Converting standby rated generator to prime rating 1

[katwalatapan]

Hello,

I would like to inquire about any maintenance or other issues that could arise when a standby rated generator is retrofitted so that it could be used for peak shaving. I understand that the engine of the generator be it prime rated or standby rated is the same. I am currently working on a 70KW 3 phase 120V/208V Natural Gas generator with stand by rating. If I wish to use this generator for peak load shaving purposes I would have to consider prime rating for the generator. To retrofit the generator and use it for prime rated application what issues would I expect?

Thank you.

 

[dpc]

If you are thinking about doing peak shaving to reduce utility demand charge and trying to accomplish this with a single generator, you might want to re-think it. The demand charge is typically based on the highest average demand over 15 min, 30 min or 60 min (depending on the utility) during the billing cycle. If the engine does not start even one time during this period, for any reason, there is no reduction in your power bill. Also, many utilities impose a "ratchet" on demand charges such that they bill every month for the highest demand incurred during the previous 12 months. In this case, if the engine is down for maintenance for even one peak period, you will pay that demand charge for the next year.

The prime rating is lower for a reason. I would try to stay below the equivalent prime rating regardless of the original intent. You will need to modify the electrical interface to allow paralleling with the utility. For a 70 kW machine, I think any possible payback would be longer than you can justify.

 

[waross]

A prime rated set must be able to supply a 10% overload for one hour in twelve. Thus a 100 KW prime rated set will supply 110 KW on demand.
For standby service the running hours per year are much less and long life as measured in engine hours is not as great a concern.
The 100 KW prime rated set will be rated at 110 KW for standby duty.
The prime rated set may have added refinements such as a larger oil sump, an optional oil cooler or other accessories not found on the standby version.
In other instances the engines may be identical with only the nameplate changed, or a name plate indicating both prime and standby ratings.
The permitted loading will be a judgement call depending on the operating profile of the plant and management risk tolerance.
BUT I agree with dpc. I would add that the utility requirements for engineering, protection and control of a grid paralleled set may well cost more than the gen-set.

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

 

[katwalatapan]

Thank you Bill and DPC was your response. I will consider the points outlined to get a better understanding on how to approach this issue.

One more thing that I wanted to discuss is that most generators below 200KW are automotive gasoline spark engines modified for natural gas service. Do engines need to be diesel engines modified for natural gas to be used for peak load shaving? Also do you foresee any maintenance or operation related issues if modified automotive gasoline spark engines are used for peak shaving rather than diesel ones?

Thank you.

 

[waross]

I would rephrase that;
Most generators between 15 KW and 200 KW are diesel engine sets.
Most generators below 200 KW intended for natural gas fuel are gasoline spark engines modified for natural gas service.

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

 

[katwalatapan]

Thank you Bill.

So do we observe any maintenance or operational issues if gasoline spark engines modified for natural gas services are retrofitted to run as prime mover for peak shaving application?