Problems with transformers and AC live wires

Single-phase transformer, current direction: transformer live wire terminal live wire electrical appliances neutral line transformer neutral terminal internal winding transformer live wire... Generally speaking, the neutral line of the transformer should be grounded, and under normal circumstances, according to Kirchhoff's law, the current is circulating in the above circuit.

Three-phase transformer, the neutral line comes back to the neutral point of the three-phase winding, the general neutral point is grounded, the potential is zero, and the three-phase voltage and current vector sum are zero under the balanced load state.

Sorry, let's sort out the idea of what is going on.

1. In physics, we theorem that the direction of the current flows from positive to negative is positive, and the opposite direction theorem is negative. These are all man-made theorems.

2. The same is true in alternating current. What we usually say is 220V for mains power (231V for transformer no-load low-voltage output voltage) which is the RMS, not the peak. He operates at a frequency of 50 Hz.

Oscillates 50 times per second according to the sine wave, and the time to complete the up and down oscillation of a sine wave is 1 50 = seconds (a 360-degree cycle is completed from an electrical point of view), and half a wave is a second. And there are 50 times per second when the voltage crosses the maximum positive value, crosses the zero value, and crosses the maximum negative value. Is that so?

3. If the load at this time is purely resistive, then the current direction is consistent with the voltage, the voltage crosses zero, and the current also crosses zero. In the case of a pure inductor (or capacitor), the electrical angle of the current direction hysteresis (or leading) voltage is 90 degrees. In other words, when the voltage crosses zero, the current is at the maximum.

4. There must be a circuit if there is voltage, so that the current can circulate. It doesn't matter if it's made up of a live wire and a ground wire (or neutral wire), or if it is made up of two live wires that are not in phase.

5. You start from the microscopic level, and the theorem is that the current flows from a high potential to a low potential (and only when it is purely resistive). I can also theorem that the current flows from a low potential to a high potential, and that's what happens with pure inductors.

6. From a macro perspective (engineering). Are we only concerned about whether this current has done work? How much merit does he produce?

How much reactive power there is. No matter how the current flows, as long as he does the work. In other words, it is possible to flow from the zero line (or ground wire) to the fire line!

Therefore, the voltage and current values we usually talk about are effective values, not peak values and average values.

If you don't score, it doesn't matter, you can cancel the question after you read it, and discuss it again if there are still questions.

The third is that the construction is wrong, and the live wire of the upper level is connected to the neutral line position of the distribution cabinet. Solution: 1. First of all, you need to use a multimeter to measure the voltage between the three-phase live wire, and about 380 volts is normal.

2. Then disconnect the load to measure the voltage of the ground wire and the neutral line, if the voltage is 0, it means that the neutral line between the distribution cabinet and the load is broken. 3. If the voltage of the neutral line and the ground wire is 220 volts after disconnecting the load, it is said that the neutral line of the distribution cabinet is incorrect, and the neutral line needs to be re-distributed.

The neutral line "changes" into a live wire for the following reasons: first, because the electrical cabinet is connected with a load; The second is because the neutral line is not connected with the neutral line of the upper level of the distribution cabinet. The third is that the construction is wrong, and the live wire of the upper level is connected to the neutral line position of the distribution cabinet.

Solution: 1. First of all, you need to use a multimeter to measure the voltage between the three-phase live wire, and about 380 volts is normal. 2. Then disconnect the load to measure the voltage of the ground wire and the neutral line, if the voltage is 0, it means that the neutral line between the distribution cabinet and the Xiaojing load is broken.

3. If the voltage of the neutral line and the ground wire is 220 volts after disconnecting the load, it is said that the neutral line of the distribution cabinet is incorrect, and the neutral line needs to be re-distributed.

This is because the neutral line is broken in the middle. The live wire passes through the electrical equipment, because there is no circuit, which causes the zero line to become the live wire. At this time, it is necessary to carefully find the location of the broken zero line, and then connect the zero line to return to normal.

Otherwise, due to or the absence of a circuit, the electrical appliances will not work normally. Special attention must also be paid to the fact that the hand must not touch the zero line, once it touches the zero line, it will cause a circuit and there is a risk of electric shock.

The reason why both the live wire and the neutral line become the live wire is that the neutral wire is short-circuited and no loop is formed. So the neutral line is also electrified.

Both the line of fire and the line of neutral become the line of fire. That's one of the most common types of circuit failures. i.e. the zero line is broken somewhere.

Because the neutral line will be fired when it is broken, the main reason is that all the negative attendants of the circuit circuit are not disconnected. The electrical appliance is equivalent to the load in the circuit, and if it is not disconnected, the leakage electrical appliance will form a loop, so that the zero line will be broken, and the fire line will be reversed.

Summary. It is not possible to use the live wire of a transformer with the neutral line of another transformer, because a transformer has three sets of coils, the same tail end of the three coils is the center point (i.e. the zero line) connected together, and the heads of the three groups of coils are three live wires, only the neutral line of the live wire in this group is used together to be the power supply of the same circuit, and the two transformers are not of the same source and cannot form a circuit, so they cannot be used together, which is also forbidden to be used in terms of safe electricity.

Electricity: If you use the live wire of one transformer, you can use the neutral wire of another transformer?

