Intermediate Electrician Technology

Author: Chief Editor: Yang Zhaoyi
Publisher:
Publish Date: 2000-02-01
Features: Based on the knowledge and skill requirements specified for "Electricians" in the "Technical Skill Level Standards for Workers of the People's Republic of China" and the "Code for Employee Skill Appraisal," this book covers the structure, principles, maintenance, common faults, and troubleshooting methods of high-voltage transformer and distribution equipment, as well as basic knowledge of lightning protection and overvoltage prevention, types, working principles, and maintenance methods of common lightning protection equipment, types, functions, and working principles of grounding, the structure, principles, and applications of 10kV high-voltage test equipment; it emphasizes the maintenance of power transformers, parallel operation of transformers, lightning protection measures for transformer substations, and construction methods of grounding devices; it also explains the construction procedures and main operation steps of overhead lines, cable laying, preventive tests of cables, and the fabrication of 10kV cable terminal heads and intermediate heads; it introduces commonly used power driving equipment in factories, including wound-rotor asynchronous motors, DC motors, pole-changing speed-regulating motors, and electromagnetic speed-regulating motors, covering their maintenance methods, installation, and commissioning, as well as installation methods of electrical equipment in explosion-proof and fire-proof environments, and the application of thyristors; it also covers the wiring methods, operating modes, and safe maintenance of transformer substations. This book provides both theoretical knowledge and operational skills, with a strong emphasis on improving practical skills, making it highly practical. It is suitable for electricians preparing for national vocational skill appraisals and graduates of vocational schools majoring in electrical engineering for pre-examination preparation, as well as for self-study reference.
Excerpt:
Training Requirements for Electrical Equipment
This chapter primarily introduces the structure, principles, and maintenance knowledge of common high-voltage transformer and distribution equipment used in factories, with special emphasis on the knowledge and skills of transformer parallel operation and maintenance. It requires learners to be familiar with these equipment, particularly to have a clear understanding of the structure, principles, operation, and maintenance of transformers, and to skillfully master the maintenance techniques for transformers.
Section: Structure, Principles, and Maintenance of High-Voltage Transformer and Distribution Equipment
High-voltage transformer and distribution equipment are critical components of power systems, playing roles in control, protection, and measurement during the generation, transmission, and distribution of electrical energy. Their performance directly impacts the stability and safe operation of power systems. High-voltage transformer and distribution equipment come in various types, which can be categorized based on their roles in power systems as follows:
(1) Transformation Equipment: Devices used to transform voltage or current, such as power transformers, voltage transformers, and current transformers.
(2) Control Equipment: Devices used to control circuit switching, such as load switches, disconnectors, and circuit breakers.
(3) Protection Equipment: Devices used to protect circuits from overcurrent or overvoltage, such as high-voltage fuses and lightning arresters.
(4) Current-Limiting Equipment: Devices used to limit current, such as reactors and resistors.
(5) Compensation Equipment: Devices used to compensate for reactive power in circuits and improve system power factor, such as power capacitors.
(6) Integrated Equipment: Devices that combine primary and secondary equipment according to specific circuit schemes, such as high-voltage switchgear and high-voltage capacitor banks.
Below is a brief introduction to the structure, principles, and maintenance of several common high-voltage transformer and distribution equipment used in factories.
I. High-Voltage Disconnector
1. Purpose of High-Voltage Disconnector
A disconnector is a type of switch used to open and switch circuits. Unlike circuit breakers, it does not have a dedicated arc-quenching device, so it cannot interrupt load current or short-circuit current. The main purposes of a disconnector are as follows:
(1) To isolate electrical equipment from the live power grid, ensuring clear break points for safe maintenance.
(2) To switch busbars and change operating modes.
(3) To connect and disconnect small load currents.
2. Structure and Working Principle of High-Voltage Disconnector
High-voltage disconnectors are classified into indoor and outdoor types based on installation location, single-pole and three-pole types based on the number of poles, and blade-type, rotating-type, and plug-type based on structural features. They can also be categorized as those with or without grounding switches. High-voltage disconnectors can be installed horizontally, vertically, or at an angle. Common indoor 10kV high-voltage disconnectors include the GN2, GN6, GN8, and GN19 series three-pole disconnectors, most of which use the CS6-1 manual operating mechanism. Outdoor types include the GW series three-pole linkage disconnectors, which use the CS8-1 manual operating mechanism and are designed to withstand harsh outdoor weather conditions. The structure of a disconnector is relatively simple. For example, the common GN19-10 indoor 10kV three-pole disconnector has all three phases mounted on the same base. It consists of a base, rotating shaft, pull insulator, support insulator, conductive moving blade, conductive static contact, and connection plate. Each phase’s conductive moving blade consists of two grooved copper plates, tightly clamped by springs on both sides of the static contact, increasing contact pressure, expanding the heat dissipation area of the blade, and enhancing its mechanical strength and electrical stability. An insulating pull is connected between the middle of each blade, which is linked to the rotating shaft installed on the base. The shaft extends from both ends of the base, and either end can be connected to the operating mechanism. The GN19 series 1000A high-voltage disconnector also installs a magnetic locking pressure plate at the blade contact point, which increases the contact pressure at the blade contact point when short-circuit current flows, improving the dynamic and thermal stability of the switch contact.