Three Phase Commutation Choke

The commutation choke is connected in the front of the rectifier, on the AC side, in order to limit the current rise during current commutation between 2 phases (short circuit operation mode over the commutating choke). In order to limit the DC voltage drop to 3-4%, the short circuit voltage has to be between 4 and 6%.

Note that the non-linear RC&RL&R rectifier load, with or without DC current smoothing choke, is the source of high current harmonics between 150Hz and 1000Hz. The size and the frequency range of the current harmonics depends on the DC output power and the rectifier type (View the design example about rectifier transformers).

Here is the design example about the 3 phase commutation choke in front of the bridge rectifier with the DC current smoothing choke.

– DC output voltage Udc=510V
– DC output current Udc = 100A
– Phase input voltage U = 0.427*(1.05*Udc+2*Udiode) =230V
– Net 3 x 400/230V, 50Hz
– AC nominal Current, 50Hz I = 0.779*Idc = 77.9A
– Inductance = 1000*0.04*U/I/(2*pi*f)=0.376 mH
– Peak current Ip=Idc=100A
– L-Type = 2
– Rectangular Cu wire
– Thermal currents.

Smoothing Choke 0 >>0

Harmonic	Current rms	Angle	I22k.rms/ldc	Angle
1	80.8	0	077.9	0
5	17.7	180	15.5	180
7	8.8	180	11.1	180
11	7.1	0	7	0
13	05	1080	6	0

– Ambient temperature Ta = 40°C
– Temperature rise dT=75°K
– Contibuous operation mode
– GO steel, not annealed
– Gap=4, 3 gaps per leg
– Gap fixing plate 2mm, insulation
– UP00, dry, no ventilation, no cooling channels
– RacRdc =1.3, no wires in parallel

INPUT

TEST

In the Test mode you can modify the caöculated parameters by hand:
– Turbs
– Wire size
– Use more wires&foils in parallel
– Ambient trmperature
– Gap
– Steel
– Currents.

Here is the result of the design: click here to get the results.

Note:
In order to calibrate the choke, connect it on the calculated calibration AC-voltage (rms value) with the calibration frequency (normally 50Hz or 60Hz) and then vary the gap until you get the calculated calibration AC-current (rms value).