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AC Capacitor bank switching is a specialist requirement of switchgear. Unlike conventional inductive or resistive loads, capacitors cause the highest voltage at the zero point on the current wave. Deenergizing a capacitor bank with the wrong switching device can cause restrikes that can damage the capacitor bank, switching device, and other system components.
Since AC switchgear relies on the current zero point for interruption, the capacitors cause the highest voltage at this point. Any switchgear that is designed to interrupt capacitors must be tested and validated to handle this higher voltage at the interruption point. Capacitor banks also tend to switch multiple times per day compared to other loads. Therefore, the capacitor switch should be able to handle at least 30 000 full load operations before maintenance is required.
Cost-effective Alternative
These additional requirements often make capacitor switches expensive.
However, NOJA Power’s OSM38 Recloser is type tested to switch capacitive loads up to 27 kV and 600A (single and Back-to-Back Capacitor Switching). This means the OSM38 can be used to
switch capacitors, offering a cost-effective alternative to traditional capacitor switches.
A type test report of the OSM38’s Capacitor switching is available from NOJA Power.
This makes NOJA Power’s OSM Recloser a popular option for capacitive switching, as shown in the following two examples.
Overhead Capacitor Bank Switching
NOJA Power’s OSM Recloser system can be used to switch overhead capacitor banks. In this example as supplied by EPRECSA, NOJA Power’s exclusive distributor for Mexico, a sensor is connected to the
mainline, connected to a capacitor bank controller inside the NOJA Power RC-10 Recloser controller.
The capacitor bank controller makes switching decisions based on the requirement for shunt capacitance.
The capacitor bank controller is wired into the NOJA Power Recloser controller inputs, allowing the controller to issue close and open commands to the Recloser.
Remote control and monitoring is also possible. The RC-10 can be integrated into a SCADA network, providing insights into local measurements, status and equipment condition.
A comprehensive document on this switchgear connection is available from NOJA Power. Enquiries can be made at the following link: https://www.nojapower.com.au/quotation
Cable Capacitor Bank Switching
The NOJA Power OSM38 Recloser can also be used for cable connected capacitor switching.
This example application for the NOJA Power OSM38 Recloser built
by RWW Engineering demonstrates an indoor capacitor bank switching array.
In this design, RWW Engineering have used the OSM38 in a vertical mount, with additional current transformers to determine the requirement for capacitive switching.
The group also used the Remote HMI capability of the RC-15 Recloser controller, opting to mount the RC-15 HMI in a separate panel. The connection is made using a fibre optic link between the HMI panel and the RC-15 Recloser control.
