A key part of an automated feeder
switching system is the automated switch. The term “automated” in
this context means the switch is designed for use on an automated or
SCADA system.
In order to be automated, existing
switches may be retrofitted with motor operators, current and voltage
sensors, RTUs and communication devices to allow the remote operation
necessary to realize the benefits available with automated feeder
switching systems.
However, switches designed for
occasional, manual operation may not be entirely suitable for
operation on an automated distribution circuit feeder. Manual
switches are typically not designed to be operated the hundreds of
times required by a fully automated system over the life of a typical
switch.
Nor are they ordinarily designed for
duty cycle fault-closing to allow the system operator to
inadvertently close into a fault from the SCADA master station—and
still leave the switch in an operable condition.
More recently, switches designed
specifically for automation have appeared in the market like the one
below.
Such switches incorporate design
features that make them particularly applicable for use in an
automated feeder switching system:
1. Duty-cycle fault-closing allows the
switch to be closed into a typical fault several times before
experiencing damage severe enough to render the switch inoperable.
2. Integrated voltage and current
sensors provide the ability to monitor voltages, currents, and loads
that are in turn used as inputs to algorithms to effect automated
switching for fault isolation and restoration and for shifting loads
for circuit optimization.
3. Integrated operating mechanisms
enable the switches to be operated remotely via computer commands.
Integration with the switch ensures optimum operation without the
need for cumbersome ground-to-switch linkages.
4. Integrated load interrupters should
be designed to allow operation under any weather conditions since it
will not be possible to visibly inspect the switch for ice or other
problems prior to operation.
5. Integrated control power sources
eliminate the need to rely on locally available control power
sources—or to install such power sources.
6. Integrated visible air-gap isolation
provides the visible air gap when needed for certain types of line
work.
In addition, an associated control
package should include switch-operating controls, a local/remote
switch, backup power for dead-line SCADA operation, a remote-terminal
unit, and data communication devices. The entire package should be
assembled and tested for proper operation by a single supplier to
eliminate the need for the utility to perform the integration.
The control box should be separately
located from the switch to allow access by technicians who are not
qualified in high-voltage operations. In underground switchgear
applications, the control should be isolated from the high-voltage
compartments of the switchgear.
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