Motor Bus Transfer Systems (MBTS

Introduction
To maintain plant operation and process continuity, motor
buses may require transfer from a present (old) source to a new
source:
- Power plants
- Industrial facilities
Motor Bus Transfer (MBT) schemes and systems are employed
to maintain process continuity in processes served by large
motors or aggregates of smaller and large motors.
Larger motors, of both the synchronous and induction variety,
may require comprehensive, integrated source transfer
strategies in order to avoid mechanical damage.
Motor Bus Transfer

The coast down period and resultant voltage and frequency decay
may take seconds, and unsupervised source transfer may cause
damage.
During improper transfer, mechanical damage may occur in the
motor, the coupling to the load or the load itself, and is primarily
caused by excessive shaft torque.
The total mission of a MBT system is not only to maintain process
continuity but also to effect source transfers so as not to cause
any damage to the motors and connected loads.
Introduction
Motor Bus Transfer

Why Transfer Motor Load Sources?
Fault on present supply
Interruption on present supply
For power supply security, transfer to on-site source when
storm approaches
Plant Start Up and Shut Down
Maintenance
Motor Bus Transfer

Unit-Connected Generator Motor Bus
MMM
Motor Bus
Unit Aux
Transformer
Startup
Transformer
G
GSU
Transformer
Other
LoadMOTOR BUS VT
MAIN VT STARTUP VT
NONC
Motor Bus Transfer

VT-M VT-SU
VT-B
52
M
STATION BUS SYSTEM
STARTUP SOURCE
N.C.
M
CT-M
N.O. 52
SU
CT-SU
UNIT AUXILIARY
TRANSFORMER
STATION SERVICE
TRANSFORMER
MAIN SOURCE
M
M-4272
Two-Breaker Configuration
Motor Bus Transfer

Combined Cycle Plant Motor Bus
Motor Bus Transfer

Typical Industrial Plant One-Line
MMM
Bus 1
Supply Source
(Bus 2 Backup Source)
Bus 2
Supply Source
(Bus 1 Backup Source)
M M M
Utility
Supply SystemIncoming 1 Incoming 2
NC NC
NO
Bus TieBus 1 Bus 2
BUS 1 VT BUS 2 VT
INCOMING 1 VT
INCOMING 2 VT
Motor Bus Transfer

STATION BUS SYSTEM
N.C.52
M1
VT-B1
NORMAL SOURCE (Main 1 )
N.C. 52
M2
VT-M2
ALTERNATE SOURCE (Main 2)
BUS 1 BUS 2
VT-B2
52T
N.O.
BUS-TIE
VT-M1
CT-M1 CT-M2
CT-B1 CT-B2
TRANSFORMER
NORMAL SOURCE ALTERNATE SOURCE
TRANSFORMER
M-4272 M-4272
M M M M
Three-Breaker Configuration
(Main-Tie-Main)
Motor Bus Transfer

Conditions across Normally Open Startup
or Bus Tie Breaker?
Immediately prior to Transfer Initiate
- Effects of a Fault - System faults can cause the internal electrical
angles of motors to differ from new source (i.e., single-phase
faults)
- System Separation between Transmission or Distribution
Incoming Supply Sources
- Supply Source Transformer Winding Phase Shift
Immediately after Transfer Initiate, but prior to
closure of Startup Source Breaker
- Transient Effects upon Disconnect of Motor Loads
Motor Bus Transfer

Motor Bus Transfer
G
M
M
M
M
M
M
M M
M
M
M
M
M
M
MM
M M M M
M
500kV
Transmission
System
230kV
Transmission
System
NC NC NC NC NO NO NO NO
Unit Aux.
Transformer
Startup
Transformer
Unit 3
3-phase fault
Nuclear
Power
Plant
29°angular difference
with a 3-phase fault
at CR3 500kV BusG
RCP RCP RCP RCP
32
Miles
Unit 5

Motor Bus Transfer
G
Load Load
802 MVA
22.5 kV
50 Hz
Standing angle
of at least 30°
786 MVA
525 kV / 22.5 kV
W2 (525 kV)
W1 (22.5 kV)
Ynd11 (YΔ )AB
W1 W1
54 MVA
22.5 kV / 10.5 kV
54 MVA
22.5 kV / 10.5 kV
W2 W2
Dyn11 Dyn11 (D Y )AC
30°
W1 (22.5 kV)
W2 (525 kV)
30°
W2 (10.5 kV)
W1 (22.5 kV)
60°
W1 (10.5 kV)
525 kV 525 kVW2 (525 kV)
W2 (525 kV)
W1 (10.5 kV)

Motor Bus Transfer
Load
YnYno
115 kV New
115 kV / 6.9 kV
30 MVA
Load
YnYno
Angle = 23°
69 kV / 6.9 kV
15 MVA
69 kV
Petrochemical Plant

Transient Effects upon Disconnect of
Motor Loads
Essentially instantaneous phase shift upon disconnect of
Motor.
- Simulation based on 7,860 hp Induction Motor operating at full
load supplied from 11,550 Vac bus.
- Instantaneous phase shift of 9 to 10 degrees in the slow direction
calculated upon disconnect.
- Effect is additive to conditions occurring due to other causes.
- Effect is followed by subsequent frequency decay, the speed of
which is dependent on inertia and loading of motor.
Same effect occurs upon disconnect subsequent to a
bus fault.
Motor Bus Transfer

Phase Angle and Motor Bus Voltage
Characteristics
Phase angle rate of change (caused by deceleration of the motors during
transfer) and the rate of voltage decay determined by the type of motors in
use and the type of loads being driven.
Motor Bus Transfer

Coast Down of Low Inertia Load on a Large
Induction Motor
Motor Bus Transfer

Motor & Load Characteristics:
Effects on MBT
Motor Size: The larger the motor, the longer the time the voltage
will take to decay on an induction motor.
Loading: The higher the load on the motors, the faster the motor
bus frequency will decay.
Inertia: The higher the inertia of the aggregate motor loads on the
motor bus, the more slowly the motor bus frequency will decay
during the disconnected coast down period. That has a direct
impact on how fast the phase angle changes.
- Low inertia loads will cause the phase angle to change quickly,
as the frequency of motor bus decays quickly, and the slip
frequency between the motor bus and the new source
quickly increases.
Motor Bus Transfer

Mix of Synchronous and Induction Motors:
- Voltage will tend to decay much more rapidly on a motor bus with all
induction motors
- On a motor bus with a mix of synchronous and induction motors, the
synchronous motors will attempt to hold up the voltage during the
transfer interval
Motor & Load Characteristics:
Effects on MBT
Motor Bus Transfer

Resultant V/Hz
Pursuant to phase angle and voltage, and their effect on
resultant V/Hz, some generalizations can be made:
- Phase Angle: As the phase angle increases between the two
sources, assuming the two source voltages are the same, the
V/Hz will increase
- Voltage: As the voltage difference between the two sources
increases, assuming the phase angle between the sources
remains the same, the V/Hz will increase
Motor Bus Transfer

V/Hz Resultant from ES and EM
ANSI STANDARD C50.41-2000
Motor Bus Transfer
C50.41 is an American National Standard
Institute standard only found under NEMA.
ANSI C50.41-2000
Status is Current.
C50.41 originally was a combined ANSI/IEEE standard, however
it is no longer under the IEEE. Four NEMA representatives
were included as part of the Working Group for the 2000
Standard. The standard is now available on the NEMA
website and it is still active as an ANSI Standard.
The link is:
http://www.nema.org/stds/results.cfmsrchString=c50.41&UserSel
ectedSubSites=12

Motor Bus Transfer
Excerpts from ANSI C50.41-2000

θcos2
22
MSMSR EEEEE −+=
ES
= 1 pu @ 0 degrees
EM
=0.81pu@-95degrees
E
R =
1.33 pu
θ
Motor Bus Transfer

Motor Bus Transfer Classification
▪ Closed Transition
- Hot Parallel Transfer
▪ Open Transition - Methods
- Fast Transfer
- In-Phase Transfer
- Residual Voltage Transfer
- Fixed Time Transfer
▪ Open Transition - Modes
- Sequential
- Simultaneous
Motor Bus Transfer

Closed Transition – Hot Parallel Transfer
▪ New source connected to the motor bus before the old source
is tripped. Transfers sources without interruption.
▪ Voltages and phase angle between the motor bus and the new
source must be evaluated prior to the transfer to assure that the
motor bus and the new source are in synchronism and that the
new source voltage is within acceptable limits.
▪ Auto Trip provisions must be incorporated such that, if the new
source breaker is closed but the old source breaker remains
closed, the transfer system must immediately trip the old
source breaker. This allows parallel transfer but prohibits
inadvertent parallel operation.
▪ Alternatively, Auto Trip provisions can be programmed to trip
the new source breaker that may have been inadvertently
closed.
Motor Bus Transfer

MMM
Motor Bus
Source 1
(Old Source)
Source 2
(New Source)
Motor Bus Transfer

MMM
Motor Bus
Source 1
(New Source)
Source 2
(Old Source)
Motor Bus Transfer

Closed Transition - Hot Parallel Transfer
Advantages
- No disruption of plant process
- Simple to implement with sync-check relay supervision across
new source breaker
- No transient torque on motors during the transfer
Disadvantages
- Will not work during transient (emergency) conditions Do not
want to connect “good” source to new source that is having
problems.
- Exposure to double-fed motor faults during parallel operation
may violate the interrupt rating for the circuit breakers and the
short term withstand ratings source transformers and damage
bus-connected equipment
- Design must ensure that a parallel condition is temporary
- The two sources may not be derived from the same primary
source and a large standing phase angle may be present
between them, precluding a hot parallel transfer
Motor Bus Transfer

Open Transition
▪ Open Transition - Methods
- Fast Transfer
- In-Phase Transfer
- Fixed Time Transfer
▪ Open Transition - Modes
- Sequential Mode
- Simultaneous Mode
Motor Bus Transfer

Open Transition
MMM
Motor Bus
Source 1
(Old Source)
Source 2
(New Source)
Motor Bus Transfer

Open Transition
MMM
Motor Bus
Source 1
(New Source)
Source 2
(Old Source)
Motor Bus Transfer

Open Transition - Methods
- Fast Transfer
- In-Phase Transfer
Bus Transfer Zones
-π
-2π
Motor Bus Transfer

Fast Transfer Method
The new source breaker will
be closed by the Fast
Transfer Method if the
phase angle between the
motor bus and the new
source is within or moves
into the phase angle limit
during the Fast Transfer
Enable (Time) Window.
One-cycle phase angle
response is required.
Closing is also supervised
by an Upper and Lower
Voltage Limit check on the
new source.
Motor Bus Transfer

In-Phase Transfer Method
The new source breaker will be closed using the In-Phase Transfer
Method by predicting movement through zero phase coincidence
between the motor bus and the new source during the In-Phase
Transfer Enable Window.
Closing is also supervised by an Upper and Lower Voltage Limit check
on the new source and a Slip (ΔF) Frequency Limit between the motor
bus and the new source.
The calculation of the predicted phase coincidence shall be compared
with the breaker closing time setting for the new source breaker for the
In-Phase Transfer method.
In order to accurately predict phase coincidence, considering the
decaying motor bus frequency, the phase angle, slip frequency and
rate-of-change of frequency between the motor bus and the new
source must be calculated and inserted in the following second order
partial differential equation to solve for the precise breaker closing
advance angle (Φ) to compensate for the breaker closing time (TB).
One-cycle response is required.
Motor Bus Transfer

In-Phase Transfer Method
Motor Bus Transfer

MMM
Motor BusG
Other
LoadMOTOR BUS VT
-30deg
+30deg 0deg
Motor Bus Transfer
In typical applications, a wye-wye or delta-delta Startup Transformer
connection is used, resulting in a net phase shift of zero between the Unit
Auxiliary and Startup Transformers. In this case Hot Parallel Transfers are
possible and Open Transition Fast Transfers are permitted given sufficiently
fast sync check supervision and breaker speeds.
Wye-Wye Startup
Transformer

Motor Bus Transfer
In some plants, a delta-wye Startup Transformer has been specified,
creating a 30 deg phase shift between the Unit Auxiliary and Startup
Transformers.
Delta-Wye Startup
Transformer
MMM
Motor BusG
Other
LoadMOTOR BUS VT

Motor Bus Transfer
The Startup Transformer source leads
the Unit Auxiliary Transformer source
by 30 deg. Hot parallel transfers are
NOT possible. After the Startup
Transformer breaker opens, the Motor
Bus will begin slowing which moves
the Bus voltage towards the Unit Aux
Transformer voltage.
Startup to Unit Aux Transfer
Fast Transfer Possibility
with Hi-Speed Sync Check
MMM
Motor BusG
Other
LoadMOTOR BUS VT

Motor Bus Transfer
The Unit Auxiliary Transformer
source lags the Startup
Transformer source by 30 deg.
After the Unit Auxiliary
Transformer breaker opens, the
Motor Bus will begin slowing which
moves the Bus voltage away from
the Startup Transformer voltage.
Unit Aux to Startup Transfer
In-Phase Transfer Possibility
MMM
Motor BusG
Other
LoadMOTOR BUS VT

Residual Voltage Transfer Method
The new source breaker will be closed by the Residual
Voltage Transfer Method if the motor bus voltage drops
below the Residual Voltage Transfer limit during the Residual
Voltage Transfer Enable Window.
Since this is otherwise unsupervised, this must prevent
closure of the new source breaker until the bus voltage drops
below a predetermined voltage limit (usually < 0.25 pu).
Setpoint accuracy MUST measure correctly and operate down
to 4 Hz.
Undervoltage settings must be coordinated with motor
undervoltage relays to prevent motor drop-out.
Residual Voltage Transfer Method may be disabled
depending on the application.
Motor Bus Transfer

Open Transition – Sequential Mode
Transfer Timing Sequence
Motor Bus Transfer
If the Sequential Mode is selected, the old source breaker
shall be tripped immediately, but closure of the new source
breaker shall be attempted only upon confirmation by the
breaker status contact that the old source breaker has
opened. Upon receipt of this confirmation, all three methods
of transfer are immediately enabled to supervise closure of
the new source breaker.
Closure of the new source breaker will then occur when
permitted by the Fast, In-Phase or Residual Voltage Transfer
criteria, whichever occurs first.

Open Transition – Sequential Mode
Motor Bus Transfer
(4 msec Delay w/M-4272)
(Window Adjustable w/M-4272)

Open Transition – Simultaneous Mode
Motor Bus Transfer
If the Simultaneous Mode is selected, all three methods
of transfer are immediately enabled to supervise
closure of the new source breaker without waiting for
the breaker status contact confirmation that the old
source breaker has opened.
Thus, the commands for the old source breaker and
the new source breaker to trip and close could be sent
simultaneously if and only if the phase angle between
the motor bus and the new source is within the phase
angle limit immediately upon transfer initiation.
Otherwise, the old source breaker will be tripped but
closure of the new source breaker must wait until
permitted by the Fast, In-Phase or Residual Voltage
Transfer criteria, whichever occurs first.

