Short Answer:

A synchronous generator and a synchronous motor are both synchronous machines, but they work in opposite ways. A synchronous generator converts mechanical energy into electrical energy, while a synchronous motor converts electrical energy into mechanical energy.

In a generator, mechanical power (from a turbine or engine) drives the rotor to produce AC electricity in the stator. In contrast, in a motor, AC electricity is supplied to the stator, and the rotor (with DC excitation) locks with the magnetic field and rotates to produce mechanical work. The key difference lies in the direction of energy conversion.

Detailed Explanation:

Difference between synchronous generator and synchronous motor

A synchronous generator and a synchronous motor are both based on the same construction and principle of synchronous operation. They both operate at a constant speed called synchronous speed, where the rotor rotates exactly in sync with the rotating magnetic field produced in the stator. However, the main difference is in the direction of energy conversion.

Let’s understand both one by one and then highlight the differences clearly.

1. Synchronous Generator (Alternator):

A synchronous generator converts mechanical energy into electrical energy. It works based on Faraday’s law of electromagnetic induction. The rotor, excited with DC current, is mechanically rotated by a turbine or engine. As it rotates inside the stator, the rotating magnetic field cuts the stator windings and induces an AC voltage.

• Input: Mechanical energy (from water, steam, or diesel turbines)
• Output: Electrical energy (three-phase AC)
• Example: Generators in power plants
• Operation: Rotor is driven mechanically
• Frequency of output depends on speed and number of poles

2. Synchronous Motor:

A synchronous motor converts electrical energy into mechanical energy. When a three-phase AC supply is given to the stator, it produces a rotating magnetic field. The rotor is supplied with DC and initially brought near synchronous speed using an external means (or damper windings). Once synchronized, it locks with the stator’s rotating field and runs at synchronous speed to drive a mechanical load.

• Input: Electrical energy (AC supply + DC excitation)
• Output: Mechanical energy (rotating shaft)
• Example: Industrial drives, compressors
• Operation: Rotor is driven by the magnetic field
• Speed remains constant under varying load

Key Differences Between the Two:

1. Energy Conversion Direction:
   • Generator: Mechanical → Electrical
   • Motor: Electrical → Mechanical
2. Power Flow:
   • Generator delivers power to the grid
   • Motor draws power from the grid
3. Starting Mechanism:
   • Generator starts with mechanical prime mover
   • Motor needs starting mechanism to reach synchronous speed
4. Application:
   • Generator: Used in power generation (power stations)
   • Motor: Used in mechanical drives (pumps, mills, fans)
5. Current Direction in Armature:
   • Generator: Current flows out from stator
   • Motor: Current flows into the stator

Though both have similar internal structures (stator, rotor, excitation system), their function and role in a power system are different. One generates power, the other consumes it.

Conclusion:

A synchronous generator and a synchronous motor differ mainly in the direction of energy conversion. The generator changes mechanical input into electrical output, while the motor does the reverse. Both machines run at synchronous speed and share construction features, but their roles are opposite in power systems—generation versus mechanical work. Understanding this difference helps in using the right machine for the right purpose.