I need some opinion. Attached is the image of the one line which shows a 3750 kVA transformer (XFMR-MSC-1). As it is a supervised location so as per NEC table 450.3(A), the transformer secondary protection is not required if the rating of transformer primary fuse is maximum 250%. However the...
I have six M-G sets from the 1940's where the synchronous motor utilizes a motor operated rheostat. The field voltage is 250VDC. The rheostats are in old and in need of replacement (or repair). I have not been able to locate a manufacturer for rheostats. I have tried Ohmite, Cutler-Hammer...
Does anyone happen to know of the best reference for theory on synchronous machines and the theory behind the various field exciter equipment options for these machines? There is alot of reference material out there on the subject but is there one that is preferred among the EEs out there?
NETA MTS-2011, Part 7.6.1.1, Section 3.2.3 indicates that the contact resistance, in this case on a molded case circuit breaker, that in absence of manufacturer's data, the standard suggests to investigate the problem if a value deviates from adjacent poles or similar breakers by more than 50%...
I have a switchgear lineup that is fed by a 6MVA 6900/480V oil transformer, Delta configuration on both sides. On the switchgear, I am getting unexplainable V(line-ground) readings as follows: Va-g=215V, Vb-g=225V, and Vc-g=390V. Normal readings would be Vline-grd=277V. Phase to Phase...
Does anyone know of a procedure for testing grounds (instrument ground) with a variable frequency impedance? Impedance would be plotted on the vertical axis vs. frequency on the horizontal axis. The test set would have to be capable of injecting amps from a test set instead of milliamps. What...
I have a 15kV class switchgear rated 1200A 3-phase, 3-wire system, delta. THe utilization voltage will be changed from 6.9kV to 12.47kV. What PT ratio should be used? I will be using 2 PTs in an open delta configuration. Standard ratios that are available are 14,400/120V (120:1) and...
I'm here in Southwest Ohio and have had problems with a reactor for a 6000 hp, 6.9kV motor. The reactor is now smoked. Does anyone know of a reactor re-wind shop (with a decent reputation) ideally in the area or outside within the eastern US? Any info is appreciated.
I am TTR testing a 9 kVA 480/240V 3-phase transformer and am getting different values for each. Here is what I got:
H1-H2 X1-X2: 1.805
H2-H3 X2-X3: 1.698
H3-H1 X3-X1: 1.580
On a three-phase TTR transformer, all reading would normally be the same, but a Scott-T uses 2-coils to get 3-phases...
I am evaluating test reports on many type of relays here on an Air Force Base. The NETA Maintenance Testing Specifications can be used as a comparison for determining if the relay is within an acceptable level, but it would be best if I had the actual trip curves from the manufacturer. The...
I need to splice into some existing 600V rated VCL cable, short for varnished-cambric lead cable. It has 3 conductors with a lead sheath encasing all 3 conductors. It has been known that PILC cable, short for paper insulated lead cable , has contained an oil inside and that it takes a special...
I work at a University where I have a 4160V, 3 phase run originating out of a distribution lineup (solidly grounded). Sorry for the lengthy description so bear with me.
It runs from this lineup to various manholes (which has a ground-rod) to pad-switches (which also has a ground rod); and from...
Article 760.61 of the NEC states the type of cable that can be used is FPLP, FPLR, or FPL depending on if it is plenum, riser, or general purpose cable. Does the code allow you to use other types of cable other than the approved substitutes if it is in conduit? I thought I've seen THHN wiring...
Can anyone tell me where in the NEC book where GFCI would be required on a submersible pump. I read Article 680.51 but that refers to pumps for fountains or near pools. I installed a >1 hp sump pump in a steam pit (190 F inside)) and it seems it would be prone to tripping and cause more harm...
I am using type CL3R wiring for speaker circuits in a fire alarm system. Article 760 states that type CMR wiring can be used as a substitute in place of type FPLR. NEC table 725-61 states that type CL3R wire can be substituted for type CMR wire. All three types FPLR, CMR, and CL3R all are...
I am using a 4200:120V three-phase P.T. and connecting it Line-to-Line on the Primary in an open delta configuration. The secondary side is an open delta as well. When I put a voltmeter on it, I am reading 120V across each phase (Vab, Vbc, Vca). But when I am reading line to ground, I get...
How do you calculate if a P.T. is suitable for a meter? I have a three phase P.T. (open delta- 4200:120V) that is 0.3WX, 0.6M, 1.2Y AND 500VA thermal rating @ 30 Degree C. The meter I am connecting it to has a 5M ohm input impedance. I want to connect 5 meters to the same P.T. Any advice guys?
Is there any phase sequence checker for voltages at 4160V or greater? I have a contractor pulling cable underground and we are having a heck of a time figuring out why our phasing is incorrect.
