3 phase short circuit

Version 6.50.00 October 2008

Short Circuit Analysis Program

ANSI/IEC/IEEE &

Protective Device Evaluation

Users Guide

EDSA MICRO CORPORATION 16870 West Bernardo Drive, Suite 330.

San Diego, CA 92127 U.S.A.

Copyright 2008

All Rights Reserved

Short Circuit Analysis Program ANSI/IEC/IEEE

i

Table of Contents

1 Unique Features of Paladin DesignBase Short circuit Program ................................................................1

1.1 Whats new in this release.....................................................................................................................1

2 Introduction.................................................................................................................................................4

2.1 Type of Faults........................................................................................................................................4 2.2 Terminology...........................................................................................................................................5 2.3 Sources in Fault Analysis ......................................................................................................................7 2.4 ANSI/IEEE Multiplying Factors (MF) .....................................................................................................9 2.5 Local and Remote Contributions .........................................................................................................10

3 ANSI/IEEE Standard Based Device Evaluation .......................................................................................11

3.1 Standard Ratings for HV and MV Circuit Breakers (CB).....................................................................11 3.2 Standard Ratings for Low Voltage Circuit Breakers (LV-CBs) ............................................................15 3.3 Standard Ratings for Low/High Voltage Fuses, and Switches............................................................18

4 DesignBase Short Circuit Calculation Method .........................................................................................21

4.1 Calculation Methods and the Corresponding Tools ............................................................................21 4.2 AC ANSI/IEEE Standard Paladin DesignBase Short Circuit Tools: .................................................22 4.3 AC Classical Short Circuit Method ......................................................................................................37 4.4 AC IEC 60909 Short Circuit Method....................................................................................................39 4.5 AC IEC 61363 Short Circuit Method....................................................................................................47 4.6 AC SINGLE Phase Short Circuit Method ............................................................................................59

5 Managing the Paladin DesignBase Short Circuit Program ......................................................................59

5.1 3P, LL, LG, LLG Fault, Cycle ..........................................................................................................59 5.2 3P, LL, LG, LLG Fault, 5 Cycle............................................................................................................62 5.3 3P, LL, LG, LLG Fault, Steady state ...................................................................................................64 5.4 3 Phase Fault, Steady State................................................................................................................66 5.5 Protective Device Evaluation (PDE) Tool............................................................................................68 5.6 Report Manager...................................................................................................................................74 5.7 Short Circuit Back Annotation..............................................................................................................79 5.8 Managing Schedule in Short Circuit ....................................................................................................82

6 Three-phase Faults IEC 61363 Method ...................................................................................................97

7 Short Circuit Analysis Input Data............................................................................................................101

7.1 Power Grid Input Data .......................................................................................................................101 7.2 Synchronous Generator Short Circuit Input Data..............................................................................102 7.3 Induction Motor Short Circuit Input Data ...........................................................................................103 7.4 Synchronous Motor Short Circuit Input Data.....................................................................................104 7.5 High Voltage ANSI/IEEE Circuit Breaker Short Circuit Input Data....................................................105 7.6 Low Voltage ANSI/IEEE Circuit Breaker Short Circuit Input Data.....................................................106 7.7 Low Voltage ANSI/IEEE Fuse Short Circuit Input Data ....................................................................107

8 Network Reduction/Equivalent ...............................................................................................................108

8.1 Introduction........................................................................................................................................108 8.2 Sample System Data.........................................................................................................................108 8.3 How to Perform Equivalent/Reduction Calculations..........................................................................109 8.4 Separating the Equivalent Part from the Rest of the System............................................................110 8.5 Specifying the Buses for the Equivalent............................................................................................111 8.6 Reporting of the Equivalent System ..................................................................................................112


ii

8.7 Computation of Equivalent System and Inspection of the Result .....................................................115 8.8 Reconstructing the Original System by Using the Equivalent ...........................................................117 8.9 Validation and Verification of the Equivalent .....................................................................................124

9 TUTORIAL: Conducting a Three-phase Short Circuit Study..................................................................127

9.1 The Calculation Tools........................................................................................................................128 9.2 Graphical Selection of Faulted Bus (Annotation) ..............................................................................130 9.3 Short Circuit Annotation Tool.............................................................................................................132

List of Figures

Figure 1: ANSI Device Evaluation, Page 1.....................................................................................................19 Figure 2: ANSI Device Evaluation, Page 2.....................................................................................................20 Figure 3: Single Line Diagram of Sample System for Equivalent Computation...........................................108 Figure 4: Part of the System to be Equivalenced (the area inside of red dotted line)..................................109 Figure 5: Selecting Options of the Short Circuit Program ............................................................................110 Figure 6: Selecting Buses where the Equivalent System to be Computed..................................................111 Figure 7: Selecting Report Manager of the Short Circuit Program ..............................................................112 Figure 8: Selecting Output Report (including report of network equivalent) ................................................113 Figure 9: Selecting Network Equivalent Report Option................................................................................114 Figure 10: Performing Short Circuit Analysis (fault current, equivalent, etc.) ................................................115 Figure 11: Sample Network Equivalent Report ..............................................................................................116 Figure 12: Reconstructing System Using the Equivalent Part .......................................................................117 Figure 13: Entering Equivalent Generator At bus BBB138 ............................................................................118 Figure 14: Entering Equivalent Generator At bus GGG138...........................................................................119 Figure 15: Entering Equivalent Generator At bus ZZZ69...............................................................................120 Figure 16: Entering Equivalent Feeder Between Buses BBB138 and GGG138............................................121 Figure 17: Entering Equivalent Transformer Between Buses GGG138 and ZZZ69......................................122 Figure 18: Entering Equivalent Transformer Between Buses BBB138 and ZZZ69 .......................................123 Figure 19: Fault Current for Buses BBB138, GGG138, and ZZZ69 ..............................................................125 Figure 20: Fault Currents for Buses BBB138, GGG138, and ZZZ69.............................................................126

List of Tables

Table 1: Recommended ANSI Source Impedance Multipliers for 1st Cycle and Interrupting Times .................................................................................................8 Table 2: Default Device X/R Values Using EDSAs Library...............................................15 Note: You can view this manual on your CD as an Adobe Acrobat PDF file. The file name is:

Short Circuit Analysis Program 3_Phase_Short_Circuit.pdf You will find the Test/Job files used in this tutorial in the following location:

C:\DesignBase\Samples\3PhaseSC


iii

Test Files: ANSIYY1, Busfault, EDM5, IEC1-60909, IEC2-60909, IEEE399, IEEEpde, MutualNet, SlidingFault, T123, T123PDE, testma1, Trib, TribNVTAP, UPSexpse, West

Copyright 2008

All Rights Reserved


1

1 Unique Features of Paladin DesignBase Short circuit Program

The salient features of the Paladin DesignBase advanced short circuit program:

9 Fault analysis of complex power systems having over 50,000 buses 9 Exact short circuit current and contributions computation using Three-Sequence Modeling 9 Simulate sliding and open conductor faults 9 High speed simulation by utilizing the state-of-the-art techniques in matrix operations (sparse

matrix and vector methods)

9 Automated reactor sizing for 3 Phase networks 9 Exporting and importing data from and to Excel 9 Import system data from Siemens/PTI format into Paladin DesignBase 9 Customize reports 9 Support of ANSI and IEC standards for PDC (protective device coordination) 9 Fully integrated with ARC flash program 9 Fully integrated with PDC

1.1 Whats new in this release

9 The network Equivalent computation is now supported in this release of the short circuit program. The method of equivalent calculation is an exact method based on the bus impedance matrix. An equivalent system at several buses (up to 100 buses) may be calculated using the EDSAs short circuit program. The report contains the sequence impedances (positive, negative and zero sequence) for the equivalent generators, lines/feeders, transformers as well as loads.

9 Data Export/Import from/to Excel has been implemented that greatly facilitates data inspection, validation, and exchange.

9 Power system data (jobfile) can be Imported from Siemens/PTI into EDSAs advanced DesignBase2

9 In this release of the program, the EDSA short circuit program supports two options for the generators and motors resistances. The first option uses constant X/R ratio (that is defined in the generator and motor input dialogs). In the second option, i.e, variable X/R (see the lower left part of the figure below), the generator/motor resistance is computed from the X/R ratio as follows:


2

RXXR/

"

= The above resistance is maintained constant for all time bands and sequences (negative, zero, positive). In this case the X/R ratio will be variable for different time bands and sequences.

