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Questions and Answers
Electric Power Distribution exclusively utilizes voltages above 35 kv.
Electric Power Distribution exclusively utilizes voltages above 35 kv.
False
Distribution transformers raise the voltage to the utilization voltage used by appliances.
Distribution transformers raise the voltage to the utilization voltage used by appliances.
False
Overhead power lines can transmit electrical energy across large distances.
Overhead power lines can transmit electrical energy across large distances.
True
Circuit breakers and switches in a power substation allow connections to be made without any disconnection.
Circuit breakers and switches in a power substation allow connections to be made without any disconnection.
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Secondary distribution lines connect residential customers directly to the primary distribution lines.
Secondary distribution lines connect residential customers directly to the primary distribution lines.
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Bare wire conductors on the line are primarily made of copper.
Bare wire conductors on the line are primarily made of copper.
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Transmission lines operate at very high voltage, while distribution lines operate at low voltage levels.
Transmission lines operate at very high voltage, while distribution lines operate at low voltage levels.
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The main purpose of the distribution line is to move electricity from the power plant to substations.
The main purpose of the distribution line is to move electricity from the power plant to substations.
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Transmission lines are typically thinner than distribution lines.
Transmission lines are typically thinner than distribution lines.
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Both transmission and distribution lines utilize a three-phase supply system.
Both transmission and distribution lines utilize a three-phase supply system.
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A short transmission line is defined as having a voltage not exceeding 66 kV.
A short transmission line is defined as having a voltage not exceeding 66 kV.
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The capacitance effect is significant for short transmission lines.
The capacitance effect is significant for short transmission lines.
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Medium transmission lines are classified as those ranging from 80 to 240 km in length.
Medium transmission lines are classified as those ranging from 80 to 240 km in length.
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In the T model for medium transmission lines, the capacitance is assumed to be concentrated at the ends of the line.
In the T model for medium transmission lines, the capacitance is assumed to be concentrated at the ends of the line.
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Long transmission lines are those that exceed 240 km in length.
Long transmission lines are those that exceed 240 km in length.
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Power transformers are typically used in lower voltage distribution networks.
Power transformers are typically used in lower voltage distribution networks.
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Distribution transformers have a maximum rating of usage less than 200 MVA.
Distribution transformers have a maximum rating of usage less than 200 MVA.
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Power transformers are larger in size compared to distribution transformers.
Power transformers are larger in size compared to distribution transformers.
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The designed efficiency of a power transformer is around 50-70%.
The designed efficiency of a power transformer is around 50-70%.
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Efficiency for distribution transformers is calculated based on the input and output in kilowatt hour over 24 hours.
Efficiency for distribution transformers is calculated based on the input and output in kilowatt hour over 24 hours.
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Study Notes
Electrical Power Distribution
- Electric power distribution is the final stage of delivering electricity from the transmission system to consumers.
- Distribution substations connect to the transmission system and lower the transmission voltage to medium voltage, ranging between 2 kV and 35 kV using transformers.
- Primary distribution lines carry this medium voltage power to distribution transformers located near customer premises.
- Distribution transformers lower the voltage further to the utilization voltage used by lighting, industrial equipment, and household appliances.
- Several customers are supplied by one transformer through secondary distribution lines, with service drops connecting to commercial and residential customers.
- Customers requiring a large amount of power may be connected directly to the primary distribution level or the sub-transmission level.
Overhead Distribution Line
- An overhead power line is a structure used in electric power transmission and distribution to transmit electrical energy across large distances.
- It comprises one or more uninsulated electrical cables (typically multiples for three-phase power) suspended by towers or poles.
- Towers are typically made of wood (grown or laminated), steel, or aluminum (either lattice or tubular poles), or concrete, and sometimes reinforced plastics.
- Conductors are usually made of aluminum (plain or reinforced with steel, or composite materials like carbon and glass fiber). Some copper is used for medium-voltage and low-voltage connections to customer premises.
- Overhead lines, with bare conductors, are simple in configuration and mounted on towers or poles.
Difference Between Transmission and Distribution Line
- Both transmission and distribution lines carry electrical power, but they differ significantly in usage, voltage level, current conduction level, thickness, and more.
- Transmission lines move electricity from power plants to substations. Distribution lines carry electricity from substations to consumers (residential and commercial).
- Transmission lines use three-phase supply systems. Distribution lines use single-phase supply systems.
- Transmission lines operate at very high voltages (e.g., 11,000 volts). Distribution lines operate at much lower voltages (e.g., 220 volts) for safety.
- Transmission lines are thicker than distribution lines due to higher current carrying capacity.
Difference Between Power Transformer and Distribution Transformer
- Power transformers are installed at power stations for generation and transmission of electricity. They step voltages up or down as needed and connect power stations.
- Distribution transformers bring down voltage/current levels of a transmission line to a predefined "safety level" for consumers in domestic and industrial use.
- Power transformers use higher voltage ratings (e.g., 400kV, 200kV, 110kV, etc), while distribution transformers use lower voltage ratings (e.g., 11 kV, 6.6kV, 3.3kV, etc).
- Power transformers are sized larger than distribution transformers.
- Power transformers are designed for maximum efficiency (100%), whereas distribution transformers operate at 50-70% efficiency.
- Power transformers are used in generating stations and transmission substations, while distribution transformers are used in distribution stations for transmitting to consumers.
AC Transmission Line
- AC transmission lines use resistance, inductance, capacitance, and leakage conductance. These characteristics, along with the load, define the line's performance.
- Short transmission lines (under 80kV or 66kV): capacitance is negligible and performance is based on resistance and inductance.
- Medium transmission lines (80-240km): capacitance is important and considered lumped, and both inductance and capacitance affect operation.
- Long transmission lines (greater than 240km): all four parameters (resistance, inductance, capacitance, and leakage conductance) are distributed along the entire line's length.
DC Transmission Line
- DC transmission is used for bulk power transmission over long distances.
- DC transmission systems are more expensive for short-distance lines due to equipment requirements.
- DC transmission is less expensive for long-distance lines with lower electrical losses compared to AC.
- Converter stations convert AC to DC at the sending end and DC to AC at the receiving end.
Differences Between AC and DC Transmission Lines
- AC transmission lines use alternating current, while DC lines use direct current.
- AC lines are typically cheaper for short distances due to easier voltage transformation.
- AC lines have inherent inductance and surges compared to DC
- AC power lines require transformers for altering voltage, while DC uses booster/choppers.
- AC lines have higher voltage drop, are more susceptible to interference, have dielectric loss, require more insulation, and have synchronizing difficulties.
Underground Transmission Line
- Underground transmission lines involve cables laid beneath the ground.
- Underground cables provide uninterruptable power and reduced risks of fault due to external factors (rain, wind).
- Disadvantages include higher costs, difficulties locating and restoring faults, and potential heat dissipation issues.
- Choosing the best type of line depends on the particular application and factors like cost, reliability, and environmental conditions.
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Description
This quiz covers the key concepts of electric power distribution, including the functioning of transformers, the characteristics of overhead power lines, and the differences between transmission and distribution lines. Test your knowledge on how electricity is distributed from power plants to residential areas along with voltage classifications and the role of circuit breakers.
