Electrical/Electronic Engeering. Underfrequecy/undervoltage problem 1

[bravo3]

Pls. i need a professional advice on these issue.
I am currently handling a job in a site and they have a problem with their CAT 3516 NG Engine, The Gen. start up on idle and when taken to rated, after 1 min it shut down on Underfrequency/Undervoltage. pls what do i do to resulve this problem

 

[waross]

We need a little more information, but if the engine is running slow you will be under frequency. The Under Frequency Roll off (URFO) feature of the Automatic Voltage regulator (AVR) will drop the voltage when the frequency is low.
If you have an electrical problem with the set, and the voltage is not building up you will also get an Underfrequency/Undervoltage trip.
If the operators are starting at idle and then ramping up the speed, they may not be setting the speed properly.
Is there any interpersonal friction on the job? The operators may be messing with your head and purposely setting the speed wrong. Watch for grins and winks between the operators.




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

 

[FreddyNurk]

Waross is right, we would need more information. I'm assuming that from the number its a high speed generator unit, and probably doesn't behave much differently from a similar sized diesel.

There are, depending on configuration and controller in use, almost hundreds of reasons on why you'd get an underfrequency / undervoltage, least of all the reasons that Waross alluded to. Is the set new? Has it been commissioned previously? Depending on controller, there are at least a couple of options I could think of to trick the unit, and thats without the possibility that its actually falling over.

Thanks to Waross for pointing out the operator possibility. I'm just thankful that no operator has ever done that to me.

 

[rbulsara]

Is it even generating the voltage?

 

[dpc]

Waross has some good suggestions. Also, if the AVR is not getting switched to auto from manual, the voltage will drop as the load is picked up.

 

[bravo3]

Thanks Waross and Freddynurk, to be precise, i have carried out some troubleshooting and find out that only 30V coming out from the Exciter Phase to Phase on rated speed, the AVR is ok, i introduc 12V to the Exciter on idle speed but all i get is 2.1V at each single Phase. Pls. some one should advice, what else i should do.Thanks
Bravo 3

 

[waross]

Generally the exciter is not accessible when ab diesel set is running (Except for very old, brush type, DC generator exciters). Do you have a PMG (permanent magnet generator)?
This is a small three phase alternator on the end of the main alternator shaft. It generates about 200 volts to power the AVR (automatic voltage regulator). Check your PMG fuses and wiring, and then check the PMG for failed windings.

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

 

[catserveng]

Most G3500 series gas engines shipped with either VR3 or DVR voltage regulators. A DVR has a small digital display, make sure it is powered up and no fault codes are flashing.

With engine running at rated speed (this engine has both low and high speed ratings, 1200/1000 low speed for 60/50 hertz, and 1800/1500 high speed for 60/50 hertz) first check PM power to voltage regulator, terminals 26, 28, 30 in generator connection box and on voltage regulator (numbering same on both models), should be about 100 VAC at 240 Hertz for 60 hertz rating, can be as low as 80 and as high as 120 VAC. Check sensing on regulator, terminals 20, 22, and 24, standard CAT configuration was 240 VAC sensing, either center tapped or by using 2:1 PT's.

Check field output, nominal CAT exciter field runs about 10-12 VDC at rated speed no load voltage.

>Stop unit, remove F1 and F2, measure resistance, should be about 3.5 to 4 ohms.

If you are flashing the field with 12 VDC and not getting near nominal voltage, likely suspect is rotating recitifer and surge suppressor assembly. CAT had quite a few problems with that assembly, both diodes and surge suppresor, and service replacement is the entire rotating rectifier assembly. You should check with your CAT dealer to get correct replacement part number, as there where several part number changes over the last few years. There have also been a fair number of pilot exciter rotor failures in some of the frame sizes you'll likely see behind that engine.

Hope that helps