Manual MRM3-2 GB
Woodward
TD_MRM3-2_09.08_GB_Rev.New
13
3.4 Digital
part
The protection relay is equipped with a powerful micro-controller, being the core element of the pro-
tection unit. With this micro-controller all tasks are completely digitally processed, from discretisa-
tion of the measuring quantities to protective tripping.
With the protection program, stored in the program storage (EPROM), the micro-processor
processes the voltages applied to the analog inputs and from this calculates the fundamental har-
monics of the current. Digital filtering (DFFT-Discrete Fast-Fourier-Transformation) for suppression
of harmonics as well as suppression of DC components during the short-circuit is used in the
process.
The micro-processor compares the existing current with the threshold value (setting value) stored
in the parameter storage (EEPROM) and up-dates the thermal image. If a current exceeds the
threshold value for longer than the trip delay or if the thermal image exceeds its rated value, a fault
signal occurs. Dependent on their settings, the output relays pick up as well. When setting the pa-
rameters, all setting values are read-in by the micro-processor and saved in the parameter storage.
The program flow is continuously monitored by the incorporated "Hardware-Watchdog". Processor
failure is signaled by the “Self supervision” output relay.
Figure 3.7: Block Diagram of Protective Functions