MRQ1

Productomschrijving

The field failure relay MRQ1 protects synchronous generators against operation outside the stable operation area due to loss of excitation. When partial or complete loss of excitation occurs on a synchronous machine, reactive power flows from the system into the machine and the apparent impedance as viewed from the machine terminals goes into the negative X region in the R-X diagram.

The MRQ1 detects the low or under impedance condition and trips the generator circuit breaker, thus preventing damage due to out of step operation and system instability.
The under impedance measurement provides two elements with separate impedance and time settings. Therefore setting according to the dynamic and steady state stability curve is possible. MRQ1 calculates the momentary impedance value from the generator current and voltage and compares this value with the two settings of the under impedance elements.

Under impedance circle no. 1 reproduces the steady state stability area of the generator. Element no. 1 may be used for alarm purposes and corrective measures like boost excitation.
Element no. 2 reproduces the dynamic stability area of the generator. The time delay is set to a lower value. It provides fast clearing on complete loss of field and backs up element no. 1. Element no. 2 should trip the generator circuit breaker quickly.

The following factors determine the setting of the two elements: Stability diagram of the generator, excitation system of the generator and the system configuration.

Features
• Digital protection relay with powerful microcontroller
• Three phase voltage supervision in delta-connection
• Current measurement in phase L1
• Alphanumeric display for easy setting of the protection relay, reading of measured and calculated values and read out of the fault memory
• Digital filtering of the measured values by use of discrete Fourier analysis to suppress higher harmonics and d.c. components induced by faults or system operations
• Optimum adaptation to the stability characteristic of synchronous machines by two under impedance elements with separate set points and time delays
• Indication of the impedance measurement: absolute, real and imaginary value
• Under voltage blocking (<10% Un) of the under impedance elements to prevent maloperation due to missing measuring voltage, e.g. fuse failure or nearby short circuit of
the generator
• Self adjusting sample frequency for precise operation between 40 Hz and 70 Hz
• External blocking and reset inputs
• Communication via serial interface RS485
• Five output relays:
– Trip relay: Under impedance elements 1 and 2
– Alarm relay: Under impedance element 1
– Alarm relay: Under impedance element 2
– Trip relay: under voltage
– Self supervision