Running diesel generator as a synchronous condenser 2

[Power0020]

In a facility with a power factor penalty, the guys there thinking about running the emergency diesel generator in parallel with grid in a synchronous condenser mode.

Two ideas here:

1- Run the DG with low driving power to supply generator losses with full reactive power support.(Generator)
2- Run the DG to catch the synchronous speed of the generator then reduce the fuel intake with excitation. (Motor)

For the 2nd option, the reverse power protection setting should be modified to avoid tripping.

Economics, running a motor from grid is cheaper than using fuel and associated carbon tax.

I am not aware of issues rising from running diesel engine at low loading? is it possible to drive the diesel generator with no fuel?

I read somewhere online that overspeeding of diesel generator in case of motoring can damage the bearing, I wonder if the motor is synchronized to the grid, why would overspeeding happen?

Any clues?

 

[HamburgerHelper]

I am just a sparky but from this thread it sounds like if lubrication gets into the air intake it can overspeed.

http://www.eng-tips.com/viewthread.cfm?qid=234346

 

[itsmoked]

Me thinks it would be better to get a synchronous condenser.

I know a company that decided to run their emergency diesel generator as their power supply during one of PG&Es greedier moments a few years back. They were loving it as it was costing them a 1/3 less. However the air quality board got wind of it and fined them a fortune for using their emergency diesel generator in a non-permitted manner.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[crshears]

Idea 1: feasible but uneconomical, due to the dead loss of the Diesel engine's pumping power consumption, unless the electricity is very cheap indeed, plus there will be unnecessary wear and tear on the engine leading to more frequent overhauls.

Idea 2: won't work; "fuel intake" [I presume you mean fuel consumption] can only be reduced by moving the fuel rack to zero. Adjusting excitation will effectively only adjust VAR production/absorption or bus voltage.

Running a Diesel engine at low or very low loadings can and often does lead to engine fouling and carbon build-up due to sub-optimal cylinder and exhaust passage temperatures.

Motoring from the grid at zero fuel rack? See idea #1 comments.

As to your last point, I agree with you; overspeed due to motoring seems a bit of an oxymoron to me.



CR

"As iron sharpens iron, so one person sharpens another." [Proverbs 27:17, NIV]

 

[Power0020]

Motoring from the grid at zero fuel rack? See idea #1 comments.

I think you mean Idea #2 ?

 

[FreddyNurk]

There was another thread recently asking a similar question about running an existing set.

Low loading of the set is less of an issue with modern engines, but still an issue nonetheless.

Whilst the load present during motoring is quite small, its still non zero, so there would be whatever losses are present in rotating the diesel that would need to be accounted for in terms of electricity consumption. There is also the issue of possible damage to the engine due to running in such a manner. The control system would likely need to be altered to allow for VAr control as well.

The most pressing issue is that the system is meant to be a backup supply, using it as power factor correction will likely compromise its ability to meet its intended purpose of backup power, which is not what you want when you need the backup supply.

The cheapest option thus far for power factor correction is capacitor based.
Using a generator unit as a synchronous condensor might make more sense if its not designated as backup plant and operating costs are cheaper than capacitors, but its unlikely. Inverter units with adequate capacity to provide the amount of VArs typically needed are far more costly than capacitors.





EDMS Australia

 

[GroovyGuy]

All in all, I believe this to be a rather lame idea.
Your best bet is to install a bank of caps.
BTW how many VARS are you looking for?


"I have not failed. I've just found 10,000 ways that won't work." Thomas Alva Edison (1847-1931)

 

[waross]

I have seen it done by a utility.
Yes you can, technically.
First, however you must obtain the permission of the utility to run a generator in parallel with their grid. There are serious issues with back-feeding the grid if there is a grid outage.
Generally if the utility does give permission they will want a lot of protective relaying to prevent back feeding into a fault or into a dead line.
If the utility grants permission:
The normal way to do this is to sync the generator to the grid and then advance the governor (in droop mode) to pick up about 3% to 55 of rated load. Now increase the excitation until the generator capability limit is reached.
Issues; Slobbering. The the combustion pressure is ported to the back of the compression rings. The rings even on a new motor may not seal well with light loading. This is an issue with older sets and I have seen it happen on a couple of brand new sets. One new set pumped enough oil out the exhaust to starve for oil and shut down on low oil pressure on its first run. Less than an hour.
As well as oil loss, slobbering can lead to blobs of burning oil being ejected fro the exhaust stack.
Another issue is engine temperature. The engine may well run too cool with little load. This may lead to accelerated wear of the pistons, rings and cylinders. If the manufacturer becomes aware of the mode of operation, you may expect the warranty to be voided.
Motoring the engine with no fuel: All of the above somewhat worse with the exception with less possibility of the oil ejected from the stack being on fire. Add to that possible damage to injectors. Some injectors are lubricated by the fuel. No fuel, no lubrication.
The pumping losses of the engine will be there regardless. You can supply them with fuel or with electricity.
A better solution which I have also seen is to replace the largest motor in the plant with an oversized synchronous motor and over excite the motor. This works even better with many problem loads as you will have extra torque available for transient overloads.
From the point of view of supplying KVARs to correct the power factor this is a good idea, but due to the issues that I have mentioned, a Good Idea may not be a Good Solution.

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

 

[cranky108]

Assumption that most of the loads are induction machines. You can use capacitors to correct power factor, or use a different type of motors. Also some types of drive systems can help with poor power factor.

If you run your generator in parallel many utilities will require additional protection on both the generator and intertie. So I don't recommend it.

 

[Hoxton]

The earlier thread referred to was, I think

Running a DG to compensate reactive power demand
thread238-421161

Taking a Typical emergency generating set and converting to mains parallel in any form is possible, but usually requires a new control panel since modifying the existing one may not be practical / economic

 

[FreddyNurk]

"The pumping losses of the engine will be there regardless. You can supply them with fuel or with electricity."

waross said it better than I.

EDMS Australia