Cuarto año Power quality · tool
Calculadora de desbalance de tensión
Enter three line-to-line voltage readings (or three line currents). The tool gives the average, the largest deviation from it, and the percent unbalance — and for voltages, the negative-sequence unbalance too.
- Promedio—
- Desviación máxima respecto al promedio—
- Desbalance (desviación máx. ÷ promedio)—
- Desbalance de secuencia negativa—
Mostrar el cálculo
Aritmética con sus tres lecturas. Cuánto desbalance aguanta un motor, y cuánto hay que reducir su capacidad, lo dicen los datos del fabricante del motor.
Guardar estos resultados
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How it works
- Average = (A + B + C) ÷ 3of the three readings
- % = max |reading − avg| ÷ avg × 100the field definition
- VUF = V negative ÷ V positive × 100sequence method, from line-to-line magnitudes
Worked: 460, 467 and 450 V
- Average = (460 + 467 + 450) ÷ 3 = 459 V.
- Deviations: 1, 8 and 9 V. The largest is 9 V (the 450 reading).
- Unbalance = 9 ÷ 459 × 100 = 1.96%.
- On a motor, expect the current unbalance to be several times that — measure it and compare.
Preguntas frecuentes
Why does a small voltage unbalance matter to a motor?
An unbalanced supply contains a small negative-sequence voltage — a component trying to turn the motor backwards. The motor’s impedance to it is low, so a few percent of voltage unbalance drives a much larger percentage of current unbalance, and that extra current is pure heat in the windings. Motor makers publish how much a motor must be derated for a given unbalance.
Should I measure line-to-line or line-to-neutral?
Line-to-line for a three-phase motor — that is what the motor sees, and it is what the negative-sequence figure here is built for. The percent-deviation method works with either, as long as all three readings are the same kind.
What is the difference between the two percentages?
The first is the common field definition: the largest difference from the average, divided by the average. The second is the "true" unbalance — the negative-sequence voltage as a percentage of the positive-sequence voltage — calculated from the three line-to-line readings. For small unbalances they come out close; the field figure is the one most motor data is written against.
Where does unbalance come from?
Single-phase loads spread unevenly across the phases, a blown fuse in a capacitor bank, a bad connection or a high-resistance contact on one leg, an open-delta supply, or unequal transformer taps. Find it by measuring at points going upstream until the unbalance disappears.
Ver también
- Unbalanced loads and neutral current
- Power quality and harmonics
- Motor troubleshooting flowcharts — runs hot? check this first
- Cómo usar un multímetro
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