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Hi All, There has been an increase in the need for Special Protection schemes as a result of the ever-changing power system. Would anyone be able to share any guidelines on how to scope, design, commission and maintain these schemes. I would appreciate any direction you can provide. Thanks

sushilksk; but i doubt any SOTF scheme put into place would beat line differential in the first place, as SOTF schemes have 1-2 cycle pickup delay. thermionic1: yeah only if the line is energised with faulty comms and there is a dead short circuit at the yard yielding no polarising voltage for...

Hello All, Just want to get your view on implementation of SOTF scheme on line diff relays? I tend to think that being a current based protection no special SOTF(overcurrent threshold based, etc.) needs to be implemented on a line diff. relay. Appreciate your views/experience on this?

VT may not be the solution as it is difficult to descriminate the fault relying on a bus VT. NPS is a good way to detect low LL fault. What about low LLL fault? Using a recloser is an excellent option; however, multiple reclosers are needed to provide remote backup during hardware failure.

Thanks David. Your view is consistent with my thinking.

Hi Davidbeach. Even though reclosers are installed there wont be any overreaching protection or upstream backup unless you install few reclosers. Also what are your views on not clearing or catering for end of line LL fault?

Hi, What is your experience with clearing LL faults at the end of rural distribution feeder with low fault current. The problem is with fault level so low, there is no discrimination against load current. Also, what are the concerns with such a low LL fault going undetected? If this fault...

Hi RRaghunath, how does the metering CT behave during an active fault and when breaker fails? The CT will go into deep saturation and not yield the 10 or 20% I required for check current. Also remember CBF delay time may complicate things further. PS: the breaker will continue to feed the active...

Thanks All, Just a question, using BCU for current checked CBF can lead to a problem, as BCUs are generally feed from measuring CTs which may saturate during the fault condition and not yield replica current required for Current check? what are your thoughts on this?

For transmission lines what are the benefits of having AR functionality reside in Bay Control Unit? I am used to relays(X & Y) doing the AR; however, of late seen some schemes where BCU does this based on the AR initiate/block signal from relay.

25MVA YNyn0d1, source side ungrounded transformer tripped on Instantaneous EF during energisation. The waveform signature revelled inrush, but the question is how did neutral current appear on the supply side when the star point is floating? Appreciate any thoughts

Hi Davidbeach, Will the ground fault contribution from the generator increase because of additional grounding path and what will be the impact of circulating current and chances of mis/no operation of protection device?

What will be the impact of having multiple grounding source connected to Substation bus during normal/fault condition. the situation is: a. 6.6kV generator connected to the bus with its neutral grounded and b. 6.6kV LV side of 3 winding transformer connected to the same bus. The LV neutral...

What is the best location for Earthing CT neutral? Protection panel or close to the CT itself? Thanks

Hi All, Can someone shed some light on TF diff stability test shorting the HV and LV winding to bypass TF impedance. How is the injected current controlled as I believe there will be theoretically 0 Z. The reason to go in this path is because of not having enough current with the standard...

Hi There, I've a query regarding use of tertiary winding for station service. We have an application where tertiary winding needs to be used for station service. Basically tertiary will feed into a station service transformer. My question is do we need to ground the corner of tertiary delta or...

Thanks for the reply. Do you have any paper or reference on this? Cheers

I'm analysing the following condition and wanted to know your views. For a radial line feeding into a transformer(Ynd-275/11kV) what will happen to the TF diff relays during the single pole reclose dead time for the line. Say for a C phase- Gnd fault, during dead time, TF HV will have A phase...

It is well known fact that transient performance of CVT is inferior to inductive VTs, however, for higher voltages, because of cost benefit, CVTs are used. My question is for distance protection application does using CVTs impact on the performance of the protection system?

Hi All, I have a query regarding Current Limiting reactor. In a 66/11kV substation with two transformers, is there any preference over voltage level the reactor should be placed? what are the factors that govern the placement of reactor? also can the reactor be installed in series with...