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 and utility output (real and reactive power, and power factor)
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)
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 utility feed and generator, marked leading or lagging
Total system losses

Source voltage and power factor

Each utility feed holds its connection at its Operating Voltage, a percent of nominal set on the utility's Study tab. The default is 100. Enter 104 to study a utility that runs 4% high; every bus it feeds rises with it. A scenario can override the operating voltage, so one scenario can run the utility high while the base design stays at nominal. Short-circuit and arc flash studies do not use it: they keep their own pre-fault voltage basis.

Each utility feed and generator shows its power factor after power flow, for example PF 0.891 lagging:

Lagging means the source supplies reactive power to the system, the usual case for motors and other inductive load.
Leading means the source absorbs reactive power, for example when capacitor banks supply more reactive power than the load uses.

The load flow report lists the same power factor in its utility feed and generator tables.

How loads, capacitor banks and reactors are modelled

Each load follows its Load Characteristic: constant power holds its power as voltage changes, constant current holds its current, and constant impedance draws power in proportion to the square of the voltage. Loads with different characteristics on one bus keep their own characteristic, so the power drawn from the source always equals the power the loads use plus the losses.

A capacitor bank is its own component. Power flow models it as a fixed admittance:

Q = Rated kvar × (Energized Steps / Installed Steps) × (V_terminal / V_rated)²

The bank also draws a small active power of Losses × kvar. Only the energized steps count: a bank with zero energized steps gives zero output. A reactor load with complete settings is also a fixed admittance: it gives its rated kvar at its rated voltage and frequency, and its output scales with the square of the terminal voltage. Operating load profiles (peak, minimum) do not scale a bank or reactor. A capacitor bank contributes no fault current, so short-circuit and arc flash results do not change when a bank is switched in or out.

A capacitor bank shows its kW, kvar, current, and output as a percent of the rated output of its energized steps. A bank whose terminal voltage is above 110% of its rated voltage, the continuous limit in IEEE Std 18, shows its terminal voltage in amber with Above 110% rated V, and the load flow report lists it under Overvoltage Conditions. The report's Capacitor Bank Results table lists every bank.

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
No connected utility feed or generator
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

Running power flow - Step-by-step guide to running analysis
Interpreting results - Understanding annotations and severity levels
Troubleshooting convergence - Fixing common analysis issues