Power Factor & Regulators 2

[PAFred]

Can someone shed some light on the possible or real effect's of inductive loading of a PM generator set that is running with loads that have power factors from as low as .20 pf to .36pf on average. And whether or not this would be the most likely cause of regulators going bad every 30 to 45 days this unit currently is on the fifth regulator.

The generator is the sole electrical power for a stone processing plant, There are two separate supplies to the plant both run through either variable frequency drive systems or soft start systems.

The max gen set KW is 1500 @ 480VAC. At the time of shut down today the load was approximately 1150 amps. The monitored DC field current output maxed out at 20 ADC.

This condition is happening randomly and once started it may run all day ok , 15 minutes or an hour before shutting down on a high voltage situation. I captured a reading of 668VAC.

 

[PAFred]

Hi, (itsmoked) you've reflected on the regulators several times so let me try and clear the air. I am merely one gen tech and not the first to be sent to this site. I am a tech that dont just change parts rather I will spend off time as well as my week ends trying to come up with solutions to problems while at home and not getting paid to do so. That being stated I usually dont here about who or how many others have been to a site for the same problem. Because I'm known as a book writer when doing my service reports and have been accused of not having a life because I spend do much time dealing with company stuff on my off time and I'm also known to dog something till I get to the bottom of it, is the reason I find oput things like the fcat that this unit has had (4) regulators.

I have put two on to date, the first one I put on because the unit was going into high voltage shut down as soon as it was started and before the breaker was closed. I did go through the back of the generator looking for the reason and thought that I had located the reason when I found several wires that had due to both the age of the unit , the fact that it is subject to considerable stone dust been worn down to the point that the copper was showing where the wires had been rubbing together and vibrating.

I changed the regulator and all seemed to be ok, then somewher around 30 to 45 days later the customer called for service again complaining of the same symptom and I happend to be in the office and heard about it. So I was sent back out to look into it. How ever I couldn't find any wires rubbed through and I'd heard that this site had become a hot plate which these kind seem to always end up on my plate to fix. So all of that being stated I go at problems like these with the thought in mind that I'm the last man standing and I have to make the problem go away for good else look very bad to the top boss.

It is for these reasons that I have come here looking for knowledge that is beyond my own in an attempt to irradicate this problems once and for all.
o the
And as to the exciter yes I am refering to the PMG and I have checked the diodes and surge supressors they are ok.

 

[PAFred]

To all those how took the time to assist me with this problem I would like to offer my extereme gratitude and thanks.

I went to the site today Monday 6-12-06 to find that the client had already started the unit and had it fial before he even got fully under load. I took your advise regarding adding droop and was able to run the unit at full load for approximately one and a half hours without failure. I monitored the voltage spikes both at the PMG and the AC output leads I recorded a max voltage of 664 VAC for a .58 milli seconds but the set didn't shut down.

I'm going to the site again tomorrow to observe it for a longer period of time to ensure no problems returning, I had to stop today due to rain.

Again thank you one and all, it is a large relief to rid this problem. Hopefully someday I can return the help.

PAFred

 

[hogdawg]

I agree with one of your respondants, increase your power factor! With such a low power factor, heating goes to the moon consequently raising the exciter current. Common on drilling rigs. Put a recording DC ammeter on your field leads and watch the trend.

Jim