P521/EN AD/B21
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MiCOM P521
Example 3
As with example 2, both the 52a and 52b auxiliary contacts are available. The
MiCOM P521 relay monitors the whole of the trip circuit whatever the CB status (CB
open or CB closed).
In this example resistor R1 needs to be fitted to prevent permanent trip coil
energisation, if the trip contact (RL1) is latched, stays involuntarily closed, or a long
trip pulse time is programmed.
MiCOM P521
+Vdc
Trip Order
RL1
52a
Opto-input
2
6
Trip Coil
- Vdc
P0040ENb
52b
Resistor R1
Figure 24: Trip coil and auxiliary contact monitoring regardless of CB
position
5.8
Unconditioned 4 wire pilot communications for distances greater than 1.2km
(P595)
In order to increase the transmission distance of EIA(RS)485 up to 10 kilometres it is
necessary to use the P595 (see PZ511 publication AFS.12.05940/1098EN)
interfacing device at each end of the line. To gain maximum performance of the
P521, the data rate must be set to 19.2kbps and the protocol set to “NRZ” (Non
Return to Zero).
Pilot isolation must also be considered, when connecting the P595. If the longitudinal
voltage exceeds 900V the PCM-FLU 10kV or 20kV isolating transformers must be
fitted in series with the P595. The PCM-FLU isolating transformer has “a”, “m” and
“b” taps on both primary and secondary windings. For all P521 applications,
connection must be made between taps ‘a’ and ‘m’, which has a maximum
frequency of 2MHz. Connection between ‘a’ and ‘b’ may result in unreliable
communications as the maximum frequency for this tap configuration is 6kHz.
Connection to ‘a’ and ‘m’ taps must be adhered to on both primary and secondary
so as to maintain a 1:1 ratio.
Refer to section P521/EN CO for connection diagrams.
