Comparing Standby, Prime, and Continuous Ratings for Generators

These robust units aren’t a one-size-fits-all
19 January, 2022 by
Comparing Standby, Prime, and Continuous Ratings for Generators
T&T Power Group.

For anyone considering a power generator investment for their industrial facility or commercial business, they have a few options to choose from: standby generators, prime power generators and continuous generators.

Selecting a generator set with the correct rating is critical to any power generation project large or small. Basing a purchase on the wrong power rating can lead to huge headaches when it comes to reliability, upfront costs and maintenance requirements.

In this article, we’ll get into what you should know about each generator type and their respective rating so that you can make the most appropriate purchase decision:

Ratings for standby generators

Standby generators are backup generators used for emergency situations such as power failures and blackouts. These generators have the ability to run for short periods of time as the main source of power, just long enough to keep operations running until the electrical grid or other prime power source recovers, but they are not suitable for continuous operation over long uninterrupted periods.

A standby generator should have a maximum average load factor of 70% and may be operated up to 500 hours per year. For example, a standby generator with a nominal rating of 500kW should be run for up to 500 hours a year with an average load factor of 350kW.

Furthermore, standby power ratings should NOT be applied in any situations outside of true emergency outages - including predetermined outages with the utility company under UL guidelines, or peak shaving and demand response programs.

Generally speaking, standby generators are most appropriate for anyone that requires a reliable access to power at all times. With highly unpredictable weather and an aging power grid, no one is immune to a blackout - but a rest assured, a standby generator will get you through the darkest and coldest periods while keeping your investments safe and your people happy

Ratings for prime power generators

Designed to run long-term, prime power generators serve as the primary or main source of power for a given operation. Suitable in situations where there is no access to power lines, these generators are often created to provide a variable power supply to be drawn over time.

Commonly used in applications such as oil and gas, mines, rock crushing plants and remote construction sites, prime power generators are most often used to establish a location that is distanced from other power sources. This includes remote building sites or areas that are more difficult to access. These generators can even serve as mobile solutions.

The rating for prime power is the maximum amount of accessible power at the variable load for an unlimited number of hours each year in a variable load setting. With that said, the variable load must not average more than 70% of the prime power rating during any operational period. It is advised to avoid any overload situations, however a 10% overload capability is available for a period of 1 hour within a 12 hour operational cycle, for a maximum of 25 hours in a single year. For example, a generator with a 500kW prime power rating may be operated for an unlimited amount of time as long as the average load factor does not exceed 350kW, and in emergency situations it can be overloaded to 550kW.

Ratings for continuous generators

Similarly to that of a prime power source, continuous generators are essentially designed to run on a consistent basis as the main source of power for an operation. However, the difference between continuous and prime generators is that continuous generators do not provide a variable amount of power, but instead provides a steady load across the periods of time it is used.

A continuous power rating is used in applications where power supply is at constant load capacity of 100% for an unlimited number of hours per year. Continuous power generators are most commonly used in parallel with the electrical grid to provide base-load power to a facility, with heat from the engine used in addition to the electricity (Combined Heat and Power).

For all of your power generator needs, T&T Power Group is here to help.

Contact our team of power generator experts to learn more about which type of unit would be the right fit for you.

Share this post