Regenerative Power

[SilverArc]

Hi,

Is there a thumb rule that an emergency diesel generator can absorb real power that is certain percentage of its capacity. for example: 10 % of total rated capacity. We have this 1600 KW, 4160 V generator for mine hoisting application.
The manufcturer told me that new generators being turbo in nature and have low inertia and cannot handle much. But looks like he was a novice and did not know much.

We are trying to justify the use of load banks if this generator cannot absorb completely.

One last point:
IF any body can advise, where in US or Canada , a company that sells USED power transformers in range of 7-10 MVA 44 KV/13.8 KV.

Regards,

 

[dpc]

It's the engine you need to be concerned with, not the generator. 10% power for how long?

 

[SilverArc]

Thanks for reply dpc.

It was just a comment actually. The power will be regenerated for 1.6 min, while the hoist is going down.

But the issue is that if this depends on engine, Does it have an relation with size of generator. I mean any percentage relation.

Any body can advise any used transformer supplier in US or Canada.

Thanks

 

[davidbeach]

Best to check with the engine manufacturer. Too much motoring of the generator can do serious damage to the prime mover. How much is too much is dependent on the prime mover.

 

[dpc]

You should check with engine supplier - we normally set reverse power relays for engines at around 10%, but if you're doing this repeatedly, it might be a different story.

 

[waross]

The first thing that happens is that the regeneration supplies the other loads on the generator. As the regeneration increases, the engine will be driven overspeed. The amount of overspeed will depend on the individual engine. There is a wide variation in the amount of drag or resistance to an external driving force between various diesel engines.
On smaller engines, up to about 500 KW, there is no immediate danger from moderate overspeed. Think of a truck with a 300 KW or 400 KW or 500 KW engine going down hill in the mountains.
If the regeneration is such as to drive the engine at excessive speeds then there is a danger of mechanical failure of bearings, connecting rods and other reciprocating parts.
There are other issues with large slow sets or older worn sets, such as wet stacking which may even occur at light loading for prolonged periods, but would not be a problem with your 1.6 minute time frame
On a genset of your size I would expect the protective relays to take it off-line on overfrequency long before the engine suffered mechanical failure.
I believe that it is good engineering practice to supply a load bank suitably sized to absorb all the expected regenerated power from a critical load such as a mine hoist.
respectfully

 

[JBinCA]

If I understand correctly, you are talking about running a drive in regen mode (while your hoisted load lowers) and trying to get the generator to absorb the real power.

Waross is right. The hoist motor becomes a generator in this scenario and the power it produces will be available to power the other loads on the system - as long as there are other loads of sufficient size. The generator will simply see this as a decrease in load and will slow down.

I have never heard of relying on reverse powering a generator to brake a load by running the drive in regen mode. The gen will only accept so much reverse power before it trips, overspeeds, or something along those lines. Then what happens to your hoisted load? I think you need to add that braking resistor.

Why not talk to the drive manufacturer about the application? The major manufacturers have industry specialized support (mining being one of those key industries).

can-Am machinery sometimes has used XFMRs of the size you're looking for (though not necessarily the voltage).

 

[itsmoked]

I do not think the engine will slow down JBinCA. But what you mean is the throttle will "come back" or reduce.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[JBinCA]

itsmoked is right. I meant reduce throttle, thereby producing less power at the same speed.

This would be the case if the generator were in an isochronous mode of regulation. If it were in a droop mode, it would actually slow down some small amount.

Regards

 

[davidbeach]

No, in droop it would speed up. In droop maximum speed is at minimum load and minimum speed at maximum load.

 

[waross]

A reduction in load will always result in an increase in speed. In droop mode the speed change will be inversely proportional to the load. In autogenous mode, the governor will detect any change in speed and correct the speed/frequency back to the set point. (Usually 50 Hz. or 60 Hz.) The corrective action may not be immediate. Those who are familiar with PID controllers will recognize the action as Reset.
respectfully

 

[apowerengr]

Try Jordan Transformer (Jordan MN), Solomon Transformer (, T&R Electric Supply (Coleman SD) or Equipment Marketing & Listing Service (Appleton MN).

 

[DanDel]

The IEEE 242 recommended max motoring power for a diesel engine prime mover is 25%. The pickup for a reverse-power relay (32) is typically set significantly lower than this.