Motor Protection Relay Block P241

Functions :-

• Measurement of all instantaneous & integrated values
• Circuit breaker, status & condition monitoring
• Programmable Scheme Logic (PSL)
• Trip circuit and coil supervision (using PSL)
• Alternative setting groups (model dependent)
• Programmable function keys (model dependent)
• Control inputs
• Programmable allocation of digital inputs and outputs
• Sequence of event recording
• Comprehensive disturbance recording (waveform capture)
• Fault recording
• Fully customizable menu texts
• Multi-level password protection
• Power-up diagnostics and continuous self-monitoring of relay
• Commissioning test facilities
• Real time clock/time synchronization – time synchronization possible from IRIG-B input, opto input or communications
• Password protection
• Read only mode

Motor Differential Protection (87) :-

Circulating current differential protection operates on the principle that current entering and leaving a zone of protection will be equal. Any difference between these currents is indicative of a fault being present in the zone. If CTs are connected as shown in the Principle of circulating current differential protection diagram, it can be seen that current flowing through the zone of protection will cause current to circulate around the secondary wiring. If the CTs are of the same ratio and have identical magnetizing characteristics they will produce identical secondary currents and hence zero current will flow through the relay.

Biased Differential Protection :-
In a biased differential relay, the through current is used to increase the setting of the differential element. For heavy through faults, it is unlikely that the CT output at each zone end will be identical. This is due to the effects of CT saturation. In this case a differential current can be produced. However, the biasing will increase the relay setting,
such that the differential spill current is insufficient to operate the relay. A dual slope percentage bias characteristic is implemented in the P24x. The lower slope provides sensitivity for internal faults, whereas the higher slope provides stability under through fault conditions, during which there may be transient differential currents due to saturation effect of the motor CTs. The through current is calculated as the average of the scalar sum of the current entering
and leaving the zone of protection. This calculated through current is then used to apply a percentage bias to increase the differential setting.