Switch Gear & protection
Chapter-03
(Busbar arrangement)
-Asiqur Rahman Milon,EETE-DIU,EEE-IEB(Con)
#What
is Bus bar?
-Bus
bar-
An
electrical bus bar is defined as a conductor or a group of conductor used for
collecting electric power from the incoming feeders and distributes them to the
outgoing feeders. In other words, it is a type of electrical junction in which
all the incoming and outgoing electrical current meets. Thus, the electrical
bus bar collects the electric power at one location.( A bus – bar is a conductor or group of
conductors and it collects electric energy from incoming feeders and
distributes them to outgoing feeders. So bus – bar is a junction where all
incoming and outgoing currents meet. Bus – bar is generally made up of aluminum
but not with copper because aluminum has special characters like higher
conductivity, lower cost, excellent corrosion resistance, etc.)
The
bus bar system consists the isolator and the circuit breaker. On the occurrence
of a fault, the circuit breaker is tripped off and the faulty section of the
busbar is easily disconnected from the circuit.
The
electrical bus bar is available in rectangular, cross-sectional, round and many
other shapes. The rectangular bus bar is mostly used in the power system. The
copper and aluminium are used for the manufacturing of the electrical bus bar.
The most common of the bus-bars are 40×4mm (160 mm2);
40×5 mm (200 mm2) ; 50×6 mm (300mm2) ; 60×8 mm (480 mm2)
; 80×8 (640 mm2) and 100×10 mm (1000 mm2).
The
various types of busbar arrangement are used in the power system. The selection
of the bus bar is depended on the different factor likes reliability,
flexibility, cost etc. The following are the electrical considerations
governing the selection of any one particular arrangement.
· The bus bar arrangement is simple and easy in
maintenance.
· The maintenance of the system did not affect their
continuity.
· The installation of the bus bar is cheap.
The
small substation where continuity of the supply is not essential uses the
single bus bar. But in a large substation, the additional busbar is used in the
system so that the interruption does not occur in their supply. The different type
of electrical busbar arrangement is shown in the figure below.
# What is the properties of bus bar?
We have different
types of bus – bar arrangements we need to choose the required arrangement.
This depends on various factors such as
1. System voltage.
2. Position of a
substation in the system.
3. Reliability of
supply.
4. Flexibility.
5. cost.
6. Availability of
alternative arrangements if outage of any of the apparatus happens.
7. Bus – bar
arrangement should be simple and easy to maintain.
8. In case of load
– growth there must be the possibility to extend the system to meet the load
requirements.
9. The
installation should be as economical as possible, keeping in view about the
needs and continuity of supply.
#What is the shape and structure of bus bar?
-The bus bar shape generally is rectangular
shape,square shape,triangle shape.It’s each height is 2m to 5m.In a bar or in a
section interconnected by clamp,nut bolt,welding etc.In a bus bar one side is
use for accept supply and another side is used for supply distribution to various
load circuit.
#Describe different types of Bus bar?
-The different types of bus bar is-
1) Indoor bus bar
2) Outdoor bus bar
3) Open bus bar
4) Enclosed bus bar
5) Oil sinking bus bar
6) Pressured gas insulated bus bar
7) With 3-phase bus bar
8) Without 3-phase bus bar
9) Isolated phase bus bar
#Mention different types of bus bar arrangement?
-The bus bar arrangement is given below-
1. Single bus-bar
arrangement.
2. The single
bus-bar arrangement with bus sectionalized.
3.Double bus
arrangement.
4. Double bus
double breaker arrangement.
5. One and a half
Breaker arrangement.
6. Main and
transfer bus arrangement.
7. Double bus
system with by pass isolators.
8. Ring main
arrangement.
9. Mesh
arrangement.
#Describe single busbar arrangement with application and advantages and dis
advantages?
- Single busbar arrangement with application and advantages and dis
advantages is-
1.
