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  1. jwatty

    Arcing Horn Design inquiry?

    prc, I believe what you're talking about could be called a spark gap as well; My read of the question is arcing horns associated with switches. Most utilities I see now adays order switches with arcing horns as a default accessory. These are typically rated to interrupt around 2A of primary...
  2. jwatty

    Is it possible for un-proper sync cause differential trip on Generator

    I've seen an SA-1 generator relay misop due to a wide sync angle on a local breaker (not the generator breaker). When that breaker closed, the local angle jerked significantly enough to cause a largish inrush into the generator. There was a recommendation from ABB to add a desensitizing resistor...
  3. jwatty

    Carrier Pilot Protection.

    I may be wrong here, but I assumed the issue with adjusting spark gaps was this may require a line outage - since the spark gap is a protective device, does cleaning and adjusting require removing the line to allow you to adjust and clean it safely? It's going to spark over as a result of...
  4. jwatty

    Three Trip Solenoids

    Point on wave tripping means you'll have separate trip commands for each phase; You certainly can have this set of coils operated by protection and point-on-wave control, but you either have to use a bunch of diodes or you'll need to have protection have three separate trip outputs (one per phase).
  5. jwatty

    Neutral Not Included in Transformer Differential Relay

    that's true for something like a 3-phase external fault (the .58pu on one side is cancelled when comparing to the 1pu on the other side). But 3I0 into a transformer on one side != 3I0 leaving the other side if it's solidly grounded on at least one winding (usually). For an out-of-zone ground...
  6. jwatty

    Neutral Not Included in Transformer Differential Relay

    Magnitudes are going to depend on system and transformer impedances. I attached a figure showing just zero sequence currents for a fictitious wye/wye/delta transformer, so hopefully this helps. If you had CTs on the 1.7pu side, each CT secondary would see 1.7pu @ 0 degrees. If connected in...
  7. jwatty

    Neutral Not Included in Transformer Differential Relay

    With Regard to distinguishing between internal and external faults, the relay is still calculating a vector sum current into the zone and typically a magnitude sum (for percentage restraint type relays). Operate quantity is the vector sum and restraint is the magnitude, sometimes divided by 2 or...
  8. jwatty

    Loadability of a Distance POTT Protection Scheme - NERC PRC-023-4 Guidelines unclear

    PRC-23 is inherently focused on not always stable conditions - you're looking at heavy overloads (150%) and depressed voltages (85%), so inherently some buses will have higher voltages than others and you're likely to see some power swing behaviors. As power flows transition from one flow...
  9. jwatty

    Loadability of a Distance POTT Protection Scheme - NERC PRC-023-4 Guidelines unclear

    Figure B-1 is simply superimposing the remote relay reach looking back towards the local relay, with Zl being the line impedance. Most of the time your pilot zone 2 is also going to be used for nonpiloted step distance (operating in something around 15-30 cycles), so more in-depth calculations...
  10. jwatty

    Relays in Coordination Study

    Not usually. Sync check doesn't involve fault clearing, and reverse power tends to be either a control function or a last to operate type thing.
  11. jwatty

    Relays in Coordination Study

    I wouldn't necessarily plot differential relaying but it's good to be cognizant of the zone so you check appropriate contingencies. A differential around a transformer may change N-1 coordination with a highside overcurrent from one line out to system intact, for example. Same with pilot schemes...
  12. jwatty

    Line Protection: Ground Instantaneous Element Setting Policy Based on Remote End Open.

    protoslash - replying to your first comment. That is precisely what the intent is. The "remote end" will be wherever there is another protective device that is expected to operate past that point, so you do not want the local instantaneous overcurrent to operate when the remote end device...
  13. jwatty

    Line Protection: Ground Instantaneous Element Setting Policy Based on Remote End Open.

    This eliminates the need for a more elaborate rule. I've seen other utilities use 125% x maximum ground current under worst case N-1; if you're following this rule you need to be cognizant of auto-reclose conditions as well. This often will look like an N-2 condition but if you have relatively...
  14. jwatty

    Generator pole slip

    Pole slip is due to electrical energy (Pe) out of the generator not matching mechanical power (Pm) in. This can happen for a variety of reasons, but the most obvious is a sag in the system voltage. If the generator's terminal voltage sags, Pe < Pm, so the generator will speed up. This means the...
  15. jwatty

    Why Transformer zero sequence impedance differ from (+)&amp;(-) sequence impedance

    The transformer impedance is dictated by leakage flux, so if the flux paths are identical for positive and zero sequence currents, you will end up with the same leakage impedance. This is clearly not true in 3 limb core form transformers. Under a zero sequence impedance test, you will short one...
  16. jwatty

    Power Swing

    Yes, depending on the system. I assume you're specifically referring to the relays looking into the hydro from the remote end - this would be similar to a distance relay at the generation site, looking into the GSU (with a little extra impedance). I've seen similar sized units used for black...
  17. jwatty

    Faster clearing Time 69 kV Substation Grounding

    It may be worth asking for fault currents and worst case operate times at the point instantaneous protection no longer works (ie, the edge of zone 1/zone 2 step distance, and the edge of 50/51 relaying). 17 cycles may well be sufficient for close in faults where instantaneous relaying may...
  18. jwatty

    Relay setting for Radial 115kv tranamission line

    Mho is likely easier to coordinate with relays looking into your substation, too. This is why a lot of generators will choose to use mho elements over voltage controlled/restrained overcurrents.
  19. jwatty

    Line differential relays - phase shift

    David's right. Upload some records if you have them. You'll get 60 degrees if you have both phasing and polarity backwards. 30 degrees is going to require a delta connection somewhere.
  20. jwatty

    Capacitor Bank Tripping, Suggestions Needed

    That sounds like a nightmare to test. If the trouble phase is in the shade, you could get some oddities as things warm up. Looking at the records, the trip settings make it look like the tap point is between groups 8 and 9 (87TP1P and 87TP2P are identical). If this is true, the CCPD's are being...

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