Load Bank Testing 

What is a Load Bank? 

A load bank is a device that applies a load to an electrical power source and converts or dissipates the resultant power output of the source.  A load bank can be further defined as a self-contained, unitized, systematic device that includes load elements with control and accessory devices required for operation.  

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What is the point of load bank testing?

The point is to test the power protection system (and component parts) under load conditions but without risking supply to protected loads. The point is that with a generator, merely starting it up is insufficient. Operators need to know it will run, fully loaded.  That is what load bank testing does – takes a power protection system for a drive in a controlled environment.

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Why is load banking important for a Generator?

Another important reason to perform load bank testing is to prevent wet-stacking. Wet-stacking is a frequent problem with diesel engines which are operated for extended periods with little or no loads applied. When a diesel engine operates without sufficient load, it will not operate at its optimum temperature or peak efficiency. An engine experiencing wet-stacking will require more maintenance and performance will be compromised.

To help reduce the effect of wet-stacking, Cummins Sales and Service recommends the periodic use of supplemental resistive load banks to exercise the engine/generator. Applying an increasing load over time until the excess fuel is burned off at or near rated output reduces the effects of wet-stacking. Conducting load bank testing in conjunction with periodic maintenance is recommended by the National Fire Protection Association (NFPA).

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How is it done and what do the results report?

Measurements are taken during testing from which it is possible to determine Generator and Engine performance. A load bank test will provide timely identification of problems with the generator and an indication of remedial actions that should be taken. In the case of a standby generator, a load bank test will indicate the engine’s ability to provide the required power; the alternator’s capability to provide the required voltage stability; stable frequency; efficiency of control systems under varying conditions of load; performance of the whole system; oil and fuel pressure. It will also help remove deposits from pistons, engine castings and exhausts, identify potential weaknesses and record results and any work that needs to be done. Load bank testing will ensure that the components within the power protection system will work and perform together as intended when called upon to support a critical load.

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What does a Load bank test indicate?

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• The engine’s ability to provide the required power output (kW) 

• Voltage regulator response time 

• The alternator’s capability to provide required voltage, and frequency stability 

• The genset control system under varying conditions of load

• Overall performance of the whole system, oil and fuel pressure 

• A load bank test will also help remove fuel deposits from pistons, engine castings and exhaust 

• With data logging software load test results can be recorded and the technician can analyze work that needs to be done 

• Condition of Engine cooling system

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NFPA 110 Emergency Generator Testing Requirements sets safety standards to protect commercial building occupants by making sure generator-powered backup lighting will operate as expected. A monthly test is performed on generators whose failure could result in death or injury. Should a generator fail this monthly test, it should undergo load bank testing for two continuous hours annually, per Section 8.2.4.3. It is not mandatory to use load banks, but most buildings’ total load values are below the higher monthly testing requirements. Under the continuous test, the generator should be operated at 25 percent of the nameplate kilowatt rating for 30 minutes, at 50 percent of the kilowatt rating for 30 minutes and at 75 percent of the kilowatt rating for 60 minutes.

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