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SKM Power*Tools for Windows
Copyright 2001, SKM Systems Analysis, Inc
All Rights Reserved
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10/29/2001
Information in this document is subject to change without notice. No part of this document may be reproduced or
transmitted in any form or by any means, electronic or mechanical, without the express written consent of SKM
Systems Analysis, Inc. No patent liability is assumed with respect to the use of the information contained herein.
Although every precaution has been taken in the preparation of this manual, the publisher and author assume no
responsibility for errors or omissions. Neither is any liability assumed for damages resulting from the use of
information contained herein. For information, address SKM Systems Analysis, Inc., PO Box 3376, Manhattan
Beach, CA 90266-1376, USA.
1999 SKM Systems Analysis, Inc. All rights reserved.
Power*Tools, CAPTOR and DAPPER are registered trademarks and HI_WAVE and I*SIM are trademarks of
SKM Systems Analysis, Inc.
Microsoft is a registered trademark and Windows is a trademark of Microsoft Corporation.
Intel is a registered trademark and Pentium is a trademark of Intel Corporation.
ACAD and AutoCAD are registered trademarks of AUTODESK, Inc.
WordPerfect is a registered trademark of Novell, Inc.
Lotus and 1-2-3 are registered trademarks of Lotus Development Corporation.
Arial is a registered trademark of The Monotype Corporation, PLC.
PIXymbols is a trademark of Page Studio Graphics
ImageStream Graphics Filters is a registered trademark and ImageStream is a trademark of ImageMark Software
Labs, Inc.
PIXymbols Extended Character Set. Copyright 1995. Page Studio Graphics. All rights reserved.For information, address Page Studio Graphics, 3175 North Price Road, Suite 150, Chandler, AZ 85224.
Phone/Fax: (602) 839-2763.
ImageStream Graphics & Presentation Filters. Copyright 1991-1995. ImageMark Software Labs, Inc. All
rights reserved.
Various definitions reprinted from IEEE Std 100-1992, IEEE Standard Dictionary of Electrical and Electronics
Terms, copyright 1992 by the Institute of Electrical and Electronics Engineers, Inc. The IEEE takes no
responsibility or will assume no liability for the reader's misinterpretation of said information resulting from its
placement and context in this publication. Information is reproduced with the permission of the IEEE.
MathType math equation editing fonts are licensed from Design Science, Inc.
1987-1996 by Design Science, Inc. All rights reserved.
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SKM Power*Tools for Windows
1.1. Component Entry for Single-Phase and Unbalanced Studies............................1-2
1.1.1. Cables ...............................................................................................................1-2
1.1.2. Transformers.....................................................................................................1-3
1.1.3. Transmission Lines...........................................................................................1-5
1.1.4. Generators ........................................................................................................1-7
1.1.5. Loads................................................................................................................1-71.1.6. Motors ..............................................................................................................1-8
1.1.7. Panels................................................................................................................1-8
1.1.8. Capacitors / Filters............................................................................................1-9
1.2. Running the Unbalanced Studies .........................................................................1-9
1.3. Study Setup ..........................................................................................................1-10
1.3.1. Demand Load Analysis...................................................................................1-10
1.3.2. Sizing Study....................................................................................................1-11
1.3.3. Load Flow Study.............................................................................................1-12
1.3.4. Short Circuit Study.........................................................................................1-13
1.3.5. Schedule Report..............................................................................................1-15
1.4. Reports and Output Displays .............................................................................1-161.4.1. Datablocks......................................................................................................1-16
1.5. Examples of Unbalanced Studies........................................................................1-19
1.5.1. When to Use Unbalanced Calculations...........................................................1-19
1.5.2. Single-Phase System.......................................................................................1-20
1.5.3. Distribution System with Single-Phase Taps .......... ........... .......... ........... ........1-22
1.5.4. Fault Current with Open Line ........... ........... ........... .......... ........... ........... ........1-23
1.5.5. Negative Sequence Current from Unbalanced Capacitor Bank ........... .......... .1-25
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The Single-Phase and Unbalanced Study module examines the power system as individual
phases. Any combination of single-phase, two-phase and three phase components
including loads, cables, transformers panels and other components can be represented.
