TELECOM Digest OnLine - Sorted: Re: 25 Hz Power

Re: 25 Hz Power
9 Mar 2006 19:30:09 -0800 wrote:

> Some electrified intercity railroads in the Northeast used 25 Hz
> power. There are, or at least were in the past, some advantages to 25
> Hz power for running locomotives.

The Pennsylvania Railroad used 25Hz 11,000 Volt from Washington to NYC
and are major branches, including commuter lines. The Reading
Company's Philadelphia area commuter network uses a similar system.
The pre-war locmotives and self-propelled cars required that type of
power supply. To this day that power continues although all the
equipment is modern.

Today's equipment uses rectifiers to convert the AC power to DC.
Newer designs use a modern type of AC motor; I believe the frequency
is varied by solid state control units to control speed.

There was some talk of converting this system to more modern power but
that would be costly and not gain anything. The most modern equipment
has switches and can run on various types of power, older equipment
must be modified in the shops.

The Reading Company had its own rotary converters and now has solid
state converters. Amtrak, which inherited the former PRR
installation, may still get 25Hz from PECO and other suppliers or
convert itself (I'm not sure of the latest arrangements).

The Erie-Lackawnna suburban NYC commuter service used DC. It was
converted to 60Hz in a rebuild; the advtg is this is commercial power
and can be taken right off the grid. The above installations have
fewer input points and have their own substations and distribution

The New Haven RR also used 25Hz 11kv but too was converted to 60 Hz.
Amtrak extended the electrification to Boston.

I wonder how the telephone company rectified AC power for its DC
batteries. For large installations, a motor-generator set known as a
rotary converter was required. Early machines would need 25Hz as
well. Later on mercury arc rectifiers came out.

Over the years the technology of power supplies dramatically improved.
The size and cost of power converters had marked improvement.

> Most of today's power companies descended from Edison's companies and
> are still reluctant to give any credit to Nikola Tesla, who conceived
> of the far more practical (for most commercial purposes) multiphase
> alternating current now universally used. (Westinghouse bought the
> Tesla patents.)

I don't know if true, but someone told me that in Europe that didn't
bother with three phase for house supply, but just give everyone 220
service. That does seem to be more efficient for house supplies.

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