In which connection does a motor run fast, star or delta?
Answer:
a motor runs faster in delta connection than in a star connection. This is because in delta connection, each phase gets the total of the line voltage, whereas in star connection, each phase gets 1/√3 of the line voltage.
The speed of the motor is proportional to the voltage applied to the stator windings. Therefore, a higher voltage means a higher speed and vice versa. However, the speed of the motor also depends on the frequency and number of poles, which are constant for a given motor¹. The synchronous speed of the motor is given by the formula:
$$N_s = f \times 120
where $N_s$ is the synchronous speed in RPM, $f$ is the frequency in Hz, and $P$ is the number of poles. The actual speed of the motor is slightly lower than the synchronous speed due to slip. Slip is the difference between the synchronous speed and the rotor speed, expressed as a percentage of the synchronous speed. Slip increases with load and decreases with voltage¹.
Therefore, a motor connected in star will have more slip than a motor connected in delta at the same load and frequency. This will further reduce the speed of the star-connected motor.
To summarize, a motor runs faster in delta connection because it receives a higher voltage and has less slip than in star connection. However, changing between delta and star connection should be done carefully, as it can affect the current, torque, and power of the motor³.