DC Protection Calculations –
An Acceptable Approach
Author(s)
R. Leach, D. Tregay & M. Berova
Abstract
As a consequence of substantial changes to the railway track layout and
implementation of a new approach to the renewal of negative bonding as part of
a Major UK Railway Signalling Infrastructure Project, the need arose for
reassessment of the existing electrical circuit impedances. This was necessary to
ensure that circuit breakers and relays, protecting the portion of the third rail DC
traction power supply network in question, had safe protection settings employed
to continue to ensure safety under electrical fault conditions.
This paper outlines the challenges that needed to be overcome in gathering,
processing and reconciling input data to arrive at a complete, coherent and
consistent set of data necessary for the calculation of the maximum fault
impedances seen from each of the circuit breakers. The paper goes on to present
the development, implementation and application of the methodology for the
calculation of the protection settings.
The process, illustrated with a flow-chart, was developed based on the
relevant railway standards and guidance documents reflecting best practice,
taking into account previous experience and the lessons learnt from other recent
Power Upgrade projects. The methodology is based on modelling the feeding
arrangement with an equivalent electrical circuit and was implemented into a
spreadsheet based calculation tool. The tool facilitates the choice of feeding
scenarios, the input and validation of data and enables sensitivity studies of the
effect of various circuit components. A particular challenge of the application of
this methodology and tool was the identification of the worst fault scenarios,
especially in large switches and crossings areas with multiple ‘Tee’ feed
connections at various points along the track. Such problems were solved by
modelling and carrying out simulations for various scenarios to determine the
worst case. The methodology and computational tool were validated for every
application by comparing the results with those obtained by an independent
computer programme.
The analysis of the protection setting calculation results demonstrated
surprising conclusions contrary to original expectations.
Keywords: power supply, DC railway, negative bonding, protection settings,
modelling, computational techniques.
Keywords
power supply, DC railway, negative bonding, protection settings,
modelling, computational techniques.
Related Book
Other papers in this volume
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