Voltages, currents and frequencies of chokes


Rated voltage: 3 x 400 V constructed for the 3., 5. and 7. harmonic
Rated inductance: according to table
Rated current: according to table

The choke currents are calculated for 100 % ED to 1,3 times 50 Hz nominal current (like capacitor conform to VDE 0560) with the following harmonic current.

Harmonic

Frequency

Current

1.
3.
5.
7.

50 Hz
150 Hz
250 Hz
350 Hz

1,06 x INom
0,04 x INom
0,31 x INom
0,13 x INom

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 = XL / XC
where XL = inductive reactance
           XC = capacitive reactance

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

fRes = fmains / wurzel-p

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

fRes = 50 Hz / wurzel007 = 189 Hz

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

Reduction factor

Resonance frequency

5,5 %
7 %
14 %

214 Hz
189 Hz
134 Hz

Standards: VDE 0550, VDE 0532, IEC 76
Test voltage: 2500 Veff 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 a* is the relationship of audible frequency impedance to 50 Hz impedance of the custoemr system. At an impedancefactor of a* > 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 the 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.
Further terms to this topic:
Reactance current, iron core choke, harmonic waves, filter choke, fourier analysis, harmonics


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