Electrical protection for alternators and motors

Like all industrial equipment, rotating electrical machines can be affected by malfunctions. These faults generally render them incapable of performing their function in the short or long term, and interfere with the operation of other equipment. Faults, as well as abnormal operating conditions, must therefore be detected as quickly as possible, and cause electrical disconnection between the machine and the network to which it is connected.

The role of electrical protection relays on alternators and motors is to detect, among the various possible faults, those of electrical origin, and to take the necessary action to signal and open the cut-off device connecting the device to the mains.

In what follows, faults are distinguished according to their origin, either internal to the machine concerned, or external. The actions provoked may be of different kinds, aiming either to limit the damage suffered by the machine, or to minimize the consequences of disturbances on machine and network operation, or both.

After a brief review of machine constitution, electrical faults are described by machine type, alternators or AC motors. The case of DC motors is not dealt with here, as this type of motor is much less widely used than AC motors (synchronous and asynchronous), and concerns specific applications.

In analog and digital technology, a given relay is generally associated with a given type of fault. Today, however, digital techniques make it possible to combine different measurement, action and monitoring functions in a single device, powered by the appropriate measuring gear. The concepts of personnel safety and operational reliability are of prime importance in this equipment, which is used in complex industrial processes.

Practical instructions for the use of the various relay types (protection diagrams) are given for the user's use.

Readers may wish to refer to the following articles in this treatise:

• in the Electrical Machines section:

  • different types of machines: Asynchronous machines [D 3 486] , Synchronous machines [D 480][D 495] , Turboalternators [D 3 530] , Hydraulic alternators...