What is Loss of Excitation Protection ? Loss of excitation (LOE) protection in a relay protects the rotor from damage during underexcited operation. LOE is a common fault in synchronous machines and can be caused by: Short circuit of the field winding Unexpected field breaker open LOE relay mal-operation Loss-of-excitation relays are normally included in the generator protection package to protect the rotor from damage during under excited operation. Impedance type relays are usually applied to automatically trip the unit with a short time delays whenever the VAR flow into the machine is excessive. Myriad Industrial Solutions LLP from Dahisar Mumbai Maharashtra India is a supplier of relay test sets to perform loss of excitation tests on protection relays. Call us for more details.