Power frequency series resonance testing is a specialized high-voltage testing method widely used in the power industry to verify the insulation performance of electrical equipment such as transformers, cables, switchgear, and GIS under nominal or equivalent power frequency voltage conditions. This method efficiently generates high-voltage, low-current test signals using the series resonance principle. It minimizes the size of test equipment and reduces energy consumption while accurately simulating real operating conditions.
Main components
Variable frequency power supply: Provides low-voltage, adjustable-frequency (typically 30–300 Hz) alternating current for circuit operation.
Excitation transformer: Increases the low voltage from the power supply to a medium level (e.g., 0–10 kV) to excite the resonant circuit.
Inductance coil (reactor): Variable or fixed inductor that forms the inductive part of the resonant circuit.
Capacitive load (DUT): The electrical equipment under test (e.g., cable or transformer), whose capacitance acts as the capacitive portion of the circuit.
Measurement and protection system: Monitors voltage, current, frequency, and partial discharge. Activates automatic shutdown when an anomaly occurs.
The core principle of this test is to use a variable inductor (reactor) and the inherent capacitance of the device under test (e.g., an extended power cord) to form a resonant circuit. Electrical resonance occurs when the inductive reactance of the reactor matches the capacitive reactance of the device at mains frequency. In this state, the reactance components cancel each other out, so that only a minimal input power from the power source is required to maintain an extremely high output voltage across the device under test. This makes the test process highly efficient, safe, and easy to control, which makes it particularly suitable for devices with high capacitance.
Critical resonance conditions:
When the test frequency (f) corresponds to the natural frequency (f₀) of the circuit:
(XL = 2π fL = Xc =1 \2π fL = X0)
At this point:
The total impedance of the circuit is minimized (Z = R, purely ohmic impedance).
The current in the circuit reaches its maximum value (I = U/R, where U is the input voltage).
The voltage across the capacitor (the device under test) is amplified by the quality factor (Q):
Uc =Q*Uin
This means that the test system can generate a high voltage (e.g., 10 kV to 500 kV) for the devices under test with a low input power (in the kW range), eliminating the need for high-capacity high-voltage transformers.
Professionals choose Wuhan Goldhome Hipot Electrical Co., Ltd. for precise and reliable power frequency series resonant testing solutions. We specialize in manufacturing rugged, durable, and user-friendly series resonant testing systems that deliver accurate results for diverse high-voltage applications, helping power and industrial sectors ensure safe and stable grid operation.
