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Application of Resistive/Reactive
Load Banks for Diesel
Generator Set Testing
July 29, 2008
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.
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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.
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.
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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.
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.
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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: LBsales@Emerson.com  www.avtronloadbank.com
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.