Which type of circuit is designed to reverse a generator's self-excited field?

The correct choice is suicide circuits, as these circuits are specifically used in situations where a generator's self-excited field needs to be reversed. This type of circuit facilitates the disconnection of the field winding in a way that it allows the generator to go from a self-excited state to a non-excited state, preventing the generator from generating voltage under certain conditions.

Suicide circuits are essential in protecting generators from potential overexcitation or fault conditions that could arise if the field remains energized when it shouldn't be. By effectively reversing the field, these circuits help maintain the stability and safety of the electrical system.

In contrast, the other options do not serve this specific purpose. Latching relays and reed relays are types of switches used for different control applications and do not inherently reverse a generator's self-excited field. Walking beams, typically associated with mechanical motion in various applications, do not relate to electrical circuits at all. Therefore, the focus on suicide circuits highlights their critical role in the management and protection of generator operations.