Single Bus-Bar Arrangement
It is a simplest form of arrangement of
bus-bar. It is used in power stations and small outdoor substations having
small number of incoming and outgoing feeders. Each generator and feeder is
controlled by a circuit breaker.
Advantages
It has low initial cost.
It required less maintenance.
Simple operation.
Disadvantages
If fault occurs on bus-bar, whole supply is
affected.
For repair and maintenance of the bus-bar,
whole of the system has need to be de-energized.
# Sectionalized single busbar arrangement with application and advantages
and dis advantages?
- Single busbar arrangement with aplication and advantages and dis
advantages is-
Single Bus-Bar Arrangement with
Sectionalization
In large power generating stations, where
several numbers of generators and feeders are required to be connected to the
bus-bar. In that cases, Single bus-bar arrangement with sectionalization is
employed. Normally the number of sections of a bus-bar is 2 to 3 in generating
station and substation.
Advantages
1.
In case, when fault occurs on
any section faulty section can be disconnected without affecting other section.
2.
This arrangement is more
reliable that single bus-bar arrangement.
3.
The repair and maintenance of
any section of the bus-bar can be carried out be disconnecting that section
only.
4.
Future extension is possible in
this arrangement.
Disadvantages
In this arrangement additional circuit
breakers and isolators are required for sectionalisation. Hence, cost is
increased.
# Ring busbar arrangement with application and advantages and dis
advantages?
- Ring busbar arrangement with application and advantages and dis
advantages-
Ring Bus-Bar Arrangement
In this arrangement, each feeder is supplied from two paths.
This is an extension of the sectionalized arrangement.
Advantages
This arrangement provides greater flexibility. In case, fault
occurs , it does not affects the other section.
The number of circuit breaker required in this arrangement
almost same as in a single phase bus-bar system. It reduces the initial cost.
Disadvantages
Extension is not possible in this arrangements. Separately
protection system is required for each circuit.
Main and Transfer Bus-Bar
Arrangements
Such a arrangement consists of
two bus-bars a “main bus-bar” and “an auxiliary bus-bar. This arrangement is
adopted where continuity of supply. Each generator and feeder may be connected
to either bus-bar with the help of bus coupler which consists of a circuit
breaker and isolating switches.
Advantages
If fault occurs on the bus-bar, supply can be maintained by
transferring it to the healthy.
The other feeders can be connected to the bus-bars without
disturbing the existing system.
Mesh arrangement:
In mesh
arrangement between the mesh formed by bus bars circuit breakers are installed
as shown in the following figure:
From the node
point of mesh, the circuit is tapped. We need to open two circuit breakers when
the fault occurs so that protection can be obtained but switching is not
possible.
Advantages of mesh system:
1. Provides
protection against the fault.
2. For substations
having a large number of circuits, this arrangement is suitable.
Disadvantages of mesh system:
1. It doesn’t
provide switching facility.
2. Not suitable
for all type of substations.
Double bus arrangement:
Double bus
arrangement has two bus bars and the incoming feeders and outgoing feeders
are connected in parallel to both buses with the help of isolators. By closing
the isolator switch we can connect the feeders either to bus – bar 1 or to bus
– bar 2. We can divide the load among two buses with the help of isolator
switches by closing the isolator switch that is connected to bus – bar 1 and
feeder the load can be connected to bus – bar 1 and by closing the isolator
switch connected to bus – bar 2 and feeder the load gets connected to bus – bar
2. This can be shown in the following figure:
We have a bus
coupler breaker which is used for bus transfer operation. When we need to
transfer load from one bus to another bus we need to close the bus coupler
first and then close isolators of the associated bus to which load is to be
connected and open the isolator switch coupled to fault bus and then open the
bus coupler breaker.
Advantages of double bus system:
1. It has greater
flexibility.
2. During fault
conditions, there is no interruption of power supply to the load.
Disadvantages of double bus system:
1. We cannot
transfer load from one bus to another bus without interruption of power supply
for few minutes.
