COP and PRP 2

[SENGUTTUVAN]

For an emergency Diesel Generator set, among the different power rating definitions , Continuous Power (COP) and the Prime Power Rating(PRP)which one is to be selected for which application. For the PRP it is indicated that the average power output is 70% of prime power over 24 hours operation where as COP rating indicates that it is 90 - 100% of continuous power rating. Whether it means that COP is better than PRP? Thanks to clarify.

 

[catserveng]

Power rating for a given displacement engine are usually based on the ability to meet projected service intervals. Say the engine you are looking at has displacement of 32 litres and has a standby rating of 1000 ekW, a prime rating of 800 ekW and a continuos rating of 650 ekW. The continuos rating will have the longest time to overhaul and will likely have lower exhaust and engine temperatures. The standby rating will have the shortest time between overhauls and highest engine operating tempertures. The prime rating will fall in between.

Most emergency standby units in actual service typically have about 40-60% of their rated power applied due to how calculations for site emergency power supplies are done. But most are required to regularly test and prove ability to provide rated power for a short period of time, usually four to eight hours.

COP isn't really "better" than PRP ratings, it really depends on what you're trying to do with the unit and how it works in your application. For awhile we used to take standby units and parallel them with the grid during peak conditions for demand response, typically we ran these standby rated units at prime or continuos power levels to minimze wear and tear on the unit, also to limit emissions.

Most standby units I'm familar with usually get less than 500 hours in 10 years of service, over half of that time below 50% (or less) of rated power. So paying extra monies for a larger unit with a lower rating may not make sense.

In general, continuos power rating are used on power systems operating a high percentage of the time with power levels at or near full load, like co-gen units, rock crushing plants, etc. Prime rated units are typical in areas like ships service generators, site power applications with peak periods, like sites with high air conditioning loads for part of the day or high demands for equipment starting then lower operating load levels. Emergency or standby rating are for short term high output requirements like hospital life safety loads, or critical data centers that would likely return to utility supply as soon as it returns.

This is where the sizing programs and the help of an experienced consulting engineer familiar with on-site generation can be used to make sure you get the right power rating for your site and application.

Hope that helps.

 

[SENGUTTUVAN]

Thank U very much catsereng for your excellent reply. Based on my understanding of your explanation , for an Emergency Diesel Generator ( the engine for my proposal is for the chemical process plant for lining up the DG for critical loads during grid pull out), it is sufficient to have Prime rating instead of COP. From your experience , can you tell how much will be the difference in cost implication between COP and Prime rating Engine?

 

[catserveng]

Likely the Prime rated unit will be fine for your application, as it will likely allow some overload capability if needed. Many standby rated machines these days have virtually no overload capacity, what you bought is what you get.

I can't speak to pricing, many issues affect the pricing on these machines, such as volume, demand, competition, etc. In very general terms, a standby rated machine would likley be a lower price than a prime rated, and the continuos machine whould likely be the most expensive per ekW, since it is usuallay a larger machine for a given power rating, has a higher warranty exposure, and likely more and larger sized support equipment, like cooling and fuel supply systems.

I am a fan of EGSA, and find their standards and reference book helpful for answering these kinds of questions.

http://www.egsa.org/standards/_docs/final/std101p.doc

Above is a link to a performance standard that applies to the questions you are asking, and you may find it helpful, as possibly other areas of EGSA's website.

Hope that helps,

 

[SENGUTTUVAN]

Thanks a lot catsereng.