Generators and motors electrical protection systems

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 relays and electrical protection systems for alternators and motors is to detect the various possible faults, including those of electrical origin, and to take the necessary action to signal faults and open the disconnecting device that isolates the machine from 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 reminder of how machines are built, and their operating requirements in relation to the networks to which they are connected, electrical faults are described for each type of machine, alternators or AC motors. For each fault considered, the principle and mode of action of the protection(s) likely to be implemented are indicated. DC motors are not covered here, as this type of motor is much less widely used than AC motors (synchronous or asynchronous), and concerns specific applications.

The article then describes relay and protection system technologies, with particular emphasis on digital protection systems, which represent the current state of the art. Such a system is not only capable of performing several protection functions, but also offers extensive possibilities for communication with an external control system, man-machine interface, self-monitoring and internal fault detection, data logging and oscilloperturbography. In addition to functional performance (including the achievement of expected protection functions), the design parameters of digital systems include reliability and availability requirements, scalability and operational safety requirements.

The conditions and installation methods for relays and protection systems are also described.