To stabilize high traction currents and increased asymmetry currents, choke transformers are used. A inductor is a inductor that can remove noise, smooth out the ripple of the current, decouple the parts of the circuit from each other at a high frequency, and also store energy in a magnetic field. The device is called the “reactor” (the latter does not need the use of a drive and other driving forces, but works on the basis of dynamics).
Thus, the main purpose of the inductor is to delay the current of a certain frequency range or to accumulate energy over a certain period of time in a magnetic field. The accumulated energy is used in various fields of industry and in domestic conditions. Let's find out more about it.
Principle of operation
The principle of operation is based on the principle of self-induction of the coil. In the design of the device there is only one winding, but due to the principle of operation and scope of application, the device is often called a choke-transformer.
The device coil consists of plates isolated between each other (most often steel or ferromagnetic). Isolation is done to prevent the formation of Foucault currents that cause interference. The core has a large inductance, but it is a powerful restraining barrier (for example, with a strong increase or decrease in voltage in the network).
The device is able to withstand various vibration ranges:
- low (from 20 Hz to 20 kHz);
- medium (or ultrasound, from 20 to 100 kHz);
- high (over 100 kHz).
High-frequency chokes differ in design from low- and mid-frequency.
Varieties
Devices are divided into:
- The low-frequency choke-transformer looks like a primitive iron transformer. The difference is the layout with one winding. The coil has a significant resistance to a change in current in the circuit - when it is lowered, the device is able to maintain the required level, and when increased, it can be reduced.
- High frequency circuits are more common. Coils of such devices are wound on cores (ferrite, steel) or on a plastic frame. When working with medium or long wavelengths, sectional winding is often used.
The throttle with a core has smaller dimensions than without it.
The main parameters of the device are inductance (unit of measure - GN) and resistance (Ohm). Important characteristics are voltage, rated current and quality factor.
Scope and purpose of DC chokes
Devices, for example, the -0.6-1000 inductor-transformer, are designed for installation on railway tracks that are equipped with automatic blocking of alternating current and direct current electric traction. Also, devices of this type are used for docking systems of electric traction.
According to their purpose, choke transformers are as follows:
- Inductors that operate on secondary switching power supplies. Initially, the coil accumulates energy from the primary source in its own magnetic field, and then returns it to the load.
- Chokes for starting engines. In this case, the devices act as a limiter of starting and braking currents. For drives whose power does not exceed 30 kW, the design of the inductor has a similar device with a three-phase transformer.
- Throttle saturation. It is used in voltage stabilizers and in some converters (for example, ferroresonance). The device is also used in magnetic amplifiers, where the core changes the inductance of the circuit by magnetizing.
- Smoothing chokes. They are used to eliminate ripple of the rectified current (for example, in the absence of capacitors in tube amplifiers).
Also, devices are widely used in welding, when installing lighting, in alarm systems, centralization, blocking automation, mechanics, etc.
The main elements of the device. Specifications
The main elements of the device are:
- core;
- yoke;
- cast iron housing;
- cap;
- coupling;
- trumpet;
- additional winding;
- sealant.
In the technical characteristics indicate: the number of turns, impedance and transformation ratio in the main and additional windings. For example, in the DT 500 choke transformer, the number of turns of the main winding is 7 + 7, the additional - 1560, 322, 1238. The impedance in this case leaves 0.2–0.22 Ohms, and the transformation coefficient is 40, 23 and 17.
The difference in color marking devices
Each device of an electronic choke-transformer is marked depending on its parameters. To simplify the decoding of long and complex abbreviations, color marking was introduced.
The latter is a cipher of several colored rings that determine the inductance of the device. The first two indicate the nominal inductance, the third the factor, and the last the tolerance. Such differences make it easy even for a novice master to easily identify a suitable device.
Important! If only 3 rings are shown on the throttle, then its tolerance is 20%.
The throttle device and its purpose on the example of the railway track
On some sections of the railways, rail AC circuits are installed. In these (electrified) areas, the contact wire is a direct current conductor to electric locomotives, and rail threads and earth serve as the reverse.
In the case when the current is passed through both rail threads, the arranged AC rail circuit is called a two-strand. In this case, the purpose of the inductor-transformer is to pass reverse traction current bypassing the insulating joints on each side. Each device has two windings: the main and additional.
During the movement of the train, current flows through both halves of the inductor-transformer winding, then the currents collide at the midpoint and branch again in the direction of the traction substation. Correct installation of devices ensures that traction current does not affect the equipment.
