Power Flow Studies Notes

Power flow analysis/studies is the preliminary step used in any Power Evacuation Studies.

Power flow calculations provide active and reactive power flows and bus voltage magnitude and their phase angle at all the buses for a specified power system configuration and operating condition subject to the generation and/or regulating capabilities of generators, synchronous condensers, static var compensators, HVDC controls, FACTS controllers, tap changing under load transformers and specified net interchange between individual operating systems (utilities). This information is essential for the continuous evaluation of the current performance of a power system and for analyzing the effectiveness of alternative plans for system expansion to meet increased load demand. These analyses require the calculation of numerous power flow cases for both normal, and emergency (contingency) operating conditions. The output from power flow studies often provide the initial conditions needed for other analysis, such as short circuit studies, transient stability, economic dispatch, dynamic stability studies.

Applications of Power Flow Study and Analysis

Power flow study has the following applications

1. Transmission expansion planning , operation planning
2. Distribution expansion planning , operation planning
3. Industrial/Commercial distribution system planning, operational planning
4. Network interconnection, Grid interconnection studies
5. Evaluation of energy transactions between various stake holders
6. Energy audit to accurately determine network losses and estimate billing losses if any
7. Sizing of transformers, cables, overhead lines, transformer tap ranges, shunt capacitors, shunt reactors, reactive power management, FACTS devices, HVDC operation
8. System security assessment via static contingency studies
9. Decision making tool in operation planning and operation of the system in load dispatch center
10. Motor starting studies using load flow type analysis, where the starting impedance of the Induction motor is modeled as constant impedance model with starting impedance.
11. Evaluation of static voltage stability using load flow technique

The following general criteria of acceptability of design is used in power flow studies

1. Voltage Drop at all buses should be within +/- 5% of the nominal rating for all operating conditions considered
2. No over load conditions of any electrical circuits for all operating conditions considered
3. Reactive power generation/import/export to be within specified limits for all operating conditions considered
4. Ensuring quality power supply to all loads, under specified contingency conditions, as per design philosophy adopted.

The following study cases/ power flow outputs are generally considered in power flow studies

1. Extreme operating conditions of maximum and minimum loading conditions will be considered to check the adequacy of the network, even though some of these conditions may not exist during normal operation
2. Contingency conditions such as outage of lines, transformers, generators will be considered and network adequacy for power evacuation will be assessed
3. Operating solutions such  as transformer taps, Generator Excitation, shunt reactive power compensations will be provided as needed.
4. Recommendations for strengthening and equipment upgradations will be provided to meet specific operating requirements.
5. Summary of load flow studies and concise reports in tabular formats and single line diagram formats will be provided, along with the summary of recommendations.