Why the transformer increases the thickness of the neutral point copper plate can reduce the resista

In the three-phase five-wire power supply and distribution system, the three-phase load can not be fully balanced, and the load type is also different (inductive, capacitive, pure resistive), then there will be unbalanced current at the neutral point, and the neutral point will have some resistance more or less, if this resistance is too large, then the voltage drop at this end will increase, and if the voltage is too large, it will lead to poor symmetry of the system.

We know that the conductivity of copper is relatively high, and increasing the thickness of the copper sheet is equivalent to increasing the cross-sectional area of the wire, so the resistance is reduced.

Since your problem is not given a certain electrical parameter, you can only do a conceptual analysis.

If you want to accurately calculate the phase of the neutral point and the magnitude of the unbalanced current, you can refer to the power triangle of electroengineering and calculate the corresponding parameters of the voltage triangle. Hope it helps!

This is because according to the lead structure of the transformer, when measuring the resistance of each phase, the length of the neutral copper bar is different, so if the resistance of the neutral copper bar is too large, it may cause the three-phase direct resistance imbalance, so reduce the resistance of the neutral copper bar as much as possible.

Increasing the cross-sectional area of the neutral point lead of the transformer can reduce the resistance of the lead and reduce the neutral displacement voltage. I don't understand what "resistance unbalance" is.

The unbalance rate is calculated by dividing the maximum number minus the minimum number in the three phases by the average number of the three phases.

Such as oa=, ob=, oc=

DC resistance unbalance rate = (ob-oc) ((OA+OA+OC) 3) = (

Unbalanced: It refers to the inconsistency of the amplitude of the three-phase current (or voltage) in the power system, and the amplitude difference exceeds the specified range.

The specified capacity is 1For power transformers above 6MVA, the phase resistance unbalance rate should not be greater than 2%, and the line resistance unbalance rate should not be greater than 1% for windings without neutral points; For power transformers with capacity and below, the phase resistance unbalance rate is generally not more than 4%, and the line resistance unbalance rate is generally not more than 2%.

From an engineering practical point of view, it can be considered that the line resistance unbalance rate is half of the phase resistance unbalance rate. It is therefore recommended that all three-phase transformers, regardless of their capacity, specify only an unbalance rate limit of 2% for DC line resistance.

In addition to the voltage divider function, the resistor also has the effect of limiting the current, and when the resistor is passed, the current also decreases. Right.

On the one hand, the current is too small to drive the load (such as a small motor), on the other hand, the unnecessary loss is very large, and the power is turned into heat by the resistance, and the motor can not get much energy.

PS: 1. Resistance step-down is generally a voltage divider, which is generally used in voltage sampling or occasions with low current requirements.

2. The efficiency of the transformer is very high, especially when it is above 100W, its efficiency can reach more than 95%, and the energy lost in the transformer is very small, and most of it can be transmitted to the electrical appliance.

The combination of resistor and capacitor can achieve resistor-capacitance step-down, which is a low-cost step-down solution, which can be used in small and simple step-down occasions, such as small household appliances, but this step-down method is not very safe, and good products will not consider using it in this way.

3rd Floor: Is it true that DC circuits can only use resistors to step down voltage? Three-terminal voltage regulator and DC-DC switching power supply can be used to step down, but pure resistance step-down, which will greatly lose power, is only suitable for providing voltage sampling, not for providing power supply.

Resistance when the transformer is missing:

1. Due to the role of DU in the resistor current limiting, the current in the circuit will also decrease, and it is not appropriate to answer some occasions when large current is needed.

2. The efficiency of the resistor transformer is very low.

Therefore, there are few resistors used as transformers, and the resistors and capacitors can achieve resistor-capacitance step-down, which is a low-cost step-down solution, which can be used in small and simple step-down occasions, such as small household appliances, but this step-down method is not very safe.

The principle is that it can, but it consumes a lot of electricity. The transformer consumes less electrical energy and is safe.

The resistor and the transformer are completely different principles of changing the voltage of the original, the transformer is the use of the law of electromagnetic induction, by changing the number of windings of its two coils to achieve the change of voltage, and the transformer can only be used in alternating current. Resistance AC and DC are OK. In a DC circuit, only resistors can be used to step down the voltage

The most unbalanced three-phase DC resistance is the poor contact of the tap-changer, followed by the poor contact of the winding leads, both of which are relatively easy to judge, 1) the DC resistance is larger, 2) the resistance value of the board-operated tap-changer will change significantly.

The possibility of a short circuit between the windings between turns cannot be ruled out, but the resistance of the faulty phase should be small, and the load current should increase significantly in the no-load test.

Absolute equilibrium is unlikely, but relatively speaking, within a certain specified value. If the difference is too large, it is most likely that the insulation is damaged, and there is an inter-turn short circuit, or a phase-to-phase short circuit.

This has something to do with the local soil. The grounding pile needs 50x50x5 galvanized angle steel, the length of meters, driven into the ground, the lead wire should be welded with electric welding, if the grounding resistance is greater than 4 ohms, and then drive the same angle steel 5 meters away, and then connect with 40x4 galvanized flat steel. until the ground resistance meets the requirements.

This should be calculated according to the soil resistivity of the location, it is possible to hit a few is enough, or it may not be able to hit dozens of roots, if it is a general loess, red soil and other clays, the resistivity is in tens of ohms. m, hit.

Seven or eight meters of 50*50*5 angle steel are connected again, and it is almost the same.

What kind of sand and soil, it is complicated, and it is impossible to say it in three or two sentences.

It is the grounding resistance of the neutral point, generally 7 piles, 5 meters apart, the total length is about 30 meters, basically can reach less than 4 ohms. If you can't reach it, hit another 30-meter one in the opposite direction.

If the three-phase resistance imbalance is caused by design, there will be no consequences in itself. However, the three-phase winding is basically symmetrical when designed, and the DC resistance should not be too different, and the large error is often due to: 1) process defects;

2) Poor contact at the joint;

3) Poor contact of tap-changers;

4) There are broken strands in the coil that is wound in parallel;

5) There is an inter-turn short circuit.

These problems are often fatal to transformers, ranging from localized heating to burn-out. Therefore, it is recommended to compare the test data with the previous historical data, and the resistance value should be converted to 20 when comparing, if it is consistent with the historical data, it can be considered that the imbalance is caused by the design, if there is a large change, the operation should be withdrawn immediately, and the cause should be found out as soon as possible.

As long as the number of laps is the same, the problem is not big, and it is within the allowable range, because the communication is mainly based on inductive reaction.

The impact of the line resistance unbalance rate of the three-phase transformer exceeds 2%: when the transformer is running, the 3-phase current and 3-phase voltage at the output terminal are unbalanced. Nothing else has any effect, transformers can still be used.

According to the current, it is divided into high electrical macro ruler blocking and high ground and low resistance slip grounding.