Electric element

An electric element is a structurally completed product manufactured under industrial conditions that is able to perform its functions as part of electrical circuits .

Content

1 Basic parameters of electrical elements
- 1.1 Ratings
- 1.2 Accuracy class
- 1.3 Electric strength
- 1.4 Power
- 1.5 loss
- 1.6 Stability
  - 1.6.1 Temperature effects
  - 1.6.2 Mechanical stress
- 1.7 Reliability
2 See also
3 References
4 Literature

Basic parameters of electric

Nominal Values

Nominal resistance R _n or R _nom .
Nominal capacity C _n or C _nom .
Nominal inductance L _n or L _nom .

Accuracy Class

Tolerance (or accuracy class) characterizes the tolerance of the value from the nominal and is not an indicator of the quality of the electrical element. The series of permissible deviations are described in GOST 9664-61 : ± 5, ± 10 and ± 20 are the most frequently used.

The tolerance limits are indicated as a percentage of the nominal value.

Dielectric Strength

The ability of an element to withstand electrical loads without loss of performance is characterized by the following parameters:

The operating voltage U _slave is the maximum voltage at which, under normal conditions, the element can remain for a guaranteed service life.
Rated voltage U _n
Breakdown voltage or breakdown voltage U _CR is the minimum voltage at which an insulation breakdown occurs.
The test voltage U _isp shows the maximum voltage at which the cell can be for a few seconds to a minute. Used for overvoltage.

Power

The rated power P _n is the maximum allowable power that the element can dissipate during the guaranteed service life under normal conditions . As a rule, this parameter is indicated for resistors , since they are specifically designed to absorb electrical energy.

Losses

Losses exist in any electrical element:

Losses on active resistance .
Dielectric polarization loss due to imperfection of the dielectric.
Loss of resistance worn by various screens , parts cores , etc.
Losses caused by various loads .
The skin effect (surface effect) occurs with alternating current in a rectilinear conductor . It reduces the effective conduction area of the conductor to the annular part of the cross section. It arises due to the divergence of the lines of the magnetic field .
The proximity effect manifests itself in nearby conductors . Due to the mutual electrical interaction between the charge carriers in the conductors (for example, the Coulomb repulsive force between electrons ), the effective cross-sectional area decreases, and the losses increase.

These losses depend on the frequency , the nature of the conductor and on the surface roughness (the path of the current lengthens and the resistance increases). Parameters characterizing the loss:

The loss tangent is tan δ , where δ is the dielectric loss angle. It is determined by the ratio of the active power P _a to the reactive P _p at a sinusoidal voltage of a certain frequency.
Q factor Q. For the coil, it is the inverse of tan δ.

The terms of quality factor and loss tangent are used for capacitors , inductors and transformers .

Stability

Stability of parameters - is the ability of an electric element to maintain its properties when exposed to external factors, such as temperature, mechanical stress ( vibration , shock ), non-standard climatic conditions (elevated temperature , humidity or ambient pressure), etc.

Temperature effects

Temperature effects are divided into reversible and irreversible. A direct change in the characteristics of an element is described by temperature coefficients: TLC shows a change in parameter X with an increase in temperature T by one degree. $\alpha _{X}={\frac {dX}{X{dT}}}$ ${\ displaystyle \ alpha _ {X} = {\ frac {dX} {X {dT}}}}$ .

Temperature coefficient of resistance or TCS

$\alpha _{R}={\frac {dR}{R{dT}}}$ ${\ displaystyle \ alpha _ {R} = {\ frac {dR} {R {dT}}}}$

Temperature coefficient of capacity or TKE

$\alpha _{C}={\frac {dC}{C{dT}}}$ ${\ displaystyle \ alpha _ {C} = {\ frac {dC} {C {dT}}}}$

Temperature coefficient of inductance or TCI

$\alpha _{L}={\frac {dL}{L{dT}}}$ ${\ displaystyle \ alpha _ {L} = {\ frac {dL} {L {dT}}}}$ In addition, you can give an example of an irreversible change in a parameter. Such changes can occur for various reasons, such as aging or a violation of the operating conditions.

TKNE - irreversible change in capacity $TKHE={\frac {dL}{L}}$ ${\ displaystyle TKHE = {\ frac {dL} {L}}}$ ,

where dT is the temperature increment, R is the resistance , C is the capacitance , L is the inductance .

Mechanical Impacts

Mechanical effects on the electrical element lead to catastrophic failures or cause leakage . The ratio of the electric element to mechanical vibrations is characterized by the following properties:

Vibration resistance is the property of an electrical element to withstand the damaging effects of vibration and, after prolonged exposure, retain the ability to perform its functions.
Vibration resistance - the ability of an electric element to perform its functions under vibration conditions. The most dangerous resonance .

Reliability

Reliability is the property of an element to perform all the specified functions for the required time under certain operating conditions, and to save the main parameters within the specified tolerances . Reliability is characterized by:

Warranty period .
The failure rate λ (t) , that is, the ratio of the number of elements n that failed during the time Δt , to the product of the number of elements n that are workable by the beginning of the interval, by the duration of this interval Δt . $\lambda (t)={\frac {\Delta n}{N_{n-1}{\Delta t}}}$ ${\ displaystyle \ lambda (t) = {\ frac {\ Delta n} {N_ {n-1} {\ Delta t}}}}$ To reduce the failure rate, you can use the lightweight mode of operation of the elements.
The likelihood of uptime.

Links

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Literature

GOST 9664-61. The series of permissible deviations of physical quantities.
GOST 12.1.012-90. Vibration safety. General requirements.