NEIEP Mechanics Practice Exam

In hydraulic pumps with wye-delta windings, what prevents simultaneous contact of both wye and delta contacts?

1. A safety switch

2. A walking beam between the two contactors

3. A transformer

4. A circuit breaker

The correct answer is: A walking beam between the two contactors

In hydraulic pumps with wye-delta windings, the purpose of having a wye-delta starting method is to reduce the starting current when the motor is energized. The transition from wye to delta allows the motor to start in a lower voltage configuration (wye) to limit the current draw, and then switch to the higher voltage configuration (delta) for full operational efficiency. The mechanism that prevents the simultaneous contact of both wye and delta configurations is a walking beam between the two contactors. This walking beam acts as a mechanical interlock. It is designed to ensure that when one configuration is engaged, the other is disengaged. Thus, it effectively eliminates any risk of both the wye and delta contacts being closed at the same time, which could lead to electrical faults or damage to the motor. This interlocking feature is critical for maintaining safe and proper operation of the hydraulic pump system, ensuring that the motor starts smoothly and operates efficiently without the potential for short circuits or excessive current that would result from both configurations being connected simultaneously.