Automatic transfer switch (ATS): purpose and classification

ATS systems are used for uninterrupted power supply of private houses, enterprises, and other facilities. Automatic switching on of the reserve increases the level of safety, prevents material losses. In some situations, it eliminates threats to human life and health. For the correct choice of components, it is necessary to familiarize yourself with the principles of operation of specialized equipment.

What is ATS device

The preservation of the working state of the power supply is ensured using special engineering solutions. In the event of an emergency, the automation switches on the generator. The required actions are carried out without careful control or intervention by the user.

The main functional components of a typical ATS system:

• control devices record changes in the electrical parameters of the power supply network;
• when registering an open circuit (SC) or deviation from the set threshold level, the automation switches off the damaged section;
• the alarm device reports a violation of the operating mode;
• the contact group connects the standby power supply.

Further, the necessary measures are taken to restore the standard system. The abbreviation (ATS) stands for "Automatic Reserve Entry". In addition to the generator on duty, switching to an operable network or a battery pack is used.

Appointment of ATS

The functionality of the system is based on the principles of ensuring uninterrupted operation of the power supply. Automation of the main processes implies the elimination of the actions of maintenance and operational personnel. Professional requirements for equipment are set out in the rules of the PUE. In particular, to connect consumers of the 1st category, an ATS circuit for 2 inputs with a sectionalizer on automatic machines is used.

Duplication of switchgear and other critical elements ensure a high level of reliability. Such units are designed for autonomous operation. During the creation of design documentation, mutual influence is excluded to prevent erroneous actions of the automatic transfer switch.     

The need to use such systems is illustrated by an example of good equipment of a private country house. As a rule, a local heating system is installed in such facilities. The control of a modern gas boiler is provided by electronics. Pumps are used for forced circulation of the coolant along the circuits. Disabling these components in severe frost provokes the destruction of pipes and radiators.

Repair and restoration work is much more expensive compared to autostarting a special generator. The presence of a standby power source is useful in case of accidents in power supply networks. If the voltage connection is made fast enough, users will not experience discomfort.

Principle of operation

To study working algorithms, you can use an example of an assembly on a simple element base.

• Continuous monitoring of the electrical parameters of the main line is provided by the contactor.
• Alternating current through the switch in a closed circuit enters the local network to consumers.
• If the voltage is lost, the induction coil will not be able to hold the stem.
• The spring will move the contact group of the reserve input through the drive for closing.
• At the same time, the main machine is turned off.
• When voltage appears in the working line, the actions are performed in the reverse order.

Lamps in the corresponding circuits signal the start of certain modes.

System Requirements

The functionality of the presented scheme is limited. If faults in the main line are accompanied by a short circuit, reclosing will cause damage to the load. The reactive characteristics of electric motors have a certain influence. When connecting a machine or a powerful fan, a voltage drop can cause a false triggering of the protection system.

Separately, you should consider the connection speed of the backup source. At significant time intervals, local protection schemes are triggered in some connected devices. Such situations are accompanied by malfunctions. They provoke breakdowns, accelerated wear of drives.

To eliminate the shortcomings, control logic circuits are used, created on the basis of electronic blocks with specialized software. Some components are equipped with mechanical interlocks. Such elements remain operational when the main and emergency power supply is completely disconnected.

Basic requirements for the ATS of a modern level:

• reliability of connecting a spare power source (IP) at peak loads and significant changes in the operating parameters of the network;
• sufficient speed to exclude damage to electricity consumers;
• adjustable setting of threshold levels of activation of the protection system;
• blocking of connection to a circuit with short circuit and parallel connection of two inputs;
• single actuation;
• automated check of the functional state of the backup IP.

Smooth switching is ensured by adding transformers to the circuit.

Choice of automation

Industrial equipment and equipment of the professional category are equipped with automatic equipment as standard. At a minimum, they offer a box with a set of contactors to reproduce the protective algorithm. An emergency button is placed in the availability zone. If necessary, turn off the unit by hand with one quick movement.

