Today, people are actively using a variety of electrical devices. Some of them work at sufficiently high voltages, and therefore can be dangerous. High-speed circuit breakers 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 circuit breakers 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 strength will increase sharply to 30-40 kA. Naturally, such colossal indicators of amperage 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, because of which the use of high-speed circuit breakers is required. In the first version, the current periodically decreases to zero and the arc fades, 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. Because of this, turning it off is much more difficult. In addition, usually the DC circuit is disconnected much earlier than the current reaches its maximum value.
High speed circuit breakers typically have tripping limits of 15 to 27 kA. Depending on certain parameters of the circuit itself, such a device will be quite enough to ensure timely disconnection.
Varieties
High-speed circuit breakers have a special mechanism that disconnects the network. According to the principle of action of this element, they can be divided into two categories. The first category is devices with a spring version of tripping, where the circuit break is achieved due to the efforts of powerful breaking springs. The second category is magnetic spring devices. They also use the force of the spring, but they also add electromagnetic interference to disconnect the circuit.
In addition, there is another point on which high-speed circuit breakers are divided into categories - the ability to respond to the direction of the current.
In this case, polarized and non-polarized devices are isolated. The first type is capable of breaking the circuit, provided that the current flows in a certain direction. The second view will open the circuit when a certain current value is reached, not paying attention to the direction in which it flows directly through the device.
It is worth noting that previously domestic high-speed circuit breakers were produced, which were widely used in traction substations. It is worth adding here that the production of some models of this equipment has already been completed, but they are still in operation.
Common models
Such types of explosives as AB-2/4, VAB-28 and VAB-43 were rather actively produced and used earlier. Today, they are being replaced by devices such as high-speed switches VAB-49 and VAB-50, as well as their various modifications.
However, it is worth noting one important detail. The AB-2/4 high-speed DC circuit breaker has not been available for a couple of decades, but it is still in active use in various kinds of electrical areas with direct current. It is designed for a working rated current of 2 kA and for 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 has a magnetic circuit, which is the main electromagnetic switch. The device of a high-speed switch implies the presence of a special arcing chamber. In this case, it is represented by a labyrinth-target type and is capable of stretching the arc to 4.5 meters. For its operation, a magnetic blast is required, which in this case develops due to powerful poles located outside on both sides of the camera.
The wires themselves are not without protection, but are built into a special magnetic circuit. On two sides of such a wire is the magnetic blast coil chamber. At the top of the wall of this chamber diverge somewhat and here are several alternating wedge-shaped partitions, forming the necessary labyrinth. Thus, it is possible to create a zigzag-type gap with which it is possible to stretch the arc.
At the very top of the chamber, the maze is interrupted. There are special flame arresting grilles, which are presented in the form of several packages of thin steel plates. They are intended for cooling, as well as for the deionization of gases and flames, which accompany the appearance of an arc.
Electrical connection
The operation of a high-speed circuit breaker consists in a snarl circuit during short circuit and on / off. To do this, the design has two special contact pins. They are designed to connect the BV to the electrical network. Connection is via busbars. The design also has an inductive type shunt, which is presented in the form of a package with several steel plates isolated 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 arcing chamber. This connection is due to the system of rods and levers.
The device of the electromagnetic type switch
The mechanism of the electromagnetic switch is located on a special cast-type frame made of cast iron. 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 rod of circular cross section, and another detail 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 shaft is designed for mounting the switching coil. The left one carries a demagnetizing coil of the main current, in other words, a coil for automatically disconnecting the circuit. In addition, there is also an additional coil for calibration. It is able to simulate the main turn during the setup of the device.
The other bar, in turn, is located between the two "cheeks". There is a special axis for fixing the anchor, which is also composed of insulated steel plates.
During the rotation of the anchor, a gap remains between it and the beam. A lever acting on movable contacts is also fixed on this axis between the cheeks. To act on the lever, there is a special breaking spring that pulls it to the right. The lever, in turn, is connected to the demagnetizing coil using a flexible conductor made of copper foil. In parallel with the same turn, an inductive shunt is also turned on.
The switch also has a fixed contact, which is connected in series to a magnetic blast coil. To connect to the external circuit, the BV has two output contacts.
Turning on the device using the example of VB-11
It is worth noting that the inclusion of equipment is carried out in two steps. After the device is turned on, by pressing the VU button, voltage is applied via a 20 A wire to the holding coil. During the flow of current through this element, a stream will be created, which is usually indicated 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 anchor is still not pressed to the poles.
Return Protection
Circuit breakers have a “return protection” button, after which the supply of electrical power to the valve begins. At the same time, compressed air begins to flow into the cylinders of the pneumatic drive. The piston of one of the cylinders will rise, turning the thrust clockwise. Because of this, the breaking spring will stretch. Due to the fact that the rods move together with the thrust, 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 downward, under the influence of compressed air. The piston has a pusher, which when moving down, will act on the contact lever and the armature. It will rotate the armature until it is pressed against the poles of an electric magnet. At the same time, there is still a gap between the main contacts. This is due to the fact that the further stroke of the contact lever is limited by the magnetic circuit, turned towards him. After that, the holding flow, previously designated as , will be strengthened, as it passes through the anchor, thereby firmly holding it.
After that, the “return protection” button is released, and almost the entire system returns to its original position, except for the anchor, which remains tightly pressed to the poles. The magnetic core will be released, and will begin to turn clockwise until it closes the main contacts.
BVP-5 high-speed switch
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: a housing, a pneumatic type drive, a control gear, an electromagnetic type holding device, an arc extinction system, and locking mechanisms.
Before proceeding with the repair of a high-speed circuit breaker of this type, it is necessary to completely release the tension of the trip springs. After that, you can proceed to the removal of pneumatic springs. After that, all the 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 pollution of the places of contact of the armature and the magnetic circuit, which can be eliminated simply by ordinary cleaning. Sometimes it happens that the lever is grazed by the walls of the arc extinction chamber.
As for the repair of the arc chamber itself, deion gratings, external walls and its internal partitions are usually removed. The grate is disassembled and thoroughly cleaned of carbon and oxides.
Electric Locomotive Switch
BV are excellent for shutting off traction motors in case of their various malfunctions. They are often used on electric locomotives. For example, on ChS2, this type of BV is installed, such as 12NS. It has a pneumatic actuator, and the design consists of such basic components as a supporting frame, which switches off the automatic contact type relay, an arc extinction device, a pneumatic actuator, and interlocking or auxiliary contacts.
The rated operating voltage of a high-speed circuit breaker for this type of electric locomotive is 3 kV, and the rated current is 2 kA.