Transmission & Grid calculator
Transmission Ring-Bus Load Flow Calculator
Calculate ring-bus section voltages, incoming-circuit power and losses. Open or close six breakers to study bus splitting and source connectivity.
GridBasis: Six-position ideal-breaker topology · balanced AC load flow
Results
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How to use this calculator
A transmission ring bus is a substation switching arrangement. It is different from a transmission network whose lines form a geographic loop. This calculator represents six substation circuit positions and the breakers linking adjacent positions. Incoming circuits enter at positions 1 and 4; outgoing demands occupy positions 2, 3, 5 and 6.
With all breakers closed, the ring is one electrical bus. Opening one breaker leaves the remaining path connected. Opening two breakers may divide it into sections; power is redistributed through whichever incoming circuits remain connected. A section without a source path is reported as an island, and the tool withholds a solved network result.
Closed breakers are ideal connections. Their individual current split cannot be uniquely obtained from this merged-bus model. Results therefore show incoming-circuit currents and section voltages, not invented ring-breaker currents or interrupting-duty ratings.
Formula
Closed breaker: Vposition_i = Vposition_j
Connected positions are merged using graph connectivity. Demands on each merged section are summed, then AC nodal power balance is solved.
Ssection = −Σ (Pload + jQload); Sᵢ = Vᵢ conj(ΣYᵢⱼVⱼ)
Iincoming (A) = |Sincoming (MVA)| × 1000 / [√3 × kVnominal × |Vsource,p.u.|]
Breaker B1 connects positions 1–2; B2 connects 2–3; B3 connects 3–4; B4 connects 4–5; B5 connects 5–6; B6 connects 6–1. Two incoming transmission circuits attach at positions 1 and 4.
Worked example
Load the default 230 kV example: four 25 MW / 8 MVAr demands, 100 MVA base and two identical incoming impedances of 0.01 + j0.10 p.u. With the full ring closed, incoming circuits share the demand and losses equally. Open B2 and B5 to form two separately supplied sections. Open B1 and B2 to isolate position 2; the tool reports a source-disconnected island.
With all six breakers closed, the ring voltage is approximately 1.018290 p.u. at −2.619°. Total active loss is 0.5316 MW; each incoming circuit supplies approximately 129.41 A at the remote source end.
Assumptions and standards
- Both incoming circuits connect to the same remote slack source. Separate source angles, generator controls and independent source voltages are not represented.
- Balanced steady-state loads and series incoming line impedances. No line charging, busbar impedance, CTs or fault model.
- Ring section membership is based on ideal closed-breaker connectivity; all displayed voltages use the nominal ring kV base.
Calculation model checked: November 4, 2026
Frequently asked questions
Does opening one ring-bus breaker split the bus?
Normally the other five closed breakers still provide a connected path around this six-position model. Two or more openings can split the bus.
Can I obtain current through each ring breaker?
Not from ideal merged nodes: internal loop-current sharing is indeterminate. A breaker-duty study requires the actual physical impedances, circuit connections, fault cases and protection assumptions.
Is an unsupplied island a converged load-flow result?
No. This calculator flags a disconnected section and does not display a solved result for the complete network.
Can I use these results for final design?
Use them for preliminary design and checking. Final designs must be verified by a qualified engineer against the code edition and standards adopted where the work is installed.
Is my data sent anywhere?
No. Every calculation runs in your browser. Nothing you type is uploaded or stored on our servers.
References and further reading
Power system calculations: formulas and model guide