Given:
- Three phase bridge inverter
- Fed from a 500 V DC source
- Operated at 180°C conduction mode
- Supplying a purely resistive, star-connected load

To find:
- RMS value of the output (line) voltage

Explanation:
To find the RMS value of the output voltage, we need to consider the operation of the three-phase bridge inverter and the properties of a resistive load.

Three-Phase Bridge Inverter:
A three-phase bridge inverter consists of six switching devices (typically MOSFETs or IGBTs) arranged in a bridge configuration. The switching devices are controlled to generate a three-phase AC output voltage from a DC input source.

Conduction Mode:
The inverter is operated in the 180° conduction mode, which means that each phase of the output voltage is present for 180° of the output cycle. During this time, the corresponding switching devices are turned on, allowing current to flow through the load.

Purely Resistive Load:
A purely resistive load means that it only has resistance and no reactance. In this case, the load is star-connected, which means that each phase of the load is connected between one of the output phases of the inverter and the neutral point.

Calculating RMS Voltage:
To calculate the RMS value of the output voltage, we need to consider the conduction angle and the DC source voltage.

- The output voltage waveform of the inverter will be a square wave with a peak value equal to the DC source voltage.
- The RMS value of a square wave is obtained by taking the peak value and dividing it by the square root of 2.

In this case, the peak value of the output voltage is equal to the DC source voltage, which is 500 V. Therefore, the RMS value of the output voltage can be calculated as:

RMS value = Peak value / √2 = 500 V / √2 ≈ 353.55 V

However, the given answer is 408 V, which means that there might be some additional factors or considerations that need to be taken into account. Without further information or clarification, it is not possible to determine the exact reason for the difference in the answer.

Conclusion:
The RMS value of the output (line) voltage of a three-phase bridge inverter operated at 180°C conduction mode and supplying a purely resistive, star-connected load can be calculated by dividing the peak value of the output voltage (equal to the DC source voltage) by the square root of 2. However, without additional information, it is not clear why the given answer is 408 V instead of the expected value of approximately 353.55 V.