Working Principles

• Electromagnetic Voltage Transformers (VTs): Operate based on the principle of electromagnetic induction. Through the iron core and windings, they transform the high voltage on the primary side into a low voltage on the secondary side in proportion. Their basic structure is similar to that of a transformer, and they normally operate in a near-no-load state.

• Capacitive Voltage Transformers (CVTs): Utilize series capacitor voltage division, followed by step-down and isolation through electromagnetic transformers to convert primary high voltage into secondary low voltage. Meanwhile, they can couple carrier frequencies to transmission lines for long-distance communication, remote measurement, etc.

Structural Features

• 110kV Voltage Transformers: Commonly adopt a two-stage cascade structure, featuring one iron core. The primary winding is divided into two parts with the same number of turns, which are respectively sleeved on the upper and lower iron core columns and connected in series. The iron core is connected to the midpoint of the primary winding, so the ground potential of the iron core is half of the working voltage (phase voltage). A balancing winding is also wound on the iron core column to balance the voltage distributed by the upper and lower primary windings.

• 220kV Voltage Transformers: Generally adopt a four-stage cascade structure with two iron cores. The primary winding is divided into four parts with the same number of turns, which are respectively wound on the upper and lower iron core columns of the two iron cores. The two iron cores are supported on insulating brackets, and their ground potentials are 3/4 and 1/4 of the working voltage, respectively. The last electrostatic screen of the primary winding is connected to the terminal "X", which is directly grounded during operation. In addition, balancing windings and coupling windings are used to maintain the magnetic potential balance of the upper and lower iron cores and transmit energy.

Main Types

• Electromagnetic Voltage Transformers (VTs): Suitable for systems below 66kV, but also applied in 110kV-220kV systems. They feature high precision and good linearity, but are prone to ferromagnetic resonance.

• Capacitive Voltage Transformers (CVTs): Widely used in high-voltage lines of 110kV and above. In addition to the voltage transformation function, they also serve as coupling capacitors, which can be used for carrier communication, high-frequency protection, etc., in power systems. They have strong anti-interference capabilities...