P54x/EN OP/La4 Operation
(OP) 5-128
MiCOM P543, P544, P545 & P546
OP
There are two modes of operation, Indication and Restrain. In Indication mode, a CTS alarm
is raised but no effect on tripping. In Restrain mode, the differential protection is blocked
during 20 ms after CT failure detection and then the setting for the Current Differential is
raised to above load current. The CTS covers 2 sets of CTs in P544 and P546 as well as
one set of CTs on P543 and P545.
In order to achieve correct operation of the scheme, it is necessary that differential CTS is
enabled at each end of the protected zone.
Differential current transformer supervision (Differential CTS) in P543 - P546 models suffix K
are only compatible with P543 - P546 models suffix K.
Figure 81 Differential CTS
3.2.2 Standard CTS (voltage dependant CTS no need of communi
cations to declare CTS)
The standard CT supervision feature (CTS) operates on detection of derived zero sequence
current, in the absence of a corresponding derived zero sequence voltage that would
normally accompany it. The voltage transformer connection used must be able to refer zero
sequence voltages from the primary to the secondary side. Therefore, this element should
only be enabled where the VT is of five limb construction, or comprises three single phase
units, and has the primary star point earthed.
CTS block
I
N
>
&
Time delay t
P2130ENa
V
N
<
CTS alarm
Figure 82 Voltage dependant CTS principle scheme
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