Motor Bus Transfer
Delays Eliminated
(4 msec Delay w/M-4272)
Window Adjustable w/M-4272)

Fast Transfer
Sequential Trip and Close of Old
and New Source Breakers (“early b” breaker status contact)
Advantages
- Fast (5 to 7 cycles)
- Transient torques are reduced due to speed of transfer
- Transfer of complete bus with reduced interrupting of process
- Rapid supervision of the phase angle just prior and just after old
source interruption is mandatory and possible with high-speed
sync-check relays
- Avoids parallel transfer operation
- Avoids exposure to breaker failure effects
Motor Bus Transfer
COMMENT: Presently, the majority of fast transfer systems
are NOT supervised by high-speed sync-check relays.

Simultaneous Trip and Close of Old
and New Source Breakers
Advantages
- REALLY Fast - minimum dead time for bus (2 to 3 cycles)
- Least exposure to transient torque in motors if system operates
as expected
- Transfer of complete bus with minimum interrupting of process
- Rapid supervision of the phase angle just prior and just after
old source interruption is mandatory and possible with high-
speed sync-check relays
- Avoids “intentional” parallel transfer operation
Considerations – Breaker Failure Scheme is a MUST !
- Failure of old source breaker to trip back feeds generator from
new source
- AND exposes equipment to double-fed faults for which it was
not designed
- Presently, the majority of fast transfer systems are NOT
supervised by high-speed sync-check relays
Fast Transfer
Motor Bus Transfer

Breaker Failure
Motor Bus Transfer
Failed
To Open

Fast Transfer
Motor Bus Transfer
Presently, the majority of fast transfer systems are NOT
supervised by high-speed sync-check relays !
Fast transfer CANNOT be correctly performed without a high-
speed sync check relay
Modern solid-state or microprocessor-based sync check
elements have a minimum time delay of 0.1 second or 100
milliseconds. By the time they respond to the phase angle
of a decaying motor bus, the possibility of a successful
transfer is long gone.
Worse yet, the contacts may be still closed and permit
transfers at excessive angles and damage critical motors.

Fast Transfer
Motor Bus Transfer

Fast Transfer
Motor Bus Transfer
Dropout Test
-23.5-28.2-170.6104 V ac/sec31 Hz/secLow Inertia
-23.2-24.1-58.694 V ac/sec20 Hz/secMedium Inertia
-22.5-24.4-5275 V ac/sec8.33 Hz/secHigh Inertia
M-4272
Digital
Motor Bus Transfer
Degrees @ Dropout
M-3410A
Digital
Sync Check
Degrees @
Dropout
M-0388
Analog
Sync Check
Degrees @
Dropout
Voltage
Decay
(Vac/sec)
Frequency
Decay
(Hz/sec)
Motor Bus

Fast Transfer
Motor Bus Transfer
Pickup Test
17.913.3No Close104 V ac/sec31 Hz/secLow Inertia
18.114.5No Close94 V ac/sec20 Hz/secMedium Inertia
19.815475 V ac/sec8.33 Hz/secHigh Inertia
M-4272
Digital
Motor Bus Transfer
Degrees @ Pickup
M-3410A
Digital
Sync Check
Degrees @
Pickup
M-0388
Analog
Sync Check
Degrees @
Pickup
Voltage
Decay
(Vac/sec)
Frequency
Decay
(Hz/sec)
Motor Bus

Fast Transfer
Motor Bus Transfer
Presently, the majority of fast transfer systems are NOT
supervised by high-speed sync-check relays !
Synchronism-Check Relay Test
General Electric Type IJS52
The purpose of this test was to determine the blocking characteristics of the IJS Relay
set for 20° and minimum time delay. Tests were run for the following conditions:
With the initial phase angle at 0° and both inputs at 60Hz, increase the line frequency
to create a slip frequency (ΔF) and measure the blocking time and blocking angle.
TEST DATA

Fast Transfer
Motor Bus Transfer
Sync Check Relay Test
The purpose of this test
is to determine the
blocking characteristics
of Sync Check Relays
set for 20° and minimum
time delay. With the
initial phase angle at 0°
and both inputs at 60Hz,
the line frequency is
increased to create a slip
frequency (ΔF) and the
blocking angle is
measured.
26.3531063.018
25.747992.7517
25.246932.516
24.935872.2515
24.63379.92.014
23.632721.7513
22.931671.512
22.33059.81.2511
222951.81.010
21.82640.10.759
21.62536.773.620.58
212328.754.000.257
20.520.623.840.320.16
2020.322.127.180.055
2020.221.40.0254
2020210.013
202020.80.0052
202020.60.0011
M-4272
Digital
Motor Bus
Transfer
Degrees
M-3410A
Digital
Sync Check
Degrees
M-0388
Analog
Sync Check
Degrees
GE IJS
Electromechanical
Sync Check
Degrees
Delta
Frequency
(Hz)

Advantages
- May operate significantly faster than residual voltage transfer
- Significantly reduces the pre-closure V/Hz due to synchronous
closing
- Permits bus transfer for out-of-synchronism initial conditions
or where large initial standing angles prevent fast transfer
- Provides an excellent backup to fast transfer systems
In-Phase Transfer
Motor Bus Transfer

Advantages
- Familiar technique that is widely used
- Simple to implement (undervoltage relays – but must
operate correctly to low frequencies and with
significant rate of change in voltage decay)
- Works properly during transient conditions
loss of synchronism
angular differences
voltage transients
Residual Voltage Transfer
Motor Bus Transfer

Disadvantages
- Slower
- Process is interrupted due to load shedding (new source cannot re-
accelerate all bus motors simultaneously)
- Analysis of plant process is required to determine effects of
transfer
- Certain motors loads may cause rapid stalling and may necessitate
a restart of the motors on the bus
- Cannot be used to transfer from new source to present source
during unit startup
- Risk of transfer to dead source unless new source is monitored
- Properly sequenced motor restart required to prevent excessive
voltage dip
- Effect of transient torque on motors during restart should be limited
to starting torque (analysis may be required depending on length of
motor supply interruption)
- Motor contactors drop out unless designed to stay in at residual
transfer voltage.
Motor Bus Transfer

Motor Bus Transfer
25.4 V (0.21 pu)24.2 V (0.20 pu)14 V (0.12 pu)104 Vac/sec31 Hz/secLow Inertia
27.9 V (0.23 pu)26 V (0.22 pu)22.4 V (0.19 pu)94 Vac/sec20 Hz/secMedium
Inertia
30 V (0.25 pu)27.5 V (0.23 pu)23.7 V (0.20 pu)75 Vac/sec8.33 Hz/secHigh Inertia
M-4272
Under Voltage
V ac @ Operate
M-3410A
Under Voltage
V ac @ Operate
M-0388
Under Voltage
V ac @ Operate
Voltage
Decay
(Vac/sec)
Frequency
Decay
(Hz/sec)
Motor Bus
Under Voltage Operate Test

Fixed Time Transfer
Designed to wait for a predetermined time, usually greater
than 30 cycles, after a bus power source is removed before
connecting the bus to new source. Voltage relays do not
supervise the transfer.
Motor Bus Transfer

Advantages
- Familiar technique that is widely used
- Simple to implement (time delay relays)
- Works properly during transient conditions
loss of synchronism
angular differences
voltage transients
Fixed Time Transfer
Motor Bus Transfer

