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%...
The readings appear to be acceptable in accordance with NETA ATS-2009. I'll reiterate what others are saying: Check with the manufacturer, verify that the 'B' phase arrestor is the same as the others, retest.
Just a follow up to my problem, the ground fault was found to be a tubular heater (strip heater) for a synchronous motor and it was connected on 'B' and 'C' phase. Thanks for your posts!
Give this website a shot. I took a course in person with the instructor and he is very knowledgeable with this subject. Copy and paste on the link below.
http://www.brainfiller.com/stores/productlist.aspx?CatId=7
Good luck!!
Our electricians record monthly readings and for years, it typically has read normal, 277V. So a change of some sort has taken place. A classic ground fault reading should have caused the faulted phase to drop to a much lower voltage. In this case, 'c' phase increased significantly.
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...
Sounds like your best option is to move or become an Amish farmer. On a more serious note, turn off all of your feeder circuits on your panelboard and then see what your getting. This may clue you in to where the problem may be occurring. If your THD problem disappears with all your feeder...
I'm with rhatcher on this one. I work at an Air Force Base with 1940's-1960's transformers and I have never seen aluminum windings on a transformer. They built transformers like tanks back in the 40's-60's. This is a "utility grade" transformer
Reasons why I think it is copper:
1. Size is...
Zogzog pretty much has it correct EXCEPT NETA says to investigate values which deviate from those of similar bolted connections by more than 50% of the lowest value. Typically, the similar connections are the different phases and you are comparing the readings on A, B, and C phases. Readings...
I am assuming "idle" means that the generating is not running but is available to be started for backup power. For general emergency backup electrical power purposes, once a week "no load" generator exercising for 1/2 hour is acceptable with at least once a year 100% load testing (for 3-4...
NEC Table 110.26.(A).(1) condition 2 says 3.5 ft. minimum in any direction. You might want to consider it in a wet location, so Section 312.2.(A) should be taken into consideration. You may want to consider a NEMA 4 enclosure which is protection against splashing water or hose directed water.
