SERVICE MANUAL R5888B
QUADRAMHO Chapter 1
Page 9 of 27
• For standard POR schemes, fast clearance will not occur for all faults along the
protected line section if there is weak or no infeed at one terminal. It is possible
with Quadramho to switch in a weak infeed feature which will allow aided
tripping of the strong infeed relay and three phase tripping of the weak infeed
relay. The feature used undervoltage logic and Zone 3 elements set to be
reverse looking.
17.5 Blocking (see Figure 8)
This scheme requires only one signalling channel for both relays.
Two forward zones of protection are available, as Zone 3 elements are required to
be reverse looking, for initiating blocking signal.
This scheme will provide similar resistive fault coverage to POR.
If a line terminal is open, fast tripping will still occur for faults along the whole of
the protected line length.
If the signalling channel fails, fast tripping will occur for faults along the whole of
the protected line, but also for some faults within the next line section.
Fast tripping will still occur at a strong source line terminal, for faults along the
protected line section, if there is weak or no infeed at the other terminal.
Section 18. TIMER SETTINGS FOR DISTANCE SCHEME LOGIC OF QUADRAMHO
18.1 Permissive underreach scheme
Operating conditions:
Zone 1 operation – –> instantaneous trip + signal transmit
Zone 2 operation + signal receive – –> instantaneous trip
Special aspects to consider:
SINGLE END FED DOUBLE CCT LINE, FAULT CLOSE UP
In the situation outlined above, end B receives a permissive trip signal from the
faulted circuit relay at end A. A trip cannot occur at end B however, because it
sees negligible fault current. When end A trips, end B sees a Zone 2 fault, but end
A
Open
BAB
a) Fault occurs – busbar voltage
low so negligible fault current
via end B.
b) End A relay clears fault and
current starts feeding from
end B.
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