High-voltage AC filter device
High-voltage AC filter device
INPAL high-voltage AC filter compensation device (hereafter referred to as device) is applicable to AC power system with 50Hz frequency and 6~35kV voltage for reducing the system harmonic content, and is equipped with a complete set of device for improving the power factor.
In an ideal power system, the electric power is transmitted to users with single and fixed frequency, sine wave voltage and current. However, if there is nonlinear load or impact load accessing to system, such as rectification equipment, variable frequency equipment, electric arc furnace, electric railway, etc., a large amount of high-order harmonic current will be generated to cause the voltage and current wave distortion and harmonic pollution of power system, thus causing damage to power equipment and electrical equipment. When the voltage distortion rate exceeds the standard requirements, it is required to take measures to govern harmonics. The high-voltage AC filter device is an economical and practical solution.
The passive filter is mainly composed of filter capacitor, filter reactor, filter resistor, etc. into LC filter, and the filter also plays a role of reactive compensation in addition to filtering. LC filter mainly includes single tuned filter, high-pass filter, C-type filter and so on, as shown in Figure 3-1.
In practical use, design several groups of filters based on the distribution and magnitude of harmonic current as well as reactive power, each group of filters presents low impedance corresponding to a certain harmonic, high-pass filter presents low impedance for the harmonics above cutoff frequency, and the C-type filter is characterized by broad tuning band and low loss. The distribution of harmonic power flow is shown in Figure 3-2.
The harmonic current injected in system is shown in Figure 3-2:
Isn =In×Xfn/(X fn +Xsn), of which the Xfn refers to the impedance of filter branch at n time (s).
Features of device
● Use high-performance capacitor and reactance components to ensure the stability of device;
● Check all high-order harmonics to ensure to avoid the resonance and harmonic enlargement;
● Improve power factor considering the requirements of reactive compensation;
● Optimize the quality factor of the set circuit to avoid the detuning condition of device as much as possible;
● The Company appoints technicians for site guidance during installation.
Composition of high-voltage AC filter device
The high-voltage AC filter device mainly includes the following equipment: high-voltage filter capacitor, filter reactor, resistor, discharge coils, zinc-oxide arrester, grounding switch,connecting wire, post insulator, cabinet body or installation framework and fence, etc.The capacitor switching switch and protective device can be listed into the complete set of goods supply according to the user demands.
The high-voltage AC filter device can be equipped with single-tuning circuit with high harmonics and high-pass filter circuit according to test data.
The high-voltage AC filter device can play a role of reactive compensation according to its different configuration.
The filter capacitor is mainly taken as a filter element and combined with other parts (such as reactor, etc.) into AC filter to use for the electrical equipment with harmonic and prevent the harmonic contamination for grid, or is connected to the power system to provide low impedance channel for one or more harmonic current (s), thus reducing the network harmonic level and improving system power factor.
The filter reactor is used for capacitor compensation cabinet and is connected in series with shunt capacitor.The capacitor compensation cabinet is usually a pure capacitance structure. This kind of capacitor cabinet not only generates switching inrush current, but also enlarges the harmonic in grid, thus damaging the safety operation of other electrical equipment. While the filter reactor not only can inhibit the instant switching inrush current, but also can inhibit and absorb harmonic current. It has a role of filtering and greatly increases the grid operation safety.
The discharge coils are directly connected in parallel with the capacitor for use. After the capacitor is disconnected from grid, they can reduce the voltage on the capacitor terminal to 50V below within 5S. The discharge coils also can provide the secondary protection signals for filter device.
The zinc-oxide arrester is mainly used for restricting the overvoltage of capacitor during switching.
The role of grounding switch is to ground the capacitor terminals during interruption maintenance in order to ensure the safety of maintenance personnel.
The cabinet body and live displaying device are mainly used for displaying the switching condition of device and providing decision conditions for cabinet body’s five-prevention interlock.