ANALYSIS OF THE DESIGN AND OPERATIONAL ADVANTAGES OF VACUUM CIRCUIT BREAKERS

ABSTRACT

The article considers medium voltage vacuum circuit breakers up to 35 kV from leading foreign companies. The design and operational advantages of vacuum circuit breakers are analyzed. Vacuum circuit breakers of various manufacturers meet the requirements and for one voltage class differ in technical parameters, purpose, type of drive and its kinematics, dimensions, weight, design and are the dominant type of switching device in networks of medium voltage class 6 kV-35 kV.

АННОТАЦИЯ

В статье рассмотрены вакуумные выключатели среднего напряжения до 35 кВ ведущих зарубежных фирм. Проанализированы конструктивные и эксплуа­та­ционные преимущества вакуумных выключателей. Вакуумные выключатели раз­личных производителей соответствуют предъявляемым требованиям и для одного класса напряжения различаются техническими параметрами, наз­на­че­нием, типом привода и его кинематикой, габаритами, массой, конструкцией и яв­ляются доминирующим типом коммутационного аппарата в сетях среднего класса напряжения 6 кВ-35 кВ.

Keywords: vacuum circuit breakers, switchgear, operating costs, SF6 gas, insulating material.

Ключевые слова: вакуумные выключатели, распределительное устройство, эксплуатационные затраты, элегаз, изоляционный материал.

In the last decade, a large number of companies and enterprises have been successfully working in the field of development and production of high-voltage vacuum circuit breakers in far abroad countries. These are ABB, Siemens, Alstom (Areva), Schneider Electric and others.

The design advantages of vacuum circuit breakers are high speed and current shutdown at its first zero crossing after the contacts are separated; high rate of restoration of the electrical strength of the intercontact gap in vacuum after the arc is extinguished; high switching and mechanical life, determined by the high wear resistance of contacts when switching rated currents and short-circuit currents; explosion and fire safety, even when working in aggressive environments; wide operating temperature range; increased resistance to shock and vibration loads; small dimensions and weight give an advantage when performing installation; the possibility of arbitrary spatial arrangement of the VDC without deteriorating the quality parameters of the circuit breaker, which creates additional convenience during installation.

Operational advantages include: high reliability; lower failure rate; shorter duration of repairs; noiselessness; no emissions of arc combustion products and external effects when short-circuit currents are switched off; lack of environmental pollution; reduction of interruptions in power supply associated with the implementation of routine maintenance; no need for current, medium and major repairs; low operating costs associated with the absence of the need to maintain oil and compressor facilities.

In addition, vacuum arc chambers do not require replenishment of the arc quenching medium; they have low power consumption in the auxiliary power supply circuit and are compatible with any existing types of cells of a complete switchgear (CSG) and a prefabricated one-way service chamber (PSC).

It should be noted that if there are no more than ten enterprises that produce vacuum interrupters in the world, then there are several times more enterprises producing vacuum circuit breakers based on these chambers. There are even more enterprises that use ready-made vacuum circuit breakers for completing switchgear cells and complete transformer substations, not to mention different companies and dealer organizations involved in the sale and supply of foreign switches and complete switchgear [6, 2].

At the same time, it is extremely difficult to find detailed descriptions of the design and features of a particular switch. Basically, these are commercial offers and promotional materials that do not allow you to evaluate the advantages and disadvantages of a particular device, the choice of which depends on many factors, ranging from personal attachments to price. Siemens is the leader in the development and production of vacuum switching equipment. Figure 1 shows Siemens vacuum technology, which covers the entire range of requirements for power switching devices with voltage classes from 6 kV to 35 kV [7].

Figure 1. Vacuum switching technology from Siemens

The basic principles of this equipment were laid several decades ago during fundamental research, which allowed Siemens specialists to create a powerful vacuum arc chute, and on its basis, in the early 70s, the first serial vacuum circuit breakers of types 3AF and 3AG.

Improved special geometry of arcing contacts, proprietary formulation and technology for manufacturing contact materials, as well as extensive experience gained in the manufacture and operation of about 300,000 circuit breakers formed the basis for the creation of a new series of 3AH circuit breakers.

These are five switches for all types of switching:

3AH1 - standard switch for 10.000 cycles, requiring no maintenance;

3AH2 - circuit breaker with increased switching life for 60,000 cycles;

3AH3 - standard high-power switch for 10.000 cycles;

3AH4 - circuit breaker with a very high switching life for 120,000 cycles;

3AH5 - circuit breaker with improved efficiency for 10,000 cycles.

