Chapter 7) 7SR23 DAD Applications Guide
©2013 Siemens Protection Devices Limited
Chapter 7 Page 22 of 42
This can be affected by a direct intertrip or CB fail scheme. Another method, as shown, uses an interlocked
overcurrent relay (ILOC). This is arranged to detect any power infeed at F3 after the circuit breaker is opened.
This relay is a three pole over current type with a time setting of about 0.3 second, its operation is inhibited until
the busbar protection operates. Where the fault persists at F3 after the circuit breaker opens, the busbar
protection remains operated, so permitting the interlocked overcurrent relay to operate and unstabilise the circuit
unit protection or send an intertripping signal to the remote ends of the circuits.
3.1.3
CTs on ‘Busbar’ Side of the Circuit Breakers
Figure 3-4
CTs on ‘Busbar’ Side of CBs
Where CTs are located on only one side of the circuit breaker some protection zones do not extend fully to the CB
and protection ‘blind spots’ are formed. The areas of primary plant between the CTs and CB may not be protected
by the relevant protection zone e.g. F3 and F4 in Figure 3-4.
Faults F1 and F2 should be correctly cleared as before.
Fault F3 will only cause operation of busbar 1 and not busbar 2 protection because the fault is outside the zone of
busbar 2 protection. Thus the zone 2 fault will remain uncleared. Arrangements must therefore be made to cause
the zone 2 CBs to be tripped to clear the fault.
F4: The circuit CB will be tripped by the circuit protection. The fault will not be seen by the busbar protection.
Where the circuit protection continues to indicate that a fault is present arrangements must be made to unstabilise
the busbar protection.
BUSBAR
PROTN
CIRCUIT
PROTN
F1
F2
F3
ILOC
PROTN
Figure 3-5
CTs on ‘Busbar’ Side of CBs
Summary of Contents for 7SR23 DAD
Page 1: ...Answers for energy 7SR23 DAD High Impedance Protection Relay Reyrolle Protection Devices ...
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Page 4: ...7SR23 DAD Contents 2013 Siemens Protection Devices Limited ...
Page 60: ...Chapter 3 7SR23 DAD Performance Specification 2013 Siemens Protection Devices Limited ...
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