Application - ABB RELION 670 SERIES Applications Manual

Section 16
Scheme communication
16.6.2
16.6.3
770

Application

To achieve fast fault clearance of ground faults on the part of the line not covered by the
instantaneous step of the residual overcurrent protection, the directional residual
overcurrent protection can be supported with a logic that uses communication channels.
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.
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:
1MRK 506 369-UUS -
Line distance protection REL670 2.2 ANSI
Application manual