Application of automatic transfer switch in low voltage power distribution

Due to the technical level and advancement and reliability of the products, it will directly affect the safety and reliability of electricity in all important places. ATS has become an indispensable and important part of low-voltage distribution systems, so it should cause height in engineering design. Pay attention to it, and it is necessary to familiarize with and understand its type, composition and working principle, main features and functions, etc., in order to correctly select and rationally apply.

ATS is mainly suitable for emergency power supply systems with an AC of no more than 1000V, and interrupts the supply of power to the load during power change. Definition according to IEC International Standard: An automatic appliance consisting of one or more transfer switch appliances and other necessary electrical appliances for detecting power supply circuits and converting one or more load circuits from one power source to another. When there are two power sources, the common power supply and the standby power supply, the ATS should specify a common power supply location, and its operating procedure consists of two automatic conversion processes. If the common power source is detected to have a deviation, the load is automatically switched from the normal power source to the standby power source; if the normal power source returns to normal, the load is automatically returned to the normal power source. The switching time can have a predetermined delay or no delay and can be in an open position. Such electrical products have been recognized in the building electrical industry, referred to as "dual power automatic transfer switch - ATS".

According to the IEC-60947-6 international standard, ATS is divided into two levels, PC or CB. The PC stage can be switched on and carried, but is not used to break the short circuit current ATS. Both the load switch and the contactor double-throw ATS belong to this category. The body can only be used as an ATS, without overload and short circuit and other protection functions. Class CB ATS with overcurrent release, its main contacts can be switched on and used to break short-circuit current. Its circuit breakers and control protector switching type ATS belong to this type of product. In addition to the main body used as ATS, it also has overload, short circuit and other protection functions to realize two or three sections of the load and other protection functions. .

主要ATS main features and functions

In view of the current domestic production of different types of ATS, its main features and functions are analyzed from the aspects of safety, reliability and protection, and its advantages and disadvantages are briefly described for reference during design selection.

â—‡Circuit breaker switching type ATS

This kind of ATS is based on two circuit breakers, plus a single (double) micro reversible motor to form an electric operating mechanism to achieve automatic conversion and control of dual power supplies. Therefore, circuit breakers are widely used, ranging from domestic to joint venture production and imported circuit breakers. Can be assembled. The main advantages of the circuit breaker switching type ATS:

(1) Two circuit breakers are adopted from the structural form, the insulation level is high, and the electrical and mechanical double interlocking function is provided to prevent the two circuit breakers from being closed at the same time in any state, which ensures the safety of the two wells. .

(2) The secondary control loop is composed of intelligent controllers. It has advanced features in weak current control, non-contact, and powerful functions, reducing peripheral components and providing reliable guarantee for power supply continuity. Reliability requirements.

(3) Provide complete overload and short circuit protection for the load, realize two or three sections of protection function, and add other protection functions such as grounding as needed; in addition, it has strong current limiting, good selection performance, cascade matching and Functions such as energy protection are extremely outstanding in terms of selection performance.

(4) It has various fault protection of power supply, fault alarm indication, adjustable operating parameters and power supply voltage display, and prevents faulty power supply from supplying power to the load; because different users or equipment have different requirements on power supply voltage and conversion time, Through the digital tuning and adjustable functions, it is greatly convenient for users to use, and provides preconditions for realizing "four remotes", and is suitable for centralized control of intelligent networks via communication interfaces.

主要 Its main disadvantages:

(1) Due to the use of two circuit breakers, the volume is large and the cost is high. Because of the micro reversible motor drive, the conversion time is long, at least 1.5s.

(2) When two circuit breakers (micro-break or molded-shell type) are used, an electric operating mechanism consisting of a miniature reversible motor is added to the handle to make the two handles reverse operation at the same time. This method is more primitive. The operating handle is easily damaged, the movement position adjustment is also very difficult, and the normal opening and closing operation is affected by vibration and the like; when the electric operating mechanism composed of two sets of micro reversible motors is used, the operation and the interlocking mechanism are also complicated. It is not easy to adjust and is prone to failures, so reliability is affected to some extent. After discovering such defects, the product operating mechanism was researched and improved to make the transmission simple, with fewer failure points and long life.

Load dump switch double throw type ATS

The ATS is assembled by two sets of load switches. It consists of a set of miniature reversible motors to form an electric operating mechanism, and the automatic conversion and control of the dual power supply is realized by the gearbox transmission. The action mode and the single-motor-driven circuit breaker switching type ATS is basically similar.

The main advantages of the double load type ATS for load shedding switch:

(1) Due to its own movement and simple and compact transmission machinery, in addition to electrical interlocking, the mechanical interlocking function can be completed through the mechanical gear transmission structure, and the safety is guaranteed.

(2) Most of the secondary control loops are integrated with switches and logic control. Due to the use of electronic products, the hidden troubles are reduced, and the reliability requirements are basically met.

(3) Limited by the structural form, without overload and short circuit protection, so the volume is moderate, the appearance is uniform and uniform, and the price is moderate.

主要 Its main disadvantages:

(1) Because it does not have any protection function and is short in short-circuit conduction capacity, the main contact system has no arc chute, and the arcing time is long when switching, which easily affects the service life of the contact.

(2) Micro-motor drive and gear shifting mechanism are adopted, so the conversion time is long, and the mechanical transmission mechanism device also has problems such as easy failure and affecting reliability, and needs further improvement and improvement.

(3) It is not suitable for frequent conversion and operation, otherwise it will affect the overall service life. The ATS uses a DC electromagnetic coil as a power, and the entire conversion action is completed by an electromagnetic excitation pulse operation.

The main advantages of the â—‡ contactor double throw ATS:

(1) In the structural form, it consists of V-shaped main contact and electric mechanical double interlock control. The DC coil is used to excite the linear drive to complete the conversion process. Therefore, the external volume is small, the structure is simple and compact, and the operation safety performance is good.

(2) Secondary control circuit Most products are integrated with switch and logic control, and are linearly positioned by mechanical parts. The positioning accuracy is high and vibration resistance is not affected by the installation direction and angle. In addition, relying on the function of the electric and V-type mechanical self-locking device, it is ensured that the two power sources are not turned on at the same time at any time, and the reliability is high.

(3) There is no overload and short circuit protection function, but the short circuit is large. Because the main contact is a flat contact, it has a separate arc extinguishing chamber and is equipped with an arc chute, which has a high current carrying capacity and can be loaded or frequently switched.

(4) It adopts electromagnetic instantaneous excitation drive, so the conversion time is fast, and the coil is not charged after the conversion is completed, which achieves the purpose of saving electricity and eliminating noise.

The main disadvantages are: further improvement and improvement of the secondary control loop, preferably using intelligent controllers, minimizing peripheral components related to operation and signal indication, improving the advanced nature of the device, making its action more secure and reliable.

â—‡Control Protector Switching ATS

This ATS is mainly composed of the KBO series main circuit basic module and other auxiliary modules. The main advantages of controlling the protector switching ATS:

Thanks to the modular structure, the integrated and internal coordination control and protection are realized in a single structural form, with various functions and advantages of circuit breakers, contactors and thermal relays, and interlocked by internal electrical and mechanical Function, relying on the electromagnetic coil to attract the drive to complete the automatic conversion process, no need to add other operations and conversion mechanism, so the structure is simple and compact, the conversion speed is fast, and the safety performance is good.