Wuhan UHV specializes in producingseries resonance (also known as power frequency withstand voltage test equipment). Next, we will share with you the frequency and current calculation of series resonance withstand voltage.

At present, there are three common types of communication testing devices:

1. Power frequency AC withstand voltage device.  

2. Inductive series resonant withstand voltage device.

3. Frequency modulation series resonant withstand voltage test device.  

Due to its large and bulky size, the power frequency AC withstand voltage device is rarely used on site and is only used during the withstand voltage test of electrical equipment at a voltage level of 10kV. The inductive type has been abandoned due to its use of adjustable iron core air gap reactors, which have disadvantages such as high noise, complex structure, and bulky equipment. IEC517 and GB7674 consider that the test frequency in the range of 10-300Hz is basically equivalent to the power frequency voltage test, so currently, most domestic and foreign countries use frequency modulation (variable frequency power supply) series resonant withstand voltage devices.

f=1/2π√IC 

During the experiment, when we choose automatic testing, we can set the parameters such as the test frequency range, test voltage, voltage change step size, excitation transformer ratio, voltage divider ratio, and test time to start the test. The device will automatically find the frequency and resonant frequency. When the device finds the resonant frequency, it will start to automatically boost to the target test voltage. After reaching the target voltage, the timer will start, and when the time is up, it will automatically step down and stop the machine.

When we use manual testing, we need to first calculate the frequency using the formula above, and then manually increase the voltage.

For example, when a certain voltage withstand test is performed, we know that the inductance of the reactor we use from a certain company is L=120H, and the measured capacitance is C=2.253uF (or approximately 0.3755uF/km according to the parameters provided by the manufacturer). Using the above formula, we calculate f ≈ 9.68Hz, which exceeds the minimum frequency output of our test equipment (10-300Hz). We need to parallel a reactor L=60H, which is recalculated to obtain f=13.69, meeting the output range of the equipment.

Experimental current calculation:

I=2πfcu/1000 

The test voltage is 52kV, and the test current I=10.8A is calculated from the above formula.