9 Also, in this release, the EDSA short circuit program supports the options for reactor sizing; one based on bus current and the second option based on branch current. In both options the voltage and existing fault are displayed and user can enter the desired fault value and then the reactor is automatically sized. However, it is recommended to implement the reactor in the system at the desired location and run the short circuit again to verify the impact of the reactor on the short circuit.


3

Where: 1 Bus ID or branch ID 2 Bus L-L voltage, in V 3 3 Phase solid bus AC fault current 4 3 Phase solid bus AC desired fault current 5 Reactor sized automatically.

1

2

3

4

5


4

2 INTRODUCTION The short circuit is an accidental electrical contact between two or more conductors. The protective devices such as circuit breakers and fuses are applied to isolate faults and to minimize damage and disruption to the plants operation.

2.1 Type of Faults

Types of Faults depend on the power system grounding method. The most common faults are:

Three-Phase Fault, with or without ground (3P, or 3P-G); Single line to ground Fault (L-G); Line to Line Fault (L-L); Line to line to ground Fault (L-L-G).

Estimated frequency of occurrence of different kinds of fault in power system is:

3P or 3P-G: 8 % L-L: 12 %; L-L-G: 10 %; L-G: 70 %.

Severity of fault: Normally the three-phase symmetrical short circuit (3P) can be regarded as the most severe condition. There are cases that can lead to single phase fault currents exceeding the three-phase fault currents, however the total energy is less than a three-phase fault. Such cases include faults that are close to the following types of equipment:

The wy side of a solidly grounded delta-wy transformer / auto-transformer; The wy-wy solidly grounded side of a three winding transformer with a delta tertiary

winding; A synchronous generator solidly connected to ground; The wy side of several wy grounded transformer running in parallel.


5

Type of Short Circuits:

a):3P three-phase; b):L-L, line-to-line; c):L-L-G, line-to-line-to-ground; and d): L-G, line-to-ground

2.2 Terminology

Arcing Time - the interval of time between the instant of the first initiation of the arc in the protective device and the instant of final arc extinction in all phases; Available Short Circuit Current - the maximum short circuit current that the power system could deliver at a given circuit point assuming negligible short circuit fault impedance; Breaking Current - the current in a pole of a switching device at the instant of arc initiation (pole separation). It is also known as Interrupting Current in ANSI Standards. Close and Latch Duty - the maximum rms value of calculated short circuit current for medium and high-voltage circuit breakers, during the first cycle, with any applicable multipliers with regard to fault current X/R ratio. Often, the close and latching duty calculation is simplified by applying a 1.6 factor to the first cycle symmetrical AC r.m.s. short circuit current. Close and latch duty is also called first cycle duty, formerly called momentary duty. Close and Latch Capability - the maximum asymmetrical current capability of a medium or high-voltage circuit breaker to close, and immediately thereafter latch closed, for normal frequency making current. The close and latch asymmetrical rms current capability is 1.6 times the circuit breaker rated maximum symmetrical AC rms interrupting current. Often called first cycle capability. The rms asymmetrical rating was formerly called momentary rating; Contact Parting Time - the interval between the beginning of a specified over current and the instant when the primary arcing contacts have just begun to part in all poles. It is the sum of the relay or release delay and opening time; Crest Current / Peak Current the highest instantaneous current during a period; Fault an abnormal connection , including the arc, of relative low impedance, whether made accidentally or intentionally, between two points of different voltage potentials;


6

Fault Point X/R the calculated fault point reactance to resistance ratio (X/R) ratio. Depending on the Standard, different calculation procedures are used to determine this ratio; First Cycle Duty the maximum value of calculated peak or rms asymmetrical current or symmetrical short circuit current for the first cycle with any applicable multipliers for fault current X/R ratio; First Cycle Rating the maximum specified rms asymmetrical or symmetrical peak current capability of a piece of equipment during the first cycle of a fault; Interrupting Current the current in a pole of a switching device at the instant of arc initiation. Sometime referred to as Breaking Current, bI , IEC60909; Making Current the current in a pole of a switching device at the instant the device closes and latches into a fault; Momentary Current Rating the maximum available first cycle rms asymmetrical current which the device or assembly is required to withstand. It was used on medium and high-voltage circuit breakers manufactured before 1965; present terminology: Close and Latch Capability; Offset Current - an AC current waveform whose baseline is offset from the AC symmetrical current zero axis; Peak Current the maximum possible instantaneous value of a short circuit current during a period; Short circuit current is the current that flows at the short - circuit location during the short circuit period time; Symmetrical short circuit current is the power frequency component of the short circuit current; Branch short circuit currents are the parts of the short circuit current in the various branches of the power network; Initial short circuit current IK" is the rms value of the symmetrical short circuit current at the instant of occurrence of the short circuit, IEC 60909; Maximum asymmetrical short circuit current Is is the highest instantaneous rms value of the short circuit current following the occurrence of the short circuit; Symmetrical breaking current Ia , on the opening of a mechanical switching device under short circuit conditions, is the r.m.s. value of the symmetrical short circuit current flowing through the switching device at the instant of the first contact separation; Rated voltage VR the phase-to-phase voltage, according to which the power system is designated; IEC UR the rated voltage is the maximum phase-to-phase voltage; Nominal Voltage Un (IEC) the nominal operating voltage of the bus. Initial symmetrical short - circuit power S "K is the product of 3 *I "*UK N System breaking power SB is the product of 3 *I * Ua N


7

Minimum time delay t min is the shortest possible time interval between the occurrence of the short circuit and the first contact separation of one pole of the switching device; Dynamic stress is the effect of electromechanical forces during the short circuit conditions; Thermal stress is the effect of electrical heating during the short circuit conditions; Direct earthling / effective earthling is the direct earthling of the neutral points of the power transformers; Short circuit earth current is the short circuit current, or part of it, that flows back to the system through the earth; Equivalent generator is a generator that can be considered as equivalent to a number of generators feeding into a given system. DesignBase Short Circuit Analysis Program is based on ANSI/IEEE and IEC Standards and fully complies with the latest ANSI/IEEE/IEC Standards: ANSI/IEEE Std. 141 1993, IEEE Recommended Practice for Electric Power Distribution of

Industrial Plants (IEEE Red Book); ANSI/IEEE Std. 399 1997, IEEE Recommended Practice for Power Systems Analysis (IEEE

Brown Book); ANSI/IEEE Standard C37.010 1979, IEEE Application Guide for AC High-Voltage Circuit

Breakers Rated on a Symmetrical Current Basis; ANSI/IEEE Standard C37.5-1979, IEEE Application Guide for AC High-Voltage Circuit Breakers

Rated on a Total Current Basis; ANSI/IEEE Standard C37.13-1990, IEEE Standard for Low-Voltage AC Power Circuit Breakers

Used in Enclosures; IEC-909 1988, International Electro technical Commission, Short Circuit Current Calculation in

Three-Phase Ac Systems; UL 489_9 1996, Standard for Safety for Molded-Case Circuit Breaker, Molded-Case Switches,

and Circuit-Breaker Enclosures A Practical Guide to Short-Circuit Calculations, by Conrad St. Pierre

2.3 Sources in Fault Analysis Power utilities, all rotating electric machinery and regenerative drives are sources in fault calculation. Cycle Network Duty The decay of short circuit current is due to the decay of stored magnetic energy in the equipment. The main impedances for the first cylce is the sub-transient impedance. It is generally used for the first cycles up to a few cycles;

The cycle network is also referred to as the sub transient network, because all rotating machines are represented by their sub transient reactance. cycle short circuit currents are used to evaluate the interrupting duties for low-voltage power breakers, low voltage molded-case breakers, high and low voltage fuses and withstand currents for switches and high-voltage breakers.


