Rockwill Electric Group
Indoor gas insulated circuit-breakers
MH4 type Indoor SF6 circuit breaker manufactured by Rockwill in China. It uses sulphur hexafluoride gas (SF6) to extinguish the electric arc and as the insulating medium. ...

Detailed description

  • Description
  • Technical data of indoor sf6 gas circuit breaker
  • Standards of indoor sf6 gas circuit breaker

MH4 type Indoor SF6 circuit breaker


ROCKWILL® Electric strives to bring our customers the latest technology and competitive pricing and best HM4 medium voltage circuit-breakers use sulphur hexafluoride gas (SF6) to extinguish the electric arc and as the insulating medium. Breaking in SF6 gas takes place without any arc chopping and without generation of overvoltages. These characteristics ensure long electrical life of the circuit-breaker and limited dynamic, dielectric and thermal stresses on the installation.

The circuit-breaker poles, which make up the breaking part, are systems with lifelong sealed pressure (IEC 62271- 100 and CEI 17-1 Stand- ards) and are maintenance-free.

The REH type mechanical operating mechanism, with stored energy has free release and allows opening and closing operations independently of the operator’s actions.

The operating mechanism and the poles are fixed to the metal structure which also acts as a support for the kinetics for operating the moving contacts. Circuit-breakers in the withdrawable version are fitted with a truck to allow racking in and racking out of the switchgear or enclosure.

The light and compact structure of the circuit-breaker ensures great sturdiness and excellent mechanical reliability.



Autopuffer breaking technique
Electric are extinction without chopped current
No restriking after breaking
Rapid recovery of the dielectric properties of the means of extinction
Withstand insulation voltage even at zero relative pressure(*)
Breaking up to 30% of the rated breaking capacity even at zero relative pressure(*)
Sealed for life poles
Test for checking gas tightness carried out three times on each piece of apparatus
Compact dimensions
Fixed and withdrawable version
Stored energy operating mechanism with anti-pumping device as standard common to the whole circuit-breaker series
Mechanical safety locks against incorrect operations
Simple personalisation thanks to a com-plete range of accessories
SF6 gas pressure control device (on request).


Fields of application

HM4 circuit-breakers are used in power distribution to control and protect lines, transformer and distribution substations, motors, transformers, capacitor banks, etc.
Thanks to the SF6 autopuffer breaking technique, the HM4 circuit-breakers do not generate operating overvoltages, and are therefore also highly suitable for retrofitting, upgrading and enlarging older installations where the motor,cable, etc. insulating materials may be particularly sensitive to dielectric stresses.


Breaking technique

The breaking technique of HD4 circuit-breakers is based on compression and self-blast techniques to obtain top performances at all service current values, with minimum arc times, gradual arc extinction without chopping, and no restriking or operating overvoltages.
The HM4 series brings to medium voltage the advantages of the “autopuffer” breaking technique already used in high voltage.

SF6 circuit-breaker   HM4-12 HM4-17 HM4-24 HM4-36 HM4-40
Standards   IEC 62271-100 CEI 17-1 (file  1375)
Rated voltage Ur [kV] 12 17.5 24 36 40.5
Rated insulation voltage Us [kV] 12 17.5 24 36 40.5
Withstand voltage at 50 Hz(1min) Ud [kV] 28 38 50 70 95
Impulse withstand voltage Up [kV] 75 95 125 170 185
Rated frequency Fr [Hz] 50/60
Rated normal current (40 °C) Ir [A] 630/800/1250/1600/2000/2500/3150/3600
Rated breaking capacity Isc [kA] 12.5/16/25/31.5/40/50
Rated short-time Ik [kA] 12.5/16/25/31.5/40/50
Making capacity Ip [kA] 31.5/40/50/63/80/100/125
Operation sequence   O-0.3s-CO-15s-CO
Opening time [ms] 45 45 45 45 45
Arcing time [ms] 10~15 10~15 10~15 10~15 10~15
Total breaking time [ms] 55~60 55~60 55~60 55~60 55~60
Closing time [ms] 80 80 80 80 80
Maximum overall dimensions H [mm] 640 649 818 730/1060 790/1123
W[mm] 493 618 730 880/955 748/805
D [mm] 496 496 620 695 833
Pole centre distance I [mm] 150 210 275 350 275
Weight [kg] 114 114 119 128 190
Absolute SF6 gas pressure [kPa] 380 380 380 380 450
Operating temperature [°C] -5~+40
Tropicalization   IEC:  60068-2-30, 60721-2-1
Electromagnetic compatibility   IEC: 60694

Standards and approvals

HM4 circuit-breakers comply with IEC 62271-100, CEI 17-1 file 1375 Standards and with those of major industrialised countries.

They have undergone the following tests and guarantee safety and reliability of the apparatus in service in all installations.

Type tests: heating, withstand insulation at industrial and impulse frequency, short-time and peak withstand current, mechanical duration, making and breaking of short-circuit currents;

Individual tests: insulation with voltage at industrial frequency in the main circuits and insulation of the auxiliary and control circuits, measurement of the main circuit resistance, mechanical and electrical operation.

The HM4 circuit-breakers are tested according to the requirements of the IEC 62271-100 Standard (class E2 - table 21) and guarantee suitability for use in overhead lines, with rapid reclosing cycle.


Service safety

Thanks to the availability of a complete range of mechanical and electrical locks (on request), safe distribution switchgear can be constructed using HM4 circuit-breakers. The locking devices have been designed to prevent incorrect operations and to carry out inspection of the installation, ensuring maxi- mum operator safety


About Us

Success References