Voltage Reg Question

[mrcoal]

We have an old style Voltage Reg and I am thinking I need to micro ohm the wipe contacts to see if there is a bad connection. Based on the operators report is there anything else I can look at while investigating this problem. Thanks

We put the unit back on line yesterday. This is the unit that had been relaying by overcurrent. We still never did find any smoking gun for why it would relay. The Tech has tested the relay about four times now and worked with system protection. The unit has been meggared a couple of times. Electrician did find that the voltage regulator was pathetically dirty and cleaned same. He also did an OHM test on it which came out ok.
When the operator left the unit yesterday it was block loaded at 3KW, voltage was at 2.3kv and the amps were at 70. He went in this morning and the unit was still at 3KW, voltage had dropped to 2.23 and amps were 80-85. The operator bumped up the voltage to 2.3 and watched the amps start to rise slowly, all three phases. at 150 amps, he barely bumped the control down and the voltage remained the same, small deflection, the amps came back down to 95. He barely bumped it down again and the amps settled back to the 80 range, voltage was still the same.

 

[electricpete]

Try the power forum:
forum238

=====================================
Eng-tips forums: The best place on the web for engineering discussions.

 

[rhatcher]

mrcoal,

I am not sure what you have but it sounds like your generator is connected to a bus. More specifically, it sounds like you are paralled with a utility or with other multiple generators.

If so, the generator voltage is determined by the bus voltage. If you increase the excitation (voltage regulator output), the generator voltage cannot change the voltage of the (infinite) bus. All you will do is produce more VARS and more current. If you increase the prime mover power (speed control), then you will still not change the voltage but will produce more power (KW) and more current.

Give us some more detail about your situation so we can give you a more specific answer.

electricpete: this is now the "Electric motors, generators & controls engineering Forum". He can probably find help here as well as the "Power" forum. I would suggest that he post to both.

 

[waross]

What are the spec's on this machine? 3 kW seems a little low for 2300 Volts. I haven't seen one of those wiper voltage regulators for about 20 years and it was old and out of service then.
By "on line" do you mean in parallel with the grid or other sets?
If you are parallel with the grid the voltage will be set by the grid. The voltage control will control the reactive current. In parallel with other sets, the excitation will partly control the voltage and partly control the reactive current.
From the operators experience it sounds as if you are in parallel with the grid.
You should not be using voltage control when in parallel with the grid. A relatively small drop in grid voltage may cause enough reactive current to overload your alternator.
Buy a modern Automatic Voltage Regulator and try PF control when in parallel with the grid.
Donate the old regulator to a museum.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[davidbeach]

I would suggest that he post to both.

No, please don't. I think that the OP needs to clarify what he is dealing with. I think, and electricpete seems to have also, that the OP is talking about a voltage regulator - you know, that thing out on the line, an autotransformer with a with a bunch of contacts that is used to keep line voltage under control as load induced voltage drop changes. You and Bill seem to think that the OP is talking about a voltage regulator - you know, that thing on a generator that attempts to keep the terminal voltage constant regardless of load. The answer for one isn't going to be of much help for the other.

If e-pete and I are right, the OP should Red Flag this thread for removal and repost in the other forum. If you and Bill are correct then the thread belongs here and there should be nothing about it in the other forum.

 

[rhatcher]

waross, I intially thought that the OP was referring to a small hydrogenerator unit because of the small size but I hesitated to suggest that because of the name 'mrcoal.' That being said, I've never seen a coal fired unit that small but, if one still exists, it must be very old. In either case, the voltage regulator that I think he is describing would be very old. However, there are several like that, mostly on small hydro units, still operating in my area. I've had the pleasure to work on most of them myself. You've got to like a voltage regulator where the components are all the size of a breadbox or larger and can be individually tested versus one where the entire system is on a circuit card with micro-components that are barely visible to the naked eye. Of course, this is just my personal, old timer, preference.

davidbeach, you are right. I am thinking a voltage regulator, the device meant to keep generator voltage constant; so is waross. And, as waross suggested, we are both thinking of a very old style voltage regulator. You are right that the OP may be referring to a line mounted, transformer type voltage regulator. If so, his question may be better served in another forum.

I guess we will have to wait and see if he responds with more information as requested.