8

The following table shows the type of device and its associated duties using the cycle network. Type of Device Duty High voltage circuit breaker Closing and latching capability Low voltage circuit breaker Interrupting capability Fuse Bus bracing Switchgear and MCC Instantaneous settings Relay

Table 1: Recommended ANSI Source Impedance Multipliers for 1st Cycle and Interrupting Times

Source Type 1/2-Cycle Calculations

Interrupting Time

calculations (1.5 to 4 cycles cpt)

Reference

Remote Utility (equivalent) "sZ sZ ANSI C37.010

Local Generator "dvZ "dvZ ANSI C37.010

Synchronous Motor "dvZ 1.5*"dvZ ANSI C37.010

Large Induction Motors: > 1000 HP or 250 HP and 2 poles

"Z

1.5* "Z

ANSI C37.010

Medium Induction Motors 50 to 249 HP or 250 to 1000 HP


9

Steady State or 30-Cycle Network

This network is used to calculate the steady state short circuit current and duties for some of the protective devices 30 cycles after the fault occurs (delayed protective devices). The type of power system component and its representation in the 30-cycle network is shown in the following table. Note that the induction machines, synchronous motors, and condensers are not considered in the 30-cycle fault calculation. Source Type 30 Cycle Calculation Impedance Power Utility /Grid "

sZ Generators '

dvZ Induction Motors Infinite impedance Synchronous Motors Xd

2.4 ANSI/IEEE Multiplying Factors (MF)

The short circuit waveform for a balanced three-phase fault at the terminal bus of a machine is generally asymmetrical and is composed of a unidirectional DC component and a symmetrical AC component. The DC component decays to zero, and the amplitude of the symmetrical AC component decays to constant amplitude in the steady-state If the envelops of the positive and negative peaks of the current waveform are symmetrical around zero axis, they are called Symmetrical. If the envelops of the positive and negative peaks current are not symmetrical around the zero axis, they are called Asymmetrical. If the DC fault component is not considered in the fault current, the fault current has the AC component only, and it is symmetrical; if DC fault component is considered, then the fault current is asymmetrical and is called asymmetrical or total fault current. The multiplying factors MF converts the r.m.s. value of the symmetrical AC component into asymmetrical r.m.s. current or short circuit current duty. The MF is calculated based on the X/R ratio and the instant of time that the fault current happens. The X/R ratio for ANSI breaker duties is calculated from separate R and X networks.

First Cycle (Asymmetrical) Total Short Circuit Current MF (Circuit Duty): Is defined as:

RX

m eMF

221

+=

For: X/R = 25, the MF is equal to 1.6. Note: In the short circuit option tab Control for ANSI/IEEE the user has the option to calculate MFm based on X/R or use MFm=1.6


10

Peak Multiplying Factor Is defined as:

)1(2 /2

RXPeak eMF

+=

where is the instant of time when fault occurs, X/R for ANSI breaker duties are calculated from separate R and X network.

For: = Cycle, and X/R = 25 to one decimal place is 7.2=PeakMF . Note: In the short circuit option tab Control for ANSI/IEEE the user has the option to calculate MFpeak based on X/R or use MFpeak= 2.7

2.5 Local and Remote Contributions

The magnitude of the symmetrical current (AC component) from remote sources remain essentially constant No AC Decay (NACD) at its initial value or it may reduce with time toward a residual AC current magnitude (ACD). If the fault is close to generator, then the AC component decays (ACD). In other words, when generator is local or close to the faulted point the short circuit current decays faster. If the generator is remote from the faulted point, the ac short circuit current decay will be slow and a conservative simplification is to assume that there is no AC decay (NACD) in the symmetrical AC component. Per ANSI Standards: A generator is a LOCAL SOURCE of the short circuit current if:

The per unit reactance external to the generator is less than 1.5 times the generator per-unit sub transient reactance on a common system base MVA.

Its contribution to the total symmetrical rms Amperes will be greater than "*4.0d

G

XE

,

where the "d

G

XE

is the generator short circuit current for a three-phase fault at its terminal

bus. A generator is a REMOTE SOURCE of a short circuit current if:

The per unit reactance external to the generator is equal to or exceeds 1.5 times the

generator per unit sub transient reactance on a common system base MVA.


11

The generator short circuit contribution may be written as:

)( "dExternalG

GXX

EI +=

Its location from the fault is two or more transformations or Its contribution to the total symmetrical rms Amperes is less than or equal to "*4.0

d

G

XE

,

where the "d

G

XE

is the generator short circuit current for a three-phase fault at its terminal bus.

The ANSI Standards provide multiplying factors (MF) based X/R ratio for three-phase faults and line-to-ground faults fed predominantly from generators and MF for faults fed predominantly from remote sources. No AC decay (NACD) Ratio The Total Short circuit Current is equal to:

moteLocalTotal III Re+= and:

Total

mote

IINACD Re=

When all contributions are remote, or when there is no generator, then 1=NACD When all contributions are local, then 0=NACD

3 ANSI/IEEE Standard Based Device Evaluation

3.1 Standard Ratings for HV and MV Circuit Breakers (CB)

The ANSI/IEEE Standards define the CB total interrupting time in cycles. However, the Contact Parting Time (CPT) needs to be known for application of breakers. The typical total rated interrupting time for Medium-Voltage Circuit Breakers is 5 cycles (ANSI C37.06 1987). However, the MV CBs interrupting time correspond to 3 cycle contact parting time for the short circuit current, in the 2 -8 cycle network.

Circuit Breaker Rated Interrupting Time, in Cycles

CPT, in Cycles S

2 1.5 1.4 3 2 1.2 5 3 1.1 8 4 1.0


12

S is the breakers asymmetrical capability factor and is determined based on the rating structure to which the breaker was manufactured. Most breakers manufactured after 1964 are breakers rated on a symmetrical current basis. Those manufactured before 1965 were rated on a total current basis. Both the symmetrical and total current rated breakers have some DC interrupting capability included in their ratings and it is a matter of how it is accounted for in the total interrupting current. Note: For circuit breakers rated on Total Current S=1.0 Medium voltage breakers duty is based on:

1. Momentary rating (C&L) 2. Peak (Crest) 3. Interrupting

The Momentary and Peak formulae apply to both breakers symmetrical and total current rated breakers. The interrupting rating is calculated differently based on the formulae shown in the next sections. Momentary Duty Calculation (C & L):

The CB Closing and Latching Capability defines the CB ability to withstand (close and immediately latch) the maximum value of the first-cycle short circuit current. The closing and latching capability of a symmetrical current-rated CB is expressed in terms of Asymmetrical, Total rms current, or peak current.

EDSA uses the following steps to calculate the circuit breaker momentary duty:

1. Calculate the cycle symmetrical short circuit (Isym,rms). 2. Calculate asymmetrical current value using the following formula:

Imom,rms,asym = MFm*Isym,rms,

where:

)1EQ(2e1 MF R/X-2

m +=

Note: In the short circuit option tab Control for ANSI/IEEE the user has the option to calculate MFm based on X/R or use MFm=1.6

3. Compare Imom,rms,asym against the medium voltage circuit breaker (C&L,rms ) value:

If Device C&L,rms rating Imom,rms,asym, then the device Pass or otherwise it fails

4. Calculate the % Rating = (Imom,rms,asym*100)/Device C&L,rms rating


13

Peak Duty calculation (Crest):

1. Calculate the cycle interrupting short circuit (Isym,rms). 2. Calculate the peak value of momentary SC using the following formula:

Imom,peak = MFp*Isym,rms

where:

)2(2)e(1 /-2

+= EQMFp RX

and

3-X/R

e*0.1-0.49 =

Note: In the short circuit option tab Control for ANSI/IEEE the user has the option to calculate MFpeak based on X/R or use MFpeak= 2.7

3. Compare Imom,peak against the medium voltage circuit breaker (Creat,peak ) value. If Device

Creast,peak rating Imom,peak, then the device pass, or otherwise it fails 4. Calculate The % rating = (Imom,peak*100)/Device Crest,peak rating

Interrupting Duty Calculation

The Maximum Symmetrical Interrupting Capability for a Symmetrical Current-Rated CB is the maximum rms current of the symmetrical AC and DC component, which the CB can interrupt regardless of how low the operating voltage is.

The interrupting fault currents for the MV & HV circuit breakers is equal to 1.5-4 cycles short circuit current. For a system other than of 60 Hz adjust the calculated X/R as follows:

(Hz)Frequency System

60*(X/R) mod)/( =RX

The following steps are used to calculate the circuit breaker interrupting. There are three options:

All Remote i.e. NACD =1.0. This is the most conservative solution; All Local; i.e. NACD =0 Adjusted, this is based on actual calculations.

