Closed Transition ATS’s
John J. Stark
Marketing Services Coordinator, Russelectric Inc.
Why Operate in Parallel with the Utility?
• Closed Transition Transfer of non-utility
generator, re-transfer and generator test
• Cogeneration
• Peak Shaving
• Curtailable Rate Structure
• Distributed Generation
Types of Operational Modes
• Open Transition
• Closed Transition
First let’s talk about open transition mode
An open transition mode of operation is a
method of transferring a load between two
sources with an interruption of power during
transfer.
Open transition ATS
N
N
LL
M1
M2
Motor #1
drives the
normal source
contacts
Open.
This is all done
with
verysource
reliable
The load
is disconnected
mechanical
for an
interlocking
and
adjustable
does
not require
period
to allow
an
elaborate
regenerative
electrical
power to decay
interlocking
design.
Motor #2
then drives the
emergency
source
contacts
closed
Closed Transition Mode
A closed transition mode of operation is a
method of either:
1) Transferring a facility’s load between the
utility and generator or 2) operating a generator
in continuous parallel with the utility service,
without an interruption of service.
Utility Concerns
• Reliability and quality of utility power to other
customers
• Safety and protection of utility service personnel
• Protection of utility equipment
Type of Parallel Operation
• Passive Momentary utility parallel
operation
– 100ms or less
Closed transition ATS
Operator #1
drives the
normal
source
contacts
open
N
S1
S2
Closed
Transition
Operation
L
The load
source is
connected to
both sources
momentarily
Operator #2
drives the
emergency
source
contacts
closed
Closed Transition
Transfer Switches
Advantages
•No interruption of power for load test and
return to utility as well as peak shave operation
•Fast transfer operation
Closed Transition
Transfer Switches
Disadvantages
•No phase lock synchronizing
•No Protective relays
•No mechanical interlock, thus no safe manual operation
•Lacks true load test function
•Higher fault current requirements
Sophisticated
Controls and Safety
Features
Full 3-Phase over and under
voltage and frequency
sensing on both normal and
emergency sources.
Protection against running over
100 msecs:
Signals to operators
Fail to Transfer Function
Provides trip signals to the
generator or utility breakers.