What are the three different types of Pantograph defects?

The three different types of Pantograph defects are intricately linked to the functional requirements of the pantograph, which is a device used to collect electric current from the overhead lines for trains. Each defect relates to the functionality of raising and lowering the pantograph, essential for proper operation and safety of the train.

Failing to raise when the "Panto Up" is pushed indicates that the mechanism is not functioning as intended, which can lead to significant issues in maintaining electric contact with the overhead line. Similarly, failing to lower when the "Train Stable" is pushed could suggest problems with the control system or mechanical linkages that prevent the device from safely disconnecting. Lastly, if the pantograph fails to lower when the "Panto Down" is pushed, it similarly reveals a lack of responsiveness that may prevent the train from entering stations safely or adhering to operational protocols.

Recognizing that all these defects represent critical operational failures highlights the importance of thorough defect identification in maintaining train safety and reliability. Hence, the correct answer encompasses all these possibilities, reflecting a comprehensive understanding of potential issues that can arise with pantograph systems.