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...
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...
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...
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...
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...
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...
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...
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...
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...
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...
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...
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...
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...
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...
