| Category | Format | Size |
|---|---|---|
| Shanghai Science Edition Ninth Grade Physics | pptx | 6 MB |
"Transmission of Electric Energy" Where does electric energy come from PPT courseware 3
Description
"Transmission of Electric Energy" Where does electric energy come from PPT courseware 3
Transmission of electrical energy
In order to make rational use of energy, power stations must be built close to these energy sources. There are many places where electricity is used, such as:
Some places are far away from power stations, so electric energy needs to be transported to distant places, which involves the problem of electric energy transmission. Right now:
1. High-voltage power transmission
The voltage of household electricity is 220V, but the voltage on high-voltage transmission lines is usually hundreds of thousands of volts.
Why use high voltage power transmission?
High-voltage power transmission - reduces power losses on transmission lines
The conductor has a certain resistance. Since the transmission line is long and the resistance is large, when the current passes through the transmission line, it generates heat Q and loses part of the electrical energy.
(1) Reduce wire resistance
According to the resistance law, R=p L/S
① Reduce the resistivity ρ of the material. Silver has the smallest resistivity, but it is expensive. Currently, copper or aluminum with smaller resistivity is used as transmission lines.
②It is not feasible to reduce the length L of the transmission line because the transmission distance must be ensured.
③The cross-sectional area can be appropriately increased. It is impossible to make it too thick, which is uneconomical and difficult to erect.
(2) Reduce the current in the transmission line
according to:
P power=UI
p loss=I2R
When the total power transmitted is constant and the voltage increases, the current will decrease, so less electric energy will be lost in the circuit. Therefore, high-voltage power transmission should be used for long-distance power transmission.
Increasing the transmission voltage is an effective way to reduce the loss of electric energy on transmission lines. High-voltage transmission is used for long-distance transmission.
1. Advantages of power transmission:
Electric energy can be transported to distant places through transmission lines. Compared with the transportation of energy such as coal and oil, which requires a large number of transportation vehicles, "convenience and economy" are its outstanding advantages.
2. Basic requirements for transmitting electrical energy:
Reliable, quality guaranteed and economical.
Reliability: refers to ensuring that the power supply line works reliably with few failures and power outages.
Quality assurance: It means ensuring the quality of electric energy, that is, stable voltage and frequency.
Economy: refers to the low cost of construction and operation of transmission lines and small power loss.
3. High-voltage electric shock and its protection
Why don't electrical appliances use high-voltage electricity directly?
The insulation protection requirements of high-voltage electricity are very high, and it is very unsafe to directly supply household appliances.
People may get electric shock if they are close to high-voltage electrified objects.
protection
(1) To prevent personal injury caused by high-voltage electric shock: you must stay away from high-voltage charged objects.
(2) If a high-voltage transmission line is found to reach the ground:
Do not approach, set up warning signs immediately, and notify the relevant power department to carry out emergency repairs.
Principles for safe use of electricity: Do not contact low-voltage charged objects and do not approach high-voltage charged objects.
Practice in class
1. High-voltage power transmission is used to transmit alternating current over long distances. my country's Northwest Power Grid is building a 750kV line. The advantages of using high voltage power transmission are ( )
A. Saves copper on power lines
B． The frequency of AC power can be adjusted as needed
C． Reduces energy losses on transmission lines
D． Can speed up power transmission
2. In the process of long-distance power transmission, in order to reduce the power loss on the transmission line, the best method that can be adopted is ( )
A. Make the power lines thicker.
B． Reduce the length of power lines.
C． Reduce power-on time.
D． High voltage power transmission is used.
3. To transmit an alternating current of a certain power over a long distance, if the transmission voltage is increased to n times its original value, then which of the following statements is correct ( )
A. The current on the transmission line increases n times
B． The voltage loss on the transmission line becomes 1/n2 of the original
C． The electrical power loss on the transmission line becomes 1/n of the original
D． If the electrical power loss on the transmission line remains unchanged, the length of the transmission line can be n2 times the original length.
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"Transmission of Electric Energy" Where does electric energy come from PPT courseware:
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Update Time: 2024-07-04
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