- #1
tim9000
- 867
- 17
Hi,
I'm going to pose my questions with a number of assumptions, so please pick me up on any that are wrong.
I want to know the design choices behind electric trains historically and current, this will mostly require some context of induction motors and inverters. I don't know exactly how EMUs work but I have some theories.
I noticed that 25 kVAC is becoming popular, I assume they rectify and invert this to control an induction motor to drive the train(?) and I was wondering why they don't rectify it for HV DC overhead, to save the train from having to invert it? Now that we can control the frequency easily with solid-state technology (inverters) I assume they use squirrel cage induction motors controlled by frequency because they are really robust?
I assume the switch to AC motors over DC is based around efficiency, or is this also because changing commutators all the time would be expensive?
I know that some older networks use 1500 VDC, did/do these invert then use AC motors, or do/did they always use DC motors? If they pretty much always inverted to use AC motors did they ever have to use wound rotor induction motors (in the old days before you could vary inverter frequency so easily), to vary the resistance of the rotor to get maximum torque for start up? Or was there some problem like maybe it was too inefficient or they couldn't get resistors big enough.
Thanks
I'm going to pose my questions with a number of assumptions, so please pick me up on any that are wrong.
I want to know the design choices behind electric trains historically and current, this will mostly require some context of induction motors and inverters. I don't know exactly how EMUs work but I have some theories.
I noticed that 25 kVAC is becoming popular, I assume they rectify and invert this to control an induction motor to drive the train(?) and I was wondering why they don't rectify it for HV DC overhead, to save the train from having to invert it? Now that we can control the frequency easily with solid-state technology (inverters) I assume they use squirrel cage induction motors controlled by frequency because they are really robust?
I assume the switch to AC motors over DC is based around efficiency, or is this also because changing commutators all the time would be expensive?
I know that some older networks use 1500 VDC, did/do these invert then use AC motors, or do/did they always use DC motors? If they pretty much always inverted to use AC motors did they ever have to use wound rotor induction motors (in the old days before you could vary inverter frequency so easily), to vary the resistance of the rotor to get maximum torque for start up? Or was there some problem like maybe it was too inefficient or they couldn't get resistors big enough.
Thanks