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  1. chadwiseman

    Parallellin CT's

    This is for protection. Unfortunately we have a 500 kVA xfmr that is being protected on 46 kV bus. The full load is only 6 A, so we need a low CT ratio to be able to provide overload protection for the transformer. What do you mean by "is the secondary current under a fault going to be a...
  2. chadwiseman

    Parallellin CT's

    I have an application where I need to use a breaker that has four sets of 300/5 CT's in its bushings. I need a much lower CT ratio (around 75/5 would be ok). Is there any reason why we cannot connect the CT's in parallel to acheive an effective ratio of 75/5? Is this something that anyone has...
  3. chadwiseman

    Substation Metering

    Assume there are some single phase loads from the 3 phase substation. I seem to recall that two (2) CT's can be used, however I cannot find a reference to suppport this. Also, I cannot get any inidication on how many PT's are required. Any ideas?
  4. chadwiseman

    Proportional/Amplifier Valve Problem

    Hi, I have a proportional valve driven by a 4-20mA signal. This directly ports oil to an amplifier stage (another valve mounted directly to the proportional valve). The amplifier spool moves very slow (can take up to 30 seconds to move from one position to the null position). The...
  5. chadwiseman

    Power System Stability

    I am referring to power stability (i.e. how much power we can push through the transmission lines). Also, does the use of synchrous condesnsers increase the capability of the system relative to the same system without them (i.e. can we operate the power system at a greater power angle and still...
  6. chadwiseman

    Power System Stability

    I am looking for information on power system stability. In particular, we use synchronous condensers and many synchronous motors, and I'm wondering how this affects the stability of our power system (increases it or decreases it). Any informatin would be appreciated. Thanks.
  7. chadwiseman

    Resistance Grounded

    How would one select the appropriate size resistor for a LV system. We are trying to select between 100 and 200 ohm to limit the ground fault. Is there any guidance out there for this?
  8. chadwiseman

    Reactive Power Compensation

    I believe if you research the subject you'll find that the 3rd harmonic is cancelled out. It works out in the math due to the firing of the thyristors. I'm not 100% positive of this, but I think that's why. If you're not into the math, then don't worry about it.
  9. chadwiseman

    Power Factor.

    If you are designing for installed load, then maybe you'd want to design the transformers and equipment to that spec as well. Which would mean overdesign, and extra cost. Design for running load as mentioned, however, as said, the higher the pf the better.
  10. chadwiseman

    Tripped Substation

    A fault on either side (primary or secondary) would be a concern. The voltage is 46/4160 and is grounded through 96 ohm resistor.
  11. chadwiseman

    Tripped Substation

    Hi, I'm trying to put together a safe work procedure for a tripped mobile substation (delta-wye) that is resistance grounded. When we have a ground fault, is there a safe way to approach the substation? While most codes say we should limit our GPR to 5000V, we have the possibility of reaching...
  12. chadwiseman

    Grounding 4160 Switch Gear

    We have multiple 46/4160 transformers in our substation that feed switchgear inside our facility. The power cables are teck, and run in multiple cable trays. In a recent inspection we noticed that there was no bare ground to each switchgear (they are old installations). Should we have...
  13. chadwiseman

    Trailing Cable

    We use a trailing cable to feed mobile mine equipment at 4160 V. I am trying to find any direction from the IEEE, NEC, or NFPA about how to handle this energized cable. The cable is appropriately insulated to be laid on the ground to feed the equipment, however there are concerns about...
  14. chadwiseman

    Over head line

    Is anyone aware of the Canadian Electrial Requirement for protecting 2/0 ACSR. I was under the impression that we had to protect it to its ampacity (255A). However, as we are in a northern climate we use a multiplying factor to increase this slightly. However, from what others are saying...
  15. chadwiseman

    False ph-ph Fault

    We have a large (3500 hp) motor, that sometimes trips on start up on a false ph-ph fault. It often starts on the second attempt. Any ideas on what the problem could be? We have changed the relay, and the CT's have been checked.
  16. chadwiseman

    Over head line

    This is an industrial setting. Fuses would be cheap, but some people are afraid of losing a phase and damaging machines, so they want reclosers (which are expensive). Has anyone had experience with overhead fuses supplying large motor loads like this?
  17. chadwiseman

    Over head line

    The problem is that the 2/0 has multiple small taps along its length. However, I am referring to the NEC.
  18. chadwiseman

    Over head line

    I have a section of 4160 overhead line that is 336ACSR and then drops down to 2/0 ACSR. According to the code I'm suppose to set my upstream breaker to protect the 2/0 ACSR. However this will cause nuisance trips as the heavier 336 ACSR has heavy loads. I've been told that the other option is...
  19. chadwiseman

    Motor Ground Setting

    My CT ratio is 50:5. Core type setup. The GF setting is 20A, no time delay (50G). Thanks.
  20. chadwiseman

    Motor Ground Setting

    Thanks for the advise. However, if I have a 500 hp 4160V motor, that would mean I wouldn't set the pickup above about 5 amps, and possibly less than one amp. We are struggling with a pickup of 10A. Any comments are appreciated.

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