Detailed explanation of transformer DC resistance error calculation formula

In power systems, transformers are important electrical equipment, and their performance directly affects the stable operation of the entire system. DCresistanceAs an important parameter of the transformer winding, it reflects the resistance loss of the winding. Accurately measuring and calculating the DC resistance error of the transformer is of great significance for maintaining the normal operation of the transformer and diagnosing faults. This article will focus on the formula for calculating the DC resistance error of the transformer and introduce relevant knowledge and application methods in detail.

1. Definition and measurement method of transformer DC resistance

The DC resistance of the transformer refers to the resistance value of the winding under the action of DC current, which is mainly determined by the wire material, resistivity and winding structure. The measurement is usually carried out using a DC bridge or a microohmmeter. The measurement results are greatly affected by factors such as temperature and contact resistance, so error calculation and correction are required.

2. Main factors affecting DC resistance measurement error

Measurement errors mainly come from temperature changes, test instrument accuracy, contact resistance, and the connection method of the test lines. Rising temperature will cause the resistance value to increase, poor contact will introduce additional resistance, and instrument accuracy limitations will directly affect the accuracy of the measurement results.

3. Calculation formula of DC resistance error

The commonly used calculation formula for transformer DC resistance error is:

Error rate (%) = [(measured value standard value) / standard value] × 100%

Among them, the measured value is the actual measured resistance value, and the standard value is the resistance value specified by the design or manufacturer. The formula is simple and clear, making it easy to quickly determine the degree of deviation of the measurement results.

4. The importance of temperature correction to error calculation

Since the resistance value changes with temperature, it is usually necessary to correct the measurement temperature to a standard temperature (such as 20°C) during measurement. The temperature correction formula is:

R20 = Rmeasurement / [1 + α × (Tmeasurement 20)]

Among them, R20 is the resistance at standard temperature, R measurement is the actual measured resistance, α is the temperature coefficient of the material, and T measurement is the temperature at the time of measurement. Calculating the error after temperature correction can improve the accuracy of error assessment.

5. Effect of contact resistance and its treatment methods

Contact resistance is a common source of error in measurements, especially at terminal blocks and test instrument connections. In order to reduce the influence of contact resistance, it is recommended to use the four-wire method for measurement, that is, using two wires for power supply and two wires for measuring voltage, which can effectively eliminate the influence of wires and contact resistance and improve measurement accuracy.

6. Instrument accuracy and error assessment

Different types of measuring instruments have different accuracy levels, and the minimum resolution and measurement error of the instrument directly affect the results. Choosing a high-precision microohmmeter and calibrating it regularly can reduce system errors. In addition, repeated measurements and averaging are also effective ways to reduce random errors.

7. Application of error analysis in transformer maintenance

By accurately calculating the DC resistance error, maintenance personnel can determine whether there are abnormalities in the windings, such as winding disconnection, short circuit or aging. When the error is too large, timely inspection and processing are required to ensure the safe operation of the transformer.

The calculation of the DC resistance error of the transformer is an important step in ensuring the safe operation and stable performance of the transformer. Accurate error calculation needs to consider many factors such as temperature correction, contact resistance and instrument accuracy. Through the rational application of error calculation formulas and measurement technology, the scientific nature and accuracy of transformer maintenance can be effectively improved, the service life of equipment can be extended, and the stable operation of the power system can be ensured. I hope this article will be helpful to relevant engineering and technical personnel in practical work.