Evaluating Alternatives for
Under/Over Voltage Conditions
Nicholas Abraitis, EIT
GRP Engineering, Inc.
Petoskey, MI
Under and Over Voltage Conditions
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Voltage Regulation Causes of Over Voltage Causes of Under Voltage Correcting Voltage Conditions Milsoft Voltage Drop Analysis Routine Case #1 Case #2 Summary
Voltage Regulation -Methods to Regulate Voltage
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Step-type voltage regulators
Load tap changing transformers
Shunt capacitors
Auto transformers
Voltage Regulation – Standard Voltage Ratings
•  System Voltage –  RMS phasor portion of the electric system –  Bounded by transformers or utilization equipment •  Nominal System Voltage –  The voltage a portion of an electric system is
designated by –  Bounded by transformers or utilization equipment
Voltage Regulation – Standard Voltage Ratings
•  Maximum System Voltage –  Highest system voltage that occurs under normal
operation –  Highest voltage equipment is rated to operate at
continuously –  Does not cause derating or damage to equipment •  Service Voltage
–  Voltage at the Point of Common Connection (PCC)
Voltage Regulation – Standard Voltage Ratings
•  Utilization Voltage
–  Voltage at the line terminals of utilization
equipment •  Nominal Utilization Voltage
–  Voltage rating of certain utilization equipment
Voltage Regulation - Standards
•  Voltage Regulation – ANSI Ranges
•  Range A –  Voltage should stay in these limits and occurrences
outside of range should be infrequent. –  Maximum Utilization and Service Voltage = 126V –  Nominal Utilization Voltage = 115V –  Minimum Service Voltage = 114V –  Minimum Utilization Voltage = 110V
Voltage Regulation – ANSI Ranges
•  Range B –  Voltage above and below Range A –  Must take corrective measures to improve voltages
to meet Range A –  Maximum Utilization and Service Voltage = 127V
–  Nominal Utilization Voltage = 115V –  Minimum Service Voltage = 110V –  Minimum Utilization Voltage = 107V
Causes of Over Voltages
•  External Over Voltages –
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Direct lightning strike Electromagnetically induced “Side Stroke” Voltages induced from changes in atmosphere along line Electrostatically induced voltages from clouds, dust or dry snow •  Internal Over Voltages –
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Surges from switching
Floating neutrals on wye-delta banks Major loads coming off-line Capacitors Voltage set point too high
Causes of Under Voltage
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Large motors starting Line to Ground faults Excessive loads Losses across lines and through transformers Loss of generation Large transformers inrush Correcting Voltage Conditions
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Over voltages –  Ground neutral on wye-delta banks –  Voltage control on capacitor banks –  Install lightning arresters every ¼ mile on overhead and every ½ - 1 mile on
underground –  Voltage regulator settings •
Under voltages –
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Install capacitor banks Adjust voltage regulator settings (LDC, voltage set point & band width) Install line regulators Install booster transformer Conductor upgrade System configuration Voltage conversion
Voltage Drop Analysis
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Voltage Drop Solution Balanced of Unbalanced Voltage Drop Tolerance Base Output Voltage Clamp Constant KVA Load Voltage at Initiate Voltage at; Flat, Source Bus Voltage, Last
Case Calculate Charging on OH Line or UG Lines Include Generators or Motors Load; Source End, Uniform, Load End, Individually
Set Regulators; None, Infinite. Step, Locked Capacitors; Last Status, Initially Off, Initially On,
Permanently Off, Permanently On
Case #1
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Loca&on of step-­‐down transformers •
Low voltage issues on
west side of circuit End of circuit is 10
miles from substation Majority of circuit load is
in the center Low voltage conditions
develop downline of
7.2:2.4kV step-down
transformers Over voltage conditions
at beginning of circuit Voltage Profile Base
•  Voltages at the substation are at
125VAC
•  Voltage at end of line is 113VAC
Case #1 – Voltage Regulators
Loca&on of step-­‐down transformers Loca&on of voltage regulators •  Improved voltages on system
•  Low voltage conditions still
exist on 2400V portions of
circuit
Voltage Profile with Voltage Regulators
•  Improved voltages, but
voltages are still out of
range at the end of the
circuit
•  Drop in voltage begins at
the step-down
transformers
Case #1 With Voltage Regulators & Voltage Conversion
•  Corrected all low voltage
conditions on circuit
•  Step-down transformer
removed from model
Voltage Profile with Voltage Regulators & Voltage
Conversion
•  Voltage profile is smooth downline of the regulators
•  Voltage conversion corrected the
low voltage condition that existed
after voltage regulator installation
Case #2
Case #2
Sec&on of 34.5kV to be rebuilt Open Point •  34.5kV Section of
line to be taken out
of service and
rebuilt •  Substation at
northwest corner
of system is to be
fed from the south
Case #2
Sec&on of 34.5kV is out of service Closed Switch New Open Point •  Substation is
now fed from the
south •  Low voltage
conditions exist
on the
distribution
circuit.
Case #2 – Circuit Upgrades
Existing #266 ACSR
will be lowered and
used as distribution
while 34.5kV line is
being rebuilt
Case #2 – Circuit Upgrades
Exis&ng #1/0 will be upgraded to #336 New Circuit to be built to &e into exis&ng distribu&on Cut Open Circuit Exis&ng #336 Feeder •  New OH will be built
to tie into existing
circuit
•  Section of #1/0 will
be upgraded to
#336
•  Cut open circuit to
east of new OH
Case #2 – Results
Summary
•  Voltages need to stay in Range A.
•  Set Base Output Voltage to account for transformer and
secondary services losses.
•  Use Unbalanced Voltage Drop.
•  Improve low voltage conditions with capacitors, conductor
upgrades, auto transformers, or voltage regulators. •  Setting bus voltages too high can lead to over voltage
conditions when load drops off. •  Be creative in configuring circuits when correcting voltage
conditions, Milsoft makes changing conductors and
configurations simple.
Contact Information
Nicholas Abrai&s Electrical Engineer nabrai&s@grp-­‐engineering.com Petoskey Office GRP Engineering, Inc. 660 Cascade W. Pkwy Suite 65 459 Bay Street Grand Rapids, MI 49546 Petoskey, MI 49770 616.942.7183 231.439.9683 616.285.6448 Fax 231.439.9698 Fax