INDUCTOR
An inductor is a component that can convert electrical energy into magnetic energy and store it. The structure of an inductor is similar to a transformer, but with only one winding. Inductors have a certain inductance, which only impedes changes in current. If an inductor is in a state where no current passes through, it will attempt to obstruct the current from flowing through it when the circuit is turned on; If an inductor is in a state where current is passing through, it will attempt to maintain a constant current when the circuit is disconnected. Inductors are also known as chokes, reactors, and dynamic reactors.
Category:
Classify by structure and cooling medium, by connection method, by function, and by purpose.
- According to structure and cooling medium: divided into hollow type, iron core type, dry-type, oil immersed type, etc., for example: dry-type hollow reactor, dry-type iron core reactor, oil immersed iron core reactor, oil immersed hollow reactor, clamped dry-type hollow reactor, wrapped dry-type hollow reactor, cement reactor, etc.
- According to the connection method: divided into parallel reactors and series reactors.
- By function: divided into current limiting and compensation.
- By purpose: Divided by specific purposes, such as current limiting reactors, filtering reactors, smoothing reactors, power factor compensation reactors, series reactors, balancing reactors, grounding reactors, arc suppression coils, incoming line reactors, outgoing line reactors, saturation reactors, self saturation reactors, variable reactors (adjustable reactors, controllable reactors), yoke current reactors, series resonant reactors, parallel resonant reactors, etc.
Function of Reactor:
The common types of reactors used in power systems are series reactors and parallel reactors. Series reactors are mainly used to limit short-circuit currents, and are also used in series or parallel with capacitors in filters to limit high-order harmonics in the power grid. The reactors in 220kV, 110kV, 35kV, and 10kV power grids are used to absorb the charging capacitive reactive power of cable lines. The operating voltage can be adjusted by adjusting the number of parallel reactors. Ultra high voltage shunt reactors have multiple functions to improve the reactive power related operating conditions of power systems, mainly including:
- The capacitance effect on lightly unloaded or lightly loaded lines to reduce transient overvoltage at power frequency;
- Improve voltage distribution on long-distance transmission lines;
- To balance the reactive power in the line as much as possible under light load, prevent unreasonable flow of reactive power, and also reduce power loss on the line;
- Reduce the steady-state power frequency voltage on the high-voltage bus when the large unit is parallel to the system, in order to facilitate synchronous parallel operation of the generator;
- Prevent self excitation resonance phenomenon that may occur in generators with long lines;
- When using a small reactance grounding device for the neutral point of a reactor, a small reactor can also be used to compensate for the phase to phase and phase to ground capacitance of the circuit, in order to accelerate the automatic extinguishing of the secondary current and facilitate its use.
The wiring of reactors can be divided into two types: series connection and parallel connection. Series reactors usually serve to limit current, while parallel reactors are often used for reactive power compensation.
- Half core dry-type shunt reactor: In ultra-high voltage long-distance transmission systems, it is connected to the tertiary coil of a transformer. Used to compensate for the capacitive charging current of the circuit, limit the system voltage rise and operating overvoltage, and ensure the reliable operation of the circuit.
- Half core dry-type series reactor: installed in the capacitor circuit, starting when the capacitor circuit is put into operation.
Current limiting and filtering functions of reactors:
The expansion of power grid capacity has led to a rapid increase in the rated short-circuit capacity of the system. On the low voltage 35kV side of a 500kV substation, the maximum effective value of three-phase symmetrical short-circuit current is close to 50kA. In order to limit the short-circuit current of transmission lines and protect power equipment, it is necessary to install reactors, which can reduce the short-circuit current and maintain the voltage of the system unchanged at the moment of short-circuit.
Install damping reactors (i.e. series reactors) in the capacitor circuit to suppress inrush current when the capacitor circuit is put into operation. At the same time, it forms a harmonic circuit together with the capacitor bank to filter various harmonics. In the capacitor circuit of the 35kV reactive power compensation device in a 500kV substation, in order to limit the inrush current when the capacitor is put into operation and suppress the high-order harmonics of the power system, a damping reactor must be installed in the 35kV capacitor circuit. When suppressing the third harmonic, a dry hollow single-phase outdoor damping reactor with a rated voltage of 35kV, a rated inductance of 26.2mH, and a rated current of 350A is used. It forms a resonant circuit with a 2.52Mvar capacitor for the third harmonic, that is, a third harmonic filtering circuit.
