Some common sense about reactors

Reactors are also called inductors. When a conductor is energized, it will generate a magnetic field in a certain space it occupies, so all current-carrying conductors have inductance in a general sense. However, the inductance of a long straight conductor with electricity is small, and the magnetic field generated is not strong. Therefore, the actual reactor is a wire wound into a solenoid, called an air-core reactor; sometimes, to make this solenoid have a larger inductance, an iron core is inserted into the solenoid, called an iron core reactor. Reactance is divided into inductive reactance and capacitive reactance. The more scientific classification is that inductive reactance (inductor) and capacitive reactance (capacitor) are collectively called reactors. However, since inductors first appeared in the past and were called reactors, the capacitors people are now talking about are capacitive reactances, and reactors specifically refer to inductors.

Structure and working principle

Reactors are devices used to adjust the inductance or capacitance in power systems. It is mainly composed of a coil (winding) and an iron core, similar to the structure of a transformer. The working principle of the reactor depends on its purpose:

1. Inductive reactor: The inductive reactor mainly adjusts the phase difference of voltage and current through the induced electromotive force and current reaction of the coil. In the power system, it can be used to improve the power factor of the circuit and reduce the reactive power in the power grid.
2. Capacitive reactor: The capacitive reactor controls the voltage and current by adjusting the capacitance in the circuit. It plays an important role in adjusting the capacitive load, filtering, and harmonics of the power system.

Classification Introduction

Classification by structure and cooling medium, by connection method, by function, and by purpose.

1. By structure and cooling medium: divided into hollow type, iron core type, dry type, oil immersed type, etc., for example, dry hollow reactor, dry iron core reactor, oil immersed iron core reactor, oil immersed hollow reactor, clamped dry hollow reactor, wrapped dry hollow reactor, cement reactor, etc.
2. By connection method: divided into parallel reactor and series reactor.
3. By function: divided into current limiting and compensation.
4. By purpose: subdivided by a specific purpose, for example, current limiting reactor, filter reactor, smoothing reactor, power factor compensation reactor, series reactor, balancing reactor, grounding reactor, arc suppression coil, incoming line reactor, outgoing line reactor, saturated reactor, self-saturated reactor, variable reactor (adjustable reactor, controllable reactor), yoke current reactor, series resonant reactor, parallel resonant reactor, etc.

Features

Incoming line reactor

1. The incoming line reactor is three-phase, all of which are iron core dry type;
2. The iron core is made of high-quality low-loss imported cold-rolled silicon steel sheet, and the gap is made of epoxy laminated glass cloth plate as a spacer to ensure that the air gap of the reactor does not change during operation;
3. The coil is wound with H-class enameled flat copper wire, which is arranged tightly and evenly, without an insulating layer on the surface, and has excellent aesthetics and good heat dissipation performance;
4. After the coil and the iron core of the incoming line reactor are assembled into one, they are pre-baked → vacuum vacuum-dipped → hot-baked, and cured. The process adopts H-class dipped The varnish makes the coil and core of the reactor firmly combined, which not only greatly reduces the noise during operation, but also has a very high heat resistance level, which can ensure that the reactor can operate safely and noiselessly at high temperatures;
5. The fasteners of the core column of the incoming line reactor are made of non-magnetic materials to reduce the eddy current heating phenomenon during operation;
6. The exposed parts are all treated with anti-corrosion, and the lead terminals are tinned copper tube terminals;
7. Compared with similar domestic products, this incoming line reactor has the advantages of small size, lightweight, and beautiful appearance, which can be comparable to well-known foreign brands.
   Output reactor
   The output reactor is also called the motor reactor. Its function is to limit the capacitive charging current of the motor connection cable and limit the voltage rise rate on the motor winding to within 54OV/us. Generally, when the cable length between the 4-90KW inverter and the motor exceeds 50m, an output reactor should be installed. It is also used to passivate the inverter output voltage (switching steepness) and reduce the disturbance and impact on the components in the inverter (such as IGBT). Output reactors are mainly used in industrial automation system engineering, especially in the case of using inverters, to extend the effective transmission distance of the inverter and effectively suppress the instantaneous high voltage generated when the IGBT module of the inverter is switched.
   Instructions for use of output reactors: To increase the distance between the inverter and the motor, the cable can be appropriately thickened to increase the insulation strength of the cable. Try to use unshielded cables.
   Characteristics of output reactor:
8. Suitable for reactive power compensation and harmonic control;
9. The main function of the output reactor is to compensate for the influence of long-line distributed capacitance and suppress output harmonic current;
10. Effectively protecting the inverter and improving the power factor, can prevent interference from the power grid, and reduce the pollution of the harmonic current generated by the rectifier unit to the power grid.
    Input reactor
    The function of the input reactor is to limit the voltage drop on the grid side when the converter is commutated; suppress harmonics and decoupling of parallel converter groups; and limit the jump of grid voltage or the current impact generated when the grid system is operated. When the ratio of the grid short-circuit capacity to the converter capacity is greater than 33:1, the relative voltage drop of the input reactor is 2% for single-quadrant operation and 4% for four-quadrant operation. When the grid short-circuit voltage is greater than 6%, the input reactor is allowed to operate. For 12-pulse rectifier units, at least one grid-side incoming line reactor with a relative voltage drop of 2% is required. Input reactors are mainly used in industrial/factory automation control systems. They are installed between frequency converters, speed regulators, and grid power input reactors to suppress surge voltages and currents generated by frequently

