GE P741, Technical Manual

Page: 382 / 560

Commissioning P74x/EN CM/Na7
MiCOM P741, P742, P743 (CM) 10-29
CM
I
bias
is fixed to a lowest value of ID>2/k2 and IDCZ>2/kCZ, the Az and Acz points will thus be
ID>2 and IDCZ>2. So I
bias
= I
1
+ I
2
= fixed value (Points A)
To test the slopes:
I
bias
is fixed to a value greater than ID>2/k2 and IDCZ>2/kCZ the Bz and Bcz points will thus
be I
bias
x k2 and I
bias
x kCZ. So I
bias
= I
1
+ I
2
= fixed value (Points B)
When we reach the point Xcz the Central Unit LED 8 and relay 8 will operate and when we
reach the point Xz the differential element will operate.
To calculate the slope k, k = (I
1
– I
2
) / (I
1
+ I
2
)
The differential current will increase twice the value

I.
Note 1: I
D
>1 alarm timer will be set to 100s during the test.
Note 2: Whenever possible, inject 2
×
I
D
>2. Alternatively, the minimum current
must be higher than 1.7
×
I
D
>2 at 60Hz and I.42
×
I
D
>2 at 50Hz in
order to ensure a 15ms tripping time
6.3.1.2 Slopes and thresholds
If a LED has been assigned in central or/and peripheral units to display the trip information,
these may be used to indicate correct operation. If not, monitor option will need to be used –
see the next paragraph.
On P741 go Central Unit GROUP1-->BUSBAR PROTECT and set I
D
>1 Alarm timer to 100s
On P742/3 go to COMMISSION TESTS column in the menu, scroll down and change cells
[Monitor Bit 1] to [BUSBAR_TRIPPING]. Doing so, cell [Test Port Status] will appropriately
set or reset the bits that now represent BUSBAR_TRIPPING (with the rightmost bit
representing Busbar Trip. From now on you should monitor the indication of [Test Port
Status]. Make a note of which elements need to be re-enabled or re-set after testing.
Test of I
D
>2:
I
D
>1 Alarm Timer should be set to 100s during testing.
Inject a I
2
current smaller than I
D
>2 and slowly increase I
2
until tripping.
Test of the operating time of the differential element:
Inject a I
2
current greater than twice I
D
>2 threshold and measure the operating time of the
differential element.
Test of I
D
>1:
I
D
>1 Alarm Timer should be set to 100ms.
Inject a I
2
current smaller than I
D
>1 and slowly increase I
2
until circuit fault appears (LED
Alarm of LED circuitry fault).
Test of I
D
>1 Alarm Timer:
I
D
>1 Alarm Timer should be set to 5s.
Inject a I2 current greater than twice the I
D
>1 threshold and check that the Circuitry Fault
Alarm is coming in 5s.
Note: Same tests can be applied for the Differential Sensitive Earth Fault Protection.
Note: the Sensitive Differential Earth Fault (SDEF) is 20ms delayed and controlled by a
settable threshold I
bias
ph> to unblock/block the sensitive element depending of the restrain
phase currents.
IMPORTANT NOTE: Check that if the SDEF is enabled, all the CTs are of the same
standard.