Power Generation: Product Operation and Maintenance

[tchatamba_inst]

We have a Caterpllar 3516 BTA diesel generator set packaged in 2004, when the unit is on load it suddenly drops all the load and it causes a reverse power trip, the engine stays running at sync speed after the breaker trips. There are no alarms indicated on the electronic technician, the load control is a woodward DSLC, we have changed out but the fault still occurs. All the connections have been checked and appear to be good.

Any ideas????

[ahmad728]

Hi

R u have any massage  after trip ?check it

R u have smock in trip time ?check it

Advice check electrical connections, change fuel oil filters and shutdown activator

(excuese me I can't write English well)

[tchatamba_inst]

there are no alarm messages, the connections have been checked and the filters changed, the unit is not shutting down, just losing power.

[romy8855]

Process of elimination. Isolate this gen, applied load, if engine power stays, then check fuel control signal from  DSLC.

[mikel]

Do you have CAT ET, or a dealer with it that can help you?

Setup a datalog, trend the throttle input (from the DSLC), along some other parameters, the datalogger has several trigger functions, if you have an EMCPII you can use a drop in load to trigger the datalog. I have found it very usefull in troubleshooting problems like this.

If you don't have ET, maybe a good DMM like a Fluke 87?  You can use the MIN MAX record feature to watch the throttle signal input from the DSLC. Have worked on a lot of DSLC's never had one with a bad PWM output, so it is likely something else.

Some other parameters you may want to watch if you can,

Fuel pressure

Fuel command, desired/actual fuel rack (depends on flash file)

Desired speed

Run signal

Manifold air pressure

You also may want to check your monitoring system setup and see if you have any derates active, in systems with DSLC's and other types of load controllers the derate in the ECM can cause some strange responses, so if you have any enabled, see if any parameters are getting close, your best bet may be to get rid on any derates.

Hope that helps, Mike L.

[tchatamba_inst]

We have had the local cat rep out.

The only alarm observed is Erratic Volts (168-2), a trend was made and the volts are steady at no load and the deviations increase with load.

They are proposing to flash the ECM and if that does not work replace the ECM.

[mikel]

OK, so if you have an alarm indicating a problem with the power supply, and a trend appears to confirm you have a problem with your power that is load related, how does that lead you to an ECM problem?  Was any other testing done, like putting a DMM on the power input to the ECM to see if the power is actually fluctuating or is the ECM incorrectly reporting a problem?

Frankly, based on the info provided so far, I would start doing a careful look at all engine wiring connections, especially ground and Battery negative.  Does the unit on-line rely on a charging alternator or a power supply to supply DC when when running?  What are they deviations you report in the power, spikes, dips, swells or sags?  If the power dipping or sagging, you could be affecting the actual fuel delivery and causing the power loss.  If the power is dropping low enough it may actually be reseting the ECM.

Before changing the ECM I would do a little more investigation, the ideal tool would be a scopemeter or trending meter with a fast enough response to capture the actual duration and magnitude of the deviations you report, A good quality DMM may work, but be sure it has an analog function or use the MIN MAX record function, or use an analog meter on the correct scale.  Also measure the power supply on the AC scale and look for ripple, if you have a high ripple (above 2 VAC), then measure it's frequency to see if you can define it's source.  Also check your ground connections and generator grounding, as it may be a possible contributor to an erratic DC power problem.

Hope that helps, Mike L.

[tchatamba_inst]

There are two sets of batteries, both have thier own chargers fed from the platform power supply, the battery voltage measured is 25 volts but the ECM displays 24 volts using electronic technician, it is this voltage that shows the ripple. It is the local Cat rep that is recommending the possible ECM replacement. The ECM is mounted on the engine an there are 4 plug connections between the DSLC and the ECM, we have checked all the connections accessable but we have not found any problems. Thanks for the help. Mike Reeby

[tchatamba_inst]

An update :: looks like the problem was with the voltage regulator going high causing the unit to go into low lag power factor, the reverse power relay picked up and tripped the breaker. Have replaced the AVR and it is now running okay...Thanks for the advise. Mike

[mikel]

Sounds like you found your problem, but I'm confused about some of the information you provided.  An AVR going to a high output and causing as low lagging power factor should not cause a reverse power trip.  The most likely trip would be overcurrent.  The DSLC is a real power controller, and are you also using it to control VAR share?

If the AVR went full field then shut off then the loss of field protection should trip, again NOT reverse power.

Oh well, at least you found it.

Mike L.