ETAP - unbalanced load flow

1. ETAP Workshop Notes © 1996-2009 Operation Technology, Inc.
Unbalanced Load Flow

2. Slide 2© 1996-2009 Operation Technology, Inc. – Workshop Notes: Unbalanced Load Flow Analysis
Real Unbalanced Power
Systems
• Distribution System
– 3-phase, 2-phase, and single-phase network
components
– Unbalanced loads
• Transmission System
– Untransposed long transmission line
– Abnormal operation with one phase out of service
– Unbalanced loads (e.g., electrical railway traction
motors)

3. Slide 3© 1996-2009 Operation Technology, Inc. – Workshop Notes: Unbalanced Load Flow Analysis
Harmful Effects of System
Unbalance
• Overheating of generators
• Nuisance tripping of protective relays
• Increased real power losses
• Transformer failure
• Radio communication interference

4. Slide 4© 1996-2009 Operation Technology, Inc. – Workshop Notes: Unbalanced Load Flow Analysis
Unbalance Factors/Indexes
• System unbalance is considered by power
quality standards as a disturbance
• Voltage/Current unbalance factors
• Ratio of zero/negative sequence to positive
sequence
• Voltage/Current unbalance indexes
• Ratio of average values to maximum
deviation of average values

5. Slide 5© 1996-2009 Operation Technology, Inc. – Workshop Notes: Unbalanced Load Flow Analysis
Unbalanced Load Flow
Analysis
• Current Injection (CI) method
• The most robust algorithm ever developed
• Converge in less iterations than other
methods, especially for heavily loaded
systems
• Sparse matrix technique
• Unique modeling concepts

6. Slide 6© 1996-2009 Operation Technology, Inc. – Workshop Notes: Unbalanced Load Flow Analysis
Sequence Models of
3-Phase Machines

7. Slide 7© 1996-2009 Operation Technology, Inc. – Workshop Notes: Unbalanced Load Flow Analysis
Unique Concepts of
3-Phase Machines
• Swing Machine
– The specified magnitude and the phase angle of the
positive sequence voltage only at the swing machine
terminal
• PV Machine
– The specified total output of 3-phase real powers and
the magnitude of the positive sequence voltage
• PQ Machine
– The specified total outputs of 3-phase real and reactive
powers

8. Slide 8© 1996-2009 Operation Technology, Inc. – Workshop Notes: Unbalanced Load Flow Analysis
Concepts of Load
Connections
• Single-Phase Loads
• Connected in the phase connection types of
AB, BC, CA, AN, BN or CN
• Three-Phase Loads
• Connected in Delta, Wye or Wye-G
• The constant individual powers in Wye are
not allowed due to multiple solutions

9. Slide 9© 1996-2009 Operation Technology, Inc. – Workshop Notes: Unbalanced Load Flow Analysis
Modeling Capabilities
• A mixture of 3-phase, 2-phase and single-
phase network components
• 3-phase machines with internal impedance
being considered
• Built-in calculator for overhead line
impedances
• Mutual coupling among overhead lines
• Transformers combined with load tap
changers (LTC) and phase shifters

10. Slide 10© 1996-2009 Operation Technology, Inc. – Workshop Notes: Unbalanced Load Flow Analysis
Modeling Capabilities
• 2-winding and 3-winding transformers of
various winding connections
• Lumped loads consisting of constant power,
constant impedance and constant current
components
• Generator exciters with AVR or Mvar / PF
controllers
• Robust library of of commonly used
overhead transmission lines and cables

11. Slide 11© 1996-2009 Operation Technology, Inc. – Workshop Notes: Unbalanced Load Flow Analysis
Study Case
• Same pretense as Balanced Load Flow with
more detailed modeling, calculations, and
results

12. Slide 12© 1996-2009 Operation Technology, Inc. – Workshop Notes: Unbalanced Load Flow Analysis
Output Results
• State-of-the-art graphic display of
results
• Graphical display of marginal and
critical under/over voltages
• Alert View displays
limit violations

13. Slide 13© 1996-2009 Operation Technology, Inc. – Workshop Notes: Unbalanced Load Flow Analysis
Reporting
• Customized output reports using Crystal Reports®
• Individual phase and sequence voltage, current,
and power
• Voltage drops, losses,
power flows, power
factor, voltage/current
unbalance factors, etc.

14. Example 1
© 1996-2009 Operation Technology, Inc. – Workshop Notes: Unbalanced Load Flow Analysis

15. Slide 15© 1996-2009 Operation Technology, Inc. – Workshop Notes: Unbalanced Load Flow Analysis
Example 2
IEEE Four Node Test Feeder
• Characteristics of the Feeder
1. Two line segments with a 3-phase
transformer bank connected between the two
segments
2. Data is specified for balanced and
unbalanced loading at the most remote node
3. Transformer is specified for different
connection testing

16. Slide 16© 1996-2009 Operation Technology, Inc. – Workshop Notes: Unbalanced Load Flow Analysis

17. Slide 17© 1996-2009 Operation Technology, Inc. – Workshop Notes: Unbalanced Load Flow Analysis
Example 3
IEEE 13 Node Test Feeder
• Characteristics of the Feeder
1. Short and relatively highly loaded for a 4.16
kV feeder
2. Overhead lines with variety of phasing
3. Shunt capacitor banks
4. In-line transformer
5. Unbalanced loading

18. Slide 18© 1996-2009 Operation Technology, Inc. – Workshop Notes: Unbalanced Load Flow Analysis