This indicates for any fault causes over current in the phase element of the relay that exceeds the setting value. In case of any Emergency condition the EPB is pressed by operator.The under voltage protection function detects voltage collapses on transmission lines and electrical machines and prevents inadmissible operating states and a possible loss of stability.Negative sequence protection detects unbalanced loads on the system.The major cause of unbalance is due to Single Phasing of motor.The tripping can be known by view the Trip Log. The same LED is used to show indication for any of above three tripping. This indicates tripping due to either of Negative Phase Sequence, Under Voltage or Emergency Push Button at motor side Pressed. by excessive voltage surges during motor starting, by excessive load moments, or by blocked rotor conditions, a trip signal will be initiated by the protective relay. If the duration of these starting attempts are lengthened e.g. Motors can quickly heated up above their thermal limits when multiple starting attempts occur in a short time. This function protects the motor against prolonged startup procedures and the consequent thermal overload of the rotor. The high current flow in the motor heats up the rotor quickly due to skin effect. As a result, the motor draws higher current to drive the excessive load. In locked rotor condition the rotor gets locked due to presence of the excessive load. Load jam in motor running condition is taken care by Locked rotor protection available in the relay. The Load Jam protection prevents overheating and mechanical damage due to a locked rotor. A trip occurs when the thermal capacity used by the motor reaches its 100 %. When the overload persists for a considerable amount of time, the motor temperature and thermal capacity will rise.

Under transient and overload conditions the Thermal Capacity of the motor rises, but within the corresponding limits. The purpose of motor thermal protection is to allow the motor to start and run within the defined thermal Capacity limit but trip if the motor heat energy exceeds those ratings because of overloads, negative-sequence current,or locked rotor starting. This indicates when any protection tripping occur causes breaker trips. Motor Protection Relay LED Configuration:

Micom p123 50n 51n