The current-limiting reactor is a coil with a stable inductive resistance. The device is connected in series to the circuit. As a rule, such devices do not have ferrimagnetic cores. A voltage drop of about 3-4% is considered standard. If a short circuit occurs, the main voltage is supplied to the current limiting reactor. The maximum allowable value is calculated by the formula:
In = (2, 54 Ih / Xp) x100%, where Ih is the rated mains current, and is the reactance.
Concrete structures
The electrical apparatus is a design that is designed for long-term operation in networks with voltages up to 35 kV. The winding is made of flexible wiring that damps dynamic and thermal loads through several parallel circuits. They allow you to evenly distribute currents, while unloading the mechanical force on a stationary concrete base.
The mode of switching on the phase coils is chosen so that the opposite direction of the magnetic fields is obtained. It also contributes to the weakening of dynamic forces with shock currents. Open placement of the windings in space contributes to providing excellent conditions for natural atmospheric cooling. If the thermal effects exceed the permissible parameters, or if a short circuit occurs, forced blowing by means of fans is used.
Dry current limiting reactors
These devices appeared as a result of the development of innovative insulating materials based on a structural basis of silicon and organic. Units successfully operate on equipment up to 220 kV. The coil winding is wound with a multicore cable with a rectangular cross section. It has increased strength and is coated with a special layer of organosilicon paint. An additional operational plus is the presence of silicon insulation with a silicon content.
Compared to concrete counterparts, the dry-type current-limiting reactor has several advantages, namely:
- Lighter weight and overall dimensions.
- Increased mechanical strength.
- The increased heat resistance.
- A larger supply of work resource.
Oil options
This electrical equipment is equipped with conductors with insulating cable paper. It is installed on special cylinders that are in a tank with oil or a similar dielectric. The last element also acts as a part for heat dissipation.
To normalize the heating of the metal case, magnetic shunts or shields with electromagnets are included in the design. They allow you to balance the field of industrial frequency passing through the turns of the winding.
Magnetic shunts are made of steel sheets placed in the middle of the oil reservoir, directly near the walls. As a result, an internal magnetic circuit is formed, which on itself closes the flow created by the winding.
Screens of the electromagnetic type are created in the form of short-circuited turns of aluminum or copper. They are installed near the walls of the tank. They induce an oncoming electromagnetic field, which reduces the effect of the main stream.
Armored Models
This electrical equipment is created with a core. Such designs require an accurate calculation of all parameters, which is associated with the possibility of saturation of the magnetic wire. A thorough analysis of operating conditions is also required.
Armored cores made of electrical steel make it possible to reduce the overall dimensions and weight of the reactor along with lowering the cost of the device. It is worth noting that when using such devices, one important point must be taken into account: the shock current should not exceed the maximum permissible value for this kind of devices.
The principle of operation of current-limiting reactors
The design is based on a coil winding having inductive resistance. It is included in the gap of the main supply circuit. The characteristics of this element are selected so that under standard operating conditions the voltage does not drop above 4% of the total value.
If an emergency situation arises in the protective circuit, the current-limiting reactor damps the predominant part of the applied high-voltage effect due to inductance, while simultaneously restraining the shock current.
The operation diagram of the device is proved by the fact that with an increase in the inductance of the coil, a decrease in the impact of the shock current is observed.
Features
The electric apparatus in question is equipped with windings that have a magnetic wire of steel plates, which serves to increase reactive properties. In such aggregates, in the case of large currents passing through the turns, saturation of the core material is observed, and this leads to a decrease in its current-limiting parameters. Therefore, such devices are not widely used.
Mostly current-limiting reactors are not equipped with steel cores. This is due to the fact that the achievement of the necessary inductance characteristics is accompanied by a significant increase in the mass and dimensions of the device.
Short circuit shock current: what is it?
Why do I need a current limiting reactor of 10 kV or more? The fact is that in the nominal mode, the supply high-voltage energy is spent on overcoming the maximum resistance of the active circuit. It, in turn, consists of an active and reactive load with capacitive and inductive coupling. The result is an operating current that is optimized using the impedance of the circuit, power and voltage.
In the event of a short circuit, the source is bypassed by accidentally connecting the maximum load in combination with the minimum active resistance, which is typical for metals. In this case, there is a lack of a reactive component of the phase. A short circuit eliminates the balance in the working circuit, forming new types of currents. The transition from one mode to another does not occur instantly, but in a protracted mode.
During this short-term transformation, sinusoidal and general values change. After a short circuit, new forms of current can acquire a forced periodic or free aperiodic complex form.
The first option helps to repeat the configuration of the supply voltage, and the second model involves the conversion of the indicator in jumps with a gradual decrease. It is formed by means of a capacitive load of a nominal indicator, considered as idling for a subsequent short circuit.