To protect a.c. motors and small generators there is need for relays with multifunctional features. Protection against thermal overload, earth-fault, overcurrent, overvoltage and phase unbalance are some important features that are provided in modern protective relays.
SPAM 150 C is a current measuring multifunction relay for the complete protection of a.c. motors. The main area of application covers large or medium-sized three-phase motors in all types of conventional contactor or circuit-breaker controlled motor drives. The motor protection relay is available in two versions, one with a trip contact and the other with a breaking trip contact.
The relay can also be used for protection of other objects, such as transformers and feeders, requiring a single-, two- or three-phase over-current and/or overload protection and non-directional earth-fault protection.
The combined multifunction motor protection unit is a secondary relay device, connected to the current transformers of the protected motor drive. The three-phase currents and the neutral current of the protected device are continuously measured. On the basis of this measurement, the thermal condition of the motor is calculated and the faults of the network are detected. In fault situations the relay will alarm or trip the circuit-breaker.