Yup. The synchronous speed of a motor is directly proportional to the frequency and number of poles in the motor. The formula RPM = 120f/p is used to solve for

Yup. The synchronous speed of a motor is directly proportional to the frequency and number of poles in the motor. The formula RPM = 120f/p is used to solve for speed given f in Hz and p is the number of poles. Poles being one of the N-S halves in a magnetic pole pair. So the minimal number of poles in an AC induction motor is 2 and increases by 2. Typically, most AC induction motors are of the 2 and 4 pole variety as well as the less common but usually available 6 pole. The same goes for generators. The more poles, the slower it turns but torque increases proportionally. In ye olde days frequency was converted using motor generators. A 50<->60 hz system matches up at 600 RPM so a 10 pole on the 50Hz side and 12 on the 60Hz side (complex and expensive designs). Using that formula, a 2 pole generator running at a synchronous speed of 3000 RPM will produce 50Hz. Using that 50Hz to power a 4 pole squirrel cage motor will cause it to run at just under synchronous speed, usually 4-5% below synchronous speed at full load (it will spin slightly faster, towards synch under no load). So about 1450 RPM. The reduction in speed is called slip and is what generates torque as the rotor has no magnetic field of its own, it depends on slip to generate the counter field to push the rotor along. Synchronous motors avoid slip by having their own magnetic field from permanent magnets or a wound armature on the rotor fed DC from slip rings or rotary transformer. Coincidently, a synchronous motor and AC generator or alternator are almost the same machine. The basic idea is a magnetic field mechanically spun around pushes electrons around in the stator windings. Sort of like a propeller pushing through water, the magnetic field lines push and pull electrons along the wires. If the field is too weak the voltage will sag as load increases. You can visualize this as weak field = propeller made of rubber, flopping about and can't push much, full strength = made of steel. If the mechanical power source is weak or overloaded, the shaft speed will drop as well as voltage. You are literally transmitting the generators rotational speed along the wires and motors follow. Adding generators means they have to be in phase so must be brought up to speed AND phased in before being connected to the grid. This is called synchronizing. So thanks to my long winded motor/generator post you can see how a large load can drag down frequency.