Disadvantages
- Slowest
- Process is interrupted due to total loss of power (new source
cannot reaccelerate all bus motors simultaneously)
- Analysis of plant process is required to determine effects of
transfer
- Cannot be used to transfer from new source to present source
during unit startup -- parallel transfer required
- Risk of transfer to dead source unless new source is monitored
- Properly sequenced motor restart required to prevent excessive
voltage dip
- Effect of transient torque on motors during restart should be
limited to starting torque (analysis may be required
depending on length of motor supply interruption)
Fixed Time Transfer
Motor Bus Transfer

Transfer Initiate
NOTE: For each of the following, transfers may be bi-directional or may
be programmed to only transfer in one direction.
▪ Protective Relay Initiate
▪ External Initiate
▪ Bus Phase Undervoltage (Auto Transfer) Initiate
When enabled, this automatically initiates transfer whenever the motor bus
voltage drops below an under voltage limit for a set time delay. MUST be
set to ride through normal bus voltage dips.
▪ Auto Close Initiate
If both breaker status contacts are in the open state, due to an external
operation that opens the old source breaker while leaving the new source
breaker open, an Open Transition, Sequential Mode Transfer is initiated.
▪ Manual Initiate
- Local
- Remote
Motor Bus Transfer

Load Shed During Transfer
NOTE: For each of the following, Load Shed may be enabled or
disabled.
▪ Load Shed Coincident with Fast Transfer
EXAMPLE: This may be used to disconnect motor loads from the aggregate bus,
coincident with the command to trip the old source breaker, if the new source is
not designed to pick up the full motor bus load.
▪ Load Shed After Fast Transfer Window and Before In-Phase
Attempt
EXAMPLE: This may be used to disconnect large synchronous motors from the
aggregate bus prior to In-Phase Transfer which may close in sync but at a high slip
rate.
▪ Load Shed Coincident with Residual Voltage Transfer
EXAMPLE: This may be used to disconnect motor loads from the aggregate bus just
prior to Residual Voltage Transfer so the remaining motors may re-accelerate.
Motor Bus Transfer

Lockouts
NOTE: The old source breaker SHALL NOT BE TRIPPED whenever any transfer
initiate is blocked by any of the lockout conditions described below or if the
new source voltage is outside the upper voltage limit and lower voltage limit .
▪ Motor Bus Voltage Lockout
Detects Motor Bus VT loss-of-potential (i.e. fuse loss) and may be programmed to
block transfer or if a transfer is required, can be programmed to proceed with
a fixed time transfer.
▪ External Lockout
External contact input blocks transfer.
▪ Incomplete Transfer (Auto) Lockout
Blocks the completion of any transfer initiated if, after the old source breaker
opens, the new source breaker fails to close after a set time delay.
▪ Transfer In Process Lockout
Once a transfer is in process, all other transfer initiate inputs are ignored.
▪ Lockout After Transfer
Subsequent transfers are blocked for a set time after any transfer occurs.
Motor Bus Transfer

Lockouts
NOTE: The old source breaker SHALL NOT BE TRIPPED whenever any transfer
initiate is blocked by any of the lockout conditions described below or if the
new source voltage is outside the upper voltage limit and lower voltage limit .
▪ “Both Breakers” Lockout
If both breaker status contacts end up in the open state, due to an
external operation that opens the old source breaker while
leaving the new source breaker open, no transfer sequence shall
be initiated. Furthermore, any subsequent initiation of a transfer
sequence while the breakers are in this state shall be blocked.
May alternatively be programmed to initiate an Auto Close
Transfer.
If both breaker status contacts are closed due to an external
operation that closes the new source breaker while leaving the
old source breaker closed, and if Auto Trip is not enabled, no
transfer sequence shall be initiated.
Motor Bus Transfer

Open Transition
MMM
Motor Bus
Source 1
(Old Source)
Source 2
(New Source)
Motor Bus Transfer
External Trip

MMM
Motor Bus
Source 1
(Old Source)
Source 2
(New Source)
Motor Bus Transfer
External Close

Bus transfer Acceptance Testing
Verify scheme operation
Perform “Ring Down” test of load bus and record
Determine relay settings by analysis of ring down
Verify continuity of switching operation
Examine transients
Difficult to simulate running conditions of plant
Used to verify computer models
(if available)
Motor Bus Transfer

Initial Steps: Dry Run, Dead Bus
• Connect transfer system and monitoring equipment
• Simulate inputs to transfer system from test equipment
(main, auxiliary, bus)
• Rack out breakers and operate on umbilical cords (at
test position)
• Test system to ensure proper operation of transfer
system, breakers, monitoring equipment
• Verify breaker times
• Simulate all types of transfer appropriate for bus
– Fast Transfer
– In-Phase Transfer
– Residual Voltage Transfer
Motor Bus Transfer

Final Running Test
• All equipment in normal operating state
• Initiate transfer and monitor for each transfer type
– Fast Transfer
– In-Phase Transfer
– Residual Voltage Transfer
• Verify acceptable operations
Motor Bus Transfer

Ringdown Analysis
A bus ringdown involves
- operation of the motor bus at expected nominal conditions
- then disconnecting the source from the bus, recording the
waveform and observing the frequency decay and voltage decay
characteristics as the motors coast down
- Computer analysis and field testing is necessary to ensure a
successful transfer – Fast and In-Phase
- Determine if motors and loads on bus have sufficient inertia to
limit the rate of change of angle (frequency decay) – Fast and In-
Phase
A tool for recording and analyzing the ringdown is
an oscillograph
- Older technology offered lightwave oscillography
- Newer technology offers digital oscillography
May be included as part of newer digital metering,
protection and bus transfer packages
Stand-alone digital fault and event recorders (DFR)
Motor Bus Transfer

Simultaneous Transfer Mode Selected: 10 ms after a transfer
initiate, the trip command signal is sent directly to the old source
breaker, and the three methods of transfer are immediately
enabled to supervise closure of the new source breaker.
The new source breaker close time starts only when the
permissive close signal is generated by either the Fast, In-Phase
or Residual Voltage Transfer Method.
Sequential Transfer Mode Selected: 10 ms after a transfer
initiate, the trip command signal is sent directly to the old source
breaker. 4 ms after the 52a or 52b breaker status aux contact
indicates the old source breaker has opened, the three methods
of transfer are enabled to supervise closure of the new source
breaker.
For Fast Transfer, depending on the status of the initial phase
angle across the new source breaker (in or out of phase limits),
the 4 ms reaction time of the supervising high-speed sync check
must be taken into account, although this occurs simultaneously
with other delays.
Ringdown Analysis Considerations
Motor Bus Transfer

For fast transfers, the fast transfer phase angle limit setting
is calculated, using the resultant V/Hz calculation shown
earlier, such that the actual V/Hz at the point of closure is far
less than the 1.33 pu V/Hz limit or, in the worst case, is not
more than this limit.
The phase angle limit setting on the fast transfer high-speed
sync check supervision relay must be set so it blocks before
the phase angle becomes prohibitively large, and the angle
setting must include the effect of the new source breaker
closing time.
Motor Bus Transfer

The in-phase transfer must be initiated at an advance angle
before the first phase coincidence.
- The advance angle is calculated for in-phase transfer by a
specialized high-speed automatic synchronizing relay capable of
predicting the advance angle, based on the new source breaker
closing time and the rapidly increasing slip frequency.
- The ΔF Limit setpoint is calculated using the resultant V/Hz
calculation shown earlier, such that the actual V/Hz at the point of
closure is far less than the 1.33 pu V/Hz limit or, in the worst case,
is not more than this limit.
The residual and fixed time transfers only need to take into
account that the motor bus voltage has fallen to 0.25 pu or less.
- The new source breaker closing time does not have to be
considered, as the angle is now not important, since the resultant
V/Hz cannot exceed 1.33 V/Hz
Motor Bus Transfer

