Thanks Tim, a bit off topic but very interesting!! I find stuff like this quite fascinating. I like how if you are a little off on your timing the motors would ring like bells as they jerk into synchronization. Definitely a good read for this morning.
Thanks, Joe On Thu, Jan 19, 2012 at 3:55 AM, <[email protected]> wrote: > Having worked at Lima Electric (Sadly No longer in Lima Ohio, Factory > Closed) for over 5 years making synchronous alternators, and 3 years in > the Engineering Test Lab I can pass on a little information on alternator > speeds. On a sychronous alternator the rotor operates with DC excitation, > either supplied by slip rings (automotive alternator) or by a excitor > rotot/stator combination.( There is also DC or AC excitation) Lima > electric pioneered alternators without sliprings, this was made possible > by solid state rectifiers. > A synchronous alternator will operate just as well as a motor if voltage > is supplied to the stator. In any case as a motor the rotor locks > exactly to the speed of the rotating magnetic field in the stator. > (unlike an induction motor where torque is produced by slip, synchronous > speed - actual speed of the motor. This can be looked up on the web) > This is what makes a synchronous motor valuable as a clock. Well in any > case in a sychronous motor shaft speed is directly proportional to input > frequency as long as the motor stays in step. (Excessive torque demands > can pull a motor out of synchronous speed) Conversly with a synchronous > alternator. Output frequency is directly proportional to rotor shaft > speed. > Rotors are most commonly made with two, four or six poles for 50 or 60 > HZ units. A 2 pole alternator will produce 60 Hz when run at 3600 RPM a > 4 pole alternator will produce 60 Hz when run at 1800 RPM and a 6 > pole alternator will produce 60 Hz when run at exactly 1200 RPM. A > synchronous motor will run at exactly the same speeds at 60 Hz. 2 > Pole=3600 4 Pole=1800 6 Pole=1200 etc. For 50 Hz 2Pole=3000RPM > 4Pole=1500RPM and 6Pole= 1000RPM > The formula is RPMsync=120 times Hz divided by the number of poles on > the rotor > For power generation on a grid or any place that more than one > alternator are working together all the alternators must run at exactly > the same speed and must be in phase. If an alternator is not in "sync" > horrible things can happen. The phase voltage and frequency must exactly > match before an alternator is brought on line with the other > alternators. This is where a synchroscope using lamps or meters comes > into use. In our test lab I had two test stands, one with a 250HP > synchrounous motor and the other with a 500HP synchronous motor. The > 500HP motor had to be manually synchronized with the incoming line > voltage before closing the main contactor. This involved using a > auxilliary motor to bring the large motor up to synchronous speed. I > then had to manually turn up the excitation voltage to the rotor using a > variac to match the incoming line voltage. A meter would indicate the > voltage phase between the motor (which was acting as a generator) and > the incoming line. The meter would slowly swing between 0volts and > 480volts. When the meter read 0 volts I had to close the contactor. If I > was off a little the whole motor would ring like a bell as the rotor was > jerked into step. If I was way off the main fuses to the plant would > blow. (I never did that, thank God!) I did blow a set of 500 amp fuses > though once. In any case for the huge Megawatt alternators in power > plants for the grid it becomes obvious that Frequency control and phase > are very important for proper operation of the grid. > Sorry this got so long. I havn't posted in a long long time and I guess > the verbage just had to vent! > Tim > > > -- > You received this message because you are subscribed to the Google Groups > "neonixie-l" group. > To post to this group, send an email to [email protected]. > To unsubscribe from this group, send email to > [email protected]. > For more options, visit this group at > http://groups.google.com/group/neonixie-l?hl=en-GB. > > -- You received this message because you are subscribed to the Google Groups "neonixie-l" group. To post to this group, send an email to [email protected]. To unsubscribe from this group, send email to [email protected]. For more options, visit this group at http://groups.google.com/group/neonixie-l?hl=en-GB.
