NEIEP Mechanics Practice Exam

What device is used to prevent the concurrent starting of wye and delta configurations?

1. Mechanical relay

2. Walking beam

3. Contactor

4. Transformer

The correct answer is: Walking beam

The device used to prevent the concurrent starting of wye and delta configurations is a walking beam. In electrical motors, especially those that utilize a star-delta starting method, the transition from wye to delta operation is critical for preventing excessive starting currents. A walking beam is a mechanical device designed to ensure that only one configuration is engaged at any one time during the start-up sequence. This mechanism allows the motor to initially start in the wye configuration, which reduces the voltage across the motor terminals and consequently decreases the starting current and torque. Once the motor reaches a certain speed, the walking beam shifts the configuration to delta, allowing full voltage and power to the motor for normal operation. The other choices do not fulfill this specific function. Mechanical relays and contactors are used for switching circuits but do not specifically ensure the sequential operation of wye and delta configurations, and transformers do not have any direct role in starting motor configurations.