Choke Design for Rectifier - WHY USE LOW GRADE CORE STEEL?
----------------------------------------------------------------------Consider the design of a single phase 500A DC choke with:
Inductance=0.0005H
Rated DC current= 500A
Ripple AC current = 80A rms at 300Hz (6x 50Hz=300hz)
It is to be used in a 3 phase circuit with a 3 phase supply transformer.
AC volts across choke terminals:
0.0005 x 2 x 3.1415x 300x 80=75.3V rms
Watts /kg=0.85
Core weight=85kg
Core losses=72.3watts
Assume the cross sectional area of the core is 193mm2 (gross)
Turns=15
Flux density =0.2Tesla
Core space factor=0.95
What type of core material should be used?
GOSS or NON-GOSS?
Use NON-GOSS - It will work AFFECTIVLEY and is more economical.
-----------------------------------------------------------------------WHY?
Look at the graph - the flux density is low; the core losses are low
Bdc=0.95Tesla
Bac=Vx10**8/4.44xNXAxSFxf =2055 gauss = 0.2Tesla (LOW!)
Btot = Bdc+Bac=1.14Tesla
The KNOWLEDGE GAP HERE IS:
--------------------------------Bdc does not conribute to the iron losses ; only the AC FLUXDENSITY
-------------------------------------------------------------------------CONCLUSION:
Hence a low grade core material can be used for the core of the choke, as the AC flux
density is low and the AC cores losses are low.
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