Effect

The common reactors used in power systems are series reactors and shunt reactors.
Series reactors are mainly used to limit short-circuit currents. They are also connected in series or in parallel with capacitors in filters to limit high-order harmonics in the power grid. 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 shunt reactors. Ultra-high voltage shunt reactors have multiple functions to improve the reactive power-related operating conditions of power systems, mainly including:

1. Capacitive effect on light no-load or light-load lines to reduce power frequency transient overvoltage;
2. Improve voltage distribution on long transmission lines;
3. Make the reactive power in the line as locally balanced as possible when light load is applied, prevent irrational reactive power flow, and reduce power loss on the line;
4. Reduce the power frequency steady-state voltage on the high-voltage bus when large units are paralleled with the system, which is convenient for synchronous paralleling of generators;
5. Prevent the self-excited resonance phenomenon that may occur when the generator carries a long line;
6. When the neutral point of the reactor is grounded through a small reactor, a small reactor can also be used to compensate for the phase-to-phase and phase-to-ground capacitance of the line to accelerate the automatic extinction of the latent current, which is convenient for use.
   The wiring of the reactor is divided into two ways: series and parallel. Series reactors usually play a current limiting role, and shunt reactors are often used for reactive compensation.
7. Half-core dry-type shunt reactor: In the ultra-high voltage long-distance transmission system, it is connected to the tertiary coil of the transformer. It is used to compensate for the capacitive charging current of the line, limit the system voltage rise and operating overvoltage, and ensure the reliable operation of the line.
8. Half-core dry-type series reactor: It is installed in the capacitor circuit and plays a role when the capacitor circuit is put into operation.
   The current limiting and filtering function of the reactor:
   The expansion of the power grid capacity has rapidly increased the rated value of the system’s short-circuit capacity.
   For example, on the low-voltage 35kV side of the 500kV substation, the maximum three-phase symmetrical short-circuit current effective value is close to 50kA. To limit the short-circuit current of the transmission line and protect the power equipment, the reactor must be installed. The reactor can reduce the short-circuit current and keep the voltage of the system unchanged at the moment of the short circuit.
   Damping reactors (i.e. series reactors) are installed in the capacitor circuit to suppress the inrush current when the capacitor circuit is put into operation. At the same time, they form a harmonic circuit with the capacitor bank to filter the harmonics. For example, in the capacitor circuit of the 35kV reactive compensation device of the 500kV substation, to limit the inrush current when the capacitor is put into use and suppress the higher harmonics of the power system, a damping reactor must be installed in the 35kV capacitor circuit. When suppressing the third harmonic, a dry-type 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 the 2.52Mvar capacitor for the third harmonic, that is, the third harmonic filter circuit.
   Similarly, to suppress the fifth and higher harmonics, a single-phase outdoor damping reactor with a rated voltage of 35kV, a rated inductance of 9.2mH, and a rated current of 382A is used. It forms a resonant circuit with the 2.52Mvar capacitor for the fifth 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 stipulated in the national standard “Reactor” GB10229-88 and the international standard IEC289-88. However, some domestic departments currently call damping reactors series reactors, which is strictly inappropriate because the name of series reactors does not exist in the above standards.

How to apply

Shunt reactor: The reactor used for the full-load test of the generator is the prototype of a shunt reactor.

Iron core reactor: Due to the attraction of alternating magnetic fields between segmented iron core discs, the noise is generally about 10dB higher than that of transformers with the same capacity. The AC passes through the shunt reactor, the role of the shunt reactor is to compensate for the capacitive reactance of the system. Usually connected in series with thyristors, the reactance current can be continuously adjusted.
Series reactor: The AC passes through it, and the role of the series reactor is to be connected in series with the compensation capacitor to form a series resonance for steady-state harmonics (5, 7, 11, 13). Usually, there are 5~6% reactors, which are high inductance reactors.

