Download automatic transfer switches

Transferring Inductive Type Loads
John J. Stark
Marketing Services Coordinator, Russelectric Inc.
(Refer to Russelectric Technical Brief:
“Eliminating Power Transients When Switching Large Inductive Loads”)
In Phase Monitor
VS
Dual Operator
For Switching Inductive Loads
•Russelectric Recommends Dual Operator
But, lets discuss both…
In-Phase Monitor for Switching Inductive Loads
or for Proper Closed Transition Switching
(between two available sources)
In-Phase Monitor, Principal of Operation
A feature within the controller (or a synchro-check relay in old designs) where voltage values from
source one and Source two are monitored through input signals to the controller. The controller
compares the two voltage levels and phase relationship between the frequencies of both sources
and will allow a transfer only when the voltage and frequency (of both sources) are within acceptable
limits.
Typical set points:
5% - 20% nominal volts
Phase angle adjustment: 6 – 20 Electrical degrees
Source 1
Source 2
ATS
In-Phase Monitor for Switching Inductive Loads
(between two available sources)
Pros:
•With some manufacturers
this feature can be a
significant cost savings
over
dual operator.
Cons:
•Introduces more sensitive
and adjustable electronics
and circuitry into the system.
•If an acceptable window of
voltage and frequency is not
achieved, desired transfer will
not happen. Example: ATS
needs to return to utility after
being in the engine generator
(emergency) position… engine
speed running erratically, no
window achieved… switch in
remote location… ATS remains
on generator until it runs out of
fuel.
ATS
Dual Operator Switching for Inductive Loads
(open transition, between two available sources)
Operator #1
drives the
normal source
contacts
open
N
LL
1
2
The load source
is disconnected
for an
adjustable
period to allow
regenerative
power to decay
Operator #2
then drives the
emergency
source
contacts
closed
Dual Operator for Switching Inductive Loads
(open transition, between two available sources)
Pros:
•Very reliable. Positive
transfer without reliance on
sensitive monitors. The
switch will always transfer
without the load
experiencing a “bump”.
•With an inherent dual
operator design, ATS has
an
ancillary benefit in that it
can also be used as a
dynamic load shed device,
completely controllable,
either automatically,
manually or in a control
scheme.
N
L
Life Safety &
Support
Branches
Utility
Source
ATS-1
Critical
Branches
ATS-2
Utility
Distribution
Switchgear
Equipment
Branches
ATS-3
ATS - 3 Sheds
Non-Critical Loads
Emergency
Distribution
Switchgear
Loss of
Engine #1
Generator
Control &
Synchronizing
Switchgear
Load
Control
Circuitry
G
G
G
E
E
E
Dual Operator for Switching Inductive Loads
(open transition, between two available sources)
Cons:
•Depending on the manufacturer
this can be an expensive solution.
N
•Slight delay on transfers
L
Power Control
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