Generator Ratings

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

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.

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 .

COPUNLIMITED Hrs per year 100% Avg. Load Factor CONSTANT Elect Load

Examples of COP Applications

The COP Rating Genset is generally used when paralleled to the utility.

Base Loading Co-generation heat and power (CHP)

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.

PRPUNLIMITED Hrs per Year 70% Avg. Load Factor VARIABLE Elect Load

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.

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.

LTP500 Hours per Year 100% Avg. Load Factor CONSTANT Elect Load

Examples of LTP Applications

Base Loading

Application:9 – C2000D6 Prime rated unitsLocation: Santo Domingo, Dominican Repbulic

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.

ESP200 Hours per Year70% of Avg. Load Factor VARIABLE Elect Load

Example ESP Applications

Application:Fully Integrated standby power system containing 2 C2250D5Location:UK

Emergency Hospital (such as backup to Life Safety, legally required or critical loads)

Example C1675D5

1028

1400 1400

1675

0

200

400

600

800

1000

1200

1400

1600

1800

COP LTP PRP ESB

ISO Ratings

kVA

De-rate on a Gen-set is caused by:

Ambient Air Temperature , affects:Engine inductionEngine & Radiator cooling capacity (LAT)Alternator temperature riseCircuit breaker de-rate

Air Density (Altitude), affects:Engine induction airRadiator cooling capacityAlternator cooling capacity

HumidityOnly naturally aspirated engines de-rate in high humidity.

Rating Conditions

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.

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.

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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