No Load Excitation Current of Synchronous Generator Increased

How did you synchronize then? The no load terminal voltage should have shot up also, making it impossible to match voltages with the incoming bus. If that did not happen then there is something wrong with the current transducer circuitry or the field winding.

If the plant synchronized successfully and there was such a large difference in voltages then someone would have noticed the bump. You need to recheck all your controls, metering and relaying settings, plus the generator field and stator windings on the next outage.

See , our Generator terminal voltage is 20 KV..It was so that to get 20 kv during voltage build up before synchronization, the excitation current needed was more than 1160Amps as against normal 875 amps...Is this the case of core saturation or some people sayings may be end ring short...please help me

If your rotor amps metering is by a resistance shunt and moving coil indicator direct in parallel with shunt, it is unlikely to be telling more current than you actually have. If it is electronic, then high reading due to indicator fault is probable.

You have not given the excitation voltage. If you need 20% more DC excitation current, it suggests shorted turns in the rotor - so a lower resistance.

Resistance = voltage/current.

Assuming your rotor temperature is similar at two run-ups, volts/amps for each run-up will give you the resistances to compare. If you have a rotor temperature indicator, you can calculate the resistances at a standard temperature before comparison.

Are you also seeing greater excitation currents on-load at rated output current and power factor than before????

67model

See , our's Generator terminal voltage is 20 KV..It was so that to get 20 kv during voltage build up before synchronization, the excitation current needed was more than 1160Amps as against normal 875 amps...Is this the case of core saturation or some people sayings may be end ring short...please help me

You have one of two problems.

1. The reading is incorrect either when it was reading 875 or when it was reading 1160 due to a problem in the monitor circuit. Not uncommon reading DC amps. Shunts are most reliable but not all that accurate but will not read high unless part of it is burnt out. Hall effect transducers are fairly accurate but may be affected by outside fields.

2. The excitation winding or connections to it have a short. Unlikely to be in the slip rings, but those can frequently be observed while in operation.

If this were my unit, I would look for the soonest (like right now!) I could pull an outage and then start checking. It could be something simple in the monitoring circuit that will not cause problems but if it is in the excitation winding itselt, it could cause a lot more expense to wait. Infrared camera monitoring might show something. I used to carry a large clip on DC amp meter with me when I worked on exciters. Usually it was metering but I have had shorts, usually in the excitation winding itself. Only once was it in the leads from the slip rings to the winding. Never was it in the slip rings.

Yes, assuminmg the generator is running ok and no signs of overheating or vibration, certainly looking like instrumentation problem, what is the on load field current and how does this compare with the normal figures?

onload rated fld current is 2075Amps..ie, at 300 MW...But the amps going near 2000 even at 250 MW..