Public transportation by rail, though not new, is an area of growth, both commercially and technologically. New imperatives of efficiency and “de-carbonisation” coupled with population growth, particularly in urban areas, puts rail transportation at the centre of urban and social planning.
Efficiency, long a subject of “lip service” in an industry whose infrastructure and labour costs, is now a matter of concern, causing new electronic solutions to be increasingly adopted – without dislodging reliability from its paramount position.
Power management or “conditioning” is now ubiquitous in all electric power installations from transmission and distribution through (renewable) power generation and power security to transportation rolling stock.
Trackside power management has been slow in relinquishing classical techniques as the focus in the Traction industry has long been on rolling stock performance and infrastructure reliability.
New environmental concerns are, however, leading to higher efficiency demands despite greater traffic density which will require new technology also in the power supply infrastructure.
THYCON offers a host of power management solutions for new designs as well as for upgrading existing installations.
THYCON’s 40 year experience in power conversion allows optimal active and reactive power support in combination with advanced electronic fault-protection and harmonic filtering, all microprocessor-based diagnostics and controls.
The most common category of trackside equipment is the basic diode rectifier and transformer.
Features include high current ratings, high overload capability, low cost, low maintenance and very rugged press-pack diode technology and high power factor.
Thyristor rectifiers have the ability to regulate the output DC voltage by phase control. This can advantageously compensate the natural voltage “regulation” (sag) of the transformer, which in traction applications is considerable.
Just as with the diode rectifier, the classical thyristor rectifier does not allow regenerative braking energy to be returned to the grid.
Features include less voltage sag or greater allowable distances between stations, correction/compensation of line-voltage distortions and asymmetry by phase control, fault-current limitation by thyristor blocking and rugged thyristor technology.
Modern rolling stock in general and on urban DC lines in particular, is usually designed to brake regeneratively but the energy returned to the line is not always returned to the AC grid but absorbed by other trains in the motoring mode (the energy which cannot instantaneously be absorbed being dissipated in the on-board braking resistors).
The ability to recover braking energy to the grid has many advantages which are of growing importance. Trains spend most of their time motoring but their braking power may be instantaneously three times their motoring powering requirements. It is in many cases sufficient to replace only a part of the trackside power supplies to efficiently absorb the braking energy peaks, thereby improving efficiency, reducing ventilation problems and stabilising the catenary voltage.
Features include less voltage sag or greater allowable distances between stations than for diode rectifiers, correction/compensation of line-voltage distortions and asymmetry by phase control, fault-current limitation by thyristor blocking, braking energy recovery and improved voltage stability, rugged thyristor technology and same component count as for diode and thyristor rectifiers.
Many existing trackside supplies are based on diode or thyristor rectifiers (single quadrant operation) and were installed at a time where energy conservation was as secondary concern.
Where such substations continue to provide satisfactory service, they may be retrofitted with thyristor inverters to return braking power to the MV grid. In general, these inverters are rated for full power but for relatively short periods of operation, typically for about one minute.
Features include braking energy recovery and improved voltage stability (2-quadrant operation), no “negative voltage regulation” (DC voltage remains clamped to the low-impedance MV network), reduced energy costs, less heat dissipation in tunnels and enclosed stations, designed for retrofitting (no need to discard existing supplies), reduced braking resistor capacity in rolling stock, and rugged thyristor technology.
