M8 power system design question

[engineerboy6561]

Random geeky question about the M8 electrical systems; the main reason that the M8s are no good below Harold is because they're only equipped with 60Hz transformers, and the 25Hz transformer would be too bulky to fit. To my knowledge, the train is set up so 25kV is transformed down to some intermediate voltage, then rectified and fed into an inverter that drives the traction motors by means of what I'm assuming is a buck converter . I'm mostly wondering if there's a reason the propulsion system is configured in that way; you could also rectify the input voltage coming off the pantograph (giving you about 35.4kV DC north of Mill River and 17-18kV DC from Mill River down to DC), and then use a push-pull converter to drop down from 17-36kV down to the 2-3kV bus voltage (which uses a buck converter back end, four switch stacks and a transformer). The key difference is that the push-pull transformer would be operating at 20-40kHz instead of 60Hz and so would be much smaller, thus giving you a frequency-independent drive system. What are people's thoughts?

Edited May 25, 2019 by engineerboy6561

[paulrivera]

I think it’d be great if there were no weight penalty. The M8’s are already quite heavy in weight, and at the end of the day having transformers on the M8’s to be compatible for anything south of Penn would be quite the waste of money and cause unneeded maintenance headaches (even if it is Connecticut’s money, they’re about as bad a shape financially as the MTA is)

The M8’s are capable of going past New Haven on the NEC catenary and also capable of running on the LIRR vía their 3rd rail. The two provisions they ever needed (Shore Line East beyond New Haven and Penn Station access) are mostly there already and that’s already more than what the M2’s were able to do.

[engineerboy6561]

3 hours ago, paulrivera said:

I think it’d be great if there were no weight penalty. The M8’s are already quite heavy in weight, and at the end of the day having transformers on the M8’s to be compatible for anything south of Penn would be quite the waste of money and cause unneeded maintenance headaches (even if it is Connecticut’s money, they’re about as bad a shape financially as the MTA is)

The M8’s are capable of going past New Haven on the NEC catenary and also capable of running on the LIRR vía their 3rd rail. The two provisions they ever needed (Shore Line East beyond New Haven and Penn Station access) are mostly there already and that’s already more than what the M2’s were able to do.

Thanks! Yeah, my thought process with doing things this way is that you'd be able to build something that would basically be universal. Hell, if you add a forward converter-based power system, options for  low-platforming doors and the option for a QSK19 or similar under the bogies to the M8 then you'd basically have a universal multiple-unit family that you could sell to anyone in America who was interested instead of needing to do one-off special designs for every individual commuter rail agency.

Edited May 26, 2019 by engineerboy6561