Alstom SHPM 101, Руководство по обслуживанию

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SERVICE MANUAL R5888C
QUADRAMHO Chapter 2
Page 54 of 74
5.16.25 Permissive overreaching scheme (POR)
The overreaching directional Zone 2 elements are used to send a signal (85X–1
and 85X–2) to the remote end of the feeder. The Zone 2 elements permit tripping
on receipt of a channel signal (via opto isolator input CRX) and in this way,
instantaneous tripping via the Zone 2 elements will only occur for internal faults.
A duplex (two frequency) channel is essential for this scheme. The trip is sealed-in
until the Zone 2 elements reset.
There is also a requirement with the overreaching scheme for a current reversal
guard feature to prevent inadvertent tripping of the circuit breaker associated with
the healthy line of a faulted parallel feeder circuit. Such a feature (t
p
and t
d
) forms
part of the Quadramho scheme logic action. Should this feature not be required it
is easily disabled (set t
d
= 0).
A further feature is provided which enables fast tripping to be maintained along
the whole length of the protected line, even when one terminal is open. This is the
“ECHO” feature and it is initiated 60ms after the “Breaker Open” opto isolator has
been energised. The 60ms time delay is provided to ensure that the received signal
is not echoed back for busbar faults. However, there will be no time delay
introduced in echoing the signal when the breaker is already open. Figure 69,
Appendix A, gives an equivalent logic diagram.
5.16.26 Weak infeed feature (POR scheme only)
When one end of the line is connected to a weak infeed terminal, the distance
measuring elements at the weak infeed end cannot operate and consequently the
operation of the scheme is affected.
In the permissive overreach scheme, the relay at the strong infeed end terminal
would not be able to operate instantaneously, in the absence of a channel signal
from the weak infeed end terminal. Also the weak infeed end fails to trip during
such conditions. However, with certain additional scheme logic, it is possible to
achieve rapid tripping of both ends for faults anywhere within the line, even during
weak infeed conditions of one terminal (see Figure 70). SW8 is provided to
enable the “weak infeed” feature, if required. With SW8 in the left hand position
the weak infeed feature is disabled and in the right hand position it is enabled,
provided that the scheme chosen is the permissive overreach scheme (CSN – 04 or
05).
The Zone 3 measuring elements at the weak infeed terminal are set to look in the
reverse direction to cover the reach of the Zone 2 elements from the strong infeed
end.
The weak infeed condition is detected by the receipt of a channel signal and the
failure of operation of Zone 3 measuring elements. For an external fault, behind
the weak infeed terminal, when the fault infeed is from the strong infeed terminal
source, the reverse looking Zone 3 would operate and block the operation of weak
infeed circuit. However, for an internal fault, the distance measuring elements at
the weak infeed terminal do not operate, thus enabling the weak infeed circuit.
When a channel signal is received by the relay at the weak infeed end, 10ms and
60ms timers are energised, provided that:
i) there has been no operation of any distance measuring units.
ii) the breaker is closed.
iii) the alarm has not operated.