1. Scope & Purpose
This guide details preventive maintenance procedures for uninterruptible power supply systems (UPS/UPS) used in critical infrastructure, including the aerospace and energy sectors. The objective is to ensure the permanent availability of energy by validating the condition of the batteries, the integrity of the filter capacitors and the functionality of the bypass devices. These interventions must be carried out in accordance with standards NF EN 62040 and NF C 15-100.
2.Safety Precautions
DANGER TO LIFE: The direct voltage (DC) internal to the UPS can exceed 400V and remain present even after the inverter has stopped. Strict compliance with the lockout procedure (LOTO - Lockout/Tagout) is mandatory before any internal handling.
Personal protective equipment (PPE) required:- Class 0 insulating gloves (1000V).
- Protective glasses against electric arcs.
- Flame-retardant clothing (ARC Flash category).
- Insulated safety shoes.
3. Tools & Materials Required
| Tool | Specification | Quantity |
|---|
| True RMS Multimeter | CAT IV 600V / CAT III 1000V | 1 |
| Torque wrench isolated | Range 5-25 Nm | 1 |
| Thermal camera | Min resolution 160x120 | 1 |
| Battery capacity tester | Adapted to bench tension | 1 |
| Impedance measuring device | Micro-Ohm Ohm Meter | 1 |
4. Pre-Maintenance Inspection Checklist
| Item | Verification | Criteria Acceptance | Notes |
|---|
| UPS cabinet | Physical state | No corrosion/deformation | - |
| Ventilation | Airflow/Filters | Free flow, clean filters | - |
| Connections | Thermography | No hot spot (> 10°C diff) | - |
| Batteries | Physical appearance | No swelling/leaking | - |
5. Step-by-Step Procedure
- Lockout and safety:
- Open the AC input circuit breaker, then isolate the ASI output.
Classic error: Forgetting to open the external bypass circuit breaker. - Check the absence of voltage on the input and output terminals with a calibrated multimeter.
- Install locking padlocks and warning labels.
- Visual inspection of capacitors:
- Inspect the DC (continuous bus) capacitors for any sign of bulging or electrolyte leakage.
Deformation, even slight, requires immediate replacement of the component. - Measure the temperature of the capacitors after 15 minutes of operation under nominal load. It must not exceed 45°C.
- Battery charge test:
- Perform a controlled discharge test at 80% of the nominal load for 15 minutes.
Never discharge below the final voltage threshold specified by the manufacturer (e.g.: 1.75V per cell for lead-acid). - Monitor the voltage of each battery pack. A difference greater than 0.2V between two blocks indicates a defective element.
- Checking the bypass switch:
- Mechanically activate the bypass (if accessible) to validate the integrity of the contacts.
Caution: Carry out this operation only outside critical load if static bypass cannot be guaranteed. - Measure the voltage drop across the closed bypass contactor. It must be less than 10mV.
- Tightening the connections:
- Check the tightness of all the main electrical connections (battery terminals, capacitors, circuit breakers) with the torque wrench.
Standard tightening torque M8: 12 Nm. Do not apply excessive torque which would damage the threads.
6. Post-Maintenance Verification Checklist
| Test | Expected result | Real | Pass/Fail |
|---|
| DC Bus Voltage | Datasheet compliant | | |
| Static bypass test | Seamless transfer | | |
| Battery test | Stable voltage under load | | |
| Alarm reminders | No active alarm | | |
7. Troubleshooting Guide
| Symptom | Probable cause | Corrective action |
|---|
| Batteries do not hold a charge | Sulfated/defective block | Replace the battery pack |
| Condenser overheating | Premature aging | Replace the capacitor |
| Bypass transfer failed | Bypass contactor stuck | Clean or replace the contactor |
| Excessive ventilation noise | Dirty/worn fan | Replace the fans |
8.Recommended Maintenance Schedule
| Task | Frequency | Estimated duration | Skill level |
|---|
| Visual inspection/thermography | Quarterly | 1h | UPS Technician |
| Battery discharge test | Annual | 4h | UPS Technician |
| Capacitor replacement | 5 years | 8h | Service engineer |
9. Spare Parts Reference
| Part description | Specification | UNITEC category |
|---|
| Lead-Acid Battery | 12V 100Ah VRLA | Stationary Batteries |
| DC capacitor | 450V 4700µF | Electronic Components |
| Fan | 24V DC 80x80mm | Cooling |
To order certified spare parts, consult our online catalog: https://www.unitecd.com/e-catalog/
10. References
- NF standard EN 62040-3: Uninterruptible power supply systems (UPS) - Performance specification and test methods.
- Standard NF C 15-100: Low voltage electrical installations.
- Technical documentation from the inverter manufacturer.