Ringdown Oscillograph Representation
52 Trip
Fast Transfer
Possible
In-Phase
Transfer
Possible
Residual & Long Time
Transfer Possible
52a opens
52b closes
Window of Acceptable
Phase Angle
Present Source Breaker
New Source
Motor Bus
Motor Bus Transfer

Ring Down Digital Waveform
Motor Bus Transfer
45.6 VRMS
BREAKER OPEN
ZERO CROSSING

Ring Down Digital Waveform without fans
Motor Bus Transfer
ZERO CROSSING
28.4 VRMS
BREAKER OPEN

Sequential Fast Transfer Digital Waveform
Motor Bus Transfer
91.8 VRMS
BREAKER S2 OPENS BREAKER S1 CLOSES

Delayed In-Phase Transfer Digital Waveform
Motor Bus Transfer
BREAKER S1 OPENS
BREAKER S2 CLOSES

Ringdown Analysis
Motor Bus Transfer
CASE STUDY
Central Ciclo Combinado
La Laguna II
Torreon, Coahuila de Zaragoza
Mexico

Ringdown Analysis
Motor Bus Transfer
Spin down Testing
The waveforms of spin down test show that
the bus decay lasted for almost one second.
The high inertia of the motor bus load
provides a stable and uniform decay, this
gives an excellent opportunity to perform a
smooth motor bus transfer. Measurements
and calculations for the Phase angle and
Delta Frequency settings for the MBT
equipment are derived from these results.

Spin Down Test
Motor Bus Transfer

Ringdown Analysis
Motor Bus Transfer
Volts per Hertz Calculations for Sequential Fast Transfer
The maximum volts per hertz across the breaker that is closing is defined in the ANSI
C50.41-2000 Paragraph 14 as 1.33V/Hz. Refer to figures below for how the measurements
were taken on the waveform. The equation for the pre-closure volts per hertz is as follows:
Where:
EPU is the per unit volts per hertz across the open breaker.
EREFPU is the per unit volts per hertz of the reference, which is the new source to which the
bus is being transferred. (1pu volts/1pu hertz) = 1
EBUSPU is the per unit volts per hertz of the bus.
Cos θ is the cosine of the phase angle between the reference and the bus.
Measurements and Calculations at breaker closing time for Sequential Fast Transfer, refer to
following figures.
Phase angle = 29.8 degrees
Bus voltage pu = 101/121 rms = 0.8347pu (voltage readings X 10)
Bus frequency = 58.82/60 = 0.9804pu (Frequency = 1/time period; 1/17.0ms)
EBUSPU = 0.8347/0.9804 = 0.8514
EPU = 0.497pu
θCosEBUSPUEREFPUEBUSPUEREFPUEPU ×××−+= 222

Spin Down Estimated Sequential Fast Transfer
Breaker Closing Time
(Measured from breaker trip = 78.5ms, breaker close time 57.5ms+10ms+8.3ms)
Motor Bus Transfer

Voltage and Phase Angle at Closing
Motor Bus Transfer

Frequency at Closing
Motor Bus Transfer

Ringdown Analysis
Motor Bus Transfer
Spin Down Measurements and Calculations for the Fast
Transfer Phase Angle Setting
Phase angle at 2.5 cycles: 10ms +8.3ms+25ms (1.5 cycle
worst case error) after breaker opens = 15.7 degrees (See
next slide.)
In this application add 6 degrees to phase measurement.
Phase angle setting is 16 plus 6 degrees for total of 22
degrees.

Ringdown Analysis
Motor Bus Transfer

Ringdown Analysis
Motor Bus Transfer
Volts per Hertz Calculations for In-Phase Transfer
The maximum volts per hertz across the breaker that is closing is defined in the ANSI C50.41-
2000 Paragraph 14 as 1.33V/Hz. Refer to figures below for how the measurements were taken
on the waveform. The equation for the pre-closure volts per hertz is as follows:
Where:
EPU is the per unit volts per hertz across the open breaker.
EREFPU is the per unit volts per hertz of the reference, which is the new source to which the bus
is being transferred. (1pu volts/1pu hertz) = 1
EBUSPU is the per unit volts per hertz of the bus.
Cos θ is the cosine of the phase angle between the reference and the bus.
Measurements and Calculations at breaker closing time for Sequential Fast Transfer, refer to
following figures.
Phase angle = 0 degrees
Bus voltage pu = 77.8/120 rms = 0.6483pu (voltage readings X 10)
Bus frequency = 55.87/60 = 0.9311pu (Frequency = 1/time period; 1/17.9ms)
EBUSPU = 0.6483/0.9311 = 0.6963
EPU = 0.3038pu
θCosEBUSPUEREFPUEBUSPUEREFPUEPU ×××−+= 222

Spin Down Estimated Sequential In-phase
Transfer Voltage
Motor Bus Transfer

Spin Down Estimated Sequential In-phase
Transfer Frequency
Motor Bus Transfer

Ringdown Analysis
Motor Bus Transfer
Spin Down Measurements and Calculations for the
In-Phase Transfer Slip Frequency (ΔF) Setting
The frequency at time of breaker closure is 56.18HZ
(1/17.8ms, see next slide); the delta frequency at
breaker closure is 3.82 HZ. In this application, set the
in-phase slip frequency (ΔF) limit setting to 4.5HZ.

Spin Down Estimated Sequential In-Phase Frequency
4 cycles Before In Phase (Breaker time + ½ cycle)
Motor Bus Transfer

Motor Bus Transfer Application-The Need for Speed
Project Background
The following example shows actual data from commissioning tests at the
Laguna II station in Mexico. This plant consists of two combustion turbines
(154MW) and one heat recovery steam plant (279MW). The plant auxiliary
loads are below:
Bus A (4KV)
3600HP High pressure boiler feed pump
1100HP Condensate pump
620HP Closed circuit Cooling pump
1500HP Gas compressor
450HP Auxiliary cooling pump
480V Service Transformers
Note that these loads are centrifugal pumps and compressors. There are no
fans or other high inertia loads in this application. In addition, the breakers
are not particularly fast, 35mSec trip and 60mSec to close.
Bus B (4KV)
1100HP Condensate pump
620HP Closed circuit Cooling pump
450HP Auxiliary cooling pump
480V Service Transformers
Motor Bus Transfer

Closing Voltage
9.82/12.00
Closing Angle=
11.7deg
Main Position
(Open)
Startup Position
(Closed)
Trip Main
Close Startup
Simultaneous Transfer Mode
•Note that the trip and
close commands
occur together.
•Transition time (old
source breaker open
to new source closed)
is about 1 cycle
Motor Bus Transfer

Closing Voltage
Closing Angle=
38.24deg
Main Position
(Open)
Startup Position
(Closed)
Trip Main
Close Startup
Sequential Transfer Operation
•Note that the close
command to the new
source occurs after
the old source
breaker indicates
open.
•Transition time (old
source breaker open
to new source closed)
is about 4 cycles
Motor Bus Transfer

Simultaneous Mode
Transfer Time: 24.2mSec
(both breakers open)
Transfer Angle: 11.7deg
Bus Voltage at Transfer: 98.2/120V
Bus Frequency at transfer: 58.4Hz
V/Hz per C50.41-2000 0.246pu
Sequential Mode
V/Hz per C50.41-2000 0.629pu
The sequential transfer was slower which allowed the motor bus
frequency and voltage to decay further, however the V/Hz quantities
are far below the 1.33pu limit.
Even in this application, which has less than ideal mechanical
inertia, the sequential mode offers significantly more security
without compromising the transfer.
In applications with faster vacuum breakers, there will be even less
difference between sequential and simultaneous operating modes.
Transfer Data Analysis
Motor Bus Transfer

