CAT Gen Set Load Sharing / Speed problem 3

[LRPSTRIKER]

We operate and maintain a floating power plant consisting of three (3) 250KW Caterpillar (3406B) Diesel Gen Sets tied into our switchgear allowing us to run two or all three units together, the gensets each utilize a Woodward 2301A Loadsharing / speed control. We parallel these as needed (based on demand) to supply power for our mobile operation. Our #2 Gen started displaying the following symptom, when load is increased (example: engine room exhaust fan turned on) the Cycles will drop to 54Hz then swing to 65Hz and eventually stabilize at 60Hz. The voltage output is not changing during this event. The other condition we are encountering is that when Units #1 and #2 are in parallel both gen sets are mildly hunting in tandem. This is observed at the actuators and on the Ampere gauges. We do not see this when #2 is in parallel with #3. We thought we possibly had a fuel supply problem with #2, we changed out the injection pump, fuel pump, and prime pump. We are still seeing the same problems with #2 by itself as well as when it is paralleled with #1. Any advice would be greatly appreciated.

 

[waross]

Sounds as if someone has been playing with the governor settings. I would guess about 20% or 30% proportional band instead of 3%. Then a lot of reset or integral when integral should be turned off for parallel operation. If the governor has derivative or pre-act, that should be turned off also.

Bill
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"Why not the best?"
Jimmy Carter

 

[waross]

Another possible cause may be "sticktion" in the governor control linkage, possibly internal. I have seen this with an electronic governor and a sticky electrically controlled injection pump.
Does your fuel have sufficient lubricating properties? "Dry" fuel may lead to sticktion related problems with some injection pumps.

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

 

[catserveng]

What actuators are installed on the 3406's? I would assume EG3P's are what is normally installed.

Have you looked at the obvious mechanical issues, like low fuel pressure, plugged air cleaner, etc?

WHat are your settings for Gain, Stability and Compensation? Fully couter-clockwise would be referred to as zero and fully clockwise 100% Also compare these settings to your other governors, usually these engines will have settings near identical.

First, What is condition of your magnetic pickup for the governor? Last time you cleaned and adjusted it? Normally this should be done at least once a year. Also read it's resistance, should be about 150 ohms if you're using a standard CAT pickup. CHeck it first at the pickup then at the governor, should be less than 1 ohm difference.

Actuator, the nominal coil resistnace of an EG3P is about 35 ohms, again check at actuator and at governor. Does the actuator mover freely when engine is off, no bind, stick or looseness? What about the ball ends on the actuator linkage, are they tight, free, not binding?

Does the actuator have a compensation needle valve? This usually near the base of the actuator, best starting point on this engine is fully in and 1/2 turn back out. Not all EG3's have this, if your does it may be turned in or out too far.

With the engine running at rated speed no load, "bump" the actuator, easiest way to do this is momentary short the actuator output, this will cause it to go towards no fuel, if it properly responds it will raise back up in speed after you remove the short, overshoot slightly, undershoot about half the magnitude of the overshoot and settle back to rated speed.

Try those things and let us know how you did.

Mike L.

 

[LRPSTRIKER]

Our actuators are Woodward OR-0970. Unfortunately we are still experiencing the same conditions after we checked and confirmed per the response recommendations. Would like thank you for the responses as they helped us eliminate certain possible causes. Are there any other ideas or suggestions that we could follow up on? This is one frustrating situation to say the least. Thanks again.

 

[catserveng]

I wouold be interested in knowing your governor settings on all the units, especially for the dynamics, gain, reset and compensation.

Something else that has been known to cause a speed fluctuation is a faulty speed adjust pot (if used), if you do have one you can jumper around it and set speed with the governor pot and see it that helps. Sometimes you can tap on the pot while the engine is running and see the speed/load change.

Mike L.