Voltages, currents and frequencies for three-phase chokes
used for current compensation and filter circuits

The currents of the choke are calculated for 100% ED at 1,3 times the 50 Hz rated current (like capacitors conform to VDE 0560). They have the following harmonics:

Harmonic           Frequency         Current
-----------------------------------------
       1.                50 Hz        1,06 x I_N
       3.               150 Hz        0,04 x I_N
       5.               250 Hz        0,31 x I_N
       7.               350 Hz        0,13 x I_N

Reduction factor: Rectifier and inverter generate harmonics in networks, which lead to extra losses, especially in capacitors of current compensation systems. A choke brings the following advantages:

• less losses and no overload of the capacitors in current compensation systems
• improvement of the impedance characteristics of the net
   

Calculation of the factor:

p = X_L / X_C

where        X_L  = inductive reactance
                X_C  = capacitive reactance

Resonance frequency: In case of resonance of the series resonant circuit choke - capacitor we get:

f_Res = f _Net /

for 50 Hz net frequency the resonance frequency is calcualted with p = 0,07

f_Res = 50 Hz /  = 189 Hz

These 189 Hz are above the net frequency and below the 5. critical harmonic wave of 250 Hz

Standards:     VDE 0550, VDE 0532, IEC 76

Test voltage:   2500 V_eff winding - core

Reactance compensation in nets with audible frequency ripple control systems (TRA)

Audible frequency ripple control systems are used in supply nets of EVUs, to do circuits via connected receivers, like tarif changes and so on. The supply net is interfered with higher frequency control voltages (audible frequency impulse), usual are frequencies in a range of 166 Hz to 1350 Hz.
The impedance factor α* is the relationship of audible frequency impedance to 50 Hz impedance of the customer system.
At an impedance factor of α * ≥ 0,5, you don’t have to deal with disturbances of ripple control systems.

Influence of compensation systems without the reduction factor

A not reduced compensation system creates a resonant circuit with the reactive net impedance. The resonance frequency “fr” of this resonant circuit decreases with increasing compensation power. Near to the resonance frequency, the impedance of the resonant circuit has very low resistance and can damp the control voltage level of the audible frequency significantly.

Critical ripple control frequencies in teh range of 270 Hz up to 425 Hz

If audible frequency trap circuit areas (range 270 Hz up to 425 Hz) are slotted in ahead of the not reduced compensation system, there is a higher possibility of resonance in close vicinity to the 5. and 7. harmonic wave.

Further terms to this topic:

Reactance current, iron core choke, harmonic waves, filter choke, fourier analysis, harmonics