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  1. drchaos

    Fast Windfarm Active and Reactive Power Response on Distribution Systems

    Thanks for that, DPC. If we had an embedded conventional generator that was not on the faulted feeder, are you saying that any sort of response that might confuse the protection is undesirable? This is confusing I know because of all the many different distribution topologies that can occur...
  2. drchaos

    Fast Windfarm Active and Reactive Power Response on Distribution Systems

    Hi All, I have a query about windfarm dynamic active and reactive response on a distribution network: Is there any reason why a distribution system operator would not want a windfarm to a) Recover its active power quickly following a voltage dip e.g. within about 0.5 - 1 second? b) Provide...
  3. drchaos

    Positive Metered Powerflow from Open Breaker?

    There are various people investigating at the moment. If the trafo was on no-load, would its no load power consumption be varying? I've attached an SLD of the relevant bit - the CB at the bottom is open. The chap who does the metering insists that something fishy is going on! Will let you know...
  4. drchaos

    Positive Metered Powerflow from Open Breaker?

    Hi, We have a windfarm that has recently energized. It currently has its breaker open, so the grid trafo 110/20kV is energized from the HV side only. Both metering and SCADA are showing a few kW flowing from the trafo into the grid. It isn't constant, but doesn't look random or noisy either...
  5. drchaos

    Synchronization and Breaker Angles

    Thanks for the paper eddiet1, and to the rest of you for responding with your experiences and wisdom! It's not an area that is covered well in any text books so far as I can see [ though the book "Power System Dynamics" by Machowski, Bialek and Bumby does have some of the maths / physics behind...
  6. drchaos

    Synchronization and Breaker Angles

    Thanks Slava, That's very useful information. We are looking at the impact of different angle settings on generators - how much does their power output wobble when breakers are closed. In particular, management are looking at the synchro-check settings when energizing blackstart paths, and...
  7. drchaos

    Synchronization and Breaker Angles

    Thanks Slava. I read some IEEE survey from 1984 on auto-recloser settings, and a lot of the utilities surveyed would allow angles of 45 degrees or higher, especially at say 400kV or higher. Do you know is it less onerous on the system to allow larger angle differences at higher nominal voltages?
  8. drchaos

    Synchronization and Breaker Angles

    I have been reading some of the old threads about synchronizing generators, and the necessity to have the angle as small as possible (<20 degrees at least). Do any similar standards apply to closing breakers on the rest of the transmission system, not necessarily near generators? Kundur has a...
  9. drchaos

    3-winding Trafo Zero-Sequence Data

    Thanks opmgr1 - what you say is what we started out thinking, and that's what's in all the textbooks. However, in the test data, there is no mention of the tertiary, and I found a presentation on 3W Trafo testing from Siemens on the net, where the tertiary is essentially left untouched for these...
  10. drchaos

    3-winding Trafo Zero-Sequence Data

    Actually I'd like to clarify the above questions: When you solve for the zero-sequence equivalent impedances Zp, Zs, Zt, we have four measurements, and so get four equations in 3 unknowns, and so get non-unique solutions. Does anyone know why this is, or how to resolve this paradox? Which...
  11. drchaos

    3-winding Trafo Zero-Sequence Data

    Hi, I'm trying to determine zero-sequence data for a 3winding trafo 220kV/110kV/10kV Ynynd5 250MVA ABB transformer to put into PSSE. In the transformer test sheets, under zero-sequence tests, there are 4 sets of numbers (Z, R, X): HV with LV open - HV with LV shorted LV with HV shorted LV...
  12. drchaos

    Critical Fault Clearance Time - Stability Criteria

    In my case, there is a PSSE option to scan for out-of-step conditions. But I also look at rotor deviation. I didn't realise that terminal voltage was something to look at - are you saying that if the terminal voltage does not recover post-fault to pre-fault levels, then this is a bad sign...
  13. drchaos

    Critical Fault Clearance Time - Stability Criteria

    Hi QBPlanner, Our protection system also operate within the time-frame you mentioned: 6 - 10 cycles. These studies are intended to show whether certain machines are more at risk of becoming unstable in the event of a protection failure etc. In my studies, I use relative angles, relative to a...
  14. drchaos

    Critical Fault Clearance Time - Stability Criteria

    Hi, I am looking at critical clearance times (CCTs) at a variety of different 220kV and 110kV buses for 3-phase and single-phase faults, using PSS/E. I've been looking at the different stability criteria people use. For instance, a previous study of this sort deemed that instability occurred...
  15. drchaos

    Electromechanical relay failing to trip

    No news, except that my boss who is a protection expert, has ruled out a high impedance earth fault as the problem. Otherwise, it's time to enjoy the weekend and not be worrying about relays!
  16. drchaos

    Electromechanical relay failing to trip

    Slavag, these are all good questions! Not sure if i have the answers though. I think I would like to put together a simple model with a few lines, short-cct MVA, model of a CT with saturation, and relay burden. THis will take time : )
  17. drchaos

    Electromechanical relay failing to trip

    Bluezee, thanks for your reply. I don't think this relay is clever enough to do the things you said! It's prob 20-30 years old. Slavag, the fault was on 110kV system, which I think is solidly earthed at trafo neutrals. We are blaming CT saturation at the moment. I will try to model the...
  18. drchaos

    Electromechanical relay failing to trip

    The fault was close in to the substation, 2 or 3 kms. I haven't got the disturbance recorder graphics unfortunately - it was looking at another line in the same substation - so those currents are estimates only. Do you think the relay maybe saw something else? Maybe bigger currents? I really...
  19. drchaos

    Electromechanical relay failing to trip

    Guys thanks for all your great work here. If I can answer some of your questions (BTW I haven't been on site - we have guys in the field who do all the tests): The line was being fed from one end only, and the fault was definitely 3 phase, as I've seen the disturbance recorder (not at that...
  20. drchaos

    Electromechanical relay failing to trip

    I've just been told that it was definitely a 3-phase fault initially - they are very common where I am (no earth-shield wires). The CT is a 5P50. On the face of it, there should not have been a problem. The cable running from the CT to the relay is 400m long and is a four-core cable with each...

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