21 - Dclf and Dcsc

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

Slide 2

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

Slide 3

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

Slide 4

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

Slide 5

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

Slide 6

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

Slide 7

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

Slide 8

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

Slide 9

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

Slide 10

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

Slide 11

LF -- Load Model • Motor – Constant P load, if Vmin