Design and application of automatic transfer switc

2022-09-22
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Discussion on the design and application of automatic transfer switch apparatus

according to the national code code for design of power supply and distribution system (gb50052-1995), code for fire protection design of high rise civil buildings (gb50045-1995, 2005 Edition) and the industrial standard code for electrical design of civil buildings (JGJ/t16-92): the first-class load should be powered by two power sources; When one power supply fails, the other power supply should not be damaged at the same time. In addition to two power supplies, emergency power supply must be added for the particularly important load in the first level load. In order to ensure the power supply of particularly important loads, it is strictly prohibited to connect other loads to the emergency power supply system. The device has undergone more than 100 technical transformations on the basis of BP's VCC experimental device process. Automatic transfer switch (ATSE) is required for class I and II loads with fixed power conversion time and power supply of fire control room, fire pump, fire elevator, smoke control and smoke exhaust civil aircraft, emergency lighting and other fire-fighting equipment. As a power conversion device for fire loads and other important loads, ATSE has been widely used in engineering. Correct and reasonable selection of ATSE can ensure the reliability and continuity of power supply for primary and secondary loads

The basic concept of

se

automatic transfer switching equipment, namely ATSE (automatic transfer switching equipment), is composed of one (or several) transfer switching appliances and other necessary appliances, which are used to monitor the power circuit and automatically convert one or several load circuits from one power source to another. ATSE generally consists of two parts: switch body and controller

se classification

at present, the products that meet the standard of GB/t14048.11 (iec60947-6-l) in China's market mainly include CB grade and PC grade

pc level: ATSE that can be connected, carried, but not used to break short-circuit current

cb level: ATSE equipped with overcurrent release, its main contact can be connected and used to break short-circuit current

se use category

use category involves ATSE connection and breaking capacity and operational performance indicators, which determine the correct use environment of its ATSE. For the selection of PC ATSE, in addition to its rated making and breaking capacity, it should also consider its short-circuit capacity under short-circuit conditions, that is, the rated short-time withstand current ICW value. See table for details

requirements for service environmental conditions

1) the altitude shall not exceed 2000m

2) the ambient temperature is not higher than 40 ℃ and not lower than -5 ℃

3) the relative humidity is not greater than 95%

4) requirements for electromagnetic compatibility (EMC): in actual use, the ATSB (especially the controller) shall not be damaged or misoperated by external electromagnetic interference, which will affect the reliability and continuity of power supply system operation. At the same time, the electromagnetic effect produced by ATSE should meet the corresponding national standards of the significance of thermal insulation materials to ensure the safe and stable operation of other links of the electrical system

4. Precautions for design selection

1) product certification: China, IEC, UL, etc. have formulated special standards for ATSE (several standards are completely equivalent), so we must choose ATSE that meets the standards

2) determine the use category of rated working voltage method of automatic transfer switching apparatus (ATSE). Pay attention to the selection of ATSE suitable for load characteristics

3) when selecting PC level or CB level in design, the starting point should not be whether the short-circuit protection function is required (the system has the same protection function as CB level by adding short-circuit protection appliances in front of PC level), but reliability and cost. With high reliability requirements, PC grade products should be selected; CB grade can be selected for low cost

4) the time to disconnect the fault power supply is different for products with different structures. For loads with high sensitivity to the fault power supply (such as phase failure), it should be noted that the excitation driven ATSE that can quickly disconnect the fault power supply should be selected. The CB level ATSE with circuit breaker does not use the ATSE with isolation (load) switch, but is driven by the reduction motor (the motor speed is generally 15-20rpm, and the contact can be disconnected only after the switch is turned to a certain angle)

does the PC front-end need to add short-circuit protection appliances? It depends on whether PC ATSE can withstand the impact of the protection current of the front-end short-circuit protection appliance. If it can bear, there is no need to add a short-circuit protection appliance in the switching box. If it cannot bear, it is necessary to add a protection appliance with a short-circuit protection current lower than the PC grade aste rated limit short-circuit current, which requires the manufacturer to provide the type and majority of protection appliances with aste rated limit short-circuit current

5) selection of ATSE three pole and four stage: in the power conversion system, according to the grounding type of the distribution system and the setting of the grounding protection device, whether the neutral current shunt and circulating current and grounding fault current shunt can be generated, so as to avoid the misoperation or refusal of the protection device, so as to determine that the patterns or elements of a are the stages of TSE designed in the scale of nano scale or 1 billionth of a meter

(1) according to article 465.1.5 of iec465, if the normal power supply and the standby generator are not in the same grounding network, the transfer switch should be a four pole switch

(2) the dual power transfer switch with residual current protection shall adopt quadrupole switch. Two power switches are equipped with residual current protection, and the power transfer switch at its lower level shall adopt quadrupole switch

(3) the power transfer switch between two different family ground systems should adopt quadrupole switch

(4) generally, TN-S, TN-C-S and systems do not need to be equipped with quadrupole switches. However, in some special cases of TN-S system (three-phase serious balance and high-order harmonic content), whether to use four level switch depends on the importance of building grade

6) application of bypass ATSE: especially important loads that have high requirements for the reliability and continuity of power supply system. In order to prevent ATSE from failure, damage or maintenance, which will affect the continuity of power supply, bypass to ATSE should be set. The bypass ATSE shall have the following functions:

(1) the bypass disconnector shall be able to bypass the power supply to the load when the power load is cut off, and the rated capacity of the bypass switch and ATSE shall be the same

(2) when bypassing the power supply, it should be able to isolate ATSE and related control power supply, so as to ensure that ATSE maintenance and replacement can safely reduce the weight - the proportion of substitute metal and plastic is mostly below 1.7

(3) there should be bypass isolation signs to display the system status

(4) there shall be electronic and mechanical interlocking to prevent misoperation

references

[1] code for design of power supply and distribution systems (GB50052-1995).

[2] code for electrical design of civil buildings JGJ/t16-92

[3] national standard GB/T 14048.11 - 2002 Low voltage switchgear and controlgear - Part 6: multifunctional appliances - Part 1: automatic transfer switching appliances

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