GE Power Management
MDP Digital Time Overcurrent Relay
2
-
3
GEK-100682D
2 OPERATING PRINCIPLES
2
8.
Tighten the screw just enough to hold the assembly in place until all four screws are aligned. When all the
screws are aligned, tighten them with gentle pressure so that the board is mounted evenly.
9.
SET THE COMMUNICATIONS ADDRESS before restoring the cradle to the case.
Figure 2–3: REAR VIEW SHOWING COMMUNICATION ADDRESS SWITCHES
2.4 MEASUREMENT
A timer internal to the microprocessor generates an interrupt every millisecond. Phase and ground measure-
ments are made at each of these interrupts. These measurements are grouped, separately for each phase and
ground, in groups of ten, and the average of the maximum value of these groups is taken.
This average is converted to a multiple of pickup TOC, the format used by the relay. This value is displayed in
5 second intervals.
2.5 INVERSE TIME UNIT
The multiple of pickup TOC measurement obtained is compared, independently for each phase and ground,
with a value, the pickup setting, that corresponds to one times (1
×
) pickup TOC. If the measurement exceeds
the fixed setting, a Pickup LED lights on the front of the relay.
The minimum current necessary to operate the Inverse Time measuring elements is never less than the set
value (
I
s
), nor greater than 10% more than (110% of) the set value.
The dropout to pickup ratio is not less than 95%, based on the actual operating value.
The MDP relay incorporates five inverse time curves and four definite times. The curve within a family is
selected by the time dial. The characteristic curves for the MDP relay correspond approximately as follows.
1.0
I
s
I
min
1.1
I
s
<
<
