+ All Categories
Home > Documents > Edsa Paladin

Edsa Paladin

Date post: 31-Oct-2014
Category:
Upload: parjoleanu-iulian
View: 78 times
Download: 8 times
Share this document with a friend
Description:
part 15
Popular Tags:
35
DC SHORT CIRCUIT CLASSICAL & IEC 61660 EDSA MICRO CORPORATION 16870 West Bernardo Dr., Suite 330 San Diego, CA 92127 U.S.A. © Copyright 2008 All Rights Reserved Version 6.00.00 October 2008
Transcript
Page 1: Edsa Paladin

DC SHORT CIRCUIT CLASSICAL & IEC 61660

EDSA MICRO CORPORATION 16870 West Bernardo Dr., Suite 330

San Diego, CA 92127 U.S.A.

© Copyright 2008

All Rights Reserved

Version 6.00.00 October 2008

Page 2: Edsa Paladin

DC Short Circuit

Table of Contents

1. Introduction ...................................................................................................................................... 1

2. Program Capabilities........................................................................................................................ 3

3. Number of Batteries ......................................................................................................................... 4

4. Number of Chargers and Distribution Panels .................................................................................. 4

5. System Voltage Considerations....................................................................................................... 4

6. Determination of Battery Duty Cycle................................................................................................ 4

7. Battery Size (Capacity) .................................................................................................................... 5

8. Sources of Short Circuit Current ...................................................................................................... 5

9. Bus Short Circuit Current Calculation .............................................................................................. 5

10. Feeder Short Circuit Calculation ...................................................................................................... 5

11. Resistance Diagram......................................................................................................................... 5

12. Inductance Diagram......................................................................................................................... 6

13. IEC DC Short Circuit Calculations ................................................................................................... 8

14. References....................................................................................................................................... 8

15. Tutorial Introduction ......................................................................................................................... 9

16. DesignBase DC Short Circuit Current Analysis Capabilities ........................................................... 9

17. Required Data for Performing DC Short Circuit Current Study ....................................................... 9

18. DC System Short Circuit Current Calculations ................................................................................ 9

19. Time Constant and Rate of Rise of Short Circuit Current.............................................................. 10

20. Short Circuit Characteristics of Battery.......................................................................................... 11

21. Short Circuit Characteristics of Power Rectifier............................................................................. 12 21.1 Power Rectifier....................................................................................................................... 12 21.2 Synchronous Converter ......................................................................................................... 13 21.3 Double-Wye Rectifier ............................................................................................................. 14 21.4 Double-Way Rectifier ............................................................................................................. 15

i

Page 3: Edsa Paladin

DC Short Circuit

ii

22. Short Circuit Characteristics of DC Generators and Motors.......................................................... 16 22.1 Generator ............................................................................................................................... 16 22.2 Motors .................................................................................................................................... 17

23. ANSI DC Short Circuit Sample File................................................................................................ 19

24. IEC DC Short Circuit Sample File .................................................................................................. 26

List of Figures

Figure 1 Typical DC System .......................................................................................................................1 Figure 2 125 V Class 1E DC System Key Diagram....................................................................................2 Figure 3 125 1E DC System Instrumentation and Alarms..........................................................................2 Figure 4 Diagram of a Feeder Short Circuit ................................................................................................6 Figure 5 Resistance Diagram for DC System of Figure 4 ..........................................................................6 Figure 6 Inductance Diagram for DC System of Figure 4...........................................................................7 Figure 7 One line Diagram of Figure 4........................................................................................................7

Note: You can view this manual on your CD as an Adobe Acrobat PDF file. The file name is:

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

C:\DesignBase\Samples\DCSC = DC Short Circuit Test Files: DC_sc2, DC_scge, Iec1

Page 4: Edsa Paladin

DC Short Circuit

DC POWER SYSTEM

1. Introduction DC auxiliary power systems play an important role in power generating station control, and in providing backup power in emergency situations. Because of its inherent reliability, battery-supplied DC power is the last chance of the electrical source for powering essential services in the event of a failure of the AC power system. The battery supplies emergency power for circuit breaker control, protective relaying, instrumentation, inverters, emergency lighting, communications, annunciators, fault recorders and auxiliary motors.

Generally, the DC system includes motors, generators, rectifiers, batteries, electrolytic cells and synchronous converters. A typical DC system consists of three major components: a battery, a charger and a distribution system. Normally, the battery is float-charged by the battery charger; that is, the battery charger supplies all continuous loads connected to the bus and supplies power to the battery to maintain it in a full state of charge. Under normal conditions the battery does not supply any loads, but is held in the fully charged conditions to supply the DC loads if all AC sources to the battery charger are lost.

Figure 1 Typical DC System The following diagram has been copied with permission of IEEE Standard Committee.

