The series resonance under UHV power can help many power workers conduct various power tests more conveniently.
1、 Preface:
In power plants, substations, and wind power construction projects, due to on-site requirements, some high-voltage cables are relatively long (close to 5km) and have large capacities, so general instruments and equipment are not capable of achieving them. The frequency series resonance test device (20-300HZ) designed with new concepts and technologies has high accuracy and sensitivity for the measured cables, and can accurately detect problems. Especially for challenging wind power projects, cables laid on mountains may be damaged due to transportation, laying, external stress, and environmental factors (low temperature). Due to the high mountains and difficult roads, it is difficult to meet the requirements for large and bulky ones. Therefore, the frequency modulation series resonance test device with simple, lightweight, and high accuracy is widely used and welcomed.
At the construction site, 380V should be applied as an AC power source. Ensure the correct wiring of the instrument and take effective safety measures (wear red and white seat belts and assign dedicated personnel to monitor the site) to ensure the safety of equipment and personnel.
This construction method has been applied in the fourth and fifth phases of the Chengde Wind Power Project and multiple power plant projects, and optimization methods have been gradually summarized. The results are significant, creating significant economic and social benefits.
2、 Characteristics of construction methods
1. The device has protection functions such as overvoltage, overcurrent, zero start, system detuning (flashover), etc. The overvoltage and overcurrent protection can be set according to user needs. During the flashover of the test sample, the flashover protection will be activated and the flashover voltage value will be recorded for experimental analysis.
2. The entire device is very lightweight, with a maximum weight of no more than 50KG. Easy to use on site.
3. The device has three working modes, which facilitate users to flexibly choose according to the on-site situation and improve the testing speed. The working modes are: fully automatic mode, manual mode, automatic frequency modulation, and manual boost mode.
4. It can store and print data in different locations, and the stored data numbers are numerical, making it convenient for users to identify and search.
5. When the device automatically scans the frequency, the starting point of the frequency can be set arbitrarily within the specified range, and the scanning direction can be selected upwards or downwards. At the same time, the LCD screen displays the scanning curve, making it convenient for users to intuitively understand whether the resonance point has been found.
6. Adopting DSP platform technology, it is convenient to add or remove functions and upgrade according to user needs, making the human-machine exchange interface more user-friendly.
3、 Scope of application
The AC withstand voltage test of various large power transformers, power cables, steam turbines, hydro generators, and other capacitive equipment must be strictly conducted regularly in accordance with the test regulations. Under power frequency conditions, due to the large capacitance of the test object or high requirements for the test voltage, there are also high requirements for the power capacity of the test device. Traditional power frequency withstand voltage devices often have large individual volumes, heavy weights, are not easy to transport on site, and are not easy to combine arbitrarily, resulting in poor flexibility. At present, a better method is to use series resonance for voltage withstand testing.
4、 Process principle
1. Equipment that uses tuned inductors and load capacitors to generate power frequency series resonance and obtain power frequency test voltage
Composed of a variable frequency power supply, excitation transformer, reactor, and capacitive voltage divider. The capacitor and reactor of the test sample form a series resonant connection; The voltage divider is connected in parallel to the test sample to measure the resonant voltage on the test sample and provide an overvoltage protection signal; The frequency modulation power output is coupled to the series resonant circuit through an excitation transformer, providing excitation power for series resonance.
The series resonance test device is the latest generation of equipment specifically designed for AC withstand voltage testing of capacitive test samples. It is widely used for AC withstand voltage testing of various high-voltage cross-linked cables, transformers, generators, GIS switches, motors, and SF6 switch frequency conversion frequency modulation series resonance series resonance AC withstand voltage testing complete sets of instruments and equipment.
2. Series resonance is mainly used for:
(1) AC voltage withstand test of 6kV-500kV high-voltage cross-linked cable
(2) AC voltage withstand test of generator
(3) AC withstand voltage test for GIS and SF6 switches
(4) Power frequency withstand voltage test of 6kV-500kV transformer
(5) AC withstand voltage test for other high-voltage electrical equipment such as busbars, bushings, and transformers.
5、 Conclusion
In the AC withstand voltage test of various large power transformers, power cables, steam turbines, hydro generators, and other capacitive equipment, series resonance is commonly used. Its characteristics determine that there will inevitably be broader application scenarios in future industrial production.
