For a system sourced by a delta, arresters should be applied with an MCOV greater than the line to line voltage. Otherwise, a ground on any phase (no fault current will flow) will subject the arresters (connected phase to neutral) to line to line voltage. The arresters will fail rather quickly...
Correction: The phase to neutral equipment connected on the phases not referenced to ground would experience line to line voltage. The next ground fault (overvoltage of the arrester) would result in a phase to phase fault. Arcing could result in a 3phase fault and explain your blown fuses. Just...
opmgr1, interesting problem. Just because I haven't seen the problem doesn't mean it doesn't exist. I have to concur will several others, the riser pole arrester is equipped with a disconnector on the ground terminal and will not require fuses/cutouts. Internal failure of the arrester can easily...
Is lightning causing so many momentary outages that you need to install additional arresters? I worked for a gulf coast utility (high incidence of lightning) who installed riser pole (ground disconnector) arresters at the first OVHD pole outside the sub and at all cap banks and pole mounted...
Last thought - make sure you look at the fault current capability of all of your disconnect switches associated with the breakers.
Good point.
I seem to remember the rating on disconnect switches was not the RMS Symmetrical rating. I remember seeing 100kA ratings that were certainly not...
The cable was carrying normal load current. The busbar was more than capable of handling the current.
A bad crimp is certainly a possibility.
Would 2000degF localized heating be dissipated by the busbar while causing insulation melting on the cable? I certainly think so but would the busbar...
I apologize for asking you to do my work for me, but I am clueless to thermodynamics. I have done a number of searches and reading, but my particular question doesn't appear in text books. Here goes:
Situation:
Compression 2-hole cable lug is bolted to 1/4"x2"x2' bus bar. Lug gets hot enough to...
I believe the evidence suggests it was not an open circuited CT. The last real piece of evidence is the consultation of ABB about their CT.
Thanks to all for your help.
I apologize. I must have given a poor description of the test. The test lead was passed through the window of the CT with the CT secondary shorted. Approximately 50Amps primary current produced by the test equipment fell to nothing as soon as the secondary was open circuited (using much...
Further explanation of setup.
MV leads pass through Diff CT's (directly above subject CT) on each phase. Neutral end of leads pass back through diff CT's from motor and make turn down to phase CT. After passing through phase CT, the lead terminates on neutral bus bar. This is all in connection...
The suspect CT is 800/5 with ~600Amps primary current. I don't know the rating but I imagine C200. Saturation shouldn't be a concern because of function (my assumption). Phase currents appeared to never exceed FLA. The motor tripped on ground fault when 3ph current sum exceeded 20Amps.
I need some help. I work for a large industrial plant and have seen a large motor trip that is being attributed to an Open Circuited CT. I would post pics but the company prohibits it.
The CT was located in the connection box and is not used for protection. It was connected to a current...
Stepping in and out simultaneously. Not sure what you mean. Did the capacitors have internal discharge resistors? Was the technician waiting 5 minutes prior to re-energization of capacitors?