1

Page 5: Edsa Paladin

DC Short Circuit

2

Figure 2 125 V Class 1E DC System Key Diagram

Figure 3 125 1E DC System Instrumentation and Alarms

Page 6: Edsa Paladin

DC Short Circuit

2. Program Capabilities This program is capable of calculating the short circuit values of loop and radial DC systems. It can handle multiple sources of short circuit, contributing loads, and all the present classes of DC motors and generators. It can also handle islanding and user defined motors and generators. This program is user friendly and can be a very powerful tool for professional engineers and designers in short circuit analysis of DC systems. The DC Short Circuit Analysis program can calculate short circuit of batteries, rectifiers, generators, and any combination of these sources of faults. The values of short circuit are calculated for every bus. DC branch current can also be calculated. CLASSIFICATION OF DC MOTORS

CLASS = "MA" CLASS = "MB" CLASS = "MC" CLASS = "MD"

Pole face winding No No No Yes Temp. rise C40° C40° C50/40 °° °40 and C60°Loading Continuous Continuous Nema Continuous Ventilation Open Open Open Forced and Open Speed Constant Constant Adjustable Adjustable Volts, Rated 115 230-250 230 230-750 Field Winding Shunt or

compound wound Shunt or compound wound

Shunt or compound wound

Shunt or compound wound

CLASS = "ME" Curve X Curve Y

Pole face winding No No Temp. rise C75° C75° Loading 1 Hour 1 Hour Ventilation Self-closed Self-closed Speed Adjustable Adjustable Volts, Rated 230 230 Field Winding Compound wound Series

CLASSIFICATION OF DC GENERATORS

Class CLASS = "GA" CLASS = "GB" CLASS = "GC" CLASS = "GD"

Pole face winding No No Yes Yes Temp. rise 40° C 40°/50° C 40° C 40° C Loading Continuous Continuous Continuous Continuous Ventilation Open Open Forced and open Forced and open Speed Constant Constant Constant Constant Volts, rated 120, 125 230-250, 300,

600 250 600, 750

Field winding Shunt or compound wound

Shunt or compound wound

Shunt or compound wound

Shunt or compound wound

3

Page 7: Edsa Paladin

DC Short Circuit

3. Number of Batteries As a minimum, a separate battery shall be provided for each engineered safety feature (ESF) division to make it independent. In nuclear power stations, for example, in a unit with four reactor protection channels, four batteries should be provided. 4. Number of Chargers and Distribution Panels As a minimum, one battery charger and the corresponding main distribution panels should be provided for each battery. Standby chargers should be considered for increased operating flexibility. 5. System Voltage Considerations The nominal voltages of 250, 125, 48 and 24 are generally utilized in station battery systems. The type, rating, cost, availability, and location of the connected equipment should be used to determine which nominal battery voltage is appropriate for a specific application. A 250 V battery is typically used to power motors for emergency pumps, and large inverters. A 125 V battery is typically used for control power for most relay logic circuits, and the closing and tripping of switchgear circuit breakers. A 48 V or 24 V battery is typically used in subsystems, as for example in specialized instrumentations. 6. Determination of Battery Duty Cycle The battery duty cycle is the load current versus time demand placed on the battery during the loss of AC power. It generally consists of various loads applied and removed during a defined period of AC power loss. Examples of such loads are: - Switchgear and load center control, tripping, closing, and indicating devices; - Inverter (DC to AC) loads; - Emergency turbine lube-oil pump; - Protective relaying; - Fire protection; - Annunciators; - Turbine-generator excitation breakers and controls; - DC emergency lighting; - Communications. The application, removal, and duration of such loads produce a load current profile of the battery known as the battery duty cycle. The duty cycle must be developed during the design of the DC system as per IEEE standard 485-1983 (5). The system designer must analyze the loads, anticipate at what times they are to be energized,

4

Page 8: Edsa Paladin

DC Short Circuit

and for how long. The DC requirements can be first tabulated and then charted for easy analysis. For example, the batteries are to supply power to the system for approximately one minute (the time between loss of off-site power and the loading of the local generator) if, after such time, the charger output and the DC loads return to normal. Such a design would be the minimum period meeting the single failure criteria. More often, the overall period of the battery duty cycle is estimated at 0.5, 1, 2, or 4 hours. After the magnitude, the time duration of each component load, and the overall period have been determined, each battery duty cycle should be constructed.

7. Battery Size (Capacity) Battery sizing is a process in which the purchaser, using the duty cycle, defines the needs of the system and, with the help of technical information supplied by the vendors, matches the requirements to standard cell designs. In general, the positive-plate design defines the cell type, and the number of plates defines the cell capacity. By varying the number of plates, a vendor is able to offer a variety of standard-size cells. Sizing may be determined by using the procedures outlined in IEEE standard 485-1983 (8).

8. Sources of Short Circuit Current The sources of short circuit current in direct current systems include motors, generators, rectifiers, batteries, etc. The short circuit characteristics in each case include equivalent circuits to represent the particular source when calculating the current initial rate of rise and the maximum short circuit current.

