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Associate

Join Date: Dec 2011
Posts: 27

### Knee Point Voltage for Generator Diffnl. ct's

08/28/2012 12:39 AM

can any one give the calculation of knee point voltage calculation of differential ct's for generator differential protection relay, type dad-N siemens, i think it is not same as transformer differential ct's calculation. thanks.

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Active Contributor

Join Date: Jul 2012
Posts: 12
#1

### Re: knee point voltage for generator diffnl. ct's

08/28/2012 1:53 AM

thank you and nice post...

Off Topic (Score 3)
Guru

Join Date: Oct 2009
Posts: 1866
#2

### Re: Knee Point Voltage for Generator Diffnl. ct's

08/29/2012 9:43 AM

Why should it matter? The CT Knee Point Voltage claculation takes into account only the maximum anticipated fault current at the CT location, the CT secondary winding resistance, the two way CT Secondary Lead Resistance & a factor of safety. Where & how does it matter if it is for a Trafo. or for a generator?

Associate

Join Date: Dec 2011
Posts: 27
#3

### Re: Knee Point Voltage for Generator Diffnl. ct's

08/30/2012 12:47 AM

thts fine sir, but only my doubt is for maximum fault primary current is Ift = kVA/ (0.415x1.732x Z) in tranformer, is this the same formulae for generator also for max. primary fault current.

Guru

Join Date: Oct 2009
Posts: 1866
#4

### Re: Knee Point Voltage for Generator Diffnl. ct's

08/30/2012 9:30 AM

Yes! But instead of %Z, you must substitute the sub-transient reactance (%x"d) of the generator. And.... please remember that this formula is true only if the fault is at the terminals of the generator or transformer. If the fault is away from the transformer or generator, then the line/cable impedances shall be used to calculate the fault current.

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Join Date: Dec 2011
Posts: 27
#5

### Re: Knee Point Voltage for Generator Diffnl. ct's

08/30/2012 10:00 AM

ok, thanks a lot sir

Associate

Join Date: Dec 2011
Posts: 27
#6

### Re: Knee Point Voltage for Generator Diffnl. ct's

12/12/2012 11:30 PM

hello sir, i posted a question but still nobody given a proper answer i hope you can help me , it was my question,

hai all,

There is a coding system for switchgears and control panels, like for 11kv panels- +k01, +k02.. and for 132kv panels E01, E02..., 33kv - H01, 02...,11kv control panels it will be WR01, WR02... for lv panels using NN01, 02... etc, some times instead of + symbol = also using. can any one tell what is the base of this coding system, is it related IEC or something, please let me where i can find the meaning of this coding and procedure for each system. let me know what will be the coding for 3.3kv panels.

with thanks