Transformers and Power Transmission
Transformers are a very important component in present-day life as they make large power systems feasible. To efficiently transfer numerous megawatts of power across countries, very high line voltages are required– in the series of 161 to 1000 kV.
Nonetheless, the highest possible functional designed voltage for large generators is about 25 kV. The ideal transformer has an output power nearly equal to the input power. While for an actual transformer, the output power is always less than input power due to power losses.
Power Transformation
The transformer has no internal moving components, and also it moves energy from one circuit to the other by electromagnetic induction. There may be external cooling which might consist of heat exchangers, radiators, fans, and oil pumps.
Transformers are generally used because a change in voltage is required. Electrical power is transformed from its primary coil to the secondary coil due to changing flux.
Principle for Transmission
This relation describes that currents are inversely proportional to the respective voltage, therefore in a step-up transformer when Vs increases, current decreases. This is the principle that is used for the electrical supply network, where the transformer increases the voltage and reduces the current, so it can be transmitted over long distances.
Power losses in Transformer
The power losses in transformers are due to the following reasons:
- Eddy Currents
The induced currents are setup due to changes in magnetic flux in the closed conducting loops. These currents are in a perpendicular direction to the flux so as to oppose the cause that produces them and is called eddy currents.
This problem can be reduced by using a laminated core between the lamination sheets. It will stop flowing eddy currents.
- Hysteresis Loss
This one is due to repeated and continuous magnetization and demagnetization of the core due to the flow of alternating current.
This problem can be solved by using a soft iron core in transformers.
Reduction in Power loss during Transmission
Generation of electrical power at low voltage is much cost-effective. Theoretically, this reduced voltage power can be sent to the receiving end. This low voltage if transmitted causes greater line current which without a doubt triggers even more power losses.
However, if the voltage of a power is increased, the current of the power is decreased which creates a decrease in ohmic or I2R losses in the system, reduction in the cross-sectional area of the conductor i.e., a decrease in capital cost of the system and also it also boosts the voltage regulation of the system.
Due to these, reduced power must be stepped up for reliable electrical power transmission. This is done by step-up transformer at the sending outside of the power system.
As this high voltage power may not be dispersed to the consumers straight, this should be stepped down to the desired level at the receiving end with the help of a step-down transformer.
MCQs
- What is the typical range of line voltages required for efficient power transmission across countries?
- A) 25 to 100 kV
- B) 161 to 1000 kV
- C) 10 to 50 kV
- D) 500 to 1000 kV
- Answer: B) 161 to 1000 kV
- Which of the following statements about transformers is true?
- A) Transformers have internal moving components.
- B) Transformers transfer energy through mechanical means.
- C) Transformers move energy from one circuit to another through electromagnetic induction.
- D) Transformers are primarily used for mechanical power transmission.
- Answer: C) Transformers move energy from one circuit to another through electromagnetic induction.
- What is the primary purpose of using transformers in power systems?
- A) To decrease voltage
- B) To increase voltage
- C) To reduce power losses
- D) To increase current
- Answer: B) To increase voltage
- Which principle governs the relationship between voltage and current in transformers?
- A) Ohm’s Law
- B) Faraday’s Law
- C) Coulomb’s Law
- D) Transmission Principle
- Answer: D) Transmission Principle
- How are eddy currents minimized in transformers?
- A) By increasing the voltage
- B) By using a laminated core
- C) By decreasing the frequency
- D) By using a soft iron core
- Answer: B) By using a laminated core
- What causes hysteresis loss in transformers?
- A) Changes in temperature
- B) Changes in magnetic flux
- C) Changes in voltage
- D) Changes in frequency
- Answer: B) Changes in magnetic flux
- Why is electrical power generated at low voltage levels?
- A) To reduce power losses
- B) To decrease the efficiency of transmission
- C) To increase line current
- D) To increase power losses
- Answer: A) To reduce power losses
- What is one advantage of increasing voltage during power transmission?
- A) Increase in line current
- B) Decrease in ohmic losses
- C) Decrease in transformer size
- D) Increase in power losses
- Answer: B) Decrease in ohmic losses
- How is the voltage increased during power transmission?
- A) By decreasing line current
- B) By increasing transformer size
- C) By using a step-up transformer
- D) By decreasing the cross-sectional area of conductors
- Answer: C) By using a step-up transformer
- What is the purpose of a step-down transformer in power transmission?
- A) To increase voltage
- B) To decrease voltage
- C) To increase power losses
- D) To decrease line current
- Answer: B) To decrease voltage
- Which type of losses occur due to eddy currents in transformers?
- A) Hysteresis losses
- B) Mechanical losses
- C) Core losses
- D) Iron losses
- Answer: C) Core losses
- How can hysteresis loss in transformers be reduced?
- A) By using a laminated core
- B) By increasing the frequency
- C) By decreasing the voltage
- D) By using a soft copper core
- Answer: A) By using a laminated core
- What does the Transmission Principle state about the relationship between voltage and current in transformers?
- A) Directly proportional
- B) Inversely proportional
- C) Unrelated
- D) Constant
- Answer: B) Inversely proportional
- Which component is responsible for transferring energy from one circuit to another in a transformer?
- A) Capacitor
- B) Inductor
- C) Rectifier
- D) Transformer
- Answer: D) Transformer
- Why is voltage increased during power transmission?
- A) To increase power losses
- B) To decrease line current
- C) To decrease ohmic losses
- D) To increase transformer size
- Answer: C) To decrease ohmic losses
- What is the primary reason for using transformers in power transmission?
- A) To decrease voltage
- B) To increase current
- C) To increase voltage
- D) To decrease power losses
- Answer: C) To increase voltage
- How are eddy currents minimized in transformers?
- A) By using a laminated core
- B) By increasing the voltage
- C) By decreasing the frequency
- D) By using a soft iron core
- Answer: A) By using a laminated core
- What type of losses occur due to the repeated magnetization and demagnetization of the core in transformers?
- A) Eddy current losses
- B) Hysteresis losses
- C) Copper losses
- D) Core losses
- Answer: B) Hysteresis losses
- How does increasing voltage during power transmission affect line current?
- A) Increases line current
- B) Decreases line current
- C) No effect on line current
- D) Increases power losses
- Answer: B) Decreases line current
Summary:
Transformers play a crucial role in modern power systems, enabling the efficient transmission of large amounts of electrical power across vast distances.
With line voltages ranging from 161 to 1000 kV, transformers facilitate this transmission by adjusting voltage levels through electromagnetic induction. Despite the theoretical ideal of output power being equal to input power, practical transformers experience losses, primarily due to eddy currents and hysteresis.
Strategies such as using laminated cores and soft iron cores help mitigate these losses. Additionally, increasing voltage during transmission reduces power losses by decreasing line current and improving voltage regulation.
Step-up transformers elevate voltage for long-distance transmission, while step-down transformers lower voltage for consumer use, ensuring reliable power distribution.