In solid-insulation enclosed switchgear, the outer enclosure is made of solid insulating material, sometimes with a semiconductive layer, and can be touched while the equipment is energized. IEC 62271-201 classifies it by categories of protection against electric shock (PA, PB1 and PB2) and sets its own earthing and internal arc rules.
Short answer
IEC 62271-201, 2014 edition, covers prefabricated solid-insulation switchgear for alternating current, with rated voltages above 1 kV and up to 52 kV, for indoor use and service frequencies up to 60 Hz. The outer enclosure is made of solid insulating material, and may carry a semiconductive or conductive layer. The standard indicates that this switchgear, when it meets its requirements, can be touched safely while energized. Access to it is restricted to authorized personnel. For the IP and IK protection degrees of the enclosure, see IP and IK protection degrees of switchgear.
Switchgear with a metal enclosure falls under IEC 62271-200. Part 201 complements the standards of each component as regards its installation within the assembly.
What a solid insulating enclosure is
Clause 3.107 defines it as the part of the switchgear that gives a specified degree of protection against external influences and against electric shock, by limiting approach or contact with live parts and moving parts. The main part is made of solid insulating material and may carry semiconductive or conductive layers.
The standard adds two boundary rules:
- If the resistance of the enclosure to the provided earthing point is, everywhere, less than or equal to 100 mΩ, IEC 62271-200 applies.
- Enclosures can have fixed and withdrawable components, and can contain a fluid (liquid or gas) as additional insulation. If there are gas compartments, the design pressure is limited to 300 kPa relative.
Categories of protection against electric shock
Clause 5.102.2 distinguishes categories according to the part of the enclosure that people may touch:
| Category | Which parts it serves | Requirements |
|---|---|---|
| PA | Parts that people touch only by accident | Those of 5.102.3, items a) to d) |
| PB1 | Parts touched when operating, when replacing withdrawable parts or in normal maintenance | PA plus additional protection: e) or f) |
| PB2 | Same as PB1, with another construction solution | PA plus an earthed conductive layer: g) |
The requirements of category PA (clause 5.102.3) are:
- The insulation between the main circuit and the accessible surface withstands the test voltages of IEC 62271-201, to earth and between phases.
- The thickness of the insulating material is sufficient for that voltage, apart from what mechanical loads require.
- The insulation between the live parts and the inner face of the solid partitions and shutters withstands at least 150 % of the rated voltage Ur.
- Capacitive and leakage currents do not exceed 0.5 mA under the test conditions.
For category PB1, one of two options is added:
- At least two layers of insulating material, one of which meets the thickness requirement, and another that only has to withstand for 1 minute the power-frequency voltage of 150 % of Ur. It must not be possible to remove the additional insulation without a tool.
- An insulating fluid inside the enclosure, so that, even if the fluid were replaced by air at normal atmospheric pressure, the insulation of the main circuit facing the inner face of the enclosure withstands 150 % of Ur for 1 minute.
For category PB2, the resistance of the earthed conductive layer is required to be at most 100 mΩ, measured at 30 A of direct current, to the provided earthing point. If it is higher, category PA applies.
- Who touches that part of the enclosure?
- Only by accident: PA, with the insulation and leakage requirements of 5.102.3
- It is touched when operating or in normal maintenance: How is the insulation backed up if it fails?
- Additional insulating layer or insulating fluid: PB1
- Earthed conductive layer of 100 mΩ or less at 30 A: PB2
Earthing
Clause 5.3 adds its own requirements:
- High-voltage conductive parts (5.3.101). All parts that need to be accessed must be able to be earthed before becoming accessible. It does not apply to withdrawable parts whose conductive parts become accessible after being separated from the assembly.
- Enclosure with conductive layers (5.3.102). In PA and PB1 the resistance to the earthing point is not prescribed. In PB2 it does not exceed 100 mΩ at 30 A.
- Withdrawable parts (5.3.104). The metallic parts normally earthed of a withdrawable part remain connected to earth in the test position, the disconnected position and any intermediate one, with a resistance that does not exceed 100 mΩ at 30 A.
- Earthing circuit (5.3.105). An earthing conductor along the whole assembly, able to carry the rated short-time and peak phase-to-earth currents of each functional unit, with a cross-section of not less than 30 mm².
Internal arc and cable test voltage
The standard reproduces the rated internal arc values of IEC 62271-200, with one important difference: it defines only one accessibility type, A, restricted to authorized personnel, with classified sides F, L and R. The R10 series applies for the current, the default value of 87 % for the single-phase current and the recommended durations of 0.1 s, 0.5 s and 1 s.
It also keeps the rated cable test voltages, Uct, AC and DC. In a note, the standard indicates that the DC Uct may be considered valid also for very low frequency tests, and refers to IEEE 400.2 for guidance.
The arc classification of metal-enclosed switchgear is explained in internal arc classification (IAC) and accessibility in accessibility A and B for internal arc. Metal-enclosed switchgear, the most common case, is presented in medium-voltage switchgear.
What not to do
- Do not require 100 mΩ at 30 A of a PA or PB1 enclosure: in those categories the standard does not prescribe the resistance of the conductive layer.
- Do not remove additional insulating layers from a PB1 enclosure: the standard requires that they cannot be removed without a tool.
- Do not assume every surface is PB2: the category requires the conductive layer and the 100 mΩ at 30 A.
- Do not specify public access: the scope of the standard limits it to authorized personnel.
When to call us
At Tiza Group we support you in specifying medium-voltage switchgear for your project, whether metal-enclosed or solid-insulated. Learn about our primary engineering design service. Write to us and we will quote it. The design is adapted to the local code and the requirements of the utility.
Related guides
- Internal arc classification IAC of a switchgear panel
- Accessibility types A and B in switchgear with internal arc
- Medium-voltage switchgear: parts, functions and tests
- Medium-voltage compact substation: parts, IAC and tests
- Earthing switch: classes E0, E1, E2
- IP and IK Protection Degrees of Switchgear Enclosures
References
- IEC 62271-201, High-voltage switchgear and controlgear - Part 201: AC solid-insulation enclosed switchgear and controlgear for rated voltages above 1 kV and up to and including 52 kV, 2014 edition, clauses 1.1, 3.103, 3.107, 4.101, 4.102, 5.3.101 to 5.3.105, 5.101 and 5.102 (5.102.1 to 5.102.3).
Frequently asked questions
What is the difference between IEC 62271-200 and IEC 62271-201?
Part 200 covers metal-enclosed switchgear. Part 201 covers switchgear with a solid-insulation outer enclosure. If the resistance of the enclosure to the earthing point is everywhere less than or equal to 100 mΩ, the standard indicates that part 200 applies.
What is category PB2?
It is the protection category with category PA insulation plus a conductive layer connected to earth, whose resistance to the earthing point does not exceed 100 mΩ at 30 A of direct current. If the resistance is higher, category PA applies.
Can solid-insulated switchgear be classified against internal arc for the public?
No. In IEC 62271-201 only accessibility type A, restricted to authorized personnel, is defined. The scope of the standard also limits access to authorized personnel.