Woodward MRM4, Manual

Page: 323 / 460

Protective Elements
•
LINV (AMZ);
•
EINV (AMZ);
•
MINV (AMZ);
•
VINV (AMZ);
•
EINV (AMZ);
•
Thermal Flat;
•
IT;
•
I2T; and
•
I4T.
Explanation:
The directional decision depends on the layout of the mains star-point or the angle between residual voltage and
ground current. The residual voltage can be measured via suitable transformers (da-dn winding – formerly: e-n)
or can be calculated, provided the VTs are in star-connection.
The earth current can be measured either directly via a cable-type transformer or detected by a Holmgreen
connection. The earth current can alternatively be calculated from the phase currents; but this is only possible if
the phase currents are not ascertained by a V-connection.
The device can optionally be procured with a sensitive earth current measuring input (in preparation).
EN MRM4 01/11 Page 323
t = Tripping delay
t-char = Time multiplier/tripping characteristic factor
IG = Fault current
IG> = If the pickup value is exceeded, the module/element starts to time out to trip.