We have synchronized 4x 2000kva generators at 6.6kv. The load voltage is reduced to 400v 3phase. This feeds 4 large port cranes with large installed power. Reverse power is experienced while in operation.

Does anybody have a way of suppressing this RPower?

I think this is from the regen action of the main hoists / 1000kw each.
What do you think about installing suitable power resistors reducing the power factor?

This to be done through a step down transformer on the generator output.

[email protected]

 

Hi Mike

How long have you been experiencing this problem? did this happen before or only recently?

 

Mike...

can you identify a pattern with regard to which/when Gen's are tripping? How about identifying protective-relaying action(s), if any?

Regards,
Phil Corso

 

Mike Arnold,

> How long have you been experiencing this problem? did this happen
> before or only recently?

I have seen a similar problem before, when, a few months after new cranes (and diesel gen-sets) were installed all of a sudden the new cranes began to experience a lot of problems--mostly the main breaker was tripping, but also the diesel gen-sets would occasionally trip on reverse power.

After a couple of days (over both shifts) of observing crane operations it could be said the cranes were being very "aggressively" operated, especially in the hour just before a scheduled break.... Usually, the operators would be moving the hook back from the ship as fast as possible and then push the joystick in the opposite direction as far as possible, or, with a box on the hook they would they would lift it as high as possible and then lower it as fast as possible while moving the hook (the latter was blamed on crane "controls"--as most operational problems usually are, eh?). Then, when the crane was "out of order" the break could begin and wouldn't end until the electrician came to reset the main breaker or the mechanic came to re-start the diesel after inspecting it and the generator and the electrician would inspect the other relays and reset the reverse power relay.

The rest of the story gets ugly, but, after the drives were essentially "re-tuned" and the operators were given another course in crane operations, most of the issues stopped--though for several months there was a constant chorus from the operators of, "The crane is too slow--and isn't as fast as it was!"

The productivity gains (boxes per hour) over the old cranes promised by the crane supplier never materialized, and productivity did increase by a couple of tenths of a box per hour, but, for all intents and purposes before and after the tripping incidents productivity was unchanged from before the new cranes were installed to after they were installed. Virtually the same number of boxes per hour were being moved through the facility regardless of the vintage of the crane.

There was a LOT of back and forth over a three-to-four week period (which was interesting to follow from a 'distance'--though the slings and arrows were always aimed at "the controls" and fired every available chance). I was fortunate to be working with an experienced field service engineer who had worked shore-side container cranes for many years, and had LOTS of stories to tell,

So, the question of when the problem started is very valid. This, in addition to possible shared governor tuning issues and possible (but not likely) digital drive tuning may be at least partially to blame. I have also seen it take a few weeks to get everything tuned for multiple diesel gen-sets to operate relatively smoothly (and most of the tuning was done by the diesel engine representatives who were adjusting governor settings--though this was long before my power generation days so I didn't really know too much about what they were doing or why or how).

Oh, and once on one new rubber-tired gantry crane in the yard the DC drive started tripping when a box was being picked up or the crane was being moved after a few months of trouble-free operation. The problem was eventually traced to water in the fuel causing the paper element in the fuel filter to swell and restrict fuel flow. I had mentioned while going over the drive that the diesel seemed to be straining more than would be expected. The diesel mechanic noticed the fuel rack was nearly full open when the unit was idling and would hit the maximum mechanical stop when a load of any sort was put on the diesel, which would cause the diesel speed to drop and the current through the drive to increase to above the trip setpoint--so the problem appeared to be the drive, but it was really the diesel. When the diesel mechanic removed the filter and cut into it it was very obvious the paper pleats were all "closed" and when we sampled the fuel it had a fair bit of water in it.

As Mr. Corso says, if you can spot patterns or trends of certain diesel gen-sets experiencing frequency fluctuations or "excessive" load swings this can be very useful in understanding what might be the cause.

So, look at all possibilities.

And, please write back to let us know what you find!