Why should the transformer measure direct resistance, and what are the characteristics of the transf

The DC resistance of the transformer refers to the DC resistance value of each phase winding, and the purpose of measuring the DC resistance is to check whether there is an inter-turn short circuit inside the three-phase winding. Because if there is an interphase short circuit inside the transformer, the short-circuit current value is very large, it is easy to burn the transformer, and the phenomenon of fault manifestation is also obvious, and the appearance is easy to judge; However, if there is a short circuit between the windings of one of the phases, the short-circuit current value is very small, and the gas protection of the transformer will act as a trip, but it is difficult to see whether the transformer itself is faulty from the appearance of the transformer. By measuring the DC resistance of each phase, it is easy to determine whether there is an inter-turn short circuit by comparing the resistance values of the three phases

The resistance value varies greatly, and there is a great possibility of inter-turn short-circuit faults; If it is substantially similar, the possibility of such a failure can be ruled out.

Because according to the structure of the transformer, the windings are almost insulated by the insulating medium of the insulated wire itself, if there are defects in the insulation treatment, and the transformer load is large, the weak part of the insulation is easy to cause inter-turn short circuit. Therefore, the purpose of measuring DC resistance is to determine whether the transformer has an inter-turn short circuit and facilitate fault handling.

Measuring the DC resistance of the transformer can be judged: short circuit, open circuit, and approximate number of turns.

Downstairs, it's not good to evaluate him...

For a transformer three-phase multi-winding, you can also determine whether the winding is damaged after the accident by looking at the balance rate of the three-phase winding.

The rechargeable battery round width group is included, and the on-site test does not require AC power, which is easy to use.

The output charging current can reach up to 2A, and the test speed is fast.

The resistance measurement range is 1 Q - 2K, and the measuring range is wide.

Using high-quality components imported from abroad, soft orange Qingliang parts are designed with multiple anti-interference programs, and the measurement results are highly accurate and repeatable.

The LCD display mode is poor stool, which is suitable for a variety of different working environments.

Hello Some people think that if the transformer is disconnected, there will be no risk of electric shock if the DC resistance of the winding is measured by the instrument, but in fact, this is a misunderstanding. The transformer is divided into two windings of the high-voltage box and low voltage, and according to the scientific laws followed by the transformer, it can be known that the reason for the high voltage winding of the high-voltage winding is that the number of turns is relatively more than that of the low-voltage winding lead group. The higher the number of turns, the higher the voltage.

As you know, the generation of back electromotive force also conforms to this law. When measuring the DC resistance of a winding using a meter, a voltage is applied to the winding. Depending on the nature of the inductor coil, the voltage cannot be abruptly changed, and a back-EMF is generated instantaneously.

The level of the electric potential is directly proportional to the number of turns in the winding, so the more turns there are, the higher the voltage, and usually the operator will be shocked. This is especially true for measuring low-voltage windings, where the voltage on the high-voltage side is even higher. Not to mention that a person is subjected to an electric shock, it can even break through the meter.

Therefore, it is best not to try to use the instrument to measure the inductive winding devices with high turns, such as transformers and ballasts. I hope the above information can be helpful to you, and I wish you a happy life.

The purpose of measuring the DC resistance of transformer windings is: to check the welding quality of the winding joint and whether the winding has inter-turn short circuit; Whether the contact between the various positions of the voltage tap-changer is good and whether the actual position of the tap-changer is consistent; Whether the lead wire is broken, whether there are broken strands in the multi-strand wire and winding, etc. The DC resistance of the windings along with the bushing needs to be measured during an overhaul of a transformer, or after a tap position, or after an outlet fault short circuit.

The measurement method is as follows.

1) Current and voltmeter method. Also known as the voltage drop method, its principle is to measure the voltage drop on the resistor by passing a DC current into the measured resistance, and the measured resistance value can be calculated according to Ohm's law. Since the internal resistance of ammeters and voltmeters has an impact on the measurement results, the way in which they are fed into the measurement circuit should be carefully considered.

2) Balanced bridge method. It is a method that uses the principle of bridge balancing to measure DC resistance, and there are two commonly used balance bridges: single-arm and double-arm bridges. When measuring the DC resistance of a transformer, it should be done after the transformer is powered off and the high-voltage leads are removed.

