When you choose a diesel generator set, you need to know the use case and the rating type. Generator sets come as standby, prime, or continuous. A data center may also use a special continuous class.
The right rating helps with generator sizing, diesel generator power ratings, load profile, load steps, starting current, and generator reliability. It also helps when you compare a standby vs prime generator. Site conditions like ambient temperature, altitude, and power factor also matter.
Gives the most power during a changing load when a utility power failure occurs or during test runs.
Up to 200 run hours each year.
Average load up to 70%.
No overload is allowed.
Gives the most power for long use with a changing load when it is used instead of utility power.
Average load up to 70%.
10% overload for 1 hour in every 12 hours.
Gives power for steady use at one load level, often for grid supply.
A special class for data center use.
Emergency systems, also called emergency standby power (ESP) systems, are often required by law for public safety. Diesel generator sets give short-term power during outages to:
Help people leave buildings and sites safely.
Support key equipment for vulnerable people.
Keep key communications networks running.
Optional standby systems use diesel generator sets to prevent business loss, delay, discomfort, or inconvenience. The owner or site manager sets the load. These jobs usually use standby-rated sets.
Prime power uses on-site generation instead of utility power, usually where utility power is not available. Key points:
Continuous use with a changing load.
Two or more generator sets are common: one runs all the time while the others give backup power.
Redundancy cuts downtime during maintenance or repair.
In peak shaving, the generator set supplies power during high-cost utility periods to cut energy costs. The controller starts and stops the set at set times.
For continuous base load, diesel generator sets send power to the grid through tie-in gear such as sync systems and switchgear. This use case fits the continuous rating.
Question: What is the main difference between standby, prime, and continuous ratings?
Short answer: Standby is for backup during utility outages, with limited yearly hours and no overload. Prime is for long use as a utility substitute with a changing load and limited overload. Continuous is for steady, constant-load use, often feeding the grid.
Question: When should I choose a standby-rated generator set?
Short answer: Use standby rating for emergency or optional standby jobs where the generator runs only during outages or tests, averages up to 70% load, operates up to about 200 hours per year, and must not be overloaded.
Question: How does prime power differ in application from optional standby?
Short answer: Prime power serves as the main source where no utility exists, running all the time at changing loads and often with multiple sets for redundancy. Optional standby supports an existing utility to prevent loss or discomfort during outages and usually uses standby-rated sets.
Question: What is 'data center continuous' and how is it used?
Short answer: It is a special rating class for data center use. It fits continuous, mission-critical data center loads.
Question: What is peak shaving and how is it implemented?
Short answer: Peak shaving uses the generator to supply power only during high-cost utility periods to cut energy costs. A controller schedules automatic start and stop at set times to work with or offset the utility during peaks.
