UHV(H) AC Resonant Test System for CVT

• 1、Due to full compensation of resonant reactive power, the power of power supply and equipment is less than 1/10 of the required capacity of the subject (1/Q >10). Small size and light weight with the same capacity, large output capacity of the device and small power capacity required, cheap, convenient and safe to use;

• 2、Series resonance is actually a current filtering circuit, so that the current passing through the subject is basically the fundamental current, and the waveform distortion rate (THD) of the output voltage is very small, which is superior to all existing ac voltage withstand equipment.

• 3、The short circuit current of the sample after flashover or breakdown is only less than 1/10 (1/Q) of the test current before short circuit, which can effectively prevent the expansion of damage to the fault point after breakdown;

• 4、After flashover, the arc will be automatically extinguished immediately. The long (number of seconds) process of restoring resonant state voltage after arc quenching is a steady-state establishment process, and there is no danger of voltage overshoot and no danger of restoring overvoltage in microsecond millisecond transient process.

• 1、Generating Stable 50Hz High Voltage: The system is specifically engineered to produce a stable, high-voltage output at a fixed frequency of 50Hz. This is a critical requirement for calibrating CVTs, as their performance must be verified at the standard power frequency. It can achieve a rated voltage of 160kV and a capacity of 80kVA.

• 2、Tunable Inductance for Resonance: The system's key functional feature is its adjustable inductance range (e.g., 65~130H). By physically adjusting the inductance, it can be tuned to achieve series resonance with the capacitance of the CVT under test at exactly 50Hz, without needing to change the frequency.

• 3、Low Input Power High-Voltage Output: Through the principle of series resonance, the system functions as a voltage amplifier. It requires only a small fraction (1/Q) of the test capacity from the mains power supply to generate the necessary high voltage for CVT calibration.

• 4、Pure Sinusoidal Waveform Output: The resonant circuit acts as a filter, ensuring that the output voltage and current waveforms are stable and have a very low Total Harmonic Distortion (THD). This is essential for accurate CVT ratio and phase error measurements.

• 5、Comprehensive Protection Functions: The system has built-in safety functions to protect itself and the operator. In the event of a test object breakdown, the resonant conditions are immediately destroyed. This causes the short-circuit current to rapidly drop to less than 1/10 of the normal test current, effectively preventing damage to the fault point and eliminating dangerous recovery overvoltages.

• 1、Portability and Maneuverability: Its compact size and light weight make it far superior to traditional bulky testing equipment. This is crucial for field work where transport and handling in substations are challenging.

• 2、Simplified On-Site Testing: By solving the problem of requiring a large-capacity power supply on-site, the system enables testing in complex geographical and logistical conditions where traditional equipment would be impractical.

• 3、Superior Safety: The inherent safety features of the series resonance circuit, which limit fault current and eliminate recovery overvoltages, protect both the equipment under test and the operating personnel.

• 4、Excellent Waveform Quality: The low distortion output ensures the accuracy and reliability of the calibration measurements, meeting the strict demands of metrological standards.

• 5、Proven Performance: The system has been widely used in China for field calibration of CVTs up to 500kV, demonstrating its maturity and effectiveness in practical applications.

• 1、Primary Application: Field calibration of Capacitive Voltage Transformers (CVTs). It is used during the commissioning, periodic verification, and troubleshooting of CVTs in high-voltage substations.

• 2、Voltage Level: The system is applicable for calibrating CVTs with system voltages up to and including 500kV.

• 3、Environmental Conditions: It is specifically designed to perform in complex, real-world field conditions, including those with limited access to high-capacity power sources and with difficult handling requirements.

• 1、Over‑current protection setting: set to 0.7 times the rated current of the control unit. Example: for a control unit rated at 27 A with a matched CT 30/5, adjust the current relay to 3.3A.

• 2、Voltage withstand time setting: program the time relay to the required duration for the dielectric withstand test.

• 3、Connection and verification: connect and check test leads per the wiring diagrams; close the console breaker and ensure the regulator is at 0 before applying main power. Without main power, adjust the reactor air gap and verify travel/limit protections.

• 4、Tuning and boosting: with main power applied, press the "boost" button; the reactor will generate high voltage. Tune by changing the air gap to reach maximum output voltage; once tuned, boost to the required test voltage. The system will automatically time the voltage‑withstand period and return to 0 after the set duration.

• 5、Monitoring and safety: during tests monitor the equipment under test; if any abnormal phenomenon occurs, immediately reduce the regulator and disconnect power.

• 1、Why is a specialized system needed for CVT calibration?
  CVT calibration requires a stable, low-distortion high-voltage source at the exact power frequency (50Hz). Traditional test transformers capable of this are extremely heavy and require large power supplies, making them impractical for on-site use. This resonant system is designed to meet the specific technical requirements of CVT testing while being portable.
• 2、How does the system achieve high voltage without a large power supply?
  It uses series resonance. The system's inductor is tuned to resonate with the CVT's capacitance. In this state, the reactive power circulates between the inductor and capacitor, so the power supply only needs to provide the small amount of active power to cover system losses, which is only 1/Q of the total test capacity.
• 3、What is the "tunable" aspect of the system?
  To achieve resonance at exactly 50Hz, the system's inductor has a variable air gap. By adjusting this gap (e.g., from 0 to 300mm), the inductance changes, allowing the operator to precisely tune the resonant frequency to match the specific capacitance of the CVT being tested.
• 4、What makes this system safer than a traditional test transformer?
  In a traditional transformer, a breakdown causes a large short-circuit current. In this resonant system, a breakdown immediately destroys the resonance condition. The voltage and current drop rapidly to a very low level, limiting damage to the CVT and posing no overvoltage risk.
• 5、What is the maximum voltage and capacity of this system?
  the system has a rated capacity of 80kVA and a rated output voltage of 160kV. This configuration is suitable for calibrating CVTs up to 500kV.

Enterprise products in strict accordance with international and national standards and rules of industry production, through the national, provincial and municipal electric power research institute and electric power authorities detection, measuring center, fully passed the ISO9001 international quality management system certification, the licence for manufacturing measuring instruments of the People's Republic of China, GB/T19001-2016 quality management system requirements, GB/T24001-2016 environmental management system requirements, GB/T45001-2020 occupational health and safety management system requirements.

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