Overview
The GN27 is an indoor high voltage AC disconnector for three-phase 50 Hz power systems of the 35 kV class with a rated voltage of 40.5 kV. Three poles are carried on a common frame, each with a copper knife and contact system on post insulators and coupled by a linkage shaft so that all three phases open together. It connects or transfers circuits under voltage but without load and provides a visible isolating gap for maintenance; it is operated by a CS6-2 manual mechanism, or a CS6-1 mechanism on the earthing-switch (D) version, and is used in fixed indoor switchgear in distribution substations.
The range is offered as a flat-mounted type or with through-wall mounting — C1 (moving knife through the wall) and C2 (static contact through the wall) — and a D version adds an earthing switch. The disconnector is interlocked with the associated circuit breaker and cannot break load or short-circuit current; it is intended for altitudes up to 1000 m and ambient temperatures from −25℃ to +40℃. Rated current and 4 s thermal-stable current are specified per the technical agreement / nameplate.
Model Designation
The type is designated G N 27 -40.5 □ / □ □ and decoded as follows:
- G — disconnector
- N — place of use: indoor
- 27 — design sequence number
- 40.5 — rated voltage in kV
- □ — rated current in A
- / □ — mounting: none = flat-mounted; C1 = moving-knife through-wall; C2 = static-contact through-wall
- □ — 4 s thermal-stable current (r.m.s.) in kA
- D — with earthing switch (uses the CS6-1 mechanism)
Construction and Operation
- Three-pole assembly. Each pole carries copper knife and contact systems on post insulators mounted on a common frame, coupled by a linkage shaft for simultaneous operation of all three phases.
- Manual mechanism. Driven by a CS6-2 manual operating mechanism, or a CS6-1 mechanism where the D earthing-switch version is fitted.
- Mounting options. Flat-mounted for standard cubicles, or through-wall (C1 moving knife / C2 static contact) to route the circuit through the panel barrier.
- Visible break. Opening the knives gives a clearly visible insulating gap for safe maintenance; it is interlocked with the associated circuit breaker and cannot break load or short-circuit current.
Technical Parameters
Rated Parameters
| Item | Unit | Value |
|---|---|---|
| Rated voltage | kV | 40.5 |
| System class | kV | 35 (three-phase, 50 Hz) |
| Rated frequency | Hz | 50 |
| Rated current | A | per technical agreement / nameplate |
| 4 s thermal-stable current (r.m.s.) | kA | per technical agreement / nameplate |
| Operating mechanism | — | CS6-2 manual (CS6-1 for D version) |
Normal Service Conditions
- Altitude: up to 1000 m
- Ambient temperature: not above +40℃ and not below −25℃
- Relative humidity: daily average not above 95%, monthly average not above 90%
- Water-vapour pressure: daily average not above 2.2 × 10⁻³ MPa, monthly average not above 1.8 × 10⁻³ MPa
- Site: free from fire, explosion, corrosion of metals, harmful gases that damage insulation and conductive dust
Installation & Wiring
Installation and Mounting
Mount the three poles on the common frame inside the cubicle at the specified phase spacing, fix the frame through the 4 × 18 × 28 mm mounting holes, and for the through-wall versions pass the moving knife (C1) or static contact (C2) through the panel opening. Couple the poles to the CS6-2 (or CS6-1 for the D version) operating mechanism, verify free travel, correct contact seating and the full visible break before energising, and bond the frame to the earth network.
Outline & Installation Dimensions
| Item | GN27-35 | GN27-35C (through-wall) | GN27-35D (with earthing switch) |
|---|---|---|---|
| Overall width (front) | 1407 | 1569 | 1407 |
| Overall height (front) | ≈ 850 | ≈ 830 | ≈ 900 |
| Depth (side) | 600 | 1045 | 600 |
| Phase spacing | 460 | 460 | 460 |
| Mounting holes | 4 × 18 × 28 | 4 × 18 × 28 | 4 × 18 × 28 |
All dimensions in mm, read from the outline drawing for the 35 kV class (rated voltage 40.5 kV) units; C denotes through-wall mounting and D the earthing-switch version.
Selection & FAQs
Selection Guide
- Confirm the rated current and 4 s thermal-stable current for the feeder with the manufacturer; they set the frame and contact size.
- Choose flat-mounted, C1 (moving-knife through-wall) or C2 (static-contact through-wall) to suit the cubicle busbar routing.
- Add the D suffix when an earthing switch is required; note it uses the CS6-1 mechanism.
- Verify the mechanism position and interlock against the associated circuit breaker.
Frequently Asked Questions
Q1: What does the type designation GN27-40.5 mean?
G is the disconnector, N the indoor place of use and 27 the design sequence number; 40.5 is the rated voltage in kV for 35 kV class systems. The trailing fields give the rated current in A, the mounting code and the 4 s thermal-stable current in kA, with D denoting an earthing switch.
Q2: What are the mounting options?
A flat-mounted type, C1 with the moving knife brought through the wall, and C2 with the static contact brought through the wall, so the circuit can pass through the cubicle panel barrier.
Q3: Which operating mechanism is used?
A CS6-2 manual operating mechanism; the earthing-switch (D) version uses a CS6-1 manual mechanism.
Q4: Can the GN27 break load or short-circuit current?
No. It connects or transfers circuits under voltage but without load and provides a visible isolating gap; load and fault currents are handled by the associated circuit breaker.
Q5: What are the rated current and thermal-stable current?
They are not fixed by the general catalogue and are specified per the order technical agreement and equipment nameplate for the chosen rating and mounting arrangement.
Q6: What are the service conditions?
Altitude up to 1000 m, ambient −25℃ to +40℃, relative humidity daily up to 95% and monthly up to 90%, and a site free from fire, explosion, corrosive or conductive contamination. See the disconnector range for related models.