration which in effect defeats the matrix phase adjustments between windings.

Thanks for any suggestion.

 

[Ohmly]

Do a Phase-N injection on the Y side, with a Ph-Ph injection on the D side (do the current distribution to work out the correct phases to use)

The current injected on the Y side is divided by the TAP setting × SQRT(3)

The current on the D side is divided by TAP only.

Note that it operates two phases at the same time, but I don't think this is an issue with numerical relays.

 

[collies99]

I should mentioned that the CT's are all wye connected as is the norm now with numerical relays. All CT's connected in Y for any DY or YD transformers

With a YDAC configuration, high side leads low side by 30, my best guess is injection Ia and Ic on the Y side with m=o where Ic=-Ia, 1pu, single phase input. Ia at O and IC at 180 degree.

If I inject 1.732 pu -Ia into the D side with m=1 it breaks down into 1pu -Ia and Ic. Ia at 180 and Ic at 0. Vector Sum of all inputs and outpus should be zero and I can start from there ?

I have never tried it yet, but if I start to reduce D side input, I should get a trip at some point, with restraint below 2 pu.

I had problems testing DYAC configuration in the past and have "always" resorted to changing to YY to make testing easier but I do not think that was a proper or correct test when the in-service configuration is YDAC.

So I need a plan for next time.

 

[Ohmly]

For a YDAC connection, inject A Phase-N on the Y side, and Aph to Bph on the DAC side.

Aph on the Y side is 0 deg, the A Ph on the DAC side is 180 deg (meaning Bph is also 0 deg)

Inject TAP1×1.732 on the Y side, inject TAP2 on DAC side - it will give you zero differential current, with restrain current = 1pu

I assume you have two sources available ?

If you inject A-C on the Y side, you need a 2-1-1 on the DAC to get no differential current.

 

[collies99]

I did a quick check for the DAC side, compensating with
| 1 -1 0|
CTC(1)= 1/(root 3)| 0 1 -1|
|-1 0 1|

Multiply Ia<180 and Ib<0

result in pu are:
Ia= 2.0<180
Ib= 1.0<0
Ic= 2.0<0

Ic is generated from the Ib component