The Challenge: Ground faults are a common problem in overhead trolley bus systems since
they require uninsulated wiring. Maintenance personnel need a reliable system to protect short
circuit faults and also a tool for tracking low level current leaks.
The Solution: A fully redundant CompactRIO system protects the fleet from large short-circuit
faults while enabling technicians to measure small current leaks accurately.
A focus on green technologies has resulted in a renaissance for Electric Trolley bus fleets. One weak spot is the susceptibility of overhead trolley wires to collisions with moving vehicles or contact with branches that drop from adjacent trees to power poles. Since the wires are uninsulted, this poses a risk to the public that requires a fail-safe fault protection system. A fully redundant ground fault sensor was required to protect the safety of the public in such occurrences. A secondary role of the ground fault system was to track and log
small current leaks that are difficult to track in a large network of trolley bus circuits.
CompactRIO was chosen for this system because the LabVIEW protection code could be written into the FPGA, protecting the system from most common software failures such as memory leaks or virus attacks. The system detects the level of ground fault and a set of contacts are closed on the DC power SCADA system according to the degree of severity. The Compact RIO also streams DC current levels through to a PC which logs data at high rates to the hard disk. Graphical analysis allows the operator to determine the
probable type of failure and remote access to the data allows operators at other locations to switch in or out different lines to pinpoint the source of failure. The primary system works in tandem with an identical compact RIO and PC DAQ system which send alarms through a wire or’ed set of relay contacts. The two systems also check each other’s health through a watchdog system and close a fail contact if any system component returns bad data. The system is designed so that no single point of failure will result in a failure to detect a ground fault.
Ground Fault Protection
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