Load Analysis, Load Flow, Fault Analysis and Sizing calculations can be performed on
the combined single-phase and unbalanced three-phase system. The study results are
reported on each phase in the system. As with all PTW Study modules, the Single-phase
and unbalanced studies use the same PTW database, so theyre compatible with existing
Projects. Typical uses include city and rural distributions with single-phase taps; military
and institutional unbalanced operating conditions such as an open line feeding a capacitor
bank; commercial systems with single-phase transformers and panels;
IN
T
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IS
C
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A
P
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1.1. Component Entry for Single-Phase and Unbalanced Studies .......... .......... ....... 1-21.2. Running the Unbalanced Studies ...................................................................... 1-91.3. Study Setup ..................................................................................................... 1-101.4. Reports and Output Displays .......................................................................... 1-161.5. Examples of Unbalanced Studies.............. ........... .......... ........... ........... .......... . 1-19
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Unbalanced / Single-Phase Studies 1-2 Reference Manual
10/29/2001
The input data for single-phase and unbalanced studies is almost the same as for balancedthree-phase studies. The differences for each component are outlined in the following
section:
The Cable input includes a check box for each phase.
The cable impedance values can be entered as sequence or phase impedances for 3-phase
cables. The sequence values are automatically converted to phase impedance, and phaseimpedance values can also be entered directly. The phase impedance data can represent
mutual coupling which is typically ignored in balanced systems. The effect of mutuals
may be more pronounced in unbalanced systems. For single-phase cables, the values are
entered as phase and neutral impedances directly.
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Unbalanced / Single-Phase Studies 1-3
SKM Power*Tools for Windows
The Transformer input includes a selection for Three Phase, Single-Phase Mid-Tap, and
Single-Phase. When Single-Phase or Single-Phase Mid-Tap is selected, you can specify
the Primary Phase designation as A, B, C, AB, BC, or CA. The Secondary phase
designation is automatically adjusted based on the Primary Selection. The Primary and
Secondary Connections are also automatically adjusted based on the Primary Phase
designation. Pay close attention to the Voltage specification, as A, B, or C primary phasedesignation expects L-N voltage entry.
A single-phase mid tap transformer can be fed by two phase conductors or a phase and
neutral conductor. In both cases, two voltages are possible on the secondary side. For a
mid-tap configuration, the a-b voltage is twice the a-n voltage. The ab, designation on the
secondary is arbitrary and could be replaced with x and y.
AB
480 V A-B
abn
240 V a-b
120 V a-n, b-n
AN
277 V A-N
abn
240 V a-b
120 V a-n, b-n
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Unbalanced / Single-Phase Studies 1-4 Reference Manual
10/29/2001
The Transformer Impedance Sub-View includes a field for no-load losses. This field
represents the internal transformer losses at no-load.
The Transformer Automatic LTC (Load-Tap-Changing) sub-view allows representation of
an Automatic LTC for 3-winding transformers in the unbalanced load flow study. The tap
will automatically adjust with load changes or operating scenarios to keep the voltage
within the Max Voltage and Min Voltage tolerance specified. The tap will move within
the Tap Limit Max Tap and Min Tap specified in the given step size increment. The LTC
function is not included in the DAPPER balanced 3-phase load flow.
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Unbalanced / Single-Phase Studies 1-5
SKM Power*Tools for Windows
The Transmission line entry includes check boxes for ABC phase combinations. There is
also alternative entry formats in Z Matrix, or Y Matrix from each end that can be used to
include mutual coupling effects.
