Capacitor Test Bed / CERN
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CERN is realizing a laboratory for the testing of high voltage storage capacitors with big capacitance values.
The testing laboratory comprises an AC source and a DC source. The AC source is constituted by 6 single phase H bridge power converters, while the DC source is made up by 2 six pulses diode bridges powered by an adjustable 3 phase voltage source.
The two sources provide a composite stress across the capacitors, made up of an AC sinusoidal voltage superposed to a DC one.
Maximum stressing values for capacitor under testing
This composite voltage is meant to supply a load constituted by a set of capacitors.
The capacitance value changes depending upon the test to be effectuated, with a maximum rms current fixed in 80Arms.
Power converter architecture
The AC source:
The AC source is the most demanding in term of power. In-fact it has to provide all the kVAr needed by the tested capacitors.
The worst conditions are met when the testing of the fully sized element is required. To keep a limit, letís consider the present capacitor value of 2mF; the following calculations give us the power needed:
The DC source:
The simplest DC source is a 3 phase diode bridge. For easier realization (and to keep compatibility with other testing requirements), a 12 pulse diode bridge is foreseen.
Two 6 pulses diode rectifiers are then connected in series.
The following values have to be considered for bridge sizing:
Control overview simplified schematic