Regarding the cable, what is of primary importance is the capacitance of the cable. This value can be obtained from the cable's data sheet or by asking the cable manufacturer. This is normally given as per foot or per meter. Simply multiply this value by the distance of the cable in question and you have your capacitance.
Next look at the capabilities of the test instrument and the voltage and frequency that you will want to apply to the cable.
Example:
The HVA34 is one of the most popular VLF units on the market.
The HVA34 can test 0.5uF (0.5E-6 F) at full voltage (24kV RMS) & max. freq. (0.1Hz)
The cable that is to be tested has a capacitance of 100pF (100E-12 F) per foot.
What is the max. length of cable that can be tested using the HVA34 at full voltage and frequency?
So. . . 0.5E-6 / 100E-12 = 5000 feet of cable!
Remember that if a lower frequency is selected, such as 0.05Hz, this will be 10,000 feet of cable (half frequency, double the length).
Also note that if the voltage is decreased, the length of cable can also be increased. If for example 16kV is applied, then a cable of about 11,000 feet can be tested.
Regarding short cables, our HVA series equipment can test cables as short as a few feet/meters as long as the cable(s) is properly terminated and the shield is grounded.
If your question is not addressed here or you need a more complete answer, please contact us here or call us at +1 (678) 445-2555 and we will be happy to assist you.
