kc2we
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« on: June 14, 2020, 08:30:21 PM » |
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Often we find in flea markets etc, ac rated power line capacitors that are always rated in kVAR (kilo Volt-Amperes Reactive). To most hams, that kVAR rating is meaningless. Well, there's an easy way to identify the value by a simple calculation. Or, use the attached chart for approximate values. Power line standard a/c primary voltages are 2400, 4800, 7200, 12,500 (actually 12,470) and others. For DC filtering service use the peak to peak ac voltage value to determine the DC voltage rating. Peak to peak at 2400 is 6720 volts. For example, the 2400 VAC capacitor is probably good well up to 5 KVDC, good enough for most amateur applications. The Formula is:
C = kVAR / (2 x (3.14159)x f x V(sqd)) in microfarad where f= 60 Hz, or use the attached chart.
The formula in an easier form is:
C uf = (kVAR) x 1000/kV (sqd) x 377, where 2400 volts in the example is 2.4 KV.
For example, a 2.4 KV rated 100 kVar line capacitor is about 46 uf. As one can see from the chart, the capacitors above 2400 (2.4 KV) are of little use for amateur radio applications since the higher voltages exhibit lower capacitance values.
Happy filtering.
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