🔍 Key Concepts

• Synchronous motor operation: how it maintains constant speed locked to supply frequency • Difference between mechanical overload and insufficient excitation current (field current) in synchronous machines • Typical causes of pull-out of synchronism and severe vibration in synchronous motors

💭 Think About

• Think about what keeps a synchronous motor ‘locked’ in step with the rotating magnetic field. Which parameter directly affects this locking action? • When a motor is mechanically overloaded, what usually happens first: does it instantly lose synchronism, or is there another typical symptom (consider torque vs. speed in a synchronous machine)? • How does changing excitation current affect the motor’s ability to carry load and its stability in synchronism?

✅ Before You Answer

• Check which condition most directly reduces the synchronizing torque in a synchronous motor • Consider whether mechanical overload alone is enough to cause immediate pull-out, or if something else must also be marginal • Verify how insufficient field (excitation) current changes the motor’s power factor and its stability margin before pull-out