Bendigo Tramways, operated by the Bendigo Heritage Trust, is a heritage tram operation which serves as a popular tourist attraction and a quirky public transport option for locals. Increasing demand for tram services has resulted in larger numbers of trams in the network at any given time. More trams in the network increases the total current draw, and consequently the risk of nuisance tripping with the existing DC protection settings.
To reduce risk of nuisance tripping, Bendigo Tramways asked Middleton Group to review the existing protection settings and propose new settings under which the network could safely operate.
This required modelling of the tram network, which posed a unique challenge: the network impedance was unknown.
To determine optimal protection settings, we completed the following:
- Accurate network impedance (resistance & inductance) data determined through on-site testing. This included creating a test plan, identifying appropriate test equipment, and safely executing tests with the assistance of Bendigo Tramways.
- Network simulations to identify maximum and minimum fault levels, and rate of change of fault current.
- Identification of suitable worst-case tram operational scenarios for modelling, incorporating tram current draw characteristics.
- Network simulations to identify maximum current draw, and rate of change of current, under reasonable worst-case operating scenarios.
Simulations were completed using MATLAB Simulink software.
Middleton Group proposed DC protection settings using risk-based assessment, using the outputs of modelling. These protection settings balance risk of nuisance tripping while still protecting the network against fault conditions.