Basic Electronics Knowledge--Working Principle of Transformer

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Basic Electronics Knowledge--Working Principle of Transformer [Copy link]

Transformer is a device that transforms AC voltage, current and impedance. When AC current flows through the primary coil, AC magnetic flux is generated in the iron core (or magnetic core), which induces voltage (or current) in the secondary coil. The transformer consists of an iron core (or magnetic core) and a coil. The coil has two or more windings, of which the winding connected to the power supply is called the primary coil, and the remaining windings are called secondary coils.
1.
Classification Classification by cooling method: dry-type (self-cooling) transformer, oil-immersed (self-cooling) transformer, fluoride (evaporative cooling) transformer. Classification
by moisture-proof method: open transformer, potting transformer, sealed transformer.
Classification by core or coil structure: core transformer (insert iron core, C-type iron core, ferrite iron core), shell transformer (insert iron core, C-type iron core, ferrite iron core), toroidal transformer, metal foil transformer. Classification by the
number of power phases: single-phase transformer, three-phase transformer, multi-phase transformer.
Classification by use: power transformer, voltage regulating transformer, audio transformer, medium frequency transformer, high frequency transformer, pulse transformer.

2. Characteristic parameters of power transformer
1. Working frequency
The core loss of transformer is closely related to the frequency, so it should be designed and used according to the frequency of use. This frequency is called 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 to be applied to the coil of the transformer, which shall not be greater than the specified value during operation.
4. Voltage ratio
refers to the ratio of the primary voltage to the secondary voltage of the transformer, which is distinguished by the no-load voltage ratio and the load voltage ratio.
5. No-load current
When the secondary of the transformer is open, there is still a certain current in the primary, which 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 50Hz power transformers, the no-load current is basically 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) caused by the no-load current on the copper resistance of the primary coil, which is very small.
7. Efficiency
refers to the percentage of the ratio of secondary power P2 to primary power P1. Generally, the greater the rated power of the transformer, the higher the efficiency.
8 Insulation resistance
indicates the insulation performance between the coils of the transformer and between the coils and the core. The insulation resistance is related to the performance of the insulation material used, the temperature and humidity.

3. Audio transformer and high frequency transformer characteristic parameters
1 Frequency response
refers to the characteristics of the transformer secondary output voltage changing with the operating frequency.
2 Passband
If the output voltage of the transformer at the intermediate frequency is U0, the frequency range when the output voltage (input voltage remains unchanged) drops to 0.707U0 is called the transformer passband B.
3 Primary and secondary impedance ratio
The primary and secondary of the transformer are connected to appropriate impedances Ro and Ri to match the primary and secondary impedances of the transformer. The ratio of Ro and Ri is called the primary and secondary impedance ratio. Under the condition of impedance matching, the transformer works in the best state and the transmission efficiency is the highest.