1. Determine if the generator is Local or Remote; 2. Calculate total remote contribution, total local contribution, then the NACD (the current is

obtained by using the (1.5-4) cycle network impedance

3. Calculate NACD (No AC Decrement) ratio

3)-(EQ Ilocal)(Iremote ItotalIlocal)-(Itotal Iremote +=NACD


14

4. Calculate the Multiplying factor based on the fault location (MFr, or MFl)

Remote If Generator current contribution to fault is less than 40% of a generator terminal fault then this generator is Remote, or equivalent impedance to generation terminals is > 1.5 times the Generator Zdv. For remote fault the multiplying factor is MFr:

)4(2e1 /

-4

+= EQS

MFrC

RX

Where C = CB Contact Parting Time in Cyc.

Local For any local fault the multiplying factor MFl is calculated using the following formula within EDSA or look up tables. The equations are not given in ANSI C37.101, but are empirical equations to match the curves within the ANSI breaker standard.

)5(2eK /

-42

+= EQS

MFlC

RX

where:

CPT K= 1.5 1.0278 - 0.004288(X/R) + 0.00002945(X/R)2 - 0.000000068368(X/R)3

2 1.0604 - 0.007473(X/R) + 0.00006253(X/R)2 - 0.0000002427(X/R)3 3 1.0494 - 0.00833(X/R) + 0.00006919(X/R)2 - 0.000000075638(X/R)3 4 1.0370 - 0.008148(X/R) + 0.0000611(X/R)2 - 0.0000002248(X/R)3

The Adjusted Multiplying Factor (AMFi) is equal to:

AMFi = MFl +NACD (MFr-MFl) (EQ-6) If AMFi is less than 1.0 then the program uses 1.0

5. Calculate Iint,

All Remote: Iint = MFr*Iint,rms,sym

All Local: Iint = MFl*Iint,rms,sym

Mixed local and remote: Iint = AMFi*Iint,rms,sym


15

6. Calculate 3 phase Device Duty by adjusting the device interrupting duty based on rated

voltage using the following formula:

6a)-(EQRating)Int Max Device*kV Voltage Operating

kVMax Rated * RatingInt Device(Min Duty Device P3 =

7 Compare Iint against the CB 3P Device Duty.

If 3P Device Duty Iint, then the device Passes, otherwise it Fails.

8 Calculate % rating = (Iint *100)/ (3P Device Duty)

3.2 Standard Ratings for Low Voltage Circuit Breakers (LV-CBs)

For Low-Voltage CBs (LV-CBs) the time of short circuit current interruption occurs within the sub transient time interval. However, the interrupting capabilities of unfused LV-CBs are sensitive to the maximum peak magnitude of the total /asymmetrical fault current. If the device library does not have a value for X/R then the following default values are used as default by the EDSA program:

Table 2: Default Device X/R Values Using EDSAs Library

Breaker Type Test %PF Test X/R Unfused Power Circuit (PCB) Breaker 15 6.59 Fused Power Circuit Breaker, MCCB, ICCB (Insulated Case CB)

20 4.9

Molded Case (MCCB), ICCB rated 10,000A 50 1.73 Molded Case MCCB), ICCB rated 10,001-20,000 A 30 3.18 Molded Case (MCCB), ICCB rated > 20,000 A 20 4.90

The following steps are used to calculate the low voltage circuit breaker interrupting:

1. Calculate the cycle interrupting short circuit (Isym,rms).

2. Calculate Low Voltage Multiplying Factor (LVF)

PCB: Power Circuit Breaker

ICCB: Insulated Case Circuit Breaker

Fused PCB / MCCB / ICCB

)7(

)e2(1

)e2(1 LVFasym

X/RTest 2-

X/R Calc2-

+

+= EQ


16

Unfused PCB / MCCB / ICCB with Instantaneous setting

)8(EQ

)e1(

)e1( LVFp X/Rtest

T2-

X/Rcalc2

-

++=

Where

3X/Rtest-

3-X/Rcalc

0.1e - 0.49

0.1e - 0.49

=

=

T

and

In Options of the short circuit Tab Control for ANSI/IEEE , the user can select to use

=T = 0.5 instead of using the empirical formula by selecting Applies 0.5 Cycles.

Unfused PCB without Instantaneous setting

If the breaker does not have an instantaneous setting then the breaker has two interrupting rating (peak and asymmetrical). Therefore the LVFp and LVFasym are calculated.

)9(

)e2(1

)e2(1 LVFasym

X/Rtest 4-

X/Rcalc 4-

+

+= EQt

t

Where t is the breaker minimum short time trip in cycles at interrupting duty. The default value used by EDSA is 3 cycles. The peak interrupting rating is calculated as follows:

)8(EQ

)e1(

)e1( LVFp X/Rtest

T2-

X/Rcalc2

-

++=

Where

3. If any of the LVF is less than 1.0 then uses 1.0

3X/Rtest-

3-X/Rcalc

0.1e - 0.49

0.1e - 0.49

=

=

T

and


17

4. Calculate adjusted Interrupting factor

Fused Breakers

Iint,adj = LVFasym* Isym,rms (the 3-8 cycle interrupting short circuit)

Unfused Breakers With Inst

Iint,adj = LVFp* Isym,rms (the cycle interrupting short circuit)

Unfused Breakers Without Inst

Iint,adj = LVFasym* Isym,rms (the 3-8 cycle interrupting short circuit)

Iint,adj = LVFp* Isym,rms (the cycle interrupting short circuit)

5. Compare Iint,adj against the CB symmetrical interrupting rating.

If Device Symmetrical rating Iint,adj, then the device passes, or otherwise it fails 6. Calculate The % rating = (Iint,adj*100)/Device Symmetrical rating


18

3.3 Standard Ratings for Low/High Voltage Fuses, and Switches

The LVFs interrupting capability is the maximum symmetrical rms current which the fuse can interrupt and still remain intact. While the fuse has a symmetrical current rating it can also interrupt the DC component up to a value based on its test X/R ratio. The interrupting capabilities of LV-Fs are classified by the UL according to symmetrical current ratings in rms Amperes. In some rare cases the fuse asymmetrical rating is provided. Evaluation procedure:

3. Calculate the cycle interrupting short circuit (Isym,rms).

4. Calculate Iasym:

Iasym,adj = MFasym*Isym(1/2 Cyc)

If the fuse is symmetrical rated, then MFasym is calculated using the following formula:

)1EQ()e2(1 MFasym X/R2- +=

If the fuse is asymmetrical rated, then MFasym is calculated using the following formula:

)10(

)e2(1

)e2(1 MFasym

X/RTest 2-

X/R Calc2-

+

+= EQ

5. Compare Iasym,adj against the fuse symmetrical interrupting rating.

If Device Symmetrical rating Iasym,adj, then the device Pass otherwise it Fails 6. Calculate The % rating = (Iasym,adj*100)/Device Symmetrical rating.

Note: For standard switches the same formulae are used


19

Perform Short-Circuit Study & Update Answer File.For frequency other than 60 Hz, then adjust the X/R where,(X/R)mod=(X/R)*60/(System Hz)

y For LVCB, MVCB & Fuses Calculate the cycle short-circuit current(Isym,rms).

y For MVCB calculate the Iint,rms,sym.y Run the PDE analysis

Fused?

LVCB

Yes

IF LVF < 1,then LVF =1

MCCB/ICCB/PCBWith Instantaneous :Iint,adj =LVF*Isym,rmsPCB Without Instantaneous:Iint,adj =LVFp*Isym,rms( Cyc)int,adj =LVFasym*Isym,rms(3-8 Cyc)

CB X/R is known?

The X/R is equal to:

PCB, MCCB, ICCB = 4.9

Calculate LVF based on EQ-8 for PCB breaker withInstantaneous Setting, MCCB and ICCB.

For PCB without instantaneous use EQ-8 & EQ-9

Calculate LVFbased on EQ-7

NOYES

NO

YES

CB X/R is known?

NO

Is Device Symmetricalrating greater or Equal

to Iint,adj?

PassFail

YesNO

Calculate%rating=Iint,adj*100/

Device rating

ANSI DEVICE EVALUATION

Fuses/ Switches

Is Device rating greateror Equal to Iasym,adj?

