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