In the AC withstand voltage test of high-voltage power cables, the series resonance testing system has become the preferred solution in the industry due to its advantages of high efficiency, energy saving, and portability. However, how to scientifically select cables of different voltage levels and lengths has always been a core issue of concern for power workers. Wuhan UHV Power Technology Co., Ltd. (hereinafter referred to as "Wuhan UHV"), based on years of industry experience, has sorted out the key points for users to choose AC resonance testing systems according to cable length.

Why does cable length determine the selection direction

The cable itself has distributed inductance and distributed capacitance. As the length of the cable increases, the total inductance and total capacitance also increase, thereby changing the natural resonant frequency of the system. Cable length and capacitance are important parameters that determine the required resonant power output capability. Accurately obtaining parameters such as cable length, cross-sectional area, and dielectric constant of the insulation medium before testing helps to more accurately calculate the resonant frequency and required power supply.

Wuhan UHV technology experts pointed out that cables of different specifications and lengths have different inductance and capacitance values, which determine different natural resonant frequencies. Therefore, the core of selection lies in matching the resonant device with the corresponding capacity based on the voltage level and length of the cable.

Matching principle between voltage level and cable length

The selection first requires determining the range of the device based on the highest voltage level of the equipment under the jurisdiction of the unit - the specifications required for 10kV distribution networks and 110kV substations are completely different.

Typical configuration scheme reference

Wuhan UHV provides specific configuration references in the product plan. Taking the UHV-75kVA/75kV series resonance scheme as an example, this device can meet the AC withstand voltage test of 1.5km of 10kV/300mm ² cable (capacitance ≤ 0.5632 μ F, test voltage 22kV), while also taking into account the AC withstand voltage test of 0.35km of 35kV/300mm ² cable (capacitance ≤ 0.0681 μ F, test voltage 52kV).

For longer distance cables, the Wuhan UHV-135kVA/108kV cable AC withstand voltage series resonant device can meet the AC withstand voltage test requirements for 1km of 35kV/300mm ² cables. The frequency range of the device is usually between 30-300Hz, which can meet the testing requirements of most power equipment.

Summary of Key Selection Steps

Based on the selection experience of Wuhan UHV, users can follow the following steps when choosing an AC resonance testing system:

Step 1: Clarify the parameters of the tested cable. Confirm the voltage level, length, and cross-sectional area of the cable. These three parameters collectively determine the required capacitance and test voltage for the experiment.

Step 2: Calculate the resonant frequency and capacity. Calculate the corresponding capacitance based on cable parameters, and then determine the resonant frequency and required power supply.

Step 3: Match the device model. Select the resonant device with the corresponding capacity based on the calculation results.

Step 4: Consider the site conditions. For outdoor scenarios with high frequency of use, it is recommended to choose models with dust-proof and waterproof casings. Simultaneously pay attention to the individual weight of the device for easy on-site handling and installation.

Wuhan UHV Power Technology Co., Ltd. has been deeply involved in the field of high-voltage electrical measurement for nearly 22 years, and has accumulated rich experience in the research and development, production, and application of series resonance test devices. The company stated that it will continue to provide professional selection consultation and technical support to users, to assist in the safe and efficient conduct of power cable withstand voltage tests.