PESHAWAR: The Chinese company that provided the BRT buses has submitted a report to the provincial government on the incidents of fire in the buses in which it blamed abnormal external conditions and failure of low capacity capacitors.
It said a significant increase in ripple current (maximum 750A) led to the failure of capacitors installed in the controller. The failure of the capacitor directly led to violent heat up and malfunction, even explosions, which consequently led to a short circuit of the high voltage power circuit and from which the fire was kindled.
The Xiamen Golden Dragon Bus Co Ltd has assured the provincial government that the buses will be operational by October 25, 2020, after modification and test run. “The company stands by its product and is fully committed to supporting the buses as per contract. We are not worried about any associated costs. We are fully committed to speeding up the extra solutions and pushing the maximum limits possible, including air shipment of heavy components, to ensure a speedy process of actions,” the company said in its report.
The Chinese company stated that due to unexpected abnormal external conditions, which included multiple parameters, there was a significant increase in ripple current (maximum 750A) as detected, which led to the failure of capacitors to smoothen the ripple current. This was beyond the capacity of capacitors installed in the motor controller and the failure of capacitor directly led to the violent heat up and malfunction.
The report further stated that peak current was supposed to be restrained by the software upgrade to limit the flow of current from the motor controller change; however, certain electronic components in the motor controller of buses have been damaged by the abnormal current before the software updating, which caused the incidents.
The bus manufacturing company has redesigned and replaced the buses, motor controllers, with different options. The TM motors controller for the 18-meter model has been replaced with an upgraded better capacitor of the temperature resistance performance of 105°C from 85°C.
Secondly, IGBTs in RM motors controllers were changed with reserve larger power capacity that will improve the performance of temperature resistance and current converting efficiency. The fuses of all batteries are to be downgraded from 630A to 400A rating to increase protection against short-circuiting and controlling such fire incidents. High voltage wires in all the buses are to be prolonged to increase the resistance of wires further to balance the resistance of the circuit and to smoothen the abnormal current peaks.
The power distributor from the motor controller to batteries has been redesigned and the new one would include a fuse that will provide additional safety if the current
crosses the benchmark value of the system, further reducing the potential risk of abnormal current to pass through the motor controller.