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High Voltage Insulation Diagnostics

High Voltage Insulation Diagnostics. WELCOME!. Presented by: Bostjan Flis bostjan.flis@metrel.si. Content overview. Application areas of HV insulation testing What influences insulation resistance Symptoms of bad insulation Testing methods

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High Voltage Insulation Diagnostics

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  1. High Voltage Insulation Diagnostics WELCOME! Presented by: Bostjan Flis bostjan.flis@metrel.si

  2. Content overview • Application areas of HV insulation testing • What influences insulation resistance • Symptoms of bad insulation • Testing methods • Insulation testing with DC test voltage - insulation characteristics • Insulation testing with DC test voltage - test parameters • Limit values • Connection schemes • Test data evaluation i.e. statistics keeping • General requirements for HV insulation testers • Metrel HV insulation testers • Metrel's solution providing, services and development

  3. Application areas of HV insulation testing • Insulation resistance testing is part of predictive maintenance of: • Rotary machines (generators, motors) • Transformers (industry, utilities, power distribution) • Cables • Measuring transducers • Distribution boards • Benefits: • Lower TCO (total cost of ownership) • increased electrical safety • prevention against fire hazard

  4. What influences insulation resistance • Thermal exposure • Overload • Moisture • Electrical shocks • Mechanical shocks (vibrations, bad transportation) • Dirt (oil, dust, conductive materials) • General ageing of insulation Symptoms of bad insulation • Insulation breakdowns in a form of electrical short-circuits • Fire • Long-term downgrading values of insulation resistance • Insulation resistance values under by standards determined values

  5. Insulation testing methods • AC insulation testing (50/60Hz, 1 minute) • Insulation surge breakdown testing • Insulation testing with switching voltage • Insulation testing with DC voltage • Dielectric losses (tgδ) • Partial discharges • - U – I characteristics

  6. Insulation testing with DC test voltage- insulation characteristics

  7. Insulation parameters Polarisation Index (PI) PI = R tot (10 Min) / R tot (1Min) Dielectric absoption ratio (DAR) DAR = R tot (1 Min) / R tot (30 Sek) Dielectric discharge (DD) DD = I DIS (1 min) / (U * CISO ) I DIS ….a discharge current measured 1 minute after disconnecting the insulation system from the test voltage C ISO …. capacitance of the insulation system U …test voltage

  8. Limit values for insulation testing with DC voltage Insulation resistance Polarisationindex (PI) Thumb rule (motors and generators): Dielektric absorption ratio (DAR)

  9. Connection schemes • Precondition! • Measuring object has to be disconnected from power supply network (voltage – free) • Surface of the insulation system has to be dry and clean Power transformer HV vs LV HV vs G Multiple devices LV vs G

  10. Test data evaluation i.e. statistics keeping • Statistics • - Always assure the same measuring conditions • (connection, temperature, test voltage, diagnostics parameters) • Regular test intervals (6 months or one year) • Results keeping for the entire life period of the equipment • Observation of downgrading trends • Temperature coefficient • (all values are to be calculated on 75ºC)

  11. General requirements for HV insulation testers • Test functions: • Insulation resistance • Step voltage test • Capacitance • PI, DD, DAR • Current in µA and mA range • Voltage AC/DC • Other features: • Guard terminal to eliminate surface insulation currents • Automatic discharging of the test object after measurement • Built-in timer • On-Line graph R = f(t) • EM immunity for usage in HV environments • EM Filters for improved accuracy • Good charging system (accus or mains or both) • Accessories: • Shielded test leads • High quality test terminals (HV, antistatic, high surface resistance) • PC Software for downloading of test results and creating test reports

  12. Metrel HV insulation testers • Integrated features: • Test voltage up to 10kV DC • Resistance measuring range up to 10TΩ • Automated calculation of PI, DAR and DD for profound insulation diagnostics • On-Line R=f(t) display • Test voltage setting in 25V steps • Shielded 12kV test leads to reduce influence of external EM fields • CAT IV/600V over-voltage category for utilities and industrial applications • New TeraLink PRO Windows PC Software for TeraOhm 5kV Plus • Handbook “Modern insulation testing” on CD

  13. Metrel's solution providing, services and development • Product training in Metrel training centre • On-Line technical support • Application training and publications • Repair & Calibration training • Calibration equipment • Repair & Calibration services • Advanced technical solutions for all product‘s segments • (Hardware, Firmware, PC Software) • Customised solutions (Instruments, Software, Accessories)

  14. WHY NOT METREL?

  15. THANK YOU! You have already made a good decision

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