Understanding power flow analysis
Power flow analysis (also called load flow) calculates the steady-state operating conditions of your electrical system. It determines voltages, currents, and power flows throughout your single-line diagram after solving the power balance equations.
What power flow calculates
When you run power flow analysis, the engine calculates:
- Bus voltages (magnitude in per-unit and angle in degrees)
- Power injections at each bus (active power in MW, reactive power in MVAR)
- Line and cable currents (magnitude and direction)
- Power flows through cables and transformers (from and to each component)
- System losses (line losses and transformer losses)
- Generator output (real and reactive power)
- Load consumption (power draw and terminal voltage)
- Transformer loading (HV and LV side currents, percentage loading)
When to use power flow analysis
Run power flow analysis to:
- Verify that bus voltages stay within acceptable limits (typically ±5%)
- Check that cables and transformers are not overloaded
- Identify voltage drop issues before they cause equipment problems
- Calculate system losses for efficiency analysis
- Validate your design meets electrical requirements
- Size equipment based on actual operating conditions
Power flow analysis should be run after major changes to your diagram, such as adding loads, modifying transformer sizes, or changing cable types.
How the engine works
ekx uses PandaPower, a Python-based power flow engine, to solve the network equations. The engine:
- Converts your SLD components into a mathematical network model
- Sets up the power balance equations for each bus
- Solves the nonlinear equations using Newton-Raphson algorithm
- Iterates until the solution converges (typically 3-8 iterations)
- Extracts results for voltages, currents, and power flows
- Returns results to ekx for display on your diagram
The Newton-Raphson method is industry-standard and provides accurate results for most power systems. For radial distribution networks, the engine can also use faster backward-forward sweep algorithms.
Prerequisites for successful analysis
Before running power flow, ensure your diagram has:
- At least one utility feed or generator (power source)
- One bus designated as the slack bus (typically the utility connection point)
- All components properly connected with no isolated islands
- Valid voltage ratings for all buses
- Load values specified in MW and MVAR (or power factor)
- Transformer ratings (kVA, voltages, impedance)
- Cable parameters (length, conductor size, material)
Missing any of these elements will cause the analysis to fail or produce incorrect results.
Result types
Power flow provides three main result categories:
Voltage results:
- Magnitude (typically 0.95 to 1.05 per-unit for distribution systems)
- Angle (phase displacement from the reference bus)
- Deviation from nominal (shows overvoltage or undervoltage conditions)
Current results:
- Cable and line currents in kA or A
- Loading percentage (current vs rated capacity)
- Direction of power flow
Power results:
- Active power (MW or kW)
- Reactive power (MVAR or kVAR)
- Power factor at each bus
- Total system losses
Convergence and iteration
Power flow uses an iterative solution method. The algorithm:
- Starts with an initial voltage estimate (flat start at 1.0 pu)
- Calculates power mismatches at each bus
- Updates voltage estimates to reduce mismatches
- Repeats until mismatches are below tolerance (typically 1e-6)
Most systems converge in 3-8 iterations. If convergence fails after 100 iterations, check for:
- Isolated buses or network islands
- Missing slack bus
- Incorrect component parameters
- Extremely heavy loading conditions
Common applications
Power flow analysis is essential for:
- Distribution system design and planning
- Transformer sizing and selection
- Cable ampacity verification
- Voltage regulator placement
- Capacitor bank sizing for power factor correction
- Evaluating system expansion scenarios
- Compliance with utility interconnection requirements
Related topics
- Running power flow - Step-by-step guide to running analysis
- Interpreting results - Understanding annotations and severity levels
- Troubleshooting convergence - Fixing common analysis issues