It is not possible to use the live wire of a transformer with the neutral line of another transformer, because a transformer has three sets of coils, and the same tail end of the three coils is the center point of the connection (i.e., zero scattered dotted wire), and the heads of the three groups of coils are three live wires.

I hope my answer can help you, dear.

Because the live wire (phase wire) at the power supply end (transformer) is a wire drawn from the transformer coil, and the neutral wire is also a line drawn from the transformer, but in the transformer circuit of the three-phase four-wire is a central point (neutral wire) of the winding coil of the three-phase wire, then the voltage of the neutral wire and any other phase wire should be 220V (China's voltage standard) under normal conditions; Because, in the power supply system, the neutral line of the transformer is grounded, so from"phenomenon"From the perspective of electrical theory, the potential of the ground wire and the neutral wire is equal (the same), and both should be"Zero potential".Therefore, in terms of measurement, the voltage of the live wire to the neutral wire and the ground wire should be the voltage value of the one-phase wire being measured--- that is, the voltage is 220V; The reason why it is divided into neutral wire and ground wire is because the neutral wire is a line that provides a current channel for the circuit when it is working normally, and the ground wire is a line designed for the safety of electrical equipment"Abnormal current"A line of the channel is set up as a protection line together with the control equipment (such as automatic air switch, etc.), and the line is strictly speaking without any value of current passing through the line when the equipment is normal, that is, the current is zero. Therefore, in terms of measurement, these two lines are connected, but the nature of the work (function) is different.

There are two wires in the lighting circuit, one is called the live wire, and the other is called the neutral wire. The difference between the live wire and the neutral wire is that they have different voltages to the ground: the voltage of the live wire to the ground is 220v; The voltage of the neutral line to the ground is equal to zero (which itself is connected to the earth).

So when one part of the person hits the line of fire and the other part is standing on the ground, and the voltage between these two parts of the person is equal to 220V, there is a risk of electric shock. On the contrary, even if a person uses his hand to grasp the zero line, if the person is standing on the ground, because the voltage of the zero line to the ground is equal to zero, the voltage between the various parts of the human body is equal to zero, and the person is not in danger of electric shock.

Summary. Hello, depending on the situation, we use 220 volts of alternating current in our lives, one of the biggest features of alternating current is that it does not distinguish between positive and negative poles, so it is not divided into zero line and live wire when the input terminal is wired. Although AC power is not divided into positive and negative poles, not all electrical equipment can be connected to the power supply without distinguishing between neutral and live wires.

For example, the screw lamp head can not be divided into zero wire and live wire wiring, and must be connected according to the corresponding zero live wire, otherwise it will bring a lot of unnecessary troubles and unsafe factors in use and later maintenance. Some people may not know what a screw lamp head is, after all, it is rarely used now, and it is generally used in street lamps or bedside lamps, but you must have seen it in your life.

If the 220V electricity is alternating current, is the live wire and neutral wire interchangeable?

Hello, depending on the situation, we use 220 volts of alternating current in our lives, one of the biggest characteristics of alternating current is that it does not distinguish between positive and negative poles, so it is not divided into zero line and live wire when the input terminal is wired. Although there is no positive and negative pole of AC power, not all electrical equipment can be connected to the power supply without distinguishing between the neutral wire and the live wire. For example, the screw lamp head can not be divided into zero wire and live wire wiring, and must be connected according to the corresponding zero live wire, otherwise it will bring a lot of unnecessary troubles and unsafe factors in use and later maintenance.

There may be some people who don't know what the screw lamp head is, after all, it is rarely used now, and it is generally used in street lamps or bedside lamps, but you must have seen it in your life.

This kind of lamp head is for the installation of the bulb of the quiet size port, why this kind of screw mouth sleepy lamp head must be connected to the power supply according to the corresponding zero line and live wire, can not be connected casually like other electrical equipment? The purpose of this connection is mainly for safety and ease of maintenance.

Categories: Education Science >> Science & Technology >> Engineering Technology Science.

Problem description: Is the neutral line of the power transformer grounded?

Is the 220V neutral wire we use coming out of the transformer directly?

Or is the neutral wire of the transformer grounded, and then we lead the wire from the ground to connect it to the appliance?

Also, what is the difference between ground and neutral?

Analysis: The neutral lead wire of the three-phase transformer is called the neutral line, and the neutral line is needed as the circuit of the power supply for single-phase load electricity.

The ground wire is a facility to ensure the safety of people and equipment, when the equipment is electrified, there is a firm ground wire to ensure that people are not electrocuted, and low-voltage equipment is not damaged by electric shock. At the same time, it also plays a shielding role.

There are two types of neutral point sub-grounding of three-phase transformers (called high-current grounding system - generally in low-voltage applications of 380V and below) and non-grounding (called low-current grounding system - generally in high-voltage applications above 6000V). The purpose of neutral grounding is to generate a large current once the line is grounded, causing the switch to trip, the fuse to be burned, and the power supply will be automatically cut off in an instant.

Electrical safety requirements do not allow the neutral wire of the transformer to be grounded, and then the wire is drawn from the ground to be connected to the appliance. The transformer can be grounded, and the neutral wire must be led from the transformer to the electrical appliance (the neutral wire and the ground wire between the transformer and the electrical equipment can be shared).