What are the main parameters of the transformer?

There are corresponding technical requirements for different types of transformers, which can be represented by corresponding technical parameters. For example, the main technical parameters of the power transformer are: rated power, rated voltage and voltage ratio, rated frequency, operating temperature level, temperature rise, voltage regulation, insulation performance and moisture resistance. The main technical parameters for general low frequency transformers are: Transformer ratio, frequency characteristics, nonlinear distortion, magnetic shielding and electrostatic shielding, efficiency, etc.

The main parameters of the transformer are voltage ratio, frequency characteristics, rated power and efficiency.

(1) Voltage ratio n

The relationship between the voltage ratio n of the transformer and the number of turns of the primary and secondary windings and the voltage is as follows: n=V1/V2=N1/N2 where N1 is the transformer primary (primary) winding and N2 is the secondary (secondary) Winding, V1 is the voltage across the primary winding, and V2 is the voltage across the secondary winding. The voltage ratio n of the step-up transformer is less than 1, the voltage ratio n of the step-down transformer is greater than 1, and the voltage ratio of the isolation transformer is equal to 1.

(2) Rated power P This parameter is generally used for power transformers. It refers to the output power of a power transformer that can work for a long period of time without exceeding a defined temperature at a specified operating frequency and voltage. The rated power of the transformer is related to the cross-sectional area of ​​the core and the diameter of the enameled wire. The cross-sectional area of ​​the core of the transformer is large, the diameter of the enameled wire is thick, and its output power is also large.

(3) Frequency characteristics Frequency characteristics refer to transformers that have a certain operating frequency range and different working frequency ranges, which are generally not interchangeable. When the transformer is operated outside its frequency range, there is a phenomenon that the temperature rises during operation or does not work properly.

(4) Efficiency efficiency refers to the ratio of the output power of the transformer to the input power at rated load. This value is proportional to the output power of the transformer, that is, the greater the output power of the transformer, the higher the efficiency; the smaller the output power of the transformer, the lower the efficiency. The efficiency of the transformer is generally between 60% and 100%.

At rated power, the ratio of the output power of the transformer to the input power is called the efficiency of the transformer, ie

η= x100%

Where η is the efficiency of the transformer; P1 is the input power and P2 is the output power.

When the output power P2 of the transformer is equal to the input power P1, the efficiency η is equal to 100%, and the transformer will not generate any loss. But in fact this kind of transformer is not available. Losses are always generated when the transformer transmits electrical energy. This loss mainly includes copper loss and iron loss.

Copper loss is the loss caused by the resistance of the transformer coil. When current is generated by the coil resistance, a portion of the electrical energy is converted into thermal energy and lost. Since the coil is generally wound by an insulated copper wire, it is called a copper loss.

The iron loss of the transformer includes two aspects. One is the hysteresis loss. When the alternating current passes through the transformer, the direction and magnitude of the magnetic field lines passing through the silicon steel sheet of the transformer change, so that the internal molecules of the silicon steel sheet rub against each other, releasing heat energy, thereby losing a part of the electric energy, which is the hysteresis loss. . The other is eddy current loss when the transformer is working. The magnetic core has a magnetic flux passing through it, and an induced current is generated on a plane perpendicular to the magnetic line. Since this current forms a circulating current in a closed loop and is spiraled, it is called an eddy current. The presence of eddy currents causes the core to heat up, consuming energy, and this loss is called eddy current loss.

The efficiency of the transformer is closely related to the power level of the transformer. Generally, the higher the power, the smaller the loss and output power, and the higher the efficiency. Conversely, the lower the power, the lower the efficiency.

How to see the parameters from the nameplate

Under the specified operating environment and operating conditions, the main technical data is generally marked on the nameplate of the transformer. Mainly include: rated capacity, rated voltage and its tap, rated frequency, winding junction group and rated performance data (impedance voltage, no-load current, no-load loss and load loss) and total weight.

A, rated capacity (kVA): rated voltage. Capacity that can be delivered during continuous operation at rated current.

B. Rated voltage (kV): The working voltage that the transformer can withstand when operating for a long time. In order to meet the needs of the grid voltage change, the high-voltage side of the transformer has tap taps, and the output voltage of the low-voltage side is adjusted by adjusting the number of turns of the high-voltage winding.

C. Rated current (A): The current allowed by the transformer under the rated capacity for long-term passage.

D. No-load loss (kW): When the rated voltage of the rated frequency is applied to the terminals of one winding, the active power drawn by the other windings is open. It is related to the performance and manufacturing process of the core silicon steel sheet and the applied voltage.

E. No-load current (%): The current passing through the primary winding when the transformer is unloaded at the secondary side under the rated voltage. Generally expressed as a percentage of the rated current.

F, load loss (kW): Short-circuit the secondary winding of the transformer, and pass the rated current at the rated winding position of the primary winding, at which time the power consumed by the transformer.

G. Impedance voltage (%): Short-circuit the secondary winding of the transformer, and gradually increase the voltage in the primary winding. When the short-circuit current of the secondary winding is equal to the rated value, the voltage applied to the primary side at this time. Generally expressed as a percentage of the rated voltage.

H, phase number and frequency: the beginning of the three phase is denoted by S, and the beginning of the single phase is denoted by D. China's national standard frequency f is 50Hz. There are 60Hz countries abroad (such as the United States).

I. Temperature rise and cooling: The difference between the temperature of the transformer winding or the upper oil temperature and the temperature around the transformer is called the temperature rise of the winding or the upper oil level. The temperature rise limit of the oil-immersed transformer winding is 65K, and the oil surface temperature rise is 55K. There are also a variety of cooling methods: oil immersion from cold, forced air cooling, water cooling, tubular, and sheet.

J. Insulation level: There are insulation grade standards. The example of the insulation level is as follows: the high voltage rated voltage is 35kV, and the low voltage rated voltage is 10kV. The transformer insulation level is expressed as LI200AC85/LI75AC35, where LI200 means the transformer high voltage lightning impulse withstand voltage is 200kV, power frequency withstand voltage For 85kV, the low-voltage lightning impulse withstand voltage is 75kV, and the power frequency withstand voltage is 35kV.

K, junction group label: according to transformer one. The phase relationship of the secondary windings connects the transformer windings into various combinations called the junction group of the windings. In order to distinguish different connection groups, the clock representation is often used, that is, the phasor of the high-voltage side line voltage is fixed as 12 on the long needle of the clock, and the phasor of the low-voltage side line voltage is used as the short needle of the clock. On a number, it is used as the label of the junction group. For example, Dyn11 means that the primary winding is a (triangle) connection, and the secondary winding is a (star) connection with a center point, and the group number is (11).

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