The impedance voltage of a transformer? Why Measure Impedance Voltage?

The impedance voltage is the ratio of the voltage applied by the primary winding (short-circuit voltage) to the rated voltage when the short-circuit current of the secondary winding reaches the rated current. The impedance voltage uk (%) is one of the important economic indicators related to the cost, efficiency and operation of the transformer and one of the main parameters for the condition diagnosis of the transformer.

1. The impedance voltage of the transformer is to short-circuit the secondary winding of the transformer, so that the voltage of the primary winding slowly increases, and when the short-circuit current of the secondary winding reaches the rated current, the ratio percentage of the voltage (short-circuit voltage) applied by the primary winding to the rated voltage. The impedance voltage uk (%) is one of the important economic indicators related to the cost, efficiency and operation of the transformer and one of the main parameters for the condition diagnosis of the transformer.

2. Reasons for measuring impedance voltage: transformers with the same capacity, low cost of small impedance voltage, high efficiency, cheap, in addition, the voltage drop and voltage change rate during operation are also small, and the voltage quality is easily controlled and guaranteed, so from the perspective of the operation of the power grid, it is better to see that the impedance voltage is smaller. However, considering the condition of limiting the short-circuit current of the transformer, it is better to see that the impedance voltage is larger, so as to avoid damage to the electrical equipment (such as circuit breakers, disconnectors, cables, etc.) that cannot withstand the action of short-circuit current during operation.

There are relevant provisions for the national standard for the impedance voltage value corresponding to transformers of different capacities.

The short-circuit impedance of the transformer is calculated by Z uk%*un squared * 1000 (100SN), where UK is the short-circuit voltage, UN is the rated voltage, and SN is the capacity.

For example, if there is a SE=100KVA,10 three-winding transformer, the short-circuit voltage UCK%= , calculate the short-circuit impedance.

Then the rated current on the 10kV side is 100 (, and the current from the low-voltage side to the high-voltage side is , and the impedance z=U ( ID)=10x1000 ( (

Hello Kiss is happy to answer this question for you. The impedance voltage (short-circuit voltage) of the transformer is calculated using the following formula: uz%=uz un 100%.

Calculation formula: ud% = short-circuit voltage 100% of rated voltage. It is to short circuit the secondary side of the transformer, gradually apply voltage on the primary side, when the secondary winding resistance passes through the rated current, the percentage of the ratio of the electric high voltage uz applied by the primary winding resistance to the rated voltage un.

The impedance voltage of the transformer refers to: the secondary side is short-circuited (usually refers to the low voltage touching the vertical side), the low voltage of the rated frequency is applied on the primary side, and when the rated current flows through the secondary side, the pressurized value of the primary side is expressed in the form of a general percentage, such as uz%. From this definition, it can be deduced that the percentage of short-circuit voltage is equal to the percentage of short-circuit impedance, so short-circuit voltage is generally referred to as impedance voltage.

The percentage of short-circuit impedance of the transformer, which is numerically equal to the percentage of the transformer's short-circuit voltage. It refers to the transformer secondary winding short circuit, in a noisy secondary winding resistance to apply voltage, when the secondary winding through the rated current, the ratio of the voltage applied by the primary winding resistance to the rated voltage percentage.

When doing the transformer load loss test, the measured test voltage (line voltage) is the impedance voltage uz of the transformer, also known as short-circuit impedance or short-circuit voltage, which is expressed as a percentage of the rated voltage uz%, and the impedance voltage should also be converted to the corresponding value when 75.

The allowable deviation of the impedance voltage is related to the magnitude of the impedance voltage. When the impedance voltage value of the main tap is greater than or equal to 10%, the allowable deviation is 10%.

The impedance voltage is small, and the short-circuit current is large. The impedance voltage is too small, the short-circuit current is too large, and when the output is short-circuited, the transformer is easily damaged by excessive electric power. Therefore, the national standard stipulates that the minimum value of the impedance voltage is shown in the following table.

Article**1What is the short-circuit impedance (impedance voltage of the transformer) of the transformer?

The short-circuit impedance of the transformer, also known as the impedance voltage of the transformer, indicates the voltage loss (percentage value) generated on the impedance of the transformer itself when the transformer passes through the rated current; For double-winding transformers, the measurement method is to short-circuit the secondary side of the transformer, and the voltage added when the rated current flows through the primary side, and then convert it into a percentage of the rated voltage; The impedance voltage of the transformer is an important parameter of the transformer, which is of great significance to the parallel operation and economic operation of the transformer, and is also an important basis for calculating the short-circuit current and protection value of the transformer.

1) The larger the impedance voltage of the transformer, the smaller the short-circuit current flowing through the transformer when a short circuit occurs on the secondary side of the transformer, and the lighter the impact on the transformer.

2) The larger the impedance voltage of the transformer, the greater the change range of the load side voltage of the transformer when the load changes, and the voltage stability is poor;

3) The larger the impedance voltage of the transformer, the greater the reactive power consumed by the transformer winding under the same load in operation. The transformer data you mentioned above is the data of a three-winding transformer;

High-medium: indicates that the impedance voltage of the transformer's high-voltage winding to the medium-voltage winding is;

High-Low: indicates that the impedance voltage of the transformer's high-voltage winding to the low-voltage winding is;

Medium-Low: indicates that the impedance voltage of the medium-voltage winding of the transformer to the low-voltage winding is.

The impedance voltage corresponds to the rated capacity of the transformer.

There are relevant requirements in and GB6451, etc.

6 10 kV class power transformer is 4; The power transformer of the 35 kV class is; 110 kV class power transformer 8 9%; Power transformers of the 220 kV class reach 12-14%.

It has a high sensitivity to check the overall insulation condition of the transformer, and can effectively detect the overall moisture of the transformer insulation, the moisture or dirt on the surface of the components, and the penetrating defects.

When the insulation penetrates the two poles, there will be obvious changes when measuring the insulation resistance, and the defects can be sensitively detected through measurement; If there is only a local defect in the insulation, and there is still insulation between the two poles, the insulation resistance decreases little or even does not change, and this local defect cannot be detected.

When measuring the insulation resistance, the method of grounding the idle winding is adopted, and its advantage is that the insulation between the measured part and the grounding part and the different voltage parts is measured, and the measurement error caused by the residual charge in each winding can be avoided.

The resistance value of transformer winding insulation and absorption ratio play a decisive role in whether the transformer winding insulation is damp. When the measurement temperature is 10 30, the absorption ratio of the undamp transformer should be within the range, the absorption ratio of the transformer with local defects inside the damp or insulation is close to the consideration of the solid insulation tension of the transformer for fibrous insulation, and these solid insulation is only a small part of the transformer insulation, and the tension part is composed of insulating oil, and the insulating oil has no absorption characteristics, so in the injection of weakly polar transformer oil, its absorption characteristics are not significant.

When the absolute value of the insulation resistance of a large transformer is large, the absorption ratio is small or unqualified.

On the contrary, if the absolute value of insulation resistance is small, the absorption ratio can reach, which makes it difficult to judge the insulation condition.

The short-circuit impedance of the transformer is calculated by Z uk%*un squared * 1000 (100SN), where UK is the short-circuit voltage, UN is the rated voltage, and SN is the capacity.

For example, there is a SE=100KVA,10 three-winding transformer, the short-circuit voltage UCK%= , and the short-circuit impedance is calculated.

Then the rated current on the 10kV side is 100 (, and the current from the low-voltage side to the high-voltage side is , and the impedance z=U ( ID)=10x1000 ( (