9. Bus Short Circuit Current Calculation The calculation of short circuit current for a bus fault can generally be done by considering each source individually, and then summing up the individual current to find the total short circuit current in the system. 10. Feeder Short Circuit Calculation A short circuit on a feeder will result in the current from all of the courses flowing together through the system elements. Refering to Fig. 4 for the indicated short circuit location, the current from all three sources must flow through a common feeder from the bus to the short circuit location. The calculation of the short circuit current in this case is performed with the aid of two-system diagrams: an inductance diagram and a resistance diagram. 11. Resistance Diagram The resistance diagram for a direct current system is similar to a system one-line diagram and shows all of the system resistances and is shown in Fig. 5. The values for the internal resistances of the sources of the short circuit current are determined on the basis of the short circuit characteristics presented in the preceeding sections. This diagram is used to calculate the maximum short circuit current for a short circuit at any point in the system. The resistances can be combined in parallel, or series, until one equivalent system resistance is determined to represent the system from the point of short circuit back to the voltage source. The total maximum short circuit current is then calculated by using this equivalent system resistance in the following expression:

5

Page 9: Edsa Paladin

DC Short Circuit

IT = EReq

amps

Where E = System voltage (Volts); Req = Equivalent system resistance (ohms); IT = Total maximum short circuit current (amps).

Figure 4 Diagram of a Feeder Short Circuit

Showing The Current Sharing The Path Through The Common Circuit Element.

Figure 5 Resistance Diagram for DC System of Figure 4

12. Inductance Diagram The inductance diagram for the DC system is also similar to a one-line diagram, and shows all the inductances in the system, and is shown in Fig. 6. The inductance values for the sources of short circuit current can be determined from the characteristics given in the preceding sections. The inductance diagram can be handled in the same manner as the resistance diagram. The inductances can be combined as parallel, or series, elements

6

Page 10: Edsa Paladin

DC Short Circuit

until one equivalent inductance is obtained to represent the entire system from the point of short circuit back to the voltage source. The equivalent inductance is then used to calculate the initial rate of rise of the total short circuit current from the expression:

diTdt

= ELeq

amps per second

Where Leq = Equivalent system inductance (henries).

Figure 6 Inductance Diagram for DC System of Figure 4

Figure 7 One line Diagram of Figure 4 Tc = Time Constant

= LeqReq

Sec.

7

Page 11: Edsa Paladin

DC Short Circuit

13. IEC DC Short Circuit Calculations The IEC DC short circuit calculation is calculated in accordance with IEC 61660. The EDSA program calculate the: Ik - Quasi steady state short circuit current Ip - Peak short circuit current Tp - Time to peak (ms) T1 - Rise time of the standard approximation function (ms) T2 - Decay time constant of the standard approximation function (ms) For detailed analysis and formulae refer to the standard. 14. References 1. Linville, T. M., "Current and Torque of D-c Machines on Short-circuit," AIEE

Transactions, Vol. 65, Part I, pages 394-402;1946.

2. Linville, T. M. and Ward, H. C., Jr., "Solid Short-circuit of D-c Motors and Generators," AIEE Transactions, Vol. 68, Part I, pages 119-124; 1949.

3. McClinton, A. T., Brancato, E. L. and Panoff, Robert. "Transient Characteristics of D-c Motors and Generators," pages 1100-1106.

4. "Maximum Short-circuit of D-c Motors and Generators," AIEE Committee Report, AIEE Transactions, Vol. 69, Part I, pages 146-149; 1950.

5. Darling, A. G.; Linville, T. M., "Rate of Rise of Short-circuit Current of D-c Motors and Generators," AIEE Transactions, Vol. 71, Part III, pages 314-325; 1952.

6. Jensen, L. E., Rettig, C. E.; "Regulation Curves and Transient Current of Double-way and Double-wye Rectifiers," AIEE TP 55-65.

7. Dortort, I. K., "Extended Regulation Curves for Six-phase Double-way and Double-wye Rectifiers," AIEE Transactions, vol. 72, pt. 1, pp. 192-198, 1952/53.

8. "Protection of Electronic Power Converters", AIEE Committee on Electronic Power Converters, AIEE Trans., vol. 69, pt. 2, pp. 818-829, 1950.