The transmission line data can be referenced from a library. The library automatically
calculates the transmission line parameters. For unbalanced calculations, the 3-Phase
Transmission Line Model is recommended to include mutual coupling effects. The 3-
Phase Transmission Line Model also includes line sag effects, bundling, multiple circuits,
and transposition. The Z phase and sequence data and the Xc Phase and Sequence data are
calculated from conductor diameter and spacing, GMR, resistance, bundle configuration,
resistivity, permeability, and sag. The data is entered on the Device Model tab and the
results are reported on the Z Phase, Xc Phase, Z Sequence and Xc Sequence tabs.
Input Data:
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Unbalanced / Single-Phase Studies 1-6 Reference Manual
10/29/2001
Earth Wires Segmented Check if there are segmented ground wires.
X, Y The coordinates of the conductor.
D, GMR, Resistance These are characteristics of the conductor. As an
example, 795000 CM 26/7 ACSR has the following
data:
Resistance (r) = 0.117 /mi at 25oCOutside
Diameter (D) = 1.108 in.Geometric Mean
Radius (GMR) = 0.0375 ft.
Bundle Numbers Number of parallel conductors to form the circuit.
The options are 1, 2, 3(Up), 3(Down), or 4.
Bundle Separation Separation between 2 parallel conductors.
Transpose Check if the conductor has a complete transposition
or rotation cycle. Each transposition section is one-
third of the total line length. The result circuit will bebalance.
Resistivity The resistivity of the conductors
Permeability The relative permeability of the conductors.
Sag The sag of the conductors.
Output Data:
Z Phase Impedance of conductor phase domain matrix (3x3)
Xc Phase Capacitance of conductor or line charging phase
domain matrix (3x3)
Z Sequence Impedance of conductor sequence domain matrix
(3x3)
Xc Sequence Capacitance of conductor or line charging sequence
domain matrix (3x3)
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Unbalanced / Single-Phase Studies 1-7
SKM Power*Tools for Windows
Although the generators are assumed to be balanced three-phase components, the
connection may affect the unbalanced study results. The generator can be connected
Delta, Wye, or Wye-Ground.
Loads can be single-phase, 2-phase, or 3-phase as defined by checking the appropriate
phase(s). The connection can also be specified as Delta, Wye, or Wye-Ground.
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Unbalanced / Single-Phase Studies 1-9
SKM Power*Tools for Windows
Capacitors and Filters can be specified as 1-phase, 2-phase or 3-phase and can be
connected Delta, Wye, or Wye-Ground, depending upon the phase specification.
The Unbalanced Studies are run from the Run>Unbalanced/Single Phase Studies menu or
by selecting the unbalanced study icon .
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Unbalanced / Single-Phase Studies 1-10 Reference Manual
10/29/2001
Each of the 5 unbalanced/single phase study modules has separate setup options.
The Demand Load analysis setup has options to include all loads, only loads that have a
demand library reference, or only loads that are checked as Energy Audit loads. The
Design load calculation can assign a separate design load factor to the largest motor and
optionally scale the remaining motor load. There is also an option to use motor rated size
to calculate the full load amps (FLA), or to reference FLA values from the MCC library.
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Unbalanced / Single-Phase Studies 1-11
SKM Power*Tools for Windows
The Sizing study setup includes the following options:
1) Maximum allowable voltage drop for sizing feeders.
2) Over-size percentage for feeders directly connected to a transformer.
3) Generate Size Report but dont write the new sizes back to the project database.
4) Generate Size Report and write the new sizes back to the project database.
5) Generator a Report of existing cable and transformer sizes but dont calculate
new sizes.
6) Generate report as a DXF file
7) Use extended characters to form a box around the report.
8) Assign default library categories for Cables and Transformers that dont already
have a category specified. The categories are specified based on voltage level.
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Unbalanced / Single-Phase Studies 1-12 Reference Manual
10/29/2001
The Load Flow Study setup includes the following options:
1) Max Iteration: This is the maximum number of iterations allowed in load flow
solution. The load flow will converge in the first few iterations for most systems.
2) Mismatch: This is the solution tolerance, whereby the solution will continue until
all phase flows in and out of each bus balance within the tolerance specified.
3) Bus Voltage Drop(%): Marks each bus in the report that exceeds the specified
voltage drop limit.
