Determining Fault Location Using New v3.04 Firmware
PUBLISHED ON Dec 20, 2010
by Bryan Gehringer
We use peak fault current to estimate fault location in our distribution system. In new stations, we can usually get the peak fault current from microprocessor-based relays. But most of my existing distribution stations have older breakers. I can’t upgrade the relay in those stations without replacing the old breakers, and that makes the cost impossible to justify. Is there any way to get the peak fault current from a Bitronics recorder into SCADA?
That’s a really good idea [speaking last August]. Suppose we just develop it for you?
[Fast-forward to December…] The peak fault current could always be read manually from a Comtrade file produced by the M571’s disturbance recorder. But with the release of firmware version 3.04, all new 70 Series IEDs can now automatically extract the peak fault current from the disturbance recorder and make that available to be read by SCADA in DNP3 protocol.
There are four aspects to the implementation:
1. Fault detection, triggering the recorder. Configured on the Recorder Triggers page of the Configurator program. This is usually an instantaneous overcurrent (device 50) threshold or a digital input that you might get from the breaker or an auxiliary contact (52A/B). The trigger event should be set to initiate the “Fault Analysis” function (a check box).
2. Data available in DNP. For each phase, the maximum magnitude of the fundamental component of the current that occurs from 10 cycles prior to the trigger until 20 cycles after the trigger is placed in a DNP analog input point. A fourth analog point is available that determines the largest magnitude of the three phase currents. In this way, the user can either read back the three-phase peak or the fault current on each of the phases. Points can be read either discretely (Object 30) or via Class 0 poll (Object 60 variation 1). A fault counter is also provided as an analog input point. The fault counter lends itself very nicely to polling via Analog-Change-Event in DNP (Object 60 variation 2, 3, 4) so no fault data may need to be included in normal polling until a fault actually occurs.
3. Targets and other indications. Each fault is characterized in two ways: First, a DNP analog input point consisting of packed bits is available where each bit represents a phase that is either involved (1) or not involved (0) in the fault. Second, there are also four binary output points that represent Targets. Targets available include Any Fault, Phase-A involved, Phase-B involved, and Phase-C involved. An entry is also made in the Sequence of Events (SOE) Log so a permanent record of fault history and multiple strikes is preserved.
4. Reinitialization. New faults are distinguished from old ones by reinitializing the targets after the information has been read by SCADA. This can be accomplished manually or automatically. Manual initialization can be done via SCADA, by sending a Control Relay Output Block to the target point in DNP after the peak fault current has been read. Or the device can be configured to automatically Reset Targets via a timer, set up in trigger logic using the Configurator program.
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