WIRELESS TRACTION POWER SYSTEMS
Technology
Overhead Contact
Systems
Multiple Suppliers of Technology
Existing Systems in Operation
Performance in Snow or Rain
Performance on
Significant Grades
Mixed Traffic Application
Dedicated ROW Application
Light Rail Application
Streetcar Application
Compatible with Multiple
Vehicle Suppliers
Ground Contact
Systems
Hybrid OESS
Battery Systems
Hybrid OESS
Capacitor Systems
Hybrid OESS
Combined Systems
Hybrid Ground
Induction Systems
Onboard Energy
Generation
Systems
On-board energy
storage system (OESS)
Most U.S. authorities have chosen
hybrid vehicles powered by an
OESS for off -wire systems. Th is
potentially decreases capital costs
by removing some, or all, of the
OCS. However, it increases longterm
maintenance costs. Current
U.S. projects use batteries within
the OESS. Supercapacitors can be
used, but only for specifi c applications.
OESS capacity is limited due
to vehicle weight and space limitations;
longer vehicles usually can
have a larger OESS since they have
more roof space. Systems using a
combination of batteries and supercapacitors
off er better charging
performance and braking energy
recapture, but require more space to
implement and are more suitable for
light rail vehicles or 5-section and
longer streetcars. Th e OESS can be
charged via an OCS, an overhead
charge bar, an embedded charge
bar similar to a single segment of
a ground contact system, or by an
inductive charging system.
Onboard energy
generation
Vehicles with onboard energy
generation systems use fuel cells,
batteries, and hydrogen to generate
power. Th eir only limitation is
the availability of fueling stations
to replenish hydrogen supply;
conventional electrical supply
infrastructure is not required. Th e
major disadvantage is the required
space and added weight of the fuel,
tanks, fuel cells and batteries.
Considerations for
wireless systems
implementation
Now that the technology for off -
wire operation is available, it
will continue to be an important
option for electrifi ed transit systems.
Power simulations are an
integral part of system selection.
Selection factors include:
58 | Mass Transit | MassTransitmag.com | SEPTEMBER/OCTOBER 2018
Substations Required
Fueling Stations Required
Charging Stations Required
High-Density Vehicle
Batteries Required
Embedded Switchgear/
Detection Required
Contact Wire and Poles Required
Visual Impact to Cityscape
Vehicle Weight
Utility Conflicts
Capital Costs
Maintenance Costs
Yes/Best/Most
No/Worst/Least
Possible/Medium/Medium
Not Enough Information
Comparative analysis
Wireless traction power systems provide benefits in specific urban
applications, and each method has advantages and disadvantages.
• Hybrid OESS systems don’t work
well on long uphill grades, due to
power requirements
• OESS using supercapacitors need
predictable travel time, and perform
better in dedicated rights of way
• OESS using batteries have greater
range and are recommended for
mixed traffi c
• Wireless regions should start and
stop at stations
• Current collection devices must
be stowed and de-energized when
operated through wireless regions
• OESS quick-charging should be
implemented at stations
• For any systems (mixed, contact
wire, wireless segments, or ground
contact), where quick-charge stations
are not implemented
• Traction power load fl ow studies
should include OESS charging
• OESS charge time should
correspond with time on wire
Jason Krause, P.E., is a principal engineer
with LTK Engineering Services.
By the
Numbers
5 to 8
years
projected
lifespace of
OESS batteries
/MassTransitmag.com