Power Quality
Mary Santori, P.E.
Senior Engineer
September 12, 2013
1
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
2
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
4
Typical Electric Utility Distribution Layout
From Transmission System
Breaker
Breaker
Breaker
Breaker
Fuse 1
Feeder A
Fuse 2
Feeder B
XX
Recloser
Customer X
Feeder C
Fuse 3
Fuse 4
Customer Y
Customer Z
Feeder D
5
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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Customer Minutes
18,000,000
16,000,000
Customer Minutes
Cumulative %
14,000,000
n = 80,714,261
12,000,000
10,000,000
60%
8,000,000
50%
40%
6,000,000
4,000,000
2,000,000
0
Cumulative %
Outages Causes (by customer minutes)
Minnesota
YTD December 2012, Internal Normalization Method
Includes Partial Restoration
100%
90%
80%
70%
30%
20%
10%
0%
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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
14
Customer Reliability Opportunities
 Customer owned back-up generation
 UPS
 Auto or Manual Transfer
 Phase Loss Protection
 Transient Voltage Surge Suppression
15
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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