The two connection modes of box transformer do not need neutral wire. Why not create neutral wire? Today I will give you a brief introduction.
(1) The box-type transformer has no neutral line, because the sum of the electric vectors at any time is zero. The box-type transformer nameplate has specified star connection and delta connection. In my country, box-type transformers below 3kW use star-type connection, and box-type transformers above 3kW use delta connection, which cannot be wrongly connected. Even if the neutral wire is connected, there is no current, so the box-type transformer has no neutral wire.
(2) The reason why the box-type transformer has no neutral line is because the voltage between the neutral line and the phase line is 220V, and the required voltage of the box-type transformer is 380V, so the box-type transformer must be connected to the power line instead of the neutral line.
Box-type transformer
(3) The function of shell grounding is to prevent some phase insulation from being damaged and the shell is electrified and causing electric shock accidents. The box-type transformer nameplate has specified star connection and delta connection. In my country, box-type transformers below 3kW use star-type connection, and box-type transformers above 3kW use delta connection, which cannot be wrongly connected.
(4) But don’t use the same grounding wire of the transformer as the ground wire of the box transformer, because the grounding wire of some transformer manufacturers with heavier moisture may age and break for a long time. In the past, there was a case where a factory burned several devices at the same time, and there was a phenomenon that the main board of the device was sparked by strong electricity, and the main board was burned. After investigation, it was found that due to the leakage of a box-type transformer, the ground wire of the factory happened to be rusted and disconnected. The ground wire of the strong current passer is reversed like the main board of the device. So there is a separate grounding point, do not share the grounding wire with the box-type transformer.
(5) In the TN-S system, the metal shell of electrical equipment such as box-type transformers should be grounded, that is, PE wire! A power supply system cannot be grounded and connected to the neutral line again! At the end of the TN-S system, the voltage difference between the neutral line and the ground line may reach ten volts or even higher due to unbalance and the influence of the third harmonic.
(6) The wiring methods of box-type transformers are: delta connection and star connection. △ represents the delta connection method, which is to short-circuit the upper and lower terminals in the junction box to obtain three pairs of electrodes, and then connect them to the live wires respectively. Means the star connection method, that is, short-circuit the upper three terminals in the junction box, and connect the lower three terminals to the live wires respectively.
