Directional Relay Testing; Introduction - ISA T1000 PLUS User Manual

DOC. MIE91093
1.5 D
IRECTIONAL RELAY TESTING

1.5.1 Introduction

These relays are used to protect MV feeders against Earth
faults by detecting the residual voltage V
I and the relative angle. Normally the current is lagging; for
o
neutral isolated lines, I
(resistance, Petersen Coil), the phase angle can be less: 40°,
60°. This is also the angle of maximum sensitivity of the relay.
Since relay inputs are one current and one voltage, we'll use I
main and V aux to perform the test.
The parameters that we will test are:
 The characteristic angle, sometimes called MTA= max
torque angle (electromagnetic relays), and the Angle
sector, that is half of the operating angle;
 The pick up of Io;
 The pick up of Vo.
When testing one parameter we have to set the other two at a
value above the pick up.
 Test MTA: we keep Vo and Io above the respective pick
ups.
 Test the Angle sector: we keep Vo and Io above the
respective pick ups.
 Test the pick up of Io: we keep Vo above the pick up,
and the current angle at the measured Characteristic
Angle.
 Test the pick up of
measured pick up, and the current angle at the
measured Characteristic Angle.
In this example we'll suppose we are testing a relay with the
characteristic displayed in the graph.
Rev. 1.34
 -90°; for other earth systems
o
Vo: we keep Io above the
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, the residual current
o