4) Branch Voltage Drop(%): Marks each branch in the report that exceeds the
specified voltage drop limit.
5) Utility Impedance: Includes the equivalent fault impedance for the Utility or SB
Generators in the load flow calculation when checked.
6) Transformer Phase Shift: Includes the transformer phase shift specifications in
the load flow calculation when checked.
7) LTC Transformer: Includes the automatic LTC Transformer setting selection inthe load flow calculation when checked.
8) Exact (Iterative): Represents all loads as defined in the load flow calculation.
9) Approximate: Represents all loads as Constant Impedance in the load flow
calculation. This solution can be used to help trouble-shoot systems that dont
converge with the Exact solution.
10) Connected Load: Uses rated size for all load specifications and does not include
any load factors assigned to the loads
11) 1stLevel Demand or Energy Audit Load: Includes load factor specified for each
load.
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Unbalanced / Single-Phase Studies 1-13
SKM Power*Tools for Windows
The Short Circuit Study setup includes the following options:
1) Fault All Buses: Reports fault current at each bus. Each bus is faulted separately.
2) Fault Selected Buses: Reports fault current for selected buses. You can choose
to fault each bus separately, or simulate a simultaneous fault at multiple buses.
3) 3 Phase: Specifies a 3-phase bolted fault simulation
4) SLG: Specifies a fault on a single phase, where A, B or C phase can be selected.
5) LL: Specifies a line to line fault, where AB, BC or CA phases can be selected.
6) LLG: Specifies 2 phase to ground fault, where AB, BC or CA phases can be
selected.
7) Induction Motor Contributions: Provides option to include or exclude induction
motors contributions from the calculation.
8) Pre Fault Voltage Load Flow: Uses the bus voltages from the most recent load
calculation as the pre-fault voltage.
9) Pre fault Voltage 1 Per Unit: Uses the nominal bus voltage for pre-fault voltage.10) Pre Fault Voltage No Load with Tap: Uses the driving voltage specified at the
Swing Bus and transfers the voltage through the system including off-nominal
transformer voltages and tap.
11) Asym Fault Current: Provides option to report RMS or Peak Asymmetrical
Currents. The Time field provides a user-defined time to report the
Asymmetrical current in addition to the standard 0.5, 2, 3, 5 and 8 cycle values.
12) Mid-Tap Trans Impedance Factor: The most severe short-circuit condition is a
line-to-neutral short circuit. Since the reactance and resistance of the transformer
are given on the basis of a full winding, it is necessary to convert to the proper
values when only one-half the secondary winding is involved as in a line-to-
neutral fault. The Impedance Factors are multiplied times the reactance and
resistance for this fault condition. Recommended impedance factors are 1.44 forresistance and 1.2 for reactance.
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Unbalanced / Single-Phase Studies 1-14 Reference Manual
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If the Fault Selected Buses option is selected, the faulted phase or phases can be
selected, and additional impedance from the fault point to ground, or between the faulted
phases can be added. Rg, Xg is the impedance between the fault point and ground. Rf and
Xf defines the impedance between each faulted phase to the fault point. The impedance is
displayed in Ohms, but can be converted from Per Unit using the p.u.=>Ohms calculator
button.
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Unbalanced / Single-Phase Studies 1-15
SKM Power*Tools for Windows
The Schedule Report Setup includes the following options:
1) Create DXF File: In addition to the text report, the schedules can be written to a
DXF file for transfer to CAD programs.
2) Report File: Specifies the name of the report generated when the Run button isselected.
3) Schedule Footer: Provides optional information at the bottom of the schedule.
The optional information includes the total load for the largest phase in the
schedule in kVA and Amps, the total load on the bus where the schedule is
attached, the date and time the schedule report was generated, the VA phase total,
and the current total for each phase.
4) Panel Format: Allows you to choose between 3 alternative panel schedule
formats. There is also an option to show the 2-pole and 3-pole loads as a total
load on the first pole, or to split the load evenly between the available poles.
