Given

The rectification efficiency of a single-phase Half Wave Controlled Rectifier can be calculated using the following formula:

Rectification Efficiency = (Vdc / Vm) * 100

Where:
Vdc = Average output DC voltage
Vm = Maximum value of input voltage

To find the average output DC voltage, we need to consider the waveform of the rectifier. In a half-wave rectifier, only one half of the input waveform is utilized, resulting in a pulsating DC output. The delay angle, also known as the firing angle, determines the portion of the input waveform that is rectified.

In this case, the delay angle is given as π/2, which means the rectifier starts conducting at the peak of the input waveform. This implies that the rectifier conducts for only half a cycle.

Let's consider a sinusoidal input voltage waveform:

Vm = Vpeak * sin(ωt)

Where:
Vpeak = Peak value of input voltage
ω = Angular frequency
t = Time

During the conduction period, the output voltage can be approximated as:

Vdc = (2 * Vpeak / π) * (1 - cos(ωt))

The average value of this output voltage can be calculated by integrating it over the conduction period and dividing it by the total time:

Vdc_avg = (2 * Vpeak / π) * (1 - (1/π))

Vdc_avg = (2 * Vpeak / π^2)

The maximum input voltage Vm is equal to Vpeak. Therefore, the rectification efficiency can be calculated as:

Rectification Efficiency = (Vdc_avg / Vm) * 100

Substituting the values, we get:

Rectification Efficiency = ((2 * Vpeak / π^2) / Vpeak) * 100

Rectification Efficiency = (2 / π^2) * 100

Rectification Efficiency ≈ 20.23%

Therefore, the rectification efficiency of a single-phase Half Wave Controlled Rectifier with a resistive load and a delay angle of π/2 is approximately 20.23%.