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'Head end power' (HEP) is a US rail term for the electrical power distribution system on a passenger train. The power source, usually a locomotive at the front or “'''head'''” of a train or a generator car, generates all the electricity for "hotel" power needed by the train. The term evolved from Hotel Electric Power which is a maritime term referring to electricity generated and used aboard a ship for purposes other than propulsion.
''See'' Electric train supply for UK history
In the days of steam locomotives, cars got their heat from steam supplied by the locomotive. Electricity for train lighting and HVAC came from generators on each car driven either by small engines or by the rotation of the axles.
Initially the new diesel locomotives incorporated steam generators to heat the existing rolling stock. In the late 1950s Chicago and North Western Railway replaced the steam generators with diesel generator sets on the F7 and E8 locomotives assigned to pull commuter trains. This was a natural evolution because commuter trains, with low speeds and short periods of sustained running, usually could not be successfully lit from batteries and axle generators and required electricity supplied by a specially equipped locomotive, even going back to the days of steam locomotives. Often such cars were equipped with propane-engine powered air conditioning. Separate and complex systems of trainlined lighting power, steam heat, and engine-driven air conditioning was ripe for replacement with HEP where a single power source provides for all these functions. However, while commuter car fleets transitioned to HEP, the intercity trains continued with steam & battery systems. It was only after the coming of Amtrak in 1971, which initially acquired cars and locomotives from the private railroads, that the intercity trains were gradually converted. All cars ordered new by Amtrak were HEP and the older cars that were retained were eventually converted during overhauls. Amtrak's initial new-built engines were equipped to pull steam-heated trains. It was not until 1975 when Amfleet cars and F40PH and P30CH locomotives entered service, that large-scale adoption of HEP started in the US.
The HEP generator can be driven by either a separate engine, mounted in the locomotive or generator car, or by the locomotive's own engine
Engine types vary, but in the US, they are mainly Caterpillar 3412 V12s and Cummins K-Series Inline 6s. Smaller under-car engines for powering short trains are also manufactured, Stadco being one popular brand of under-car generator.
The engine must rotate the HEP generator at a constant speed (rpm) to maintain the required 60 Hz AC frequency output. Therefore, a typical EMD locomotive, in HEP mode, will operate at its full engine speed of 900 rpm, driving the generator at 1800 rpm through a 1:2 gearbox. As a noise reduction method, the locomotive's main (traction) generator can also supply HEP, usually at 720 rpm. However this operating mode is only available when stopped.
The advent of power electronics has allowed the engine to operate over a larger speed range and still supply a constant HEP voltage and frequency by means of inverters.
All power consumed by HEP is at the expense of traction power. The 3200 horsepower (2.4 MW) P32 and the 4000 horsepower (3.0 MW) Genesis-Series P40 reduce to 2900 (2.2 MW) and 3650 horsepower (2.72 MW), respectively, when in HEP mode.[1]
HEP power supplies the lighting, HVAC, dining car kitchen and battery charging loads. Individual car electrical loading ranges from 20 kW for a typical car to more than 150 kW for a Dome car with kitchen and dining area, such as Princess Tours Ultra-Dome cars operating in Alaska.[2]
Because of the lengths of trains and the high power requirements, HEP is supplied as three-phase AC at 480 V (standard in the US and for Canada's VIA), 575 V (GO Transit, Toronto), or (rarely) 600 V. Transformers are fitted in each car for reduction to lower voltages.[2]
1. TRAINS magazine
2. Northwest Rail
3. Northwest Rail
★ Northwest Rail HEP products
★ Stadco rail gens
★ ANSI HEP regulations
★ ANSI HEP regulations
| Contents |
| History |
| UK |
| US |
| Engine |
| Separate engines |
| Locomotive engine |
| Electrical loading |
| References |
| External links |
History
UK
''See'' Electric train supply for UK history
US
In the days of steam locomotives, cars got their heat from steam supplied by the locomotive. Electricity for train lighting and HVAC came from generators on each car driven either by small engines or by the rotation of the axles.
Initially the new diesel locomotives incorporated steam generators to heat the existing rolling stock. In the late 1950s Chicago and North Western Railway replaced the steam generators with diesel generator sets on the F7 and E8 locomotives assigned to pull commuter trains. This was a natural evolution because commuter trains, with low speeds and short periods of sustained running, usually could not be successfully lit from batteries and axle generators and required electricity supplied by a specially equipped locomotive, even going back to the days of steam locomotives. Often such cars were equipped with propane-engine powered air conditioning. Separate and complex systems of trainlined lighting power, steam heat, and engine-driven air conditioning was ripe for replacement with HEP where a single power source provides for all these functions. However, while commuter car fleets transitioned to HEP, the intercity trains continued with steam & battery systems. It was only after the coming of Amtrak in 1971, which initially acquired cars and locomotives from the private railroads, that the intercity trains were gradually converted. All cars ordered new by Amtrak were HEP and the older cars that were retained were eventually converted during overhauls. Amtrak's initial new-built engines were equipped to pull steam-heated trains. It was not until 1975 when Amfleet cars and F40PH and P30CH locomotives entered service, that large-scale adoption of HEP started in the US.
Engine
The HEP generator can be driven by either a separate engine, mounted in the locomotive or generator car, or by the locomotive's own engine
Separate engines
Engine types vary, but in the US, they are mainly Caterpillar 3412 V12s and Cummins K-Series Inline 6s. Smaller under-car engines for powering short trains are also manufactured, Stadco being one popular brand of under-car generator.
Locomotive engine
The engine must rotate the HEP generator at a constant speed (rpm) to maintain the required 60 Hz AC frequency output. Therefore, a typical EMD locomotive, in HEP mode, will operate at its full engine speed of 900 rpm, driving the generator at 1800 rpm through a 1:2 gearbox. As a noise reduction method, the locomotive's main (traction) generator can also supply HEP, usually at 720 rpm. However this operating mode is only available when stopped.
The advent of power electronics has allowed the engine to operate over a larger speed range and still supply a constant HEP voltage and frequency by means of inverters.
All power consumed by HEP is at the expense of traction power. The 3200 horsepower (2.4 MW) P32 and the 4000 horsepower (3.0 MW) Genesis-Series P40 reduce to 2900 (2.2 MW) and 3650 horsepower (2.72 MW), respectively, when in HEP mode.[1]
Electrical loading
HEP power supplies the lighting, HVAC, dining car kitchen and battery charging loads. Individual car electrical loading ranges from 20 kW for a typical car to more than 150 kW for a Dome car with kitchen and dining area, such as Princess Tours Ultra-Dome cars operating in Alaska.[2]
Because of the lengths of trains and the high power requirements, HEP is supplied as three-phase AC at 480 V (standard in the US and for Canada's VIA), 575 V (GO Transit, Toronto), or (rarely) 600 V. Transformers are fitted in each car for reduction to lower voltages.[2]
References
1. TRAINS magazine
2. Northwest Rail
3. Northwest Rail
External links
★ Northwest Rail HEP products
★ Stadco rail gens
★ ANSI HEP regulations
★ ANSI HEP regulations
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