Using traditional synch check relays, measurement time is a very slow (up to
100msec). This long measurement time could prevent the traditional scheme from
detecting unacceptable conditions which could result in an improper transfer.
•In an attempt to minimize this effect, traditional transfer systems are set to
operate at the highest possible speed (simultaneous mode).
•The safety of the simultaneous mode relies on a fast and reliable breaker failure
scheme. Frequently, these schemes are assembled from auxiliary relays and
wiring that are rarely tested. High speed measurements allows the LUXURY of
waiting until the old source breaker is open before issuing the close command to
the new source.
Bus Transfer Application
Simultaneous Mode
V/Hz per C50.41-2000 0.246pu
Sequential Mode
V/Hz per C50.41-2000 0.629pu
Motor Bus Transfer

It should be noted that in some applications, very little back-EMF and inertia is
present and therefore operation in simultaneous mode is required.
•A reliable breaker failure scheme is mandatory
•High speed measurement provides the ability to rapidly detect unacceptable bus
voltage changes caused by the fault and block the transfer.
Simultaneous Mode
V/Hz per C50.41-2000 0.246pu
Sequential Mode
V/Hz per C50.41-2000 0.629pu
Bus Transfer Application
Motor Bus Transfer

CASE STUDY
Central Ciclo Combinado
Felipe Carrillo Puerto
Valladolid, Yucatan
Mexico
Motor Bus Transfer

GERENCIA REGIONAL DE PRODUCCIGERENCIA REGIONAL DE PRODUCCIÓÓN SURESTEN SURESTE
SUBGERENCIA REGIONAL DE GENERACISUBGERENCIA REGIONAL DE GENERACIÓÓN TERMOELECTRICA PENINSULARN TERMOELECTRICA PENINSULAR
CENTRAL FELIPE CARRILLO PUERTOCENTRAL FELIPE CARRILLO PUERTO

GERENCIA REGIONAL DE PRODUCCIGERENCIA REGIONAL DE PRODUCCIÓÓN SURESTEN SURESTE
SUBGERENCIA REGIONAL DE GENERACISUBGERENCIA REGIONAL DE GENERACIÓÓN TERMOELECTRICA PENINSULARN TERMOELECTRICA PENINSULAR
CENTRAL FELIPE CARRILLO PUERTOCENTRAL FELIPE CARRILLO PUERTO
Punto 2.- Problemática
2.1 DEFINICIÓN DE LA PROBLEMÁTICA
ESTANDO ENLAZADOS LOS AUXILIARES DE LA TURBINA DE
VAPOR A UNA TURBINA DE GAS, ANTE UN EVENTO DE
DISPARO DE LA TURBINA DE GAS SE GENERA UN COMANDO
DE INICIACION POR PROTECCION AL MODULO DE
TRANSFERENCIA.
REALIZÁNDOSE EN UN TIEMPO DE TRANSFERENCIA DE 140
MILISEG, LO QUE OCASIONA EL DISPARO DE LOS EQUIPOS
AUXILIARES DE LA TURBINA DE VAPOR POR PROTECCIÓN DE
BAJO VOLTAJE DERIVANDO EN EL DISPARO DE LA UNIDAD 3.

Punto 2.- Problemática
Unidad
Disponibilidad Factor de Planta
Real Real
Propia
Meta Real Meta
2.1 DEFINICIÓN DE LA PROBLEMÁTICA
Since the auxiliaries for the steam turbine and the gas
turbine are interconnected, before a gas turbine trip,
the protection generates an initiate command to the
transfer module.
The transfer time of 140 milliseconds causes a trip of the
steam turbine auxiliary equipment by undervoltage
protection resulting in the trip of Unit 3 (the steam
turbine).
Motor Bus Transfer

Motor Bus Transfer
Motor Bus Transfer System

M-5802 Syncrotran® Bus Transfer System
Motor Bus Transfer

M-4272
Digital Motor Bus Transfer System
Motor Bus Transfer

Hot Parallel Transfer (Manual Only)
Supervision of Parallel Transfer:
Sync Check
– Accurate phase angle, delta voltage and delta frequency measurement
– Fast blocking response
– Time delay for tripping adjustable
Timers
– Time window for transfer (1 to 50 cycles)
M-4272 Motor Bus Transfer System
Functionality Provided
Motor Bus Transfer

Fast Transfer (Manual or Automatic)
Supervision of Fast Transfer:
High Speed Sync Check
– Accurate phase angle, delta voltage and delta frequency measurement
– Instantaneous blocking and pickup (<1 cycle) if phase moves at the time
of transfer
Voltage Level Check – New Source
– Verify voltage integrity of new source
Timers
– Time window for transfer
Load shedding
– Programmable Load shedding with no time delay
Motor Bus Transfer

In-Phase Transfer (Manual or Automatic)
Supervision of In-Phase Transfer:
High Speed Synchronizer
– Predictive advance angle calculation that compensates for circuit breaker
closing time
– Frequency and voltage difference supervision
– Two breaker time settings available for bi-directional transfers
Voltage Level Check - New Source
– Over/under voltage level supervision for new source verification
Timers
– Time window for transfer
Load shedding
Motor Bus Transfer

Residual Voltage Transfer (Manual or Automatic)
Voltage Level Check - Motor Bus
– Undervoltage relay applied on motor bus to sense safe level for reclosing.
– Voltage measurement accuracy independent of frequency from 4 to 67 Hz
Voltage Level Check - Motor Bus
Over/under voltage level supervision for new source verification
Load shedding
Motor Bus Transfer

Fixed Time Transfer (Automatic)
A transfer has been initiated when the motor bus voltage drops below the bus
undervoltage relay (27B) limit setting, but it is not possible to monitor the motor
bus voltage due to Bus VT fuse loss during a transfer operation.
The close command to new source breaker is issued after a selectable fixed
time delay (30 to 1000 cycles)
Load shedding
Motor Bus Transfer

Bus Phase Undervoltage (27B) for transfer initiate and/or load
shedding
Frequency (81) and Rate of Change of Frequency (81R) for load
shedding
Breaker Failure (50BF), Source 1 and Source 2
Sixteen Output Contacts
– Four output contacts (two trip and two close) for Present Source
and New Source
– One lockout/blocking output contact
– Eleven programmable output contacts (ten Form 'a' and one Form
'c')
Two RS-232 ports (front and rear) and one RS-485 port (rear)
IRIG-B time synchronization
Motor Bus Transfer

Eighteen Control Status Inputs
– Six Breaker Status inputs (a, b, and sp (service position) for the
Present Source and New Source breakers
– Twelve programmable digital inputs.
All functions can be enabled or disabled, except those listed as
"Common Function Settings”
Four trip and close circuit monitoring inputs
Remote/Local control selection
M-3931 Human-Machine Interface (HMI) Module
M-3972 Target Module (24 status LEDs and 8 output LEDs)
There are additional 4 status LEDs, 8 output LEDs and 12 input
LEDs located on the front panel.
Motor Bus Transfer

Options
RJ45 Ethernet Port Utilizing MODBUS over TCP/IP Protocol
5 A or 1 A models available
60 and 50 Hz models available
Motor Bus Transfer

