RME Review - Wye Delta Starters

What is the primary purpose of a wye-delta starter?

• To increase the motor's starting torque

• To reduce the inrush current during motor startup

• To regulate the motor's speed during operation

• To reverse the motor's direction

Answer explanation

The primary purpose of a wye-delta starter is to reduce the inrush current during motor startup. This helps prevent damage to the motor and electrical system by limiting the initial surge of current.

For a wye-start, delta-run connected motor, the selection of branch-circuit conductors on the line side of the controller shall be based on the motor full-load current. The selection of conductors between the controller and the motor shall be based on _____ percent of the motor full-load current.

• 58

• 73

• 15

• 25

Answer explanation

For a wye-start, delta-run motor, conductors between the controller and motor should be sized at 58% of the motor's full-load current to ensure proper operation and prevent overheating.

In which configuration does the motor initially connect in a wye-delta starter?

• delta

• wye

• series

• parallel

Answer explanation

In a wye-delta starter, the motor initially connects in a wye configuration to reduce the starting current and voltage. After a brief period, it switches to delta for normal operation, allowing full power.

What happens when the motor transitions from wye to delta configuration?

• The motor receives full line voltage

• The motor speed decreases

• The motor reverses direction

• The motor is disconnected from the power supply

Answer explanation

When the motor transitions from wye to delta configuration, it receives full line voltage, allowing it to operate at higher power and efficiency. This is crucial for maximizing performance in applications requiring more torque.

Why is the wye configuration used during the starting phase?

• To supply the motor with reduced voltage and starting current

• To provide high starting torque

• To ensure continuous power supply

• To reverse the motor's rotation

Answer explanation

The wye configuration is used during the starting phase to supply the motor with reduced voltage and starting current, which helps prevent damage and allows for a smoother start.

What is the primary role of the timer in a wye-delta starter?

• To regulate motor speed during operation

• To disconnect the motor from the power supply

• To allow the motor run partial speed

• To delay the transition from wye to delta

Answer explanation

The timer in a wye-delta starter is primarily used to delay the transition from wye to delta configuration, allowing the motor to start in a lower voltage state before switching to full power.

Which type of motor is commonly used with a wye-delta starter?

• single phase

• DC motor

• 3 phase motor

• synchronous motor

Answer explanation

A wye-delta starter is specifically designed for 3 phase motors. It reduces the starting current and allows for a smooth transition to full speed, making it ideal for large 3 phase induction motors.

What is the main limitation of a wye-delta starter?

• It cannot start motors larger than 10 HP

• It causes high starting current

• It requires more maintenance than other starters

• It provides reduced starting torque, which may not be suitable for heavy loads

Answer explanation

The main limitation of a wye-delta starter is that it provides reduced starting torque, which may not be suitable for heavy loads. This can lead to inadequate performance when starting larger or more demanding motors.

What happens to the current when the motor transitions from wye to delta?

• It increases to the full-rated current of the motor

• It decreases to half the starting current

• It remains constant

• It inacreases to 58%

Answer explanation

When a motor transitions from wye to delta, the current increases to the full-rated current of the motor. This is because the delta configuration allows for higher voltage and thus higher current draw compared to the wye configuration.

What happens if the motor fails to transition from wye to delta?

• The motor continues to run in the wye configuration with reduced power

• The motor stops immediately

• The motor operates at full torque

• The motor stalls

Answer explanation

If the motor fails to transition from wye to delta, it will continue to run in the wye configuration, which provides reduced power. This allows the motor to keep operating, albeit at a lower efficiency.