Below is a summary of comparison of
switching schemes for substations.
A. SINGLE BUS SCHEME
Advantages
1. Lowest cost.
Disadvantages
1. Failure of bus
or any circuit breaker results in shutdown of entire substation.
2. Difficult to do
any maintenance.
3. Bus cannot be
extended without completely deenergizing substation.
4. Can be used
only where loads can be interrupted or have other supply
arrangements.
B. DOUBLE BUS DOUBLE BREAKER SCHEME
Advantages
1. Each circuit
has two dedicated breakers.
2. Has flexibility
in permitting feeder circuits to be connected to either bus.
3. Any breaker can
be taken out of service for maintenance.
4. High
reliability.
Disadvantages
1. Most expensive.
2. Would lose half
of the circuits for breaker failure if circuits are not connected to
both buses.
C. MAIN AND TRANSFER BUS SCHEME
Advantages
1. Low initial and
ultimate cost.
2. Any breaker can
be taken out of service for maintenance.
3. Potential
devices may be used on the main bus for relaying.
Disadvantages
1. Requires one
extra breaker for the bus tie.
2. Switching is
somewhat complicated when maintaining a breaker.
3. Failure of bus
or any circuit breaker results in shutdown of entire substation.
D. DOUBLE BUS, SINGLE BREAKER SCHEME
Advantages
1. Permits some
flexibility with two operating buses.
2. Either main bus
may be isolated for maintenance.
3. Circuit can be
transferred readily from one bus to the other by use of bus-tie
breaker and bus selector disconnect switches.
Disadvantages
1. One extra
breaker is required for the bus tie.
2. Four switches
are required per circuit.
3. Bus protection
scheme may cause loss of substation when it operates if all circuits
are connected to that bus.
4. High exposure
to bus faults.
5. Line breaker
failure takes all circuits connected to that bus out of service.
6. Bus-tie breaker
failure takes entire substation out of service.
E. RING BUS SCHEME
Advantages
1. Low initial and
ultimate cost.
2. Flexible
operation for breaker maintenance.
3. Any breaker can
be removed for maintenance without interrupting load.
4. Requires only
one breaker per circuit.
5. Does not use
main bus.
6. Each circuit is
fed by two breakers.
7. All switching
is done with breakers.
Disadvantages
1. If a fault
occurs during a breaker maintenance period, the ring can be separated
into two sections.
2. Automatic
reclosing and protective relaying circuitry rather complex.
3. If a single set
of relays is used, the circuit must be taken out of service to
maintain the relays. (Common on all schemes.)
4. Requires
potential devices on all circuits since there is no definite
potential reference point. These devices may be required in all cases
for synchronizing, live line, or voltage indication.
5. Breaker failure
during a fault on one of the circuits causes loss of one additional
circuit owing to operation of breaker-failure relaying.
F. BREAKER AND A HALF SCHEME
Advantages
1. Most flexible
operation.
2. High
reliability.
3. Breaker failure
of bus side breakers removes only one circuit from service.
4. All switching
is done with breakers.
5. Simple
operation; no disconnect switching required for normal operation.
6. Either main bus
can be taken out of service at any time for maintenance.
7. Bus failure
does not remove any feeder circuits from service.
Disadvantages
1. 1 1/2 breakers
per circuit.
2. Relaying and
automatic reclosing are somewhat involved since the middle breaker
must be responsive to either of its associated circuits.
nice article.It helped me a lot.Thank you
ReplyDeleteHelpfully published .that help me correct answer. A lot of thanks.
ReplyDeleteInsightful and concise. Thank you
ReplyDeleteSuperb it's helps me a lot
ReplyDeleteAdvantages and disadvantages of tie bus syste
ReplyDelete