What are the main differences between electromagnetic and capacitive voltage transformers?
l Compared with electromagnetic voltage transformers, capacitive voltage transformers have the following characteristics:
1) Small size, light weight, low cost and small floor space.
2) In addition to being a voltage transformer, it can also be divided into capacitors and coupling capacitors for high-frequency carrier communication.
3) The impulse insulation strength of the capacitive voltage transformer is higher than that of the electromagnetic type.
4) The error characteristics and transient characteristics are not as good as the electromagnetic type, and the output capacity is small.
l The main difference between electromagnetic and capacitive voltage transformers
An electromagnetic voltage transformer is a voltage transformer that converts a primary voltage into a secondary voltage by electromagnetic induction. This transformer does not add other electrical components such as capacitors that change the primary voltage.
A capacitive voltage transformer is a voltage transformer that draws a voltage from a series capacitor and then transforms it into a voltage source such as a meter or a relay protection. The capacitive voltage transformer can also couple the carrier frequency to the power line for long distance. Communication, remote measurement, selective line high frequency protection, remote control, teletype and so on. Therefore, compared with the conventional electromagnetic voltage transformer, the capacitive voltage transformer has many advantages in economy and safety in addition to preventing ferromagnetic resonance due to saturation of the voltage transformer core.
Capacitive voltage transformers are mainly composed of a capacitor divider and a medium voltage transformer. The capacitor divider consists of a porcelain sleeve and a plurality of series capacitors mounted therein. The porcelain sleeve is filled with insulating oil maintaining a positive pressure of 0.1 MPa, and a steel bellows is used to balance different environments to maintain oil pressure. The capacitor partial pressure can be used as a coupling capacitor. Connect the carrier device. The medium voltage transformer consists of a transformer installed in the sealed oil tank, a compensating reactor and a damping device, and the space at the top of the fuel tank is filled with nitrogen. The primary winding is divided into a main winding and a fine-tuning winding, and a low-loss reactor is connected in series between the primary side and the primary winding. Since the nonlinear impedance and inherent capacitance of the capacitive voltage transformer sometimes cause ferromagnetic resonance in the capacitive voltage transformer, the damping device is used to suppress the resonance. The damping device is composed of a resistor and a reactor, and is connected across the secondary winding. Above, under normal circumstances, the damping device has a high impedance. When the ferromagnetic resonance causes an overvoltage, before the medium voltage transformer is affected, the reactor is saturated and only the resistive load is left, so that the oscillation energy is quickly reduced.