All 3AH series circuit breakers provide high speed and synchronization capability, automatic reclosing for currents up to 31.5 kA, breaking of short-circuit currents with a very high current slope, switching of overhead and cable lines, switching of electric motors, switching of transformers and reactors, switching of capacitor banks, switching circuits of electrostatic precipitators and electric arc furnace power supply (for this task, a 3LH5 switch with improved efficiency is used).

In voltage classes from 6 kV to 35 kV, the 3AH series covers the entire range of switching powers. At the same time, the circuit breakers reliably operate both during long breaks between shutdowns and in the mode of frequent switching, which makes them indispensable for use in urban power supply networks and industrial enterprises.

Switches of the series have a long service life, are characterized by increased reliability and do not require maintenance and care during the entire service life. This is ensured by the use of bearings with non-wearing friction surfaces and the use of special ageless lubricants, as well as high workmanship [5].

Vacuum circuit breakers HVX Alstom advanced development for use in modern switchgear with air insulation (Fig. 2). The HVX series vacuum circuit breaker is an advanced development for the latest air insulated switchgear applications. It is characterized by compact structure, small overall dimensions, operator-friendly control system and modern multifunctional industrial design.

Figure 2. Alston vacuum circuit breakers

Thus, the circuit breaker fully meets modern market requirements, while its compact dimensions, without the use of additional solid insulating material, when installed in switchboards, provide sufficient dielectric strength.

Main characteristics of HVX Alstom circuit breakers:

• design versatility;
• compact and reliable single-shaft spring drive mechanism;
• functional placement of working and signal elements of the system;
• controls for the operator;
• absence of unprotected poles;
• hanging vacuum chamber, protected from external forces;
• the pole shell performs the functions of an insulating support;
• the pole sheath provides a high degree of mechanical protection;
• does not require maintenance.

Applications: Overhead transmission lines; cable power lines; electric motors; transformers; generators; capacitors

Schneider Electric's HVX vacuum circuit breakers are the latest series of vacuum circuit breakers that combine the latest technology. Schneider Electric HVX vacuum circuit breakers are suitable both for use in new air-insulated switchgear and as replacements for obsolete circuit breakers in refurbishments. Schneider Electric's HVX vacuum circuit breakers are designed to meet the latest requirements and have a simple and reliable design, simple and safe to operate, which ultimately allows you to significantly reduce your operating costs in the future. Schneider Electric HVX vacuum circuit breakers provide protection for all connections (fig. 3).

Figure 3. Schneider Electric HVX vacuum circuit breakers

One of Schneider Electric's vacuum circuit breakers is the three-pole SF2 medium voltage circuit breakers designed for indoor installation. They are used as switching and protection devices in primary and secondary distribution networks of 20 and 35 kV.

The auto-compression method of arc extinguishing used in the circuit breakers makes it possible to turn on and off any loads, capacitive and inductive, without overvoltages at the moment of switching. Thus, the SF6 switch is well suited for controlling capacitor banks (Fig. 4). Vacuum circuit breakers, due to their merits, are already a serious competitor to circuit breakers with SF2 insulation for voltages of 110 kV and higher, although SF2 circuit breakers are serious competitors for these voltage classes.

Figure 4 Vacuum circuit breaker SF2

At the same time, the creation of vacuum circuit breakers for voltages of 500 kV and higher presents serious, and possibly insurmountable, difficulties. In addition, on the basis of vacuum circuit breakers, it is hardly possible to create complete switchgears isolated from the external environment, as is the case when using SF2 gas.

Thus, we considered the design features of vacuum circuit breakers presented on the market of switching equipment, the state and prospects for the development of modern vacuum and SF2 circuit breakers and complete switchgears (cells) based on them.

Conclusion

1. Significant advantages of vacuum circuit breakers over other types of switching devices and one can say their only drawback today is the cost.
2. The main disadvantage of SF2 circuit breakers is the impact of SF6 gas on the environment, while vacuum circuit breakers are environmentally friendly devices.
3. Vacuum circuit breakers are the main mass switching device for voltages of 6kV - 35 kV and, possibly, they will replace the positions of SF2 devices for voltages of 110 kV - 220 kV.

References:

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