busbar blocking system
Post on 12-Jul-2015
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BUSBAR BLOCKING SYSTEM
KKKL 4043PROTECTION AND SAFETY POWER
SYSTEMLECTURER: DR HUSSAIN SHAREEF
BY NORALINA ABDUL AZIZ A117805
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.
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
REQUIREMENTS
TYPES OF PROTECTION
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.
SINGLE BUS WITH ONE INCOMING FEEDER OPERATION
50
50 50 50 50 50
A
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
FAULT EXTERNAL TO BUSBAR ZONE
50
50 50 50 50 50
BL
OC
K
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.
B
FAULT ON THE BUSBAR
50
50 50 50 50 50
A
BL
OC
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.
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
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
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
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
THANKS FOR
THE TIME
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