Automatic transfer switches (ATS) are a crucial component of power supply systems, providing backup power in case of main source failure. Despite the simplicity of their operating principle, ATS are complex electromechanical devices, with key elements including an electronic board and switches. Improper use or maintenance of such devices often leads to serious malfunctions, overloads, or even emergency shutdowns of the entire line.
Purpose of ATS and the Importance of Proper Use
The main function of ATS — automatic load switching from the primary source to the backup one in case of power failure. This ensures continuity of processes in hospitals, data centers, industrial facilities, or private homes.
Approximately 87% of ATS failures are related to human factors — improper installation, poor maintenance, or lack of diagnostics.
The goal of today's article is to help specialists avoid typical mistakes, extend the service life of certified UEC equipment, and improve power supply reliability.
Main Causes of ATS Failure Due to Improper Operation
The reliability of ATS operation determines the uninterrupted functioning of critical facilities: hospitals, manufacturing plants, etc. However, even the most modern automatic transfer switch fails if operating and maintenance conditions are violated.
Errors in Installation and Configuration
The most common issues are related to incorrect connection of cable lines/control circuits. Due to errors in the connection scheme, the system either fails to switch or does so with a delay, leading to interruptions in backup power.
Typical installation errors:
- Phase confusion. If phases are connected incorrectly, reverse rotation sequence of motors or dangerous potential differences may occur at the ATS output.
- Insufficient cable cross-section. An improperly selected conductor cannot handle the current load, causing overheating and subsequent shutdown.
- Poor quality of contact connections. Insufficient bolt tightening in contactor terminals or power buses leads to sparking, oxidation, and loss of contact.
Errors in the control scheme also have serious consequences. For example, an incorrectly set delay for backup activation leads to “fluctuations” — frequent on-off cycles during short-term voltage drops. This creates additional mechanical stress on the automatic transfer switch and reduces its service life by 2–3 times.
Conditions for Reliable Operation of UEC ATS in Automatic Mode
For correct and uninterrupted switching of the automatic transfer switch (ATS), it is recommended to adhere to the following parameters:
- Peak power — at least 1800 W to ensure stable switching.
- Supply voltage — stable, within 220 V ±10% (198–242 V).
- Unstable voltage or insufficient power from the primary or backup source can cause ATS malfunctions.
- The type of sine wave does not affect the operability of SB-ATS.
Violations of Operating Modes
Even a properly installed automatic transfer switch can quickly lose functionality due to incorrect operating modes. The most common is exceeding rated loads. With prolonged current exceeding passport values by 10–20%, contact temperature rises by 40–50 °C, accelerating insulation degradation. Every 10-degree increase in temperature inside the switching unit reduces its operating life by 15%.
Other violations:
- When the system is used for testing too frequently (more than once a day), the mechanical resource of ATS is depleted several times faster.
- Installation in unheated or humid premises without condensate protection leads to contact oxidation, short circuits, and control circuit failures.
- If the ATS lacks selective protection, during network emergencies, simultaneous emergency shutdown of primary and backup inputs is possible, completely halting power supply.
Maintenance Errors
Proper maintenance of UEC automatic transfer switches is critically important for extending equipment life.
Non-Compliance with Maintenance Regulations
One of the most common problems is the lack of a systematic approach to scheduled maintenance. In practice, maintenance is often performed “as needed” — after failures appear, instead of preventive measures. During this time, dust and moisture accumulate inside the UEC cabinet, leading to terminal corrosion and increased contact resistance. At temperatures above 80°C, connections may melt.
Consequences of skipping checks:
- Dust accumulation → increased node temperatures.
- Contact oxidation → increased resistance.
- Loosened connections → sparking and malfunctions.
Improper Maintenance
Another common category of errors is incorrect actions by personnel during maintenance. Many emergency cases occur due to attempts at independent “repair” of the automatic transfer switch without proper qualifications.
As a result, a cascade of failures occurs: contact overheating → sticking → emergency shutdown or complete ATS failure.
| Violation Category | Failure Share, % | Typical Consequences |
|---|---|---|
| Installation Errors | 32 | Incorrect unit operation, loss of backup power |
| Operating Violations | 26 | Overheating, overload, contact welding |
| Insufficient Maintenance | 29 | Oxidation, insulation breakdown, emergency shutdown |
| Other (aging, manufacturing defects) | 13 | Mechanical failures, contact wear |
To avoid ATS failures, it is necessary to:
- Check tightening torques according to technical datasheets.
- Regularly test ATS operability in simulated power outage mode.
- Conduct thermographic control of switching nodes every six months — overheated areas indicate increased contact resistance.
- After each scheduled maintenance, make a brief entry about the automatic transfer switch in the operation log, noting the date, responsible person, and check results.
Errors in System Modernization and Expansion
Any intervention in an existing scheme carries risks of technical incompatibilities, especially if changes are made without detailed load analysis and involvement of qualified engineers.
Changing Network Parameters Without Recalculation
Each ATS system, according to IEC 60947-6-1, is designed for specific rated current, voltage, and power parameters. Changing these without updating technical calculations is the most common error.
Most common errors:
- The enterprise adds new production lines or ventilation systems, often exceeding allowable load levels. This leads to heating and premature wear of contact groups.
