Your questions answered: Understand the benefits of a fixed versus withdrawable vacuum circuit breaker
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:
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.