Running prime rated generator for few hrs. 1

[katwalatapan]

Hello,

To my understanding generators could run either in standby rated configuration and prime-rated configuration i.e. 24/7. Running the generator at rated configuration would affect the life of generator components.

What impact would it have on generator components if the requirement is to run the generator for 6hrs every day? It would not be on standby nor prime mover. Is there such a configuration where we could run a generator in such manner and what would be its potential ramifications?

Thank you.

 

[waross]

Can you organize your question before I organize an answer.
A standby set may identical to a prime rated set, or, the prime rated set may have extra accessories to extend the life. Extra equipment may include oil coolers, larger oil sumps, more features in the protection package, and anything else you may think of.
The standby set is often a "Plain Jane" set with a minimum of extras.
In the smaller sizes the same set may be rated either as a standby or as a prime power set.
Eg: 110 KVA standby, no overload permitted, or 100 KVA prime with a limited 10% overload permitted.
What is your application, your load and your generator size?

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

 

[katwalatapan]

Hello Waross,

Thank you for your response. I apologize if my question was not organized properly.

My application is to run a prime-rated generator for 6hrs a day to "Load Shave" i.e. take some load off the electrical grid. Now I wanted to know if there any ramifications to the life of the prime-rated generator as well as any maintenance issues, by running it for 6hrs a day rather than 24/7 operation for which it is rated.

Generator size I'm considering is 180KW 3 phase Natural Gas. The load I'm planning for the generator to take on is about 140KW.

 

[waross]

Simple arithmetic predicts about 4 times longer life. Four starts a day will take a some hours off the life but you may get 5 or 6 years before you need an overhaul. At that size, it is cheaper to sell it and buy a new set.
I have a small (6 KW) diesel set with 18000 hours and it still works fine. It will probably last for quite a few years on occasional standby duty.
A prime set at 78% of rated load should have no issues. (Either with overload or underload.)

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

 

[catserveng]

Here is a short excerpt from CAT's Application Guide,

Emergency Standby Power
Typical usage of 50 hours per year with a maximum of 200 hours per
year. Typical variable load factor of 70%.
Standby Power
Maximum usage 500 hours per year, up to300 hours of which may be continuous running with varying loads. No overload is available.
Rating is equivalent to Prime +10%.
Load factor maximum is 70% of Standby rating.
Prime Power
Unlimited hours of usage. Load factor (70% maximum /80% if no
extra cost) of the published Prime power over each 24 hour period.
10% overload limited to 1 in 12 hours but not to exceed 25 hours
per year. The 10% overload is available in accordance with ISO
3046-1 (2002). Life to overhaul of the engine is dependent on operation as outlined in ISO8528 (2005) and time spent during operation above 100% load may affect the life to overhaul.
Continuous Power
Unlimited hours of usage. Load factor 100% of the published
Continuous Power. Generally, as ISO 8528 (2005) Continuous power.
Note: Operating above these rating definitions will result in shorter life and higher generator and engine costs per year.
The International Standards
Organization (ISO)ISO 8528-1 (2005) defines three types of duty:
· Continuous Operating Power(COP)
· Prime Running Power (PRP)
· Limited-Time running Power(LTP)
Continuous Operating Power
COP)Continuous operating power is the
power a generator set can operate at a continuous load for an unlimited number of hours under stated ambient conditions. Maintenance according to the manufacturer must be followed to reach these standards.
Prime Running Power (PRP)
Prime running power is the maximum power a generator set hasduring a variable power sequence for an unlimited number of hours under stated ambient conditions. Maintenance according to the manufacturer must be followed to reach these standards.
Limited-Time Running Power (LTP)
Limited-time running power is the maximum power that a generator set delivers for up to 500 hours per year under stated ambient conditions. Only 300 hours can be continuous running. Maintenance according to the manufacturer must be followed to reach these standards.
Specifications are often stated inISO terms and standards. Table 1
shows ISO genset ratings and correlating Caterpillar genset ratings.
Generator Set Ratings
ISO Caterpillar
ESP Emergency Standby Power
LTP Emergency Standby
PRP Prime
COP Continuous

In general terms, I would describe your application as PRIME. Depending on your actual engine arrangement the ability to do daily starts and stops will probably not affect your overall service life. On an engine that size I would recommend a prelubrication pump and a jacket water heater to assure start wear is minimized. Also for a natural gas engine you need to assure proper warmup and that the exhaust system is properly designed to deal with the condensation at start on a daily basis.

Frankly, your engine dealer should be able to provide you the best information on your specific unit. Also things like exhaust aftertreatment or any heat recovery equipment you might install may need special attention for daily starts and stops.

Hope that helps, Mike L.

 

[katwalatapan]

Thank you very much Mike and Bill.