Advanced Protective Relaying Based on Rogowski Coil Current Sensors Ljubomir A. Kojovic Martin T. Bishop Cooper Power System Thomas A. Edison Technical Center Franskville, Wisconsin, USA

Iron-Core Current Transformer Rogowski Coil Ip RB Iron Core Ip Air Core RB M IP IS IP IS VB VB IE Lm RB RB High Impedance Burden Low Impedance Burden IS VB  0 IE  90 I’P IP’

V-I Characteristics Voltage Non-Gapped Iron-Core Current Transformer No Air-Gap Increasing Air-Gap Air-Gap 1 Air-Gap 2 Linear Coupler Operating point Rogowski Coil Current

Design Criteria Relative Position of the Primary Conductor inside the Coil Loop The Impact of Nearby Conductors (external electromagnetic fields)

Printed Circuit Board Rogowski Coil Relative Position of the Primary Conductor inside the Coil Loop Printed Circuit Board Rogowski Coil Winding imprints S n i(t) m RB Air Core (non-saturable) v(t) - = dt di(t) M nS t v ) ( m

Electromagnetic Fields External Electromagnetic Fields Current Voltage v(t) PCB1 PCB2 PCB2 wound in opposite direction to PCB1 i(t)

Designs Interior Applications Exterior Applications Split-Core Type Rogowski Coil Parallel Conductors

Printed Circuit Board Rogowski Coil Shielded Cable and Connectors Comparison to CTs Heavy Gauge Wires Multi-Function Relay Primary Current 2000/5 A, C800 Current Transformer 10 cm Terminal Blocks Weight: 90 kg 64 cm 30 cm Printed Circuit Board Rogowski Coil Multi-Function Relay Primary Current Width 2 cm Weight: 2 kg 30 cm Shielded Cable and Connectors

Spot Networks SN1 SN2 SN3 Rogowski Coil Circuit Breaker Network Protector Fuse

Integrated Relay Protection Solutions Zone 1 R Network 1 G Zone 5 Network 2 Zone 4 Bus Zone 2 Zone 3 Load

Integrated Relay Protection Solutions Zone 1 RC1 RC2 R Network 1 G Relay2 Network 2 Relay1 RC3 Load

Integrated Relay Protection Solutions Network 1 G Network 2 Zone 2 RC1 RC2 Fiber Optic Cable Relay1 Relay2 Load Ethernet Switch other IEDs

Busbar Protection Summing Block Protected Busbar Relay Rogowski Coils

Traveling Wave Based Protection

Traveling Wave Based Protection

Rogowski Coil Current Sensors Field Experience with Differential Protection of Power Transformers Based on Rogowski Coil Current Sensors Ljubomir A. Kojovic Martin T. Bishop Cooper Power System Thomas A. Edison Technical Center Franskville, Wisconsin, USA

Differential Protection of Power Transformers Fault RMS Difference False differential current causes nuisance protection operation CT

Differential Protection of Power Transformers Blocking Zone Differential Current Restraint Current Operating Zone with Current Transformers Expanded Operating Rogowski Coils

Differential Protection of EAF Transformers Split-Core Rogowski Coil Non Split-Core Rogowski Coil EAF Transformer Water Cooled Leads 50 kA – 100 kA Tap position EAF Multifunction Relay

Differential Protection of EAF Transformers B C 34.5 kV 1000 V “Water-Cooled” Conductors EAF Transformer Multi-function Relay Primary RCs Secondary RCs Tap Position Shielded Cables with Connectors

Differential Protection of EAF Transformers 25 MVA 32 kV/395 V 138 kV/32 kV Filter C L Current Measurement 200/5 A Rogowski Coils Rogowski Coils Multi-Function Relay Tap Transformer

RMS Values averaged per one second 10 20 30 40 50 60 70 80 90 Time [minutes] Current [kA] EAF C-Phase Currents RMS Values averaged per one second 10 20 30 40 50 60 70 80 90 100 Time [minutes] Current [kA] EAF C-Phase Currents Min and Max Values averaged per one second Max Min

0.12 0.14 0.16 0.18 -4000 -2000 2000 4000 Time [s] Current [A] 0.02 0.04 0.06 0.08 -4000 -2000 2000 4000 Time [s] Current [A]

0.02 0.04 0.06 0.08 A-Phase -4000 -2000 2000 4000 Time [s] Current [A]

Circuit Breaker Operates Relay Operates Fault Inception Primary Currents Secondary Currents Operate Signals Restraints Signals Trip Signals