Today, people actively use a variety of electrical devices. Some of them operate at sufficiently high voltages, and therefore can be dangerous. High-speed switches are designed just to turn on and off electrical circuits, as well as to automatically disconnect this circuit when a short circuit occurs.
General Description
Now we can safely say that switches of this kind are both switching and protective equipment.
For example, in DC traction networks, where the voltage reaches 3 kV, when a short circuit occurs, the current will sharply increase to 30-40 kA. Naturally, such colossal current strength indicators pose a huge threat to any equipment connected to this network. Most often, these are thermal and dynamic effects, leading to equipment failure.
The difference between the DC circuit and the need for BV
It is important to note here that there is a significant difference between AC and DC circuits, which requires the use of high-speed switches. In the first variant, the current periodically decreases to zero and the arc dies out, while in the second, the current constantly increases until a certain value is reached. Moreover, as practice shows, it takes only a few hundredths of a second for the current to reach its maximum value. This makes turning it off much more difficult. In addition, the DC circuit is usually switched off much earlier than the current reaches its maximum values.
High speed circuit breakers typically have trip limits of 15 to 27 kA. Depending on certain parameters of the circuit itself, such a device will be quite enough to ensure timely shutdown.
Varieties
High-speed switches have a special mechanism that turns off the network. According to the principle of operation of this element, they can be divided into two categories. The first category is devices with a spring disconnect option, where a circuit break is achieved due to the force of powerful disconnect springs. The second category is magnetic spring devices. They also use the force of a spring, but they also add an electromagnetic action to disconnect the circuit.
Besides this, there is another point on which high-speed circuit breakers are divided into categories - the ability to respond tocurrent direction.
In this case, polarized and non-polarized devices are distinguished. The first type is capable of breaking the circuit, provided that the current flows in a certain direction. The second type will open the circuit when a certain current value is reached, regardless of the direction in which it flows directly through the device.
It is worth noting that earlier domestic high-speed automatic switches were produced, which were very popular at traction substations. It is worth adding here that the production of some models of this equipment has already ended, but they are still in operation.
Common patterns
Previously, such types of BV as AB-2/4, VAB-28 and VAB-43 were quite actively produced and used. To date, they are being replaced by such devices as high-speed switches VAB-49 and VAB-50, as well as their various modifications.
However, there is one important detail to note here. The AB-2/4 high-speed DC switch has not been produced for a couple of decades, but is still in active use in various electrical sections with direct current. It is rated for an operating rated current of 2 kA and a voltage of 4 kV.
AB-2/4 device
To mount this device, it has four insulators, which are located on the frame of a special roll-out cart. The design hasmagnetic circuit, which is the main electromagnetic switch. The device of the high-speed switch implies the presence of a special arc chute. In this case, it is represented by a labyrinth-target type and is able to stretch the arc up to 4.5 meters. Its functioning requires a magnetic blow, which in this case develops due to powerful poles located outside on both sides of the chamber.
The wires themselves are not without protection, but are built into a special magnetic circuit. On both sides of such a wire there is a chamber of the magnetic blast coil. At the top, the walls of this chamber diverge somewhat, and here there are also several wedge-shaped partitions interspersed with each other, forming the necessary labyrinth. Thus, it is possible to create a gap of a zigzag type, with the help of which it is possible to stretch the arc.
At the very top of the chamber, the maze breaks. Here are located special flame arresters, which are presented in the form of several packages of thin steel plates. They are designed to cool as well as deionize gases and flames that accompany arcing.
Electrical connection
The function of the quick-acting switch is to open the circuit during a short circuit and turn on / off. For this, the design has two special contact outputs. They are designed to connect the BV to the electrical network. The connection is made via electrical busbars. The design also has a shuntinductive type, which is presented as a package with several steel plates insulated from each other and dressed on a copper bus.
BV has a block of contacts. They are connected to the main contacts located at the bottom of the arc chute. This connection is carried out by a system of rods and levers.
