Introduction and Installation Work of Substation Equipment

A substation is a power facility in the power system that transforms voltage, receives and distributes electric energy, controls the flow of power, and adjusts voltage. It connects the power grids of all levels of voltage through its transformers.

Various components are required in the substation, and these devices are collectively referred to as substation equipment. There are many types of these equipment, including transformers, switches, four small appliances, and reactive devices, as well as other equipment and auxiliary devices, such as wave traps, insulators, high-voltage bushings, guide wires, and grounding devices, secondary equipment, high voltage DC equipment, etc.

1. Types of substation equipment

There are many types of power transmission and transformation equipment, mainly including power transmission, power transformation, power distribution and various special-purpose electrical equipment. Insulating oil is widely used in power transmission and transformation equipment such as transformers, oil circuit breakers, oil-filled cables, power capacitors, and bushings. It plays the role of insulation, cooling, and arc extinguishing, and can effectively maintain the normal operation of electrical equipment.

The power transmission and transformation system is composed of a series of electrical equipment. The powerful electric energy generated by the power station can only be delivered to the power users through the power transmission and transformation system. Figure 1 shows a schematic diagram of the main equipment of the substation equipment. In addition to the electrical equipment such as transformers, wires, insulators, transformers, lightning arresters, disconnectors, and circuit breakers shown in Figure 1, there are also capacitors, bushings, wave traps, cables, reactors, and relay protection devices. These are indispensable equipment in the power transmission and transformation system.

1.1 Transformer

A transformer is an electrical device that uses the principle of electromagnetic induction to transform the AC voltage on both sides of the transformer. The main components of a transformer are iron core, coil and various insulating materials. Among them, the iron core and coil are immersed in transformer oil, isolated from air and moist gas. The structure of the transformer is shown in Figure 2.

Transformer oil can achieve good insulation between the wire ends of the transformer, between the high and low voltage coils, between the coil and the ground core and the wall of the oil tank, so as not to cause short circuit and arc. When the transformer is running, current flows through the coil, and part of the power is lost due to resistance, which is called "copper loss". When the current passes through the iron core, the power loss caused by the change of the magnetic flux of the iron core is called "core loss". These two parts of power loss are manifested in the form of heat. The transformer oil in operation dissipates heat to the atmosphere through the convection of cold and heat circulation, so that the operating temperature of the transformer will not be too high.

Usually according to the transformer voltage level, it is divided into 66 ~ 110 kV, 220 ~ 330 kV and 500 kV or more types.

1.2 High voltage switch

The high-voltage switch is an electrical machine whose function is to complete the connection and cut-off of the circuit, so as to achieve the purpose of circuit conversion, control and protection. High-voltage switch is an important transmission and distribution equipment in the electric power industry, and plays a very important role in the power system. Domestic 500kV gas circuit breakers have been widely used in the power grid, and 110kV, 220kV and 330kV enclosed combined electrical appliances are also widely used in the power grid. With the acceleration of urban power grid construction in our country, closed combined electrical appliances will be widely used. The main types of high-voltage switches are divided into: oil circuit breakers, air circuit breakers, vacuum circuit breakers, sulfur hexafluoride circuit breakers, solid gas circuit breakers, magnetic blow circuit breakers, etc. according to the arc extinguishing medium. Oil circuit breakers use transformer oil as the arc extinguishing medium, and are divided into two types: oil-rich and oil-less.

1.3 Wave trap

The wave trap is an indispensable high-frequency communication component for carrier communication and high-frequency protection. It prevents high-frequency current from shunting to other branches and reduces high-frequency energy loss. The wave trap is usually composed of inductance coils, tuning components and lightning arresters, etc., and is supported by post insulators or suspension insulators. The heating defects of the wave trap coils and various components can be found through infrared detection. Common infrared detection heating defects and their causes are as follows:

1.3.1 Poor contact of contacts. The lead wire contacts of the wave trap heat up, and the thermal image features centered on the terminal contacts are obvious. The main reason is the poor contact of the contacts caused by looseness, corrosion, oxidation and other reasons.

The wiring board of the 500kV wave trap is hot.

The wiring board of the 220kV wave trap is hot, and the hot spot temperature is 48.51°C.

The wiring board of the 35kV wave trap is hot, and the hot spot temperature is 108.1°C.

1.3.2 The body heats up. Partial or overall heating of the wave trap body, usually due to overload, partial inter-turn short circuit, etc.

The body of the 500kV wave trap is hot, with a surface temperature of 70.4°C.

The temperature of the outer surface of the 330kV wave trap and the tie rod is abnormal, and the surface temperature is 66.2°C.

The 220kV wave trap is heated as a whole, the surface temperature is 120.9°C, and the wave trap is overloaded.

2. Rating and classification of substation equipment

Substation equipment ratings are classified as follows:

2.1 Class I equipment

The technical health of the equipment is good, the operation is flexible, the operation is safe and reliable, the appearance is clean, there is no rust, leakage and other defects, the technical data is complete, the records are filled in correctly and clearly, the insulation strength of the equipment matches the level of the polluted area, and the anti-accident safety measures and technical measures have been completed.

