38 kV Switches for Medium-Voltage Switchgear Engineering
Understanding 38 kV Switchgear
When a facility receives power at 34.5 kV, operators need to control the incoming source, isolate equipment and divide the electrical system into manageable sections. That’s where 38 kV switches and custom switchgear manufacturing comes in.
These switches are placed in utilities substations, renewable-energy facilities, data centers, mining operations, large industrial plants and campuses with significant power demands.
38 kV switchgear describes the equipment’s maximum voltage class. It’s used on electrical systems with a nominal operating voltage of 34.5 kV.
The difference between nominal system voltage and maximum equipment voltage gives the equipment insulation room needed for normal voltage variations. Although voltage class is only part of the specification. You’ll need to define continuous current, short-circuit current, load-interrupting capability, fault-closing rating and basic impulse level, or BIL.
38 kV Fused Switches and Power Fuses
A 38 kV fused switch combines a load-interrupter switch with medium-voltage power fuses. The switch controls normal power flow and provides isolation, while the fuses protect against overcurrents and short circuits.
This design is used for transformer primaries and radial feeders. It can provide switching, isolation and fault protection without requiring a circuit breaker, protective relay and an instrument-transformer package.
Fuse selection needs to account for transformer full-load current, magnetizing inrush, available fault current, permissible overloads and coordination with downstream protection. An undersized fuse can operate when the transformer is energized. An oversized fuse may not provide the required protection.
Facilities that operate at lower distribution voltages may use 15 kV switches for many of the same switching, isolation and transformer-primary applications discussed here. Also see how 15 kV switches work in medium-voltage switchgear, including the differences among load-interrupter switches, fused switches, feeder switches and tie-switch arrangements.
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How 38 kV Load-Interrupter Switches Work
A 38 kV load-interrupter switch controls the normal flow of electricity through a medium-voltage circuit. It can energize or de-energize a feeder, transformer or bus section while operating within its rated load-interrupting capability.
When energized contacts separate, an electrical arc occurs. The switch uses an arc-control system and a quick-make, quick-break mechanism to interrupt the current. Stored energy allows the contacts to move quickly instead of depending on how fast the operator moves the handle.
A load-interrupter switch isn’t necessarily intended to clear high-level fault current by itself. Medium-voltage fuses or a relay-controlled circuit breaker normally perform that protection function.
Main, Tie and Feeder Switch Arrangements
Custom 38 kV metal-enclosed switchgear can incorporate main, tie and feeder switches in a coordinated lineup.
The main switch controls incoming power from a utility, generator or upstream substation. A tie switch connects or separates two bus sections. Feeder switches control outgoing circuits serving transformers, buildings, substations or other switchgear.
In a main-tie-main arrangement, two main switches normally supply separate bus sections while the tie remains open. If one source becomes unavailable, a switching sequence allows the remaining source to supply both sections.
What does 38 kV class mean?
Is 38 kV switchgear the same as 34.5 kV switchgear?
What does a 38 kV load-interrupter switch do?
Can a 38 kV switch clear a short circuit?
Why are fuses installed with 38 kV switches?
What is a 38 kV tie switch?
Can 38 kV switches be operated remotely?
When should a circuit breaker be used instead of a fused switch?
Why is 38 kV equipment larger than 15 kV equipment?
Radial and Loop Power Distribution Systems
A medium-voltage feeder switch allows one outgoing circuit to be isolated without shutting down the entire bus.
In a radial power distribution system, each load has one electrical path to the source. This design is comparatively simple, but an upstream outage can interrupt all connected downstream equipment.
Loop power distribution systems provide more than one potential path through the distribution network. Operators can isolate a damaged cable section and restore power from the opposite direction. This improves service continuity, but it also requires a carefully planned switching sequence, properly rated equipment and coordinated protection.
Transformer-Primary Switch Applications
A 34.5 kV transformer-primary switch is installed between the medium-voltage source and a transformer. It allows the transformer to be energized, de-energized and isolated without opening the entire upstream system.
Fused load-interrupter switches are often used in this position. The switch performs routine switching and isolation, while the fuses provide fault protection.
Primary fuses must coordinate with the transformer’s characteristics and the secondary main protective device. Where the system design permits, a secondary breaker should clear a downstream fault before the primary fuse operates. At the same time, the primary fuse protects the transformer without responding unnecessarily to normal energization inrush.
38 kV Switches Versus Circuit Breakers
A fused switch may be suitable when the application needs normal switching, visible isolation and straightforward fault protection. A 38 kV circuit breaker (rated for up to 38,000 volts) can interrupt both load current and fault current within its ratings.
Protective relays monitor current, voltage, frequency and other system conditions. When a qualifying fault occurs, the relay commands the breaker to open.
Circuit-breaker switchgear makes sense when you need adjustable protection, frequent operation, remote control, event recording, communications or advanced protection for transformers, generators and buses. The decision should consider coordination, switching frequency, maintenance resources, automation requirements and the consequences of an outage, not just equipment cost.
Specifying Engineered 38 kV Switchgear
When specifying engineered 38 kV switchgear, begin with an accurate one-line diagram. Identify the nominal voltage, grounding method, continuous load, available fault current and equipment served.
You’ll also need to define the main, tie and feeder arrangement; fused or unfused positions; manual or motor operation; interlocking; metering; control power; cable entry and provisions for expansion.
Cable requirements are important at this voltage. The design needs space for 35 kV-class cable, terminations and stress-control components. Indoor and outdoor installations may also require different enclosures, heaters, ventilation and environmental protection.
BCS Switchgear can engineer indoor or outdoor medium-voltage lineups around your sources, loads, transformers, operating sequence and installation requirements. Coordinating the complete system helps ensure that the switches, fuses, breakers, bus and cables work together as intended.
BCS Switchgear is an industry leader in new and obsolete electrical control and distribution equipment. Since 1997, BCS has been servicing customers to extend electrical life of low and medium voltage electrical power equipment.
Cody can be reached by email: [email protected]
