Three-phase alternating current is a form of electrical energy transmission, called three-phase energy. Three-phase AC power is a power supply consisting of three AC potentials with the same frequency, amplitude and phase differences of 120° from each other. Three-phase alternating current has many uses. Most AC electrical equipment in industry, such as motors, uses three-phase AC, which is the often-mentioned three-phase, four-wire system. In daily life, single-phase power supply, also called lighting power, is mainly used. When lighting electricity is used for power supply, one phase of the three-phase power supply is used to power electrical equipment, such as household appliances, and the other wire is the fourth wire among the three-phase wires to four wires, which is the neutral wire. The neutral line is drawn from the neutral point of three-phase electricity.
The concept of "three-phase electricity" is: when the coil rotates in the magnetic field, the wire cuts the magnetic field lines to produce induced electromotive force, and its changing pattern can be represented by a sinusoidal curve. If we take three coils and place them at a 120 degree angle from each other in space, the three coils will always rotate at the same speed in the magnetic field and three induced emfs of the same frequency will be induced. Since the spatial positions of the three coils differ by 120 degrees from each other, the current generated is also a three-phase sinusoidal change, called three-phase sinusoidal alternating current. Many places in industrial equipment use three-phase power, such as three-phase AC motors.
The tension between twox phases is 380 VAC and the voltage at any relative neutral point is 220 VAC. Divided into phase A, phase B and phase C. The lines are represented by L1, L2 and L3. (Three phase AC also has 660VAC and 6000VAC power supply due to different usage).
A generator capable of producing potentials with equal amplitudes, equal frequencies and a phase difference of 120° is called a three-phase generator; a three-phase generator is used as the power source, called a three-phase generator; three-phase power supply; a three-phase power supply The circuit which supplies the energy is called a three-phase circuit. U, V and W are called three phases. The voltage between the phases is the line voltage and the voltage is 380 V. The voltage between the phase and the neutral point is called phase voltage and the voltage is 220 V. The neutral line is connected to the neutral point and to any live wire to supply currentsingle-phase power.
Power plants use three-phase generators, which emit three-phase alternating current. the electricity generated by each three-phase generator has three phases A, B and C and one phase N (neutral wire). The neutral wire is generally not transmitted externally. There are five wires visible on the high voltage iron tower. The first two are lightning protection wires and the last three are three-phase live wires A, B and C.
There is a time difference in the current flowing in each wire, it It is therefore not necessary to have six wires to provide energy. Instead, only three windings are connected in some way inside the generator to use three or. four wires for power. The alternating current emitted by each winding of the generator is called one phase of the three-phase alternating current, which is the useful single-phase alternating currentized.
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Problems that need to be paid attention to in transmission lines< /p>
1 , path selection
PathSelection and investigation are the key to all line design. The rationality of the plan plays an important role in economic and technical indicators as well as in the conditions of construction and operation of the line.
2. Selection of poles and towers
Different types of poles and towers are different in terms of cost, land use, construction, transportation and operational safety. for about 10% of the entire project, 30% to 40%. Reasonable selection of tower type is the key.
3. Foundation design
As an important part of the transmission line structure, the tower foundation accounts for a large part of the entire line project in terms of cost, pperiod of construction and labor. consumption. The construction period accounts for about half of the total construction period, the transportation volume accounts for about 60% of the entire project, and the cost accounts for about 20% to 35% of the entire project. The quality of foundation selection, design, and construction directly affects the construction of the line project.
Baidu Encyclopedia-Transmission lines
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