Alstom SHPM 101, Service Manual

Page: 24 / 336

SERVICE MANUAL R5888B
QUADRAMHO Chapter 1
Page 8 of 27
If the relay is for use with miniature circuit breaker to break the VT supply, then the
opto used for reset Zone 1 extension is on case terminals A9 and A10 – shared
function with signal received if an aided scheme is selected.
17.2 Zone 1 extension (see Figure 4)
• This scheme does not require a signalling channel.
• Normally Zone 1 phase and ground fault comparator reaches are extended by
an amount to overreach the remote end of a protected line section.
• Scheme is intended for use with autoreclose equipment. After a fault occurs, the
autoreclose equipment gives a reset signal to the extension facility so that
Zone 1 phase and ground fault reaches fall back to normal setting.
• Scheme provides fast clearance of most transient faults. On the basis that most
overhead line faults are transient in duration, the scheme will allow fast
clearance of most faults along the protection section and also those just out of
the section. Lack of discrimination does not matter as autoreclosure of the
protection section circuit breaker(s) will take place.
The operation of the autoreclose relay is used to reset the extension facility so
that if the fault is permanent, upon reclosure, the faulted section of line will be
cleared permanently by its own protection as in the BASIC scheme.
• Scheme would not normally be used for cable circuits although its use might be
considered for hybrid circuits.
17.3 Permissive underreach transfer tripping (PUR – see Figure 5)
• This scheme requires only one signalling channel for both relays, as channel is
keyed by underreaching Zone 1 elements.
• Provided underreaching Zone 1 element reaches "overlap", fast clearance of
faults along the whole line section will be effected. If a line terminal is open,
then a fast tripping will only occur for faults within the Zone 1 reach of the
closed end relay.
• If the signalling channel fails, the line relays will still provide BASIC protection.
• Fast clearance will not occur for all faults along the protected line section if
there is little or no infeed at one terminal.
17.4 Permissive overreach transfer tripping (POR – see Figures 6 and 7)
• This scheme requires duplex signalling channels; one frequency for each relay,
as channel is keyed by overreaching Zone 2 elements.
• This scheme may be more advantageous than PUR for protecting short lines –
the resistive coverage of the Zone 2 mho circles would be greater than that of
the Zone 1 reach set to a small value. Thus POR enables fast tripping for higher
resistance faults along a line than does PUR.
• For standard POR schemes, if a line terminal is open, then as with PUR, fast
tripping will only occur for faults within the Zone 1 reach of the closed end
relay. However, with Quadramho a "signal echo" feature is included in the
scheme logic, which is initiated when the local line terminal is open (CB aux
contact initiation). By such means the closed end relay will be able to provide
fast tripping for faults along the whole length of the line.
• If the signalling channel fails the line relays will only provide BASIC protection.