Can elevators and escalators be powered by three-phase four-wire system?

Three-phase and four-wire power supply for elevators and escalators is strictly impossible at present, but elevators installed in earlier years are used. Most of them have also been changed to three-phase five-wire system.

Three-phase five-wire system includes three-phase wires (A, B and C wires) and neutral wires (N wires) of three-phase electricity; And a ground wire (PE wire).

The neutral line (N line) is the zero line. When the three-phase load is symmetrical, the sum of the current vectors flowing into the neutral line of the three-phase line is zero, but for the single phase, the current of the neutral line (N line) is not zero. When the three-phase load is asymmetric, the sum of neutral line current vectors is not zero, and the voltage to ground will be generated.

Three-phase five-wire system is divided into TT grounding mode and TN grounding mode, in which TN is divided into TN-S, TN-C and TN-C-S.

TT grounding mode:

The first letter T indicates that the neutral point of the power supply is grounded, and the second letter T indicates that the metal shell of the equipment is grounded. This method is widely used in high-voltage systems, but it is not suitable when there are large-capacity electrical appliances in low-voltage systems.

TN-S grounding mode:

The letter S stands for separating N from PE, connecting the metal shell of equipment with PE, and connecting the neutral point of equipment with N. ..

Its advantage is that there is no current in PE, so the metal shell of the equipment has zero potential to ground. It is mainly used for data processing, precision detection and power supply system of high-rise buildings.

TN-C grounding mode:

The letter C indicates that N and PE are merged into PEN, which is actually a four-wire power supply mode. The neutral point and metal shell of the equipment are connected with N. Because there are three-phase unbalanced currents and harmonic currents flowing when N is normal, the metal shell of the equipment has a certain voltage to the ground when N is normal, which is generally used in general power supply places.

TN-C-S grounding mode:

N part is separated from PE, which is a four-wire and half-system power supply mode. Used in places with poor environment.

When n and PE are separated, they are not allowed to merge again.

For elevators and escalators, three-phase five-wire TN-S power supply mode is adopted now.