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Power QualityPower Quality

Mary Santori, P.E.

Senior Engineer

September 12, 2013

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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

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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

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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

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Typical Electric Utility Distribution Layout

Customer X

Customer Y

Customer Z

Breaker BreakerBreakerBreaker

Feeder A Feeder B

Feeder C

Feeder D

From Transmission System

Fuse 1

Fuse 3

Fuse 2

Recloser

Fuse 4

XX

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Typical Electric Utility Capacitor Bank Switching Waveform at Customer

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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

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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)

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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)

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Step 3: Set Recording Meters if Needed

Monitor current and voltage at customer’s transformer or service entrance

Possibly monitor at neighboring customers

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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..

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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

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Outages Causes (by customer minutes)

Minnesota YTD December 2012, Internal Normalization Method

Includes Partial Restoration

0

2,000,000

4,000,000

6,000,000

8,000,000

10,000,000

12,000,000

14,000,000

16,000,000

18,000,000

Cu

sto

mer

Min

ute

s

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

Cu

mu

lati

ve %

Customer Minutes

Cumulative %n = 80,714,261

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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

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Customer Reliability Opportunities

Customer owned back-up generation

UPS

Auto or Manual Transfer

Phase Loss Protection

Transient Voltage Surge Suppression

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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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