2.2 Class II equipment

There are general defects in the equipment, and the unqualified individual minor components or minor test results will not affect the safe operation, or have a minor impact on the safe operation. The main technical information is sound and basically in line with reality. Overhaul and preventive tests are over-period but not more than half a year. The insulation strength of equipment is close to the level requirements of polluted areas. Anti-accident safety measures and technical measures are being implemented but not yet completed.

2.3 Three types of equipment

There are serious defects or critical defects in the equipment, such as serious oil leakage and air leakage, and the appearance is very untidy. The safe and reliable operation of the equipment cannot be guaranteed, and the main technical information of the equipment is not complete. The overhaul and preventive test lasted more than one cycle, the insulation strength of the equipment was lower than the level requirements of the polluted area, and the anti-accident safety measures and technical measures were not implemented.

Class I and Class II equipment are called intact equipment.

3. Unit division of substation equipment

The unit division of substation equipment rating is as follows:

3.1 Power Transformer

Taking a power transformer as a unit, it includes the power transformer cooling device, lightning arrester, neutral point grounding device, on-load voltage regulating device, etc. (The power transformer is single-phase, according to each single-phase unit, and the arrester is based on "phase" as the unit)

3.2 Circuit breaker

Taking the substation equipment connected to the circuit breaker as a unit, it includes the power-side isolating switch, load-side isolating switch, grounding switch, current transformer, reactor, coupling capacitor, line arrester, structure, etc. connected to the circuit breaker. (Current transformers, lightning arresters, and coupling capacitors are in units of "phase")

3.3 Power Capacitors

A group of power capacitors is taken as a unit, including drop fuses, cables, discharge voltage transformers, neutral point current transformers, etc. of each power capacitor. (Voltage transformers and current transformers are based on "phase".)

3.4 Reactor

Take a reactor as a unit, including the auxiliary equipment of the reactor, etc.

4. Installation work of substation equipment

4.1 The conditions that should be met before the installation of substation equipment:

4.1.1 The approved construction design documents are complete, mainly including:

4.1.1.1 Design specification, project quantity sheet, equipment sheet and main material sheet.

4.1.1.2 Catalogs and drawing numbers of standard drawings and general drawings.

4.1.1.3 All kinds of construction drawings that should be provided according to the composition requirements of design documents.

4.1.1.4 Construction organization design and revised total budget.

4.1.2 The housing construction and foundation construction have been completed and meet the design requirements. The reserved holes and embedded parts in the housing project meet the requirements of the design drawings.

4.1.3 The roads and fences in the site have been completed.

4.1.4 The main equipment, materials and processing parts have been confirmed.

4.2 All kinds of construction tools, machine tools, electrical test instruments, safety appliances and measuring tools shall be inspected and tested before starting work, and shall be kept in good condition, and unqualified ones shall not be used.

4.3 For the construction of the traction substation equipment, records of unpacking of equipment, records of hidden projects, records of equipment installation and commissioning, and quality inspection records after completion of each process should be made.

4.4 The transportation and hoisting of various prefabricated structures and electrical equipment should strictly abide by the relevant safety technical regulations and product manuals, and special measures should be formulated for the transportation and hoisting of large special equipment.

4.5 When the reinforced concrete poles are transported and stored, they should be placed with liners according to the fulcrum specified by the factory. The stacking height should not exceed four floors, and the low point of stacking should be solid and flat.

4.6 Precautions for equipment transportation and hoisting:

4.6.1 Porcelain parts shall not be squeezed by any external force.

4.6.2 The lifting point and traction point should be selected according to the center of gravity of the equipment or hoisted according to the position specified by the manufacturer.

4.6.3 The selection of transport and hoisting equipment should take into account the site permitting conditions and the safety of the surrounding installed equipment.

4.6.4 For equipment that is heavy at the top and light at the bottom, measures should be taken to prevent overturning.

4.6.5 Cables and twisted wires should be rolled up on reels for transportation, hoisted, and properly packaged. During transportation, reels should be upright and fixed firmly.

4.7 All kinds of electrical equipment and spare parts should be properly kept when they are transported to the construction site. If the products have special requirements, measures should be taken according to the requirements of the factory. Oil-filled equipment should be regularly tested for insulation according to regulations. The test items and cycle shall comply with relevant regulations.

4.8 When all equipment and spare parts are transported to the construction site, they should be unpacked and checked, and records should be made.

4.8.1 Confirm that the outer packaging is intact.

4.8.2 The packing list, certificate of conformity and instructions are complete.

4.8.3 Check the quantity and confirm that the specifications and models are consistent with the design.

4.8.4 There is no defect in the visual inspection.

4.8.5 All kinds of accessories and spare parts are in good condition.

4.9 After completion of the traction substation equipment, completion documents shall be submitted. Content includes the following:

4.9.1 Original design documents and design change drawings and notices.

4.9.2 Opening and completion reports, construction organization design.

4.9.3 Completed project quantity and equipment table.

4.9.4 As-built drawings.

4.9.5 Product delivery certificate, instruction manual, construction, installation and commissioning records, test report and handover list of relevant spare parts.