Technical Requirements for A.C. Electrification Transformers
|Publication Date:||7 March 2020|
The scope of this document (Module A) covers requirements for Network Rail ' s 25 kV traction transformers and transformers used to derive auxiliary supplies from 25kV traction supplies.
In addition to the general requirements of BS EN 50329 this module covers specific requirements for the following equipment types used by Network Rail as part of their 25 kV electrification:
a) Traction auto-transformers, rated up to 20 MVA
Traction auto-transformers are used in 25-0-25 kV traction auto-transformer systems to reduce the voltage drop along the line, increase traction power, and the distance between substations. Traction auto-transformers are connected between the overhead contact wire and the auto-transformer feeder with a mid-point connection to the running rails (return circuit).
b) Traction booster transformers
Traction booster transformers are used as part of 25 kV classic traction system for the suppression at source of electromagnetic interference on a.c.electrified lines and to reduce the level of interference induced into adjacent signalling & communication circuits. Traction booster transformers are single phase transformers with a unity turns ratio (1:1) and possess low impedance values. The primary voltage is 25 kV to neutral and the nominal current is usually in the range 100-300 A.
c) Traction isolating transformers
Traction isolating transformers are used at interfaces between a.c. and d.c.electrified lines. The transformers provide electrical isolation between the two systems thereby preventing d.c. traction current entering the AC system.Traction isolating transformers are 25/25kV single-phase with a power rating upto 5 MVA. Due to the d.c. immunity requirements, an air gapped core design is necessitated for isolating transformers. Over-voltages are higher than normal,due to the air gapped core and the d.c. currents, which are present at switching when the train passes cut-off sections.
d) Traction auxiliary transformers and voltage regulators, rated up to 450 kVA.
Traction auxiliary transformers and associated voltage regulators are used to provide supplies from the overhead line to signalling and other auxiliary equipment.
A procurement specification should be produced by the client/client ' s representative when placing an order on any of the units covered by this module. This document is to be read in conjunction with the relevant procurement specification.
Module A defines the requirements for the design, manufacture, and testing of auto-transformers, booster transformers, isolating transformers, auxiliary transformers, and voltage regulators for 25 kV a.c. traction supplies & auxiliary supplies derived from traction supplies.
The standard is aimed to mitigate the following risks:
• Unclear requirements leading to difficulties in procuring transformer components;
• Increased costs from different routes and projects working to different sets of requirements;
• Non-compliance of procured components to BS EN 50329