Transformer (Transformer) is a device that uses the principle of electromagnetic induction to change the AC voltage. The main components are the primary coil, the secondary coil and the iron core (magnetic core). The main functions are: voltage transformation, current transformation, impedance transformation, isolation, voltage stabilization (magnetic saturation transformer), etc. According to the purpose, it can be divided into: power transformers and special transformers (electric furnace transformer, rectifier transformer, power frequency test transformer, voltage regulator, mining transformer, audio transformer, intermediate frequency transformer, high frequency transformer, impact transformer, instrument transformer, electronic transformer , Reactors, transformers, etc.). Circuit symbols often use T as the beginning of the number. Example: T01, T201, etc.
Characteristic Parameters:
working frequency
The 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 operating frequency.
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.
Rated voltage
Refers to the voltage allowed to be applied to the coil of the transformer, which shall not exceed the specified value during operation.
Voltage ratio
Refers to the ratio of the primary voltage to the secondary voltage of the transformer. There is a difference between the no-load voltage ratio and the load voltage ratio.
No-load current
When the transformer secondary is open, the primary still has a certain current, and this part of the current is called no-load current. No-load current is composed of magnetizing current (generating magnetic flux) and iron loss current (caused by iron core loss). For a 50Hz power transformer, the no-load current is basically equal to the magnetizing current.
Load loss
Refers to the power loss measured at the primary of the transformer 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. This part of the loss is very small.
effectiveness
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.
Insulation resistance
It indicates the insulation performance between each coil of the transformer and between each coil and the iron core. The insulation resistance is related to the performance, temperature and humidity of the insulating material used.
The relationship between transformer voltage and number of turns
All the coils of the transformer are wound on a closed core, and the magnetic flux Φ passing through each section of the core is the same.
U1/N1 represents the induced electromotive force of each turn of the coil on the primary side;
U2/N2 represents the induced electromotive force of each coil on the secondary side;
The induced electromotive force E=-dΦ/dt, since the magnetic flux Φ in the iron core is the same, the induced electromotive force of each turn of the coil is the same. Therefore, there are:
U1/N1=U2/N2
Slightly deform it to get:
U1/U2=N1/N2
Analysis of the relationship between the number of turns and the voltage ratio of the low frequency transformer
1. The purpose of the experiment
1. Understand the basic structure of the transformer;
2. Explore the relationship between the voltage across the transformer and the number of turns;
3. Learn to use the controlled variable method to analyze the relationship between physical quantities.
2. Experimental principle
Keep the number of turns of the primary coil unchanged and change the number of turns of the secondary coil. When the primary of the transformer is connected to both ends of "0" and "400" turns, the secondary is connected to both ends of n2 ("0", "200" turns) and n%272 ("0", "800" turns). Use the AC voltage file of the multimeter to measure the secondary voltage, record the data U2+, U%272, and compare whether the relationship between the ratio of the two secondary voltages and the turns ratio meets:
Keep the number of turns of the secondary coil unchanged and change the number of turns of the primary coil. When the primary of the transformer is connected to the two ends of n1 ("0", "100" turns) and n%271+ ("0", "400" turns), the secondary is connected to both ends of "0" and "200" turns . Measure the secondary voltage with the voltage file of the multi-purpose voltmeter. Record the data U2+, U%272+, and compare whether the relationship between the ratio of the secondary voltage and the turns ratio meets:
3. Experimental equipment
1 detachable transformer, 1 student power supply (AC 0~12V adjustable), 1 multi-meter (including 0~50V AC voltage file), and several wires.
4. Experimental design and process
1. Observe the transformer carefully and understand its structure.
2. Disconnect the student's power supply, connect the power modulated AC 2V to n1%3D100 turns of the primary coil, adjust the student multimeter to the maximum AC voltage level and connect it to the secondary "0" and "200" terminals. Turn on the power and measure the voltage roughly. Turn off the power switch, adjust the multimeter to an appropriate range of AC voltage, turn on the power again, and measure the voltage across the secondary coil.
3. Disconnect the power supply, without changing the voltage and the number of turns connected to the primary coil, set the student multimeter to the maximum AC voltage level and connect it to the secondary "200" and "800" terminals; "800", "1600" Terminal; "200", "1600" terminal; "0", "1600" terminal. Measure separately according to the measurement method in step 2.
4. Disconnect the power supply, connect the power modulated AC 10V to n1%3D200 turns of the primary coil, adjust the student multimeter to the maximum AC voltage level and connect it to the secondary "0" and "400" terminals. After the inspection is correct, connect it Power supply, roughly measure the voltage. Turn off the power switch, adjust the multimeter to an appropriate range of AC voltage, turn on the power again, and measure the voltage across the secondary coil.
5. Disconnect the power supply and keep the power supply's AC 10V gear unchanged. The primary level is connected to the terminals "200" and "800"; terminals "800" and "1600"; terminals "200" and "1600"; "," 1600" terminal, keep the student's multi-meter at the maximum AC voltage level connected to the secondary "0", "400" terminal unchanged, and measure them according to the measurement method in step 4.
6. Turn off the power switch. After the experiment, organize the experimental equipment.
Five, collect data
1. Keep the number of turns of the primary coil n1 and voltage U1 unchanged, change the number of turns of the secondary coil n2, and study the + influence of n2 on the secondary coil voltage U2.
2. Keep the number of turns of the secondary coil n2 and voltage U1 unchanged, change the number of turns of the primary coil n1, and study the influence of n1 on the secondary coil voltage U2.
Six, analysis and demonstration
Within the allowable range of error, it is not difficult to sum up the relationship between the voltage of the primary and secondary coils and the number of turns using mathematical induction.
Seven, error analysis
1. Most of the magnetic flux produced by the current in the primary coil and the secondary coil passes through the iron core, and a small part leaks out of the iron core. Therefore, the voltage ratio can only be slightly greater than the turns ratio for this experiment with a transformer.
2. Because of the resistance of the primary and secondary coil, the terminal voltage of the coil is less than the induced voltage. The improvement method is to replace the smooth surface between the whole iron core and the bar-shaped iron yoke with an iron core laminated with mutually insulating silicon steel sheets, and clean without rust spots and stains, and the iron core and the bar-shaped iron yoke should be tightened with screws.
8. Matters needing attention:
1. Use a low-voltage AC power supply for the test power supply, and the voltage should not exceed 12V. You cannot use a DC power supply, nor can you use a high-voltage AC power supply.
2. After the circuit is connected, several students in the same group will independently check the power supply.
3. To connect the circuit, cut off the power supply. Do not touch the exposed wires and terminals when adjusting.
4. For the safety of multi-meters, when using AC voltage, first use the largest range to test, roughly determine the measured voltage, and then select the appropriate range for measurement.
5. The number of turns of the secondary coil should vary from small to large, and the number of turns of the primary coil should vary from large to small.
This is the end of the relevant introduction about low-frequency transformers. I hope this article will give you a more comprehensive understanding of low-frequency transformers.