A Real UPS Failure Case Study and What We Learned
In instrumentation and control systems, the UPS is often called the “heartbeat of the plant.”
It keeps critical systems like DCS, field instruments, and control loops running—even during power disturbances.
Most of the time, everything looks fine during routine inspection.
But one real incident reminded us of a hard truth:
👉 Sometimes, a system failure is caused by something as small as a single screw.
📍 Incident Overview
Time: February 16, 2026 – 12:04
Location: UPS cabinet room
Alarm: “DCS External Power Failure”
Impact: Potential risk to the entire control system
⚡ What Happened?
At 12:04, the control room received an alarm:
👉 DCS external power failure
Operators immediately coordinated with the electrical team and confirmed:
The secondary power supply had tripped
Emergency inspection was initiated
🔍 On-Site Investigation
After arriving at the UPS room, engineers checked:
Key Findings:
West-side UPS system (parallel units)
Completely blacked out
No input / output power
East-side UPS system
Alarmed but still operating
Continued supplying power to DCS
ATS (Automatic Transfer Switch)
Found in manual mode
Unable to switch automatically
Root Cause Identified
👉 A loose screw inside an electrical drawer
👉 Contacted the cabinet housing
👉 Caused a short circuit and tripping
🔧 Root Cause
👉 A single loose screw caused a short circuit inside the electrical drawer
This led to:
Power trip on secondary supply
Loss of redundancy
System-wide risk
✅ Recovery Process
Electrical team removed the fault point
Tightened internal components
Checked insulation and safety
Restored secondary power
🕐 By around 13:03:
UPS systems returned to normal
DCS alarm disappeared
Full system operation restored
💡 Why This Incident Didn’t Cause a Shutdown
This could have been a major accident—but it wasn’t.
Two key reasons saved the system:
1️⃣ UPS Redundancy (Critical Protection)
Dual UPS design (East & West)
One side failed → the other kept running
👉 This prevented total DCS shutdown
2️⃣ Fast Cross-Team Response
Control room + electrical + instrumentation teams
Immediate coordination
Full recovery within 1 hour
⚠️ Hidden Risk We Cannot Ignore
👉 The ATS switch was in manual mode
If the second UPS had failed:
❗ The entire system would have gone down
This is a serious operational risk
🔥 What We Learned: 3 Critical Power Monitoring Practices
1. UPS Visualization in DCS ⭐ MUST DO
Make UPS status visible directly in DCS.
Key data to monitor:
Input/output voltage & current
Battery capacity & backup time
Operating mode (Normal / Bypass / Battery)
Alarm status
💡 PRO TIP:
A visible UPS dashboard = early warning system
2. Full Power Loop Monitoring ⚠️ HIGH RISK AREA
Don’t just monitor UPS—monitor the entire power chain:
👉 Power grid → ATS → UPS → Distribution → DCS
Recommended monitoring points:
ATS switch status
STS system status
UPS output
DC power systems (24V / 110V)
Distribution circuits
Use relay signals + DCS DI inputs for real-time status detection.
3. Alarm Logic & System Design
Key principles:
Clear alarm naming
Alarm prioritization
Automatic pop-up alerts
Example:
👉 “DC24V Power Failure – Cabinet A”
Result:
Faster response
Accurate fault location
Full traceability
🚀 Final Solution: Build a Power Monitoring System
By combining:
UPS communication
Relay-based loop detection
DCS visualization
You can build a complete system that delivers:
✅ Real-time monitoring
✅ Early warning
✅ Fast response
✅ Reduced shutdown risk
🔚 Final Takeaway
👉 Power system failures are often not caused by major faults
They are caused by:
Loose connections
Small installation mistakes
Lack of monitoring
Small detail → Big risk