Woodward
Manual MRM3-2 GB
6
TD_MRM3-2_09.08_GB_Rev.New
1. Introduction and Application
The motor protection relay MRM3-2 offers reliable protection for LV and MV motors which are ei-
ther operated via power contactors or power circuit breakers.
The following functions are integrated into this relay:
•
Overload protection acc. to IEC 255-8 in consideration of the initial load factor
(thermal
image)
•
Definite undercurrent protection
•
Definite time over current protection (DMT)
•
Inverse time over current protection (IMT) with select-able trip characteristics
•
Short-circuit
protection
•
Load unbalance supervision with definite or inverse trip characteristics
•
Earth-fault detection with suppression of harmonics
The MRM3-2 recognizes the “Start-Up“ and “Motor Running“ phase.
Motors with a limited number of starts can be controlled by the start limiting function of the relay.
The earth-fault supervision is either realized in Holm-green connection or by means of a core-type
current transformer.
The motor can be stopped in delayed or undelayed mode via digital inputs.
The MRM3-2 is available with rated currents of 1A or 5A.
Important:
For additional common data of all MR-relays please refer to manual "MR - Digital Multifunctional re-
lays". On page 45 of this manual you can find the valid software versions.