📋 Case Study

Industrial Plant Power Design: Chemical Processing Facility in Texas

Frequent lightning-induced tripping of DCS I/O modules and PLC failures due to inadequate bonding and SPD placement

🏗️ Project Overview

New 200 MW chemical processing plant with hazardous area classifications

🎯 Challenge

Frequent lightning-induced tripping of DCS I/O modules and PLC failures due to inadequate bonding and SPD placement

🔧 Design Approach

Redesigned equipotential bonding grid using exothermic welds, installed Type I+II SPDs at service entrance and Type III at all control cabinets, implemented shielded twisted-pair cabling with 360° connector bonding

📐 Design Diagram

_p,down < U_p,up − (2·L·di/dt) = 1.2 kV Ground Grid Surge Protection Flow

AI-generated project design illustration

📐 Key Calculations

Bonding Conductor Sizing

≥ 50% of main grounding conductor per NEC 250.102(C)(1)

Result: 1/0 AWG Cu

Ensures low-impedance fault path for surge currents

SPD Coordination Margin

Up_downstream < Up_upstream − (2 × L × di/dt)

Result: 1.2 kV margin

Prevents back-feeding into upstream SPD during fast transients

📊 Results

Zero SPD-related outages over 24 months; DCS uptime improved from 92% to 99.98%; eliminated $1.2M/year in unplanned downtime

💡 Lessons Learned

• •Single-point grounding alone is insufficient without high-frequency bonding
• •SPD coordination must account for cable inductance in industrial environments

✅ Key Takeaways

• 1Single-point grounding alone is insufficient without high-frequency bonding
• 2SPD coordination must account for cable inductance in industrial environments