Reverse power trip.

Reverse Power trip is directly rated to speed of machine, hence governor.. The first place I would start looking is the governor..

The machine that is tripping will be slowing down for whatever reason, and you should be seeing negative watts..

Is the governor linkage free and well lubricated?

Is the actuator for governor full of hydraulic fluid?

Is there a shutdown soloenoid that is malfunctioning causing the fuel rack to be restricted?

In the past I have had problems with the shutdown / start block soloenoid malfunctioning causing intermittent reduction in speed of engine by forcing fuel rack towards 0 position. We spent days looking for this problem as it was intermittent.

As far as a voltage problem this would cause the generator to trip on reverse vars (reactive power) not reverse power..

Let me know what you find.. Happy Hunting

Hi,

It was happened on my two Diesel generator sets last week and what I just did was reverse the wire termination of S1 & S2 from alternator internal CT which is on terminal A & B from the voltage regulator and my genset works fine. we encountered the same problem with my generators.

============== CAUTION for CT WIRING !!! =============

Be careful if you are going to play with CT secondary wiring. DO NOT do this with the unit running and current flowing through the CT. If current is flowing through the hole of the CT and you remove the secondary (small) wires it may explode in your face. Only get a very experienced electrician to do this. DO NOT OPEN the secondary CT circuit with current flowing through the CT. The CT secondary leads must be shorted out to themselves if current is flowing if you intend to play with the relay CT connections. CAUTION !

=========

I do not think it is a CT 'direction' issue as you would not have this problem sporadically. If the active load on the problem unit is going up and down when the load on the bus is stable then there may be a voltage regulation problem. If the speeds are not matched as pointed out by others, then you will have a reverse power regardless of load. The engine governor needs looking at, again, pointed out by others, or depending on the engine type the fuel rack could be sticking and when the governor finally builds enough torque to break it free it may send a momentary speed spike through and trip out. Remove the governor linkage and see if the fuel rack travel stop to stop is smooth and free of hangups.

I don't understand it when you say it trips out running by itself. It can't do this unless you are paralleled to 'something' such as utility. It if trips on reverse power running alone then the trip coil in the breaker is getting a false signal from the reverse power relay or some other relay that is contaminating the reverse power relay trip signal.

Let us know what you find for learning, please!

Take care.

Hi Petropower,

Thanks for your reminder for not playing with the CT while its running, I don't think that the guest asking about his problem will be the one to do it, 1. hi was just an opertor.2. they have the engineers looking after and responsible for the trouble shooting and repair. what I anticipate in giving him advised that he can bring it up to their engineers. as I said it was my actual experience on my generator sets and the problem was been corrected as mentioned the problem he is telling us are all the same on what I encountered. The unit will work when he is not in parallel with other, but the moment you put them on parallel he will either give you reverse power alarm indication, or showing more higher reading on the maximum required and suddenly he will shut off automatically. there will be no damage may caused if you reverse the termination of CT S1 & S2 from AVR terminal A & B, but of course in doing this the unit must be off and with safety tag out/lockout as well as the emergency stop from the unit and the control system must be in off position as safety procedure. Just go ahead and tell your engineer to try what I said and let us know.

One more thing I can advise, your Plant manager should be involve and have the Alternator manufacturer as well as the control system module manufacturer be called, they usually have technical support that can assist and guide your engineer on what to do if trouble arises as what you experiencing now.

Reverse power in a parallel generator configuration is due to the loss of the prime mover, Diesel Engine, losing its input to the generator. In short, your diesel engine is intermittently losing its ability to carry the generator when under load.

When this happens, the generator that is connected in parrallel is running the defective generator as a syncronys motor resulting in a term called reverse power.

The reverse power detection relay is doing its job by shutting down the generator.

My advise would be to place the generator in question off line and completely inspect the fuel system components as well as taking a fuel sample analysis.

Remove the injectors and inspect the atomization cups for corrosion or clogged ports.

Also check the fuel filters and fuel pressure.

Just a quick note: This scenario can also happen when not in parallel to another generator. Motor loads can also cause reverse power shut down due to an intermittent loss of the prime mover.

