Specifying a DC Choke
by J.A. Edwards – Engineer
Express Transformers manufactures D.C.Chokes to Customers Requirements but to ensure the most economical design, the following parameteres should be specified:
Inductance and Tolerance
Nominal DC Current
Thermal Rating (RMS Current)
Permissable roll-off at overload
Insulation Class and Maximum Temperature Rise
Maximum System Voltage for insulation purposes.
Explanation of Roll-off
The most economical design is one that uses the smallest gap that will withstand the D.C. magnetisation without saturation. Often some saturation and hence a lower inductance is permissable at overload levels and this can be catered for in the design.
The Ripple Frequency if not specified will be assumed to be 300Hz.
The Ripple Amplitude if not specified will be assumed to be insignificant.
Insulation Classes from Class A(105øC) through to Class H(180øC) are available.