Paralleling a Deisel and Turbine 1

[RonShap]

I have a telco client that wants to Parallel a 750kW Deisel and 750kW Turbine. The turbine is existing, and the deisel will be new. A new deisel is cheaper than a new turbine to buy. Clearly we will upgrade the govenor and voltage regulator on the turbine, but can a deisel play nicely with a turbine sharing load? Especially during load chages?
Anyone have some suggestions?
I have paralleled turbines together without problems. I have parralled deisels together without a problem, but not a deisel and a turbine together.

 

[jbartos]

Suggestion: Visit

http://www.basler.com

etc. for more info

 

[alehman]

I would think this should be doable. You said you are upgrading your turbine controls. Consult with the control manufacturer and make them aware of the diesel manufacturer and type of control system furnished with it - if possible before the new system is purchased. They should be able to offer suggestions.

 

[RonShap]

Thanks,
My main concern is how the two different types of machines will react to load changes, since the turbine is such a stiff source as compared to the deisel.

 

[AusPowEng]

RonSharp,

Your concerns are justified if the two units are islanded (ie. is this a backup supply?) as during faults they will clearly behave differently.

The load sharing issue can be resolved with the use of a modern controller.

A transient study would be the next move to quantify the system stability during faults and application/loss of loads, however accurate modelling the governors is always a pain with Diesel units, let alone these small turbines. Is your turbine an aero-derivative (i.e. Pratt & Whitney) or industrial (i.e Solar) ?

Regardless of the prime mover response, the two packages will have different moments of interia and this alone requires further review.

Being a TelCo client, a full stability study may be justified for assessment of supply continuity.

Regards,

AusPowEng

 

[AusPowEng]

RonSharp,

A clarification to my first sentence:

Your concerns are justified if the two units are islanded from the grid (ie. assume this a backup supply rather than co-generation?) as during faults they will clearly behave differently (than when operating in parallel with the grid).

 

[RonShap]

These are islanded for backup service, not in parralel with the utility.

I have to do some research into stability studies. Any suggested reading?

 

[zqew05]

An outfit called Mustang Engineering will have your solution. They were our contractors for our electrical issues. We have turbine and diesel gensets in our jobsite. I don't know their website.

 

[GerH]

We have done a 5MW Gas turbine CHP ( Allison KB7) plus 2.2MW Mirlees diesel on one site and a 4.2MW Gas turbine CHP ( Allison KB5S) plus 3.4MW Mirlees diesel on another site with no issues. As far as I know the diesel has more momentum than a corresponding size GT. The diesels are set for droop ( speed and voltage).

 

[advidana]

Why does the client want to parallel a different type of engine generators ion the first place. A side from all the other discussions if it is possible- maintence, training and spare parts would be different and very costly. Usually it is better to have one type of system.

But I like deisel engines, they are tuff . But, if you have turbines, stay with the same type of system or replace the turbine too with a desiel. Look at the long term cost not just first cost. I believe the life and maintence are longer with turbines, less moving parts.

Look at the long term cost not just first cost.

 

[RonShap]

advidana,
This client has many many sites throughout the country. Many turbines and many deisels. In this case, considering first cost will be similar to the whole picture. The turbine is in good operating order, and the cost of a 750kW turbine is much more than an equivelent sized deisel.

 

[alehman]

RonShap - You say the turbine is a stiff source compared to the diesel. Do you mean the intertia of the turbine is greater than the diesel, or are you refering the electrical impedance of the machines?

I agree with the concern that numerical modeling of these systems will be difficult. Obviously there are many components that must be considered (machine, prime mover, governor, voltage regulator, exciter, etc). Unless you have software that is known to accurately model the specific equipment, I think it would be unlikely to get meaningful results. CYME's CYMSTAB program includes a number of generator control models. They may be able to provide what is needed.

It is important match the generator electrical characteristics (e.g. impedance, winding pitch, fault decrement), as closely as possible to minimize circulating currents. In a telco application your load is likely to have significant harmonic distortion. This makes matching electical charcteristics more important. Your control system should include automatic VAR sharing (some inexpensive schemes do not).

I assume keeping the machines separate is not an option? If you operate them in parallel and either one fails you loose all your load. Consider keeping them separate (or using automatic load shedding) so if one fails you only loose half the load.

Also see
thread238-64661

 

[EddyEE]

I had a similar project paralleling two different diesel generators with three steam-turbine driven generators. You said that the governors and voltage regulators of the turbine-gen will be upgraded/retro-fitted and the diesel-gen is new. The most important that you should consider here is the compatibility of your governors and voltage regulators. In other words, your governors should be of the same brand (i.e. woodward) and your voltage regulators are also of the same brand (i.e. basler). Of course the type and model may vary depending on your equipment. Next is your application. How are you going to operate them? Dividing the load equally at all times? In my project, the diesel-gens are running isochronously with fixed base-load (more economical) while the turbine-gens take the variable loads. Here, response time is no problem.
I hope this helps.

 

[jbartos]

Suggestion: Visit

http://www.turbowinds.com/windiesel.html

etc. for more info

 

[Foofoo]

Ron,

I have experience paralleling steam, diesel and gas turbine units of vastly differing capacities on one site without any problems whatsoever.
You just have to tweak your control systems properly otherwise the turbine may try to hog the load.
Go for it.

Colin.

 

[mikhe]

A natural gas reciprocating engine has much closer load acceptance profile to the turbine than the diesel. Diesels react to the load very quickly and , as I understand it will grab the load. This contradicts what another commentator has said. (perhaps I'm wrong ?) It has also been said that modern controllers can compensate for this imbalance of load acceptance capability, and this is true but you will have significant efficiency loses. The gas engine will be best in my view.

 

[harshal]

Hi,
I am with Cummins Indai and wehave being doing this job all tne time.
One of our major job was paralleling 5 DG sets with 2 x * MW turbines.
I do agree that transient analysis can be helpfull.Pl remmember that for DG alternators the Xd'is very low and hence we need to consider fault level currents.
However with our expereinces it should not be a major problem
Rgds

 

[zqew05]

Whatever you do, pay the extra money to get assistance from people who does this for a living, no matter how great the inhouse talent is. You might have an increase in first costs but you prevent screw-ups and long-term added costs. We made the mistake one time of copying another facility's construction blueprint to save on R&D. It was a great idea until some Engineer decided to reduce the physical size of the new facility to bare minimum, to save more money. The redesign/rewiring/re-engineering costs sdded to the total bill, was big enough that we could have built another one of the photocopied facility, then some more.