Manual MRG3
SEG Electronics GmbH
DOK-TD-MRG3, Rev. D
13
3.1.2 Analog input circuits
The protection unit receives the analog input signals of the phase currents IL1 (B3-B4), IL2 (B5-
B6), IL3 B7-B8) and the current IE (B1-B2), phase voltages U
L1
(A3 - A4), U
L2
(A5 - A6); U
L3
(A7 -
A8) and residual voltage U
0
(A2
– B1), each via separate input transformers.
The constantly detected current measuring values are galvanic ally decoupled, filtered and finally
fed to the analog/digital converter.
The voltage measuring circuits can optionally be star- or delta connected (see chapter 4.3.1)
For the unit type with earth fault directional features (MRG3-IER) the residual voltage U
E
in the
secondary circuit of the voltage transformers can internally be formed. The device shall then be en-
coded as described in chapter 3.1.8. Thus, star connection of voltage trans-formers is imperative.
For the detection of residual voltage from the open delta winding, the voltage transformer can di-
rectly be connected to B1 and A2. Connection of voltage trans-formers in isolated/compensated
grids is explained in chapter 4.7.3.
3.1.3 Output relays
The MRG3 is equipped with 5 output relays. Apart from the relay for self-supervision, all protective
functions can be optionally assigned:
Relay 1: C1, D1, E1 and C2, D2, E2
Relay 2: C3, D3, E3 and C4, D4, E4
Relay 3: C5, D5, E5
Relay 4: C6, D6, E6
Relay 5: Self-supervision C7, D7, E7
All trip and alarm relays are working current relays, the relay for self supervision is an idle current
relay.
3.1.4 Blocking input
The blocking function can be set according to requirement. By applying the auxiliary voltage to
D8/E8, the previously set relay functions are blocked (see chapter 4.8 and 5.9.1).
3.1.5 External reset input
See chapter 5.10.9.
3.1.6 Serial interface
The serial interface is an RS485 interface that is used for the parameterization of the MRG3 via
HTL/PL-Soft4 and for the sorting of recorded sequences of events. The terminal conditions are
specified in chapter 5.2 of the description MR
– Digital Multifunction Relay.
3.1.7 Auxiliary voltage supply
The MRG3 is supplied with auxiliary voltage by means of the terminals C9
– D9. It has to be made
sure that the device is connected to ground by means of terminal D9.