- Switching from three-phase to combined scheme or integrating alternative sources (backup from diesel generators, solar inverters, etc.) without correcting control unit logic causes switching failures.
- Adding new feeders without phase balancing and selectivity check of protections.
Equipment Incompatibility
Another common issue is using uncertified automatic transfer switches or components from different manufacturers. At first glance, minor design differences seem insignificant, but in practice, they can disrupt logic and lead to electrical failures.
Main causes of incompatibility:
- Use of non-original spare parts. For example, replacing a UEC power ATS with an analog having less current margin leads to loss of switching capacity under peak loads.
- Lack of communication bus parameter checks. When integrating ATS into SCADA systems, it is important to coordinate data transfer speed and interface type (Modbus, CAN, Profibus).
Organizational Errors
The reliability of automatic transfer switch operation often depends not only on the technical condition of the equipment but also on the organization of operating processes.
Personnel Issues
One of the main causes of electrical system failures is insufficient personnel qualification. Operators who do not undergo regular training misinterpret ATS signals, leading to incorrect actions during emergencies.
Typical situations:
- Lack of knowledge about the automatic switching algorithm between sources.
- Violation of safety rules — working under voltage without insulating protective equipment.
- Independent intervention in the connection scheme without approval from the technical department.
Consequences of Improper Operation
Improper operation or maintenance of the automatic transfer switch leads not only to ATS failure but also to serious technical and safety risks.
Recommendations for Proper Operation
For the automatic transfer switch to operate long-term, a comprehensive approach to operation is necessary — combining technical, organizational, and preventive measures in accordance with DSTU EN 60947-6-1:2017.
Organizational Measures
- Develop clear operating instructions considering the specifics of the ATS connection scheme.
- Conduct personnel training at least once a year.
- Maintain an operation log and record every emergency shutdown.
Technical Measures
- Use only original UEC components compatible with the current connection scheme.
- Adhere to the maintenance schedule — contact checks, dust cleaning, connection tightening.
- Ensure stable backup power for key consumers to avoid power supply interruptions.
Preventive Measures
- Conduct thermographic control every six months to detect overheating and overloads.
- Perform ATS testing to verify functions.
- Analyze every emergency shutdown case to prevent recurrence.
| Action Type | Frequency | Responsible | Note |
|---|---|---|---|
| Visual ATS Inspection | Monthly | Electrician | Check housing, contacts, and indication condition |
| Connection Scheme Check | Quarterly | Energy Engineer | Test automatic switching logic correctness |
| Thermographic Diagnostics | Every 6 months | Technical Personnel | Detect overload zones |
| Test Switching | Every 6 months | Electrician | Check backup power |
| Full Maintenance | Annually | Certified Specialist | Control unit check |
| Emergency Shutdown Analysis | As Occurs | Engineer | Form recommendations to eliminate causes |
Typical Practical Examples
- Failure Due to Overload
At an industrial facility, the number of consumers increased, but the ATS connection scheme was not updated. As a result, the rated current exceeded the allowable by 25%. Due to lack of protective setting correction, the control unit did not recognize the dangerous mode, leading to emergency shutdown. - Contact Welding Due to Lack of Maintenance
At a backup diesel substation, no preventive inspections were conducted for two years. Due to dust accumulation and increased contact resistance, partial contact welding occurred during ATS activation, disabling one pole of the switching unit. Repair costs amounted to about 35% of the automatic transfer switch price. - Accident Due to Incorrect Settings
During modernization of an old backup power system, the engineer left the standard switching delay at 0.5 s. During short voltage sags, the ATS switched to backup unnecessarily, creating cyclic switching. This caused erroneous generator activations.
Appendices
| Check | Status | Comment |
|---|---|---|
| Visual Housing Inspection | ☐ | No Damage |
| Bolt Tightening Check | ☐ | No Play |
| Contact Cleaning | ☐ | Used Isopropyl Alcohol |
| Backup Power Switching Test | ☐ | Time ≤ 1.0 s |
| Control Unit Indication Check | ☐ | All Lamps Working |
| Temperature Check | ☐ | Not Above +60°C |
| Contact Resistance Measurement | ☐ | ≤ 200 µΩ |
| Maintenance Log Update | ☐ | Entry Made |
Typical Maintenance Schedule
Monthly:
- Visual check of panel, housing, and ventilation condition.
- Monitor for unusual noises.
Quarterly:
- Check tightening torque of screw connections.
- Test backup power switching.
Every Six Months:
- Clean contact groups, check connection scheme.
- Measure main contact circuit resistance.
Annually:
- Full ATS maintenance with replacement of worn elements.
- Assess insulation condition, update check protocols.
List of Regulatory Documents
- DSTU EN 60947-6-1:2017 — Switchgear and controlgear. Part 6-1: ATS.
- DSTU IEC 60364-5-53:2016 — Requirements for isolation, switching, and control devices.
- DSTU EN 60204-1:2018 — Safety of machinery. Electrical equipment of machines.
- Electrical Installation Code (PUE), sections 1.7 and 6.3.
- Order of the Ministry of Energy No. 476 dated 19.12.2020 — Regulations for operating backup power sources.
For consultation, selection, and service maintenance of automatic transfer switches, contact UEC specialists. We guarantee safe operation of your equipment and full compliance with regulatory requirements.
