Alstom MiCOM P546 - Page 472

P54x/EN AP/La4 Application Notes
(AP) 6-28 MiCOM P543, P544, P545 & P546
AP
R
Z6
Z6'
R6R6'

+jX
ZT
LOAD

32
A
O

P1976ENa
Figure 8 R6
MAX
determination (Distance option only)
β = 32 + 90 – α
Z load min = OA
R6MAX < Zload min x cos β
Where:
 Zload min is the minimum load impedance radius calculated above which already has
built in sufficient margin
 32 deg is the load angle that corresponds to the lower power factor of 0.85
 ‘α’ is the load blinder angle that matches ZT angle
The setting of negative resistance R5’ should equal the R5 to accommodate the ‘load import’
condition. Starting from the limit values R5
MIN
and R6
MAX
the actual R5 and R6 (including the
corresponding R5’ and R6’) reaches will be set in conjunction with the ‘Delta t’ setting below.
Note: R6
MAX
reach must be greater than the maximum resistive reach of any
distance zone to ensure correct initiation of the 25 ms and ‘Delta t’
timers. However, the R5
MIN
reach could be set below the distance
maximum resistive reach (inside the distance characteristic) if an
extensive resistive coverage is required, meaning that Out of Step
protection does not pose a restriction to the quad applications.