Detailed Explanation of Selection Criteria for High-Voltage Testing Transformers

发布时间：2022-03-30

High‑voltage testing transformers are used in power systems, industrial and mining enterprises, research institutions, and other settings to conduct insulation‑strength tests on various high‑voltage electrical devices, components, and insulating materials under power‑frequency or DC high voltage. They are indispensable, critical equipment in high‑voltage testing. Through routine communication with customers, we have observed that many clients struggle to determine the appropriate rating—such as capacity—for their test transformers. Selecting a transformer with excessive capacity results in “using a heavy horse to pull a light cart,” which not only increases capital investment but also leaves the transformer operating at no load for extended periods, thereby raising reactive power losses. Conversely, choosing a transformer with insufficient capacity can subject it to prolonged overload conditions, significantly increasing the risk of burnout. Guoce Huanneng Electric hereby provides several illustrative examples to clarify this issue.

When selecting a test transformer, the following key considerations should be taken into account: Voltage. Based on the requirements of the test specimen, first choose a test transformer with an appropriate rated voltage, ensuring that the high‑voltage side rated voltage Un exceeds the test voltage Us of the specimen, i.e., Un > Us. Next, verify that the low‑voltage side voltage required by the test transformer is compatible with the site’s supply voltage and the voltage regulator. Current. The rated output current In of the test transformer should be greater than the current Is required by the test specimen, i.e., In > Is. The current required by the specimen can be estimated from its capacitance: Is = Us · ω · Cx, where Cx includes both the specimen’s capacitance and any additional capacitance (in farads).

Capacity. Based on the rated current and rated voltage of the test transformer, its capacity can be determined as P = UnIn. According to national standards, the voltage levels for test transformers in China include 5, 10, 25, 35, 50, 100, 150, and 300 kV; the capacity ratings are 3, 5, 10, 25, 50, 100, 150, and 200 kVA. Once the required capacity is calculated, the appropriate test transformer can be selected by consulting the relevant national standards. For special requirements, it is generally possible to place an order with the manufacturer for a test transformer of custom specifications.

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