Overview:
The primary system refers to a system composed of generators, transmission lines, transformers, circuit breakers and other equipment for power generation, transmission, transformation, and distribution.
The primary system is the main body of the power supply system and the carrier of the power load. High voltage or high current is the main feature of the primary system.
The correct selection of the structural scheme, cables and electrical equipment of the primary system and correct construction are the basis for ensuring the normal operation of the power supply system.
All the electrical equipment in the primary system is called primary equipment. Commonly used primary equipment includes high-voltage fuses, high-voltage isolating switches, high-voltage load switches, high-voltage circuit breakers, and high-voltage switch cabinets.
All devices in the secondary circuit are called secondary devices. Commonly used secondary equipment includes metering and measuring meters, control and signaling devices, relay protection devices, automatic devices and telecontrol devices.
Classification:
Primary equipment can be divided into low-voltage equipment and high-voltage equipment according to the working voltage.
(1) Low-voltage equipment is electrical equipment with a working voltage of 1.0kV and below.
(2) High-voltage equipment refers to electrical equipment with a working voltage higher than 1.0kV. Among them, high-voltage equipment from 1.0kV to 35kV (including 35kV) is called medium-voltage equipment, electrical equipment higher than 35kV to 110kV is called high-voltage equipment, electrical equipment from 220kV to 500kV is called ultra-high voltage equipment, electrical equipment higher than 500kV is called UHV equipment.
Primary equipment can be divided into control equipment, protection equipment, transformation equipment, compensation equipment and complete sets of equipment according to their functions.
(1) The control equipment is the switching equipment that controls the on-off of the primary circuit, including isolating switches, transfer switches, load switches, fuses and circuit breakers.
(2) Protection equipment is the equipment that protects the system and equipment when they may be subjected to overvoltage, overcurrent and possible leakage current. Such as fuses, lightning arresters, anti-surge voltage devices and residual current protection devices.
(3) The conversion equipment is the equipment that changes the voltage or current to meet the working requirements of the power supply system, such as transformers and converters for energy transmission, voltage or current sampling and detection for voltage transformers, current transformers, etc.
(4) The compensation equipment is the electrical equipment that compensates the reactive power of the power system to improve the power factor of the system, such as power capacitors.
(5) The complete set of equipment is based on the requirements of the primary circuit wiring scheme, combining the relevant above-mentioned primary equipment and secondary equipment into an integrated electrical assembly of transformation, distribution and control. Such as high-voltage switchgear, low-voltage distribution panel, power distribution box, lighting distribution box and control distribution box, etc.
Composition of primary system:
The entire system that constitutes the power transmission and distribution channel of the factory is called the primary system of the factory power supply. The basic components of a primary system are substations, distribution stations and power lines.
A substation is a step-down station that converts the grid voltage into the voltage required by the load and distributes the electric energy to the load through the power distribution device. The electric energy of the substation and distribution station is transmitted to the user through the power line.
Factories with large scale and distributed loads may need to transmit electric energy through multi-stage power transformation and distribution. Under the premise of meeting the needs, the number of substation stages should be reduced as much as possible to reduce power loss.
In order to shorten the power line, the substation and distribution station should be built in the load center as much as possible.
Primary system equipment
The equipment of the primary system mainly includes power transformers, switching appliances, non-switching appliances directly related to the primary system (such as transformers, lightning arresters, fuses, power conditioning appliances, etc.), busbars, and power cables.
Classification of a system
According to the number of substations, the primary power supply system of the factory can be divided into no substation system, single substation system and multi-level substation system.
The non-substation system is often a step-down substation shared by several relatively centralized, low-voltage power supply factories, and each factory only has a low-voltage distribution station.
In the single substation system, only the workshop substation 6, 10kV or 35kV incoming line is supplied by the adjacent step-down substation.
The common way of multi-level substation system is a two-level system with main step-down substation and multiple workshop substations, the main step-down station is powered by 35, 110kV or 220kV lines of regional substations.
The general step-down substation is set up independently. The workshop substation is seldom set up independently. Most of them are combined with the workshop. They are designed as external, internal or underground. When the capacity is not large, they can also be designed as pole-mounted.
