📋 Case Study

Hospital Emergency Power System Coordination

Critical life-support loads (ICU, OR, imaging) required <100ms transfer and no false trips during generator paralleling transients

🏗️ Project Overview

750-bed acute care hospital in Houston, TX with dual utility feeds and 3×2.5MW black-start generators

🎯 Challenge

Critical life-support loads (ICU, OR, imaging) required <100ms transfer and no false trips during generator paralleling transients

🔧 Design Approach

Adaptive relay settings with generator mode detection, harmonic-blocking for VFD-rich loads, and dedicated ground-fault coordination zones

📐 Design Diagram

_{gf_min} = 1.8 A | T_inrush window = 120 ms T_set > 120 ms <100 ms transfer False Trip Risk

AI-generated project design illustration

📐 Key Calculations

Generator Inrush Rejection Window

T_set > 3 × T_inrush_decay

Result: 120 ms

Prevents nuisance trip during 12-cycle inrush decay

Ground-Fault Sensitivity Threshold

I_gf_min = 1.25 × I_load_unbalance

Result: 1.8 A

Detects insulation degradation before failure

📊 Results

Zero unintended transfers during 17 utility outages; 100% critical load continuity; 40% reduction in Nuisance Alarms after adaptive logic implementation

💡 Lessons Learned

•Load unbalance monitoring is essential for GF sensitivity tuning
•Paralleling transient harmonics require 5th/7th harmonic restraint
•NFPA 99 Chapter 11 mandates zone-specific coordination documentation

✅ Key Takeaways

1Load unbalance monitoring is essential for GF sensitivity tuning
2Paralleling transient harmonics require 5th/7th harmonic restraint
3NFPA 99 Chapter 11 mandates zone-specific coordination documentation