In Mumbai Monorail project in India, one typicat problem is being faced . Traction Subststion of 750 V DC supply uniform DC volatge at no load but at load i.e when the monorail start running or accelerating at a speed of 30 km/hr or more there are volatge fluctuations in the system , which are measured at 20 m sec sampling rate at the input of DC to AC traction Inverter , Conductor Rail ( having contact with current collector with conductor rail as the train moves and there is no bouncing of the curren collector , which is checked on the web camera) . Amplitudue of the Voltage fluctuate is more than No load voltage of Traction substation i.e 1000 V on the max side and 550 V on the minimum side . Voltage fluctauation amplitude starts increasing as train moves away from the Traction Sub station and its duration also increases . Surprising when profile of the DC volatge is checked at the Traction substation at rectifier 12 pulse Full wave , 2 M watt diode , it is noted that there is no volatge fluctuations and smooth 750 V DC supply is flowing even at full load . However it is imperative to mention that connection between the Traction substation to the conductor rail is though the 4 run of 1 x 240 sq mm Copper cable ( Conductor rail is the Aluminum rail with steel top to avoid the wear and tear but since the conductuctivity of Aluminium is more than Steel therefore most of the current passes through the alumimum )
As there is no loading(fluctuation),at substation, and as the contact of current collector, are considered perfect(no bouncing), then the voltage fluctuation, which increases, with distance, with perfect catenary(capable of taking required loading), means may be due to considerable voltage drop, in the return path, the aluminum rail, with distance, at higher current demand. Can be reduced by providing,more parallel return path, with increased distance or using, larger cross section rail..
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