Vacuum Switching Technology and Components for Medium Voltage
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Vacuum Switching Technology and Components for Medium Voltage Your Guide Power Transmission and Distribution

Proven vacuum switching technology from Siemens meets all requirements placed on circuit-breakers and contactors in medium-voltage switchgear up to 40.5 kV.

Overview of medium-voltage components 4 Switching devices Non-switching components Selection of components by switching applications 6 with undisturbed operation with disturbed operation Selection of components by ratings 8 Medium-voltage components in detail 10 Vacuum switching technology Switching duties Outdoor vacuum circuit-breakers 16 Switching duties Switching duties Switching duties Switching duties Arc-extinguishing principle Surge arresters and limiters 27

Medium voltage is defined as the range above 1 kV and up to and including 52 kV (alternating voltage). This term refers to a section of the high-voltage range, as there are only two voltage levels available according to international rules: Low voltage up to and including 1 kV alternating or 1.5 kV direct voltage, and high voltage greater than 1 kV alternating or 1.5 kV direct voltage. Voltage levels from the generator to the consumer High voltage Alternating voltage

Introduction to the world of medium-voltage components High voltage is used to transport electrical power over very long distances and to distribute it regionally into the load centres. The term “medium voltage” has been established as a result of the various high-voltage levels which have developed in the eld of power transmission and distribution. Power station locations follow the availability of primary energy sources, cooling systems and other environmental conditions, and are therefore often located away from the power consumption centres. The power transmission and distribution...

Overview of medium-voltage components Switching devices Circuit-breakers (see page 12) Circuit-breakers must make and break all currents within the scope of their ratings, from small inductive and capacitive load currents up to the short-circuit current, and this under all fault conditions in the power supply system such as earth faults, phase opposition, etc. Outdoor circuitbreakers have the same applications, but are exposed to weather inuences. Switches (see page 18) Switches must make and break normal currents up to their rated normal current, and be able to make on existing short...

Non-switching devices Fuses (see page 25) Fuses consist of a fuse base and a fuse link: With the fuse base, an isolating distance can be established when the fuse link is pulled out in de-energized condition (like in a disconnector). The fuse link is used for one single breaking of a short-circuit current. Instrument transformers (see page 26) Instrument transformers are electrical components which transform normal currents and operating voltages into proportional and phase-identical measured values that are suitable for the connected devices – measuring instruments, meters, protection...

Switching applications with undisturbed operation Appearing load Switching duties in inductive circuits formers (neutral earthing transformer) Furnace transformers Earth-fault reactors Compensation reactors during start Switching duties in capacitive circuits Capacitor banks capacitive Filter circuits capacitive Parallel connection capacitive Unloaded cables capacitive Unloaded overhead lines capacitive Ripple control systems capacitive © Current © Main problem < 2 7r High switching rate < 2000 A Transient recovery voltage with rate of rise £ 6 kV / us £ 7r Transient recovery voltage with...

Switching applications with disturbed operation Appearing load Switching duties in case of short-circuits ) Current (3) Main problem Terminal short-circuit Short-circuit current limiting reactors Double earth fault Blocking motors Transient recovery voltage Overvoltage protection for with rate of rise £ 6 kv7 us generators with I'\ s 600 A Transient recovery voltage with rate of rise < 4 kV7 us Transient recovery voltage with rate of rise s 10 kV/us For motors with /start£ 600 A, 3EF surge limiters are suitable level, surge limiters type 3EF3 120-1 should be used. Individually compensated...

The switching devices and all other equipment must be selected for the system data available at the place of installation. This system data defines the ratings of the components. Earthing switch Make-proof earthing switch Non-switching components Fuse link Surge arrester Influence on selection of component ■ No influence on selection of component 1) Limited short-circuit making capacity 2) Rated discharge current of arresters 3) Short-circuit current strength in case of overload of arresters Rated insulation level The rated insulation level is the dielectric strength from phase to earth,...

Rated peak withstand current The rated peak withstand current is the peak value of the first major loop of the short-circuit current during a compensation process after the beginning of the current flow, which the device can carry in closed state. It is a measure for the electrodynamic (mechanical) load of an electrical component. For devices with full making capacity, this value is not relevant (see rated short-circuit making current). Rated breaking current The rated breaking current is the load breaking current in normal operation. For devices with full breaking capacity and without a...

Medium-voltage components in detail Vacuum switching technology Terminal disc Fixed contact Moving contact Arching chamber Metal bellows Arc quenching During the galvanic separation of the contacts, the current to break produces a metal-vapour arc discharge. The current ows through this metal-vapour plasma until the next current zero. Near the current zero, the arc extinguishes. The metal vapour loses its conductivity after few microseconds already – the insulating capability of the contact gap recovers quickly. To maintain the metal-vapour arc discharge, a specic minimum current is...