Page 3 - Basic PD Theory

Basic PD Theory

Table of Contents

INTRODUCTION .............................. 1 B. ON-LINE MONITORING .......... 58

1 STATOR WINDINGS ................ 3 C. VISUAL INSPECTIONS ........... 58
1.1 Stator Winding Design ....................... 3
1.2 Types of Insulation ............................. 5 D. FAILURE MECHANISMS ........ 59
1.3 Coil Manufacturing Process .............. 7
1.4 Installation Process ............................ 10 E. ZONE OF COVERAGE ............ 60
1.5 Operational Issues .............................. 11
1.6 Stator Failure Mechanisms ................ 13
F. PRIME NUMBERS ................... 62
2 BASIC PD THEORY ................. 14
2.1 PD as a Symptom ................................ 14 G. PD FLOWCHARTS .................. 64
2.2 Partial Discharge or Corona.............. 14
2.3 Void Formation .................................. 14 H. REFERENCES ......................... 67
2.4 Electrical Discharges .......................... 15
I. GLOSSARY ............................. 68
3 DETECTION OF PD ................. 21
3.1 PD Sensors .......................................... 21 J. INDEX ...................................... 73
3.2 Termination Box ................................. 23
3.3 Data Collection ................................... 23 K. OFF-LINE TESTS .................... 75
3.4 Noise and Disturbances ...................... 24 1. Capacitance Testing ........................... 75
2. Dissipation Factor ............................... 75
4 DATA TYPES ........................... 28 3. Power Factor (cos θ) ........................... 76
4.1 Pulse Height Analysis (PHA) ............. 28 4. Partial Discharge ................................ 77
4.2 PD Summary Variables ..................... 28 5. Surge Test ............................................ 77
4.3 Phase Resolved Plots .......................... 29 6. Direct High Voltage Testing .............. 77
7. Alternating Voltage Hipot ................. 78
5 ON-LINE PERIODIC TESTS..... 33 8. Wedge Tap Test .................................. 78
5.1 Periodic Testing .................................. 33 9. Ozone Monitoring ............................... 79
5.2 Continuous – Guards & Tracs .......... 34 10. Coil-to-ground Resistance .................. 79
5.3 Quality Flags or Flames ..................... 35 11. Side Clearance Check ......................... 79
5.4 Errors .................................................. 35 12. Insulation Resistance .......................... 79
13. Endwinding Vibration Response ....... 83
6 PD INVESTIGATIONS .............. 36 14. Winding Resistance ............................ 83
6.1 Trend Analysis .................................... 36
6.2 Database Comparison ........................ 39
6.3 Phase Comparison .............................. 41
6.4 Pulse Distribution ............................... 41

7 PD PATTERNS ......................... 42
7.1 Discharges in the Slot ......................... 42
7.2 Endwinding Discharges ..................... 48
7.3 Other Arcing and Sparking ............... 51
7.4 Summary - Failure Processes ............ 55

A. OFF-LINE TESTING ................. 56