Micom P721, Technical Manual

Page: 289 / 334

Commissioning and Maintenance P72x/EN CM/C21
MiCOM P721/P723 Page 19/28
Checks:
Alarm message on the LCD.
Alarm LED flashes.
[95] tSup LED on (if programmed).
Trip output does not close
(If
Diff I Threshold [87] 2 2 Idiff Sup I Threshold [95] 2 2
× × < < × ×
and the [95] Fault
timer t Sup has elapsed).
[95A] tSup A output closes (if programmed).
[95B] tSup B output closes (if programmed).
[95C] tSup C output closes (if programmed).
[95] Fault Timer tdiff check:
Apply a current onto phase A and measure the time delay [95A] tDiff A by pre-setting the
current above the 2
× √
2
×
[95] Threshold I Sup (2
×
2
× √
2
×
[95] Threshold I Sup < I
injected < 2
× √
2
×
[87] Threshold I Diff). Repeat the same test for phases B and C using
[95B] tSup B and [95C] tSup C respectively.
4.6 Earth bus wire supervision ([95N] Earth Bus-Wire Sup)
Three P721 relays are required to use the P721 in three phase applications. In this case,
the [95N] Earth Bus-wire Sup should be tested the same way as the [95] Phase Bus-wire
Sup in the P723. [95N] Sup and [95N] tSup should be verified. Check section 4.5 for further
test details.
4.7 REF/BEF Primary Injection Tests
Primary injection tests will be used to check that the current transformers for the high
impedance differential scheme are correctly connected.
4.7.1 Correct set up check
Before commencing any primary injection tests it is essential to ensure that the circuit is
dead, isolated from the remainder of the system and that only those earth connections
associated with the primary injection test equipment are in position.
The stability of the scheme can be checked by injecting through the neutral current
transformer and each phase current transformer in turn. This test is required when the P72x
is used in a high impedance REF.
Figure 7 shows the connections for the P721 and P723 when the relays are used in a high
impedance differential scheme.