What are the specifications of the transformer? What are the transformer capacities?
What are the specifications of the transformer? What are the transformer capacities?
The specifications and types of commonly used transformers can be summarized as follows:
1. According to the number of phases:
(1) Single-phase transformer: used for single-phase load and three-phase transformer group.
(2) Three-phase transformer: used for the rise and fall voltage of the three-phase system.
2, according to the cooling method:
(1) Dry-type transformer: relying on air convection for natural cooling or increasing fan cooling, it is mostly used for small-capacity transformers such as high-rise buildings, high-speed toll stations, local lighting, and electronic circuits.
(2) Oil-immersed transformer: rely on oil as cooling medium, such as oil-immersed self-cooling, oil-immersed air-cooled, oil-immersed water-cooled, forced oil circulation, etc.
3. According to the purpose:
(1) Power Transformer: used for the rise and fall voltage of transmission and distribution systems.
(2) Instrument transformers: such as voltage transformers, current transformers, measuring instruments and relay protection devices.
(3) Test transformer: It can generate high voltage and carry out high voltage test on electrical equipment.
(4) Special transformers: such as electric furnace transformers, rectifier transformers, regulating transformers, capacitive transformers, phase shifting transformers, etc.
4, according to the form of winding:
(1) Double winding transformer: used to connect two voltage levels in the power system.
(2) Three-winding transformer: Generally used in power system regional substation, connecting three voltage levels.
(3) Autotransformer: A power system used to connect different voltages. Can also be used as a normal boost or post-down transformer.
5, according to the iron core form:
(1) Core transformer: Power transformer for high voltage.
(2) Amorphous alloy transformer: Amorphous alloy core transformer is a new type of magnetic conductive material, the no-load current is reduced by about 80%, which is an ideal distribution transformer for energy saving, especially suitable for loads in rural power grids and developing regions. The rate is lower.
(3) Shell-type transformer: special transformer for high current, such as electric furnace transformer, electric welding transformer; or power transformer for electronic equipment and television, radio, etc.
6, according to the voltage level: 1000KV, 750KV, 500KV, 330KV, 220KV, 110KV, 66KV, 35KV, 20KV, 10KV, 6KV and so on.
7, according to the design energy-saving sequence points: SJ, S7, S9, S11, S13, S15.
The rated capacity of transformers in China is calculated according to the R10 priority coefficient, that is, the multiple of 10 times the power of 10, mainly:
50KVA, 80KVA, 100KVA, 125KVA, 160KVA, 200KVA, 250KVA, 315KVA, 400KVA, 500KVA, 630KVA, 800KVA, 1000KVA, 1250KVA, 1600KVA, 2000KVA, 2500KVA, 3150KVA, 4000KVA, 5000KVA, etc.
The transformer consists of a core (or core) and a coil. The coil has two or more windings. The winding connected to the power supply is called the primary coil, and the other winding is called the secondary coil. It can change the AC voltage, current and impedance. The simplest core transformer consists of a core made of a soft magnetic material and two coils of different numbers placed on the core.
The role of the core is to strengthen the magnetic coupling between the two coils. In order to reduce the eddy current and hysteresis loss in the iron, the core is laminated by a lacquered silicon steel sheet; there is no electrical connection between the two coils, and the coil is wound by an insulated copper wire (or aluminum wire). One coil is connected to the AC power source called the primary coil (or the primary coil), and the other coil is called the secondary coil (or the secondary coil).
The actual transformer is very complicated, and copper loss (coil resistance heat), iron loss (core heat generation), and magnetic flux leakage (air-closed magnetic induction line) are inevitably present. For the sake of simplicity, only the ideal transformer will be described here. The ideal transformer is established by ignoring the leakage flux, ignoring the resistance of the primary and secondary coils, ignoring the loss of the core, and ignoring the no-load current (the current in the coil of the primary coil of the primary coil). For example, when the power transformer is running at full load (the rated output power of the secondary coil), it is close to the ideal transformer.
