SEG Electronics GmbH
Manual MRG3
6
DOK-TD-MRG3, Rev. D
1. Overview and Application
The MRG3 is a universal mains decoupling device that covers all the protection functions which are
required by VDEW and by most other utilities for the mains parallel operation of power stations
such as:
over/and under voltage protection,
over/and under frequency protection,
extremely fast generator mains decoupling in case of vector surges or rate of change of
frequency df/dt
The MRG3 can furthermore be equipped with a multi-purpose over current time and earth fault pro-
tection re-lay and it has been designed as to be also used for grids with isolated and compensated
star points respectively. It is applicable for the mains parallel operation of power generating gen.-
sets and includes the following protection functions.
Independent (Definite) time over current relay,
dependent time over current relay with selectable characteristics, independent short
circuit protection
two-element (low and high set) earth fault protection with definite or inverse time
characteristics,
integrated determination of earth fault direction for application to power system networks
with isolated star point or earth fault compensation (ER/XR-relay type),
two-step protection for the residual voltage
For applications where only individual protection functions are required SEG Electronics GmbH
can, of course, also offer the following MR-relays as individual devices:
MRU3-1
four step independent over-/ and under-voltage protection (also used for
generator earth fault protection).
MRU3-2
two step independent over-/ and under-voltage protection with evaluation
of the symmetrical voltage components.
MRF3
four step independent over/ and under- frequency protection and two step
frequency gradient supervision df/dt.
MRI3-I
Independent (Definite) time over current relay, inverse time over current
relay with selectable tripping characteristics, independent short circuit
protection
MRI3-E
two-element (low and high set) earth fault protection with definite or inverse
time characteristics,
General Note
The description of the digital multifunction relay MR is a part of the present description and it in-
cludes technical data and details valid for most of the MR devices.