Generators are ordinarily subject to considerable electrical and mechanical stresses and temperature rises that contribute to their wear and tear. Even when used properly, generators with many years left in their warranties might contend with a few issues owing to these factors. To this end, it is essential to take several steps to protect the machine against problems that make it a safety hazard and increase its fuel consumption and breakdown incidences.
The best choice for reducing your frequency and expenses of electric motor repair, among other issues that call for generator repair will depend on your circumstances. As such, walking into any shop dealing with generators and picking a protective device or solution that fits your machine and budget is not an option. The following are some of the alternatives available for your generator’s protection.
Rotor Distortion Protection
The cooling rates after your generator’s shutdown at the bottom and top of the casing are different. The uneven temperature this generates often distort the rotors. To negate this, the rotor should turn at low speed during the machine’s cooling period. Most manufacturers also fit shaft eccentricity detectors to avert the distortion of rotors in large generators.
Stator Earth Fault Protection
Once the stator neutral is earthed using a resistor, a current transformer will be mounted in a neutral- to-earth connection. If the generator connects directly to the bus bar, an inverse time relay is inserted across the CT relay. This is because the earth faults relay is needed for grading with the other fault relays in your machine. If on the other hand, your generator gets power using a delta star transformer, you will use an instantaneous relay. Here, the faulty earth loop will be limited to the primary and stator windings of your machine’s transformer. There is thus no need for discrimination or grading with the fault relays in your machine.
Stator Overheating Protection
The overloading of your machine can result in the overheating of its stator winding. The same can be caused by the failure of the cooling systems, stator laminations or insulation. Overheating of your windings will be detected by inbuilt temperature detectors across several points. These detectors are generally resistance elements that form an arm of the circuit. In small generators with voltages below 30MW, a thermal relay is used to measure the stator winding’s current. This arrangement nonetheless only protects against overheating of the windings caused by overloading.
Low Vacuum Protection
This is generally in the form of regulators that compare the atmospheric pressure and the vacuum in generators set above 30MW. In normal conditions, the generator will unload its set through a secondary governor until it restores regular vacuum conditions. If the conditions do not, however, improve at less than 21 inches, the stop valves will close and the circuit breaker trips.
Buying and installing a generator in your premises is only part of the battle towards uninterrupted power supply for your commercial and residential use. Without the above protective measures, you will be left contending with frequent breakdowns that will cost you considerably. You should thus have an expert technician assess your generator vis-à-vis your needs and recommend the ideal protective measures for it.