The transformer is a stationary appliance made by the principle of electromagnetic induction. When the original coil of the transformer is connected to the AC power source, an alternating magnetic flux is generated in the core, and the alternating magnetic field is represented by φ. φ in the primary and secondary coils are the same, φ is also a simple harmonic function, and the table is φ=φmsinωt. According to Faraday's law of electromagnetic induction, the induced electromotive force in the primary and secondary coils is e1=-N1dφ/dt, e2=-N2dφ/dt.
In the formula, N1 and N2 are the number of turns of the primary and secondary coils. It can be seen from the figure that U1=-e1, U2=e2 (the physical quantity of the original coil is indicated by the lower corner 1 and the physical quantity of the secondary coil is indicated by the lower corner 2), and the complex effective value is U1=-E1=jN1ωΦ, U2=E2=-jN2ωΦ, Let k = N1/N2, called the transformer's ratio. From the above formula, U1/U2=-N1/N2=-k, that is, the ratio of the effective value of the transformer primary and secondary coil voltages is equal to its turns ratio and the phase difference between the primary and secondary coil voltages is π.
Transformer core loss has a large relationship with frequency, so it should be designed and used according to the frequency of use. This frequency is called the working frequency.
At a specified frequency and voltage, the transformer can operate for a long period of time without exceeding the output power of the specified temperature rise.
Refers to the voltage that is allowed to be applied to the coil of the transformer and must not be greater than the specified value during operation.
Refers to the ratio of the primary voltage to the secondary voltage of the transformer, which has the difference between the no-load voltage ratio and the load-to-voltage ratio.
When the secondary of the transformer is open, there is still a certain current in the primary. This part of the current is called no-load current. The no-load current consists of magnetizing current (generating magnetic flux) and iron loss current (caused by core loss). For a 50 Hz power transformer, the no-load current is substantially equal to the magnetizing current.
Refers to the power loss measured at the primary when the transformer is open secondary. The main loss is the core loss, followed by the loss (copper loss) of the no-load current on the primary coil copper resistance, which is small.
Refers to the percentage of the ratio of the secondary power P2 to the primary power P1. Generally, the higher the rated power of the transformer, the higher the efficiency.
It indicates the insulation performance between the coils of the transformer and between the coils and the iron core. The insulation resistance is related to the performance of the insulating material used, the temperature and humidity.
Satons transformers mainly use the principle of electromagnetic induction to work. Specifically: when the alternating current voltage U1 is applied to the primary side of the transformer, and the current flowing through the primary winding is I1, the current will generate an alternating magnetic flux in the iron core, so that the primary winding and the secondary winding are electromagnetically connected, according to the principle of electromagnetic induction. .
The alternating magnetic flux passes through the two windings to induce an electromotive force, the magnitude of which is proportional to the number of winding turns and the maximum value of the main magnetic flux. The voltage on the side with a large number of winding turns is high, and the voltage on the side with a small number of winding turns Low, when the secondary side of the transformer is open, that is, when the transformer is unloaded, the secondary terminal voltage is proportional to the number of turns of the secondary winding, that is, U1/U2=N1/N2, but the primary and secondary frequencies are consistent, thereby achieving The change in voltage.
At rated power, the ratio of the output power of the transformer to the input power is called the efficiency of the transformer, ie
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 produce any losses. 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. The first is the hysteresis loss. When the alternating current passes through the transformer, the direction and magnitude of the magnetic field lines passing through the transformer silicon steel sheet 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. In the iron core, magnetic lines of force pass through, and an induced current is generated on a plane perpendicular to the magnetic lines of force. Since this current forms a circulating current from the closed loop and is spiral, it is called eddy current. The presence of eddy currents causes the core to heat up and consume energy. 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 ratio of loss to output power, and the higher the efficiency. Conversely, the lower the power, the lower the efficiency.