The automatic transfer switch (ATS) is the component that transfers the electrical load from the primary source of power to a backup generator in case of failure of the main power source, and back again when the mains is available. The automatic transfer switch monitors the supply and initiates the generator. Without it, someone has to start the generator and change over by hand.
Search interest in automatic transfer switches has only started showing in Google Trends for the UAE in the last year, and the question behind it is simple: how does backup power actually take over? This guide discusses how an ATS functions, its various kinds, how to size an ATS, what needs to be tested, and the ATS compatible genset offered by GENAVCO.
Operation of Automatic Transfer Switch
- Stage 1 - The ATS controller detects voltage and frequency in the mains supply.
- Stage 2 - In case of failure or variation beyond set values, there is a time delay for validation purposes to rule out any false signals.
- Stage 3 - A start signal is issued to the generator.
- Stage 4 - Once the voltage and frequency of the generator stabilize, the switch is activated to switch over to the generator supply.
- Stage 5 - Upon stabilization of mains, the ATS switch switches back to the mains.
- Stage 6 - The generator operates for a period of cooling down and then shuts off to await further action.
Each delay can be adjusted individually. If timed properly, this ensures that there will be no nuisance start-ups when the input voltage drops momentarily.
Manual vs Automatic Transfer Switch
| Factor | Manual transfer switch | Automatic transfer switch |
| Who changes over | A person at the panel | The ATS controller |
| Typical outage time | Minutes, depending on who is on site | Seconds, set by the start and transfer delays |
| Best for | Small sites with staff always present and non-critical loads | Unattended sites, critical loads, night and weekend cover |
| Risk | Human error, delayed response | Settings and testing must be maintained |
Types of Transfer Arrangement
- Open transition (break before make): the load is disconnected from one source before connecting to the other. Simple and common, with a short break in supply.
- Closed transition (make before break): sources are paralleled for a moment on the return to mains, avoiding a second break. It needs synchronising controls and utility approval.
- Load shedding: the ATS or controller connects priority circuits first and adds others as capacity allows, which helps when the generator is smaller than the full building load. Our guide to backup generator planning covers critical load lists.
Sizing an Automatic Transfer Switch
- Current rating: the ATS must carry the full current of the load it switches, with margin for future growth.
- Poles: three-phase systems usually need three or four poles, depending on how the neutral is arranged.
- Fault rating: the switch must withstand the fault current available at that point in the installation.
- Generator match: the generator must cover the load the ATS transfers, including motor starting. See our guide to generator sizing.
Sizing and protection must be designed and signed off by a qualified electrical engineer in line with local authority rules.
ATS-Ready Generators From GENAVCO
1. GPS Industrial Range (10 kVA - 2,500 kVA)
- Confirmed specification: product range from 10 kVA to 2,500 kVA with a closed canopy for sound attenuation, additional silencer options in hospital, residential and industrial grades, supply as 50 Hz or 60 Hz, and in-built fuel tanks with an option for external tanks.
- Confirmed controls integration: compatible with BMS, ATS and synchronisation, so the set can start automatically on mains failure through an ATS and work alongside the building management system.
- Application fit: standby and prime power for buildings, industrial plants and infrastructure that need automatic changeover.
Planning standby power with automatic changeover?
Send us your critical loads, supply arrangement and the outage time you can accept. We will propose the generator and changeover arrangement.
What an ATS Installation Includes
- Switch: motor-operated switches/contactors based on the load rating.
- Controller: to sense the supply, set the delays and start the generator.
- Wiring/cable & protective devices: selected based on the load and fault level.
- Generator start-up wiring: for signaling between ATS and the generator.
- Building Management System connection: Optional connection via the BMS.
In comparing the quotation for a generator, one has to see whether the ATS and its installation are included.
Testing the ATS
Untested ATS is wishful thinking. Running periodic tests on a fully loaded system will demonstrate whether the generator started, there was a proper transfer and the delays were correctly set.
- Monthly: perform a test start of the generator using the ATS test facility and verify the transfer.
- Periodically: perform a simulated main failure test on a fully loaded system in the presence of the facility personnel.
- Following changes: perform tests after changes in loads, settings or control panels. Log all tests and delay settings for faults.
Automatic Transfer Switches Under UAE Conditions
- During summer: Peak demand due to cooling loads; ensure that the generator and ATS can still handle the demand in August.
- Heat in panel room: Ventilate the switchgear room since heat reduces the life span of controllers and contacts.
- Dust: Ensure that enclosures are closed to prevent dust from getting in.
- Sensitive sites: Hospitals, data rooms, and cold storage should have minimal transfer time. GPS Series comes with hospital-quality silencers.
Why Choose GENAVCO for Standby Power
- ATS-ready generators: the GPS Industrial Range is compatible with BMS and ATS. See the GPS power generation range.
- Installation and commissioning: GENAVCO handles installation and commissioning for Green Power sets and supports GPS equipment with installation and maintenance.
- One of the Juma Al Majid Group Companies since 1967: An experienced UAE dealer, ISO 9001 accredited, with accredited technicians and genuine spare parts.
Common Faults in Using an Automatic Transfer Switch
- Undersized ATS for anticipated future loads: will require replacement in case of additional load.
- Too short delays: even minor drops can result in false starts and transfers.
- No testing under load: any issues may arise only in the event of a power failure.
- Generator not powerful enough to handle transferred loads: voltage and frequency drop in case of motor starting and may even trip the ATS.
- No prioritization of loads to transfer.
Frequently Asked Questions
What is the function of an automatic transfer switch?
It senses the loss of mains power supply, engages the standby generator, and switches the load after the generator is stabilized, and again when the mains power supply is restored.
How quickly can an automatic transfer switch switch to the generator?
Generally within seconds, subject to confirmation time, generator startup time, and switching times. Essential loads that require uninterrupted power supply also require a UPS system.
Do I need an ATS for my generator?
Yes, when the generator is in an unmanned location or the load is critical because a switch is controlled manually and requires people to be present to start the generator and change over.
Will the GENAVCO generators work with the ATS?
Yes, the GPS Industrial Range 10 kVA to 2,500 kVA works with BMS, ATS and synchronisation.
Ready to Plan Automatic Changeover?
An automatic transfer switch turns a generator into dependable backup power. GENAVCO supplies power generators in the UAE and diesel generators ready for automatic changeover, sized for your electric generator output needs.
Tell us your loads and supply arrangement. We will propose the right generator and ATS and price it properly.
Serving Dubai, Abu Dhabi, Sharjah, Al Ain and the wider UAE.
