ABB SafeGear Installation, Operation And Maintenance Manual page 18

Appendix C
Antisingle Phasing
What is a Phase Loss?
When one phase of a three-phase system is lost, a phase loss occurs. This is also called 'single phasing'. Typically, a phase loss is caused by a blown fuse, thermal
overload, broken wire, worn contact or mechanical failure. A phase loss that goes undetected can rapidly result in unsafe conditions, equipment failures, and costly
downtime.
Voltages and currents in a three-phase system do not typically just drop to zero when a phase is lost. Often measurements yield confusing values that require a
great deal of complex analysis to correctly interpret. Meanwhile, damage and downtime of the equipment continues to rise.
What happens with a phase loss?
When a 3-phase motor runs with one phase missing, the remaining 2 phases will take more load from the missing phase making them work harder, over heat and
burn out.
To avoid the above condition the SafeGear MCC controller has a blown fuse mech that envires thar all 3 phases and disconnect if only a single or two fuses blown.
Blown fuse mechanism
1
1. The fuse is working in the right position.
1. When a fuse is blown, the mechanism is activated.
3
This configuration is available and depends of relay's programming by others.
NOTE:
15 SafeGear Motor Control Center Controller Installation, Operation and Maintenance Manual
®
2
1. The "sensor" is not transmitting a signal.
1. The "sensor" is transmit a signal to the relay and the
4
3-phases are disconnected.