Choke transformer DT 1000
Such a device is designed for a 1000 A traction current through each section of a new winding. On average, the output of the winding is 2000 A.
The range of operating temperatures of the device is from minus 50 to +45 degrees.
The transformation coefficient in the given model can be 40, 23, 17. Overall dimensions: 670 x 480 x 380 mm. The mass of the DT 1000 throttle transformer is 157 kg (± 3 kg).
Throttle Analogs
Most are dimensional. In order to save the parameters and at the same time reduce the area of the inductor, the coil is replaced with a semiconductor stabilizer. The result is an electronic choke.
The choke-transformer device is able to stabilize voltage fluctuations and reduce its ripple.
Important! Since the inductor is a semiconductor device, it cannot be used in high-frequency devices.
Throttle calculation
The choke-transformer calculation methods use fuzzy logic methods, neural networks, La Grange resolution, etc. Modern programs allow you to calculate the necessary parameters of the device in just a few minutes. The whole calculation process consists of the following steps:
- The necessary data are entered (points of the magnetization curve, core material, etc.).
- Further, the program provides data on the magnetization curve, corrects values and errors.
- The system calculates the geometric parameters of the core model.
The air gap in the device can be calculated independently, using the formula:
L • I 2 / V, where:
L is the inductance of the inductor winding, GN;
I is the strength of the direct current passing through the winding, A;
V is the volume of the iron core.
The value of ∂, which is necessary to calculate the clearance of the steel core, is found from a special nomogram.
For example, under the conditions that L = 20 H, I = 60 mA, V = 40 cm 3 , then
L • I 2 / V = 10 • 3600 • 10-6 / 40 = 9 • 10 -4 .
The nomogram determines the value ∂ = 20 • 10-3 = 0.2 mm.
Based on this, the gap on each side should be 1 mm.
How to make a throttle yourself
In order to independently make a transformer from the inductor, it is necessary to calculate the number of turns per volt for the existing core. Then the inductor is carefully disassembled and the winding process of the future transformer is performed. When assembling, it should be borne in mind that the gap that was present in the throttle before disassembly should be eliminated.
You can also make a transformer from chokes. The amount of material used depends on the purpose of the invention.
Choke Transformer Replacement Process
Reinstalling and removing the throttle transformer is performed in the following order:
- After obtaining permission to conduct work, the power supply is removed.
- Next, the protective cover is dismantled.
- After carrying out the above operations, isolate the cable entry pipe from the ground and clean the cable supply.
- Next, the nuts of the mounting bolts are unscrewed and the cover of the cable rack is removed.
- Then the cable cores are disconnected and the cable is pulled out of the insulating pipe rack.
Installing electric traction connectors bypassing is performed in the following order:
- One connection of the throttle plug-rail and the rail on both sides of the insulating joints is dismantled, for which on each of them it is necessary to unscrew and remove the lock nut, unscrew the nut to the end of the thread, knock the plug out of the rail, disconnect the jumper from the rail.
- Install plug connectors in openings. Screw nuts on them and fasten them all the way.
Installation and installation of the inductor-transformer is carried out in the reverse order to dismantling.
Important! Before installation, you should carefully read the instructions and the procedure for the work. It is necessary to take into account the installation location of the throttle (at the supply end or in sections), depending on its type and purpose.
Work safety
When installing a line reactor choke-transformer, you must adhere to the rules of safety and labor protection:
- Work is carried out by a team, one of whose members is required to monitor the movement of trains. Before carrying out work, a safety training should be given.
- The throttle transformer at the end of the rail circuit from which the power is supplied is replaced when the voltage is removed by disconnecting the wires from the transformer winding in the relay cabinet of the signal installation or by removing the arms on the cross tripod of electrical centralization. After the voltage is removed, using measuring instruments, make sure that there is no voltage in the previously disconnected wires. At the place of disconnection from the power supply by the electric current, a prohibition sign “Do not turn it on! People work. ”
- All earthwork is carried out in mittens.
- When carrying out loading and unloading operations, it is forbidden to be in the area of cargo handling.
Important! Before starting work, it is necessary to ensure an uninterrupted circuit of the reverse traction current flow by installing temporary jumpers of the required cross section bypassing the insulating joints.
If a train approaches during work, leave the object in a safe distance in advance and remove the tool.
In urgent cases, it is necessary to provide first aid to the victim, call an ambulance team and report the incident to the head of the site.
Connection of any portable meters to electric circuits that are energized is allowed only if there are special terminals with insulation on the instrument wires.
Naturally, a team that has not undergone special training and safety training is not allowed to work.