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,
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,
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,
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...
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...
Sir,
We have a substation with a 110/11kv , 10 MVA ynyn transformer and 11kv feeders from the l.v side of the transformer. In the same substation compound, we have a 11/0.44kv dyn transformer for auxiliary purposes. Can we connect the neutral on the 0.44kv side of the transformer to...
Sir,
Can we measure the ground reistance of a test object by means of a dc currnet injection kit in the following way ?
Connect one lead of dc injection kit to test object.( In earthmegger, C1 and P1 are connected to test object.) Connect the other lead to a spike...
Sir,
In our one substation, we get electrical shock from the portion of the lightning arrester where the counter is connected from the lower side of the lightning arrester. The lightning arrester is connected in one 66kv line incoming side to the yard. The details of the lightning...
Sir,
We have one 18MVA and 144 MVA units. In seperate occasions the megger values of stator windings were found low. The xd'',xd' and xd values of these units are about 15,25 and 90 percent respectively. These units are working in 11 kv system and the power is stepped up to higher voltage...
Sir,
What is the purpose of giving pilot wire relays in all terminals? Is it not enough providing (summation)CTs in all terminals and providing pilot wire relay at one only and also providing intertrips to other terminals from the relay?
What is the purpose of providing resistance to...
Sir,
Consider a 66/11kv transformer (star-star earthed at both side neutrals) in a solidly earthed system. Also consider one 11/0.44kv Delta/star transformer is connected to 11kv side of the 66/11kv transformer. The supply is fed from 66kv side of the 66/11kv transformer and this is stepped...
Sir,
How does the shaft current measurement is done in hydro machines? I know that the earthing brush is connected at turbine(driving) side and the guide bearings are not insulated to earth while the bearings at the other (nondriving) end is insulated to earth. My doubt is if the...
Sir,
Please explain the method for demagnetising a saturated CT. Can we assure 100% success in demagnetising the saturated CTs of all types with these methods?
with regards,
appunni
