Wuhan UHV specializes in producingseries resonance (also known as power frequency withstand voltage test equipment). Next, we will share with you the conditions for resonance in series and parallel circuits. Do you know.
1. In a series resonant circuit of resistors, capacitors, and inductors, the phenomenon of power supply, voltage, and current being in phase occurs, which is called series resonance. Its characteristics are: the circuit is purely resistive, the power supply, voltage, and current are in phase, the reactance X is equal to 0, and the impedance Z is equal to the resistance R. At this time, the impedance of the circuit is the smallest and the current is the largest. High voltages that are many times larger than the power supply voltage may be generated on the inductor and capacitor, so series resonance is also known as voltage resonance.
2. Parallel resonance refers to the phenomenon in which the voltage at the circuit end and the total current are in phase in a resistor, capacitor, or inductor parallel circuit. Parallel resonance is characterized by complete compensation, where the power supply does not need to provide reactive power, only the active power required by the resistor. During resonance, the total current of the circuit is minimized, and the branch current is often greater than the total current in the circuit. Therefore, parallel resonance is also called current resonance.
Series resonance refers to the series connection of a power supply and an LC circuit. When XL=XC is satisfied, the LC equivalent impedance is almost zero, and the output current of the power supply is extremely high, so it is also known as "current resonance".
Current phenomena of series resonance and parallel resonance
1. When series resonance occurs, the current in the circuit is at its maximum.
2. When parallel resonance occurs, the current in the circuit is minimized.
Advantages of series resonance in power systems:
1. The required power capacity is greatly reduced.
The power supply generates high voltage and high current through resonance between the resonant reactor and the tested capacitor. In the entire system, the power supply only needs to provide the active consumption part of the system. Therefore, the required power supply for the test is only 1/Q of the test capacity.
2. The weight and volume of the equipment have been greatly reduced. In a series resonant power supply, not only is the bulky high-power voltage regulating device and ordinary high-power power frequency test transformer eliminated, but the resonant excitation power supply only requires 1/Q of the test capacity, greatly reducing the system weight and volume, usually 1/10-1/30 of ordinary test devices.
3. Improve the waveform of the output voltage. A resonant power supply is a resonant filtering circuit that can improve the waveform distortion of the output voltage, obtain a good sine waveform, and effectively prevent the accidental breakdown of the test sample by harmonic peaks.
4. Prevent large short-circuit currents from burning the fault point. In the series resonance state, when the weak point of the insulation of the test sample is broken down, the circuit immediately disengages and the loop current rapidly drops to 1/Q of the normal test current. However, when conducting voltage withstand tests in parallel resonance or test transformer mode, the breakdown current immediately increases by several tens of times. Compared with the two, the short-circuit current is hundreds of times different from the breakdown current. So, series resonance can effectively identify insulation weaknesses without the concern of large short-circuit currents burning the fault point.
5. There will be no overvoltage recovery. When the test sample breaks down, due to the loss of resonance conditions, the high voltage immediately disappears, the arc immediately extinguishes, and the process of re establishing the recovery voltage is long. It is easy to disconnect the power supply before reaching the flashover voltage again. This voltage recovery process is an intermittent oscillation process of energy accumulation, which is long and does not result in any recovery overvoltage.
