I thank all of you for your valuable contributions. The transformer is a new one and we will be complaining very soon to the manufacturer. It hasn't got an auxiliary winding for station supply. We will put it back into service and measure the phase currents. If the windings were wrongly...
My utility recently commissioned a zig-zag earthing transformer with the following rating: 33kV, 2000A for 10 seconds, 19.4 ohms on one of its 33kV network. Two days after commissioning, it was detected that oil was dripping from the transformer as a result of overheating. The grounding of the...
Jghrist, you are right about the nature of our distribution system. Our trafo sizes range from 50KVA in the rural areas to 500KVA in the city centres. They are usually overloaded to about 150%. We estimate that the average load per customer is 3KVA, so you can imagine the number of customers on...
Thank you jghcrist and fredpar for your contributions. We define commercial losses as all the losses that are not due to technical considerations. E.g. power theft, illigal connections, limitations of billing systems etc. We estimate commercial losses to be about 10% and technical losses to be...
The distribution network in my country is a 4-wire star system. Most of the load in the system are single phase, 230V. The system loss figure is estimated at 25% consisting of both technical and commercial. We have tried to bring down this figure but our efforts have not yielded much. I want to...
Thank you all for the various responses. I am from Africa, specifically from Ghana. The design of our distribution system is based mainly on European standards and as far as I can remember our system has only one star-star 33/11 KV transformer with the neutrals grounded. I believe your various...
I attended an interview on Monday and one of the questions asked was that I should tell why star-star transformers are usually not used. According to the questioner, there is a particilar problem with them that makes their use not advisable. I have read a lot about transformers but have not come...
Does the duty cycle of a circuit breaker have anything to do with autoreclosing? We have a CB with duty cycle of CO-15s-CO. We are to implement an autoreclosing scheme consisting of one fast reclosing of 0.5sec and one delayed reclosing of 15sec. I have been wondering whether the CB is suitable...
