Load Bank Testing
Generator Load Testing
At PPSPower we recommend that your back-up generators are tested on load either through a load bank or against the building load.
Data centres and health-care facilities have some of the best and most thorough procedures for testing their emergency on-site power systems. For obvious reasons, these operations must have 100% confidence in their critical systems, and they invest heavily to insure that these systems will operate as expected, when needed. Large facilities are often regulated and mandated to have sophisticated test procedures in place.
Testing for large facilities can involve basic testing, which is generally held on a weekly basis, plus much more rigorous testing held quarterly, semi-annually or annually. Mission-critical facilities usually hold extended tests that require the emergency generators to run for as long as 4 hours under varying loads.
Smaller operators, on the other hand, often develop their own test methods and testing schedules. While monthly testing to the depths seen at health-care facilities is not required, smaller facilities should still develop a proper test schedule for their equipment.
Running a generator under load is the only true way to test its capability to operate as specified. There are many engine and generator components that must see real operating conditions to provide confirmation of their ready-state. Consider these questions:
Will the automatic transfer switch transfer the load within the required time limits?
Is it properly sensing the generator’s voltage and frequency?
Will the transfer switch properly retransfer to the normal source when the exercise function is terminated?
Engine cooling systems are rated to perform at a certain ambient temperature while under a certain load level. Is the cooling radiator system fouled?
Will the water pump circulate the coolant mixture at the specified rate?
Fuel systems can only be truly tested when the engines are running near full load. Fuel flow rates at no-load are only a fraction of the demand that will exist when the engine operates at 80% load. Will the fuel flow be sufficient?
Are the filters clogged and possibly restricting the flow of fuel at the higher demand rates?
Is the alternator overheating when under load?
Is the generator operating at a steady speed, or is it fluctuating outside of the specified governed speed as loads change?
Diesel engines should not operate for extended periods of time at load levels below 60% of their rated output capacity. Light loading of diesel engines usually leads to wet stacking. Excessive carbon build-up on injector and valves, and oily drips on the exhaust piping, are all common indicators of issues related to improper combustion due to insufficient loads.
PPSPower can offer you two options:
1. Load Bank Testing:
If you do not wish to disrupt your building operations by the short power interruptions associated with a building load test, consider investing in a load bank test.
Our engineers can arrive on your site with the correct size load bank and connect up to your generator. This allows our engineers to test and exercise your generator(s) to verify its overall reliability, and its ability to run at its full rated KW output. Typically, a generator is running at a level far less than the units rated output capability. Load banking ensures the engines ability to perform and provide the required horsepower when called upon in an emergency. When a load bank is used, the artificial load it provides brings the engine up to an acceptable operating temperature.
Fully loading the standby generator stresses all of its components. It is, therefore, preferable to identify any potential weakness under controlled conditions than to wait until the lights are out!
2. ‘Black Start’ or ‘Building’ Load Test:
Our engineers will carry out a full test of the installed generator(s) and switching systems designed to operate on the occasion of a break in the supply of electricity to the facility. A black start test commences with the opening of the circuit breakers on the incoming mains feeders and concludes with the successful reconnection of the facility to the mains feeders.
The purpose of the black start test is to prove that the emergency electricity supply performs as an integrated system in the restoration and continued delivery of power supplies to critical areas in an orderly manner. It is also used to prove the orderly restoration of supplies once the normal source of power supply has been restored. A black start test must be planned, designed and executed to demonstrate the proper operation of the entire system, rather than to demonstrate the correct operation and/or exercise of just component parts of the system.
Our engineers will conduct the test with all normal loads connected and operating to replicate, as far as possible, the circumstances that may exist at the time of random failures. Critical items of equipment should not be isolated as the test should be used to gain an understanding of the performance of all equipment and procedures under conditions of power failure and restoration. It is also imperative that loads should be representative of actual operations to demonstrate the capability of generators and ancillary systems such as load staging.
A test is only deemed successful if, under normal operating conditions, the system works as designed, results in power being supplied to the essential areas and continues to operate for at least one hour.
If you spent thousands of pounds on a car, would you leave it on the drive for a few years and then expect it to perform on a motorway at full speed without any problems?