Question

A three-phase diode bridge rectifier is feeding a constant DC current of \(100\;A\) to a highly inductive load. If three-phase, \(415\;V,\;50\;Hz\) AC source is supplying to this bridge rectifier then the rms value of the current in each diode, in ampere, is _____________.

Answer 1

Concept:

In a three-phase diode bridge rectifier, each diode conducts for 120° out of 360°.

The average value of the current through each diode \({{I}_{DA}}=\frac{{{I}_{0}}}{3}\)

The RMS value of the current through each diode \({{I}_{DR}}=\frac{{{I}_{0}}}{\sqrt{3}}\)

Calculation:

In a three phase diode bridge rectifier,

RMS value of diode current \(= \frac{{{I_0}}}{{\sqrt 3 }}\;\)

Given that \({I_0} = 100\)

\(\Rightarrow \frac{{{I_0}}}{{\sqrt 3 }} = \frac{{100}}{{\sqrt 3 }} = 57.7\;A\)

Important Points:

In a three-phase full converter,

The average value of the source current (ISA) = 0

The rms value of the source current \({{I}_{SR}}={{I}_{0}}\sqrt{\frac{2}{3}}\)

The average value of the current through each diode \({{I}_{DA}}=\frac{{{I}_{0}}}{3}\)

The rms value of the current through each diode \({{I}_{DR}}=\frac{{{I}_{0}}}{\sqrt{3}}\)