What Is Induced Voltage?

When the power transmission line and electrical equipment of the power system are working, due to the continuous change of current, a changing magnetic field will be generated around it. When the changing magnetic field encounters a conductor, it will induce a potential. This process of generating electromotive force is called electromagnetic induction. The voltage generated by electromagnetic and electrostatic induction on conductors near power lines and electrical equipment is called induced voltage. Induced voltage can cause injury to people when they form a conductive loop; there is a safety hazard if a conductive loop is not formed. The induced voltage should be limited to a certain range.

The farther the distance between the power outage equipment, lines and other conductors from the running high-voltage transmission lines and equipment, the lower the induced voltage. Because high voltage transmission lines and equipment operate, induced voltages are generated on the surrounding conductors, because there are varying magnetic and electric fields around the wires. The magnitude of the magnetic field strength is related to the magnitude of the current delivered by the wire. The larger the current, the stronger the magnetic field, regardless of the voltage of the transmission line. The strength of the electric field is proportional to the voltage of the transmission line. The higher the voltage level, the stronger the electrostatic induction to the surrounding, that is, the stronger the alternating electromagnetic field radiation. With the increase of the distance between power outage equipment, lines and other conductors and running high-voltage transmission lines and equipment, the electric and magnetic fields quickly decrease, and the induced voltage naturally decreases. ^[1]

Induced voltages generated on power outage lines and equipment are hidden, deceptive, and dangerous. Therefore, induced voltage electric shocks and injuries often occur, which seriously threatens personal safety. It should be paid great attention to by relevant personnel. The following measures can be adopted to prevent the harm of induced voltage electric shocks.

(1) The power design department should fully consider the impact of electromagnetic radiation of high-voltage electrical equipment and transmission lines on people's production and life when designing. High-voltage transmission lines should be avoided as far as possible from residential areas, factories, enterprises, institutions and villages.

(2) For 110kV and above high-voltage transmission lines, phase-to-phase transposition should be performed to improve the three-phase-to-ground capacitance balance.

(3) Residents should not build residential houses near high-voltage equipment areas and near high-voltage power transmission lines. They should stay away from high-voltage power transmission and transformation equipment as much as possible. Plastic sheds are built under high-voltage transmission lines. If conductive materials are used in the sheds, they must be reliably grounded. Of course, it is better not to build under the high-voltage line.

(4) Minimize the time spent in high-voltage equipment area. Personnel who have been working in high-voltage equipment areas for a long time should take local protective measures, such as grounding equipment that is out of power and limiting working hours to reduce the chance of generating induced voltage shocks.

(5) The design of the transmission line height should conform to national standards. The possible induced voltage shock should be controlled to an allowable level. For example, it is required that the maximum induced current of a car or other metal object near the transmission line does not exceed 5 mA.

(6) According to the actual test, under the high-voltage transmission line, the field strength in severe weather (thunder, torrential rain, snow, high wind, etc.) is 100 times the strength of the electric field in the clear and windless weather; Therefore, in severe weather, it should be far away from high-voltage lines and high-voltage equipment.

(7) Test the power correctly. Non-electrical workers, before touching the power-off equipment line, test whether it is live according to the following method. Just touch it with the back of your finger. If the equipment line has induced voltage, your hand will rebound. At this time, you must not touch it with your finger. Because if there is induced electricity, the normal response of a person is to contract, and they will grab the equipment and lines that have induced voltage and cannot escape. ^[2]

= BLV

B: Magnetic field size

L: lead length

V: Speed of cutting magnetic lines

The difference between the induced voltage and the actual voltage: In a series circuit, the larger the resistance, the greater the divided voltage on the resistance, but the smaller the current through the resistance. The induced voltage between the object and the AC line due to the capacitive effect. When you take a measurement with a voltmeter, it is equivalent to AC power passing through the capacitor and the resistance of the voltmeter to form a loop to ground. However, the capacitance in this circuit is very small, so the capacitive reactance is very large, and its impedance is above 100K; and the resistance of the voltmeter is also very large. Therefore, according to Ohm's law, the voltage divided by the voltmeter is the value measured by the voltmeter, and how much current is passed at this time-very small.