A RISK MITIGATION TOOL

Transcription

1 HIGHLIGHTING THE BENEFITS OF CONTINUOUS PD MONITORING FOR GENERATORS: A RISK MITIGATION TOOL Dr Marco Tozzi, PhD Sr Product Manager Camlin Power Ltd

2 The Picture for Asset Manager How to quickly understand which machine is in a more critical condition? How to quickly understand at which operating condition the PD are higher?... Without being an expert in PD? 2

3 60 years of history of PD testing State of the Art PD measurements are periodically done: Off-line: External source used phase by phase No correlation with Operating Conditions No phase to phase stress Equal voltage profile along the coils On-line Real voltage profile and phase/phase stress Better correlation with operating condition Data sent to PD experts 3

4 Limits of periodical test Poor correlation with load, temperatures and other important operating conditions which influences PD Poor data repeatability preventing meaningful comparison and trending Start/Stop machine condition missed for the most of time Manpower cost, including time consuming procedure for attempting to perform the test at different load conditions Need for PD expert analysis (costly and avoidable) 4

5 Partial Discharge (PD)!?!? Why Me?

6 6 274 mv GOOD 275 mv BAD????????????? What is a PD expert? No clue of machine design No clue of machine history No clue of operating condition

7 Example #1 start/stop MVA, PD decrease with load -> discharges in voids within insulation PD pattern at machine-start PD pattern after 2 hours PD activity stronger at machine start PD disappear in less than 2 hours, when copper temperature increases Unknown information from periodic testing

8 Example #2 temperature MVA, PD increase with temperature -> discharges at semicon layers PD pattern at C PD pattern at C PD activity stronger at higher temperature PD more asymmetrical at higher temperature Slot PD increased by temperature effect

9 Partial Discharges rapidly change influenced by load, temperature and other operating parameters. Real time correlation with machine operating condition is the key to provide Users with intuitive graphical tools describing machine insulation status and suggesting actions. 9

10 A new scenario The penetration of Renewable Energy Resources causing a decrease of power generation and unexpected hourly changes in the schedule, moving from operating the turbines at base load to sudden and quick start/stop operation. Better operating flexibility request - > from base-load to peak-load plants Load cycling power plant: thermal, mechanical, and electrical stresses on the machinery Difficulty to vary the load to perform PD test at different Operating Conditions (OC) difficult to capture start/stop condition. Remote operated plant: no PD test Pumped-storage plants: difficult to control OC 10

11 IEC

12 Y axis: Copper Temperature 12 - TimeStamp - Power 120 MW - Temperature 55 C High Load High Temp Low Load Low Temp X axis: Active Power

13 Colors: PD Energy (PDE) High PD at cold machine Low PD at hot machine Distributed voids/cavities in ground wall insulation

14 PDE Map operating conditions area 14 SS HT MT LT Area Legend: SS: Start/Stop HT: High Temperature MT: Medium Temperature LT: Low Temperature

15 Head-head comparison (same stator design) 15 Generator #1 Generator #2 SS HT MT LT hour/year - Hot copper - Higher PDE at high temperatures - Cycling - Operates at max load keeping copper temperature below 75 C - Few PD only at machine start -> disappears with temperature increase

16 Slot PD degrading semicon in the slot SS HT MT 16 LT Laminated iron (stator core) SS HT Stator bar MT LT No significant PD activity

17 Generator A Generator B

18 18 Temperature effect at same Load +5 C effect hydrogen temperature raised from 90 F to 95 F this in turn raised the stator slot 33 temperature from 53 C to 58 C at the low load.

19 PDE based Ranking 19

20 A new scenario While maintenance and re-investment planning has been driven for decades by technical decisions from Operation and Maintenance managers, now, in the modern deregulated market, there is a need for different management methods taking into account the risk involved for postponing reinvestment and maximizing the profits. Maintenance is becoming a financial tool, increasing the profits and converting maintenance cost and engineering expenditures into cash flows. Due to the many challenges and budget issues, the best technical solution is not always possible, requiring, in general, decision support tools suggesting and driving remedial actions. Online monitoring for Generators can provide a clear picture allowing to compare different machines and better plan the maintenance 20

21 Examples- US Immediate personal gain for Asset manager: PD monitor deployment will limit generator outage times and increase their availability (which they get compensated for) On the large units, there are yearly outages, if we can save 2 days of that it equates to roughly $50k per unit per year from a direct company revenue perspective

22 Conclusion 24 hours monitoring + correlation with operating condition: Extract meaningful data that be converted into information without the need of an expert in PD theory to translate Allow immediate comparison between machines. Understand where maintenance can be deferred. Trend and compare PD activity recorded under same operating condition Enabling Asset Managers to easily identify critical assets and better manage capital expenditures Manage generator operating condition to reduce insulation degradation 22