9. Herskind, C. C., "Rectifier Fault Current, II," AIEE Trans., vol. 68, pt.1, pp. 243-251; 1949.

10. Dortort, I. K., "Equivalent Machine Constants for Rectifiers," AIEE Trans., vol. 72, pt. 1, pp. 435-438; 1952/53.

11. Dillard, I. K.; Baldwin, C. J., Jr. "Rectifier Arc-back Study on the Analogue Computer," AIEE Trans., vol. 73, pt. 1, p. 198;

12. Jensen, L. E., "Mercury Arc Rectifier D-c Short-circuit Current Transients," DF-53-AD-38.

13. Schmidt, A., Jr., "Fault Current in D-c Systems Which Include Rectifiers," DF-86706.

14. IEC 61660 “ Short Circuit Currents in d.c. Auxiliary Installations in Power Plants and Substations” Part 1, 2, and 3

8

Page 12: Edsa Paladin

DC Short Circuit

Tutorial 15. Tutorial Introduction This tutorial illustrates step-by-step instructions for creating a DC system and performing DC short circuit current calculations. The purpose of the tutorial is to familiarize the user with many of the functions of DesignBase program (i.e. data entry, performing analysis and reporting). Tutorial overview: 1. DesignBase DC Short Circuit Current Analysis Capabilities 2. Required Data For Performing DC Short Circuit Current Study 3. Start DesignBase program 4. Define Bus Record 5. Define Branch Record 6. Run DC Short Circuit Current Study and Review and Print Report 16. DesignBase DC Short Circuit Current Analysis Capabilities The DesignBase DC Short Circuit Analysis program is capable of calculating the short circuit values of a loop and radial DC systems. It can handle multiple sources of short circuit, contributing loads, and all present classes of DC motors, DC generators and rectifiers. The short circuit values are calculated for every bus, and the DC branch current can also be calculated. There may be multiple batteries or generators in a DC distribution system. Each SC bus code (ie. battery, rectifier, generator and DC motor) has its own pick list. 17. Required Data for Performing DC Short Circuit Current Study In order to perform the calculations, the network topology must be defined. The required information are: 1. DC system alignment 2. Cable data: from/to, length, and size 3. Sources of short-circuit current (i.e. battery, rectifier, DC generator and/or DC motor)

The network file is made up of three parts: Master information, Nodes and Branches. 18. DC System Short Circuit Current Calculations The sources of short circuit current in DC systems include batteries, rectifiers, motors, generators, etc. The short circuit characteristics in each case include equivalent circuits to represent the particular source when calculating the current initial rate of rise and the maximum short circuit current. The calculation of short circuit current for a bus fault can generally be done by considering each source individually, then summing up the individual current to find the total short circuit current in the system. A short circuit on a feeder will result in the current from all of the sourses flowing together through the system elements.

9

Page 13: Edsa Paladin

DC Short Circuit

The resistance diagram for a DC system is similar to a system one-line diagram and shows all of the system resistances. The resistances can be combined in parallel or series until one equivalent system resistance is determined to represent the system from the point of short circuit back to the voltage source. The total maximum short circuit current is then calculated using this equivalent system resistance in the following expression:

= SCI EReq

amps

Where, E = System voltage (Volts) Req = Equivalent system resistance (Ohms) = Total maximum short circuit current (Amps) SCI The inductance diagram for the DC system is also similar to a one-line diagram, and shows all the inductance in the system. The inductance diagram can be handled in the same manner as the resistance diagram. The inductance can be combined as parallel, or series, elements until one equivalent inductance is obtained to represent the entire system from the point of short circuit back to the voltage source. The equivalent inductance is then used to calculate the initial rate of rise of the total short circuit current from the expression:

secondper amps LeqE

dtdiT

=

Where, Leq = Equivalent system inductance (henries) The time constant is the time after the fault at which the current is equal to 63.2% of the maximum short circuit value. Therefore, the total short circuit current has a value equal to 63.2% at E/Req at a time of Leq/Req seconds after the short circuit occurs. Also, at a time equal to two (2) times the time constants, the short circuit current is equal to approximately 87% of the maximum short circuit current. Therefore,

Tc = Time Constant = LeqReq

Sec.

19. Time Constant and Rate of Rise of Short Circuit Current The inductance (LBC) in the equivalent circuit represents the inductance of the conductors connecting the cells.

RB LC Rcir+Rcell

Battery TerminalsEB

The initial maximum rate of rise of the short circuit current is: .secper amps

LCC + LBCEB

dtBdI =

10

Page 14: Edsa Paladin

DC Short Circuit

Where, LCC = Inductance of battery cells connector (Henries) LBC = Inductance of battery circuit (Henries) The inductance (in Henries) is calculated as follows: Henries

60Hz)Freq377(for X

Frequency*PI*2X L

===

Time Constant: TC = Sec.

Req)LBCLCC( +

20. Short Circuit Characteristics of Battery If the user select ANSI standard for the short circuit calculations then the available types of battery are:

1. Custom (IEEE) 2. Max Short Circuit @ Terminal 3. 1 Minute 4. 8 Hour Rating 5. IEC 61660 Model

If Battery type selected is Custom (IEEE) then the battery resistance Rb is calculated from the battery curve in the library in accordance with IEEE 946-1992.

