0.4kV 0.4kV

Incoming A Incoming B

Bus Coupler

Transfer Scheme

Modes of Bus Transfer

• Manual Bus Transfer

• Automatic Bus Transfer

Manual Bus Transfer

i: Without Voltage Interruption

ii: With Voltage Interruption:• Slow changeover• Fast changeover

0.4kV 0.4kV

Incoming A Incoming B

Bus Coupler

Manual Bus TransferWithout Voltage Interruption

1

2

Manual Bus TransferWithout Voltage Interruption

• Involving Brief Parallel Operation

• Fault level rising

• Not used in the normal course

• In case of an emergency

0.4kV 0.4kVBus Coupler

Manual Bus TransferWith Voltage Interruption

1

2

Incoming A Incoming B

Manual ChangeoverWith Voltage Interruption

• Slow Changeover

• Fast Changeover

Slow Changeover

• Not fault level rising

• Decay of residual voltage of motors connectedto the bus to sufficiently (about 20 per cent of therated voltage)

• Starting current inrush, heavy voltage drop

• Pre-selected number of non-essential auxiliarymotors (less than 15% drop voltage )

Fast Changeover

• Before residual motor voltage vector has fallen

• Motor speed dropped down only marginally

• Only a small rise of current

• Phase Comparison Relay

Automatic Bus Transfer

• Under Fault Condition (Voltage Drop)

• Automatic Changeover with Voltage Interruption

ATS

• The reduction of the voltage below a pre-selected value and after a pre selected timeperiod the affected incoming breaker will trip.

• After the breaker has disconnected the main thebus-tie breaker will close.

• This operation will not take place if the incomerwas tripped by any future protection device.

0.4kV 0.4kV

Open

Close

Transfer Scheme

ATS1

2

Remote

Local

0.4kV 0.4kV

Transfer Scheme

1

2

Open

Close

ATS

Remote

Local

Return to Normal Operation(Re-Transfer)

• It shall be manually.

• Re-closing of either incoming breaker results inmomentary parallel switching of the main,followed by manually opening of the bus-tiebreaker.

• Manually opening the bus tie breaker, followedby manually closing the incoming.

0.4kV 0.4kV

Close

Open

Transfer Scheme

Local1

2

Remote

ATS

0.4kV 0.4kV

Bus Coupler

27R

3

VS.S

27RVS.S

3

I3

0.4kV 0.4kV

Incoming A Incoming B

Bus Coupler

Normal Operation

27R27R

0.4kV

12

3

Panel ReadyCommon Fault

50,51

5

Openor

No Service

27R

0.4kV

4

In ServiceTCS

CloseServiceNo 27i

6

7

Initial Conditions

A B

0.4kV

12

3

Panel ReadyCommon Fault

50,51

5

Openor

No Service0.4kV

4

27R

In ServiceTCS

CloseServiceNo 27i

6

7

Initial Conditions

A B

Closing Bus Coupler

• Test

• ATS

• Remote

Closing in Test position

Test Position

Start

Stop

ClosingCoil

-

+

InitialConditions

Incoming AOpen or No ServiceRelay not operated

Relay

Busbar A(27R)

&

ClosePB

ClosingCoil

&Close

Command

Service PositionTCS

LocalSelectorSwitchATS

Remote

Incoming BClose & Service &Relay not operated

27i not operated

Remote

&

&

Local

ATS

Opening

• Local

• Trip

• Remote

Opening-Local

ShuntTrip

OFF

+

-A

ir C

ircui

t Bre

aker

0.4kV 0.4kV

Incoming A Incoming B

Bus Coupler

Opening-Trip

27R27R

1

2Both Incomings are Open

or ClosedOr no in Service.

Opening-Remote

ShuntTrip

Remote

+

-A

ir C

ircui

t Bre

aker

+

-

Signal Lamp

TCSTestDeactivateSignalFrom

Remote

ServiceFaultOpenClose