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GE Power Management MDP Digital Time Overcurrent Relay 1-

GEK-100682D 1 INTRODUCTION

The instantaneous overcurrent unit can be applied in many instances to reduce the fault clearing time for high

fault currents. This unit is normally set to pick up only on internal faults in the protected zone. Significant tran-

sient overreach can be experienced under certain conditions, and this must be taken into account by selecting

a pickup setting that is higher than that which would be dictated by the maximum steady state external fault

current.

IMPORTANT: If one unit (instantaneous or inverse) operates, the other unit (inverse or instan-

taneous)

will also

operate. The MDP fault report will record the first fault that occurred. When

the fault is cleared, the fault LEDs will display Phase-Phase, Phase-Ground, Instantaneous,

and Inverse Time faults. See display section on how to interpret the display for various fault

conditions. The MDP generates a new fault report when the fault current drops below the pick-

up value and a new fault occurs.

Contact converter input CC1 and the output select switch of the MDP allow a zone selective interlocking of the

MDP relays. This scheme provides instantaneous operation (with a minimum time delay) of the upstream relay

for faults between the upstream and downstream relays. Refer to Figure 4–4: TYPICAL EXTERNAL CON-

NECTIONS, ZONE SELECTIVE INTERLOCK on page 4–4 for a typical scheme and settings considerations.

Note that all the feeders must be radial, with no (or very weak) source.

1.4 INTERFERENCE SUPPRESSION GROUND CONNECTION

The MDP relay contains high frequency interference protection consisting of a series of capacitors connected

between the input terminals and the case.

The case stud of the relay should be connected to ground, so these interference suppression circuits can per-

form their protective function. This connection should be as short as possible, to assure maximum protection.

Braided #12 AWG conductors are recommended.

NOTE

Courtesy of NationalSwitchgear.com

GE MDP User Manual

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