Kurt Uhlir President Standby Power System Consultants, Inc. Technical Panel Session. Sunday January 11, 2015. DC System Failure Modes- Utilities Kurt Uhlir President Standby Power System Consultants, Inc. IEEE PES SBC Winter Meeting. January 11 – 15, 2015. New Orleans, LA

Typical Utility DC Power System Operating Voltages 250 VDC 125 VDC 48 VDC 32 VDC 24 VDC IEEE PES SBC Winter Meeting. January 11 – 15, 2015. New Orleans, LA

Utility DC Power System Applications Switchgear and control Communications Microwave SONET Emergency Lighting Emergency pumps UPS SCADA Smart Grid Distribution Automation Instrumentation IEEE PES SBC Winter Meeting. January 11 – 15, 2015. New Orleans, LA

IEEE PES SBC Winter Meeting. January 11 – 15, 2015. New Orleans, LA Substation 125 VDC System IEEE PES SBC Winter Meeting. January 11 – 15, 2015. New Orleans, LA

Typical Utility DC Power Systems IEEE PES SBC Winter Meeting. January 11 – 15, 2015. New Orleans, LA

Typical Utility DC Power Systems IEEE PES SBC Winter Meeting. January 11 – 15, 2015. New Orleans, LA

Typical DC Power System SPD Inverter Eng/Gen Utility AC Utility Infrastructure AC Input Rectifiers Batteries DC Distribution Protected AC Loads IEEE PES SBC Winter Meeting. January 11 - 15, 2015. New Orleans LA

Class 1E Nuclear Plant 125 Volt Battery IEEE PES SBC Winter Meeting. January 11 – 15, 2015. New Orleans, LA

Class 1E Nuclear Plant 125 Volt Battery IEEE PES SBC Winter Meeting. January 11 – 15, 2015. New Orleans, LA

Utility DC Power System Failures DC System Grounds Palisades Nuclear – Loss of Class ESF 125 VDC Bus Battery main breaker overcurrent trip Battery charger main breaker overcurrent trip Overcurrent Protection Coordination of overcurrent devices DC rating vs AC rating Maximum rated voltage DC Distribution Panel Design IEEE PES SBC Winter Meeting. January 11 – 15, 2015. New Orleans, LA

Utility DC Power System Failures IEEE PES SBC Winter Meeting. January 11 – 15, 2015. New Orleans, LA

Utility DC Power System Failures IEEE PES SBC Winter Meeting. January 11 – 15, 2015. New Orleans, LA

Typical Utility DC Power Systems IEEE PES SBC Winter Meeting. January 11 – 15, 2015. New Orleans, LA

Sources of Battery Grounds Commercial ground detectors Water in conduit Water entering junction boxes or switch/sensor terminations Wire splices soaking in water Wildlife Sharp objects piercing wire insulation Constant abrasion wearing away wire insulation Wires that have pulled out of their terminations and touch ground or water Failed capacitor or semiconductor surge suppressors Wire insulation cracking IEEE PES SBC Winter Meeting. January 11 – 15, 2015 New Orleans, LA

Source of Battery Grounds Grounds can occur on the battery itself Electrolyte in a cell is conductive Racks are grounded IEEE PES SBC Winter Meeting. January 11 – 15, 2015. New Orleans, LA

Sources of Battery Grounds Water is the Number 1 causes of most grounds because it often forms the bond between the exposed conductor and earth ground IEEE PES SBC Winter Meeting. January 11 – 15, 2015. New Orleans, LA

Figure 1 – Single Battery Ground (Normal Operation) IEEE PES SBC Winter Meeting. January 11 – 15, 2015. New Orleans, LA

Figure 2 - Two Battery Grounds (Misoperation) At a minimum, a floating battery system requires at least two battery grounds before misoperation can occur. IEEE PES SBC Winter Meeting. January 11 – 15, 2015. New Orleans, LA

Typical DC Power System SPD Inverter Eng/Gen Utility AC Utility Infrastructure AC Input Rectifiers Batteries DC Distribution Protected AC Loads IEEE PES SBC Winter Meeting. January 11 - 15, 2015. New Orleans LA

IEEE PES SBC Winter Meeting. January 11 – 15, 2015. New Orleans, LA Poor distribution panel design that attributed to dc power system failure during maintenance activity IEEE PES SBC Winter Meeting. January 11 – 15, 2015. New Orleans, LA