ETAP 5.0 DC Load Flow DC Short-Circuit
Copyright 2003 Operation Technology, Inc.
Why DC System Studies? DC systems play an ever increasing role in: • Substation and generating station instrumentation and control systems (IEEE Std 946) • Class 1E power system for nuclear power generation station – providing power to reactor trip system and engineered safety features (IEEE Std 308) • Provide back-up energy for emergencies in hospital, generation station, production line, data processing and communication, etc. (IEEE Std 446 Orange Book) Copyright 2003 Operation Technology, Inc. – Workshop Notes: DC Load Flow/DC Short-Circuit
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Why DC System Studies? Due to the importance of DC systems, it must be: • Reliable – Having redundant sources and can operate under single failure in the system • Adequate – Capable of providing sufficient power at required system voltage in specified time duration
Copyright 2003 Operation Technology, Inc. – Workshop Notes: DC Load Flow/DC Short-Circuit
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Type of Studies • Load Flow – Determine system operating conditions and verify equipment continuous ratings • Short-Circuit Calculation – Determine system SC current and verify equipment SC capability • Battery Sizing and Discharge Calculation (IEEE Std 485) – Determine sufficient battery size to provide required power in specified time duration • Control System Diagram, Vd Calc – Determine and verify sufficient voltage for control circuit operation Copyright 2003 Operation Technology, Inc. – Workshop Notes: DC Load Flow/DC Short-Circuit
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DC System Elements • DC System Source – Charger/Converter and Battery
• DC System Loads – Static Load, DC Motor, Lump Load , and DC Elementary Diagram
• DC System Branch – Cable and Impedance
• DC System Other Elements – Bus and Node, DC Converter, DC Composite Motor, and Inverter Copyright 2003 Operation Technology, Inc. – Workshop Notes: DC Load Flow/DC Short-Circuit
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Purpose of DC LF Study • To determine system operating conditions -bus voltages, branch flows, and power provided by various sources • To verify equipment continuous ratings
Copyright 2003 Operation Technology, Inc. – Workshop Notes: DC Load Flow/DC Short-Circuit
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LF -- Battery Model • Constant voltage source behind battery resistance . • Active voltage source if Vbus < Vrate • Inactive voltage source if Vbus > Vrate
Copyright 2003 Operation Technology, Inc. – Workshop Notes: DC Load Flow/DC Short-Circuit
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LF -- Charger Model • Constant voltage source, if I < Imax • Constant current source, if I > Imax, injecting Imax into system • Inactive if Vout < Vbus • Constant power load to AC system
Copyright 2003 Operation Technology, Inc. – Workshop Notes: DC Load Flow/DC Short-Circuit
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LF -- Inverter Model • Constant voltage source to AC system • Constant power load to DC system
Copyright 2003 Operation Technology, Inc. – Workshop Notes: DC Load Flow/DC Short-Circuit
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LF -- UPS Model • If auction diode option is checked, then DC system provides power to UPS AC load if Vdc > Vac. • If auction diode option is not checked… – and UPS AC input bus is energized, then UPS becomes a source to DC system, similar to a charger. – and UPS AC input bus is not energized, then DC system provides power to UPS AC load.
• Constant power load to DC system Copyright 2003 Operation Technology, Inc. – Workshop Notes: DC Load Flow/DC Short-Circuit
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LF -- DC Converter Model • Constant voltage source to output bus, if IImax, injecting Imax into the bus • Constant current load to the input bus • Inactive if Vout < Vbus
Copyright 2003 Operation Technology, Inc. – Workshop Notes: DC Load Flow/DC Short-Circuit
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LF -- Load Model • Motor – Constant P load, if Vmin
• Static Load – Constant resistance load
• Lumped Load – Constant power, resistance, current load
• Elementary Diagram Load – Constant resistance load Copyright 2003 Operation Technology, Inc. – Workshop Notes: DC Load Flow/DC Short-Circuit
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Constant Power Loads • DC Motor • DC Lumped Load (motor load part) • Inverter • UPS
Copyright 2003 Operation Technology, Inc. – Workshop Notes: DC Load Flow/DC Short-Circuit
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Constant Impedance Loads • Static Load • DC Elementary Diagram Editor • DC Lumped Load (static load part)
Copyright 2003 Operation Technology, Inc. – Workshop Notes: DC Load Flow/DC Short-Circuit
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Constant Current Loads • The current remains constant even if the voltage changes. • DC Constant current loads are used to test Battery discharge capacity. • DC Lump load can be used to represent constant current load.
Copyright 2003 Operation Technology, Inc. – Workshop Notes: DC Load Flow/DC Short-Circuit
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LF -- Branch Model • Cable – Constant resistance at maximum operating temperature
• Impedance – Constant resistance
Copyright 2003 Operation Technology, Inc. – Workshop Notes: DC Load Flow/DC Short-Circuit
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LF- Adjustments • Cable Length Tolerance – Positive adjustment for DCLF & DCBS – Negative adjustment for DCSC
• Cable Resistance based on Temperature – Copper / Aluminum – Use Maximum Temperature for DCLF & DCBS – Use Minimum Temperature for DCSC
Copyright 2003 Operation Technology, Inc. – Workshop Notes: DC Load Flow/DC Short-Circuit
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Purpose of DC SC Study • To determine short-circuit fault currents and fault contributions from different sources. – Maximum fault current – System equivalent impedance at fault location – Time constant for SC current rise
• To verify protective equipment capability.
Copyright 2003 Operation Technology, Inc. – Workshop Notes: DC Load Flow/DC Short-Circuit
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SC -- Battery Model • Constant voltage source -- (Voc) behind battery resistance – Voc may be calculated based on battery specific gravity (SG) – Open Circuit Voltage (Voc) from library – User-Defined value (% Vpc)
• Constant current source – Ksc * One_Min_Discharge_Current Copyright 2003 Operation Technology, Inc. – Workshop Notes: DC Load Flow/DC Short-Circuit
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SC -- Charger Model • Constant voltage source behind AC system impedance (converted to DC side) • Constant current source, Ksc * Ifl
Copyright 2003 Operation Technology, Inc. – Workshop Notes: DC Load Flow/DC Short-Circuit
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SC -- UPS & Inverter Model • UPS -- Constant current source Ksc * Ifl
• Inverter -- Not considered in DC short-circuit study
Copyright 2003 Operation Technology, Inc. – Workshop Notes: DC Load Flow/DC Short-Circuit
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SC -- DC Converter Model • Constant current source, Ksc * Ifl, to faults on output side of the system • Short-circuit contribution calculation stops at DC converters
Copyright 2003 Operation Technology, Inc. – Workshop Notes: DC Load Flow/DC Short-Circuit
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SC -- Load Model • Motor – constant voltage behind transient impedance • Static load and ED load are considered in calculation
Copyright 2003 Operation Technology, Inc. – Workshop Notes: DC Load Flow/DC Short-Circuit
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SC -- Branch Model • Cable – Constant resistance at minimum operating temperature
• Impedance – Constant resistance
Copyright 2003 Operation Technology, Inc. – Workshop Notes: DC Load Flow/DC Short-Circuit
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