Automatically attempts the following transfer types in order:
- Fast transfer
- In-phase transfer
- Residual voltage transfer
- Fixed time transfer
Offers Sequential (break-before-make) and Simultaneous break and
make operation modes
Provides five methods to initiate transfer
- Protective relay initiate (one-way or bi-directional)
- Bus phase undervoltage initiate (one-way or bi-directional)
- Auto close initiate (bi-directional)
- Manual initiate via Front Panel, contact input or communication
Provides trip and close to old and new source breakers
Provides programmable load shedding for Fast, In-Phase, Residual
Voltage and Fixed Time Transfers
Motor Bus Transfer

Standard Features
Circuit Breaker Control :
Control of two circuit breakers with two individual programmable
breaker closing times
Three-breaker configuration can be provided by two M-4272 devices
Breaker failure monitoring
Motor Bus Transfer

Lockout/Blocking
A transfer is blocked when any of the following lockout/blocking
conditions described below is active:
Voltage Blocking – If prior to a transfer, the new source voltage
exceeds the Upper or Lower voltage limits, all transfers are blocked
as long as the voltage remains outside these limits.
External Blocking – When this control input contact is closed, all
transfers are blocked.
Incomplete Transfer Lockout – Blocks any transfer initiated by a
protective relay initiate or an automatic initiated transfer or manual
transfer if the last transfer has not been completed within the time
delay. A time delay can be set from 50 to 3000 Cycles. The MBTS
remains in the lockout condition until manually reset.
Motor Bus Transfer

Communications
M-3872 ISScom™ Communications Software package for setpoint
interrogation/modification, metering, monitoring, and downloading
oscillographic records.
Metering of all measured inputs, measured and calculated
quantities
Phasor diagrams
Synchroscope display
Single line diagram mimic display
Sequence of Event logs and Transfer Event logs
Oscillograph recording
ISSplotTM
Oscillographic Analysis Software graphically displays
waveforms to facilitate analysis, and also prints captured waveforms
Modbus,Modbus/TCP Communications
RS-232, RS-485, Ethernet
IRIG-B Time Synchronization
Motor Bus Transfer

Power Source
Two power supplies
Power Input - Flexibility and Range
110/120/230/240 V ac or 110/125/220/250 V dc
AC Range 85 – 265 V ac or DC Range 80 – 312.5 V dc
24/48 V dc
DC Range 18 – 56 V dc
Motor Bus Transfer

Can accommodate two and three-breaker configurations
Multiple setpoint profiles for various application requirements
Integrated control, supervisory functions, sequence of events,
Transfer Event Log and oscillographic recording in one device
Extensive commissioning tools, including “ring-down” analysis
Motor Bus Transfer

Standard Features
Initiating Automatic Transfer:
Transfer initiated by protective relay external to the MBTS system
Transfer initiated through ISSLogic
Automatic Transfer after a loss of the motor bus Source 1 supply
based on the internal programmable undervoltage element. This
provides a selectable backup feature if a manual or protective relay
transfer is not initiated.
Motor Bus Transfer

Standard Features
Types of Automatic Transfer:
Fast Transfer with adjustable Δ θ , Δ V and Δ F limits
Sequential and Simultaneous break-before-make operation modes
Delayed In-Phase Transfer at the first phase coincidence if Fast
Transfer is not possible
Residual Voltage Transfer at an adjustable low residual voltage limit
if Fast Transfer and Delayed In-Phase Transfer are not possible
Fixed Time Transfer after an adjustable time delay
Programmable Load Shedding with Fast, Delayed in-phase,
Residual voltage and Fixed time Transfer
Motor Bus Transfer

Standard Features
Manual Transfer:
Make-before-break (Hot Parallel) operation mode with Sync Check
function.
Break-before-make operation with Fast, Delayed In-Phase, Residual
Voltage.
Programmable Load Shedding.
Transfer initiated manually by contact input, front panel HMI or
through serial communication.
Motor Bus Transfer

System Setup
The System Setup consists of defining all pertinent information regarding the
connection environment.
Motor Bus Transfer

System Setpoints
The MBTS System Setpoints consists of entering the following:
Common settings
Automatic, Manual and Auto Trip Transfer settings
Enabling the functions and entering the desired settings
Designating the output contacts each function will operate, and which
control/status inputs will enable or block the transfer.
The programmable output/input choices include 11 programmable output
contacts (OUT5–OUT16) and six breaker status inputs (IN1–IN6) for Source
1 and Source 2, plus 12 other programmable inputs. A block or fixed time
transfer choice for bus fuse loss logic operation.
Motor Bus Transfer

System Setpoints
The System Setpoints screen consists of defining all Common, Automatic and
Manual Transfer settings, and Function settings.
Motor Bus Transfer

System Setpoints
The Display All feature of the System Setpoints screen contains the settings for each
MBTS function within a single window to allow scrolling through all MBTS setpoint and
configuration values
Motor Bus Transfer

System Setpoints
The Configure feature of the System Setpoints screen contains a chart of programmed
input and output contact configuration settings for each MBTS function within a single
window to allow scrolling through all MBTS configuration values
Motor Bus Transfer

System Setpoints
Common Function Settings, Inputs and Outputs
Motor Bus Transfer

System Setpoints
Common Function Settings Inputs
Motor Bus Transfer

System Setpoints
Common Function Settings Outputs
Motor Bus Transfer

System Setpoints
Automatic Transfer Settings
Motor Bus Transfer

System Setpoints
Manual Transfer Settings
Motor Bus Transfer

System Setpoints
Auto Trip Settings
When the Auto Trip is enabled, the MBTS will trip the breaker that was
originally closed within an adjustable time delay (0 to 10 Cycles in increments
of 1 Cycle) after the other breaker is closed by external means (breaker
control close switch for example).
Motor Bus Transfer

System Setpoints
60FL Bus VT Fuse Loss Settings
A Bus VT Fuse-Loss condition is implemented by comparing the voltage on
both sides of the closed breaker.
Motor Bus Transfer

System Setpoints
60FL Bus VT Fuse Loss
Input/Output Selection
Motor Bus Transfer

System Setpoints
27 Bus Phase Under Voltage
Motor Bus Transfer

System Setpoint
27 Bus Phase Under Voltage initiate
Motor Bus Transfer

System Setpoints
50BF #1 Source 1 Breaker Failure
Motor Bus Transfer

System Setpoints
Motor Bus Transfer

System Setpoints
Initiating Input/Output Selection
Motor Bus Transfer

System Setpoints
Trip Circuit Monitor
Motor Bus Transfer

ISSlogicTM
ISSlogic is programmed utilizing the M-3872 ISScom Communications
Software. ISScom takes the control/status input status, system status and
function status, and by employing (OR, AND, NOR and NOT) boolean logic
and timers, can activate an output, change setting profiles, initiate transfer, or
block transfer. An ISSlogic Function can not be used to initiate itself.
Since there are six ISS Logic Functions per setting profile, depending on the
number of different MBTS settings defined, the scheme can provide up to 24
different logic schemes.
There are six initiating input sources:
– Initiating Outputs
– Initiating Function Time Out
– Initiating Function Pickup (including the ISSlogic functions themselves)
– Initiating System Status
– Initiating Inputs
– Initiation using the communication port
Motor Bus Transfer

ISSlogicTM
There are three blocking input sources:
– Blocking Inputs (contacts)
– Blocking through system status conditions
– Blocking using the communications port
The activation state of the input function selected in the Initiating Function can be
either timeout (trip) or pickup.
The desired time delay for security considerations can be obtained in the ISS
Logic Function time delay setting.
The ISS Logic Function can be programmed to perform any or all of the following
tasks:
– Change the Active Setting Profile
– Close an Output Contact
– Be activated for use as an input to another ISS Logic Function
– Initiate a Transfer
– Block a Transfer
Motor Bus Transfer

