Continue to Site

Eng-Tips is the largest engineering community on the Internet

Intelligent Work Forums for Engineering Professionals

  • Congratulations cowski on being selected by the Eng-Tips community for having the most helpful posts in the forums last week. Way to Go!

Search results for query: *

  • Users: PWR
  • Order by date
  1. PWR

    Ruptured 3.3kV fuses

    Medium voltage current limiting power fuses that rupture do so in most cases because they are attempting to open with too LITTLE current rather than too MUCH current. Most such fuses are intended to operate on short circuits only and must be protected below their minimum current operating...
  2. PWR

    4160 phase rotation verification

    They are correct if all three phases go to near zero difference simultaneously. It is best to have two meters to do the test as incorrect rotation will not permit two phases to go to zero difference at the same time. If you can control the speed accurately enough you could move the meter...
  3. PWR

    Is zone selective interlocking necessary on smaller systems?

    Issues to consider in making your decision: ZSI allows you to have instantaneous tripping of the main breaker without, in theory, the risk of tripping it when a feeder breaker could have cleared the fault. What if you skip the ZSI feature and just set the instantaneous on the main to trip at...
  4. PWR

    Is zone selective interlocking necessary on smaller systems?

    I would long and hard at spending the 50K. First of all, presumably you are talking with ZSI you will have Category 0 on your switchgear bus? I find it hard to believe that selecting a main breaker with a short time setting of 0.1 sec is going to take you from zero to category 2. As in an...
  5. PWR

    Silver plated versus tin plated copper bus

    Also be aware that tin plating is susceptible to galling on sliding connections. It does not work well where breaker primary stabs connect on draw out units. In one particular case I am familiar with, a manufacturer lost several 2000A breakers to severe overheating on the breaker connections...
  6. PWR

    What is the min. striking distance between energized parts and covers?

    For live part clearance to ground, the NEC Article 490 value of 5 inches for nominal 13.8kV equipment is a reasonable value.
  7. PWR

    Testing of medium voltage solid dielectric cable.

    I feel compelled to reply to the statement by LWS that a DC hipot test is "close to useless". Leaving aside the fact that he contradicts himself by describing a problem that was detected by a DC hipot test (improper elbow installation), it is important to distinguish between maintenance...
  8. PWR

    Testing of medium voltage solid dielectric cable.

    Were the measured currents in each phase nearly the same? Did the currents continue to decrease during the 15 minute hold at 56kV? Given the cable characteristics you have, what level of current do you calculate should be present? While 60 micro amps sounds high to me as well, it may be...
  9. PWR

    3333KVA dry substation question

    Being in the service business, I have seen dozens of bolted pressure switch failures. I have also seen many used successfully over an extended period. The big issue is maintenance. Most facilities that go the cheap route (BPS versus breaker) don't do any maintenance on them. Many breakers...
  10. PWR

    parallel feeders

    Actually, the run I documented above was only about 30 ft total length. The length only has to be long enough to establish a significant difference in the total impedance of each conductor. The current is going to divide based on the difference in the impedances even if the total impedance...
  11. PWR

    parallel feeders

    I have seen this problem on many installations. It occurs due to unequal reactance when the conductors are randomly place in the tray and when they are neatly installed with all the phases grouped together. The latter insures the worst case scenario. As an example I documented some years ago...
  12. PWR

    Nuisance Tripping on Ground Fault

    The last five words of your post describing how the shield on the nuisance tripping feeders..."passes through the GF CT" is likely the explanation for your problem. The shield should not pass through the CT. Electrically that is usually accomplished by bringing the grounding connection to the...
  13. PWR

    Generator grounding & protection with a wye-wye transformer

    In none of the comments have I seen the issue of unstable neutral. Be aware that if the neutral of the generator is not connected to the neutral of the transformer, there will be no defined phase voltage to ground/neutral. You can solidly ground the transformer but if the generator neutral is...
  14. PWR

    Arrestor Connection

    I have a different take on the situation. We see lightning arresters routinely installed in padmount transformers. I believe it is for good reason but that is another discussion. The #6 wire is a little small but the 600V insulation would not concern me unless the clearance between any portion...
  15. PWR

    XLPE cable puncture

    I am not familiar with "R and Y core" terminology. But, I believe you are describing that two phase conductors are in contact with each other a short distance from their ending terminations. If the touching occurs in the region where the shield has been removed, the voltage stress is uneven...
  16. PWR

    synchronous motor vs induction motor

    The synchronous starter is more complicated because it requires a means to supply and control the field of the machine. The added level of complexity is a relatively small factor in a machine the size you are considering however. The protective relaying costs are slightly higher. The unique...
  17. PWR

    What HP justifies 13.2kV Rating?

    A customer is currently in the process of starting up a new 4000V rated 8000Hp compressor. He is considering something in the 8000-10000 Hp range for another new facility. Should he go to a higher voltage for that size? If so which? Are there many motor shops (this is in the US) that can...
  18. PWR

    synchronous motor vs induction motor

    Your application sounds like the decision of whether to go with induction vs synchronous will easily be made for the latter. You will learn there are many factors to consider. One advantage of synchronous that does not get the attention it deserves is reduced inrush. Because the starting...
  19. PWR

    Surplus/Used Equipment Dealers?

    Try Dave King at Instel Power Products 864 963 1856. If he doesn't have he can tell you who does.
  20. PWR

    Grounding 4160 Switch Gear

    The transformers and switchgears may well be properly grounded by connection to an underground grid. Quite frankly "they are old installations" usually means a pretty conservative approach was utilized for grounding. If the 4160V system is resistance grounded, there is less concern that a high...

Part and Inventory Search