How current transformer works

What is a current transformer? What is its role? Transformers are important equipment in the power supply system. Their faults are initially accompanied by local or overall temperature abnormalities. Infrared thermal imaging cameras can detect and diagnose simply, safely, real-time and intuitively. Equipment failure to ensure equipment safety and long-term operation.

Introduction to current/voltage transformers

In order to ensure the safe and economical operation of the power system, the operation of power equipment must be monitored and measured. However, general measurement and protection devices cannot be directly connected to primary high-voltage equipment. Instead, the high voltage and high current of the primary system need to be proportionally converted into low voltage and small current for use by measuring instruments and protection devices. The most common device that performs these transformation tasks is what we usually call a transformer. The voltage conversion is performed by a potential transformer (potential transformer), referred to as PT. The transformer that performs current conversion is a current transformer, or CT for short.

The function of current transformer:

1. Convert a large primary current into a standard 5 amps;

2. Provide current for measuring devices and coils of relay protection;

3. Isolate primary equipment and secondary equipment.

The function of the voltage transformer: convert high voltage into a standard secondary voltage of 100V or lower in a proportional relationship for use in protection, measurement, and instrumentation devices. At the same time, the use of voltage transformers can isolate high voltages from electrical workers.

1. Current transformer overheating generally has the following reasons:

1. Overheating due to loose inner and outer joints, primary overload or secondary open circuit.

2. Overheating due to loose iron core or parts, improper electric field shielding, secondary open circuit or floating potential, open circuit at the end screen and insulation damage.

2. Voltage transformers generally overheat for the following reasons:

1. Poor product quality: If the insulation of the product itself, the core lamination and the winding process are not up to par, etc., the voltage transformer may generate excessive heat and cause the insulation to operate at high temperatures for a long time, resulting in accelerated aging of the insulation and forming a vicious cycle. .

2. Overload, three-phase unbalance, and resonance cause the internal winding heating of the PT to increase. Especially when the voltage is higher than the rated voltage of the PT, the internal heating of the PT becomes more serious.

3. Infrared thermal imaging cameras generally have the following applications:

a) Detect overheating caused by poor joint connection, loose or over-tightened bolts and washers.

b) Current transformers and voltage transformers may suffer from oil shortage or false oil level due to oil leakage. Due to the large difference in thermal physical parameters of the medium above and below the oil surface, an obvious temperature gradient corresponding to the oil level will be generated on the outer surface of the equipment, which can also be discovered using infrared detection methods.

c) Detection of local overheating of equipment due to overheating/three-phase imbalance/resonance.

d) Detect local overheating of the core caused by poor core quality or local insulation damage between sheets.

In addition to taking infrared images, Fluke's patented IR-Fusion technology also captures a digital photo and fuses them together to help identify and locate faults so they can be repaired correctly the first time.

Fluke Ti Series thermal imaging cameras come with powerful software for storing and analyzing thermal images and generating professional reports. The software enables adjustments to key parameters such as emissivity, reflected temperature compensation and color palette stored in images downloaded from the thermal imaging camera, all in the office, increasing the safety and convenience of inspections.

4. What problems may be encountered during operation?

If there is no load operation or the load is very low, the heating of the equipment failure will not be obvious. Even if there is a serious failure, it will not be exposed in the form of characteristic thermal anomalies. Only when the equipment is operating at rated voltage and the load is greater, the heat generation and temperature rise will become more serious, and the characteristic thermal anomalies at the fault point will become more obvious. Therefore, when performing infrared testing, try to ensure that the equipment operates at rated voltage and full load. Even if continuous full load operation cannot be achieved, an operation plan should be prepared so that the equipment can operate at full load before and during the test. Allow a period of time (such as 4 to 6 hours) to give the faulty part of the equipment enough time to heat up and ensure that its surface reaches a stable temperature rise.

Internal equipment faults occur inside the electrical equipment, so the temperature rise reflected on the surface of the equipment is very small, usually less than 1°C. Detecting this kind of fault requires high sensitivity of the thermal imager.

5. How to take clear thermal images?

Transformers are usually at ambient temperature. To get a clear infrared heat map, we recommend:

1. When used in situations with small temperature differences, try to choose a thermal imager with higher thermal sensitivity.

2. For highly reflective equipment surfaces, appropriate measures should be taken to reduce the impact on solar radiation and radiation from surrounding high-temperature objects. Or change the detection angle and find the best angle to avoid reflection for detection.

3. First use the automatic mode to measure the temperature range of the device; then manually set the level and span, set the temperature range to the minimum, and include the previously measured temperature range (the minimum temperature range of each instrument is different).

4. It is best to set the palette mode to grayscale or iron red, so that the thermal image will be clearer.

Okay, the above is the little knowledge about infrared thermal imaging cameras that Antai Testing has summarized for you. The application of this knowledge requires everyone to continuously summarize it in practice.