NpII

VVRcell /1221⎟⎠⎞

⎜⎝⎛

−−

=

and Rb = Rcell x Nc Where; V1, V2, I1, I2 are the battery initial voltages and current from the battery library Np is the number of positive plate Nc is the number of cells

Otherwise; The battery internal resistance (RB) of the battery is determined by the formula: RB =

Idc x MFEB

Where: RB = Battery internal resistance EB = Battery actual voltage Idc = Battery DC rated current in amps MF = Short-circuit current Multiplying Factor

11

Page 15: Edsa Paladin

DC Short Circuit

For MF, 10 times the one minute ampere rating (based on IEEE std. 946-1992 Section 7.9.1), 100 times eight-hour-ampere-rating, or the maximum short-circuit current may be used to calculate the battery internal resistance. If custom rating is selected, the battery equivalent R (OHMS) and X (OHMS) can be entered. The total equivalent resistance is equal to: eqR

CellBatteryeq RRR +=The maximum short circuit current (IB) is calculated by: IB = amps

Rcell + RBEB

21. Short Circuit Characteristics of Power Rectifier The available types of rectifier are:

1. Custom 2. Max Short Circuit @ Terminal 3. Double-Wye Rectifier 4. Double-Way Rectifier 5. Synchronous Converter 6. Power Rectifier

Power rectifiers are a major source of power for direct current systems in industry. Knowledge of the short circuit characteristics of the power rectifier is essential for engineers who operate and design direct-current systems that incorporate a rectifier. The material presented here will provide assistance in determining the short circuit characteristics of the power rectifier. For more detailed information refer to the GE Industrial Power System Data book. The determination of rectifier short circuit characteristics (i.e. current-time curve for a bolted fault at the rectifier terminals) is fairly simple, since the AC system (rectifier transformer included) is the controlling factor. It is necessary to develop an equivalent circuit to represent the rectifier for short circuit calculations. This rectifier equivalent circuit would have an equivalent resistance and an equivalent inductance that would be used as constants for calculating DC fault current. The equivalent impedance for every type of rectifier is addressed in detail later in this tutorial.

21.1 Power Rectifier The following information are needed to define a Power Rectifier.

System Volt: Rectifier rated voltage Rated DC Current: Rectifier rated current (Amps) Per Unit Z: Rectifier per unit AC impedance (If total AC Z is known, this value is

12

Page 16: Edsa Paladin

DC Short Circuit

calculated automatically)

The rectifier Total AC Z (Ohms) is equal to:

currentDCRatedRectifier Voltage Actual x2.3unit x per Zac(ohms) Z =

The rectifier equivalent resistance (RR) is calculated as follows:

current DC RatedRectifier x 1.15Voltage Actualunit x per ZacRR =

The rectifier equivalent inductance (henries) is equal to:

IDS*Frequency x 6Voltage ActualLR =

Where, IDS = Rectifier Short-Circuit Current (amps) for bolted fault

unit-per Zac(Idc)Current DC RatedRectifier x 1.02IDS =

The rectifier reactance

XR = 2*PI*Frequency*LR

21.2 Synchronous Converter The following information is needed to define a Synchronous Converter.

System Volt: Rectifier rated voltage Rated DC Current: Rectifier rated current (Amps) PU Resistance: Rectifier per-unit resistance, used to calculate the rectifier resistance

(RR) PU Rate of Rise: Current rate of rise, used to calculate the rectifier inductance (Henries)

The synchronous converter resistance (RR) is equal to:

Current DC RatedRectifier Voltage Actual* resistance PU RR =

The synchronous converter inductance (LR) is equal to:

(Henries) RiseofRatePU*Current DC RatedRectifier

Voltage Actual LR =

The rectifier reactance

XR = 2*PI*Frequency*LR

13

Page 17: Edsa Paladin

DC Short Circuit

21.3 Double-Wye Rectifier

The following information is needed to define a Double-Wye Rectifier.

System Volt: Rectifier rated voltage Rated DC Current: Rectifier rated current (Amps) Per Unit AC Z: Rectifier per unit AC impedance (If total AC Z is known, this value is

calculated automatically) AC Resistance: Total AC resistance including rectifier transformer and AC system AC Reactance: Total AC reactance including rectifier transformer and AC system

It should be noted that:

( ) ( )22 Reactance AC Resistance AC ZAC Total += The rectifier Total AC Z (Ohms) is equal to:

currentDCRatedRectifier Voltage Actual x2.3unit x -per Zac(ohms) Z =

The short circuit current is calculated in accordance with the methodology of GE Industrial Power Systems Data Book (Section .172) The resistance and reactance constants (K3 & K4) for determining peak fault current factor (K1) are calculated as follows:

Reactance ACReactanceCircuit *2 3K =

Reactance ACResistanceCircuit *2 Resistance AC 4K +

=

The rectifier equivalent inductance (henries) is equal to:

IDS*Frequency x 6Voltage ActualLR =

Where, IDS = Rectifier Short-Circuit Current (amps) for bolted fault

unit-per Zac(Idc)Current DC RatedRectifier x 1.02IDS =

The rectifier reactance

XR = 2*PI*Frequency*LR

14

Page 18: Edsa Paladin

DC Short Circuit

21.4 Double-Way Rectifier

The following information is needed to define a Double-Way Rectifier.