PassFail

YesNO

Calculate%rating=Isym,adj*100/

Device rating

MVCB

Go toPage 2

The X/R is equal to:

PCB, ICCB = 6.59MCCB, ICCB rated 20,000 A = 4.9

Fuse / Switch Symmetrical Rating, selected:y Calculate MF based on EQ-1

Fuse / Switch Asymmetrical Rating selected:y Calculate MF based on EQ-10

Figure 1: ANSI Device Evaluation, Page 1


20

ANSI DEVICE EVALUATIONPage 2MVCB From

Page 1

CalculateImom,asym=MFm*Isym,rms

Calculate MFp using EQ-2

Calculation Based on Generation:y All Remotey All Localy NACD

Calculatey MFr using EQ-4y Iint=MFr*Iint,rms,sym

Calculatey MFl using EQ-5y Iint=MFl*Iint,rms,sym

Calculate:y NACD using EQ-3y MFr using EQ-4y MFl using EQ-5y AMFi = using EQ-6.y If AMFl less than 1 use 1.0y Iint = AMFi*Iint,rms,sym/S

Is Device peak (crest)rating greater or Equal to

Imom,peak?

PassFail

YesNO

Calculate%rating=Imom,peak*100/device peak (crest) rating

Calculate 3 phase deviceduty using EQ-6a

Is Device Int rating greateror Equal to calculated Iint?

PassFail

YesNO

Calculate %rating=Iint*100/3P device Int rating

Is Device C&L,rms ratinggreater or Equal toImom,rms,asym?

PassFail

YesNO

Calculate%rating=Imom,rms,asym*100/

device C&L,rms rating

Calculate:y Total Remote Contributiony Total Local contributiony Total Contribution (Iint,rms,sym)y NACD using (EQ-3)y If NACD=0 then all contribution are Localy If NACD=1 then all contribution are Remote

ALL Remote

All Local

NACD

In the short circuit option tabControl for ANSI/IEEE the userhas selected the fixed MF factor

NO

NO

CalculateImom,peak=MFp*Isym,rms

Calculate MFm using EQ-1

YES

MFp = 2.7

YES

MFm = 1.6

Peak Duty(Crest)

MomentaryDuty (C&L)

Peak Duty(Crest)

MomentaryDuty (C&L)

Interrupting Duty

Figure 2: ANSI Device Evaluation, Page 2


21

4 DesignBase Short Circuit Calculation Method 4.1 Calculation Methods and the Corresponding Tools

In order to launch DesignBase Short Circuit program, click the short circuit icon as presented below:

While in Paladin DesignBase Short Circuit program, both the short circuit analysis method and the corresponding short circuit tools are displayed as indicated below:

Paladin DesignBase provides several short circuit calculation methods based on the ANSI/IEEE Standards and the IEC Standards, for both AC three-phase and single-phase networks. The following short circuit calculation methods are implemented:

AC ANSI/IEEE (separate R and X, as per ANSI/IEEE Standard); AC Classical, (Z complex method, X/R from the complex Z); AC IEC 60909; AC IEC 61363; AC 1 Phase; DC Classical; DC IEC 61660.


22

4.2 AC ANSI/IEEE Standard Paladin DesignBase Short Circuit Tools:

Paladin DesignBase Short Circuit Program: Short Circuit Tools The Short Circuit tools are presented in the Figure above, and are listed below:

AC Short Circuit Options;

Report Manager;

Short Circuit Back Annotation;

Analyze;

Reactor Sizing.


23

The Short Circuit Analysis Basic Option Icon:

Short Circuit Analysis Option has two tabs:

Calculation Tab, with the same fields for: AC ANSI/IEEE, AC Classical, AC IEC 60909, AC IEC 61363 and AC Single Phase calculation. AC Single Phase, faults can be performed only at all buses in this release,

Control Tab: this tab depends on the short circuit method that user selects.

Click on this icon to launch the Short Circuit Analysis Options. The Short Circuit Option Dialog Window is opened and presented in the Figure below. It has two tabs: Calculation and Control for ANSI/IEEE:

Short Circuit Analysis Basic Option

Note: For L-G fault, phase A; for L-L and L-L-G fault phase B and C For L-G fault, phase B; for L-L and L-L-G fault phase A and C For L-G fault, phase C; for L-L and L-L-G fault phase A and B


24

Calculation Tab allows the user to select the followings:

Base voltage: Adjusted by tap/turn ratio if power transformer is run on off nominal taps; System voltage;

Prefault voltage represents the bus voltage at the instant the fault is applied at that bus. It can be: system voltage, load flow calculated bus voltage or actual/name plate voltage;

Default output: Annotation or report; Contribution level: levels away from the fault location for the output results. The

calculated results are displayed either on the one-line diagram (if Default Output: Annotation is selected by the user) or printed in the output report (if Default Output: Report is selected by the user);

Fault impedance. This option is applied if the fault is calculated at one bus only; Fault location: selected buses, all buses, sliding fault or series fault; (Sliding and series

fault does not apply to IEC61363 or AC Single phase calculation) Miscellaneous options: use only X to calculate the faults, and apply phase shift; Duty type for PDE based on: maximum branch fault flow or total bus fault current.

Fault Location

Fault at one or more buses in the same run; Fault at all system buses, when the buses are faulted individually, not simultaneously.

Depending on the specified fault type, the program will place a three-phase, line-to-ground, line-to-line, and line-to-line-to-ground fault at each bus which is faulted for short circuit studies. The bus faults are displayed at all buses simultaneously.

Selection of One Bus:

The Bus can be selected:

Graphically on the one line diagram, by a simple click on the desired bus, or; Highlight the bus ID in the Short Circuit Option and then click on the Add button; the

selected bus will be transferred to the Selected Buses list. To remove a bus from the Selected Buses list highlight the bus ID and click on Remove button. The highlighted bus will be transferred to the All Buseslist.

If One Bus is selected, then any fault type at that bus is calculated, branch contribution to that fault, bus post-fault voltage and fault summary are generated.

Selecting More Than One Bus:

Graphically on the drawing space: click onto the desired first bus, then hold down the

shift key; while the shift key is being held down, select each bus individually; Menu Driven: highlight the desired bus ID in the Short Circuit Option and then click on

the Add; the selected buses will be transferred to the Selected Buses list. To remove a bus or several buses from the Selected Buses List highlight the bus ID and click on Remove button. The highlighted bus/buses will be transferred to the All Buses List.

Notes:

Faults at more than one bus, are faulted individually in turn, not simultaneously. Depending on the specified fault type, the program will place a three-phase, line-to-


25

ground, line-to-line, and line-to-line-to-ground fault at each selected bus which is faulted for short circuit studies;

On the drawing are displayed only the bus fault current value: Symmetrical rms, DC rms, Asymmetrical rms, IPeak instantaneous value, as per user selection in the Short Circuit Back Annotation.

Selecting All Buses:

Fault at all buses can be selected from the Short Circuit Analysis Basic Option only, by selecting All Buses option.

Faults at All Buses, are faulted individually, not simultaneously. Depending on the specified fault type, the program will place a three-phase, line-to-ground, line-to-line, and line-to-line-to-ground fault at all buses which are faulted for short circuit studies;

On the drawing are displayed: Symmetrical rms, DC rms, Asymmetrical rms, IPeak instantaneous value, as per user selection in the Short Circuit Back Annotation.

All buses are colored in Red. The Short Circuit Report will provide:

Bus Fault Current (3P, L-L, L-L-G, L-G, depending on the user selection); Branch currents (3P, L-L, L-L-G, L-G, depending on the user selection); Short Circuit multiplying Factors; Fault Summary;


26

Sliding Fault:

The Paladin DesignBase Short Circuit Program can simulate a fault along a feeder/cable/transmission line. Using this option eliminates the need to create a dummy bus at a location along the feeder. The figure below shows examples of evenly spaced sliding faults (F1, F2, F3, and F4) and single point sliding fault and a specific location (F).

F1 F2 F3 F4F

From Bus To Bus

Click on this button to open the Short Circuit Option dialog window. In the Calculation Tab, select Sliding Fault.


27

Sliding Fault


28

Selecting a Feeder / Branch: Highlight the desired Feeder/Cable in the All Feeders and Cables Box and then click on the Add button; the selected Feeder/Cable will be transferred to the Selected Feeders and Cables Box. To remove a Feeder/Cable from the Selected Feeders and Cables box, highlight the Feeder/Cable and click on Remove button. The highlighted Feeder/Cable will be transferred to the All Feeders / and Cables Box / List. In this release, only one Feeder/Cable can be selected for Sliding fault calculation at a time. Select a feeder 3C 12, and then press on the OK button; the Sliding Fault Report Manager is displayed as presented below: Note: Sliding fault does not apply to IEC61363 and AC Single Phase calculation. Sliding Fault: Report Manager


29

The program allows the user to introduce the Fault position on the selected Feeder: Any Position away From Bus or select the Number of Fault Spots evenly spaced alongside the selected feeder. The program automatically divides the feeder/line into as many equidistant segments and fault currents are calculated for each intermediate points. Contributions from both ends of the feeder/line for each fault location as well as the voltages at the faulted location and at both ends are also reported. In case only one fault location is selected, then the exact fault location (i.e. 300 Feet down from sending end) should be specified. Fault type:

3-Phase Fault; Line-to-line fault; Line-to-ground fault; Double-Line-to-Ground fault.

