 |
|
|
|
|
|
|
 |
General information
|
|
|
|
|
|
|
| |
|
|
|
Description
|
| |
|
|
|
|
Principle
Due to high transmission losses, DC systems do not reach high recuperation
rates except in very dense urban networks.
The situation may be somewhat improved by making electric substations
“reversible”, meaning that they can also operate in the reverse, feeding energy
from the catenary to the public mains. If substations are equipped with
inverters, recovered energy can be fed back into the supply grid whenever no
other train is running close enough to use the recovered energy.
Technical details
The architecture and power electronics of DC substations are almost identical
in most mass transit systems and mainly based on diode rectifiers.
If an antiparallel inverter is added to the diode rectifier, the power flow
of the substation can be reversed, i.e. energy can be fed back into the supply
grid. The inverter is only activated when recovered energy is available. The
inverter setpoints have to be controlled in such a way that a certain share of
the regenerated energy is available to be used by other trains for
acceleration.
So the priority for the use of recovered energy is given to other trains.
Only if no other train can take up the energy, it is fed by the inverter unit
into the supply grid. |
|
|
General criteria
|
|
|
|
|
|
|
| |
|
|
|
Status of development: in use |
| |
|
|
|
|
Inverter-enhanced substations are a mature technology that is already in use in some local DC systems, e.g. an inverter unit is run by Kölner Verkehrs-Betriebe AG (KVB), Cologne, Germany, in one of its substations. |
|
|
|
|
| |
 |
|
|
Time horizon for broad application: 5 - 10 years |
| |
|
|
|
|
(no details available) |
|
|
|
|
| |
|
|
|
Expected technological development: (no data) |
| |
|
|
|
|
(no details available) |
|
|
|
|
| |
|
|
|
Motivation:
|
| |
|
|
|
|
Energy savings |
|
|
|
|
| |
|
|
|
Benefits (other than environmental): none |
| |
|
|
|
|
(no details available) |
|
|
|
|
| |
|
|
|
Barriers: high |
| |
|
|
|
|
Costs
Investment costs for inverter unit are high. KVB Cologne estimates a payback
time of ten years. |
|
|
|
|
| |
|
|
|
Success factors:
|
| |
|
|
|
|
(no details available) |
|
|
|
|
| |
|
|
|
Applicability for railway segments: low |
| |
|
|
|
Type of traction: electric - DC
|
| |
|
|
|
Type of transportation: passenger - regional lines, passenger - suburban lines
|
| |
|
|
|
|
The installation of an inverter unit will not be economic at all substations
in a network. The following local conditions favour the use of inverters (cf.
Moninger (no year)):
- Long headway of trains (low train frequency)
- Large distances between passenger stations
- Slopes in track topography
|
|
|
|
|
| |
|
|
|
Grade of diffusion into railway markets:
|
| |
|
|
|
Diffusion into relevant segment of fleet: < 5% |
| |
|
|
|
Share of newly purchased stock: not applicable |
| |
|
|
|
|
Systemic measure. |
|
|
|
|
| |
|
|
|
Market potential (railways): low |
| |
|
|
|
|
High investment costs currently impede a wide-spread introduction. |
|
|
|
|
| |
|
|
|
Example:
|
| |
|
|
|
|
Kölner Verkehrs-Betriebe AG (KVB), Cologne, Germany |
|
|
Environmental criteria
|
|
|
|
|
|
|
| |
|
|
|
Impacts on energy efficiency:
|
| |
|
|
|
Energy efficiency potential for single vehicle: 2 - 5% |
| |
|
|
|
Energy efficiency potential throughout fleet: < 1% |
| |
|
|
|
|
KVB made a contract with its energy supplier to refund the energy fed back into the supply grid on the basis of a flat rate. This flat rate covers an amount of energy corresponding to approx. 5% of the gross energy intake at the substation. Given that the system can operate economically only at some substations, the system-wide saving potential (in one particular network) will be somewhat lower. |
|
|
|
|
| |
|
|
|
Other environmental impacts: neutral |
| |
|
|
|
|
(no details available) |
|
|
Economic criteria
|
|
|
|
|
|
|
| |
|
|
|
Vehicle - fix costs: none |
| |
|
|
|
|
(no details available) |
|
|
|
|
| |
|
|
|
Vehicle - running costs: significant reduction |
| |
|
|
|
|
Since the price of regenerated energy fed back into the grid is usually lower than for the consumed energy, as much energy as possible should be used by other trains rather than fed back into the supply grid. |
|
|
|
|
| |
|
|
|
Infrastructure - fix costs: high |
| |
|
|
|
|
Given the high investment costs of such a system, a thorough assessment of the most profitable site for installation (cf. General criteria - Applicability for railway segments) has to be carried out. |
|
|
|
|
| |
|
|
|
Infrastructure - running costs: increased |
| |
|
|
|
|
Although the inverter unit increases the complexity of the substation, maintenance costs are not necessarily high. KVB Cologne have made positive experience with virtually no downtimes in three years of operation. |
|
|
|
|
| |
|
|
|
Scale effects: medium |
| |
|
|
|
|
In case of a more wide-spread use of inverter units for substations in mass transit systems, a certain drop in prices is to be expected. |
|
|
|
|
| |
|
|
|
Amortisation: > 5 years |
| |
|
|
|
|
(no details available) |
|
 |
Application outside railway sector (this technology is railway specific)
|
|
|
Overall rating
|
|
|
|
|
|
|
| |
|
|
|
Overall potential: promising |
| |
|
|
|
Time horizon: mid-term |
| |
|
|
|
|
The installation of inverter units in substations of local DC systems can make a substantial contribution to energy efficiency if the substation is carefully chosen in order to maximise the saving potential. For present prices, payback is critical and may be up to ten years. A comparative economic assessment of the use of inverter enhanced substations has to be made with respect to other solutions (mainly stationary energy storage). |
click icon to print 
date created: 2002-10-09