Electromagnetic type switch device
The electromagnetic switch mechanism is located on a special cast iron frame. The mechanism has a magnetic circuit, which is represented by two cast bars with a rectangular cross section. They, in turn, are fastened together by a round rod, and another part is put on it - a holding coil. On one of the bars there is also a U-shaped magnetic circuit. It is represented by several steel plates, each of which is isolated from the other. The magnetic circuit has two rods. The right rod is intended for fastening the closing coil. The left one carries the demagnetizing coil of the main current, in other words, the coil of the automatic circuit breaker. In addition, there is also an additional coil for calibration. It is able to simulate the main coil during instrument setup.
Another beam, in turn, is between the two "cheeks". There is a special axle here for attaching the anchor, which is also assembled from insulated steel plates.
During the rotation of the anchor, there is a gap between it and the beam. On this axis betweencheeks also fixed the lever acting on the moving contacts. To act on the lever, there is a special opening spring that pulls it to the right. The lever, in turn, is connected to the demagnetizing coil by means of a flexible conductor made of copper foil. Parallel to the same coil, the inductive shunt is turned on.
The switch also has a fixed contact, which is connected in series to the magnetic blowing coil. To connect to an external circuit, the BV has two output contacts.
Turn on the device on the example of VB-11
It is worth noting that the equipment is switched on in two steps. After turning on the device, pressing the VU button, voltage is supplied through the 20 A wire to the holding coil. During the flow of current through this element, a flux will be created, which is usually denoted by the letter F. However, it is weakened. This is due to the fact that it closes through the air gap between the poles of the electromagnet, since the armature is still not pressed against the poles.
Return protection
Circuit breakers have a "protection return" button, after pressing which the electrical power supply to the valve starts. At the same time, compressed air begins to flow into the pneumatic drive cylinders. The piston of one of the cylinders will rise, turning the rod clockwise. This will stretch the opening spring. Due to the fact that together with the pull upthe rods also move, the magnetic circuit will rotate around the axis, but already counterclockwise.
Together with the movement of the first piston, the second one also moves, moving down, under the influence of compressed air. The piston has a pusher, which, when moved down, will act on the contact lever and anchor. It will carry out the rotation of the armature until it is pressed against the poles of the electric magnet. At the same time, there is still a gap between the main contacts. This is due to the fact that the further travel of the contact lever is limited by the magnetic circuit turned towards it. After that, the holding current, previously designated as F, will increase as it passes through the anchor, thereby holding it firmly.
After that, the "protection return" button is released, and almost the entire system returns to its original position, except for the armature, which remains tightly pressed to the poles. The magnetic circuit will be released and will begin to turn clockwise until it closes the main contacts.
BVP-5 high-speed circuit breaker
Like other types of this device, this one is designed to break the circuit and protect it from short circuit. As for the design, there are several main parts: housing, pneumatic type drive, KU, electromagnetic type holding device, arc extinguishing system, locking mechanisms.
Before proceeding with the repair of this type of fast-acting circuit breaker, it is necessary to completely loosen the tension of the opening springs. After that you can go toremove air springs. After that, all moving parts of the device will be released from tension and they can be turned in any direction convenient for repair.
As for breakdowns, most often this is contamination of the points of contact between the armature and the magnetic circuit, which can be easily eliminated by simple cleaning. Sometimes it happens that the lever touches the walls of the arc extinguishing chamber.
As for the repair of the arc chute itself, deion gratings, outer walls and its inner partitions are usually removed for this. The grate is disassembled and thoroughly cleaned of carbon deposits and oxides.
Electric Locomotive Quick Breaker
BV are great for turning off traction motors in case of a variety of malfunctions. They are often used on electric locomotives. For example, on ChS2, such a type of BV as 12NS is installed. It has a pneumatic drive, and the structure is composed of such main parts as a carrier frame, an automatic contact type trip relay, an arc extinguishing device, a pneumatic drive, and interlock or auxiliary contacts.
The rated operating voltage of this type of quick-acting circuit breaker is 3kV and the rated current is 2kA.