System Volt: Rectifier rated voltage Rated DC Current: Rectifier rated current (Amps) Per Unit AC Z: Rectifier per unit AC impedance (If total AC Z is known this value is

calculated automatically) Total AC Z: Rectifier AC impedance in Ohms impedance (If Per Unit AC Z is known

this value is calculated automatically) AC Resistance: Total AC resistance including rectifier transformer and AC system AC Reactance: Total AC reactance including rectifier transformer and AC system

It should be noted that:

( ) ( )22 Reactance AC Resistance AC ZAC Total +=

The rectifier Total AC Z (ohms) is equal to:

currentDCRatedRectifier Voltage Actual x0.6unit x -per Zac(ohms) Z =

The short-circuit current is calculated in accordance with the methodology of GE Industrial Power Systems Data Book (Section .172) The resistance and reactance constants (K3 & K4) for determining peak fault current factor (K1) are calculated as follows:

Reactance AC*2ReactanceCircuit 3K =

Reactance ACResistanceCircuit *0.5 Resistance AC 4K +

=

The rectifier equivalent inductance (henries) is equal to:

IDS*Frequency x 6Voltage ActualLR =

Where, IDS = Rectifier Short-Circuit Current (amps) for bolted fault

unit-per Zac(Idc)Current DC RatedRectifier x 1.02IDS =

The rectifier reactance

XR = 2*PI*Frequency*LR

15

Page 19: Edsa Paladin

DC Short Circuit

22. Short Circuit Characteristics of DC Generators and Motors It is not unusual for 15,000 kW of generation and a similar or greater amount of load to be connected to one bus at 600 Volts. Likewise, at 250 Volts, concentrations of several thousand killoWatts of source capacity and a similar amount of load on one bus are not uncommon. The magnitude of the short circuit current available from such concentrations of power is often not fully appreciated. This section presents the fundamental information on the short circuit characteristics of DC motors and generators. Knowledge of these characteristics should provide the practicing engineers a better appreciation of short circuit current. DC motors and generators are probably the most common sources of short circuit current in a DC system. The equivalent circuits used to represent the DC machine during short circuit is calculated in accordance with the methodology of GE Industrial Power Systems Data Book (Section .171).

22.1 Generator The available types of Generator are:

1. GA 120-125V, No Pole Face Winding 2. GB 230-250V, No Pole Face Winding 3. GC 250V, Pole Face Winding 4. GD 600-750V, Pole Face Winding 5. Custom

The following information is needed to define a generator.

Rated Volt: Generator rated voltage Generator Class: Available options are: Type GA, GB, GC, GD, custom Rated Output Power: Generator rated output in KW Rated Current: Generator rated current in Amps Rated Speed: Generator rated speed in RPM

Calculation of Generator Equivalent Resistance: The generator per-unit resistance (Rpu) is obtained by calculating (KW*Rated Speed/100,000). The actual resistance is calculated using the following formula:

Current DC RatedRpu * Voltage Rated RG(Ohms) =

For calculating short circuit current, the resistance is adjusted based on System Voltage:

2

SC Voltage SystemVoltage Rated*RG RG ⎟⎟

⎞⎜⎜⎝

⎛=

Calculation of Generator Equivalent Reactance: For Type GA, GC, and GD generator, the armature circuit unsaturated inductance in henries is calculated

16

Page 20: Edsa Paladin

DC Short Circuit

as follows:

(Henries) 1000*Current DC Rated*Frequency*120

Voltage Rated*Cx*19.1 Lgen =

For Type GA Cx = 0.6 For Type GC & GD Cx = 0.2 Xgen = 2*PI*Frequency*Lgen

For Type GB generator, the inductance in millihenries is based on (KW*Rated Speed/1000). For calculating rate of rise of short-circuit current, the reactance is adjusted based on System Voltage:

2

SC Voltage SystemVoltage Rated*Xeq XG ⎟⎟

⎞⎜⎜⎝

⎛=

22.2 Motors

The available type of Motors are:

1. MA 115V, No Pole Face Winding, Constant Speed 2. MB 230-250V, No Pole Face Winding, Constant Speed 3. MC 230V, No Pole Face Winding, Adjustable Speed 4. MD 250-700V, Pole Face Winding, Adjustable Speed 5. ME 230, No Pole Face Winding, Mill 6. Custom

The following information are needed to define a motor.

