As any electrician knows, theoretical knowledge is crucial. It guides practical experience and forms the foundation for electrical work. Of course, mastering industry terminology is also essential; otherwise, communication with professionals can be quite awkward.
1. Electric Current: The regular flow of free electrons or ions within a conductor under the influence of an electric field is called electric current. The direction of positive charge movement is defined as the positive direction of the current. Electric current is represented by the letter I, and its unit is ampere-ampere (A).
2. Current intensity: A physical quantity that measures the strength of an electric current. The amount of charge passing through the cross-sectional area of a conductor per unit time is the current intensity, represented by the letter I, and conventionally referred to simply as current.
3. Current density: The magnitude of the current passing through a unit cross-sectional area is called current density. The unit is A/mm2.
4. Electric Potential: In an electric field, the work done by the electric field force when a unit positive charge moves from point a to a reference point is called the electric potential of point a relative to the reference point. In theoretical studies, an infinitely distant point is often taken as the reference point for electric potential; in practical engineering, the earth is often taken as the reference point. The unit of electric potential is V.
5. Electromotive force (EMF): The work done by non-electrostatic forces on a unit positive charge as it is displaced from a lower potential to a higher potential is called electromotive force. It is represented by the letter E, and its unit is V.
6. Resistance: A conductor can conduct electricity, but at the same time it resists the flow of current. This ability to impede the flow of current is called resistance, represented by the letter R or r, and the unit is Ω.
7. Resistivity: Also known as resistivity coefficient. It is a physical quantity that measures the electrical conductivity of a material, represented by the letter ρ, and its unit is Ω·m. Its value refers to the resistance of a uniform conductor with a length of 1m and a cross-sectional area of 1mm² at a temperature of 20℃, which is the resistivity of the conductor.
8. Temperature coefficient of resistance: A physical quantity that represents the change in resistivity of a material with temperature. Its value is equal to the ratio of the change in resistivity to the original resistivity when the temperature increases by 1℃. It is represented by the letter d and the unit is 1/℃.
9. Conductivity: The ability of a material to conduct electric current is called conductivity. It is the reciprocal of resistance, represented by the letter G, and its unit is s (Siemens). 10. Conductivity: Also called the conductivity coefficient. It is a physical quantity that measures the electrical conductivity of a material. Its value is the reciprocal of resistivity. It is represented by the letter γ, and its unit is S/m (sieverts per meter).
11. Self-inductance: When the current in a closed circuit changes, the magnetic flux generated by this changing current and passing through the circuit itself changes accordingly, inducing an electromotive force (EMF) in the circuit. This phenomenon is called self-inductance. The proportionality between the magnetic flux passing through the area enclosed by the circuit and the current that generates this flux is called the circuit's self-inductance coefficient, or simply self-inductance. Its value is equal to the EMF caused by the self-inductance when the current changes by one unit per unit time, denoted by the letter L, and its unit is H (Henry).
12. Mutual Inductance: When the current in one of two adjacent coils changes, an induced electromotive force (EMF) is generated in the other coil. This electromagnetic induction phenomenon is called mutual inductance. The resulting induced electromotive force is called the mutual induced EMF. It is represented by the letter M, and the unit is H. Inductance: A general term for self-inductance and mutual inductance.
13. Capacitance: Any two conductors separated by an insulating medium constitute a capacitor. The amount of charge stored on each plate under a unit voltage is called the capacitance of the capacitor, represented by the letter C, and the unit is F (farad).
14. Inductive reactance: When alternating current flows through an inductor, the inductor impedes the flow of alternating current. This effect is called inductive reactance, denoted by XL, and the unit is Ω.
15. Capacitive reactance: When alternating current flows through a circuit with a capacitor, the capacitor has the effect of impeding the flow of alternating current. This effect is called capacitive reactance, denoted by XC, and the unit is Ω.
16. Impedance: When alternating current passes through a circuit with resistance, inductance, and capacitance, the effect of these components in hindering the passage of the alternating current is called impedance.
17. Direct current (DC): Current whose magnitude and direction do not change with time is called direct current. Alternating current (AC): Current whose magnitude and direction change periodically with time is called alternating current.
