Cause of single-phase voltage fluctuation in low-voltage lineBased on context alone
The single-phase voltage fluctuation of low-voltage lines mainly has the following reasons:
** 1. Power Source Side **
1. ** The generator output is unstable **
- The speed fluctuation of the generator will affect the frequency and magnitude of the output voltage. For example, when the speed governing system of the generator's prime motor (such as a steam turbine or a water turbine) fails, the speed may change. If the rotation speed increases, according to the formula [E = 4.44fN 'Phi]([E] is the induced EMF,[f] is the frequency,[N] is the number of coil turns, and [Phi] is the magnetic flux), the frequency [f] increases, and the induced EMF [E] also increases, causing the output voltage to fluctuate.
2. ** Transformer problem **
- The tap setting of the transformer was unreasonable. If the tap position of the transformer was not selected properly, for example, when the voltage needed to be increased, the tap was set to the step-down position, which would cause the output voltage to deviate from the rated value and cause voltage fluctuations.
- Transformer malfunction. If the winding was short-circuited, it would change the equivalent induction and resistance of the transformer, thus affecting the voltage output. After a turn-to-turn short circuit, the short-circuit winding's inductivity will decrease. According to U = L_frac{di}{dt}_(U_is the voltage, L_is the inductivity, I_is the current, and t_is the time), the voltage will decrease under the condition that the current rate of change is constant. Due to the unstable state of the short-circuit fault, the voltage will fluctuate.
** 2. Load-side factor **
1. ** Connection and removal of high-power single-phase load **
- When high-power single-phase equipment (such as large welding machines, single-phase electric furnaces, etc.) suddenly connected to the low-voltage line, it would cause a sudden increase in the line current. According to the value of U = IG (U = IG)(U = voltage, I = current, and R = line resistance), the voltage drop on the line will increase, causing the voltage at the load to decrease. When these devices were suddenly removed, the current would decrease rapidly, and the voltage would rise again, causing voltage fluctuations.
2. ** Unbalanced load **
- In a three-phase four-wire low-voltage system, if the three-phase load was seriously unbalanced, there would be a current flowing through the neutral wire. When there is resistance in the neutral line, there will be a voltage drop of U_N = I_NRN (U_N is the neutral line voltage drop, I_N is the neutral line current, and R_N is the neutral line resistance), which will cause the single-phase voltage to fluctuate. For example, if a certain phase is overloaded, the voltage of that phase will decrease, and the voltage of the light-loaded phase will increase.
** 3. Route factor **
1. ** Line Resistance **
- The aging of the line or the small diameter of the line will increase the resistance of the line. When the load current passes through, according to U = IG, a large voltage drop will occur. As the load current changed, the voltage drop would also change, causing voltage fluctuations.
2. ** Line inductivity and capacity **
- Long-distance low-voltage lines had the effect of inductance and capacity. When the current in the circuit changed, the inductors would generate an induced electromagnetic force to hinder the change in the current, and the condensers would charge and discharge. These processes would cause fluctuations in the line voltage. For example, in some rural long-distance low-voltage power supply lines, the influence of this kind of inductance and capacity may be more obvious.
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