A good transfer switch is able to transfer the load from an alternative source with zero or minimal loss of power. So far this can be achieved with static transfer switches, but the investment costs are substantial and there are technical limits due to the drastic short circuit constraints. For these reasons conventional medium voltage circuit breakers are still installed widely in power genera on plants and utilities.

1. Phone: 1.866.551.8362 (604.540.6600) Website: www.tavrida-na.com
Office: 1105 Cliveden Ave, Delta, British Columbia, Canada
ISM_Shell Series Breakers and Fast Transfer
A good transfer switch is able to transfer the load from an alternative source with zero or minimal loss of
power. So far this can be achieved with static transfer switches, but the investment costs are substantial and
there are technical limits due to the drastic short circuit constraints. For these reasons conventional medium
voltage circuit breakers are still installed widely in power generation plants and utilities.
However due to the relatively slow opening and closing times of conventional circuit breakers, power is
typically interrupted for more than 5 cycles, and even interruptions of 8 or more cycles are not uncommon.
For industrial applications this can result in significant slowing down of motors, which produces a phase angle
between the “lost source” and the alternative source. If the interruption is too long, the motor can be severely
damaged. Thus many industrial systems actually do not perform “live transfer” in order to mitigate risks of
losing expensive investments. At the same time any down-time of industrial processes or customer outages
leads to significant costs or penalties.
Tavrida Electric has revolutionized circuit breaker design by developing a new generation of circuit breakers
and controls with exceptionally fast opening, closing and response times. This enables transfer times as fast
as 2 cycles with the SEL 451 in a closed transition (“make before break”) and less than 3 cycles for an open
transition (“break before make”).
Transfer switching with breakers....in less than 2 cycles
PT PT
Breaker Control Breaker Control
SEL-451
Breaker #1
Normally Closed
Breaker #2
Normally Open
Main Source Backup Source
Motor Loads
M M
FAULT
Transfer to Backup Source
<2 Cycles • Complete power transfer in less than two cycles
• Overcurrent protection for main source and
backup
• Implementation of breaker failure logic for both
circuit breakers
• Tracking of average and last circuit breaker oper-
ating time
• Setting of alarm or protect against system fre-
quency voltage and frequency excursions using
built-in voltages and frequency elements

2. Phone: 1.866.551.8362 (604.540.6600) Website: www.tavrida-na.com
Office: 1105 Cliveden Ave, Delta, British Columbia, Canada
ISM_Shell Series Breakers and Fast Transfer
Fast Transfer Switch Package
Component Description
ISM15_Shell_2(FT) Shell type breaker, rated 15kV - 2000A - 25kA - 95kV BIL
CM_1501_01(4) Breaker control module, 85 - 265 VAC / VDC input with 4 ms reaction time
SEL-451® Schweitzer Engineering transfer switch relay assembly + options
Timing Details
Product Parameters Designation Response time
Tavrida SHELL CB opening time (including fast control
module response time)
Topen
8 ms
(<1/2 cycle)
Tavrida SHELL CB interrupting time (including fast control
module response time)
Tinterrupt
16.3 ms
(<1 cycle)
Tavrida SHELL breaker closing time (including fast control
module response time)
Tclose
22 ms
(1.32 cycles)
SEL-451 Open Phase Detection Logic trip time TSEL451
10 ms
(0.6 cycles)
Transfer switch time closed transition “make-before-break”
with SEL-451 Open Phase Detection Logic
TSEL451+ Tclose
32 ms
(<2 cycles)
Transfer switch time open transition “break-before-make”
with SEL-451 Open Phase Detection Logic
TSEL451+ Tclose + Topen
40 ms
(<2.5 cycles)