Units:

For fault Current: Amps or KiloAmps, with the user defined decimal places; For Capacity: KVA or MVA, with the user defined decimal places; For Bus Voltages: Volts or Kilo Volts, with the user-defined decimal places. Per Unit MF, %X/R: with the user-defined decimal places.


30

Sliding Fault Report: 300 Feet away from From Bus.

A partial Report is presented below:

3-Phase Short Circuit Project No. : Page : 2 Project Name: Date : Title : Time : 01:14:44 am Drawing No. : Company : Revision No.: Engineer: Jobfile Name: T123 Check by: Scenario : 1 : mode1 Date : -------------------------------------------------------------------------------- Electrical One-Line 3-Phase Network for ANSI PDE ------------------------------------------------------------- Fault Spot Report for Sliding Fault Bus Results: 0.5 Cycle--Symmetrical--3P/LL/LG/LLG Faults ------------------------------------------------------------- Fault Feeder : 3C ->12 Fault R(Ohms) : 0 From Bus : 12 Fault X(Ohms) : 0 To Bus : 3C Length(Feet) : 300 Fault Spot : 150 Feet away from 'From Bus' Thevenin Imped. Complex Pre-Flt 3P Flt. LL Flt. LG Flt. LLG Flt --------------- ------ Bus Name V A A A A Z+(pu) Zo(pu) 3P X/R ------------------------ ------- ------- ------- ------- ------- ------- ------- ------ --Fault Spot--- 480 31748 27494 29176 31828 3.7886 4.8206 3.0819 --------------------------------------------------------------------------------------- ---------------------------------------------------------------- Branch Report for Sliding Fault Branch Results: 0.5 Cycle--Symmetrical--3P/LG Faults ---------------------------------------------------------------- Fault Feeder : 3C ->12 Fault R(Ohms) : 0 From Bus : 3C Fault X(Ohms) : 0 To Bus : 12 Length(Feet) : 300 Fault Spot : 150 Feet away from 'From Bus' System Volt: 480 V Base Volt: 480 V Prefault Volt: 480 V Fault Type : 3-phase L-L L-G L-L-G Spot RMS( A ): 31748 27494 29176 31828 Spot X/R : 3.08 * Stands for the Low or Mid. voltage side of a transformer or To Bus --> Fault Spot for Sliding Fault Feeder. 3-Phase Fault Line-Ground Fault Thevenin --------------- ------------------------------- --------------- From Bus (A) From Bus (A) Impedance Branch Name V Ia Va Vb Ia 3Io Z+(pu) Zo(pu) ------------------------ ------- ------- ------- ------- ------- ------- ------- ------- 3B ->11 0 0 0 3C ->12 28.8 29373 38.6 98.2 27050 27163 2.9297 2.5561 3C ->12 * 2.4 2426 3.1 100.4 2194 2135 3.7253 4.6677


31

Series Fault: Series fault types (one phase open, two phases open, and unequal series impedances) with or without neutral unbalance are supported in the Paladin DesignBases short circuit program. The series fault types are shown in the below figure. It should be noted that series faults are meaningful only if pre-fault load has been taken into account (i.e. load flow solution is considered). For series faults, the equivalent voltage at the opening point is computed from the pre-fault system current at the unbalance point. The default fault impedances Za, Zb, and Zn are:

For one phase open (phase A), Default values: Zb=Zn=0.0 +j0.0 For two phases open (phases B and C) Default values: Za=Zn=0.0+j0.0 For Series Unbalance (phases A, B, and C) Default values: Za=Zb=Zn=0.0+j0.0


32

In Paladin DesignBase short circuit Analysis Option, select Series Fault field to perform open phase

study.


33

Select the feeder / branch: Highlight the desired feeder / cable in the All feeders and Cables box and then Click on the Add button. The selected feeder / cable will be transferred to the Selected feeders box as is presented below: To remove a feeder / cable from the Selected feeders highlight the feeder/cable and click Remove button. The highlighted feeder/cable will be transferred to the All feeders and Cables box. For series fault, only one feeder can be selected at a time. Click OK.

1

2 3


34

Series Fault Report Manager:

The program allows the user to select:

one phase (one phase open); two phases open; unbalanced series fault.

At the fault (opening location) the user can select the fault impedance in ohms. Units:

For current: Amps or KiloAmps; For capacity: KVA or MVA; For voltages: volts or Kilo Volts.

Output File: to CSV or text file.


35

Report is listed below:

EDSA

3-Phase Short Circuit Project No. : Page : 1 Project Name: Date : Title : Time : Drawing No. : Company : Revision No.: Engineer: Jobfile Name: T123 Check by: .. Scenario : 1 : mode1 Date :.. -------------------------------------------------------------------------------- Electrical One-Line 3-Phase Network for ANSI PDE Base MVA : 100.000 System Frequence(Hz) : 60 # of Total Buses : 48 # of Active Buses : 48 # of Total Branches : 47 # of Active Sources : 3 # of Active Motors : 4 # of Active Shunts : 0 # of Transformers : 5 Reference Temperature(C) : 20.0 Impedance Displaying Temperature(C) : 20.0 Calculating Series Fault Classical Calculation Complex Z for X/R and Fault Current Transformer Phase Shift is not considered. Base Voltages : Use System Voltages Prefault Voltages : Use Load Flow Results ------------------------------------ Feeder/Cable Series Fault Report ------------------------------------ Fault Feeder : 3C ->12 Prefault Voltage System Base -------------------------- Bus Bus Name kV kV kV % Degree ----- ------------------------ -------- -------- -------- -------- -------- From 04 0.48 0.48 0.48 100.03 0.00 To 12 0.48 0.48 0.48 99.94 -0.0 Fault Impedance(Ohms) : Za = 0 +j 0 Zb = Zc = 0 +j 0 Zn = 0 +j 0 Fault Current Direction : From Bus --> To Bus Phase Sym Fault Current at 1/2 Cycle (Magnitude in A , Angle in Degree) ---- One Phase Open ------ Item Phase A Phase B Phase C ----- -------- -------- -------- Magn. 0 95 94 Angle 0 -122 109.4 ---------------------------------------------------------------------------------------


36

Control Tab:

AC ANSI/IEEE Standard: The AC ANSI/IEEE method is based on a separate R and X matrix method:

Fault current multiplying factors allow the user to set up a marginal coefficient while fault calculations are performed. The tab provides also information on ANSI Standard impedances first cycle and interrupting cycles: 2-8 cycles as per ANSI/IEEE Std. For calculating the MF the user can select:

Based on X/R using the equations in section 2.0 Or regardless of the X/R value, the MF is fixed

In calculating the MF the user can also select to use: Empirical value for ; Or = T = 0.5.


37

The short circuit program supports two options for the generators and motors resistances. The first option uses constant X/R ratio (which is defined in the generator and motor input dialogs). In the second option, the generator/motor resistance is computed from the X/R ratio as follows:

RXXR/

"

= The above resistance is maintained constant for all time bands and sequences (negative, zero, positive).

4.3 AC Classical Short Circuit Method The AC Classical is based on the Complex E/Z calculation method and the X/R ratio is extracted from the complex impedance matrix (X/R). The Calculation Tab is the same as in AC ANSI/IEEE Standard and provides the same options.

Fault Current Multiplying Factors allow the user to set up a marginal coefficient while fault calculations are performed. The user can also select the Machine Current Decay, in cycles. The short circuit program supports two options for the generators and motors resistances. The first option uses constant X/R ratio (which is defined in the generator and motor input dialogs).


38

In the second option, i.e, variable X/R (see the lower left part of the above figure), the generator/motor resistance is computed from the X/R ratio as follows:

RXXR/

"

= The above resistance is maintained constant for all time bands and sequences (negative, zero, positive). In this case the X/R ratio will be variable for different time bands and sequences.


