HGI generator circuit breaker – ABB

Application

The circuit-breakers type HGI can be used as generator circuit-breaker in all types of power plants with unit sizes between 60 – 180 MVA and nominal voltages up to 21kV.

If used as feeder breakers in industry plants, the nominal voltage can be up to 24kV.

The breakers are also suited for retrofit or replacement in existing powerplants, when these are modernised, extended or automated.

Main characteristics

• 3-pole, open breaker with operating mechanism and supervisory and control elements, fully assembled on a common frame
• For indoor installation
• The phase distance can be selected to suit the phase distance of the connected busbar
• No additional auxiliary equipment necessary
• Horizontal or vertical operating mechanism
• Easy erection and putting into service due to the fact, that the circuit-breaker is delivered as a fully assembled and tested unit
• Maintenance necessary only after 15 years or 10.000 mechanical close-open operations. However, this also depends on the interrupted current.

Frame size

The circuit-breaker type HGI is manufactured in two frame sizes. Both sizes HGI 2 and HGI 3 are designed for the voltage range 17.5kV/21kV and 24kV, respectively. The nominal current (6300A resp. 8000A) and the interrupting current (50kA resp. 63kA) define the size.

Standards

The circuit-breakers type HGI meet the decisive standards, i.e. IEEE (ANSI) Std C37.013 and IEC 60694, IEC 60358, IEC 61166, IEC 60529.

Design and method of operation

The 3 circuit-breaker poles together with hydraulic spring operating mechanism, supervisory and control elements are mounted on a common frame.

The circuit-breaker type HGI, with SF6 as arc extinguishing medium, functions by the self-pressurizing principle: the arc energy itself is used to heat the SF6 in the interrupting chamber (heating space), thus creating the necessary pressure difference for the gas flow, which cools and interrupts the arc. As a result, the self-pressurizing principle reduces the energy of the operating mechanism necessary during the tripping operation.

A built-in small puffer secures the interruption of small currents (transformer no-load currents). The small amount of SF6-decomposition products, produced by the arc during the interruption in the SF6 gas, is bound by an adsorber and does not influence the circuit-breaker operation (Fig. 1).

The contacts carrying the service current (main contacts) are separated from the interrupting (arcing contact). This results in low steady state electical loss of the service current and little contact wear.

A hydraulic spring operating mechanism actuates the three interrupting chambers via a common drive shaft.

Operating mechanism, control and supervision

The circuit breakers are actuated by a hydraulic spring operating mechanism type HMB-1 for the HGI 2 resp. AHMA-4 for the HGI 3 breaker size. This operating mechanism combines the advantages of mechanical energy storage and hydraulic power transmission.

Energy storage is accomplished with the aid of a disc spring column, with the advantages of high long-term stability, reliability and negligible temperature changes. Tripping of the operating mechanism and energy output are based on proven design elements of the hydraulic operating technique, such as control valves and hydraulic cylinders. Pressure vessel standards are not applicable to this operating mechanism.