Transformer
1. Explain the principle and use of a transformer in an alternating current circuit.
Solution:
A transformer is a device that changes alternating voltage and current to alternating voltage and current of different values, but of the same frequency.
A single-phase transformer has these parts:
- Core made of soft steel (closed)
- Primary coil (N1, U1, I1) connected to the source of alternating current
- Secondary coil (N2, U2, I2) serves as the source of the transformed current and voltage
2.Complete the table:
Solution:
3.The transformer has N1 = 1000 and N2 = 150 turns. The primary coil is connected to a voltage U1 = 220V and carries a current I1 = 0.3A. What is the voltage and current at the terminals of the secondary coil?
Solution:
Analysis:
At the terminals of the secondary coil, the voltage is U2 = 33V and the current is I2 = 2A.
4.The primary coil of the transformer carries a current of 0.2A at a voltage of 220V. The secondary coil carries a current of 6A and the voltage at the coil terminals is 6.3V. Determine the efficiency of the transformer.
Solution:
Analysis:
The efficiency of the transformer is η = 86%.
5.The primary coil of a transformer has 1000 turns, the secondary 1500 turns. The transformer is connected to a harmonic alternating voltage of 220V. What is the voltage at the secondary coil if the transformer is not loaded? What is the voltage at the secondary coil if the resistance of its winding is R2 = 2Ω and it carries a current I2 = 4A?
Solution:
Analysis:
N1 = 1000, N2 = 1500, U1 = 220V, R2 = 2Ω, I2 = 4A.
The voltage at the secondary coil, if the transformer is not loaded, is U2 = 330V; when the transformer is loaded, it is U‘2 = 322V.
6.An induction furnace consists of a transformer whose secondary coil is a single closed turn in the form of a trough into which the material to be melted is placed. Calculate the current flowing in the secondary circuit with a resistance of 0.01Ω. The primary coil connected to the AC source of 240V has 60 turns. What amount of Joule heat is released in the secondary coil in 1 minute?
Solution:
Analysis:
In the secondary coil, 96kJ of heat is released.
7.The primary coil of a transformer has 2400 turns and input power of 2000W. What is the voltage and current in the secondary coil if the transformer has an efficiency η = 90% and the secondary coil has 120 turns? The voltage at the primary coil is 2200V.
Solution:
Analysis:
At the secondary coil, the voltage is U2 = 110V, the current is I2 = 16.4A.
8.The primary coil of a transformer has 2400 turns, a resistance of 120Ω, is connected to AC voltage of 2200V and has an input power of 2000W. The secondary coil has 120 turns and a resistance of 0.05Ω.
- Determine the voltage and current in the secondary coil if η = 90%.
- What energy losses are due to heating of the coils per 1 second?
Solution:
Analysis:
- In the secondary coil, U2 = 110V and I2 = 16.4A.
- 112.57 J of heat is consumed for heating the coils.