Generator Set Ratings Explained
A critical aspect of generator performance is matching the right genset to specific applications across industries. This guarantees that the power system used to supply the generator is in accordance with the genset’s capabilities, which guarantees that the generator performs as advertised and features the longevity and long-term reliability you need to deliver exceptional customer service.
Various organizations and governmental agencies have established specific rating systems for generator use based on generator type, power output, emissions, and application. There are four primary rating categories you’ll have to consider under these frameworks:
- Industry Standard ratings
- Manufacturers’ ratings
- Governmental Emissions ratings
- Custom industry ratings
Industry Standard Ratings
The International Organization for Standardization (ISO) regularly updates a series of basic generator set ratings (see ISO-8528-1:2018). These baseline categories are based on four different operational functions, each determined by the genset’s maximum power output as it pertains to running time and load profile.
Emergency Standby Power (ESP)
This generator set rating involves the maximum allowable power output that a generator can deliver, designed to provide emergency power to facilities in the event of outages or disasters. ISO-8528 does not limit runtime of generators during these types of outages.
Prime Power (PRP)
The PRP rating allows a generator to temporarily supply off-grid power to a source, rather than receiving it from a standard utility. These ratings are often used in remote working situations where traditional power grid access is unavailable.
Limited-Time Running Prime (LTP)
Gensets rated for LTP are generally used by utility companies to provide supplementary electrical power as part of particular types of financial arrangements. Per ISO standards, a LTP-rated genset must provide power for up to 500 hours per year.
Continuous Power (COP)
This rating applies to gensets that power applications independent of any grid-based utility service. The generator is solely responsible for providing constant load and is often used alongside other gensets to provide continuous power.
The above ISO standards are only a baseline for generator set ratings. Most companies need specific applications or performance capabilities that are tailored to their customers’ needs.
Genset ratings must take into account gross power output versus net power output. For example, generators may have a third-party cooling package installed in a different location than the generator itself. This type of remote power draw must be taken into account when evaluating the generator’s overall power output.
If the PRP genset output is lower than its ESP rating, the generator has overload capability. This allows the generator to operate at a higher power level for restricted time periods, as defined by ISO standards.
A generator’s load factor rating is determined by genset’s size, power output, and loading capabilities. Generally, higher load factors correlate with a lower cost of ownership.
Maximum Run Time
While ISO standards dictate how long ESP-rated generators may run under test conditions, there’s no regulation for how long they may run during actual power outages. Companies may create their own maximum allowable run times based on their previous experiences.
Governmental Emissions Ratings
Guidelines set forth by the U.S. Environmental Protection Agency (EPA) regulate the allowable output of commercial gensets based on the genset’s application and horsepower.
Stationary Emergency Engines
These engines may be used without restriction during power outages. Gensets with this rating must conform to the EPA’s tiered rating system for diesel generators in Canada.
Any stationary generator not classified as an emergency genset features unique restrictions for its use and conform to Tier 4 emission standards.
Mobile gensets are classified as a non-emergency engine, but feature a unique qualification: the Transition Program for Equipment Manufacturers (TPEM). This regulation offers a type of mobile flexibility wherein mobile gensets can use the same tier requirements as previously-accepted mobile gensets, for a limited period.
Custom Industry Ratings
Certain agencies have created their own set of generator ratings to conform to specific operations standards. The most noteworthy example of this is the Uptime Institute, a data center regulation agency that has created generator rating guidelines to ensure data safety:
- Gensets for high-level data centers do not have restrictions on consecutive operating hours when loaded to certain level of demand;
- Gensets that do feature these restrictions are suitable only for lower-level data centers;
- Companies wishing to provide generators for data center use must often provide written documentation of genset specifications before their gensets can be installed.
Understand Your Generator Set Ratings
Generator set ratings vary across industry and application, and different manufacturers may rate their generators in unique ways. As such, you’ll need to ensure that you fully understand the capabilities of your system before committing to a provider. Doing your research ahead of time and working with trusted Canadian diesel generator installers are the best ways to get the most out of your genset solution.