Rated Voltage: Motor rated voltage Motor Class: Available options are: Type MA, MB, MC, MD, ME, None (custom) Rated Output Power: Motor rated output in HP Rated Current: Motor rated current in Amps Rated Speed: Motor rated speed in RPM

For Type ME DC motors select winding type as Series or Compound winding. Calculation of Motor Equivalent Resistance: The motor per-unit resistance (Rpu) is obtained by calculating (HP*Rated Speed/100,000). The actual resistance is calculated using the following formula:

Current DC RatedRpu * Voltage Rated RM(Ohms) =

For calculating short circuit current, the resistance is adjusted based on System Voltage:

17

Page 21: Edsa Paladin

DC Short Circuit

18

2

SC Voltage SystemVoltage Rated*RM RM ⎟⎟

⎞⎜⎜⎝

⎛=

Calculation of Motor Equivalent Reactance: For Type MA, and ME motor, the armature circuit unsaturated inductance in henries is calculated as follows:

(Henries) 1000*Current DC Rated*Frequency*120

Voltage Rated*Cx*19.1 Lmotor =

For Type MA & ME Cx = 0.4 Xmotor = 2*PI*Frequency*Lmotor

For Type MB and MC motors, the inductance in millihenries is based on HP. For Type MD motors, the inductance in millihenries is based on (HP*Rated Speed/1000). For calculating rate of rise of short-circuit current, the reactance is adjusted based on System Voltage:

2

SC Voltage SystemVoltage Rated*XMotor XM ⎟⎟

⎞⎜⎜⎝

⎛=

Page 22: Edsa Paladin

DC Short Circuit

23. ANSI DC Short Circuit Sample File Please go to your DesignBase2\Samples\DCSC folder:

19

Page 23: Edsa Paladin

DC Short Circuit

Proceed to open the DC_sc2.axd file:

Click on the DC Short Circuit Tools icon as shown above. The DC Short Circuit Toolbar will appear (below):

20

Page 24: Edsa Paladin

DC Short Circuit

The icon Option: allows the user to select the Default Output: Annotation or Report and Contribution levels away, as can be seen in the capture figure below:

21

Page 25: Edsa Paladin

DC Short Circuit

Report Manager:

This feature allows the user to select: Output Reports:

Time Constant / Rate of Rise; Matrices;

Input Data; Abbreviation; Report Style Unit; Print Style; Unit Settings.

22

Page 26: Edsa Paladin

DC Short Circuit

Back Annotation: The user can select: Color and Font; Components to be displayed; Unit: Volatge;

Current; Capacity.

23

Page 27: Edsa Paladin

DC Short Circuit

Click “Analyze” icon. The analysis will run and the below screen is displayed. The output results are sent to a file browser, where it can be printed, saved to a file, or sent to the clipboard to be pasted in a word document. From the main menu press “Clipboard”, then , then “Done”. The output report is displayed below. The DC Short Circuit report is displayed: EDSA DC Short Circuit v6.00.00 Project No.: DC Short Circuit Page : 1 Project Name: Date : 10/31/08 Title : Time : 11:01:04PM Drawing No.: Company : Revision No.: Engineer : JobFile Name: DC_SC2 Check by : Scenario : 1: CheckDate: Base kW : 100 Cyc/Sec : 60 -------------------------------------------------------------------------------- DC Short Circuit Tutorial ----------------------- System Information ----------------------- Total Number of Nodes Entered: 7 Total Number of Nodes: 7 Total Number of Branches: 6 Number of Active Sources: 3 Number of Inactive Sources: 0 Number of Active Motors: 1 Number of Inactive Motors: 0 Number of Open Switches: 0 Number of Islands: 1 Matrix Size: 28 Elements 224 Bytes Calculation Methodology: Classical

24

Page 28: Edsa Paladin

DC Short Circuit

EDSA DC Short Circuit v6.00.00 Project No.: DC Short Circuit Page : 2 Project Name: Date : 10/31/08 Title : Time : 11:01:04PM Drawing No.: Company : Revision No.: Engineer : JobFile Name: DC_SC2 Check by : Scenario : 1: CheckDate: Base kW : 100 Cyc/Sec : 60 -------------------------------------------------------------------------------- DC Short Circuit Tutorial --------------- Bus Results --------------- Thevenin Resistance Inductance Sustain Time Const Rate of Rise Bus Name Cd mOhms mH Amps mSec Amps/Sec ------------------------ -- ---------- ---------- ------- ---------- ------------ BATT-1A BT 5.2373 0.00016 47734.8 0.0302 1580054144 CHARGER RT 5.3699 0.00327 46555.5 0.6097 76357096 GEN-A GN 7.1272 0.00359 35077.0 0.5040 69592672 GEN-BUS 8.0138 0.00333 31196.2 0.4159 75003112 MAIN-BUS 5.1183 0.00307 48843.9 0.6005 81338008 MOTOR MT 20.9434 0.00360 11936.9 0.1720 69415592 MTR-BUS 14.0026 0.00334 17853.9 0.2384 74904192

25

Page 29: Edsa Paladin

DC Short Circuit

24. IEC DC Short Circuit Sample File From the DesignBase2\Samples\DCSC folder open file IEC1.AXD.

By clicking on the DC Short Circuit icon the DC Short circuit tool bar below will appear.

