New Practical Electrician's Handbook

Author: Chief Editor: Liu Yongming
Publisher:
Publishing Date: 1997-03-01
Features: The book is a concise and practical electrician's manual designed for technicians and installation/maintenance workers in the electrical industry across urban and rural areas. During revision, special attention was paid to the novelty of the content, with a focus on incorporating newly collected products, model numbers, and the latest technical data. The book covers 27 chapters, including: basic electrical knowledge, planned power consumption, low-voltage electrical appliances, power lines, electric transport equipment, high-voltage switchgear, power system layout for computer rooms, principles and maintenance of telephone and telecommunication equipment, as well as the principles and maintenance of modern household appliances. It is suitable for urban and rural electricians with a junior high school education or higher; can serve as training materials and reference books for electricians at all levels; and can also be used as a reference for teachers and students in secondary vocational schools and technical schools with electrical courses.
Excerpt:
Resistivity
Resistivity is a physical quantity that measures the conductivity of a material, denoted by the letter ρ. Numerically, it equals the resistance of a conductor with a length of 1 meter and a cross-sectional area of 1 square meter. The unit is Ω·m. The relationship between resistivity and temperature is given by ρ = ρ?(1 + αt), where α is the temperature coefficient of resistance.
Temperature Coefficient of Resistance
The temperature coefficient of resistance is a physical quantity that represents how the resistivity of a material changes with temperature. Its value is the ratio of the increase in resistivity per 1°C rise in temperature to the original resistivity. The unit is 1/°C.
Electrical Conductance
Electrical conductance is a physical quantity that reflects a conductor's ability to conduct current. In a direct current circuit, the value of conductance is the reciprocal of resistance and is denoted by the letter G. The unit is Siemens, symbolized as S.
Conductivity
Conductivity is a physical quantity that measures the conductivity of a material, with a value equal to the reciprocal of resistivity. It is denoted by the letter σ. The unit is S/m.
A conductor is a material that has a large number of charged particles capable of free movement under an external electric field, allowing it to conduct current well. Metals and electrolytes are examples of conductors.
Dielectric
A dielectric, also known as an insulator, has a very low conductivity, such as glass and mica.
Permittivity
Permittivity is a physical quantity that represents the electrical properties of a dielectric. It is a coefficient that indicates the insulating ability of the dielectric and is denoted by the letter ε. The unit is F/m.
Relative Permittivity
Relative permittivity is a physical quantity that represents the electrical properties of a dielectric. It is the ratio of the permittivity ε of any material to the permittivity ε? of a vacuum and is denoted by the letter ε?.
Breakdown
Breakdown refers to the phenomenon of intense discharge or conduction in an insulating material under a certain electric field strength. For example, lightning during thunderstorms can break down the air. Another example is when excessive voltage is applied between the plates of a capacitor, causing the dielectric between the plates to break down. The critical voltage that causes breakdown in the dielectric is called the breakdown voltage, and the corresponding electric field strength is called the breakdown field strength. The unit is kV/cm.
Series Connection
In a series connection, electrical components are connected one after another in the circuit (the head of one component is connected to the tail of the next), with the same current flowing through each component. The total voltage equals the sum of the voltage drops across each component. This method of connection is called series connection.
Parallel Connection
In a parallel connection, electrical components are connected side by side (heads connected to heads, tails to tails). The voltage across the terminals of each component is equal, and the total current equals the sum of the branch currents. This method of connection is called parallel connection.
Compound Connection
A compound connection in a circuit refers to a method where components are connected both in series and in parallel.
Electromotive Force (EMF)
Electromotive force is a physical quantity that characterizes the properties of a power source. It reflects the ability of the non-electrostatic force in the power source to do work. Numerically, it equals the work done by the non-electrostatic force when a unit positive charge moves around a closed loop. It is denoted by the letter E and the unit is volts (V).
Induced Electromotive Force
When the magnetic flux through a closed circuit changes, an induced current is generated in the loop. This phenomenon is called electromagnetic induction, and the electromotive force caused by it is called induced electromotive force.
Self-Induced Electromotive Force
The electromotive force induced in a coil due to a change in the magnetic flux caused by the current in the same coil is called self-induced electromotive force.
Mutual Induced Electromotive Force
When the current in one of two coils that are close to each other or wound on the same iron core changes, the changing magnetic flux through the second coil induces an electromotive force in it. This is called mutual induced electromotive force, and the phenomenon is known as mutual induction.