How to test the DC resistance test of dry type transformer detection

Dry-type test transformer winding DC resistance measurement.

First, the purpose of winding DC resistance measurement.

Whether the welding or mechanical connection at the connection of the winding wire is good, and whether there is welding or poor connection.

Whether the connection between the lead-out wire and the housing, and the lead-out wire and the tap-changer is good.

Whether the soldering or mechanical connection between the leads is good.

Wire specifications. and whether the resistivity meets the requirements.

Is the resistance of the windings of each phase balanced?

The temperature rise of the transformer winding is based on the cold resistance of the winding before the temperature rise test and the instantaneous thermal resistance of the port power supply after the temperature rise test.

calculated, so the temperature rise test needs to measure the resistance value.

Second, the measurement conditions.

The temperature of the winding being measured and the winding terminals should be recorded.

The measurement should be done using direct current.

Care should be taken to minimize the effects of self-inductance effects in the measurements.

The stationary time of the transformer in a constant temperature environment should not be less than 3h

The winding temperature should be measured at the same time as the winding resistance.

Third, the inspection standard.

For the following transformers, the difference between the phases should generally not be greater than the average value of the three phases.

4%, the difference between lines should generally not be greater than 2% of the average value of the three phases

4. Calculation of measurement results.

r0=rm*(235+t1) (235+t2) copper-235 aluminum-225

Interline resistance conversion is connected to y.

5. Precautions when measuring.

The current used to measure DC resistance should be the rated current.

2%-10%, not more than 20% of the rated current, to avoid the current causing heating of the winding.

Temperature-induced errors.

When there is a current i in the DC circuit, the transformer core magnetic field will produce high voltage when it is disconnected, which may endanger personal safety and damage the instrument. Therefore, a discharge circuit is required so that the current flows slowly from i through the loss on the resistor. Disconnect the line after an hour.

Huayi power reminds the analysis, each time the resistance value of the side must be converted to the same temperature for comparison, if the comparison results in the DC resistance does not exceed the standard, but the value of each amount has increased, it should also attract enough attention. Such as transformer neutral point.

When there is no lead-out and the unbalanced value of the three-phase line resistance exceeds 2%, it is necessary to convert the line resistance to the phase resistance in order to find the defect.

Phase-by-phase measurement using a DC resistance meter.

Transformer DC resistance tester is a commonly used high-voltage electrical testing equipment, which is mainly used to measure the DC resistance of power transformers. It is also widely used in the power industry, but many people are not aware of its measurement and discharge work. Therefore, this article introduces how to use a transformer DC resistance tester to measure and discharge the transformer DC resistance tester.

Transformer DC Resistance Tester Measurement.

After connecting the test cable, turn off the power switch, the power indicator turns on, press the "Start and Stop" button, and the meter head shows "E0000". Select the resistance range according to the measured value, press the gear switch, the gear indicator light is on, and the stable value displayed on the four and a half LCD screens is the measured resistance value. When reading a numeric value, pay attention to the units (m k) in the selected range.

When measuring large inductance samples, such as power transformers, other coils other than the test circuit, it is best to measure short circuits to avoid electromagnetic interference.

Transformer DC resistance tester discharge.

After the test, the main power supply is cut off directly. If, in the perceptual test, the power supply should not be removed immediately after operation, the instrument should have a continuous discharge process, generally for at least 20 seconds, otherwise, the back EMF of the inductor will endanger personal safety.

The measurement and discharge of the transformer DC resistance tester is its commonly used function, which requires the skilled operation of electrical workers.

Respondent: Huatian Power.

First, the wiring on all sides of the transformer is disconnected.

The two ends of the DC resistance tester are connected to both ends of a certain winding, and the DC resistance at both ends is measured. The current transfer test is carried out sequentially, and then the connection method of the windings is considered, and the resistance of each phase is folded to the judgment according to its unbalance value.

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.

The purpose of testing the DC resistance of a transformer:

1. Check the welding quality of the winding joint, and whether the winding has an inter-turn short circuit;

2. Whether the contact between the positions of the on-load tap-changer is good, and whether the actual position of the tap-changer is consistent with the indicated position;

3. Whether the outgoing line is broken;

4. For three-phase power transformers, calculate the unbalance rate of the three-phase DC resistance according to the test results to determine whether it meets the design or relevant standards.

The DC resistance of the transformer is measured with a DC resistance tester.

Measuring DC resistance is an important item in transformer testing. By measuring the DC resistance, it is possible to check whether the conductive circuit of the device has defects such as poor contact, poor welding, coil failure, and wiring error. In the actual measurement of small and medium-sized transformers, the DC bridge method is mostly used.

When the resistance value of the measured coil is greater than 1, it is generally measured with a single-arm bridge, and when the resistance value is less than 1, it is measured with a double-arm bridge. When using a double-arm bridge for wiring, the potential pile head of the bridge should be close to the resistance to be measured, and the current pile head should be connected to the potential pile head.

Before measuring, the resistance of the coil to be tested should be estimated, the bridge ratio knob of the DC resistance tester should be placed in the appropriate position, the untested coil should be shorted to ground, and then the power switch should be turned on. Turn on charging. After the power supply is sufficient, press the galvanometer switch to quickly adjust the measuring arm, so that the pointer of the current detector moves to the neutral line in the middle of the galvanometer scale, and fine-tunes it to the value when the pointer is stable and the recording resistance stops at the zero position.

At this time, the resistance value of the coil to be measured = the resistance value of the multiplier measuring arm. After the measurement, turn on the galvanometer button and then release the power switch.

In the measurement process, in addition to strictly following the electrical safety regulations and equipment test procedures, the following points should also be noted:

1) When the temperature of the coil is stable, the temperature difference between the upper and lower parts of the transformer tank shall not exceed 3;

2) Due to the inductance of the transformer coil, the charging current is unstable during measurement. It is necessary to count after the current is stabilized, and if necessary, shorten the charging time;

3) The contact resistance of the conductor in the test circuit should be reduced as much as possible. The tap joints of the transformer in operation are often affected by dirt such as oil film, so that the contact is poor. Generally, it is necessary to switch several times before measuring to avoid misjudgment;

4) When measuring the low-voltage side of the transformer, all personnel should keep a safe distance from the high-voltage side;

5) During the test, the test wire clamp must be fixed firmly. One of the large transformers applied a large current during the test, and if the wiring is not reliable enough, it is easy to produce arcs; Secondly, if the clip falls off during the test, it is easy to damage the instrument (high voltage).

6) The transformer DC resistance tester should avoid strong vibration, direct sunlight and magnetic field during transportation, storage and work. When storing and keeping the instrument, attention should be paid to the ambient temperature and humidity. It should be placed in a dry, ventilated place without corrosive gases.

Do not allow moisture, rain and sun exposure. It should be handled with care and care.

Dear, if you want to measure the DC resistance of the transformer with a multimeter in the sail state, you can follow the steps below:1First, adjust the multimeter to the resistance setting and insert the test leads into the pen jack.

2.Then, connect one end of the test lead to one terminal of the transformer and the other end to the other. 3.

Next, read the resistance value on the orange multimeter and record it. 4.If you need to test another terminal of the transformer, you can repeat the above steps.

It should be noted that when testing the DC resistance of the transformer, the transformer should be de-energized first and wait for a period of time to allow the charge inside the transformer to dissipate so as not to affect the test results. In addition, the appropriate multimeter gear should be selected according to the frontal state of the transformer, the constant voltage and current, to ensure the accuracy of the test.