Automatic transfer switch (ATS) and diesel genset auto start

ATS – automatic standby infeed to restore the power of consumers. You should not confuse Automatic Transfer Switch, ATS, with AVR, Automatic Voltage Regulator. The task of ATS is monitoring the parameters of the electric mains, and for this, voltage-check relays or micro-based units can be used.

The structure is an ATS panel or switchboard with contactors, as well as contact-breakers or motor-driven automated devices.

Boards with power and control devices are inside. Cabinets usually have three cable lead-ins: input ones and from the diesel genset and the outgoing line for loading. The power parts include lead-in lines (input bus), output buses connected with corresponding automated devices, contactors (contact-breakers or motor-driven automated devices). Automatic control of the automatic control power circuit is carried out using voltage transformers (relays), time switches, diesel genset controllers, as well as PLC – programmable logical controllers. 2 inputs ATS switchboard with motor-driven automatic devices are suitable for use at a rated current of 250-6300 A. When the current on the primary input is lost, special electric motors receive a signal and lead up the springs of the needed switch switching the load to another input. As a rule, a front panel with LEDs and mnemonic circuits where one can monitor the status of the power supply of facilities is mounted on all ATS.

ATS (automatic transfer switches) for diesel gensets

АВР (автомат ввода резерва) для дизельных электростанций – фото 1 из 5

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ATS switchboards with 60 - 160 А current are mounted version, ATS switchboards with 160-400 A - floor version. ATS panel consists of the body and writing board. The design of the cabinet body ensures the input of feed lines and output of outgoing lines from the top and from below.

ATS can be designed on contactors, motor-driven switches, or automatic motor-driven switches. ATS consists of

• a controller, voltage transformers
• voltage-check relays (RCP), time switch
• Starters, contactors
• Automatic motor-driven switches (QF, SF)
• motor-driven contact-breakers

The main element of the control of input voltage in ATS circuits is the voltage-check relay (relay control panels RCP, voltage watch monitor). The relay controls voltage value, phase sequence, one-phase open fault, neutral wire break, confusing when connecting phases, and a neutral wire. The options for relay control panels:

• - ABB CM-PVE, SQZ3

• - Schneider Electric RM17, RM35

• - Siemens 5TT3, 3UG35, 3ug46

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The main switching device is switches (contactors) or automated device. It is cheaper to use a contactor and an automatic switch for low currents (up to 400А); for high currents from 1000 Amperes – an automatic device is better. When using a contactor in the 630 A ATS circuit, the contactor coil at this high current will be always live.

The ATyS line by Socomec is motor-operated switches with electrical and mechanical blocking up to 3200 A. Electrical commands are operated with a motor-operated unit, which is controlled by two types of flow charts:

• emote control: the ATyS switch is controlled by dry contacts, which put it in the 1, 0 or 2 positions. The signals of these contacts may come from external control circuits
• automatic control: the ATyS 6 switcher fulfills all control functions, equipped with timers and a relay for regular/emergency switching.

ATyS 6e and 6m switches feature the function of remote control. Motor-operated and control modules are easily replaceable without switching off feeding cables.

When building schemes using logical controllers, a UPS is a required element especially when working with a diesel generator for the I category of consumers. It is not recommended to use the same UPS for ATS controller operation as the one used for the load (in the case of failures the ATS panel becomes inoperable).

ATS remote control

Dispatching ATS – the remote control of ATS parameters, supply-line voltage and control (switching on and off of the ATS, switching to another input) is carried out using an RS-232/RS controller according to the ModBus/RTU data communications protocol.

Controller for ATS start

An automatic transfer switch with a diesel generator can be built using a special controller (for example, ComAp InteliATS or DSE 335) and an ATS panel. An example of the operation of an ATS with two inputs (or one input) and a diesel generator:

When the voltage on 1 and 2 inputs is lost, the voltage-check relays turn off and the contact of the controlling built-in relay returns to its starting position, in 5 s delay time from the controller output periodically gives the diesel generator startup signal lasting 10 s. if the DG does not start within 52 s, the controller gives the "DG FAILURE " signal, the start cycle stops. The DG controller is powered by UPS if there is no 220 voltage.

When the input voltage is recovered, the contactor of the input switching device switches off from the diesel generator, the “STOP” signal is given with a delay to the DG, it will work for 15 s at idle for cooling.

Standard ATS design version:

• 2 inputs and 1 load;
• 2 inputs and 2 loads with partitioning;
• 2 inputs with the priority of the first input;
• 2 inputs and input from diesel genset, with partitioning or without it;
• 1 input and input from diesel genset.

3 inputs ATS panels are one of the most reliable power sources and are used for the consumers of the first category of electric reliability. 3 inputs ATS panels operate according to two schemes:

1 – one section of consumers is powered by three independent lines. The load will be connected where the voltage is normalized.

2 – two sections of consumers are powered by two lines, which are independent from each other. The third input is connected to a standby power, which in the case of an emergency connects to one of the sections.

Input switching device with ATS is used for electricity acceptance and registration, as well as protection of the buildings from short circuits or overload. Input switching device cabinets with ATS consist of cable inlet and outlet unit, ATS and a consumed electricity accounting block.

АВР (автомат ввода резерва) для дизельной электростанции 100 кВт – фото 1 из 5

АВР (автомат ввода резерва) для дизельной электростанции 100 кВт – фото 2 из 5

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ATS panel for diesel generator startup can operate automatically or manually (depending on the degree of DG automation and control panel). When there is no power supply on input 1, ATS sends a signal to start the generator. After the generator starts operating normally and the voltage on input 2 reaches the required level, the mechanism switches to the backup source.  Thanks to the set time relay, the second input will not be connected to the generator until it starts working as normal. Once the power supply is restored on the main source, the generator switches off, and the supply will switch to input 1.

In main distribution panels, ATS switches the load between incoming switches from the mains and from the standby power supply from diesel generators (gives start and stop commands).

Even if the switching is instantaneous, it will take time for the diesel genset to start, that’s why delays are set (presets from 10 seconds and longer secure the system from the false response of ATS in the case of voltage slump).

Prices for ATS panels for diesel generator sets manufactured by Techexpo 

For comparison – prices for ATS for FG Wilson diesel gensets (China - UK)

Video: Socomec motor-driven ATS on a breaker switch, 400 А current: double-throw switch, power module, and control. Control voltage value, delay time, and input priority are pre-set. Contacts always switch through a zero value. When supplying power voltage to Input 1 and Input 2, power is supplied from input 1 to the load. If the voltage gets on the primary input, there is a switch to the 2^nd working input. When normal voltage is restored on the primary input, the panel switches to input 1.