26

Page 30: Edsa Paladin

DC Short Circuit

By clicking on the options icon the following screen is activated. The user can select the Default Output and contribution levels.

27

Page 31: Edsa Paladin

DC Short Circuit

By clicking on the report manager icon the user will have the option to display in the report the input data, output results or save to a file by selecting the desired data to be displayed. The square next to each category will change its color from black to red (Black – turned off, Red- data to be displayed in the output report). By pressing OK, the analysis will run and the output report is displayed.

28

Page 32: Edsa Paladin

DC Short Circuit

Click Analyze. The output report is sent to the clipboard to be pasted in a word document. From the main menu press clipboard, then “OK”, then “Done”. EDSA DC Short Circuit v6.00.00 Project No.: Page : 1 Project Name: Date : 10/31/08 Title : Time : 11:10:25PM Drawing No.: Company : Revision No.: Engineer : JobFile Name: IEC1 Check by : Scenario : 1: CheckDate: Base kW : 100 Cyc/Sec : 50 -------------------------------------------------------------------------------- ----------------------- System Information ----------------------- Total Number of Nodes Entered: 7 Total Number of Nodes: 7 Total Number of Branches: 6 Number of Active Sources: 2 Number of Inactive Sources: 0 Number of Active Motors: 1 Number of Inactive Motors: 0 Number of Open Switches: 0 Number of Islands: 1 Matrix Size: 28 Elements 224 Bytes Calculation Methodology: IEC61660

29

Page 33: Edsa Paladin

DC Short Circuit

EDSA DC Short Circuit v6.00.00 Project No.: Page : 2 Project Name: Date : 10/31/08 Title : Time : 11:10:25PM Drawing No.: Company : Revision No.: Engineer : JobFile Name: IEC1 Check by : Scenario : 1: CheckDate: Base kW : 100 Cyc/Sec : 50 -------------------------------------------------------------------------------- ---------------------- Impedance Matrix ---------------------- Bus Name R (ohms) L (mH) ------------------------ ------------ ------------ BATTERY 0.00591 0.02168 CAP 0.00590 0.02203 CHARGER 0.00590 0.02203 F1 0.00590 0.02203 F2 0.00604 0.02577 F3 0.00705 0.02961 MOTOR 0.00604 0.02577

30

Page 34: Edsa Paladin

DC Short Circuit

EDSA DC Short Circuit v6.00.00 Project No.: Page : 3 Project Name: Date : 10/31/08 Title : Time : 11:10:25PM Drawing No.: Company : Revision No.: Engineer : JobFile Name: IEC1 Check by : Scenario : 1: CheckDate: Base kW : 100 Cyc/Sec : 50 -------------------------------------------------------------------------------- --------------- Bus Results --------------- Sustain Peak Peak Rising Decline Thevenin Ik Ip Tp T1 T2 Bus Name Cd R(Ohm) L (mH) Amps Amps mSec mSec mSec ------------------------ -- ------- ------- ------- ------- ------- ------- ------- BATTERY BT 0.0059 0.0217 42276 51446 11.00 3.67 100.00 CAP CP 0.0059 0.0220 42358 51926 11.20 3.73 100.00 CHARGER RT 0.0059 0.0220 42359 51935 11.20 3.73 100.00 F1 0.0059 0.0220 42359 51935 11.20 3.73 100.00 F2 0.0060 0.0258 41395 50094 12.80 4.27 100.00 F3 0.0070 0.0296 35463 41575 12.60 4.20 100.00 MOTOR MT 0.0060 0.0258 41395 50094 12.80 4.27 100.00 EDSA DC Short Circuit v6.00.00 Project No.: Page : 4 Project Name: Date : 10/31/08 Title : Time : 11:10:25PM Drawing No.: Company : Revision No.: Engineer : JobFile Name: IEC1 Check by : Scenario : 1: CheckDate: Base kW : 100 Cyc/Sec : 50 -------------------------------------------------------------------------------- -------------------- Branch Results -------------------- Branch Currents in Amps Fault at Fault at Fault at Fault at Fault at Fault at Branch Name BATTERY CAP CHARGER F1 F2 F3 ------------------------ ------- -------- -------- -------- -------- -------- BATTERY ->F1 -26077 15312 15312 15312 14882 12750 F1 ->F2 -4509 -4677 -4677 -4677 36625 31377 F2 ->F3 35463

31

Page 35: Edsa Paladin

DC Short Circuit

32

EDSA DC Short Circuit v6.00.00 Project No.: Page : 5 Project Name: Date : 10/31/08 Title : Time : 11:10:25PM Drawing No.: Company : Revision No.: Engineer : JobFile Name: IEC1 Check by : Scenario : 1: CheckDate: Base kW : 100 Cyc/Sec : 50 -------------------------------------------------------------------------------- -------------------- Branch Results -------------------- Branch Currents in Amps Fault at Branch Name MOTOR ------------------------ ------- BATTERY ->F1 14882 F1 ->F2 36625


Recommended