Similarly, in order to suppress the 5th and higher harmonics, a single-phase outdoor damping reactor with a rated voltage of 35kV, rated inductance of 9.2mH, and rated current of 382A was used. It forms a resonant circuit with a 2.52Mvar capacitor for the 5th and higher harmonics. It plays a role in suppressing high-order harmonics. It should be noted that the use and technical conditions of damping reactors are specified in both the national standard GB10229-88 for reactors and the international standard IEC289-88.
Application of reactors:
- Parallel reactor: The reactor used for full load testing of generators is the prototype of a parallel reactor. Due to the attraction of alternating magnetic fields between segmented iron core cakes, the noise of iron core reactors is generally about 10dB higher than that of transformers of the same capacity. The AC passing through the shunt reactor is used to compensate for the capacitive impedance of the system. Usually connected in series with thyristors, it can continuously adjust the reactive current.
- Series reactor: AC is passed through it, and the function of the series reactor is to be connected in series with the compensating capacitor, forming series resonance for steady-state harmonics (5th, 7th, 11th, 13th). Usually, there are 5-6% reactors, which belong to high inductance reactors.
Tuned reactor: AC power passes through it, and the function of the series reactor is to connect with the capacitor in series, forming series resonance with the specified nth harmonic component, thereby absorbing the harmonic component, usually n=5, 7, 11, 13, 19.
- Incoming reactor: also known as commutation reactor, used in power grid incoming lines, passing AC current. The function of the incoming reactor is to limit the voltage drop on the grid side and the current rise rate di/dt and voltage rise rate du/dt of the thyristor during inverter commutation, as well as to decouple the parallel inverter group.
- Current limiting reactor: Current limiting reactors are generally used in distribution lines. Limited current reactors are often connected in series on branch feeders from the same bus to limit the short-circuit current of the feeder and maintain the bus voltage, so as not to be too low due to feeder short circuits.
- Damping reactor: (usually also known as series reactor) is connected in series with a capacitor bank or dense capacitor to limit the inrush current of the capacitor when it is closed. This function is similar to that of a current limiting reactor. A filtering reactor is connected in series with a filtering capacitor to form a resonant filter, which is generally used for 3rd to 17th order resonant filtering or higher order high pass filtering. The converter stations, phase controlled static compensation devices, medium and large rectifier devices, electrified railways, and all high-power thyristor controlled power electronic circuits of DC transmission lines are harmonic current sources that must be filtered out to prevent them from entering the system. The power department has specific regulations on harmonics in the power system.
- Arc suppression coil: Arc suppression coils are widely used in resonant grounding systems ranging from 10kV to 63kV. Due to the oil-free tendency of substations, many arc suppression coils below 35kV are now dry-type cast.
- Smooth wave reactor: Smooth wave reactors are used in rectified DC circuits. The number of pulses in a rectifier circuit is always limited, and there is always ripple in the output rectified voltage. This kind of ripple is often harmful and needs to be suppressed by a smoothing reactor. The converter stations for DC transmission are equipped with smoothing reactors to make the output DC close to the ideal DC. In DC powered thyristor electrical transmission, smoothing reactors are also indispensable.
The smoothing reactor is an important component in rectifier circuits, and its main function in intermediate frequency power supplies is to:
- Limit the short-circuit current, (simultaneous conduction of the inverter thyristor during commutation is equivalent to a direct short-circuit of the rectifier bridge load) without a reactor.
- Suppress the impact of intermediate frequency components on the power grid.
- The filtering effect (rectified current contains AC components; high-frequency AC is not easily passed through large inductors) makes the rectified output waveform continuous. If it is not continuous, there will be a time when the current is zero, and the inverter bridge will stop working, causing the rectifier bridge to open circuit.
- DC controlled saturable reactor: A choke or self saturating saturable reactor connected in series in a circuit. During the period of the voltage sine wave, the saturable reactor absorbs a certain amount of volts seconds before saturation, reaches saturation, and then enters a fully open state. Therefore, its output voltage is non sinusoidal, and the function of this saturated reactor is similar to that of a thyristor.
The main components of an electrical circuit are resistors, capacitors, and inductors Inductance has the function of suppressing current changes and shifting the phase of alternating current A wound type static induction device with inductive function is called a reactor.
Product Standard:
GB/T 1094.6-2011 IEC 60076-6：2007
GB/T 1094.1-2011 IEC 60076-1：2011
GB/T 1094.3-2017 IEC 60076-3：2013
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