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Diagnostic Insulation Testing

Diagnostic Insulation Testing. Predictive Maintenance issues Basis of Insulation Tests Spot Tests & Polarisation Index Dielectric Discharge Test Power factor testing AVO Range. Maintenance Regimes. Corrective maintenance Preventive (Periodic) Maintenance

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Diagnostic Insulation Testing

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  1. Diagnostic Insulation Testing • Predictive Maintenance issues • Basis of Insulation Tests • Spot Tests & Polarisation Index • Dielectric Discharge Test • Power factor testing • AVO Range

  2. Maintenance Regimes • Corrective maintenance • Preventive (Periodic) Maintenance • Predictive Maintenance(Record & trend data to determine next action - variable maintenance periods) • Appropriate regime varies

  3. Test Techniques - DC Testing • Total Current has 3 components • Capacitive Current - Charging • Absorbtion Current -Polarisation • Leakage Current • TIME DEPENDENT • Temperature Dependent

  4. Insulation Test Currents 100 I/uA Charging Total 10 Leakage Absorption 1 0,1 1 10 T

  5. Insulation Equivalent Circuit Leakage Capacitance Absorption

  6. Diagnosis from Insulation Tests • Record & Trend • Spot Tests- Record conditions as well (Temp, RH) • Time resistance tests - Polarisation Index Test (PI) • Step Voltage Test (SV) • Dielectric Discharge Tests (DD)

  7. Insulation Test as a Go/NoGo Test • Spot Test carried out for given time (1 minute) • Commissioning • National /Manufacturer’s Standards

  8. Time Resistance Tests • Independent of equipment size and temperature • Some information without past results • Options; • Curves • Time - Resistance Ratios

  9. Time ResistanceTest R Absorbtion current visible Absorbtion current not seen t1 t2 Time

  10. Time Resistance Tests Polarisation Index (10 min/1 min ratio) <1 1,0 - 2,0 2,0 - 4,0 >4,0 Insulation Condition unsatisfactory dubious good very good

  11. Time Resistance Tests Dielectric Absorption Ratio (60 s/30 s) <1 1.0 - 1.4 1.4 - 1.6 >1.6 Insulation Condition unsatisfactory dubious good very good

  12. Step Voltage Test • Test voltage is increased in 5 steps • Lower insulation resistance values at higher voltage indicate presence of cracks/holes

  13. Step Voltage Test 5000 V Resistance 2000 V 1000 V Voltage

  14. Dielectric Discharge Test • Test is run until currents stabilise • Measurements made on dischargeDD = Current after 1 min Voltage x Capacitance

  15. Dielectric Discharge Test + - - - - - - + - + + - + - + - + + - - + - + + - - + - + + + + + + - - + -

  16. Dielectric Discharge Test DD Value >4 2.0 - 4.0 <2.0 Insulation Condition unsatisfactory dubious good

  17. Tan Delta Testing • Polarisation and capacitive current dominate • Aging (moisture/dirt) sensitive • Low voltages can be used

  18. Perfect Insulation I (capacitive) ITOTAL IR = 0 V (applied)

  19. Facts about Insulation • In a “REAL insulation system” there is also a loss current flowing in-phase with the voltage // = IR ITOTAL IC

  20. REAL Insulation I (capacitive) IC ITOTAL IR V (applied)

  21. Facts about Insulation • In practice NO insulation is perfect • Resistive loss current is always present • Total current leads the voltage by a phase angle  and lags capacitive current by angle 

  22. REAL Insulation I (capacitive) IC ITOTAL d  IR V (applied)

  23. What is Tan Delta? Tan Delta is the ratio of in-phase (resistive) current to the 90-degree (capacitive) current Tan Delta equals Dissipation Factor