5) MCC Format: Allows basic customization to the MCC layout, including the
selection and order of columns to print.
6) SWBD Format: Allows you to choose between 2 alternative switchboard
schedule formats.
The Output window automatically displays errors, warnings and study-related messages
when a study is run.
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Unbalanced / Single-Phase Studies 1-17
SKM Power*Tools for Windows
The datablock editor includes a selection for largest phase, phase summation, or specific
phases and an option to display Magnitude, Magnitude and angle, Magnitude and power
factor, or real + imaginary values.
A sample datablock report follows showing unbalanced cable phase currents and power
flows. The datablock reports can be printed directly or saved in Excel format.
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Unbalanced / Single-Phase Studies 1-19
SKM Power*Tools for Windows
The single-phase / unbalanced studies have a wide variety of uses including:
1) Single-phase distribution.studies
2) Three-phase distribution with single-phase taps.
3) Unbalanced loads or operating conditions.
4) Simultaneous faults.
5) Open line faults.
6) Setting negative sequence relays.
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Unbalanced / Single-Phase Studies 1-22 Reference Manual
10/29/2001
The following example shows an over-head distribution system with single-phase mid-tap
transformers. Phase currents and voltages are displayed in the datablocks.
BUS-0001
3PLF_VoltageA: 7617.5 / -0.0 V
B: 7617.1 / -120.0 V C: 7618.2 / 120.0 V
UTIL-0001
OH9-C
T7-C
C: 10.57 / 82.82 Amps
OH10-C
L7-C
B7-C
3PLF_VoltageA: 119.9 / -60.0 V
C: 111.7 / 119.7 V
T8-C
C: 10.58 / 82.82 Amps
OH11-C
L8-C
B8-C
3PLF_VoltageA: 119.9 / -60.0 V
C: 111.7 / 119.7 V
OH5-B
T4-B
B: 10.58 / -157.19 Amps
OH6-B
L4-B
B4-B
3PLF_VoltageB: 111.6 / -120.3 V
C: 119.9 / 60.0 V
T5-B
B: 10.58 / -157.20 Amps
OH7-B
L5-B
B5-B
3PLF_VoltageB: 111.6 / -120.3 V
C: 119.8 / 60.0 V
T6-B
B: 10.58 / -157.20 Amps
OH8-B
L6-B
B6-B
3PLF_VoltageB: 111.6 / -120.3 V
C: 119.8 / 60.0 V
OH1-A
T1-A
A: 10.58 / -37.20 Amps
OH2-A
L1-A
B1-A
3PLF_VoltageA: 111.6 / -0.3 V
B: 119.8 / 179.9 V
T2-A
A: 10.59 / -37.21 Amps
OH3-A
L2-A
B2-A
3PLF_VoltageA: 111.5 / -0.3 V
B: 119.8 / 179.9 V
T3-A
A: 10.59 / -37.21 Amps
OH4-A
L3-A
B3-A
3PLF_VoltageA: 111.5 / -0.3 V
B: 119.8 / 179.9 V
PD-0001 PD-0002 PD-0003
Fault currents are displayed at the main and each load bus.
BUS-0001
InitSym3PA: 43716.5 A
B: 43716.5 A C: 43723.9 A
UTIL-0001
OH9-C
T7-C
OH10-C
L7-C
B7-C
InitSym3PA: 9659.5 A
C: 9659.5 A
T8-C
OH11-C
L8-C
B8-C
InitSym3PA: 9642.7 A
C: 9642.7 A
OH5-B
T4-B
OH6-B
L4-B
B4-B
InitSym3PB: 9650.4 A
C: 9650.4 A
T5-B
OH7-B
L5-B
B5-B
InitSym3PB: 9610.7 A
C: 9610.7 A
T6-B
OH8-B
L6-B
B6-B
InitSym3PB: 9586.2 A
C: 9586.2 A
OH1-A
T1-A
OH2-A
L1-A
B1-A
InitSym3PA: 9602.7 A
B: 9602.7 A
T2-A
OH3-A
L2-A
B2-A
InitSym3PA: 9565.0 A
B: 9565.0 A
T3-A
OH4-A
L3-A
B3-A
InitSym3PA: 9554.2 A
B: 9554.2 A
PD-0001 PD-0002 PD-0003
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Unbalanced / Single-Phase Studies 1-23
SKM Power*Tools for Windows
The following example demonstrates how fault current can continue to flow even after a
fuse operates for a single-line-to-earth fault condition.