For large-scale large-capacity power transformer, because the charging time constant of RL series circuit is very large, each measurement takes a long time to wait for the current, voltmeter indication is stable, thus the work efficiency is very low, often use special instruments (such as constant current power supply) to replace the power supply in the test, so that the test time can be greatly shortened. The standard for measuring the DC resistance of transformer coils is: for transformers above 1600kva, the difference between the winding resistance of each phase should not be greater than 2% of the average value of the three phases, the difference between the lines should not be greater than 1% of the average value of the three phases for the windings without neutral point lead wires, and for the transformers of 1600kva and below, the difference between the phases is generally not more than 4% of the average value of the three phases, and the difference between the lines is generally not more than 2% of the average value of the three phases, and the change should not be greater than 2% compared with the previous values measured in the same parts.

Measurements are made with a DC bridge.

The DC resistance of the winding of the small power transformer can be directly measured with the resistance level of the multimeter.

The windings of high-power transformers can be measured with bridges. In order to prevent the influence of self-induced electromotive force of the transformer winding, the reading should be read after the reading is stable; The high-power high-voltage transformer should also be connected with a high-power resistor in parallel on the winding under test to absorb the back EMF when the measurement circuit is disconnected and avoid ignition damage to the instrument.

The detection of DC resistance of transformer winding assesses the test of longitudinal insulation and current loop connection of winding, which can reflect the defects and faults such as short circuit between winding turns, broken strands of winding, contact state of tap changer and difference of wire resistance and poor joint contact, and is also an effective means to judge whether the DC resistance of each phase winding is balanced and whether the voltage regulating switch gear is correct. Therefore, the DC resistance of the transformer is not measured by the specified high voltage and low voltage, and the DC resistance of the high-voltage winding or low-voltage winding must be measured, and they must meet the requirements of the standard.

The DC resistance test of transformer winding is one of the main items of transformer factory and preventive test

Check the quality of winding welding;

Check whether the contact between the various positions of the tap changer is good;

Check whether there are any breaks in the winding or lead wire;

Check the correctness of the parallel branch, whether there is one or more disconnections in the winding made of several parallel wires;

Check whether there is a short circuit between the layers and turns;

Determine the average temperature rise of the windings.

The high and low voltage sides need to be measured, and the resistance of the coil is measured, and each group of coils needs to be measured.

The DC resistance on the high-voltage side is smaller, and the resistance on the low-voltage side is larger. The output is low-voltage and the input is high-voltage. High voltage terminated power supply (380V or 220V).

Transformer ratio test method. Zhuoya Power.

First, the purpose of the ratio test.

Power transformers.

The transformer ratio of all taps of the winding is measured during handover, winding replacement, and after internal wiring changes.

In the case of no load of the transformer, the ratio of the voltage U1 of the high-voltage winding to the voltage U2 of the low-voltage winding is called the transformer ratio. The transformer ratio of a three-phase transformer is usually based on the line voltage.

Compute. The purpose of the spring pressure ratio test is to check whether the number of turns in the winding is correct, check the condition of the tap changer, check whether there is a metallic short circuit between the layers (turns) of the winding, etc., so as to provide a basis for whether the transformer can be put into operation or run in parallel.

2. Transformer ratio test method.

The transformer ratio laboratory applies voltage on one side of the transformer, measures the other voltage with a meter or instrument, and then calculates the transformer ratio based on the measurement results. Methods for determining the transformer ratio include the bridge method and the dual voltmeter.

and standard transformer methods.

3. Analysis of the results of the variable ratio test.

1.The voltage ratio of each phase connector and the nameplate.

There should be no significant difference in the values, and they should be regular.

2.The voltage of the transformer with a voltage ratio of less than 35kV and a voltage ratio of less than 3 is 1%; For other transformers, the allowable deviation of the rated tap voltage ratio is , and the voltage ratio of other taps should be the percentage of the transformer impedance voltage value.

1 to 10, but not more than 1%.

4. Transformer ratio test equipment.

Multi-functional variable ratio tester.

Special transformer ratio tester.

The formula for calculating the transformation ratio of a transformer.

How to calculate the voltage regulation.

The formula for calculating the PT variable ratio.

Transformer ratio test principle.

Handover test content formula.

The qualified chain of transformer DC resistance test generally refers to the high unbalance rate of three-phase DC resistance, which meets the requirements of the national standard and the temperature conversion results are consistent with the factory test results of semi-finished products. The variable ratio is to check whether the voltage ratio of the high-voltage and low-voltage shed beams meets the design requirements.

Misremember, this kind of wrong plum resistance type test Changchai is in place, and the variable ratio can't be measured, what's going on? It may be that some of the other party's telegrams have failed, and other personnel can solve this fault.

The transformer direct master test is qualified, and the variable ratio can not be measured, so he has some kind of internal purchase of the kind of system that has a crack in the air system, so you should check it well.