SERVICE MANUAL R5888B
QUADRAMHO Chapter 5
Addendum 3
Page 1 of 1
NEW RECOMMENDATIONS FOR TIMER SETTINGS
IN THE CURRENT REVERSAL GUARDS
Permissive Overreach Scheme 04 or 05
If the current reversal guard is not required, ie there is no parallel line or the
Zone 2 reach is not set to more than 150% of the line length, then set t
D
= 0 and
t
p
= 90ms.
If the guard is required, recommended t
p
= 30ms – minimum signalling channel
operating time.
(The nearest available setting should be selected if the exact value is not
available).
To give satisfactory scheme operation the value selected for t
p
must also be
less than mimimum time from fault inception to current reversal minus
(30ms + maximum signalling channel operating time).
Recommended t
D
– 25ms + maximum signalling channel reset time.
(The nearest available setting above should be selected if the exact value is not
available).
Blocking Scheme 06 or 07
Recommended setting for t
p
= maximum signalling channel operating time + X
(The nearest available setting above should be selected if the exact value is not
available).
X = 30ms for quadrilateral/mho version of the relay.
= 35ms for mho/lenticular (a/b = 1).
= 40ms for mho/lenticular (a/b = 0.69).
= 45ms for mho/lenticular (a/b = 0/41).
Recommended setting for t
D
= 25ms – minimum signalling channel reset time.
(The nearest available setting above should be selected if the exact value is not
available).
Note: The new recommendation for t
D
is to bring it in line with the approval
panels results on SHNB (Micromho Protection) that where a single
frequency signalling channel is used, during current reversals the block
signal to the relay should be continuous until the external fault has been
cleared.
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