Electric motors will have a predetermined service life that typically ranges from 30000-40000 hours. This depends on their proper maintenance. One of the critical parts of an electric motor is its excitation system. This will provide the required field current to your machine’s rotor winding. The amount needed for your motor’s excitation system will depend on your load power factor, machine speed, and load current.
A failure of your excitation system is one of the most common issues that call for electric motor repair services. Unfortunately, it is not easy to pick the problems with your motor’s excitation system. It is, therefore, important to have some know-how on how the excitation system of your motor works to appreciate a deviation from its normal operation, as well as know the typical method in your application.
The following are the excitation methods used for most electric motors.
The Self-Excited or Shunt Method
This features a cost-effective and straightforward design for power flow to your automatic voltage regulator (AVR). The method will call for no extra wiring or components to your electric motor. The AVR, in this instance, will have sensors that will monitor the stator’s output. It will supply power to the exciter that is then rectified to a direct current that is then induced into your stator for load output.
The primary drawback of the self-excited excitation method is that the AVR will be affected by the powered generator load. To this end, the shunt excitation method is solely used for linear loads.
Excitation Boost Systems
These comprise the basic components that receive outputs and supply inputs to and from the AVR. They also include the excitation boost generator (EBG) and excitation boost control module (EBC). The EBC module receives the AVR signal while the EBG will supply power to the controller with a shift in your generator’s rotation. The additional power feed of excitation boost systems supports the starting and recovery of your excitation voltage. They are primarily designed for backup and emergency applications rather than continuous power applications.
Permanent Magnetic Generators
These are mounted along your generator shaft’s driven end. They supply isolated power to your AVR on a rotation of the generator shaft while extra power will be used for supplying non-linear loads like those needed when starting your motor. The excitation fields of permanent magnetic generators do not collapse and allow for a sustained clearance of short circuit faults.
This uses a distinct excitation field but has nothing attached to your generator shaft’s driven end. Shaft rotation and a permanent generator or magnet will supply extra excitation. The auxiliary winding is generally used for large generators, such as those in industrial and marine applications.
The above information might seem overwhelming for most people. Understanding what is going on with your electric motor allows you to appreciate better what a repair expert will recommend when your generator is not working as it should. While it might seem simple for you to tweak a few things to get your excitation system working as it should, this almost always causes grave issues and affects the other components of your motor.