Double bus double breaker arrangement:
In double bus
double breaker arrangement we connect a feeder in parallel to both
buses with the help of two circuit breakers and isolator switches instead of
bus coupler as shown in the following figure:
Here we energize
both the feeders and divide feeders among both the buses but we can connect the
desired feeder to the desired bus at any time for this purpose we need to close
the isolator and then circuit breaker associated with the required bus – bar and
later open the circuit breaker and then isolator from which it has to be
disconnected.
Advantages of double bus double breaker system:
1. During fault
conditions, the load can be transferred to one bus so there will not be an
interruption in power supply.
2. Here we are not
using a bus coupler so there will not be much delay in power supply while
closing circuit breaker to transfer load from one bus to another bus.
3. High
flexibility.
Disadvantages of double bus double breaker system:
1. The number of
circuit breakers used is high so cost is very high.
2. Maintenance
cost will also be high.
So this type of
arrangement is used very rarely.
One and a half breaker arrangement:
Because of the
high cost of double bus double breaker arrangement we use one
and a half breaker arrangement. Here the two feeders are fed through their
corresponding bus – bars and these two feeders are coupled by a third circuit
breaker called tiebreaker as shown in the following figure:
During normal
conditions, all the three circuit breakers are closed and both circuits operate
in parallel and power is fed to feeders from the two bus – bars. If the fault
occurs on one bus bar then with the help of the second bus – bar feeder circuit
breaker and tiebreaker power are fed to feeders. This means each feeder breaker
has to be rated to feed both feeders which are coupled by tiebreaker.
Advantages of one and a half breaker system:
1. There will be
no interruption of power in case of fault because all the feeders can be
transferred to another healthy bus immediately.
2.
Additional circuits can be easily added to the system.
3. Cost is less
compared to double bus double breaker arrangement.
Disadvantages of one and a half breaker system:
1. This
arrangement is complicated because during fault two circuit breakers are to be
opened.
2. Maintenance
cost is high.
#why do sectionalized in a bus bar?
In this scheme, the main bus is
sectionalized by a bus coupler breaker & two nos. isolators by which the
main busbar can be done separately as when required. The shutdown of one
portion of the busbar can be taken for any maintenance work purpose. It is
shown in the below fig.
The advantage & disadvantage of
sectionalized single bus system is given below:-
Advantage:
- The operation of
this system is a simple as that of the single busbar system.
- Maintenance cost
is low.
- For maintenance or
repairing of the busbar, only one-half of the busbar is required to be
de-energized, hence the possibility of a complete shutdown is thereby
avoided.
- It is possible to
utilize the busbar potential for the line relays.
Disadvantage:
- The main
disadvantage, when a circuit breaker of any circuit of this system fails,
power can not be given the said circuit until rectification of the circuit
breaker.
- For regular
maintenance work at busbar, one of half busbar is required to be
de-energized, hence feeders & transformer of that portion will be kept
in off condition.
- If at any stage, a
circuit is required to be added to the existing system, half of the busbar
is to be de-energized during the period the work is carried out.
Switching
Schemes:
Switching
schemes implies different methods employed to connect electrical circuits in
the power system to transfer the electrical power in reliable manner. Switching
schemes helps in deliver the electrical power to power system if any part of
the system is faulty or under maintenance.
Substations
use different types of busbar arrangements or switching schemes depends upon
the application, reliability of the supply and cost of installation. In every
substations busbars plays a common role to connect different circuits. However
switching is possible in the power system with the help of circuit breakers and
isolators.
Considerations
for selection of busbar arrangement:
Different
types of busbar arrangements are employed based on the voltage, reliability of
the supply, flexibility in transmitting power and cost. The other aspects
considering in designing the busbars arrangements are:
1. Simplicity in the design
2. Maintenance of different elements without interruption in
the power supply
3. Future expansion feasibility
4. Economical in cost of installation and operation
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