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  1. gordonl

    Generator diagnostic-Partial discharge

    Do you also monitor and compare based on loading of the machines? I'm looking at putting a system in shortly and was thinking that machine loading would be important, but perhaps temp (stator I assume) would naturally compensate for this.
  2. gordonl

    HV cable

    I don't think you'll find any "mini" 50KV cable. Even though your talking small power you need substantial insulation thickness for the voltage stress.
  3. gordonl

    Disconnect on VFD output

    One method I've used is puttinng a drive E-stop button next to the disconnect with a label on the disconnect to push switch first. The E-Stop then did a drive shutdown before opening the disconnect.
  4. gordonl

    Unusual Ground Fault Trip

    Depending on the size and bonding of the system your L-G-L fault could have a signifigant impedance in the ground path to limit the fault current. Could the 4160V system have been affected by the path of fault current? If the 4160V is within the system (between the two faults) you could get...
  5. gordonl

    Unusual Ground Fault Trip

    I would think tour "ground" arcing evidence was caused by a L-L fault through earth as rraghunath suggested. The 50/51N could them have tripped on false relaying with the relatively heavy fault current. What also sometimes occurs is that the phasing of the CT's is wrong, a CT is shorted, or...
  6. gordonl

    Sensitive earth fault protection - medium voltage

    I haven't tried to protect a high impedance grounded system but it could have challenges. Ie: discriminating between charging current during faults and ground fault current, at MV this could become a factor depending on the size of the system. Selectivity could also be a challenge.
  7. gordonl

    Disconnect on VFD output

    Motors need to be disconnected for worker safety whether the supply is variable or fixed frequency.
  8. gordonl

    EAF transients

    Could it perhaps be a resonance condition at 17Khz being excited by the arc from the airblast breaker? (I don't think restrike is commom with air-breakers, vacuum mainly)
  9. gordonl

    How to Ground a Barbed Wire on Top of a Fence According to IEEE Standa

    Generally every few posts there is a tap off of the ground grid that runs up the fabric to the the barbed wire. It is connected to the mesh,posts, and barbed wire with mechanical connectors.
  10. gordonl

    Power engineering Commissioning Book

    Try these links to NETA standards. Although not in reference directly to power plants, they cover a lot of the equipement contained there in. http://www.netaworld.org/Category.cfm?CategoryID=25 http://www.netaworld.org/Category.cfm?CategoryID=26 Regards, Gord
  11. gordonl

    Integral Earthing

    This a real shot in the dark but: Special breakers are often available which rack into empty cells to ground the load side stabs for maintenance purposes. This "integral ground" breaker may have this function built in such that load side stabs are automatically grounded after the breaker is open.
  12. gordonl

    Power of a sewage pump instalation

    Transformers have very long thermal time constants, so the thermal affects of motor starting aren't a consideration. (If the motors are VFD controled than there is no large starting current) 10MVA of transformers is definetly enough for 5.25MVA of motors. If your aim is redundancy you may...
  13. gordonl

    any comment on this excitation spec

    I would suggest you get a hold of IEEE Std. 421.4 "IEEE Guide for the Preparation of Excitation System Specifications" For a generating station this large I would expect some sort of regulating authority would have requirements for reliability (redundancy), stability, response time, etc. I...
  14. gordonl

    High volatge cable selection

    In Canada (and the US I beleive) there are three grades of cable used with low resistance grounded systems as we call them. 100% insulation - ground faults clear within 1 minute 133% insulation - ground faults clear within 60 minutes 173% insulation - ground faults can persist indefinitely An...
  15. gordonl

    medium voltage cable insulation rating?

    In Canada (and the US I beleive) there are three grades of cable used with low resistance grounded systems as we call them. 100% insulation - ground faults clear within 1 minute 133% insulation - ground faults clear within 60 minutes 173% insulation - ground faults can persist indefinitely
  16. gordonl

    Stress on coil insulation volts per mil

    This is usually the voltage stress on the ground wall insulation, the insulation between the coil and the core iron. The voltage stress between coil turns is lower than that between the coil and ground. A typical value for this insulation is 55V/mil, so a machine designed to operate at 13.8KV...
  17. gordonl

    3 Phase Feeder Capacitive Charging Current

    I would say 1.73A if each phase normally has a 1A charging current. I don't follow the Ia+Ib+Ic=1 during normal operation, I would think Ia+Ib+Ic=0 because it is a balanced three phase capacitive load. Then when you get a fault your charging current on the high phases increases to 1.73 times...
  18. gordonl

    AARRGHH!!!

    I hate to sound rude but, are my posts even up on the board. The very rule the inspector is quoting contradicts him. If you plainly layout for the inspector your system with transformer ratings, cable ratings, and protection settings and how it meets the code under rules 26-258.3 and 14-100.d...
  19. gordonl

    Panel Board installation

    CE 26-402.2 states that the panel board must be "installed as high as possible", but no higher than 1.7m to the highest handle. They want them around eye level when possible. As an aside here in Canada, for "barrier-free design" CE suggests consulting building codes for mounting heights.
  20. gordonl

    AARRGHH!!!

    I think the wording of 26-258.3 is equally clear that where the proper protection is in place less than 125% is "legal". The 125% requirement is in response to 26-256 where 125% overcurrent protection is permitted, but as 26-258.3 states when less than 125% protection is used corresponding...

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