Multi–Function Protection Relay Block 7SJ551

Type : 7SJ551

FEATURES :

1. Thermal overload protection of rotating devices:
– seperate thermal replica for stator and rotor based on True RMS current measurement
– up to 2 heating time constants for the stator thermal replica
– seperate cooling time constants for stator and rotor thermal replica
– ambient temperature biasing of thermal replica
– incorporation of additional heating effects of asymmetrical currents.
2. Thermal overload protection of non–rotating devices:
– up to 2 heating time constants with extremely wide setting ranges for optimal thermal protection of cables and
transformers
– externally adjustable time constant
– ambient temperature biasing of thermal replica.                                                                                                 3. Connection of up to 8 RTD sensors.
4. Multi–curve over current and earth–fault protection:
– insensitive for transients and DC components
– separate two stage tripping characteristics for phase and earth elements                                                                 5. Curve Switch and Blocking functions offer an adaptive feature to change the relay characteristics according to prevailing system conditions.                                                                                                                                                 6. Separate setting tables for the protection of rotating and non–rotating network components.
7. Equiped with highly sophisticated protection algorithms which offer optimal flexibility in grading with other protection relays and with the thermal limit curves of primary components.                                                                        8. Software matrix for signalling and tripping relays.
9. Real Time Clock: last 3 events are stored with real time stamps of alarm and trip data.
10. Fault recording

This Multi–Function Protection Relay Block is easily insert in your schematic diagram and connect as you like way.

APPLICATIONS:

1. Multi–function protection relay for rotating electric machines, especially asynchronous motors.
2. Thermal overload, over current and earth–fault protection for transformers and cables.
3. Back–up protection for differential and distance relays in high voltage feeder protection schemes.
4. Earth–fault direction protection for isolated, compensated and high–ohmic earthed networks.
5. Directional over current and earth–fault protection in combination with external connected directional unit like 7SP20.                                                                                                                                                                             The relay uses a thermal memory to resemble the remaining thermal capacity of the protected device. This is a measure for the allowed heating of the protected device. The thermal capacity can be obtained from the True RMS phase currents, taking into account the effect of asymmetrical current. A pre–alarm signal is issued when the thermal memory reaches the warning level. The start inhibit function permits starting of the motor only when the thermal reserve of the motor is sufficient for a complete start.The thermal capacity available can be adjusted according to the actual ambient temperature as monitored by an RTD– sensor. The ”under voltage function” protects devices against operating on too low voltage. The ”over voltage function” protects devices against operating under too high phase, line or zero sequence voltage.