MGFR-1-ZB, MGFR-2-ZB, MGFR-20-ZB:
Inst. 0.1 sec, 0.2 sec, 0.4 sec,
MGFR-1-AB, MGFR-2-AB, MGFR-20-AB:
0.6 sec, 1.0 sec, 3.0 sec, 5.0 sec.
MGFR-200-ZB, MGFR-200-AB, MGFR-1200-ZB:
Inst. 0.1 sec, 0.2 sec, 0.3 sec,
MGFR-1200-AB, MGFR-SE-ZB :
0.4 sec, 0.6 sec, 0.8 sec, 1.0 sec.
Once the relay picks up, the relay will trip at the time set by the user, regardless of the magnitude of the fault
current. Once the red cursor is set at any of the eight positions of the time setting switch, the figure in between
the two black lines pointed by the middle line of the red cursor, indicates the desired time setting.
2.3.2 IDMT CHARACTERISTICS
There are two sets of IDMT characteristics available in the MGFR series. One set is available in models MGFR-
2-ZB, MGFR-2-AB, MGFR-20-ZB and MGFR-20-AB. The other set is available in models MGFR-200-ZB, MGFR-
200-AB, MGFR-1200-ZB and MGFR-1200-AB. The slope of the curves is 63° and trip time is represented by the
following equation:
T(M1.96) = K for 1.2 < M < 10 ------ (1)
where,
M = Multiple of pick-up setting
T = Trip time in seconds
K = Relay Constant
As indicated, the above equation is valid for a fault current of magnitude between 1.2 X pick-up to 10 X pick-up.
So, for a relay to trip according to any of the IDMT curves represented by Eqn. (1), the fault current must have
a value of just above the pick-up. For M > 10, the trip time is definite and matches with the DMT settings of a
specific relay, as shown in section 2.3.1. Both sets of IDMT curves have similar mathematical representations as
shown in Eqn. (1), but the relay constants are different to match different minimum operating times.
The IDMT and DMT characteristics applicable to MGFR-1-ZB, MGFR-2-ZB, MGFR-20-ZB, MGFR-1-AB, MGFR-
2-AB, MGFR-20-AB are shown in Figure 2.
The IDMT and DMT characteristics applicable to MGFR-200-ZB, MGFR-1200-ZB, MGFR-SE-Z, MGFR-200-AB,
MGFR-1200-AB are shown in Figure 3.
As seen from the figures, there are eight curves in either of the sets. The CURVE SELECT switch should be set
to either DMT or IDMT position, as required.
Example: For a relay MGFR-20-ZB, the pick-up is set at 5.0A and the time-setting switch is set at 1.0 sec in
IDMT mode. If a ground fault current of 25A (5x pickup setting) is sensed by the relay, it should operate in
approximately 3.9 seconds (refer to Fig. 2).
2.4 DISPLAY
All models of the MGFR series have a three digit, numeric, LED display on the faceplate for indicating the fault
current in per unit. The fault value at which a relay picks up is 1.00 per unit. Thus, in the above example, the relay
should show ‘1.00’ when it senses a fault current of 5.0A (measured at the sensor primary). Any value of fault current
below or above the pick-up will be shown as a multiple of pick-up on the display. The relays measure the RMS value
of ground fault current, compute it in terms of per unit of pick-up and show it on the LED display.
Summary of Contents for MGFR Series
Page 1: ...C 322EM Instruction Manual March 2015 GROUND FAULT RELAY GROUND FAULT RELAY MGFR ...
Page 17: ...FIGURE 1 BLOCK DIAGRAM OF MGFR RELAYS ...
Page 21: ...FIGURE 5 CONNECTION DIAGRAM FOR MGFR RELAYS ...
Page 22: ...FIGURE 6 CONNECTION DIAGRAM FOR MGFR SE ZB RELAYS ...
Page 24: ...www i gard com Phone 905 673 1553 Toll Free 1 888 737 4787 Fax 905 673 8472 sales i gard com ...
