Capacitive Voltage Transformers are large-scale measuring transducers. They are intended for operation in AC electric systems of frequency 50 Hz.
The main distinction feature of these transformers is that secondary voltage is proportionally to primary voltage. Thus, a voltage of electricity transmission lines is transformed with a definite transformation ratio into a secondary one. A deviation during transformation (error) is determined by secondary windings' accuracy class.
Two-step voltage reduction lies in the basis of CVT operation principle. Capacitive voltage divider is used as the first step. Second step is a transformer of electromagnetic device (hereafter – EMD).
For maximum measurement accuracy securing a combined paper-film dielectric is used in a voltage divider design, impregnated with a synthetic dielectric fluid. This combination permits to keep a required capacitance value in all range of working temperatures from + 40°С up to -60°С.
Elements made from paper-film dielectric are assembled into packets and placed into a porcelain or composite insulator filled with impregnating fluid. Impregnating fluid is ecologically safe and biodegradable. Metallic bellows from stainless steel are installed on dividers for compensation of thermal expansion of dielectric and also for prevention of insulators explosion caused by emergency pressure growth.
The main task of CVT is a commercial electric energy metering and a transmission of measurement information signal to indicators, protection and control devices. With the help of these transformers it is also possible to organize a high frequency communication at the frequencies 30 – 1000 kHz, for that there is an output on the back panel of transformer for connection of communication equipment
Electromagnetic Device is an intermediate transformer placed in a hermetic metal tank fulfilled with transformer oil. Electromagnetic Device tank is made from steel with anticorrosive coating. Secondary windings outputs are placed in a special box on the front panel of tank, at that secondary windings outputs are intended for commercial accounting. There is a possibility of sealing.
In case of need it is possible to produce a transformer with different power values of secondary windings.
Transformer can be used at temperatures from +40 up to -60 °С, at heights up to 1 000 m from the sea level. The standard creepage distance of transformer corresponds to a high degree of pollution III - 2,5 cm/kV. In case of need it is possible to produce the transformer for installation in regions with very high degree of pollution IV—3,1 cm/kV
Types and basic characteristics are represented in the table:
|Type||UH primary, V||UH secondary, V||Frequency, Hz||Accuracy class – power, VA||Divider capacitance, nF||Weight, kg|
Accuracy class 0,2 – 50*
* Possible production of secondary windings with different power values.