Ground Current Still
Flows Through Load
From Other Fuses
Blown Fuse
Results from PTW unbalanced fault analysis:
Phase to-ground fault on phase A.
Phase A Open
C-1Isc SLG
A: 0.0 / 0.0 A
B: 31.5 / -84.3 A C: 31.5 / -84.3 A
Fault LocationIsc SLG
A: 63.1 / -84.3 A B: 0.0 / 0.0 A
C: 0.0 / 0.0 A
C-2Isc SLG
A: 63.1 / 95.7 A
B: 31.5 / -84.3 A C: 31.5 / -84.3 A
Source
M-1
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Unbalanced / Single-Phase Studies 1-24 Reference Manual
10/29/2001
Same case reporting sequence current magnitude. Valuable information for selecting
negative sequence or zero sequence relay settings.
Phase to-ground fault on phase A.
Phase A Open
C-1Isc SLGPos 10.5 AIsc SLGNeg 10.5 A
Isc SLGZero 21.0 A
Fault Location
C-2Isc SLGPos 31.5 A
Isc SLGNeg 31.5 A
Source
M-1
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Unbalanced / Single-Phase Studies 1-25
SKM Power*Tools for Windows
The following example demonstrates negative sequence currents when one phase of a
three-phase capacitor bank is open.
Blown Fuse X
UTIL-0001
I_Pos 46.312 AI_Neg 2.758 A
CBL-0001
I_Pos 46.312 AI_Neg 2.758 A
XF2-0001 I_Pos 46.312 AI_Neg 2.758 A
BUS-0003
CBL-0002
I_Pos 163.905 A
CAP-A
I_Neg 0.000 A
Ph-A
MTRI-0001 CAP-B
I_Pos 9.148 AI_Neg 9.148 AI_Zero 9.148 A
Ph-B
I_Pos 9.148 AI_Neg 9.148 AI_Zero 9.148 A
CAP-C
I_Pos 9.147 AI_Neg 9.147 AI_Zero 9.147 A
Ph-C
I_Pos 9.147 AI_Neg 9.147 AI_Zero 9.147 A
A B C
Notice that negative sequence current flows in the 3-phase system when one phase of the
capacitor bank is lost.
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Index I*SIM i
SKM Power*Tools for Windows
C
Cables, 1-3
Capacitors, 1-10
Component Entry, 1-3
Crystal Report, 1-19
D
datablock report, 1-18
Datablocks, 1-17Demand Load Analysis, 1-11
Distribution with Single-Phase Taps, 1-24
DXF File, 1-16
F
Fault Current with Open Line, 1-25
G
Generators, 1-8
L
Load Flow Study, 1-13
Loads, 1-8
LTC Transformer, 1-13
M
Motors, 1-9
N
Negative Sequence Current from Unbalanced Capacitor Bank, 1-
27
P
Panels, 1-9
R
Reports, 1-17
Running the Unbalanced Studies, 1-10
S
Schedule Report, 1-16
Short-Circuit Study, 1-14
single-phase, 1-27
Single-Phase, 1-1, 1-2, 1-3, 1-4, 1-21, 1-24
Single-Phase System, 1-21
Sizing Study, 1-12
Study Setup, 1-11
TTransformer Automatic LTC, 1-5
Transformers, 1-4
Transmission Lines, 1-6
U
Unbalanced Examples, 1-20
Unbalanced Studies, 1-1, 1-2, 1-3, 1-10, 1-20
Unbalanced
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Device Evaluation ii Reference Manual
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