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Electrical characteristics of medium voltage
capacitors
"ALL-FILM" MEDIUM VOLTAGE CAPACITORS
MEDIUM VOLTAGE RANGE
Medium voltage capacitors are composed of
elementary or partial capacitances, generally
connected in several series-parallel groups, providing
the required electrical characteristics for the unit.
The nominal voltage of a capacitor depends on the
number of groups in series
The nominal power of a capacitor depends on the
number of partial capacitances in parallel per group
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External view of an "all-film" MV capacitor
1. Connection
2. Porcelain terminal
3. Fixing lug
4. Stainless steel case
5. Active part
Each elementary capacitance is made of two sheets
of aluminium foil forming the reinforcements or the
electrodes and special high quality polypropylene film
which is rough to assist impregnation, forming part of
the insulation.
This wired capacitance assembly, referred to as the
"active part", is positioned in a stainless steel case,
which has insulated porcelain terminals or bushings at
the top for connecting the device.
After the "active part" has been dried and treated, is
impregnated under vacuum with a liquid dielectric of
the following type:
- Non-chlorinated
- Non-toxic
- Biodegradable
With the polypropylene film, this liquid dielectric,
which has a remarkably high chemical stability,
a high gas absorption capacity and a high partial
discharge extinction capacity (discharges for which
the flash point is approximately 150°C), ensures total
insulation between electrodes. This "all-film" capacitor
technology has the following main characteristics:
- Excellent resistance to strong electrical fields
- Very low power losses, leading to considerable
savings for high power capacitor banks
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