Your questions answered: Understand the benefits of a fixed versus withdrawable vacuum circuit breaker
Webcast presentation on Feb. 23, 2016, by Sherry Rollins, senior offer management specialist, Schneider Electric; with James Stacy, director of medium voltage, offer strategy, U.S. Energy Business, Schneider Electric, participated in the question and answer session.
James Stacy tackled unanswered questions from the Feb. 23, 2016, webcast on fixed versus withdrawable vacuum circuit breakers.
Q: Can I have terminals that use elbow fittings?
James Stacy: Elbow termination availability varies by manufacturer. Most commonly used elbow terminations are seen in pad-mounted switchgear and gas-insulated switchgear. Schneider Electric’s traditional fixed breaker switchgear, HVL/cb uses stress cones. However, our newest Premset offer will use elbow connections. For more information about our newest offer, follow us on Periscope to learn more @semediumvoltage.
Q: Please elaborate on how the ground switch will be for fixed-type switchgear? I know that for withdrawable type switchgear, we usually get a ground switch bucket that we can use to ground specific feeders.
Stacy: The market requires a visible disconnect. In withdrawable switchgear, this is accomplished by removing the breaker from the connected position. In fixed mounted switchgear, the visible isolation is accomplished via the use of a disconnect switch.
- The grounding switch in Schneider Electric’s HVL/cb switchgear has an optional feature.
- The grounding switch in Schneider Electric’s newest "Premset" offer is always provided.
Each of these offers have the ability to ground the load side of a feeder.
Q: Is it required that the switch blades be visible?? Not too long ago, we specified units with cameras.
Stacy: The code requires a visible disconnect. In withdrawable switchgear, this is accomplished by removing the breaker from the connected position. In fixed mounted switchgear, the visible isolation is accomplished via the use of a disconnect switch.
Q: Could you provide a representative cost per kVA for fixed and withdrawable switchgear?
Stacy: It depends on the offer. For example, fixed switchgear can be up to 20% less expensive than a comparable withdrawable offer.
Q: On the fixed breaker, do you need rear access, and if not, how do you install the cables?
Stacy: For some manufacturers, you can pull the cables through the front of side of the switchgear. You can have rear access on a fixed breaker option. Again, that is based on who manufactures the equipment.
Q: Are there installations, such as hospitals, where withdrawable breakers ever become code or standard requirements?
Stacy: There are no known codes that dictate the use of fixed versus withdrawable in any specific application. All switchgear must have a visible disconnecting means.
Q: Is the smallest switchgear ampacity for 15 kV 1,200 amps?
Stacy: For 15 kV, you can go up to 4,000 amps with some manufacturers. It is based on what the manufacturer supplies.
Q: Do you make NEMA 3R HVL/cb yet? How about walk-in NEMA 3R?
Stacy: No, HVL/cb is only available in a NEMA 1 option at the moment. A PZ house is recommended for an N3R option.
Q: Can you use the same relays for fixed and withdrawable breakers and will the fault/arc flash times be the same?
Stacy: Yes, you can use the same relay as long as it fits within the means of the low voltage box of the switchgear. Fixed switchgear will traditionally have a smaller low voltage box that could restrict the size of your relay, but not the capability of the relay. For example, a 751-amp arc flash relay can be used in either fixed or withdrawable switchgear.
Q: Are there limitations on basic insulation level (BIL) ratings on either switchgear design?
Stacy: Yes, BIL will be limited to 95 kV for fixed switchgear. This is because the IEEE standard for fixed switchgear (C37.20.3) only requires up to 95 kV.
Q: Please list the standards again.
Stacy: Switchgear standards:
IEEE C37.20.3-2013: IEEE Standard for Metal-Enclosed Interrupter Switchgear (1 kV to 38 kV)
IEEE C.37.20.2-2015: IEEE Standard for Metal-Clad Switchgear
IEEE C37.04-1999 (R2006): IEEE Standard Rating Structure for ac High-Voltage Circuit Breakers
IEEE C37.06-2009: Standard for ac High-Voltage Circuit Breakers Rated on a Symmetrical Current Basis – Preferred Ratings and Related Required Capabilities for Voltages Above 1,000 V
IEEE C37.09-1999 (R2007): IEEE Standard Test Procedure for ac High-Voltage Circuit Breakers Rated on a Symmetrical Current Basis.
Q: Please address arc flash and arc flash mitigation techniques. Will there be a future seminar on this topic?
Stacy: Arc flash is a diverse topic that requires a dedicated Webcast to discuss arc flash mitigation solutions and how they should be selected for each project.
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