Transformer: A device that uses two coils wound on the same core to change voltage, current and power by mutual inductance coupling.
1. Principle The transformer is a device that converts AC voltage, current and impedance. When an AC current is passed through the primary coil, an AC flux is generated in the core (or core) to induce a voltage (or current) in the secondary coil. ). 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. In the generator, whether the coil motion passes through the fixed coil through the magnetic field or the magnetic field, the potential can be induced in the coil. In both cases, the value of the magnetic flux is constant, but the number of magnetic fluxes intersecting the coil is Change, this is the principle of mutual induction. A transformer is a device that uses electromagnetic mutual induction to transform voltage, current, and impedance. The primary secondary voltage and the number of coil turns have the following relationship: U1/U2=N1/N2, current ratio: I1/I2=N2/N1, electric power: P1=P2 (P1=P2+ P3... for multiple secondary coils)
The transformer has three operating states, namely: 1. changing the voltage; 2. changing the current; 3. changing the impedance.
The first working state: the transformer can change the voltage, that is, the so-called transformer;
The second working state: the transformer can change the current, that is, the current transformer, that is, the current transformer;
The third working state: the transformer can change the impedance, that is, the line transformer, the output transformer, the matching transformer, and the like.
Commonly used for transformer protection are: primary protection (gas and differential) to protect internal faults. Backup protection is fast and overcurrent. There is also a semi-insulated structure of neutral point overvoltage protection (arrester), oil temperature alarm and other gas protection: to deal with various faults in the transformer and the reduction of oil level, in the high-power oil-immersed transformer differential protection: response to the transformer Fault backup protection on windings, bushings and lead-out lines: When the main protection does not operate for various reasons, after a short delay (the delay time is based on the requirements of each circuit), another protection will start and act and will fail. The loop jumps open.
Second, the types and characteristics of commonly used transformers
1. The classification of common transformers can be summarized as follows:
(1) According to the number of phases:
1) Single-phase transformer: for single-phase load and three-phase transformer group. 2) Three-phase transformer: used for the rise and fall voltage of three-phase systems.
(2) According to the cooling method: 1) Dry-type transformer: It relies on air convection to cool, and is generally used for small-capacity transformers such as local lighting and electronic circuits. 2) Oil-immersed transformer: rely on oil as cooling medium, such as oil-immersed self-cooling, oil-infiltrated 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 conduct high voltage insulation strength test on high voltage electrical equipment, electrical parts and insulation materials.
4) Special transformers: such as electric furnace transformers, rectifier transformers, adjusting transformers, etc. (4) According to the winding form:
1) Two-winding transformer: used to connect two voltage levels in the power system.
2) Multi-winding transformer: Generally used in power system regional substation, connecting three voltage levels.
3) Single (auto-coupled) winding transformer: used to connect different voltage power systems. It can also be used as a normal boost or post-down transformer.
2. Characteristic parameters of power transformer (1) Operating frequency Transformer core loss has a great relationship with frequency, so it should be designed and used according to the frequency of use. This frequency is called the working frequency.
(2) Rated power Under the specified frequency and voltage, the transformer can work for a long time without exceeding the output power of the specified temperature rise.
(3) Rated voltage refers to the voltage allowed on the coil of the transformer, and shall not exceed the specified value during operation.
(4) The voltage ratio refers to the ratio of the primary voltage to the secondary voltage of the transformer, and has the difference between the no-load voltage ratio and the load voltage ratio.
(5) When the no-load current transformer is open secondary, 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.
(6) No-load loss refers to the power loss measured at the primary when the secondary of the transformer is open. 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.
(7) Efficiency 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.
(8) The insulation resistance represents the insulation performance between the coils of the transformer and between the coils and the iron core. The level of insulation resistance is related to the properties of the insulation used, the temperature and the degree of humidity.
1. Principle The transformer is a device that converts AC voltage, current and impedance. When an AC current is passed through the primary coil, an AC flux is generated in the core (or core) to induce a voltage (or current) in the secondary coil. ). 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. In the generator, whether the coil motion passes through the fixed coil through the magnetic field or the magnetic field, the potential can be induced in the coil. In both cases, the value of the magnetic flux is constant, but the number of magnetic fluxes intersecting the coil is Change, this is the principle of mutual induction. A transformer is a device that uses electromagnetic mutual induction to transform voltage, current, and impedance. The primary secondary voltage and the number of coil turns have the following relationship: U1/U2=N1/N2, current ratio: I1/I2=N2/N1, electric power: P1=P2 (P1=P2+ P3... for multiple secondary coils)
The transformer has three operating states, namely: 1. changing the voltage; 2. changing the current; 3. changing the impedance.
The first working state: the transformer can change the voltage, that is, the so-called transformer;
The second working state: the transformer can change the current, that is, the current transformer, that is, the current transformer;
The third working state: the transformer can change the impedance, that is, the line transformer, the output transformer, the matching transformer, and the like.
Commonly used for transformer protection are: primary protection (gas and differential) to protect internal faults. Backup protection is fast and overcurrent. There is also a semi-insulated structure of neutral point overvoltage protection (arrester), oil temperature alarm and other gas protection: to deal with various faults in the transformer and the reduction of oil level, in the high-power oil-immersed transformer differential protection: response to the transformer Fault backup protection on windings, bushings and lead-out lines: When the main protection does not operate for various reasons, after a short delay (the delay time is based on the requirements of each circuit), another protection will start and act and will fail. The loop jumps open.
Second, the types and characteristics of commonly used transformers
1. The classification of common transformers can be summarized as follows:
(1) According to the number of phases:
1) Single-phase transformer: for single-phase load and three-phase transformer group. 2) Three-phase transformer: used for the rise and fall voltage of three-phase systems.
(2) According to the cooling method: 1) Dry-type transformer: It relies on air convection to cool, and is generally used for small-capacity transformers such as local lighting and electronic circuits. 2) Oil-immersed transformer: rely on oil as cooling medium, such as oil-immersed self-cooling, oil-infiltrated 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 conduct high voltage insulation strength test on high voltage electrical equipment, electrical parts and insulation materials.
4) Special transformers: such as electric furnace transformers, rectifier transformers, adjusting transformers, etc. (4) According to the winding form:
1) Two-winding transformer: used to connect two voltage levels in the power system.
2) Multi-winding transformer: Generally used in power system regional substation, connecting three voltage levels.
3) Single (auto-coupled) winding transformer: used to connect different voltage power systems. It can also be used as a normal boost or post-down transformer.
2. Characteristic parameters of power transformer (1) Operating frequency Transformer core loss has a great relationship with frequency, so it should be designed and used according to the frequency of use. This frequency is called the working frequency.
(2) Rated power Under the specified frequency and voltage, the transformer can work for a long time without exceeding the output power of the specified temperature rise.
(3) Rated voltage refers to the voltage allowed on the coil of the transformer, and shall not exceed the specified value during operation.
(4) The voltage ratio refers to the ratio of the primary voltage to the secondary voltage of the transformer, and has the difference between the no-load voltage ratio and the load voltage ratio.
(5) When the no-load current transformer is open secondary, 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.
(6) No-load loss refers to the power loss measured at the primary when the secondary of the transformer is open. 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.
(7) Efficiency 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.
(8) The insulation resistance represents the insulation performance between the coils of the transformer and between the coils and the iron core. The level of insulation resistance is related to the properties of the insulation used, the temperature and the degree of humidity.
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