Dielectric

R.Acharya BHARAT HEAVY ELECTRICALS LIMITED, HYDERABAD

CONDITION MONITORING Condition monitoring involves *Off line diagnostic testing,on or off site,preferably nondestructive, on the machine or its component,such as -HVDC withstand tests, Tan delta,IR,PI,PD measurements on generator winding *On-line measurement of several parameters, related to operating stresses,ageing and controls which together help to diagnose the condition of the machine

PURPOSE • Improve reliability of power supply by reducing or eliminating forced outages • Prevent catastrophic failures that can result in costly & delayed remedial actions & affect the safety to personnel and the environment • Reduce costs with improved equipment utilisation • Optimise maintenance costs - move from periodic or preventive maintenance to a condition based one • Extend life of equipment with optimal loading • Residual life assessment to take investment decisions for replacement / refurbishment • Reliable failure analysis that helps to improve the design of the Equipment & the system

NEEDS • Condition monitoring is a joint effort between power equipment manufacturers, utilities, developers of monitoring equipment & research institutions • Need to integrate with the larger and longer term issues of Station and T & D automation • Develop standards for hardware, software and communications protocols and Integration of metering data collection, protection & controls

NEEDS • Optimise costs with ability to use a stepped or modular approach to on-line condition monitoring implementation • Continue to extract or develop information from available data within the substation. Final diagnostic is likely to use Data mining & Expert systems & knowledge base is a must • Standardise and expand on failure / diagnostics

DIELECTRIC MEDIUM

CROSS SECTION OF TG STATOR SLOT

HIGH VOLTAGE INSULATION OF STATOR BARS

GENERATOR STATOR A) HIGH VOLTAGE TEST & MEASUREMENT OF LEAKAGE CURRENT B) I.R.& P.I. MEASUREMENT C) CAPACITANCE & TAN δ MEASUREMENT D) DIELECTRIC LOSS ANALYSIS E) PARTIAL DISCHARGE MEASUREMENT F) CORE LOSS/ELCID TEST G) RECORDING OF WEDGE DEFLECTION

PARTIAL DISCHARGE - SMALL ELECTRICAL SPARKS OCCURING WITHIN THE INSULATION A) ULTRASOUND TECHNIQUE B) MEASUREMENT OF DISCHARGE IN pC C) MEASUREMENT IN MILIVOLTS. D) INITIAL VALUE AT MFG STAGE ,2000 PC DESIRABLE. E0 OPERATIONAL LIMITS BELOW 10,000 Pc.

Winding vibration measurement a) Mechanical, Thermal and Electrical stress b) bad wedging c) Gravitational Force d) Fatigue of End Winding e) Moisture contamination.

Winding vibration measurement Effect: a) Cracking of Insulation b) Broken bandage and Ripple spring c) Delamination d) Reduced Electrical and Mechanical Strength e) Puncture of Insulation Limitaions: , 200 microns

ELCID TEST Electromagnetic Core Imperfection Detector a) Use of Reduced Voltage b) Detection of Eddy Current to detect core short c) Less risky than RING FLUX TEST. Limitaions: , 100 miliamps

Loss Tangent Measurement. Tan Delta is a measure of active discharges in the insulator a) Tand delta = Cos PHI b) Traditional method c) Trend rather than the absolute value is important. Limitaions: , 2% at 20% of En.

GENERATOR ROTOR A) WINDING RESISTANCE AND AC IMPEDANCE MEASUREMENT B) I.R. MEASUREMENT C) ROTOR MAGNETIZATION CHECK D) RSO ( Recurrent Surge Oscillograph)Test. E) Grounding Brush monitoring. F) IR of Brg. And monitoring of circulating current.

GUIDE LINES FOR VOLTAGES TO BE APPLIED DURING INSULATION RESISTANCE TEST WINDING RATED IR TEST VOLTAGE ( V ) VOLTAGE (V) < 1000 V

500 V

1000 - 2500 V

500 - 1000 V

2501 - 5000 V

1000 - 2500 V

5001 - 12000 V

2500 - 5000 V

> 12000 V

5000 - 10000 V

RECOMMENDED MINIMUM INSULATION RESISTANCE VALUES IN M? AT 40 ºC IRI (MIN.) = FOR MOST WINDINGS MADE Kv + 1 BEFORE ABOUT 1970 IRI (MIN.) = FOR MOST DC ARMATURE AND 100 AC STATOR WINDINGS BUILT AFTER ABOUT 1970 IRI (MIN.) = 5

FOR MOST MACHINES WITH WOUND COILS AND FORM WOUND COILS RATED BELOW 1 kV

VOLTAGE RANGE UPTO 3.3KV IR (1 MINUTE) IN M? S PI

ABOVE 3.3 KV TO 6.6KV

ABOVE 6.6 KV TO 11KV

ABOVE 11KV

10 TO 15000

10 - 10000

15 - 20000

100 2000

1.3 TO 7.0

1.3 TO 5.5

1.5 TO 7.0

2.0 TO 6.0