A specialized ATS switchboard can be purchased assembled, or you can create a functional analogue yourself. When choosing a finished product, you should pay attention to the reputation of the manufacturer. A preliminary study of customer reviews and the opinions of experienced experts will be useful.

Products of dubious origin are presented in the lower price range. If a single-phase ATS costs up to 1500-2000 rubles, one can hardly count on a long service life and high reliability. Fakes are characterized by poor assembly, low quality of contact groups. Quite often, low-power electronic keys are used in such models, which are not adapted to voltage surges and loads with pronounced inductive characteristics.

From 4,000 to 8,000 rubles you can find quality AVRs of little-known brands. Reliable equipment kits use electromechanical functional components.

In the range of 20,000 rubles. and above are the products of responsible manufacturers. These products come with an official warranty. Speed ​​and other important parameters are controlled in each individual consignment.

Automation without controller

The decoding of the designation emphasizes the main feature of the equipment of this category. The "automatic" way of connecting a state-of-the-art backup does not only mean the absence of user intervention. The electronic controller provides an on-line check of the state of the supply and backup network.It blocks the execution of erroneous operations, prevents the occurrence of potentially dangerous situations. When choosing an ATS, you should check the presence of this useful component in the kit.

ATS in 0.4 kV networks

For switching power circuits in networks with a relatively low voltage (0.4 kV), serial contactors with a magnetic drive are used. Also used starters complete with AB. The components of the circuit are selected taking into account the current loads (power consumption).

Electricity metering devices, protection devices against impulse voltage surges, a relay with a delay function to create an additional time interval before connecting the load are installed in typical ATS boards for 2 inputs.

ATS classification and implementation options

The following schemes for organizing working algorithms are applied:

• One-sided means connecting a backup input if necessary. For example, for temporary power supply from the battery.
• In a double-sided version, both sections are equivalent. Such a solution is used if it is possible to switch to a backup network with similar parameters.

The logic of the recovery process is determined separately. Use:

• subsequent automated connection to the main line;
• transfer to backup power supply with manual mode change.

Features of working with household generators

The popularity of this solution is due to the simplicity of choosing the equipment of the required power. In the corresponding market segment, they offer generators driven by gasoline (diesel, gas) motors for connection to single and three-phase networks. They are designed for long-term continuous operation without careful monitoring. Autonomy actually depends only on the fuel supply.

To start the power unit, the sectional automation cabinet is equipped with a specialized control unit. It supplies power to the starter according to the established algorithm. In particular, the program can be set to preheat the diesel engine in winter conditions.

ATS on accumulators

Such backup power supplies supply direct current to the line. To convert to a sinusoid of a certain amplitude (220 or 380 V), an inverter is used. The limited autonomy of this option should be understood. However, by connecting several batteries in parallel, you can provide the required time interval. A promising direction is lithium-ion energy storage. They are superior to lead-acid counterparts in the main technical characteristics. The high price limits its widespread use. However, as demand increases and production expands, manufacturers begin to offer quality products at an acceptable cost.

Connecting the battery is easier compared to the generator. In this version, the ATS can be assembled according to the standard scheme without a special engine start control unit.

Logic controller application

Such blocks are used to fine tune the algorithm of working operations. Special regulators set the permissible percentage of voltage deviation from the nominal, time intervals, and other parameters. Control signal circuits are connected to switching devices.

Organization of automatic transfer switch in high-voltage circuits

To simplify the control of the operating parameters of the network, a step-down transformer is used. With a certain number of turns, the voltage is reduced from 1000 to 100 V. If a phase control relay is added to the control circuit, the reserve is connected when at least one line is broken.

Connection diagrams

The best option is chosen taking into account:

• operating parameters of the power supply network;
• type of loads;
• special requirements for the speed of transferring the reserve and other parameters.

For single-phase networks when connecting a private house or a small commercial facility, you can use the simplest option on modular contactors with two-pole AB. An ATS circuit with a phase control relay for two inputs is used when connecting powerful loads.In the corresponding version, in addition to the voltage level, the distortion of the sinusoid and the correct phasing are monitored. If it is supposed to work with several sources (more than two), create a system with the required number of inputs.