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Power Quality

Power Quality. Mary Santori, P.E. Senior Engineer September 12, 2013. Topics discussed. Causes of Disturbances Normal utility operations that can cause problems with sensitive equipment How Xcel Energy works with customers on power quality issues Reliability Key Indices and Outage Causes

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Power Quality

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  1. Power Quality Mary Santori, P.E. Senior Engineer September 12, 2013

  2. Topics discussed • Causes of Disturbances • Normal utility operations that can cause problems with sensitive equipment • How Xcel Energy works with customers on power quality issues • Reliability Key Indices and Outage Causes • Preventive Maintenance

  3. Causes of disturbances • On-site interference • Caused by loads inside a facility affecting the power in such a way as to cause other loads to malfunction • Neighboring interference • Caused by loads outside a facility affecting the power in such a ways as to cause other loads to malfunction • Natural phenomena and accidents • Events such as lightning, storms, cars hitting power poles and dig-ins to underground cable • Utility operations and problems • Normal utility operations or malfunctioning utility equipment

  4. Normal utility operations that can cause problems with sensitive equipment • Protective devices operating under fault (i.e. breakers, fuses, reclosers) • Normal equipment operation (i.e. capacitor bank switching) • Single phase events (one phase of a three phase service is out) – Recommend phase protection • Xcel Energy RMS voltage guideline: + 5% secondary, + 10% primary and transmission

  5. Typical Electric Utility Distribution Layout

  6. Typical Electric Utility Capacitor Bank Switching Waveform at Customer

  7. Process for power quality issues • Gather background information from customer • Try and correlate disturbance to utility events • Set Recording Meters if Needed • Review Findings and Discuss Mitigations

  8. Step 1: Review Issue With Customer • What happened? • Dates and times (important to keep log) • Note anything else that happened in facility at the same time • Discuss customer’s electrical layout • If customer has monitoring, note location of meters (service entrance ideal)

  9. Step 2: Correlate Disturbance to Xcel Energy Electrical System • If 0 volt condition, review outage logs • If voltage sag condition, review outages on transmission system and neighboring taps and feeders • If voltage sag or surge condition, review distribution lines device operation (i.e. capacitor banks and voltage regulators)

  10. Step 3: Set Recording Meters if Needed • Monitor current and voltage at customer’s transformer or service entrance • Possibly monitor at neighboring customers

  11. Step 4: Review Findings and Discuss Mitigations • After reviewing monitoring data, may need to repeat Step 2 • Note current and voltage relationship • Utility mitigation may include investigating malfunctioning equipment (cap bank, voltage regulator, etc..) • Customer mitigation may include installing ride through equipment, soft start on motors, etc..

  12. Reliability Indices Reported to the MN PUC (many different formats) • SAIFI – System Average Interruption Frequency Index • Total Number of Sustained Customer Interruptions Total Number of Customers • CAIDI – Customer Average Interruption Duration Index • Total Customer Minutes of Sustained Outages Total Number of Sustained Customers Interruptions • SAIDI – System Average Interruption Duration Index • Total Customer Minutes of Sustained Outages Total Number of Customers • MAIFI – Momentary Average Interruption Frequency Index • Total Number of Customer Momentary Interruption Events Total Number of Customers

  13. Outages Causes (by customer minutes)

  14. Preventive Maintenance Efforts • Vegetation Management – Continual Condition Assessment/5-Year Maintenance Cycle • Infrared Testing – Semiannual Condition Assessment • Substation Transformers • Circuit Breakers • Surge Arrestors • Bushings • Regulators • Animal Control – Ongoing/Condition Based • Capacitor Banks – Annual Condition Assessment (Metro Areas) • Upgrading with Centralized Controls

  15. Customer Reliability Opportunities • Customer owned back-up generation • UPS • Auto or Manual Transfer • Phase Loss Protection • Transient Voltage Surge Suppression

  16. Power Quality Consultants(Note: Xcel Energy does not recommend any one consultant) • EPRI, Mark Stephens, 865-218-8022 • Hunt Electric, 651-646-2911 • OlympiaTech, 763-559-1900 • Parsons Electric, 763-571-8000 • ColliSys, 763-535-6000 • Hypertect, 651-631-0172

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