18. Sinusoidal alternating current: Alternating current that varies with time according to a sinusoidal law is called sinusoidal alternating current. Non-sinusoidal alternating current: Alternating current that does not vary with time according to a sinusoidal law is called non-sinusoidal alternating current.
19. Pulsating direct current: A current whose magnitude changes with time but whose direction remains unchanged is called pulsating direct current.
20. Frequency: The number of times the direction of an alternating current changes within 1 second is called the frequency, represented by the letter f, and the unit is Hz (Hertz).
21. Period: The time required for an alternating current to complete one cycle is called the period, represented by the letter T, and the unit is s (seconds).
22. Instantaneous value: The value of alternating current at any instant is called the instantaneous value, which is represented by lowercase letters, such as i, u, and e, which represent the instantaneous values of current, voltage, and electromotive force, respectively.
23. Maximum value: The maximum amplitude value among instantaneous values is called the maximum value, which is represented by an uppercase letter with the subscript m, such as Im, Um, and Em, which represent the maximum values of current, voltage, and electromotive force, respectively.
24. Effective Value: If the heat generated by an alternating current passing through a resistor for a certain period of time is equal to the heat generated by a direct current passing through the same resistor for the same period of time, then the value of the direct current is called the effective value of the alternating current. In other words, the effective value of the alternating current is the direct current value equivalent to its thermal effect. The capital letters I, U, and E represent the effective values of current, voltage, and electromotive force, respectively.
25. Average value: The average value of alternating current refers to the ratio of the total charge flowing through a circuit over a certain period of time to that period of time. The average value of sinusoidal alternating current usually refers to the average value within the positive half-cycle.
26. Electrical work: The work done by electric current is called electrical work, represented by the symbol W, and the units are J (joule) and kW·h (kilowatt-hour).
27. Electric power: The work done by an electric current per unit time (1s) is called electric power, represented by the symbol P and the unit is W or kW.
28. Instantaneous power: The power at any instant in an AC circuit is called instantaneous power, represented by the symbol Pt, and the unit is W or kW.
29. Active power: The average value of the instantaneous power of a sinusoidal AC circuit over one cycle is called active power, represented by the letter Pa, and the unit is W or kW.
30. Apparent power: The product of the effective values of current I and voltage U is called apparent power, represented by the letters S or Ps, and the unit is V·A or kV·A.
31. Reactive power: In a circuit with inductance or capacitance, during half a cycle, the energy of the power source is converted into the energy of the magnetic field (or electric field) and stored. During the other half cycle, the energy stored in the magnetic field (or electric field) is released and returned to the power source.
It only exchanges energy with the power source without consuming energy. The amplitude of the rate at which energy is exchanged with the power source is called reactive power, represented by the letters Q or Pr, and the unit is var (voltaic) or kvar (kilovar).
32. Power factor: The ratio of active power to apparent power is called the power factor cosφ.
33. Efficiency: Energy is always consumed during conversion or transfer, meaning the output is less than the input. The ratio of output energy to input energy is called efficiency, denoted by the letter η.
34. Phase voltage: In a three-phase circuit, the voltage between a phase line and the neutral line is called the phase voltage. Line voltage: In a three-phase circuit, the voltage between two phase lines is called the line voltage.
35. Phase current: In a three-phase circuit, the current flowing through each phase is called the phase current. Line current: In a three-phase circuit, the current in the three terminal lines is called the line current.
36. Loss electric field: When a charge (or charged body) is introduced into the space around another charged body, it will be subjected to a force, that is to say, an electric field exists around the charged body.
37. Electric field strength: A physical quantity that represents the strength of an electric field. Numerically, it is equal to the force exerted on a unit positive charge at that point, and its direction is the direction of the force on the positive charge. It is represented by the letter E, and its unit is V/m.
38. Breakdown: The phenomenon of a dielectric undergoing violent discharge or conduction under the action of an electric field is called breakdown. Insulation strength is also called breakdown electric field strength.
39. Dielectric constant: A coefficient representing the insulating ability of a material, denoted by the letter ε, with units of F/m. Relative dielectric constant: The ratio of the dielectric constant ε of any material to the vacuum dielectric constant ε0 is called the relative dielectric constant, denoted by the symbol εr.
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