Definition
DC chokes and AC line reactors are usually defined by their impedance as a ratio Z% commonly referred to per unit. To refer to this or any other number in this paper in percent, multiply by 100 and add the % symbol. Examples: 0.03 becomes 3% and 5% equals 0.05. If L is the inductance value of the choke and f is the frequency of the mains power supply, Z% is defined by:
Z is a virtual impedance defined by:
Where:
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V is the RMS value of the phase-to-neutral voltage of the mains power supply and
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I1 is the RMS value of the fundamental current in one phase.
Z% becomes:
For 3-phase drives, I1 can be calculated using the active power Pactive at the drive input:
Where:
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φ1 is the phase shift angle of current I1 to the phase-to-neutral voltage V of the mains power supply.
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cosφ1 ≈1 for drives
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U is the RMS value of the phase-to-phase voltage of the mains power supply:
Z% becomes:
Pactive can be calculated by:
Z% becomes:
A 3% choke is defined by Z% = 3%, which means:
