BUS BAR PROTECTION PPT BY:-R.K.PANDIT

TOPIC :-TOPIC :-BUSBAR BUSBAR PROTECTIONPROTECTION

SUBMITTED TO : -SUBMITTED TO : -MR.MANTOSH MR.MANTOSH KUMARKUMAR

PRESENTED BY : -PRESENTED BY : -RAGHVENDRA KUMAR RAGHVENDRA KUMAR PANDITPANDITCourse :-Course :-B.TECH 3B.TECH 3RDRD YEARYEARSECTION :-SECTION :-A2A2 ENROLL NO. –ENROLL NO. –MUR1301260MUR1301260

Department of Electrical Engineering

What is a bus bar?What is a bus bar?

Bus is derived from Latin word

“OMNIBUS” (common for all).

Nerve centre of the power system where various circuits are connected together.


Cause of FaultCause of Fault

Breakdown of insulation because of over voltages, foreign objects, etc

Weakening of insulation because of ageing ,corrosion ,salty water,etc.


Suitable ProtectionSuitable ProtectionDifferential protection Why differential protection?Terminals of the system are near to each

other.Hence by installing CT’s on the two sides of

the bus, comparison can be made between the current entering it & leaving it. Any difference in current will immediately signal an internal fault.

The difference in current can be used to excite the coil of a differential relay via CT secondary and thus issue trip commands to CB on both sides of the bus to isolate it.


Selection of CT RatiosSelection of CT Ratios That means the method of selecting

CT ratio on the basis of maximum primary current seen by an individual feeder is not correct.

CT ratios for all CT’s in bus differential schemes is = (max out of all feeder currents/1Aor 5A)


Types of FaultsTypes of FaultsFaults may be broadly classified as :

-

a)External Fault(through fault) & b)Internal Fault. Requirement of a unit protection is

that the differential scheme should respond to internal faults and should not respond to external fault.


Internal FaultInternal Fault Department of Electrical Engineering

External FaultExternal Fault The maloperation of bus bar differential scheme on external faults is caused due to non ideal behavior of CT carrying excessive primary current, during fault conditions.


CorrectionCorrection when due to external faults one of the CT’s get

saturated, the differential relay coil needs to be restrained from tripping.

We can easily accomplish this by connecting a high resistance known as stabilizing resistance in series with the differential relay coil

The stabilizing resistance should be of such a value,that under the worst case of maximum external fault and full saturation of CT,the current through differential coil is less than its pick up value and at the same time it should respond to minimum internal fault current.


Dot Convention Dot Convention

Dot markings are used to know the direction of circulating current in the CT secondary circuit.

Rule of dot convention says that :- “When current enters the dot mark on the

primary side of a CT, the current must leave the similarly marked dot mark on the secondary side & vice versa”.


Why PS Class Only ?Why PS Class Only ? Protection class CT’S such as 5P10,5P20 may

produce undesired difference current in the CT secondary due to following reasons -

1. Two or more CT’S of class 5P10 may have different accuracy (in this case for 10 times the rated current)

2. Even if the CT’S are identically manufactured, deterioration of core properties over time may differ & they may behave differently over time.


ConclusionConclusion

Thus it is concluded that the bus bar protection is an important part of the power system, as the system voltage has been increasing and short circuit capacities are building up.

So, it is not advisable to leave the bus bars unprotected on a primary basis.


THANTHANKK

YOUYOU
