Hello dear readers! Today we will disassemble the automatic transfer switch (ATS), we will also consider how it works and what it is needed for.
Earlier we looked at what it is. Let's remember.
ATS is a device that is a component of relay protection and automation systems, and serves to ensure uninterrupted power supply to consumers of electrical energy. It transfers power in automatic mode from the main power supply to the backup power supply in the absence of voltage at the current input as a result of an emergency or erroneous actions. The reverse action occurs automatically when the power supply is restored.
Automatic reserve input is installed for special consumers who, for various reasons, cannot remain without electricity. Loss of electricity can lead to tangible financial losses and, in some cases, to death. For example, in hospitals during surgery, etc.
Classification
Devices are divided according to the principle of operation.
- One-sided. The circuit contains two sections: power supply and backup. The latter is connected when the main voltage is lost.
- Double-sided. Any of the lines can be both working and backup.
- Recovering AVRs. When the main power is restored, the old circuit is automatically put into operation, and the backup is turned off.
- No automatic recovery. Setting the operating mode with the main power supply is done manually.
Requirements that must be met by ATS
- The speed of switching on in the shortest possible time after disconnecting the power from the main voltage source.
- Reliability, switching on in any conditions in case of power failure in case of any faults on the supply line or in the event of a power transformer failure. An exception is blocking the automatic transfer switch when the arc protection is triggered in order to reduce damage to the network from a short circuit.
- Selectivity or selectivity, for example, lack of response from voltage drops as a result of starting powerful equipment from the consumer.
- Single action, prevention of multiple switching on of equipment due to unresolved causes of a short circuit or other malfunction.
How does ATS work and why is it needed
In case of a voltage drop in one of the phases, as well as frequency changes or voltage dips, that is, when these parameters leave the specified limits of the main power circuit, the phase control relay opens the contacts of the contactor at the main input and closes the contacts of the contactors of the backup input. Then the switches are triggered, consumers are disconnected from the main power supply and connected to the backup. Most ATS schemes tend to work according to this principle.
When the parameters of the current in the main circuit are restored, the contacts of the contactor of the main circuit are closed with simultaneous opening of the contacts of the reserve contactor. As a rule, the circuits additionally have a blocking of the simultaneous operation of the coils.
With the help of the ATS, you can prevent the simultaneous inclusion of two lines at once (main and backup). In circuits in which sectioning is applied, the automatic transfer switch will block the inclusion of sectional "AB". If necessary, ATS are equipped with a special mechanical blocking system.
These devices can be installed in separate cabinets. Depending on the power consumption, they can be: small-sized, full-sized, two- and three-sectional. Also, ATS can be placed in distribution and lead-in cabinets.
How does the ATS know that it needs to be triggered?
Automatic input of backup power is a full-fledged mechanism with its own logic and its own senses and controls. Who actually understand the situation, and make the only correct decision to trigger the mechanism.
The backup voltage input device, as a rule, includes a number of relays. They are connected to the section of the circuit that needs to be protected. An understanding device includes a phase control relay, it monitors the full-phase operation of an electrical installation. The voltage relay is also important, it serves to protect your equipment, turning off the electricity if its parameters differ from the frames installed in it.
Simply put, if the voltage in your outlet deviates greatly from two hundred and twenty volts, the relay will simply disconnect the contact and break the circuit. After that, a signal will be sent to another part of the circuit, and the switching on of the backup input is triggered.
Simple circuit and principle of operation of ATS
In low-voltage networks, it is convenient to use special relays that control the voltage in protection circuits. ATS is preferable here, since not all equipment is able to withstand frequent power supply changes. This device is clearly visible in a simple diagram.
- The EL-11 relay controls the three-phase voltage, monitors the phase imbalance, their breakage and alternation.
- Electromagnetic relays with powerful contacts are used to connect loads. In normal mode, the coil of the magnetic starter of the main input is powered from it and by its contacts KM 1 connects the power supply to the load.
- When the voltage in the main circuit disappears, the KM 1 relay is disconnected, and power is supplied to the coil of the KM 2 relay, which connects the backup input.
This ATS scheme can be used in private houses, industrial and office buildings, where the switched load reaches tens of kilowatts.
Also, it should be remembered that petrol or diesel generators are irreplaceable sources of additional power. The latter are widely used due to their economy and higher power.
The principle of operation of the ATS and the generator
In case of frequent power failures in the network, it is better to establish a reserve in the house, since the durability of household appliances, as well as comfortable living conditions, depend on this. In apartments, uninterruptible power supplies are installed on batteries, which are mainly used for electronic equipment. Generators are most commonly used as backup power supplies for private homes.
The generator, in its simplest form, is connected to the power supply of the house through a toggle switch. This prevents a short circuit in the event of an erroneous introduction of a reserve, when the automatic power supplies to the house are not turned off. The switch is selected with three positions, where the middle one completely cuts off the electricity.
ATS can be installed in automatic mode if the generator is equipped with an automatic starting device and controlled from the cabinet using contactors that also switch inputs.
Automation works on microprocessor control, for example, on Easy relay controllers. To enter the reserve ATS, voltage sensors are used. As soon as the power is cut off, the generator engine starts immediately. It takes some time to reach the operating mode, after which the ATS switches the load to the reserve. Such delays are acceptable for domestic needs.
Generator automatic start unit (BAZG)
The automatic generator start unit is a system that enables the start and control of a backup generator in the event of a power failure. It makes five start-up attempts within 5 seconds in each interval after the voltage on the main input disappears. In addition, it controls the air damper, closing it at the moment of starting.
If voltage reappears at the main input, the device switches the load back and stops the generator engine. When the generator is idle, the fuel supply is shut off by a solenoid valve.