  24. What is Power Factor? • Power factor is the ratio in-phase (resistive) current to the total current.

  25. Tan Delta Testing I(capacitive) IR Tan d = IC IC ITOTAL IR Power Factor = d ITOTAL  IR V(applied)

  26. Tan Delta v. Power Factor • Both values are similar up to 20% power factor and tan delta; beyond 20% they diverge.

  27. Tan Delta 3 Terminal Test Low voltage (L) High voltage (H) CHL CLG CHG Ground Connection (G)

  28. Tan Delta 3 Terminal Test Configuration Measures GST L-GND CHL + CHG GST L-Guard CHG UST CHL GST H-Guard CLG GST H-GND CHL + CLG

  29. Why perform theTan Delta Test? Normal insulation resistance testing limited to 5kV dc Tan Delta is up to 12kV ac Most test specimens normally operate with AC voltage Much closer resemblance to the normal operating condition of the insulation

  30. Tan Delta Testing • Comparison with name -plate values • Very sensitive to small changes • a.c. test at rated voltage • Larger, heavier test equipment

  31. Insulation Test Diagnosis

  32. Tests Performed On Transformers Circuit Breakers Rotating Machinery Insulating Liquids High Voltage Bushings Surge Arrestors High Voltage Coils

  33. MEGGER BM11D • Portable, IP54 , large PbAcid battery • Readings to 500 GOhm • Display is large, clear & Easy to Use • Safety features • Automatic discharge, locking test leads, Hazard display • Integral Timer

  34. MEGGER BM21 All BM11D features plus; • Readings up to 5TOhm • Selectable Test Voltage • Selectable Test Time • Checks Capacitance at test End • Can show current as well as resistance • Burn mode

  35. MEGGER BM25 As BM21 features plus; • Automated tests • Polarisation Index • Step Voltage • Dielectric Discharge • RS232 download results every 5 s • Download software & lead

  36. MEGGER S1-5005 As BM25 with 5 mA test current. BM25 has 2 mA test current.

  37. MEGGER S1-5010 • Heavy Duty - Mains & Battery • Automated Tests • Results Storage • RS 232 communications • Graphical Display

  38. MEGGER S1-5010

  39. MEGGER S1-5010 • Memory for 75 sets of results • Windows PC software • remote operation • results storage • External output for HV “ON” indicator • Switchable digital filter for noise rejection • IP54 weatherproofing

  40. S1-5010 and S1-S1 software S1-5010

  41. S1-S1 software • Duplicates the S1-5010 on your PC screen. • Control the S1-5010 from your PC via an RS232 link. • Download tests to your PC • in real time. • as a batch at the end of testing. • Annotate the tests results with details of the test. • Recreate graphs etc. in other software.

  42. BIDDLE Delta 2000 • 500 V - 12 kV power factor tester • Automatic bridge operation • High noise immunity • Menu driven display • Measures voltage, current, power (loss), power factor/tan-delta and capacitance

  43. BIDDLE Delta 2000 • Results storage • Printer for on-site results • Downloading test data • Accessories • Oil test cell • Bushing connectors • Bar code wand

  44. BIDDLE Delta 2000

  45. BIDDLE 2.5 & 12 kV semi-automatic units • 2.5 kV single unit construction • 12 kV control unit and • Measure capacitance, dissipation factor and Watts

  46. CB-100 Low Voltage Bridge • 28 V test voltage • Safe • Compact • Low cost • Often used on bushings & transformers

  47. Testing with Safety • How does the electrical risk appears ? • - When an electrical line or conductor is unexpectedly still live - When current sources are not properly isolated- When power generators are connected to the network- When there are atmospheric phenomenons such as lightning- Through induced currents

  48. Testing with Safety • However, it has also been observed that the most common causes of unexpected presence of voltage on electrical lines or installations were due to:- A mistake in operating a switch- A mistake in identifying the work to perform- A "faulty" switch (one of the links for example remaining partially engaged)

  49. Testing with Safety • How does the electrical risk disappear ? • 1. By observing Simple Electrical Safety Rules directed by common Sense(even if Working Practices vary from a country to another, GOLDEN RULES always apply).2. By using Simple, Light and Reliable Electrical Safety Equipment.

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