Busbar Blocking System

1. BUSBAR BLOCKING SYSTEM
KKKL 4043
PROTECTION AND SAFETY POWER
SYSTEM
LECTURER: DR HUSSAIN SHAREEF
BY NORALINA ABDUL AZIZ A117805

2. INTRODUCTION
• The protection scheme for a power system should cover the
whole system against all probable types of fault.
Unrestricted forms of line protection, such as overcurrent and
distance systems, meet this requirement, although
faults in the busbar zone are cleared only after
some time delay. But if unit protection is applied to feeders
and plant, the busbars are not inherently protected.

3. INTRODUCTION
• Busbars have often been left without specific protection, for
one or more of the following reasons:
 the busbars and switchgear have a high degree of
reliability, to the point of being regarded as
intrinsically safe
 it was feared that accidental operation of busbar
protection might cause widespread dislocation of the
power system, which, if not quickly cleared, would
cause more loss than would the very
infrequent actual bus faults
 it was hoped that system protection or back-up
protection would provide sufficient bus protection if
needed

4. REQUIREMENTS

5. TYPES OF PROTECTION

6. BUSBAR BLOCKING
• The application of busbar blocking technology has lagged
behind that of other protection functions. But, busbar
blocking technology is now readily available.
• The very latest developments in the technology are included,
such as extensive use of a data bus to link the various units
involved, and fault tolerance against loss of a particular
link by providing multiple communications path.
• The development process has been very rigorous, because
the requirements for busbar protection in respect of
immunity to maloperation are very high.

7. SINGLE BUS WITH ONE INCOMING FEEDER
OPERATION
50
A
50 50 50 50 50
B
One incoming feeder supplies a number of outgoing radial
feeders from unsectioned busbar. Three phase overcurrent and
earth faulth relay, from blocking are already provided. A busbar
blocking scheme need to be configured which will give fast
tripping of the incomer for the busbar fault at A while remaining
stable for the feeder fault at B. the feeder fault would be cleared
by overcurrent protection tripping

8. FAULT EXTERNAL TO
BUSBAR ZONE
50
50 50 50 50 50
B L O C K
B
The fault at B will typically cause operation of IDMT phase fault or
earth fault elements of the blocking protection relay. These element
are designed to trip the relay output contacted assigned. Each of
these element have instantaneous start output contact. In busbar
blocking schemes, these start output contacts are use to block
tripping of the incoming feeder element which is nominally set to
provide busbar protection.

9. FAULT ON THE BUSBAR
50
A
50 50 50 50 50
B L O C K
BACKTRIP
Rather than wait for the incoming feeder IDMT protection element to
clear the fault, busbar blocking are used. These blocking element will
trip on detecting fault current above setting, provided that a block
signal has not been received from outgoing feeder. Because the
connection of blocking signals between relays is hardwired. The
blocking element must allow sufficient time for any start to be issued
by an outgoing feeder relay, and then to recognize that the block onto
input has been energized, allowing the block to be applied. For the
busbar fault at A, no block would be received and incoming feeder
tripping would be subject to the short time delay set.

10. ADVANTAGES
• Very lost or no cost system
• Simple
• Faster than faults cleared by back-up relays
• Covers phase and earth faults
• Adequate sensitivity – independent of number of circuits
• No additional CT
• Commissioning is simple – no primary current stability tests

11. DISADVANTAGES
• Only suitable for simple busbars
• Additional relays and control wiring for complex busbars
• Beware motor in-feeds to busbar faults
• Sensitivity limited by load current

12. APPLICATION
MiCOM Busbar Blocking Scheme
• MiCOM relay is busbar protection achieved by simple
interconnection which already specified for their primary task
of the feeder protection.
MiCOM P740 range busbar
protection relay

13. APPLICATION
MiCOM Busbar Blocking Scheme
Advantages:
faster busbar fault clearance compared to tripping
initiated by upstream feeder protection
busbar protection at minimal additional cost
Fault and disturbance records stored for busbar faults
Blocking scheme can be easily modified

14. THANKS FOR
THE TIME