BUS BAR PROTECTION
BY EMD
WHAT IS BUS BAR AND MODELS
• An electrical bus bar is defined as a conductor or a group of conductor used
for collecting electrical energy from the incoming feeders and distributes them
to the outgoing feeders
• Types of Bubar Arrangements:
1.Single Bus bar Arrangement
2.Single Bus-Bar Arrangement With Bus Sectionalized
3.Main and Transfer Bus Arrangement
4.Double Bus Double Breaker Arrangement
5.Sectionalized Double Bus Bar Arrangement.
6.One and a Half Breaker Arrangement
7.Ring Main Arrangement
8.Mesh Arrangement
SINGLE BUS BAR ARRANGEMENT
ADVANTAGES
DISADVANTAGES
1. Simple in Design
In case of bus fault or bus
2. Easy Maintenance
bar isolator fault or
3. Less Expenditure
maintenance , Total
4. Good Appearance
Substation is out of service.
SINGLE BUS WITH CB SECTIONALISER SYSTEM
ADVANTAGES
DISADVANTAGES
1. One complete section can 1. In case of any fault in
be taken out for maintenance
bus bar /bus connected
without disturbing the
isolator maintenance
continuity of other section.
all connected feeders
2. Even if a fault occurs on
of that section will be
one section of the bus, that
out of service .
faulty section along will
2. Bay CT/CB
be isolated while the other
maintenance can be
section continues to be in
carried out results
service
feeder will be out of
service
SINGLE BUS & TRANSFER BUS SYSTEM
ADVANTAGES
DISADVANTAGES
With this arrangement, all
the feeders are normally on
the main bus. If at
any time, a line breaker
maintenance is required,
that particular feeder, can
be transferred on to the
transfer bus. The feeder
protection thus gets
transferred to trip bus
couple breaker.
1. On fault occurrence or
maintenance, entire bus
becomes de-energised.
2. Only one line at a time
can be transferred on the
transfer bus
DOUBLE MAIN BUS & TRANSFER BUS SYSTEM
Salient features:-
•
This has got flexibility of transferring
any line to any of the main buses.
•
For maintenance or any fault
occurrence, only one bus becomes
dead while
•
other bus continues to be in service.
•
Any line breaker can be taken out for
maintenance by transferring it to
•
transfer bus, transferring its
protection to transfer bus coupler
breaker.
ONE AND HALF CIRCUIT BREAKER SYSTEM
Salient features:1. No changeover of line from one bus to the other
is required.
2. For breaker maintenance of any line, the load
gets transferred to the other bus.
3. For maintenance or an occurrence of a bus
fault, all the interconnections will be on healthy
bus.
4. Even if both buses become dead, lines can still
be in service through the tiebreaker.
This has got many such advantages to maintain the
system stability.
WHY BUS BAR PROTECTION REQUIRED ?
Slow fault clearance.
Busbar faults at F1 and F2 are cleared
by remote time delayed
Protection on circuits feeding the faults:
Time Delayed Over current or Time
Delayed Distance Protection
Fast clearance by breakers at the busbars instantly
Where busbars are sectionalised,Protection can limit
the amount of system disruption for a busbar fault
BUS BAR PROTECTION TYPES
Two types of Busbar protection are implemented and used
• Frame Leakage Protection
• Differential protection or Circulating Current Protection
• High impedance BBP
• Low Impedance BBP
• Centralised Busbar Protection
• Decentralised busbar Protection
(Digital Busbar Protection)
FRAME LEAKAGE PROTECTION OF BUSBAR
•
In this, the bus bar supporting frame will be
earthen through a current transformer. When the
fault in busbar, the fault current flow through
supporting frame’s earthing arrangement. The
Current transformer in the earthen frame reads
the fault current and if this fault current higher
than the pickup current, then the relay operates.
• Disadvantages: Careful construction of the system is
of utmost importance in this case, as the switchgear
must be insulated from ground, usually by standing it
on concrete and the foundation bolts must not touch
the steel reinforcement.
THEORY BEHIND BBP
• Busbar Protection is the Differential scheme
in which current entering and leaving the bus
should be equal
• During Normal Load Conditions , The sum of
these currents is equal to Zero. When fault
occurs in protected zone , the differential
current will flow through the relay and causes
opening of connected breakers on the
particular bus.
HIGH IMPEDANCE BBP
High impedance is nothing but a where the
impedance value of the circuit is high which means
when the circuit operates in high voltage with low
current is called high impedance circuit.
1. The parallel CT must have same CT ratio
2. The CTs must be connected in same polarity
Burden of the all parallel CTs should be same. In
order to avoid the voltage, drop across the CT
3. CT accuracy should be same
4. CT cannot be shared with other circuit’s equipments
LOW IMPEDANCE BBP
Low impedance circuits are exactly opposite to the high impedance circuits, which means the
circuit operates low voltage with high current such a circuit is called Low impedance circuit. The
low-impedance bus differential relays can share the CTs with other relays, meters, transducers,
etc
• Centralised Busbar protection : In this solution, all copper wires from current transformers and
status of disconnections, as well as the tripping circuits to the circuit breakers, are connected to
a central panel, where the busbar protection IED is installed.
• Decentralized busbar protection : In this case bay units are installed in the individual bay
protection panels to provide the interfaces from the primary equipment to the busbar
protection system. The bay units will be installed in the switchyard, close to the primary
equipment.