Part I Basic knowledge of electrotechnics
A. the circuit basis
1. Circuit: All paths through which current flows are called circuits. It is a group of electrical devices or devices. The
2. Power supply: A device that provides power or electrical signals in the circuit. The
3. Load: Devices that absorb energy or output signals in a circuit are called loads. 4. Excitation: The current or voltage of a power supply is called an excitation function or stimulus. 5. Response: The current or voltage on the load is called the response. The
6. Circuit Components: The idealized model of a circuit device is called a circuit element.
7. Capacitance element: Has the property of storing or releasing electric field energy, ie, the electric field effect.
8. Inductor: It has the property of storing or releasing magnetic energy, ie magnetic field effect. The
9, Voltage: The difference between the two potentials in the circuit is called the potential difference, or voltage.
10. Kirchhoff's law includes current law (KCL) and voltage law (KVL). The
11. Kirchhoff's (first law) current law (KCL): For any node in any circuit, the algebraic sum of all branch currents flowing out of that node is zero at any instant. The
12. Kirchhoff (second law) voltage law (KVL): For any closed loop in any circuit, the algebraic sum of all branch voltages flowing out of the closed loop is zero at any instant.
13. AC circuit: Circuits in which the current or voltage changes in size or direction over time are called AC circuits. The
14, sinusoidal AC circuit: current or voltage in accordance with the sine law changes the circuit called sinusoidal AC circuit. The
15, the maximum value (amplitude): the magnitude and direction of the sinusoidal current or voltage instantaneous value changes with time, the maximum range of amplitude changes is called the maximum or amplitude. The
16. Period: The sine function is a periodic function. The time required to repeat changes once is called the period. The period is denoted by T and the unit is seconds (s). The
17. Frequency: The reciprocal of the period is called frequency. The frequency is denoted by f, and the unit is Hertz, referred to as Hz. The
18, corner frequency: sinusoidal current changes a period, the change of the amplitude of 2 radians, the number of arcs per unit time change in the number of 2 / T, called the corner frequency. Expressed in radians in radians per second. =2f=2/T. The
19. Phase: The amplitude of the sinusoidal current (t+i) is called the sine phase. Phase is a function of time and represents the progression of sinusoidal changes. The phase i at t=0 is called the initial phase of the sine. The
20, the three elements of the sine quantity: the amplitude of the sine wave, the angular frequency (or frequency) and the initial phase are the three basic parameters that determine the sine quantity, and are the basis for comparing and distinguishing each sine quantity. Elements. 21. The difference between the two sinusoidal phases is called the phase difference. The phase difference of the same frequency sine is equal to the difference of the initial phase. It is independent of t and t. That is, the phase difference is a constant.
21. The difference between the two sinusoidal phases is called the phase difference. The phase difference of the same frequency sine is equal to the difference of the initial phase. It is independent of t and t. That is, the phase difference is a constant.
22, sinusoidal current, voltage or electromotive force, their instantaneous value changes with time, it is equal to the maximum only at certain moments. In order to measure the ability of sinusoids to do work, it is usually not the maximum or instantaneous value, but the effective value. The calculation value of the effective value I of the sinusoidal current is to first square the instantaneous value of the current i, then take the average value in one cycle, and finally take the square root of it, so the effective value is also called the square root value. It can be seen that the meaning of the effective value is that the periodic current is the same as the direct current that is numerically equal to the effective value. The
23, three-phase electromotive force: Three-phase sinusoidal electromotive force, its frequency is the same, the amplitude is equal, and the initial phase differs 120 degrees successively, call symmetrical three-phase electromotive force.
24, phase sequence: The order in which the three-phase electromotive force reaches the maximum or zero value, or the order from the leading phase to the lagging phase is called the phase sequence. The
25, three-phase circuit connection: usually three-phase circuit, either power or load, can be connected into a star or triangle.
26. In a star-connected three-phase four-wire system, the voltage between the end-line and mid-line of each phase is called the phase voltage, and the voltage between the end-line and the end-line is called the line voltage. And the effective value of the line voltage is 3 times of the effective value of the phase voltage.The line voltage phase is ahead of the corresponding phase voltage by 30 degrees.
27. In a star-connected three-phase four-wire circuit, the current flowing through each phase of the power supply or load is called a phase current, and the current flowing through each terminal is called a line current. And the phase current is equal to the line current.
28. In a delta-connected circuit: the line voltage is equal to the phase voltage; when the phase currents are symmetrical, the line current is also symmetrical. And the effective value of the line current is 3 times of the effective value of the phase current. The phase of the line current lags the phase current by 30 degrees.