Generator set ratings
Generator Set Ratings According to ISO 8528-1
The generator set rating under ISO 8528-1 is an important parameter that defines generator performance under various operating conditions. ISO 8528-1 classifies generator sets by type, conditions of use and operating modes. According to this standard, the rating is established based on the following criteria:
Emergency Standby Power (ESP)
Emergency standby power is the maximum power available for a variable load during an outage of the main power grid. The average load factor over 24 hours of operation must not exceed 70% of the engine's ESP rating. Typical engine operating time is 200 hours per year, with maximum use of 500 hours per year. This includes an annual maximum of 25 hours per year at the ESP rating. No overload capability is permitted. The engine must not be used for sustained utility paralleling applications.
This is the maximum power a generator can deliver for a limited time (typically up to 200 hours per year) in emergency or standby operation.
Prime Rated Power (PRP)
Prime Power is the maximum power available for an unlimited number of operating hours under variable load. The average load factor must not exceed 70% of the engine's PRP rating over 24 hours. A 10% overload is permitted, but it is limited to 1 hour in every 12 hours.
This is the maximum power a generator set can deliver in continuous operation for an unlimited time under variable load, allowing for periodic maintenance.
Continuous Operating Power (COP)
COP-rated generators deliver power for a continuous constant load (average output range of 70–100%) for an unlimited number of hours per year, but without overload capability.
This is the power a generator can deliver under a constant load for an unlimited time, provided the load level remains constant.
Data Centre Power (DCP)
The DCP rating is defined as the maximum power a generator set can deliver while supplying a variable or continuous electrical load for an unlimited operating time. Depending on the delivery sites and the availability of reliable power systems, the generator set manufacturer is responsible for determining the power level it can provide to meet this requirement, including through hardware or software solutions or an adapted maintenance plan.
Limited-Time running Power (LTP)
An LTP unit must be able to run at least 500 hours per year at an average load factor of 100%. Note that ISO 8528-1 does not define the expected load variation for an LTP unit.
The choice of an appropriate generator rating depends on the specific power supply requirements. For example, for facilities where continuous operation without overloads is important, Continuous Operating Power (COP) is suitable. For facilities that need a backup power source in emergencies, Emergency Standby Power (ESP) is what matters.
Compliance with ISO 8528-1 ensures that the generator set meets reliability, efficiency and safety requirements, which is essential for stable operation of electrical consumers under any conditions.
Choosing a diesel generator requires considering several important ratings that determine its performance and reliability. PRP (Prime Power Rating) indicates the power a generator can deliver for an unlimited time under variable load. ESP (Emergency Standby Power) is the maximum power available during emergencies. COP (Continuous Operating Power) defines the power a generator can deliver continuously under constant load. DPD (Data Power Density) indicates the efficiency of energy use relative to the volume or weight of the generator. These ratings will help you choose the best generator for your needs.
