MWTU Reverse Power Relay - Setting Advice

[cflatters]

Gents

I need to check some existing protection settings on an MWTU01 (5A relay) reverse power protection relay, I do not have the corresponding Alstom document and would appreciate some assistance.

The relay is used to prevent excess power export to the DNO (ie to ensure that the power export limit is not exceeded).

Plimit = 2.64MW @ 11kV
CT = 800/5
VT = 11,000/11O

I = 2.64E6 / (1.732 * 11,000) * 5 / 800 = 0.866A

Therefore 0.866A / 5A * 100 17.3% (ie Pn% = 17.3)

I am informed that the esisting relay setting is 30% (the sheet indicates Pn = 317.5 W which I can make little sense of - see below). If I am correct is equivalent to a reverse power setting of;

5A * 30% * 800/5 * 1.732 * 11,000 = 4.57MW

This is in excess of the clients export limit / agreement.

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Thanks

 

[RalphChristie]

Your calculations seem to be correct.

See

http://www.areva-td.com/static/largefiles/R8122C MWTU14.pdf

and

http://www.areva-td.com/static/largefiles/R6127C.pdf

 

[cflatters]

Cheers Ralph

Doh, just sussed my error / oversight;

I am happy that I am correct now that I have seen the connection with the 317.5W (I had taken the value of the clients protection drawing as being the relay setting, whereas it is actually the relay rating - which becomes obvious when looking at the schematic for the MWTU 01).

The 317.5W does then make sense since it is a phase quantity, therefore;

3*317.5W * 800 / 5 * 11,000/110 = 15.24 MVA (ie = 800A)

& Pn% = 2.64 / 15.24 * 100 = 17.3% (ie same as previously calculated).