How to detect the quality of power transformer

How to detect the quality of power transformers

There are many types of transformer measurements. I don't know your measurement intent. There are usually measurements of power-off and power-on conditions. In the case of no electricity, first measure whether the conduction of the main and auxiliary coils (input and output) is smooth. This is measured with the resistance gear r10o of the multimeter. The resistance value is almost zero or very small, indicating that the transformer is smooth. The resistance value is unmeasurable, indicating that the transformer is not smooth and there is a problem with the transformer. After power-on, measure the voltage at the output first. Use AC gear. The reading should be adjusted to be larger than the recognized value of the transformer, from large to small to accurate stop. This process can not be wrong, otherwise it is easy to burn out the multimeter.

 

If you measure the general power frequency low-power step-down power transformer, use the resistance gear of the multimeter to measure the resistance of the primary side should be several hundred ohms (if it can't be measured, it means an open circuit, if it is a few ohms to tens of ohms, it means the primary short circuit), The secondary resistance should be a few ohms (if it can't be measured, it's an open secondary, if it's close to zero ohms, it's a shorted secondary).

 

If it is a high-frequency transformer, it has nothing to do with the multimeter except to test the open circuit. Since the resistance of the primary of the high-frequency transformer is very small (for example, some of the secondary are less than 1Ω), it is not easy to detect whether there is an internal short circuit. Only by testing its inductance or leakage inductance with the aid of a bridge can you accurately determine whether there is a short circuit or a damaged core.

 

Detect the quality of power transformers

 

The quality of the power transformer is considered "good" only after a four-step inspection.

 

1. All primary and secondary coils are not open. In general low-power step-down transformers, the primary coils are thin and many, which are easy to break, while the secondary coils are thick and few, and are rarely broken.

 

The primary resistance is generally tens to hundreds of ohms. The lower the power, the higher the measured resistance. 181Ω, normal, the transformer is estimated to be 4~5W. The secondary resistance is much smaller. It should be from a few ohms to 0 euros.

 

2. There is no short circuit or leakage between the primary and secondary coils. Use the high-resistance gear of the multimeter, and connect the two probes to one outlet of the primary and secondary coils respectively. The indication value should be more than a few megohms, and a large amount is better.

 

3. The primary and secondary coils must not be short-circuited or leaked with the iron core. See point 2 for measurements.

 

4. There is no inter-turn short circuit between the primary and secondary coils. If the transformer is in a no-load state, the cause of abnormal energization must be considered. Also, turn-to-turn shorts cannot be measured with a multimeter.
 

 

Detect the quality of power transformers

 

How to detect the quality of transformer through dynamic and static test

 

You can judge normal movements by listening to them. When the power transformer is energized, the current passes through the iron core to generate an alternating magnetic flux, which emits a "humming" uniform electromagnetic sound. The intensity of the sound is proportional to the magnitude of the load current.

 

How to detect the quality of power transformers

 

1. "Squeak".

 

After adjusting the tap changer voltage, the sound becomes worse. The measured DC resistance value of the double-arm bridge exceeds the original data by 2%, which is caused by poor contact and dirt on the contacts.

 

Solution: Unscrew the rain cover of the tap changer, remove the locking screw, and use the handle to turn the shaft of the tap changer back and forth 10 to 15 times. This phenomenon can be eliminated. Recovery can be installed immediately after the repair.

 

Secondly, the lead wire from the terminal bar to the lower fuse is made of bare aluminum or bare copper stranded wire, but the tension is not good, which is caused by the loose wire binding of the porcelain bottle. At dusk and dawn, small sparks can be seen making a "squeak" sound, which is distinctly different from the "squeak" inside the power transformer.

 

Solution: Arrange power outages for maintenance during holidays and troubleshoot.

 

2. "Crackling" the loud sound of the hammer.

 

This is the discharge sound of the high-voltage porcelain bushing entering the casing of the power transformer through the air, which is caused by the lack of oil in the upper part of the oil tank of the power transformer.

 

Treatment method: Insert a clean and dry funnel into the oil storage tank