How to understand diesel engine power ratings.

There are many diesel engine power ratings for use in driving generator sets.  This post will allow you to understand them.

The important ones that I will cover here are:

• Standby
• Emergency Standby
• Prime Power
• Continuous
• Peak Shaving

Diesel Engine Power Ratings – Emergency, Standby, Prime, & Continuous

When you look at most generator drive diesel engine specification sheets, you will notice that there are always more that one power rating available.

Also, most of these ratings are provided in a couple of different units (HP, kW, PS).  This allows for the use of this information by power generation professionals around the world.

The manufacturers give you all of the information you need to select the correct engine for you or your customer’s application.

The most common three ratings are: standby, prime, and continuous, so I will discuss those first.

Standby Power Rating

Standby is the highest of the diesel engine power ratings available.

It is not meant to supply power for long periods of time, but only as a backup power source.

It is intended for facilities that are normally powered by grid power, but require a backup source during power interruptions.

Since this is the highest engine rating available, there usually isn’t any overload capability.

Durability can be affected by running at these highest diesel engine power ratings.  So all engine manufacturers put an annual limit on how often the unit can be run.

These limits can vary, but a typical one is 200 hours per year.

This allows for use during all power interruptions through the year.

Also required are annual, or semi-annual load tests.  Here generator is hooked up to a load bank and the entire system is checked for operational readiness.

There are a few different types applications for standby power: critical, emergency, and optional standby.

Prime Power

This rating is used when a facility generates power for it’s own use on-site.

One reason for this could be because the electrical grid hasn’t yet reached the facility.  This is a common occurrence in remote or northern villages, mining and oil filed explorations, or military camps.

Another reason for generating your own power on-site is to make use of waste heat.  It could be used to preheat water for boilers or as radiant heat for the facility.  This type of setup is called combined heat and power (CHP) or simply cogeneration.

The annual usage of an engine at this power level is unlimited, however the load does have to vary at times.

Continuous Power

This is the most heavy duty of the diesel engine power ratings.  So it makes sense that it also the lowest power rating as well.

A continuous generator set is usually run in parallel with the grid utility.  They cover the power requirements of a facility, selling the leftover power into the grid.

The load rating never changes, and there is no limit to the annual usage.

A typical continuous power installation will make use of CHP cogeneration.

That was a summary of the most common diesel engine power ratings.

Some engine manufacturers break it down even further.  One that I’ve work with had two different continuous ratings, others differentiate between legally-required standby and optional standby.

Please interact with me on Twitter or LinkedIn if you have questions about interpreting diesel engine power ratings from your manufacturer.