The neutral current in a three-phase, four-wire wye system represents the imbalance of the three-phase conductors, also known as the "hot" conductors. If the three hot conductors are equal, as in the case of supplying a three-phase motor, there is no imbalance and the neutral current is zero. In a single-phase system, the neutral carries only the imbalance of the two hot conductors, an easy calculation. However, in a three-phase wye system, even if only two of the three phases and the neutral run a single-phase load, you must use the neutral formula.
Things You'll Need
- Scientific calculator
- Pencil or pen
Note the neutral formula. If A, B and C are the three phase currents, the formula to find the neutral current is the square root of the following: (A^2 + B^2 + C^2 - AB - AC - BC).
Use example phase currents of five amps, eight amps and 10 amps. Square each of the phase currents and add the total of the three numbers. Using these examples, the squared numbers are 25, 64 and 100. The sum of these numbers is 189.
Subtract each multiplied pair of numbers from the current total. AB, or five multiplied by eight, is 40; AC, or five multiplied by 10, is 50; and BC, or eight times 10, is 80. The total of these numbers is 170. This number subtracted from 189 leaves 19.
Take the square root of the calculated number. The resulting number is the neutral current. The neutral current in the example is about 4.36 amps.
- "Electricity 3: Power Generation and Delivery"; Jeffrey J. Keljik; 2009
- Photo Credit electric scheme image by Sergey Galushko from Fotolia.com
How to Calculate Three Phase Amperage
Three phase power circuits are often used in power transmission lines and large electric motors because they allow lower line voltages and...
How to Calculate 3 Phase Power
A 3-phase power circuit consists of three conductors of alternating current combined into a single power line. The current in each conductor...
How to Calculate Transformer Inrush
Inrush transformer current is the current a transformer experiences when first turned on. It's an instantaneous current that ramps up quickly and...
How to Calculate Three-Phase Power & kWh
Three-phase power is used primarily in power distribution systems such as the power systems that power homes and businesses. Three-phase is referred...
How to Calculate a Single-Phase Transformer
In a single-phase power distribution system, all the voltages of the supply vary in unison; in contrast, a three-phase system is where...
How to Calculate 3-Phase Line-To-Ground Voltage
Three-phase systems are prevalent in many power distribution systems. This is because 3-phase systems have built in efficiencies for high power transmission...
How to Calculate Voltage Imbalance
Voltage imbalances apply in 3-phase power distribution systems. In a 3-phase system, three separate lines carry three identical alternating currents that are...
Single Phase Vs. Three Phase Wiring
Electric utility companies generate three-phase power for transmission and distribution to customers. Commercial and industrial customers, along with some farms, make up...