Tech Tip

MTE   USING 3-PHASE REACTORS ON SINGLE PHASE APPLICATIONS


The illustration shown below (Figure 1) demonstrates how a 3-phase line reactor can be used for a single-phase application. Using the mathematical method described below, you can calculate the inductance to determine what type of reactor is needed.

Reactors for Single Phase Applications

MTE three-phase Line/Load Reactors can be Figure 1 used for single-phase applications by routing each of the two supply conductors through an outside coil, and leaving the center coil disconnected. For the drive input application shown in Figure 1, the incoming supply lines connect to terminals A1, C1, and outgoing  lines from A2, C2. The "B" terminals for the center coil are not connected. The sum of the inductance of the two coils is the total inductance applied to the circuit.

As an example, consider a single-phase application of 2HP supplied by 240VAC. The reactor must carry 12A (fundamental current) according to the NEC table for single-phase motor current. A 5% impedance is desired. For a 60Hz supply, the formula to calculate required inductance is:  L = (ZV) / (377I), where L is inductance in Henries, Z is percent impedance, V is supply voltage, and I is full load amps.

For above example:  0.00265 = (0.05 x 240) / (377 x 12), indicating a total required inductance of 2.65mH. Based upon this result, MTE part number RL-01201, which has an inductance per coil of 1.25mH, a fundamental current rating of 12A, and a maximum continuous current rating of 18A will work. When connected for a single-phase application, the sum of the two coils will provide a total inductance of 2.5mH, or an effective impedance of 4.7%, calculated as Z = (I x 377 x L) / V, or .047 = (12 x 377 x .0025) / 240. For a 50Hz supply, modify the formulas by substitution of the factor 314 in place of 377.


Single-Phase Motor Drive Applications Selection Table
These selections provide typical percent impedance rating of 5%

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3phaseReactor (rev#1-10/17/02)