One communication channel is used in each direction, which can transmit an on/off
signal if required. The performance and security of this function is directly related to
the transmission channel speed and security against false or lost signals.
In the directional scheme, information of the fault current direction must be transmitted
to the other line end.
With directional comparison in permissive schemes, a short operate time of the
protection including a channel transmission time, can be achieved. This short operate
time enables rapid autoreclosing function after the fault clearance.
During a single-phase reclosing cycle, the autoreclosing device must block the
directional comparison ground-fault communication scheme.
The communication logic module enables blocking as well as permissive under/
overreaching schemes. The logic can also be supported by additional logic for weak-
end infeed and current reversal, included in the Current reversal and weak-end infeed
logic for residual overcurrent protection (ECRWPSCH, 85) function.
Metallic communication paths adversely affected by fault generated noise may not be
suitable for conventional permissive schemes that rely on signal transmitted during a
protected line fault. With power line carrier, for example, the communication signal
may be attenuated by the fault, especially when the fault is close to the line end,
thereby disabling the communication channel.
To overcome the lower dependability in permissive schemes, an unblocking function
can be used. Use this function at older, less reliable, power line carrier (PLC)
communication, where the signal has to be sent through the primary fault. The
unblocking function uses a guard signal CRG, which must always be present, even
when no CR signal is received. The absence of the CRG signal during the security time
is used as a CR signal. This also enables a permissive scheme to operate when the line
fault blocks the signal transmission. Set the tSecurity to 35 ms.
3.13.1.2 Setting guidelines
The parameters for the scheme communication logic for residual overcurrent protection
function are set via the local HMI or PCM600.
The following settings can be done for the scheme communication logic for residual
overcurrent protection function:
Operation: Disabled or Enabled.
SchemeType: This parameter can be set to Off , Intertrip, Permissive UR, Permissive
OR or Blocking.
Section 3 1MRK504116-UUS C
IED application
730
Application manual
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