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Technology / Engineering guide
Active, Reactive & Apparent Power in Wind Projects
A kW rating, a kVA value and a kvar requirement describe different electrical quantities. Define the measurement boundary and applicable waveform conditions before comparing them. A turbine nameplate does not provide every converter or load rating.
Keep the quantity and its definition together.
Power factor relates active and apparent power; it is not a generator efficiency measurement.
01 / Active power
Distinguish average transfer from a voltage-current product.
Active power is the average of instantaneous voltage multiplied by current over the stated measurement period.
Active power is the average of instantaneous voltage multiplied by current over the stated measurement period. It is expressed in watts or kilowatts. The averaging basis and direction convention belong with a measured value.
RMS voltage multiplied by RMS current is not generally the same active power. Tektronix’s AC-power reference explains why waveform and phase relationships matter. A voltage and current display alone cannot justify an assumed kW result.
02 / Apparent power
Use VA without relabelling it as useful kW.
For a single electrical path, apparent power is the product of RMS voltage and RMS current, expressed in VA.
For a single electrical path, apparent power is the product of RMS voltage and RMS current, expressed in VA. Multi-phase totals require a stated definition appropriate to the system and instrument.
The confirmed MARSTON turbine ratings are 5, 10, 20, 30 and 50 kW. They do not establish kVA ratings for every selected controller or converter. Keep the turbine rating and downstream equipment capacity as separate entries.
03 / Reactive power
Keep the definition’s conditions visible.
For a sinusoidal single-phase example, reactive power is associated with the quadrature relationship between voltage and current and is expressed in var.
For a sinusoidal single-phase example, reactive power is associated with the quadrature relationship between voltage and current and is expressed in var. The familiar relation S² = P² + Q² uses the corresponding sinusoidal definitions.
In a hypothetical sinusoidal example, 3 kW active power and 4 kvar reactive power correspond to 5 kVA apparent power. This is a mathematical illustration, not a MARSTON capability. Do not extend the simple triangle to an unspecified distorted or unbalanced measurement.
04 / Power factor
Separate true and displacement definitions.
For a consistently defined path, power factor is active power divided by apparent power.
For a consistently defined path, power factor is active power divided by apparent power. HIOKI’s terminology distinguishes this ratio from displacement power factor based on the fundamental phase relationship. With distorted waveforms, those two definitions need not give the same value.
Power factor does not express conversion efficiency. Efficiency compares energy or power across input and output boundaries; power factor compares quantities at one electrical boundary. A low or high value also does not prove a specific fault or control feature.
05 / Direction and time
Record signs and aggregation with the values.
Identify whether positive power means generation, consumption, import or export in the actual record.
Identify whether positive power means generation, consumption, import or export in the actual record. Reactive sign and lead/lag labels can also depend on documented conventions. Do not combine records merely because their units match.
Retain whether each value is instantaneous, an interval average or another reported statistic. Summing powers across devices requires comparable timing and boundaries. The interface guide helps identify those physical locations.
06 / Capability review
Separate a reported value from controllable range.
A measured kvar value does not establish a converter’s supported reactive-power range.
A measured kvar value does not establish a converter’s supported reactive-power range. Likewise, a power-factor display does not prove an adjustable power-factor function. Review the actual equipment evidence for any required capability.
Use the power-quality guide for broader connection assessment. No MARSTON power factor, reactive-control range or kVA output rating is asserted here; the proposed package needs its own documented interface.
Continue the review with Wind Power Harmonics & THD Measurement Records.
Continue the review with Wind Power Meter CT Ratios & Data Scaling.
Continue the review with Wind Power Load-Step Response: Evidence Review.
Continue the waveform quantity review with RMS, peak and crest factor.
General background: Tektronix: active and apparent power, power factor and sinusoidal limitations · HIOKI 3196 terminology: power factor and displacement power factor. These references explain industry concepts; they are separate from the applicable MARSTON product and project documents.
Prepare the information for this review.
Use the checklist to organise the project information. Mark unavailable items and retain document references.
| Review item | Information to provide | Purpose |
|---|---|---|
| Quantity | P, Q or S with units and definition | Avoid substituting kW, kvar and kVA. |
| Boundary | Measurement location and included paths | Compare like electrical points. |
| Conditions | Waveform and phase-system assumptions | Use applicable relationships. |
| Sign and time | Direction convention and aggregation period | Interpret recorded values. |
| Capability evidence | Selected equipment range and applicable conditions | Separate measurement from functionality. |
Engineering questions.
Are kW and kVA interchangeable?
No. They describe active and apparent power respectively.
Is power factor the same as efficiency?
No. They compare different quantities and boundaries.
Does the simple power triangle apply to every waveform?
No. Retain the sinusoidal and system-definition conditions.
Does a kvar reading prove reactive-power control?
No. A measured quantity is different from an adjustable capability.
Do the five turbine kW ratings confirm converter kVA?
No. The selected converter has its own documented capacity.
What should accompany a power value?
Quantity definition, units, boundary, signs, time basis and applicable waveform conditions.
Technical enquiry
Bring your project information to the discussion.
A kW rating, a kVA value and a kvar requirement describe different electrical quantities. Share the available information and the equipment scope you want reviewed in a technical quotation.