39

4.4 AC IEC 60909 Short Circuit Method

The AC IEC 909 Paladin DesignBase Short Circuit program tools are shown below.

Options;

Report Manager;

Back Annotation;

Analyze;

Reactor sizing;


40

The method is based on IEC60909 Standard. The Calculation Tab is similar to the AC ANSI/IEEE Standard and provides the same options. The user can select the calculation based on:

1988 Version or 2001 Version

The short circuit program supports two options for the generators and motors resistances. The first option uses constant X/R ratio (which is defined in the generator and motor input dialogs). In the second option (variable X/R, see the lower left part of the above figure), the generator/motor resistance is computed from the X/R ratio as follows:

RXXR/

"

= The above resistance is maintained constant for all time bands and sequences (negative, zero, positive). In this case the X/R ratio will be variable for different time bands and sequences. While in the IEC 60909 standard, the control tab allows the user to select:

Fault Current Multiplying Factors; The method which is employed in calculating the Peak Current (method A, B, C or EDSA

Thevenin).


41

Also, as per IEC 60909 standard, the user can select:

System Voltage; IEC maximum Voltage; IEC minimum Voltage.

Peak current method:

Method A: uniform ratio R/X. The smallest X/R ratio determines the k factor; Method B: applies to the calculation of peak current in mesh networks X=1.15 multiplied

by the Xb. Xb from Fig.8 page 47 IEC 60909 Std.; Method C: applies to the calculation of peak current in mesh networks; The value of X is

calculated from Fig. 8, IEC 60909 and depends on X/R ratio of the network; EDSA Thevenin: X is calculated from the Thevenin equivalent.

Impedance correction factors: 1. Apply gK factor to Generator gZ impedance: This field should be selected by the user when calculating the initial short circuit current in systems fed directly from generators without unit transformers. This is the situation when the user calculates the short circuit current at generator terminal.


42

The gK factor is given by formula (18) IEC Std.:

GdrG

nG X

cUUK sin1 "

max

+= (18, IEC Std.) Where:

nU - is the system rated voltage;

rGU - the generator rated voltage; "dX - generator sub transient reactance referred to generator rated impedance;

Gsin - generator phase angle between current and terminal voltage.


43

2. Apply tK factor to network transformer tZ :

The Paladin DesignBase user should check the above field if the short circuit occurs from a network transformer. A network transformer (see the figure capture below) is when a transformer is connecting two or more networks at different voltages (IEC Std.). For two-winding transformers with and without on-load tap-changer, an impedance correction factor KT is to be introduced in addition to the impedance evaluated according to IEC (equation (7) to (9)).

TT X

cK6.01

95.0 max+= (IEC eq. 12a)

Where:

TX is the relative reactance of the transformer and maxc is from table 1 is related to the nominal voltage of the network connected to the low-voltage side of the network transformer. This correction factor shall not be introduced for unit transformers of power station units (IEC, see 3.7). This factor is active only if the user selects the filed Network Transformer (used in IEC 60909 method) in the transformer editor, as presented below:


44


45

3. Apply Adjust tZ factor by using actual tap: If the user selects this field, then EDSA adjusts TZ by using actual transformer tap. In this situation the program consider the transformer impedance as a function of the transformer tap position.

If the user select the 1988 IEC 60909 version then the c factor values are provided by the program, as follows:


46

If the user select the 2001 IEC 60909 version then the c factor values are provided by the program, as follows:

A

cmax cmin Standard: Above 1000 V: 1.1 1 Low Voltage networks: 230/400V, 3P3W Other voltage levels, 3P3W

1.05 1.05

1 1

Low voltage networks: 230/400V, 3P4W Other voltage levels, 3P4W

1

1.05

0.95

1

User Defined: Above 1000 V: Per user selection per user selection Low voltage networks: 230/400V, 3P3W/4W Other voltage levels 3P3W/4W

per user selection per user selection

per user selection per user selection

cmax cmin Standard: Above 1000 V: 1.1 1 Other

1.05

0.95

User Defined: Above 1000 V: Per user selection per user selection Other

per user selection

per user selection


47

4.5 AC IEC 61363 Short Circuit Method

IEC 61363 Standard calculates the short circuit instantaneous current as a function of time and displays its instantaneous values. The method provides an accurate evaluation of the short circuit current for sizing protective devices and coordinating relays for isolated systems (off-shore platforms and ships electrical design). The machines sub transient reactance and time constants are used by this method. The Calculation Tab is similar to the AC ANSI/IEEE Standard and provides the same options.

EDSA AC IEC 363 Short Circuit program tools are shown below:

Options;

Report Manager;

Back Annotation;

Analyze;


48

Options: The Options features are similar to ANSI Method.


49

Report Manager:

As can be seen from the window dialog above, the Short Circuit Report can be:

Fast; User Defined; Curve with Time.


50

Fast Report: If Fast Report is launched, the following dialog window is displayed:

Select the items be displayed in the Report.


51

User Defined Fault Report displays:

Time Bands: 0 cycle; - cycle; 1 cycle; 3 cycle; 5 - cycle; 8 cycle; 30 cycle. User defined output options: Td DC Time constant, in seconds; Iac Short circuit AC symmetrical component, rms value; Idc Short circuit DC component; Ienv- Short circuit envelope; Input Report & Abbreviations; Input Data and Abbreviation. Report Style, Units & Log. Print Layout, Unit, View Log File.


52

The AC IEC 61363 Short Circuit program Abbreviations are displayed below:

The work is identical with that presented for AC ANSI standards. In order to display the Report of Short Circuit Results varying with time, the following steps need to follow: Step1: select the bus: bus 18; Step2: launch the short Circuit program, by clicking the program icon ;

Step3: click the Report Manager icon : Select Graph Output and then click OK button: The following window is displayed:


53

Step4: click icon. The following graphs are displayed:

The displayed graph components are user defined. However, the user can select the Short Circuit Current components to be displayed such as:

Idc dc component of SC Current; iac instantaneous ac component; Ienv Upper Envelop of Sc current; i - Instantaneous total short circuit current; Im magnitude of ac component.


54

Idc dc component of the Short Circuit Current:


55

iac instantaneous ac component of the Short Circuit Current:


56

Ienv Upper Envelop of the Short Circuit Current:


57

i Instantaneous - Total Short Circuit Current:


58

Im magnitude of the ac component of the Short Circuit Current:


59

4.6 AC SINGLE Phase Short Circuit Method

The AC Single Phase Method is based on the Complex E/Z calculation method and the X/R ratio is extracted from the complex impedance matrix (X/R). The Calculation Tab is the same as in AC ANSI/IEEE Standard and provides the same options.

5 Managing the Paladin DesignBase Short Circuit Program 5.1 3P, LL, LG, LLG Fault, Cycle

In the Short Circuit Option feature select the output results: Annotation or Report; From the Report Manager, the user can select:

Fast or User Defined Report:


60

In the SC Report Manager select Fast option, then the user can select the Fault Types as shown below: 3-P, L-G, L-L, LL-G. Time Bands cycle.

Click OK and then launch the program by clicking the Analyze icon.

The rms short circuit currents values at 1/2 Cycle are calculated at a selected bus/buses or at all buses as per user bus selection (on the short circuit options dialog or directly onto the drawing).

The positive, negative, and zero sequence sub-transient reactance X are used in modeling both the generators and motors. Motors are normally not grounded and therefore the grounding option should be none.

Notes:

In all the unbalanced fault calculations it is assumed that the negative sequence impedance of a machine is equal to its positive sequence impedance

Generator, motor, and transformer grounding types and winding connections are taken into consideration while building up the system positive, negative, and zero sequence networks.


61

The Results are listed in the Partial Text Report, as presented below:

3-Phase Short Circuit Project No. : Page : 2 Project Name: Date : Title : Time :. Drawing No. : Company : Revision No.: Engineer: Jobfile Name: T123PDE Check by: Scenario : 1 : mode1 Date : -------------------------------------------------------------------------------- Electrical One-Line 3-Phase Network for ANSI PDE ------------------------------------------------------------- Bus Results: 0.5 Cycle--Symmetrical--3P/LL/LG/LLG Faults ------------------------------------------------------------- Thevenin Imped. ANSI Pre-Flt 3P Flt. LL Flt. LG Flt. LLG Flt --------------- ------ Bus Name kV KA KA KA KA Z+(pu) Zo(pu) 3P X/R ------------------------ ------- ------- ------- ------- ------- ------- ------- ------ MAINBUS 0.48 31.82 27.55 34.47 33.53 3.7805 2.9070 5.6944 ---------------------------------------------------------------------------------------


62

5.2 3P, LL, LG, LLG Fault, 5 Cycle

In the SC Report Manager select 5 cycle and the type of faults: 3-P, L-g, L-L, LL-G. Select 5

cycle, then Click OK. Launch the short circuit program by clicking Analyze icon .

