This document discusses generator ratings based on ISO 8528-1 standards. It defines four modes of operation: continuous operation at constant load, continuous operation at varying load, limited time operation at constant load, and limited time operation at varying load. It then explains the ratings for continuous power (COP), prime power (PRP), limited time power (LTP), and emergency standby power (ESP). The COP, PRP, and LTP ratings specify power levels for continuous or limited time operation at constant or varying loads. The ESP rating specifies emergency backup power for utility outages. Examples are given for applications of each rating type. Factors that can de-rate generators like temperature, altitude, and humidity are also summarized.

1. Generator Ratings

2. Understanding ISO 8528-1
Not Limited Limited
Constant
Variable
Operating
hours
Load
COP
PRP
LTP
ESP
Purpose : All genset manufacturer to speak the same
language
International Standard for reciprocating internal combustion engine driven
alternating current generating sets

3. ISO8528 – Modes of Operation
-Four combinations of two variables
 Continuous Operation at Constant Load
– Example – Base load in parallel with the utility such as a
combined heat and power plant.
 Continuous Operation at Varying Load
– Example – Primary source of power where there is no utility
present (or an unreliable utility).
 Limited Time Operation at Constant Load
– Example – Base load in parallel with the utility only during
periods of peak power consumption.
 Limited Time Operation at Varying Load
– Example – Backup power when the utility fails.

4. Continuous Power (COP)
Continuous Power is defined as being the maximum power which
the generating set is capable of delivering continuously while
supplying a Constant Load when operated for an Unlimited
number of hours a year .
COP
UNLIMITED Hrs per year
100% Avg. Load Factor
CONSTANT Elect Load

5. Examples of COP Applications
 The COP Rating Genset is generally used when
paralleled to the utility.
 Base Loading
 Co-generation heat and power (CHP)

6. Prime Power (PRP)
Prime power is defined as being the maximum power which a
generating set is capable of delivering continuously while supplying a
Variable electrical load when operated for an Unlimited number of
hours per year.
PRP
UNLIMITED Hrs per Year
70% Avg. Load Factor
VARIABLE Elect Load

7. Application:
Kone Cranes
500kVA generator powers
the dockside rubber tyred
gantry cranes.
Examples of PRP Applications
 Applications that use on–site
generation in lieu of a utility
electricity supply, typically where
utility power is not available.
 Peak shaving and rate
curtailment.

8. Limited Time running Power (LTP)
Limited-time running power is defined as the maximum power
available, under the agreed operating conditions, for which the
generating set is capable of delivering for up to 500 hours of
operation per year.
LTP
500 Hours per Year
100% Avg. Load Factor
CONSTANT Elect Load

9. Examples of LTP Applications
 Base Loading
Application:
9 – C2000D6 Prime rated units
Location: Santo Domingo,
Dominican Repbulic

10. Emergency Standby Power (ESP)
Emergency Standby Power is defined as the maximum power available
during a variable electrical power sequence, under the stated operating
conditions, for which a generating set is capable of delivering in the
event of a utility power outage or under test conditions for up to 200
hours of operation per year.
ESP
200 Hours per Year
70% of Avg. Load Factor
VARIABLE Elect Load

11. Example ESP Applications
Application:
Fully Integrated standby power
system containing 2 C2250D5
Location:
UK
 Emergency Hospital (such as backup to Life Safety, legally
required or critical loads)

12. Example C1675D5
1028
1400 1400
1675
0
200
400
600
800
1000
1200
1400
1600
1800
COP LTP PRP ESB
ISO Ratings
kVA

13. De-rate on a Gen-set is caused by:
Ambient Air Temperature , affects:
Engine induction
Engine & Radiator cooling capacity (LAT)
Alternator temperature rise
Circuit breaker de-rate
Air Density (Altitude), affects:
Engine induction air
Radiator cooling capacity
Alternator cooling capacity
Humidity
Only naturally aspirated engines de-rate in high humidity.
Rating Conditions

14. Exceeding ISO8528
 Nominal vs. Guaranteed
– ISO don’t define the minimum power value. The
Cummins ratings are a guaranteed minimum.
– A Cummins generator is guaranteed to produce
enough power to either meet or exceed the published
rating value.
– Some competitors publish a nominal rating with a
tolerance. Their actual power output capability could
be below their published rating value.

15. Radiator Power
– ISO8528-1 paragraph 13.1 states:
• The power of the generating set is the power output available
for consumer loads at the generating set terminals excluding
the electrical power absorbed by the essential independent
auxiliaries.
– A Cummins generator will drive its radiator and supply the full
published kW value at the same time
– When using an electrically driven remote radiator, be sure the
alternator is sized for customer load plus the radiator load.

16. Data Center Continuous Rating
 Definition: The maximum power which the generator is capable of
delivering continuously to a constant or varying electrical load for
unlimited hours in a data center application.
 No run time limit! Required by The Uptime Institute.
 www.cumminsdatapower.com
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