Online monitoring applications for power cables Joona Mörsky

Content Why? Failure modes Monitoring methods – Distributed temperature sensing – Measuring PD:s Summary Joona Mörsky

Why? Availability requirements – Power quality – Downtime predications Safe operating window estimation Predictive maintenance Economic factors – Maintenance and investment budget planning – Cables produces income only when operational! Joona Mörsky

Failure modes Cables decay over time – Environmental causes Moisture Soil thermal resistance Frost Electrochemical reactions – Over voltages and PD – Over temperatures or over load – Mechanical damage Ground movement Vibrations Source: Elka Joona Mörsky

”Circle of decay” PD Decay Heat Insulation heats up Soil heats up Soil moisture dries out Soil thermal resistance rises Stress to insulation Over voltage Stress to cable Joona Mörsky

Condition monitoring Important is to detect or prevent elements from “circle of decay” – Temperature measurements Soil Cable – PD event detection – Leak current detection Joona Mörsky

Distributed temperature sensing Laser pulses are send through optical fiber inside or next to power cable – Mechanical stress Raman effect (pressure causes signal damping) – Location and Temperature OTDR (Optical Time Domain Reflectometry) OFDR (Optical Frequency Domain Reflectometry) – Suitable only for new installations Require optical fibre inside or next to power cable Joona Mörsky

Distributed temperature sensing Source: NKSYSTEMS Joona Mörsky

PD measurements PD causes high frequency components to current – PD:s can be detect by measuring high frequency current components Source: Emerson Joona Mörsky

Summary Distributed temperature sensing + Real-time information about thermal operating window + Detects location of problems + Detects mechanical stress -Require optic fibre inside or next to cable -> only suitable for new installations PD measurements + Can be installed in existing cables -Detects only problems, not the cause -Doesn’t provide location information Joona Mörsky

Questions? Joona Mörsky