Introduction:
In electrical engineering, a universal motor is a type of electric motor that can operate on both AC and DC power sources. It is called a "universal" motor because it is designed to work with a wide range of input voltages and frequencies. The speed of a universal motor is directly proportional to the voltage applied to it. In this scenario, we are comparing a universal motor connected to a 220 V, 50 Hz supply with a different frequency and voltage.

Explanation:
To understand why a universal motor requires less voltage at low frequency, we need to consider the operating principles of the motor and the effect of frequency on its performance.

1. Operating Principles of a Universal Motor:
A universal motor operates on the principle of electromagnetic induction. It consists of a stator and a rotor. The stator is the stationary part of the motor, while the rotor is the rotating part. Both the stator and rotor have windings that generate magnetic fields. When an electric current flows through these windings, the interaction between the magnetic fields produces a torque that causes the rotor to rotate.

2. Effect of Frequency on Motor Performance:
The frequency of the power supply affects the motor's performance in terms of speed and torque. The speed of a motor is directly proportional to the frequency of the power supply. In other words, a higher frequency results in a higher speed, while a lower frequency results in a lower speed. The torque produced by the motor also depends on the frequency. At low frequencies, the motor may experience a decrease in torque.

3. Voltage and Frequency Relationship:
In a universal motor, the speed is directly proportional to the voltage applied to it. When the voltage is increased, the motor speeds up, and when the voltage is decreased, the motor slows down. However, the relationship between voltage and frequency is not as straightforward.

4. Voltage and Frequency Relationship in a Universal Motor:
For a given output and speed, a universal motor requires less voltage at low frequency. This is because the voltage and frequency are inversely proportional in a universal motor. When the frequency decreases, the voltage needs to be decreased to maintain the same speed and output. This is due to the impedance of the motor windings, which increases with decreasing frequency. By reducing the voltage at low frequency, the motor can operate efficiently and maintain the desired speed and output.

Conclusion:
In conclusion, a universal motor requires less voltage at low frequency to maintain the same speed and output. This is because the voltage and frequency are inversely proportional in a universal motor, and the impedance of the motor windings increases with decreasing frequency. By reducing the voltage at low frequency, the motor can operate efficiently and maintain its performance.