Why do we need capacitors? Connecting the capacitor
An electric capacitor is a device,which can accumulate the charge and energy of the electric field. Basically it consists of a pair of conductors (plates) separated by a dielectric layer. The thickness of the dielectric is always much less than the size of the plates. On the electric circuit of replacement, the capacitor is designated by 2 vertical parallel segments (II).
Basic values and units of measure
There are several basic values,which determine the capacitor. One of them is its capacity (Latin letter C), and the second - its working voltage (Latin U). The electrical capacity (or simply capacity) in the SI system is measured in Farad (F). And as a unit of capacity 1 farad - this is a lot - in practice, almost never applied. For example, the electric charge of planet Earth is only 710 microfarads. Therefore, the capacitance of capacitors in most cases is measured in terms of derivatives of Farad values: in picofarads (pF) with a very small capacitance (1 pF = 1/106μF), in microfarads (μF) at a sufficiently large value (1 μF = 1/106 F). In order to calculate the electrical capacity, it is necessary to divide the amount of charge accumulated between the plates by the potential difference module between them (voltage on the capacitor). The charge of a capacitor in this case is a charge accumulating on one of the plates of the device under consideration. On two conductors of the device they are identical in modulus, but differ in sign, so the sum of them is always zero. The charge of the capacitor is measured in pendants (Кл), and is designated by the letter Q.
Voltage on an electrical appliance
One of the most important parameters of theThe device is a breakdown voltage - the difference in the potentials of the two conductors of the capacitor, which leads to an electric breakdown of the dielectric layer. The maximum voltage at which the device does not break down is determined by the shape of the conductors, the properties of the dielectric and its thickness. Working conditions, in which the voltage on the electrodes of the appliance is close to the breakdown, are unacceptable. The normal operating voltage on the capacitor is less than the breakdown voltage several times (two or three times). Therefore, when selecting, attention should be paid to the rated voltage and capacity. In most cases, the value of these values is indicated on the device itself or in the passport. The inclusion of a capacitor in the network for a voltage exceeding the nominal one, threatens its breakdown, and a deviation of the value of the capacitance from the nominal can lead to the release of higher harmonics into the network and overheating of the device.
Appearance of capacitors
The design of capacitors can be itselfdiverse. It depends on the value of the electrical capacity of the device and its purpose. The parameters of the device in question should not be affected by external factors, so the plates have a form in which the electric field created by electric charges concentrates in a small gap between the conductors of the capacitor. Therefore, they can consist of two concentric spheres, two flat plates or two coaxial cylinders. Consequently, the capacitors can be cylindrical, spherical and flat, depending on the shape of the conductors.
By the nature of the change in the electrical capacityCapacitors are divided into devices with a constant, variable capacity or trim. Let us examine each of these types in more detail. Instruments whose capacitance does not change during operation, that is, it is constant (the value of the capacitance can still fluctuate within the permissible limits depending on the temperature), are permanent capacitors. There are also electrical appliances that change their electrical capacity in the process of work, they are called variables.
What determines C in the capacitor
The electrical capacity depends on the surface area of itconductors and the distance between them. There are several ways to change these parameters. Consider a capacitor, which consists of two types of plates: movable and fixed. Movable plates move relatively fixed, resulting in a change in the capacitance of the capacitor. Analog variables are used for analog device settings. And the capacity can be changed during operation. Trim capacitors in most cases are used to adjust the plant equipment, for example, to select the capacitance empirically when calculation is impossible.
Capacitor in the circuit
The device in the DC circuitconducts a current only at the moment of its inclusion in a network (thus there is a charge or a recharge of the device to pressure of a source). Once the capacitor is fully charged, no current flows through it. When the device is turned on in an alternating current circuit, the discharge and charging processes alternate with each other. The period of their alternation is equal to the period of oscillation of the applied sinusoidal voltage.
Capacitor depending on the stateelectrolyte and the material from which it consists can be dry, liquid, oxide-semiconductor, oxide-metal. Liquid capacitors are well cooled, these devices can operate under heavy loads and have such an important property as self-healing of a dielectric in breakdown. The considered dry type electrical devices have a simple design, a little less voltage loss and leakage current. At the moment, it's dry appliances that are most popular. The main advantage of electrolytic capacitors are cheapness, compact dimensions and high electrical capacitance. Oxide analogs are polar (incorrect connection leads to breakdown).
How to connect
Connecting the capacitor to a circuit with a constantcurrent occurs as follows: plus (anode) current source is connected to the electrode, which is covered with an oxide film. In case of non-compliance with this requirement, a breakdown of the dielectric may occur. It is for this reason that the liquid capacitors need to be connected to a circuit with an alternating current source, connecting two identical sections in succession in succession. Or apply the oxide layer on both electrodes. Thus, we obtain a non-polar electrical appliance operating in networks with both constant and sinusoidal currents. But in both cases the resultant capacity becomes two times less. Unipolar electrical capacitors have significant dimensions, but can be included in circuits with alternating current.
The main application of capacitors
The word "condenser" can be heard from employeesvarious industrial enterprises and design institutes. Having dealt with the principle of operation, characteristics and physical processes, will we find out why capacitors are needed, for example, in power supply systems? In these systems, batteries are widely used in construction and reconstruction in industrial plants to compensate for the reactive power of MRC (unloading the network from undesirable power flows), which reduces energy costs, save on cable products and deliver the best quality to the consumer. The optimal choice of capacity, method and location of connection of reactive power sources (Q) in the networks of electric power systems (EPS) has a significant impact on the economic and technical performance indicators of EPS. There are two types of IRM: transverse and longitudinal. With transverse compensation, the capacitor banks are connected to the buses of the substation in parallel with the load and are called shunt (SHBK). With longitudinal compensation, the batteries are cut into a power transmission line and are called CPC (longitudinal compensation devices). Batteries consist of separate devices that can be connected in various ways: serial or parallel capacitors. Increasing the number of devices connected in series increases the voltage. CPCs are also used to equalize the loads in phases, increase the productivity and efficiency of arc and ore-thermal furnaces (with the inclusion of CPC through special transformers).
On substitution schemes for transmission lines withvoltage above 110kV capacitive conductivity on the ground is denoted as capacitors. The EP of the line is due to the electrical capacitances between the conductors of different phases and the capacitance formed by the phase conductor and the earth. Therefore, the properties of the capacitor are used to calculate the operating modes of the network, the parameters of the transmission lines, and the location of the damage to the electrical network.
More about the areas of application
This term can also be heard from employeesrailways. Why do we need capacitors for them? On electric locomotives and diesel locomotives, these devices are used to reduce the sparking of contacts of electrical apparatuses, smoothing the pulsating current produced by rectifiers and pulse choppers, and to generate a symmetrical sinusoidal voltage used to power the motors.
However, this word is most often heard from the mouthradio amateurs. Why do we need capacitors for it? In radio engineering they are used to create high-frequency electromagnetic oscillations, they are part of smoothing filters, power supplies, amplifiers and printed circuit boards.
In the glove box of every car enthusiast can be founda couple of these electrical appliances. Why do we need capacitors in a car? There they are used in amplifying equipment of acoustic systems for high-quality reproduction of sound.