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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.

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1987-1996 by Design Science, Inc. All rights reserved.


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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

H

IS

C

H

A

P

T

E

R

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

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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


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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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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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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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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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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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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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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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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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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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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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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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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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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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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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


C: 111.7 / 119.7 V

T8-C

C: 10.58 / 82.82 Amps

OH11-C

L8-C

B8-C


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


B: 119.8 / 179.9 V

T2-A

A: 10.59 / -37.21 Amps

OH3-A

L2-A

B2-A


B: 119.8 / 179.9 V

T3-A

A: 10.59 / -37.21 Amps

OH4-A

L3-A

B3-A


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


C: 9659.5 A

T8-C

OH11-C

L8-C

B8-C


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


C: 9610.7 A

T6-B

OH8-B

L6-B

B6-B


C: 9586.2 A

OH1-A

T1-A

OH2-A

L1-A

B1-A


B: 9602.7 A

T2-A

OH3-A

L2-A

B2-A


B: 9565.0 A

T3-A

OH4-A

L3-A

B3-A


B: 9554.2 A

PD-0001 PD-0002 PD-0003


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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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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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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


CAP-C


Ph-C


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


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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reference unbalanced

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