Tuned reactor: AC passes through it. The function of the series reactor is to connect it in series with the capacitor to form a series resonance for the specified nth harmonic component, thereby absorbing the harmonic component, usually n=5, 7, 11, 13, 19.
Incoming line reactor: also known as phase-changing reactor, used in the power grid incoming line, AC passes through it. The function of the incoming line 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 when the converter is commutated, as well as the decoupling of the parallel converter group.
Current-limiting reactor: Current-limiting reactors are generally used in distribution lines. Current-limiting reactors are often connected in series on branch feeders derived from the same bus to limit the short-circuit current of the feeder and maintain the bus voltage so that it will not be too low due to the feeder short circuit.
Damping reactor: (also commonly called series reactor) is connected in series with capacitor banks or dense capacitors to limit the closing inrush current of capacitors. In this respect, the function is similar to that of current limiting reactors. Filter reactors are connected in series with filter capacitors to form resonant filters, which are generally used for 3rd to 17th-order resonant filtering or higher-order high-pass filtering. Converter stations of DC transmission lines, phase-controlled static compensation devices, medium and large rectifiers, electrified railways, and even all high-power thyristor-controlled power electronic circuits are sources of harmonic currents, which must be filtered out to prevent them from entering the system. The power department has specific regulations for harmonics in power systems.
Arc suppression coils: Arc suppression coils are widely used in resonant grounding systems of 10kV-63kV levels. Due to the oil-free trend of substations, many arc suppression coils below 35kV are now dry cast.
Smoothing reactors: Smoothing reactors are used in DC circuits after rectification. The number of pulses in the rectifier circuit is always limited, and there are always ripples in the output rectified voltage. This ripple is often harmful and needs to be suppressed by a smoothing reactor. The converter station of DC transmission is equipped with a smoothing reactor to make the output DC close to the ideal DC. Smoothing reactors are also indispensable in the thyristor electric transmission of DC power supply.
Smoothing reactors are an important component in the rectifier circuit. Their main functions in the medium frequency power supply are:

1. Limit short-circuit current (the inverter thyristor is turned on at the same time when switching phases, which is equivalent to the rectifier bridge load being directly short-circuited). Without a reactor, it is directly short-circuited.
2. Suppress the influence of the medium frequency component on the power frequency power grid.
3. Filtering effect (rectifier current has AC components; high-frequency AC is not easy to pass through large inductors) to make the rectifier output waveform continuous. If it is not continuous, there will be a time when the current is zero. At this time, the inverter bridge stops working, causing the rectifier bridge to open.
4. The input power of the parallel inverter circuit has a reactive component throughput, and there must be an energy storage element reactor in the input circuit of the inverter bridge.
   DC-controlled saturated reactor: a choke type or self-saturated saturated reactor connected in series in the circuit. During the period of the voltage sine wave, the saturated reactor absorbs a certain amount of volt-seconds before saturation, reaches saturation, and then becomes fully open. 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 resistance, capacitance, and inductance. Inductance has the function of suppressing current changes and can shift the phase of alternating current. A wound static induction device with inductive action is called a reactor.

Application and function

Reactors have many applications in power systems:

1. Improve power factor: Inductive reactors can improve the power factor of the circuit by increasing inductive reactive power, thereby improving the efficiency and stability of the power system.
2. Power transmission: In the process of long-distance power transmission, the reactor can be used to adjust the waveform of current and voltage, and reduce line loss and power loss.
3. Power load regulation: For power systems that need to dynamically adjust the load, the reactor can adjust the current and voltage in the power grid to keep the system running stably.
4. Harmonic filtering: Capacitive reactors are usually used to filter out harmonics in the power grid to prevent harmonics from affecting equipment and systems.

Wiring method

ABCXYZ has six terminals, ABC can be used as the reactor input terminal, XYZ as the reactor output terminal; XYZ can also be used as the reactor input terminal, and ABC as the reactor output terminal. There is no specific order requirement for the input and output lines, and it can be connected in any way, which will not affect the inverter. Just pay attention to one point: the two sets of terminals ABC and XYZ cannot cross each other when wiring.

Service life

The long-term normal operation time of the reactor under rated load is the service life of the reactor. The service life of the reactor is determined by the material it is made of. The materials used to make reactors are divided into two categories: metal materials and insulating materials. Metal materials are resistant to high temperatures while insulating materials will gradually lose their original mechanical and insulating properties under the influence of high temperatures, and electric and magnetic fields for a long time, such as becoming brittle, weakening mechanical strength, and electrical breakdown. This gradual process is the aging of insulating materials. The higher the temperature, the faster the mechanical and insulating properties of insulating materials weaken; the more water the insulating materials contain, the faster they age. The insulating materials in the reactor must withstand the loads generated by the operation of the reactor and the effects of the surrounding environment. The sum, intensity, and duration of these loads determine the service life of the insulating materials.