Diesel Generator Power Ratings: Standby vs Prime vs Continuous

Diesel generator sets are commonly used in a variety of sectors due to their dependable performance and high efficiency. They can be used for emergency power supply in the event of a power cut or used in places without connection to a power grid. When selecting a diesel generator for your home or business, you need to consider many factors, such as generator’s ratings. In this article, we’ll explain the three basic rating types - standby, prime, and continuous in diesel generators.

ISO-8528-1:2018 defines basic generator set rating categories based on four operational categories: Emergency Standby Power (ESP), Prime Power (PRP), Continuous Power (COP) and Limited-Time Running Prime (LTP). Read on and learn the application of power ratings for engines used in generating sets.

Standby Power Rating

Standby Power(ESP) is used to supply emergency power when the external power supply is interrupted, such as power outages. Standby power rated generators can supply reliable electricity as the main source of power for short periods of time. They are commonly used in many situations including residential, commercial and industrial areas and are ideal for critical organizations such as hospitals and data centers .

Typically, a backup diesel generator can be wired to an Automatic Transfer Switch (ATS), which will automatically transfer the load circuit to the diesel generator when it senses a failure or outage in the primary source. It will automatically shut down once it detects that mains power has been restored to the building. Standby diesel gensets paired with an ATS can ensure a seamless transition between power sources, maintaining continuous and reliable power supply.

Please note that stand power has no overload capability. This power rating should be applied where there is a reliable public power supply. The engine is allowed to operate at an average 80% load for no more than 200 hours per year at the standby power level.

Prime Power Rating

According to ISO-8528-1, a prime power (PRP) generator set must provide power for an unlimited number of hours per year, with reference to agreed operating conditions and crucially with maintenance intervals being carried out as per the manufacturers guidelines. Prime power rated generators can run anytime and continuously operate under variable load maximum power. These generators are good for situations where mains power is inaccessible. They are commonly used in applications such as oil and gas, mines, and remote construction sites.

Prime power rated diesel generators are used to supply electrical energy where power can be purchased. The prime power class has the following two application categories.

Infinite time running mode

The engine operates at a prime power level under variable loads for an unlimited time per year. The variable load here means that the average load does not exceed 70% of the prime power during any 250 continuous hours, and the total time of operation at 100% load per year should not exceed 500 hours. Allow the engine to run at 10% overload for 1 hour in a 12-hour cycle. The total running time of 10% overload per year shall not exceed 25 hours.

Time-limited run mode

Prime power levels are applied under non-variable loads that limit run time. This mode is used in the case of tight power supply. The engine does not exceed the basic power and runs in parallel with the mains at a fixed load for a maximum of 750 hours per year. But users should be aware that any engine used under high load for a long time will affect its lifespan. Continuous power level should be used if operating at base power level for more than 750 hours.

Continuous Power Rating

Continuous power (COP) can be applied to supply electricity at full load for an unlimited time per year. The continuous power rating has no overload capability. Continuous power rated generators are most widely used in applications where having no access to the power grid, such as mining, agriculture or military operations. They are similar to the prime power rated units, but the difference is that continuous power generators do not provide a variable amount of power, but instead provide a steady load across the periods of time it is used.

Need help with choosing a diesel generator?

With the information above, you should have a basic understanding of the generator power ratings. But investing in a diesel generator for your business is not an easy task, you need to take into account other factors such as generator size, noise level, fuel efficiency, budget, etc. If you are not sure which generator best fits your needs, contact Dingbo Power today. Our team is here to help and can help you find the right generator for your business.