FKN12A-12D Indoor High-Voltage Air-Puff Load Break Switch Thomas Electric

Product Overview

The FKN12A-12D indoor air-puff load break switch and the FKRN12A-12D switch-fuse combination unit are three-phase switching units for distribution systems of 12 kV and below. They control and protect transformers, cables and overhead line sections, and are used mainly in urban and rural terminal substations, box substations, and ring-network or double-radial supply units. The load break switch makes and breaks load current and overload current; in the combination unit the circuit is completed with back-up fuses, so line short-circuit current is cleared as well. Switch, earthing switch, fuses and mechanism are carried on a single frame, which keeps the unit compact and easy to install.

Product Display

FKN12A-12D Indoor High-Voltage Air-Puff Load Break Switch - display

Model Designation

FKN12A-12D Indoor High-Voltage Air-Puff Load Break Switch - model

Model format: FKN12A-12D/T 630-20 (load break switch) and FKRN12A-12D/T 125-31.5 (switch-fuse combination unit)

F: load break switch; K: air medium, air-puff design; N: indoor type
12: design sequence number; A: derivative code; 12: rated voltage, kV
D: with earthing switch; T: spring mechanism
630: rated current, A; 20: rated short-time withstand current, kA
R: combined with fuse; 125: rated current of the fuse, A; 31.5: rated short-circuit breaking current, kA

Service Conditions

Ambient temperature: +40 °C upper, -25 °C lower
Altitude: not more than 1000 m
Relative humidity: daily average not more than 95%, monthly average not more than 90%
Seismic intensity: not more than 8 degrees
Site condition: no fire, explosion hazard, chemical corrosion or violent vibration
Pollution level: II

Construction

Load break switch, earthing switch, fuses and mechanism are mounted on one frame, which can be combined flexibly and keeps the unit compact and easy to install. The break is arranged upright, so the dynamic and thermal stability ratings are high and each operation is completed in one stroke.

Static contact covers provide structural isolation inside the ring-main cubicle, which removes the need for inter-phase insulation boards and gap insulation plates and helps resist internal arcing faults. After the load break switch opens, a shutter closes automatically over the open gap, improving protection for personnel working on the panel.

Technical Data

No.	Item	Unit	Value
1	Rated voltage	kV	12
2	Rated current of the load break switch	A	630
3	Rated short-time withstand current	kA	20
4	Rated current of the fuse, combination unit	A	125
5	Rated short-circuit breaking current, combination unit	kA	31.5
6	Overall width	mm	868
7	Overall height	mm	940
8	Mass	kg	70

Selection note: the table lists the values printed on the type designation and outline drawings of this series. Rated peak withstand current, short-circuit duration, power-frequency and lightning impulse withstand voltages, mechanical life and rated transfer current are confirmed against the full technical data sheet, and non-standard current or fuse combinations are subject to agreement between manufacturer and purchaser. Final parameters are subject to nameplate data and approved specifications.

Standards

The source page does not quote a standard number for this switch. The usual references for indoor high-voltage load break switches are IEC 62271-102 / IEC 60265-1 and GB/T 3804; confirm the applicable edition with the factory when ordering.

Technical note: rated peak withstand current, short-circuit duration and insulation levels are confirmed against the full technical data sheet.

Installation & Dimensions

Installation Diagram

FKN12A-12D Indoor High-Voltage Air-Puff Load Break Switch - installation

The three-pole unit is bolted into the cubicle frame across an overall width of 868 mm with an overall height of 940 mm and a mass of 70 kg; check busbar and cable clearances against the approved outline drawing before the frame is torqued. Charge the spring, confirm the closed, open and earthed positions on all three poles, verify the interlocking between load break switch, earthing switch and fuse compartment, and on the combination unit fit the specified 125 A back-up fuse and confirm the striker engagement.

Dimension	Value
Overall width (W)	868 mm across the three poles
Overall height (H)	940 mm including the live-part covers
Phase spacing (D)	210 mm between adjacent poles
Mass	70 kg for the assembled three-pole unit
Panel cut-outs and busbar drilling	see outline drawing for both operation arrangements

Safety notice: installation, operation and maintenance must be performed by qualified professionals. Before maintenance, open the load break switch, close the earthing switch and verify absence of voltage; the shutter then covers the live gap. Do not use the load break switch to interrupt short-circuit current, and replace a blown fuse only with the same rated type.

FAQs

It is an indoor three-phase 12 kV air-puff load break switch for switchgear cubicles, used to make and break load current and overload current, to isolate the circuit and to earth the de-energised side for maintenance. It controls and protects transformers, cables and overhead line sections in urban and rural terminal substations, box substations and ring-network or double-radial supply units.

F is the load break switch, K the air medium with air-puff design, R combined with fuse, N indoor type, the first 12 the design sequence number, A the derivative code, the second 12 the rated voltage in kV, D the earthing switch and T the spring mechanism. 125 is the rated current of the fuse in A and 31.5 the rated short-circuit breaking current in kA. Without the R, FKN12A-12D/T 630-20 describes the plain switch at 630 A and 20 kA.

The break is made in air: the operating stroke compresses air in a puff cylinder and blows it over the arc, so there is no vacuum chamber and no SF6 gas to monitor. The upright break gives high dynamic and thermal stability, and static contact covers provide structural isolation inside the ring-main cubicle, which removes the need for inter-phase insulation boards and gap insulation plates.

After the load break switch opens, a shutter closes automatically over the open gap, improving protection for personnel working on the panel. Reliable mechanical interlocks between the load break switch, the earthing switch and the fuses satisfy the five-prevention requirements of switchgear.

Yes. Manual operation is standard, and motorised operation with an AC or DC control supply is available, which suits the remote control and telemetry arrangements of unattended substations. The outline drawing offers side installation with right-hand or left-hand operation.

The three-pole unit is 868 mm wide overall, 940 mm high including the live-part covers, with 210 mm phase spacing and a mass of 70 kg. Confirm which operation arrangement the cubicle needs before ordering, as the mechanism and terminal positions differ between the right-hand and left-hand versions.

FKN12A-12D Indoor High-Voltage Air-Puff Load Break Switch