Three-phase voltage imbalance method - Database & Sql Blog Articles

Probe current voltage pin 420*4450 head diameter 5.0 over current current and voltage pin

TP-IP4220CZ6 5V 0.35PF breakdown voltage 6V SOT

Shunuo varistor / ESD varistor / product complete / Sunlord first-class agent

Photocoupler

First, the disconnection failure

If one phase is disconnected but not grounded, or the circuit breaker and the isolating switch are not connected, the voltage transformer fuse is blown and the three-phase parameters are asymmetrical. When the previous voltage level line is disconnected, the voltage of the next voltage level shows that the three phase voltages are reduced, one of the phases is lower, and the other two phases are higher but the voltage values ​​of the two are close. When the line of this stage is disconnected, the voltage of the disconnected phase is zero, and the voltage of the unbroken phase is still the phase voltage.

Second, the ground fault

When the line is disconnected and single-phase grounded, although the three-phase voltage is unbalanced, the voltage value does not change after grounding. Single-phase grounding is divided into metallic grounding and non-metallic grounding. Metal grounding, fault phase voltage is zero or close to zero, non-fault phase voltage rises 1.732 times, and lasts forever; non-metallic grounding, ground phase voltage is not zero but decreases to a certain value, the other two phases rise It is less than 1.732 times higher.

Causes of resonance With the rapid development of industry, the nonlinear power load is greatly increased. Some loads not only generate harmonics, but also cause fluctuations and flicker of the supply voltage, and even cause three-phase voltage imbalance. There are two types of three-phase voltage imbalance caused by resonance:

One is the fundamental frequency resonance, the characteristic is similar to single-phase grounding, that is, the voltage of one phase is lowered, and the voltage of the other two phases is increased. It is difficult to find the fault point when looking for the cause of the fault. At this time, the special user can be checked. If it is not grounding, it may be Caused by resonance.

The other is frequency-divided resonance or high-frequency resonance, characterized by a simultaneous increase in three-phase voltage.

In addition, it should be noted that when the air-drop busbar cut-off part line or single-phase ground fault disappears, if a grounding signal occurs, and the one-phase, two-phase or three-phase voltage exceeds the line voltage, the voltmeter pointer hits the head and moves slowly at the same time, or The three-phase voltage alternately rises above the line voltage. In this case, it is generally caused by resonance.