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Sir, I was thinking about inserting resistor in series with coil of the contactor but in parallel with NC contact of the contactor on the assumption that the current in the coil increase after the contactor is closed. And I thought that the increase in current will increase the heat loss...

Sir, We have three old 180kw induction motors in our pump house. On the back but lateral side of the motors I saw terminals with ferrules s1 and s2. I could not understand the use of those terminals. I measured the resistance between the terminals and found that the value was in the...

Sir, I wish to include resistance in the coil circuits of some contactors, which uses for running motors in order to limit holding current as minimum. For that we have planned to connect the resistances across the NC contacts of the contactors so that the resistance will come in series...

Sir, In one of our 144MVA generator, we got tan delta value as given below: 1.Phase-to-Phase values: R-Y: 40% Y-B: 38% B-R: 20% 2. Phase to Neutral values: R-N: 2% Y-N: 3% B-N: 3% All measurements were with 6.5KilotVolts AC supply. Last year, the phase-to-phase...

Sir, In one generator maintenance manual, I read that the polarity of dc supply to rotor poles through slip rings may be reversed once in a year in order to minimize wear and tear of the machine. When I asked about it to the engineer in charge of the power station, he said that that...

Sir, In one of our substations, we have to extent 110V dc supply to motor control panels which are 600 meter away. We have 16sq. mm aluminium cable. Can we use it for dc supply extension? Is there any problem in using aluminium cable for this purpose? If copper is to be used what should...

sir, Yes. This system is radial in 11KV side. The same 66KV feeder which supply power to this substation also feeds another similar substation. With regards, appunni

Sir, I request for your valuable comments for the explanation I have given last. With regards, appunni

Sir, One of our testing team tested a transformer of which some name plate details of the transformer is as given below: 16/20MVA, 66/33KV, 3phase, imp.volgae:10.11% at working tap(13). When core balance test was conducted with a 230V single phas...

Sir, In my case, the primary side of the transformer is connected in star and earthed. Then how would be the effect? The jumper opening is in the 66KV line. The delta star connected transformers are on the 11KV side of the star-star(earthed at both sides) 66/11KV transformers...

To Kiribanda, Yes sir. It is 12%. With regards, appunni

Sir, We have one substation where 66KV is stepped down to 11KV through two 4 MVA, 66/11KV Ynyn transformers, which are connected in parallel. From 11KV side there are 6 outgoing feeders. In these 11KV feeders there are some 11/0.44KV Dyn transformers for power distribution. The 66KV supply...

Sir, We have procured a new 66.67 MVA, 11/220KV delta/star transformer which is to be kept as spare. We decided to give 415Volts 3 Phase supply on 220KV side and to short 11KV side in order to get a heating effect during idle conditions. But somebody said me that if one phase became open...

Sir, I have seen in some power stations that the directional earth fault relays are used for generator stator earth fault protection. I did not see any such protection scheme in IEEE standards for generator protection. What is the purpose for giving derectional sensitivity for stator...

Sir, Thanks for your replies. The reason for replacing 200/1A to 400/1A is to completely utilise the current carrying capacity (which will come around 360A) of the feeder completely. My analysis is like this. 200/1A CT means one turn in primary and 200 turns in secondary. If two such...

Sir, We have a 200/1-1A CT in one substation. The classes of cores of CT are PS and PS respectively. We want to enhance the CT ratio from 200 to 400A and only one core is enough for application. There is no provision for enhancing the ratio both in primary and secondary of the CT...

Sir, We have a 200/1-1A CT in one substation. The classes of cores of CT are PS and PS respectively. We want to enhance the CT ratio from 200 to 400A and only one core is enough for application. There is no provision for enhancing the ratio both in primary and secondary of the CT...

To dandel: The outgoing feeders are 11kv feeders. The subtation auxiliary supply is of 440volts. The fuse blowing on the 440v side was found for a particular 11kv feeder fault. There is no 440volts outgoing feeder. Thanks. with regards, appunni

Sir, In the book 'IEEE GUIDE FOR SAFETY IN AC SUBSTATION GROUNDING' (IEEE Std 80-2000) , it is mentioned that hazards are possible if low voltage neutral wires are connected to substation ground due to potential rise during ground fault current flow. Please see section 17.9.3 in page...

Sir, We have a substation where 110kv is stepped down to 11kv via a 10MVA ynyn transformer . Three 11kv feeders are used for ditribution. The 11kv and 110kv side nuetrals are solidly grounded . The substation auxiliary supply is maintained through an 11/0.44kv Dyn transformer of which...