Medium-voltage switchgear is the equipment that lets you switch, protect and isolate a circuit somewhere between about 1 kV and 36 kV. It is where a fault gets cleared, where maintenance gets made safe, and where most of the specification mistakes happen. This guide covers what the equipment does, the types you will be choosing between, and the ratings that actually need your attention.
What Switchgear Has to Do
Four functions, and every specification is a variation on them:
- Switch – make and break load current under normal conditions.
- Protect – detect a fault and clear it before it damages the transformer or the cable.
- Isolate – provide a visible, lockable break so work downstream is safe.
- Earth – apply a safety earth to a de-energised circuit before anyone touches it.
The Main Types You Will Be Choosing Between
| Type | What it is | Where it goes |
|---|---|---|
| Ring main unit | Compact switch-and-fuse or breaker unit for ring or radial circuits | Distribution substations, compact substations, renewable collection |
| Withdrawable circuit breaker panel | Breaker on a truck that racks out for maintenance | Larger substations where downtime is expensive |
| Fixed circuit breaker panel | Breaker bolted in place, cheaper, needs more downtime to service | Industrial plants with planned shutdowns |
| Gas insulated switchgear | Sealed-for-life, compact, insensitive to environment | Tight sites, harsh or dusty environments, high altitude |
The choice is usually made on maintenance philosophy and space rather than on price alone. A withdrawable panel costs more and lets you swap a breaker in minutes. A ring main unit costs less and suits points that are rarely touched.
Ratings That Need Attention
- Rated voltage. Must match or exceed the system voltage. This is where an 11 kV panel gets specified onto a 12 kV system and fails at commissioning.
- Rated short-time withstand and peak. Your fault level, with margin for future network changes. Ask what the fault level will be in ten years, not what it is today.
- Rated normal current. Set by the load, but check the outgoing feeders individually. The incomer rating does not cover a heavily loaded feeder.
- Internal arc classification. Whether the panel is designed to contain an internal arc and where it vents. This is a safety decision and increasingly a requirement in utility specifications.
- Degree of protection. Indoor panels usually need less than outdoor enclosures, and dusty or coastal sites need more than either.
Protection and Control
Protection is set to your single-line diagram rather than to a default schedule. Overcurrent, earth fault, and where the design calls for it differential or directional protection, with relay settings issued on the drawings for your engineer to check before the panel is built. Interlocking between switches, earthing switches and access doors is what prevents the mistakes that injure people, and it is function-tested on the finished assembly. More on this on the switchgear control page.
Gas Insulated or Air Insulated
Gas insulated switchgear costs more per function and takes less room. It is sealed for life, which means it is not affected by dust, humidity, altitude or vermin, and it suits compact substations where space is the binding constraint. Air insulated switchgear is cheaper, easier to modify and easier to work on, and it remains the right answer for a conventional switchroom with space to spare.
Standards
The applicable standard and clause set are agreed against your project specification before production. IEC 62271-200 covers metal-enclosed switchgear assemblies; where a project names it, we work to those clauses and issue routine test reports with the equipment. Utility specifications frequently add requirements on top, and those are confirmed in writing at the drawing stage.
What to Send for a Quotation
- The single-line diagram, including protection requirements.
- System voltage, frequency and the fault level at the point of connection.
- Load current per circuit.
- Indoor or outdoor, and the site conditions.
- Any utility or consultant specification that applies.
Our MV switchgear range covers the arrangements above. If your diagram does not fit one of them, it is still worth sending – most of what we build starts from someone else’s drawing.
If you are still fixing the ratings, our MV switchgear selection guide works through the five numbers that decide the arrangement before you look at a catalogue.
Frequently Asked Questions
What voltage range counts as medium voltage?
Roughly 1 kV to 36 kV, though the boundary is defined differently by different standards and utilities. What matters for a purchase is the rated voltage of the equipment against your system voltage, not which band the label falls in.
Do I need gas insulated switchgear?
Where space is tight, or the environment is dusty, humid, coastal or at altitude, gas insulated equipment earns its cost. In a conventional switchroom with room to spare, air insulated equipment is usually the better value.
What is internal arc classification?
It describes how a panel behaves if an arc forms inside it, and whether people standing near it are protected. It is a safety requirement written into many utility specifications now, and it is worth confirming which class your project needs.
Can protection settings be changed later?
Settings can be revised, but the protection functions and current transformer ratios are built into the panel. That is why relay settings are issued with the drawings for review before the panel is manufactured.
Get a Drawing and a Price
Send the single-line diagram, the load list and the site conditions – altitude, ambient range, indoor or outdoor, enclosure rating. We come back with a proposed arrangement, the standard set we would work to, and a quotation. Email info@xsdfftransformer.com or call +8615867897761.