A reliable generator is a crucial piece of equipment for any operation. Companies and organizations of all stars and stripes use them, including oil & gas operations and healthcare facilities. Before you invest in a generator, it’s important to understand the ratings and specifications.
Luckily, there is an industry standard for power ratings and operational ratings. These values help you identify the best generator for your specific application. However, they aren’t always easy to understand.
Below, we clarify what these ratings represent.
What is a generator rating?
A generator rating is a metric that shows the power capacity and reliability of a generator set. If the rating is too low for your purpose, it causes more downtime and more repairs. A higher rating means you spend more on a level of capacity you don’t need.
What do the different ratings mean?
There are four different power ratings to look at. Each is based on the maximum output, load profile, and how long the set can run.
Here are the four operational ratings:
- Prime (PRP)
- Emergency Standby (ESP)
- Standby
- Mission Critical Standby
Prime
Prime means that a generator set is a primary source of power, not a backup. The PRP rating shows you the generator’s capacity for an unlimited amount of time each year.
These ratings are most important for:
- Healthcare facilities and hospitals
- Mining operations
- Operations without a power source
Emergency Standby
Emergency generators help provide power during emergencies and power outages. The industry standard is for them to provide power “for the duration of the outage.” Typical designs handle up to 200 hours per year.
Standby
For a standby application, your generator set provides emergency backup power at a specified rating throughout an outage. The average load factor is limited to 70% of the rating, applying to various loads. It can run for up to 500 hours each year.
Example: A 3MW standby generator set provides power for up to 500 hours per year with an average load of 2.1MW.
Mission Critical Standby
In a mission critical generator rating, the set provides emergency power at the displayed rating for the entirety of an outage. Set the average load factor no higher than 85% of the displayed rating. These sets can run up to 500 hours per year.
Generally, peak demand is 100% of the rating for 5% of the operating time. Using the 3MW example, a mission critical set provides power for the duration of an outage, running up to 500 hours a year. The average load is up to 2.55MW.
Load Management
Continous
These are similar to Prime generators. They supply power for an unlimited number of hours per year. The main difference is that the load is constant.
Limited Time Running Prime
These generators supply power to a utility as part of a financial agreement.
Every generator requires maintenance to ensure it remains in good condition. Proper maintenance extends the lifespan of your generator and reduces downtime.
How do I choose the right generator rating?
The key to choosing the right rating is the application. Here are questions to consider:
- Is it a primary power source or backup?
- Does it need consistent power?
- How many hours per year do you need the set to run?
- What’s the maximum required power?
- Does it run isolated or connected to a utility?
Our Power Requirement Calculator can help you determine the right rating for your job.
Need help finding the right generator set?
Generator ratings protect consumers. They help you find the right capacity, load, and run time for your job. Choosing the right rating is a balance of all these factors.
The goal is to find the optimal combination of installation cost and cost of ownership (long-term). If you still have trouble understanding these ratings, contact our team for personalized assistance.