The rms short circuit currents values at 5 Cycle are calculated at a selected Bus/Buses or at All Buses as per user bus selection (on the short circuit options dialog or directly onto the drawing). Follow the steps presented above at 3P, LL, LG, LLG fault at Cycle.

Notes:

The positive, negative, and zero sequence sub-transient reactance is used for modeling both the Generators and motors;

In all the unbalanced fault calculations it is assumed that the negative sequence impedance of a machine is equal to its positive sequence impedance.

Generator, motor, and transformer grounding types and winding connections are taken into consideration while building up the system positive, negative, and zero sequence networks.


63


3-Phase Short Circuit Project No. : Page : 2 Project Name: Date : Title : Time : Drawing No. : Company : Revision No.: Engineer: Jobfile Name: T123PDE Check by: Scenario : 1 : mode1 Date : -------------------------------------------------------------------------------- Electrical One-Line 3-Phase Network for ANSI PDE ------------------------------------------------------------- Bus Results: 5 Cycle--Symmetrical--3P/LL/LG/LLG Faults ------------------------------------------------------------- Thevenin Imped. ANSI Pre-Flt 3P Flt. LL Flt. LG Flt. LLG Flt --------------- ------ Bus Name kV KA KA KA KA Z+(pu) Zo(pu) 3P X/R ------------------------ ------- ------- ------- ------- ------- ------- ------- ------ MAINBUS 0.48 30.03 26.01 33.05 31.99 4.0055 2.9070 5.6944 ---------------------------------------------------------------------------------------


64

5.3 3P, LL, LG, LLG Fault, Steady state

In the Report Manager select Steady and the type of faults: 3-P, L-g, L-L, LL-G. Click OK

button. Launch the program by clicking Analyze icon .

The rms short circuit currents values at Steady State/ 30 Cycle are calculated at a selected Bus/Buses or at All Buses as per user bus selection (on the short circuit options dialog or directly onto the drawing).

Notes:

It is assumed that the negative sequence impedance of a machine is equal to its positive sequence impedance in all the unbalanced fault calculations.

Generators are modeled by their positive, negative, and zero sequence reactance; Short circuit current contributions from motors are ignored. Generator, motor, and transformer grounding types and winding connections are

taken into consideration while building up the system positive, negative, and zero sequence networks.


65


3-Phase Short Circuit Project No. : Page : 2 Project Name: Date : Title : Time : Drawing No. : Company :. Revision No.: Engineer: Jobfile Name: T123PDE Check by: Scenario : 1 : mode1 Date : -------------------------------------------------------------------------------- Electrical One-Line 3-Phase Network for ANSI PDE ------------------------------------------------------------- Bus Results: 30 Cycle--Symmetrical--3P/LL/LG/LLG Faults ------------------------------------------------------------- Thevenin Imped. ANSI Pre-Flt 3P Flt. LL Flt. LG Flt. LLG Flt --------------- ------ Bus Name kV KA KA KA KA Z+(pu) Zo(pu) 3P X/R ------------------------ ------- ------- ------- ------- ------- ------- ------- ------ MAINBUS 0.48 28.78 24.93 32.03 30.93 4.1790 2.9070 5.6944 ---------------------------------------------------------------------------------------


66

5.4 3 Phase Fault, Steady State

In the Report Manager select fault type 3-P and Time Bands Steady.Click OK and then

launch the program by clicking Analyze icon .

The rms short circuit currents values after 30 cycles are calculated (as per ANSI/IEEE Standards or IEC 60909 Standard as per user selected fault calculation) at a selected bus/buses or at all buses as per user bus selection (on the short circuit options dialog or directly on the drawing). The short circuit current contributions from motors are ignored, and the generators are modeled by their positive sequence transient reactance X.


67


3-Phase Short Circuit Project No. : Page : 2 Project Name: Date : Title : Time :04:23:01 am Drawing No. : Company : Revision No.: Engineer: Jobfile Name: T123PDE Check by: Scenario : 1 : mode1 Date : -------------------------------------------------------------------------------- Electrical One-Line 3-Phase Network for ANSI PDE ------------------------------------------- Bus Results: 30 Cycle -- 3 Phase Faults ------------------------------------------- Pre-Flt Isym X/R Thevenin Bus Name kV KA Ratio Z+(pu) ------------------------ ------- --------- --------- --------- MAINBUS 0.48 28.78 5.6944 4.1790 ---------------------------------------------------------------------------------


68

5.5 Protective Device Evaluation (PDE) Tool

Paladin DesignBase PDE is a fast and accurate tool, which evaluates the protective switching devices such as: LV, MV and HV CBs, fuses, and switches.

A number of enhancements have been implemented in this version of the program. The salient features added to the PDE program are:

The equipment operating voltage is selected by the user, and it can be: o Load Flow calculated Voltage; o Actual Voltage; o System voltage.


69

The user can introduce from the keyboard the multiplying factors for calculating the peak and asymmetrical short circuit current as per the standard employed:

The PDE program includes the CB impedance and CBs X/R ratio; The PDE Output Text Report has been reorganized. The output results are organized as

per: o Equipment Input Rated Data; o PDE Calculated Data; o Circuit Duty calculated data.

The PDE output results are either graphically displayed onto the one line diagram (in green if the switching equipment passes or in red if they fail), or as a Text Report, based on the user selection.

The fault study is per the Standard selected by the user: IEEE/ANSI C37 Standard. The program calculates momentary symmetrical and asymmetrical rms, momentary asymmetrical crest, interrupting symmetrical rms, and interrupting adjusted symmetrical rms short circuit currents at faulted buses.

The circuit duties are checked against equipment interrupting capabilities, and if:

IntrrEquipDutyCircuit II _._ Then equipment passes, otherwise it fails.


70

The Protective Device Evaluation List is displayed, as presented below:

One bus selected by the user:

All buses selected by the user:


71

The program lists all the equipment connected to the selected bus and displays: equipment code, type, location, description and equipment status: pass or fail.

Partial Summary Report

Protective Device Evaluation Project No.: Page : 1 Project Name: Date :. Title : Time :.M Drawing No.: Company : Revision No.: Engineer : JobFile Name: ANSI-YY Check by : Scenario : 1: CheckDate: Base MVA : 10.00 Cyc/Sec : 60 -------------------------------------------------------------------------------- --------------------------------------- ANSI - Summary PDE Report Based On Bus Duty (* Used by Program) ---------------------------------------- ----------- Device Rating ----------- -----Short Circuit Duty ------ Branch -----Location----- Std ------0.5Cy(KA)-------- Int -------0.5Cy(KA)------- Int Name Bus kV Categ. Sym Asym Peak KA Sym Asym Peak KA Status -------------- ---------- ------- ------ ------- ------- ------- ------- ------- ------- ------- ------- --------- A1 BUS 1 13.80 8 Tot. 40.00 20.92 31.91 21.05* Int -Fail T1P 31.91 21.05 A10 Bus 2 13.80 3 Sym. 40.00 20.98 31.04 20.47* A10P 31.03 20.47 A10F A10P 13.80 Fuse 25.00 20.39 * T7_PRI 20.39 A2 BUS 1 13.80 8 Tot. 40.00 20.92 31.91 21.05* Int -Fail G1 31.91 21.05 A3 BUS 1 13.80 8 Tot. 40.00 20.92 31.91 21.05* Int -Fail A3P 31.91 21.05 A4 BUS 1 13.80 8 Tot. 40.00 20.92 31.91 21.05* Int -Fail A4P 31.91 21.05 A4F A4P 13.80 Fuse 25.00 20.97 * T3_PRI 20.97 A5 BUS 1 13.80 8 Tot. 40.00 20.92 31.91 21.05* Int -Fail A5P 31.91 21.05 A6 Bus 2 13.80 3 Sym.

3 phase short circuit

Documents

mv circuit breakers

standard ratings

ac iec

fault analysis

corresponding tools

llg fault

calculation methods

lowhigh voltage fuses