ISSlogic
TM
Setup Screen
Motor Bus Transfer

ISSlogic
TM
Setup Screen Selections
Motor Bus Transfer

Metering and Status
The Digital Motor Bus Transfer System provides metering of voltage,
current, and frequency of the Source 1, Source 2, and the Motor Bus.
Metering accuracies are:
Voltage: ± 0.5 V or ± 0.5%, whichever is greater
Current: 5 A rating, ± 0.1 A or ± 3%, whichever is greater
1 A rating, ± 0.02 A or ± 3%, whichever is greater
Frequency: ± 0.02 Hz (from 57 to 63 Hz for 60 Hz models; from
47 to 53 Hz for 50 Hz models)
Phase Angle: ± 0.5 degree or ± 0.5%, whichever is greater
Motor Bus Transfer

Metering and Status
Secondary Metering and Status Screen
Motor Bus Transfer

Metering and Status
Primary Metering Screen
Motor Bus Transfer

Metering and Status
The Phasor Diagram provides the user with the ability to evaluate a selected
reference Phase Angle to Phase Angle data from other sources. The Phasor
Diagram also includes a Freeze capability to freeze the data displayed on the
Phasor Diagram.
Motor Bus Transfer

Metering and Status
The Sync Scope screen provides the user with the ability to observe the Delta
Frequency relationship between the Bus and the New Source, illustrated in a
Fast or Slow direction based on Delta Frequency.
Motor Bus Transfer

Metering and Status
The Single Line Diagram provides the user with the ability to observe the Delta Phase
Angle, Delta Voltage and Delta Frequency relationship between the Bus and the New
Source. The Single Line Diagram also displays the metering, the status of S1 and S2
breakers and the status of Manual Transfer Ready, Lockout/Blocking, Remote/Local and
Device On/Off.
Motor Bus Transfer

Oscillographic Recorder
Samples at 16 or 32 (50 or 60 Hz) Samples/Cycle.
The Oscillographic Recorder can be triggered by a control/status inputs
or output contact signals.
Supports COMTRADE file format
User-defined, post-trigger delay period
Motor Bus Transfer

The following parameters are captured by the Oscillographic Recorder:
– MBTS start (initiate) signal. It can be manual transfer initiate,
protective relay initiate, internal bus undervoltage initiate or external
bus undervoltage initiate.
– Source 1 and Source 2 breaker status (Closed or Open)
– Trip and close commands to the Source 1 breaker
– Trip and close commands to the Source 2 breaker
– Source 1 voltage waveforms, single-phase or three-phase
– Source 2 voltage waveforms, single-phase or three-phase
– Source 1 current waveforms, single-phase if available
– Source 2 current waveforms, single-phase if available
– Bus voltage waveforms, single-phase or three-phase
Motor Bus Transfer

The following parameters are also captured by the Oscillographic
Recorder:
– Delta Phase Angle
– Delta Frequency
– Trip Circuit Monitor (TCM) or Close Circuit Monitor (CCM) open
signal
– Inputs 1-18
– Outputs 1-16
Motor Bus Transfer

Oscillographic Recorder Setup Screen
Motor Bus Transfer

Oscillographic Recorder Retrieve Record Screen
Motor Bus Transfer

Oscillographic Recorder Record Opened in ISSplot
TM
Motor Bus Transfer

Transfer Event Log
Each transfer event log (total of 4) includes the following parameters:
– Start Signal. The signals that can trigger a transfer are an external protective relay
initiate, external undervoltage relay initiate, internal automatic bus undervoltage relay
initiate, and manual initiate (either local, remote or through serial communications).
– Source 1 RMS value of voltage and current at time of trip (or close)
– Source 2 RMS value of voltage and current at time of close (or trip)
– Bus RMS value of voltage at time of close (or trip)
– Positive and Negative Sequence values
– Delta Voltage between bus and new source* at time of close command (or trip
command)
– Delta Voltage between bus and new source* at the time of actual breaker close (or
breaker open)
* The 'new source' is defined as the source to which the bus is being transferred.
Motor Bus Transfer

Transfer Event Log (cont.)
– Bus frequency, at time of close (or trip)
– Resultant Volts/Hertz at time of actual breaker close
– Element(s) operated, for example: 27B, 81, 81R, 50BF, TCM and CCM Functions
– Element(s) picked up, for example: 27B, 81, 81R, 50BF, TCM and CCM Functions
– Input/output contact status changes
– Trip and close commands
– Delta Phase Angle between bus and new source* at time of close command (or trip
command)
– Delta Phase Angle between bus and new source* at time of actual breaker close (or
breaker open)
– Delta Frequency between bus and new source* at time of close command (or trip
command)
Motor Bus Transfer

Transfer Event Log (cont.)
– Delta Frequency between bus and new source* at time of actual breaker close (or
breaker open)
– Breaker closing time (time from when the close command is issued to when the
new source breaker status contact closes
– Breaker opening time
– Open transition time (time from when the old source breaker status contact opens
to when the new source* breaker status contact closes)
– Close transition time in Hot Parallel Transfer only (time from when the new
source* breaker status contact closes to when the old source breaker status
contact opens)
– Type of transfer completed: Fast, Delayed In-Phase, Residual Voltage, Fixed
Time or Hot Parallel
Motor Bus Transfer

Transfer Event Log (Detail)
Motor Bus Transfer

System Status and Transfer Start Signal Status Screen
Motor Bus Transfer

Sequence of Events Recorder
In addition to the Transfer Event Log the Digital Motor Bus Transfer
System provides Sequence of Events Recording.
The Sequence of Events Recording stores every change in the input
status, trip commands, close commands, any signal to initiate a
transfer, type of transfer, change in any breaker status, change in
setpoint and status reset.
Each of these Running Events are time stamped with the date and time
in 1 ms increments whether the IRIG-B is present or not.
The Running Event Log stores the last 512 events, when a new event
occurs the oldest event is removed.
A reset feature is provided to clear this log through the serial
communications.
Motor Bus Transfer

Sequence of Events Setup Screen
Motor Bus Transfer

Sequence of Events File Details Screen
Motor Bus Transfer

Conclusions
The fast transfer requires a ringdown or simulation analysis to
determine the phase angle limit at the instant of connection to
the new source.
Worst case scenarios should be considered that include rapid
external system changes, changes in loading that include
inertia, and mixture of synchronous and induction machines.
The sync check equipment to be used for supervising fast
transfers must be able to detect a phase angle pickup or
block very rapidly if the angle moves in or out of the desired
range.
Sync check relays used for traditional applications do not
have the required speed of operation to effectively
pickup or block if required.
Conclusions
Motor Bus Transfer

The in-phase transfer offers an opportunity to synchronize a
motor bus on the first available slip cycle
- This type of transfer will enable process continuity as the
motors are still spinning and the resultant V/Hz for an in-
phase close is well below the 1.33 pu maximum
Specialized high speed synchronizing equipment permits in-
phase transfer that can determine the deceleration of the
motor bus and effect a new source breaker closure at phase
coincidence.
Undervoltage relays classically used for residual voltage
transfer exhibit setpoint error at low frequency that could
permit an out-of-phase transfer well above the maximum
acceptable resultant V/Hz standard of 1.33 pu.
Undervoltage relays must be selected exhibiting
setpoint accuracy down to low frequencies.
Motor Bus Transfer
Conclusions
©2008 Beckwith Electric Co., Inc.

Motor Bus Transfer Systems (MBTS

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