Why do we need capacitors? Condenser connection

An electric capacitor is a device that can accumulate charge and energy of an electric field. Basically it consists of a pair of conductors (plates) separated by a dielectric layer. The thickness of the dielectric is always much smaller than the size of the plates. On the electrical circuits of replacement, the capacitor is designated by 2 vertical parallel segments (II).

Basic values and units of measurement

There are several basic values that 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 very much - in practice, almost not applied. For example, the electric charge of planet Earth is only 710 microfarads. Therefore, the electric capacitance of capacitors is in most cases measured in derivatives of Farad values: in picofarads (pF) with a very small capacitance (1 pF = 1/106 μF), in microfarads (μF) at a sufficiently large value (1 μF = 1 / 10 ⁶ F). In order to calculate the electrical capacity, it is necessary to divide the value of the 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 the appliance

One of the most important parameters of the device under consideration is the 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 breakdown of the device does not occur 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 into the network of higher harmonics and overheating of the device.

Appearance of capacitors

The design of capacitors can be very diverse. 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 centers 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.

Constant capacitors

By the nature of the change in electrical capacitance, capacitors are divided into devices with a constant, variable capacitance 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 its conductors and the distance between them. There are several ways to change these settings. 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 factory equipment, for example, to select the capacitance empirically, if calculation is impossible.

Capacitor in the circuit

The device under consideration in the DC circuit conducts the current only when it is turned on (in this case, the charge or charge of the device to the source voltage occurs). 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 characteristics

The capacitor, depending on the state of the electrolyte and the material from which it is made, 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 is 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 the DC circuit is as follows: the plus (anode) of the current source is connected to an electrode that 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 a variable current source, connecting two identical sections in succession in succession. Or apply the oxide layer on both electrodes. Thus, a non-polar electrical appliance is produced, operating in networks with both constant and sinusoidal currents. But in both cases the resultant capacity becomes two times less. Unipolar electric 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 employees of various industrial enterprises and design institutes. Having dealt with the principle of operation, characteristics and physical processes, we will find out why capacitors are needed, for example, in power supply systems? In these systems, batteries are widely used in the construction and reconstruction of industrial plants to compensate for the reactive power of PCM (unloading the network from undesirable 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 CRM: 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 referred to as 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 power lines with voltages above 110 kV, the capacitive conductance to ground is denoted as capacitors. The EP line is due to electrical capacitances between the conductors of different phases and the capacitance formed by the phase conductor and ground. Therefore, the properties of the capacitor are used to calculate the modes of operation of the network, the parameters of the transmission line, and the location of damage to the electrical network.

More about the areas of application

This term can also be heard from railway workers. 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, to smooth the pulsating current produced by rectifiers and pulse interrupters, and to generate a symmetrical sinusoidal voltage used to power the motors.

However, this word is most often heard from the mouth of a radio amateur. 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, you can find a 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.