High-Voltage Electrical Equipment On-Site Test Technology 365 Questions

Author: Wu Weizhong
Editor-in-Chief: Li Liyan
Publisher:
Publish Date: 2001-09-01
Features:
Content Summary
This book is systematically presented in the form of Q&A based on the practical needs of on-site tests for high-voltage electrical equipment, covering 365 common technical questions. The book is divided into eight chapters, including basic electrical knowledge, power systems and overvoltage, instruments and meters, dielectric physics, general testing techniques, transformers and their tests, high-voltage circuit breakers and their tests, other equipment and their tests, and an appendix (related term definitions). This book is suitable for technicians and workers engaged in on-site tests of high-voltage electrical equipment, as well as for reference by other relevant personnel.
Excerpt:
4. What are the contents of Kirchhoff's first and second laws?
Kirchhoff's first law: For any node, any plane, or any closed region in space, the sum of the incoming currents is always equal to the sum of the outgoing currents, i.e., the algebraic sum of the incoming currents (or outgoing currents) is zero.
Kirchhoff's second law: For any closed loop, the sum of the voltage drops across each segment is equal to the sum of the electromotive forces.
5. What is the content of Thevenin's theorem?
Any linear voltage-source two-terminal network can be equivalently replaced by a single voltage-source branch for external circuits. The electromotive force of this voltage-source branch is equal to the open-circuit voltage of the voltage-source two-terminal network, and its impedance is equal to the input impedance of the voltage-source two-terminal network when converted into an unpowered network.
6. What consequences does an electrical short circuit cause?
A short circuit can cause overheating of electrical equipment, even burning it, leading to fires. Additionally, the short-circuit current can produce significant electromagnetic forces, causing damage to electrical equipment.
7. What is the left-hand rule used to determine? What is the right-hand rule used to determine?
The left-hand rule is used to determine the direction of the force exerted by a magnetic field on a current-carrying conductor. The right-hand rule has two applications: one to determine the direction of induced electromotive force, and the other to determine the direction of the magnetic field generated by current.
8. How should an electric field be understood? What are the physical concepts represented by the three calculation formulas for electric field strength?
An electric field can be understood from the following three aspects:
(1) An electric field is a special form of matter, and any charged body placed in an electric field is subjected to the force of the electric field.
(2) When a charged body moves in an electric field, the force of the electric field does work on the charged body, and the electric field possesses energy.
(3) Electric fields exist around charged charges, around current-carrying conductors, and in the vicinity of alternating magnetic fields.
The three formulas represent the following physical concepts:
(1) This studies the properties of the electric field from the perspective of the force experienced by a test charge, serving as the definition of electric field strength and applicable to the electric field strength of any electric field.
(2) This is the formula for calculating the electric field strength at a point in the electric field of a point charge or at a point outside a uniformly charged spherical surface, but it is not applicable to other electric fields.
(3) This calculates the electric field strength from the perspective of the relationship between field strength and voltage variation and is applicable to uniform electric fields.
9. What magnetic properties do ferromagnetic materials possess?
The magnetic properties of ferromagnetic materials mainly include three aspects:
(1) High magnetic permeability. Its relative permeability can be as high as hundreds, thousands, or even tens of thousands.
(2) Magnetic saturation. When ferromagnetic materials are magnetized, their magnetic induction intensity does not increase infinitely with the increase of the external magnetic potential. Instead, when the external magnetic potential reaches a certain value, the magnetic induction intensity approaches a certain constant value, entering a saturated state.
(3) Magnetic hysteresis. When ferromagnetic materials are magnetized under alternating magnetic potential, their magnetization curve is a hysteresis loop. Due to magnetic hysteresis, ferromagnetic materials generate hysteresis loss during magnetization. If the magnetic field is removed, they still retain a certain amount of residual magnetism.