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Power systems, explained
Short pages that each explain one concept in plain English, with a diagram you can play with. You do not need Phasor to learn here — but each page shows you where the concept appears in the software.
Fundamentals
- PhasorsOne arrow that describes a full sine wave.
- Three-phase systemsWhy the grid uses three waves, 120 degrees apart.
- Wye & delta connectionsSame parts, same supply — three times the power in delta.
- Active & reactive powerP does the work. Q holds the voltage. S is the total.
- ImpedanceResistance, reactance, and how a network pushes back.
- The per-unit systemOne scale for every voltage level in the network.
- Voltage dropWhy the voltage falls along a feeder, and what controls it.
- Thévenin & grid strengthAny network, seen from one bus: a source and an impedance.
Power flow
- Power flow basicsWhat the study answers, what it needs, and what it returns.
- Power through a lineTwo voltages and an impedance set P, Q and direction.
- Bus typesSlack, PV and PQ: what is fixed, and what the solver finds.
- Nodal analysis & the Y-busThe whole network as one matrix, built branch by branch.
- Newton–RaphsonHow the solver finds the answer: guess, measure, correct.
- Load modelsConstant power, current or impedance — and why the choice matters.
- Voltage bandsThe rule that decides what counts as a violation.
- Voltage & reactive-power controlThe four levers that hold a bus voltage — and their limits.
Faults & protection
- Short circuit basicsWhat happens in a fault, and what sets the current.
- Fault typesThree-phase, line-to-line, and faults to earth.
- Symmetrical componentsHow one unbalanced problem becomes three balanced ones.
- Sequence networksThree simple circuits, wired differently for each fault.
- Transformer vector groupsDyn11 decoded: windings, neutrals, and the 30° clock.
- Fault current valuesI″k, ip, Ib and Ik — four numbers with four jobs.
- X/R ratio & peak currentWhy the first peak is the biggest, and what κ means.
- Earthing arrangementsThe neutral connection that sets the earth-fault current.
- TCC curves & gradingTime–current curves, and devices that wait their turn.
- Earth-fault loop impedanceThe LV check that proves a fault trips the breaker.
- Protection zonesEvery meter protected twice: primary first, backup in reserve.
- Directional overcurrentWhen amps alone cannot tell which side the fault is on.
- CT saturationWhen the current transformer can no longer copy the fault.
Power quality
- Unbalance & neutral currentUnequal phase loads, and where the difference flows.
- HarmonicsDistorted waves are sums of clean ones.
- Triplen harmonics in the neutralWhy third harmonics stack in the neutral instead of canceling.
- Harmonic aggregationHarmonic sources add as phasors, not as amps.
- ResonanceWhen a capacitor bank and the network make an amplifier.
- Passive harmonic filtersA tuned trap for one harmonic — and the new peak it creates.
- THDOne number for how distorted a wave is.
- Motor starting & voltage sagSix times the current, and the whole bus feels it.