Wp Reactive

This information is general in nature and intended to give the reader an overview of the issues involved. Specific recommendations can only

be made after a review of the equipment involved, installation parameters, applicable codes and national standards by competent personnel.

Please consult Avtron LoadBank, Inc. with comments or questions about the information contained herein.

Application of Resistive/Reactive Load Banks for Diesel Generator Set Testing

July 29, 2008




RESISTIVE/REACTIVE LOAD BANKS

Resistive load banks are the most commonly used load banks for testing of generator sets and

power systems. They can provide full KW loading to the power source to completely evaluate the

engine cooling, exhaust and fuel systems. They will not load the generator to its full nameplate

KVA capacity at 0.8 Power Factor. In order to load the generator to its full KVA rating, reactive load

banks will be required.

RESISTIVE LOAD BANKS

The resistive load bank can be related to the actual horsepower produced by an engine under load.

Just as the horsepower produced by the engine is real mechanical power, the KW of the resistive

load bank is real power in electrical terms. When a resistive load bank is used to test an engine

generator set the engine will produce its full horsepower rating, dissipate essentially the same

amount of engine exhaust gases and heat, and produce the same amount of thermal energy into

the engine coolant as it would with a reactive load. The resistive load bank will completely test the

engine and its various systems. The only difference is that the generator will not produce the full

KVA rating since the power produced is at 100 percent power factor.

REACTIVE LOAD BANKS

The resistive/reactive combination load banks are used to test the engine generator set at its rated

power factor. In most cases this is 0.8 power factor. The reactive component of the load will have a

current that lags the voltage. The resulting power is described in two terms, the KW, or real power

and the KVA or apparent power. Since the current lags the voltage in the reactive load the total

power is not the direct sum of the two but their vector sum. That vector is the phase angle

difference between the voltage and the current. The combination of resistive and reactive current in

the load will allow for the full nameplate KVA rating of the generator windings to be tested. Even

though the generator set is producing more KVA it is actually not producing more KW. The real

power or horsepower required from the engine is essentially the same.




ACCEPTANCE TESTING

Since most generator sets are the product of established manufacturers with engineering prototype

development it can be argued that the generator set is a known quantity and does not need to be

tested on-site since its performance has been previously tested by the factory. It is important to

understand the need to test the generator set in its installed location. While the generator may

have been tested at the factory, the installation variables of altitude, ambient temperature, fuel,

exhaust and cooling systems can be significantly affected by the installation. The on-site

acceptance test is a valuable tool for the engineer, building owner and maintenance personnel to

determine the operating capabilities of the generator in its installed location.

These parameters are not affected by the use of reactive load banks and more commonly available

resistive load bank can be used to test these installations properly. It is a matter of policy with

some engineering specifications to test these systems at full nameplate values which would require

the use of resistive/reactive load banks.

Most engine generator sets will be nameplate rated at 0.8 power factor. This will require a reactive

load equal to 75% of the resistive rating. In other words if we test a 1000 KW, 1250 KVA generator

set we would need a load bank system rated at 1000 KW resistive and 750 KVAR reactive to load

the generator set to its nameplate capacity.

PARALLEL SYSTEMS

When testing installations with multiple generator sets operating in parallel the use of

resistive/reactive load banks is justified. Having the ability to fully load the generator with the

reactive component is usually required to properly calibrate the load sharing and voltage regulating

systems of parallel generator systems. The load bank system can be connected to the common

paralleling bus and be used for testing individual engine generators or any combination of engine

generators operating in parallel. A 3000 KW load bank could be used to test a single 1500 KW

generator set at full KW or two 1500 KW generators in parallel at full nameplate KW load. If the

1500 KW generator sets were on line in parallel we could load them to two-thirds of their combined

or individual KVA rating.




The proper installation and use of a load bank can be used to effectively determine the operating

capability of the engine generator system and used to maintain the system and extend its useful

life. Avtron can provide practical solutions to these problems and the support to assure you that

your power system will provide many years of safe operation.

For Additional Information Contact:

Avtron

6255 Halle Drive Cleveland, Ohio 44125

216 573-7600 fax: 216 573-5953

email: [email protected] www.avtronloadbank.com

Wp Reactive

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