With the continuous development of technology, on-site wiring detection equipment is becoming increasingly advanced, and many types of equipment have the function of displaying vector graphics, such asThree phase presentField verificationceremonyThe emergence of these devices has saved a lot of energy for on-site wiring personnel and provided convenience for daily work, improving work efficiency. However, in order to understand phasor diagrams, it is necessary to understand the drawing method of phasor diagrams.
To draw a phasor diagram for wiring, it is necessary to first draw a wiring diagram based on the on-site wiring, and then draw a phasor diagram for modifying the wiring based on the wiring diagram.
We need to use the correct wiring of a three-phase three wire inductive load as an example to draw a phasor diagram. The method and steps are as follows.
1. Draw a wiring diagram
Draw the correct wiring diagram, as shown in Figure 1-6.
Select coordinate points and draw phase voltage phasor
Due to the fact that three-phase AC power is generated by a three-phase generator, and the voltage generated by the three-phase windings of the generator is 120 ° different from each other in space, the phasor of the three phase voltages of three-phase AC power is also 120 ° different from each other.
We draw the phasor of phase b and c based on the phasor of phase a voltage. First, draw a vertical line representing Ua; as Ub lags behind Ua by 120 °, rotate it clockwise by 120 ° to draw the phasor of Ub; Due to Uc lagging behind Ua by 240 °, Ua rotates clockwise by 240 ° to draw the phasor of Uc, as shown in Figure 1-7
3. Draw voltage phasor
From the wiring diagram, it can be seen that the line voltage applied to the first component is Uab, and the voltage applied to the second component is Ucb. Draw the phasor of Uab and Ucb according to the parallelogram rule, Uab=Ua-Ub=Ua+(-Ub）,Ucb=Uc-Ub=Uc+(-Ub), As shown in Figure 1-8.
4. Draw current phasor
Draw the phasor of current based on voltage phasor.
The current of the inductive load lags behind the voltage, so the current phasor of the first component is based on Ua, rotated clockwise by €, and the phasor of Ia is drawn; The current phasor of the second component is based on Uc. Rotate € c clockwise and draw the phasor of Ic, as shown in Figure 1-9.
5. Mark the phase angle based on known conditions
Connect the line voltage phasor and current phasor of the first component with a curved line, and mark their angle of 30 °+€ a (because the angle between Uab and Ua is 30 °, the angle between Uab and Ia is 30 °+€ a). Connect the line voltage phasor and current phasor of the second component with a curved line, and mark the angle of 30 ° - € c * (because the angle between Ucb and Uc is 30 °, the angle between Ucb and Ic is 30 ° - € c), as shown in Figure 1-10.
After completing the five steps, the phasor diagram for changing the wiring method is drawn, and its phasor diagram is shown in Figure 1-10