In electrical engineering, active and reactive resistance is usually called a value that characterizes the reaction force section of the electric circuit directed (ordered) movement of particles or quasiparticles - carriers of the electric charge. This opposition is formed by converting electricity into other forms of energy. In the event of an irreversible change in the electrical energy of a chain link into other types of energy, the reaction will be active.
Content
- Feature of active and reactive resistance
- Electrotechnical law of reactance
- Electrical impedance
Feature of active and reactive resistance
An alternating current network has an irreversible transformation and transfer of energy to the elements of an electrical circuit. By exchanging electricity with circuit components and a power source, the resistance will be reactive.
If we consider a microwave oven as an example, electrical energy in it is irreversibly converted into heat, as a result of which the microwave oven receives active opposition, as well as elements that transform electrical energy into light, mechanical, etc. etc.
The alternating current, passing through the lumped electrical elements, forms reactance, which is mainly caused by inductance and capacitance.
Active resistance is in direct proportion to the number of complete cycles of change in the electromotive force (EMF) that occurred in one second. The larger this amount, the higher the active resistance.
However, many consumers have inductive and capacitive properties at the time of the passage of alternating current through them.. These include:
- capacitors;
- chokes;
- electromagnets;
- transformers.
It is necessary to take into account both active and reactive resistance, which is due to the presence of a capacitive and inductive characteristic in an electrical consumer. Interrupting and closing the DC circuit passing through any of the windings in parallel with the current conversion there will also be a change in the magnetic flux inside the winding itself, as a result, an electromotive force appears in it self-induction.
A similar situation will manifest itself in the winding.connected to a circuit with alternating current, with the only difference that in this case the current continuously changes both in parameter and in direction. Hence, it follows that the parameter of the magnetic flux penetrating into the winding, in which the electromotive force of self-induction is induced, will continuously change.
At the same time, the vector of the electromotive force is invariably such that it prevents the conversion of the current. Consequently, with an increase inside the winding, the electromotive force of self-induction will set its the purpose of stopping the increase in the current, and when decreasing - on the contrary, it will try to keep the decreasing current.
It turns out that the EMF that appears inside the conductor (winding) involved in the AC circuit will constantly oppose the current, preventing it from changing. In other words, EMF can be regarded as an auxiliary resistance, which, together with an active the resistance of the coil creates a synergistic effect of counteraction against the alternating current passing through the coil current.
Electrotechnical law of reactance
The formation of reactive resistance occurs with the help of a drop in reactive power consumed to create an electromagnetic field in the electrical circuit. The drop in reactive power is formed by connecting a device with an active resistance to the converter.
A two-terminal device connected to the circuit turns out to accumulate only a limited fraction of the charge until the voltage polarity changes to the diametrically opposite. Thanks to this, the electric current does not drop to zero, as in DC circuits. The accumulation of charge by a capacitor directly depends on the frequency of the electric current.
The formula for reactance is the imaginary part of the impedance:
Z = R + jX, where Z - complex electrical resistance, R - active electrical resistance, X - reactive electrical resistance, j - imaginary unit.
The magnitude of the reactive electrical resistance can be expressed through the values of the capacitive and inductive resistance.
Electrical impedance
The impedance of an alternating current circuit, or impedance, is a reflection of the current transformed over time. In electrical literature, it is designated by the Latin letter Z. Impedance is a two-dimensional (vector) quantity that includes two independent scalar one-dimensional characteristics: active and reactive resistance to alternating electric current. Simply put, impedance is the total resistance and the reactance.
The active impedance component, denoted by the letter R, is a measure of the level at which a material resists the flow of negatively charged particles among its atoms. Low-resistance materials are considered to be:
- gold;
- silver;
- copper.
High-resistance materials are called dielectrics or insulators. The list of such materials includes:
- polyethylene;
- mica;
- plexiglass.
Substances with an intermediate degree of resistance are classified as semiconductors. This group includes:
-
metal oxides; - sulfur compounds;
- compounds with selenium;
- chemical elements (arsenic, germanium, phosphorus, silicon, sulfur, tellurium, carbon, galen, etc.).
The impedance is calculated by the formula: Z = √ R2 + (XL - XC)2, where: R - active electrical resistance; XL - inductive reactance, unit of measurement Ohm; XC is the capacitive reaction, the unit of measurement is Ohm. The total resistance is calculated step by step. First, a diagram is drawn, then equivalent resistances are calculated individually for the active, inductive and capacitive components of the load, and the total resistance of the electrical circuit is calculated.
