Load Bank Applications

  • Battery Discharge
  • Containerised ISO
  • Controls
  • Data Centres
  • Duct Mounted
  • Emission Control
  • Marine Water Cooled
  • Permanently Installed
  • Pollution
  • Portable
  • Power Factor Testing
  • Radiator Mounted
  • Reactive & Resistive
  • Reactive Modules
  • Rentals Service
  • Trailer Mounted
  • Used & Ex Rental
  • Workshop Testing

Load Bank Models

  • DCM Series
  • CL Series
  • Manual, Auto Min. Loading, Mimic Remote, Remote Control, Data Logging
  • LS Series
  • RCI Series
  • LS Series, LSMC Series, RCI Series
  • LSMC Series
  • BL Series
  • LS Series, LSMC Series
  • CL Series, TR Series, WA Series
  • CL Series, RM Series, WAR Series
  • RCI Series
  • CL Series, WAR Series
  • RM Series
  • CL Series, WA Series
  • WA Series
  • CL Series, WA Series
  • CL Series, WA Series

LOAD BANK TESTING of Engine / Generator Sets

Engine/generator sets (otherwise known as gensets), represent a substantial capital investment. Their failure to perform properly when pressed into service is almost always accompanied by actual or potentially dangerous conditions and/or significant financial loss. Ongoing periodic maintenance and testing is vital to ensure that the unit correctly performs its duties when called upon to do so.

Plant engineers with genset responsibilities are well aware of the need for preventive/predictive maintenance and periodic operational test-running of their units. If the genset is an emergency unit required by building safety code (rather than a standby unit installed at the owner’s discretion), a set of applicable codes prescribe required minimum test conditions and frequency of testing.

Understanding the Importance of Generator Load Bank Testing

Periodic load bank testing is a vital part of a comprehensive genset predictive maintenance program, but it is seldom specifically required by code. An example of one of the rare exceptions is found in NCPA 110 (USA) Emergency and Standby Power Systems, which requires load bank testing for mandated emergency units serving critical areas in hospitals.

A load bank (dummy load) is a stationary or mobile piece of equipment that provides operator-adjustable electrical resistance or resistance and reactance to simulate the actual electrical load the genset is intended to power. Load bank testing simulates the electrical demands of one or more items of electrical equipment, specific processes within the plant, or an entire facility. The test monitors the engine and generator to ensure that each unit is carrying out its prescribed job.


Effect of Power Factor on the Engine/Generator

Industrial electrical loads comprise resistance and inductive reactance, with the latter induced by all electro-magnetic devices. Inductive reactance causes current flow to lag the applied voltage by 90 electrical degrees. Solid state electronic devices are nonlinear and their current waveform does not conform to the applied voltage waveform. They, too, cause current to lag the applied voltage in the manner of electromagnetic loads.

The vector resultant of resistance and reactance is the circuit impedance (see illustration). Current flow through the resistive component yields kilowatts (kW), and the kW level determines the horsepower load that will be imposed on the genset engine. Current flow through total impedance yields kilovolt-amperes (kVA), which translates directly into the heating that will be imposed on the generator.
The circuit parameter known as “power factor,” or PF, is the ratio of kW to kVA. Power factor is usually expressed as a percent value – for instance, a PF of 080 is typically expressed as 80%. Power factor decreases with increased reactance, and increases as the ratio of resistance to reactance increases. In a purely resistive circuit, kVA is equal to kW, and PF is 1, or 100%.

There are few purely resistive loads in industrial plants; their existence is essentially limited to incandescent lighting and resistance heaters. Polyphase induction motors have power factors ranging from 50% to 90%, with the lower power factors applying to smaller and lower-speed motors. Power factor of welding machines ranges from 50% to 70%, are furnaces from 80% to 90%, and induction furnaces from 60% to 70%.

Recommended Application of a Generator Load Tester

The following recommendations for an overall engine/generator PM program are to be taken as general guidelines only, and should be modified in accordance with specific circumstances.



The system should be started and operated for 30 to 40 minutes, either with or without electrical load imposed on the unit. A visual check should be made for oil and fuel leaks, and any abnormal noises should be investigated. Engine fluids, gauges and instruments should all be checked. 


The unit should be run for 30 to 40 minutes under actual load, and all weekly-check items observed. (Scheduled load bank testing increases in importance in cases where it is not feasible to test gensets under load on a regular basis.) Engine cranking battery electrolyte levels should be checked, and battery specific gravity hydrometer readings should be taken. 


Every six months (or 250 engine-operating hours), a thorough inspection should be made of the following systems: cooling, fuel, starting, lubricating oil, and air intake/exhaust. Oil should especially undergo spectrophotometry and infrared analysis to confirm its integrity. System safety control systems and unit control panels should also be checked. The generator and exciter stator and rotor windings should be checked with a megohmeter to detect any insulation degradation. 


Every year (or 250 engine-operating hours), engine oil and oil, air, and furl filters should be changed. An engine coolant condition analysis should also be performed. The engine/generator should undergo a resistance/reactance load bank test over its full load range for a minimum of two hours. 


Every two years, the engine coolant system should be thoroughly flushed and refilled. Upper and lower radiator hoses, belts and block heater hoses should be replaced.

Resistance-Only vs Resistance/Reactance Testing 

Some genset test load banks (dummy loads) contain resistance elements only. As such, they cannot provide a true simulation of the loading that the engine/generator will be subjected to in actual service. Many gensets are rated in kW at a specified power factor – for example, 1000 kW at 80% OF. Such ratings reflect the actual load conditions that the unit will be called upon to satisfy. 
A resistance-only load test confirms the engine’s ability to crank out a given kW, as well as the generator’s ability to deliver an equivalent amount of kVA. It does not put the generator through the same paces it would experience under actual operating conditions. In effect, only engine performance is validated in a resistance-only test. 
With a resistance/reactance load bank (dummy load), inductance and resistance are selected to yield a value of impedance that collectively exposes the engine and generator to the loading that they will experience in service. 


Load Bank Test Verification of Voltage Regulator Operation

Only reactive load bank testing can verify the true performance of the genset voltage regulator; the regulator is not fully challenged in a resistance-only load bank test. The voltage regulator is what enables the system to recover quickly from large load changes. When large block loads are applied, engine speed drops momentarily before recovering to its steady-state condition. 
The recover interval is known as the “transient response.” If the regulator is not functioning properly, recovery might not be possible. In some cases, the generator magnetic field might collapse, thereby rendering the generator useless. 
Testing with a resistance/inductance load bank (dummy load) allows block loads to be introduced, having the same impedance characteristics as actual in-service loads. 

Problems Eliminated by Periodic Load Bank Testing

It is advisable to perform load bank testing on an annual basis, because it can eliminate problems brought on by neglect and underutilization. Weekly test operation under no-load or light-load conditions does not permit engine fluids to attain proper operating temperature. Cooling system controls will not be properly exercised, preventing coolant from circulating through radiators, and inviting failures stemming from inactivity. Engine safety shutdown systems are not subjected to actual operating conditions, and are therefore not fully tested. 
Diesel-driven units are subject to a particular malady known as “wet stacking” or “slobbering” that stems from operation under no-load or light-load conditions. Such operation causes fuel deposits to collect on the combustion chamber, injector nozzles, piston rings, turbocharger, and exhaust system. The result is diminished engine output capacity. Regular load bank testing burns off accumulated deposits and preserves engine output capability.