Could you elaborate on the reverse power trip taking place when operating a single unit on the bus being caused by motor loads?

Thanks,

Curious Guest

I had this happen to me while stationed at Loring Air Force Base in Maine in 1968. ( now closed)

When there is a sudden loss of prime mover power, whether it be from diesel or gas or turbine , the magnetic flux that is built up in the motor windings will revert back to the generator windings causing a slight reverse power effect. This is mostly apparent in older motors.

We operated the generators to power up 25 and up horsepower motors once a week as an exercise procedure. Also ran the generators at 110 percent load via load banks during maintenance and repair operations.

With a load bank and the proper test equipment, you will be able to pin point the problem. I would first start with the fuel system though. You may find your injectors are faulty or you have a loss of fuel pressure.

Let me know how you make out.

Talk to you in a bit.

Jerry D.

I've seen this before...it was water in the gas (or rather, the diesel). I also saw it on the varidrive when the belt was slipping, and needed to be replaced or tightened. We electricians hunted for days to find it...and when it happened again, I got to be the hero for adding some anti-gelling anti freeze to the diesel oil to fix it. Worn teeth on the driver-generator adaptor "might" be the problem too, check the lash. If the generator bangs around under load changes, I am told you can sometimes get momentary back emf spikes which drive the voltage regulator crazy.

Let us know what you find!

Do you have a "Loss of Excitation Relay", even momentary interruption of excitiation can shear keys or dowels and cause rotor and stator to collide.

I would connect a power factor test set with recording capability to the generator leads (Volts and Amps) and have the test set connected to a computer with a big hard drive to collect data that can be observed while on-line and have it collecting fast enough for analysis at time of trip. The external power factor test set correctly connected should confirm all other wiring.

I agree "reverse power relay" trip should be on loss of power input to the generator, unless of course the relay is configured wrong and is in fact tripping on "Over Current" instead of loss of current.

But the real problem is why is the load ramping up ? Are you monitoring frequency to know that the governors are not sticking and then suddenly trying to recover ? Is there a sudden load being applied, a short in a station transformer or other susbstation gear ? Are more generators reacting the same ?

Changing load may cause a sticky governor to over-react, has anyone "cleaned" the oil system, if the governor uses pressurized oil ? Is there any foaming in the oil reservoir ? I have also seen "hold-in relays" on hydraulic governors with "weak" coils that would not stay energized.

If electronic governor, when the unit is shut down, check all screw connections in the switchgear and on the breakers aux switches looking for loose ones, remember line PT circuits will still have voltage and the exciter circuit CT feed may have current flow depending upon the type of compensation circuit.

For safety NEVER open a CT circuit without the bus it is on being confirmed de-energized!

Is the voltage stable when the current flow suddenly increases, i.e. is the voltage regulator operating correctly ?

Wow, thanks to all for your suggestions, this site rocks. Well to answer some questions when the machine that is giving the reverse power is on bars by itself it still may sometimes trip out the same way as I described. The engineers in the plant changed an excitation realy day before and the day after it still tripped. I am in agreement with those who say that it may be more or less a speed control problem i.e. governor and other related equipment. I doubt that its water in the gas sine I am in the tropics, and that may affect all machines not just one. I am reporting to work today and will do some minor checks since I am only a trainee.I take a look at the governor actuator oil level etc.

Thanks again for all your sugestions.

What about fuel pressure ?

Any leaks in the inlet side to the fuel pump that could interupt or lean out the mixture?

Hi people,

I have encountered this problems many times on our diesels. All those times we found the cause to be the fuel control side (sticky injection pumps, loose control linkages, faulty fuel actuators, loose governor cablle connections, faulty stop solenoid, worn contacts on stop solenoid control relays, and one time, a stuck-up actuator), never with CTs nor with the alternator side. After eight years most the control relays for start/stop solenoids and the associated connectors and cabling are aged and should be replaced. Going for the CTs is not advisable. The CTs should otherwise have given this problem right from commissioning. I think you want a solution and not a band-aid. Check the fuel control system. It is not responding to the KW demand from the controller.

That is my take and experience with this problem.