Generator Condition Assessment through EMI Diagnostics Doble Power Services

The leader in diagnostic test instruments and knowledge services for electric power for 90 yrs Doble Material Laboratories Cable & Switchgear Diagnostics Transformer Diagnostics Circuit Breaker Diagnostics Protection Diagnostics Rotating Machinery Diagnostics Doble Power Services (Testing & Consulting Services) Doble Client Services and Product Engineering Teams 2

Why Test Rotating Machines? 3 Early recognition of insulation degradation, predictive maintenance –Identify potential problems previously unknown –Monitoring a known problematic machine which customer is concerned condition may worsen Input for condition-based and reliability centred maintenance –Focus maintenance on equipment as needed when deterioration is indicated – Identify where maintenance is not needed – Not over maintain and waste resources Prevent in-service failures Optimize reinvestments in plant and equipment.

4 What is EMI? EMI (also called radio frequency interference or RFI) by a loose definition is an unwanted disturbance that affects an electrical circuit due to either electromagnetic conduction or electromagnetic radiation emitted from a defect within the electrical circuit or from an external source. EMI of interest is the signal generated from a defect within the component being tested. Every defect yields a signal at a different frequency and amplitude. Patterns at various frequencies caused by defects include corona, gap discharges, random noises and arcing. Typical known radio frequencies that can be also be seen include AM radio, FM radio, SW radio, TV and power line carriers and data transmitters (to name a few). These would NOT be considered EMI except in special cases.

EMI Diagnostics Electromagnetic interference testing: Precise frequency domain measurement and identification of RF energy that results from electrical activity at defects. It is a non-intrusive testing technique that is performed while the component is on line. Unlike PD, this testing does not require the permanent installation of any high-voltage connections to the generator. Data is collected from the temporary placement of a split core radio frequency current transformer while the machine remains in service terminals and does not introduce any signals into the system. 5

EMI Diagnostics Electromagnetic interference testing: No hot connections are required to any energized conductor and no interference with operation for data collection. No arc flash risk to collecting data. This one test location permits a global survey of the entire component and associated system that can detect a wide variety of electrical system components defects in: –Generators –Motors –Transformers –Phase bus –Switchgear and cables –Associated electrical system components. 6

7 Over 8,000 tests conducted since More than 500 different machine designs 25 hp - 1,400 MW. Fossil, hydro, geothermal, nuclear, industrial, petrochemical, oil rig platforms etc. EMI Diagnostics is applicable to all Power Systems 25, 50, 60 Hz. Best results 2,300 Volts ac and higher. Some success with 250 & 600 V dc power systems. EMI Diagnostics

Data collected from split core radio frequency current transformer. RFCT has a 12 cm window. The frequency range is to 100 MHz. 8

EMI Diagnostics STG placement for an RFCT is often around the neutral conduit.. 9

EMI Diagnostics A power conduit is best location to collect data from small generators. 10

EMI Diagnostics 11 Resulting radio frequency spectrum, or EMI Signature, is unique for each physical location & type of defect present within electrical system.

EMI Diagnostics 12 Data is displayed in a log-log format to better show large and small quantities. CASE STUDY 1

13 EMI Signature with slip ring arcing and minor end winding contamination. EMI Diagnostics CASE STUDY 2

14 EMI Signature with slip ring arcing and minor end winding contamination. EMI Diagnostics CASE STUDY 2

15 EMI Diagnostics CASE STUDY 3 Indications of shaft currents through a bearing.

16 EMI Diagnostics CASE STUDY 3 A hand held EMI “Sniffer” is used to further locate each location of the EMI, slip rings, bearing stator, or power cables.

Generator Conditions Detected through EMI Diagnostics Summary: – EMI Diagnostics is an expert based technology that has been an important part of a generator condition based maintenance programs since 1980 – EMI Diagnostics has the ability to detect and classify a variety of patterns generated by electrical and mechanical system defects – Scheduled condition based maintenance can then be focused on only the system components where deterioration is indicated – In-service failures can be greatly reduced – Success of repairs can be determined as soon as equipment is returned to service. 17