NOJA Power News

Issue 5

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Fault Diagnosis Using Event Logs And TELUS

Event data downloaded from the OSM recloser can be used to determine the likely cause of faults on a feeder. TELUS software is used to download this data so it can be viewed, graphed or exported to spreadsheets for further analysis. The result is a powerful tool for understanding how a fault occurred.

The OSM recloser uses Rogowski current sensors and capacitive voltage sensors on all six bushings to measure the following data:

• Phase to Earth Voltages
• Line to Line Voltages
• Phase Currents
• Residual Current
• Active, Reactive and Total Power
• Power Factor
• Frequency

Recloser and controller events are also recorded to give a full picture of the fault and the resultant actions taken by the device. For this example we will use actual data from an OSM recloser that is currently installed in the field. The device is located on an 11kV feeder in a semi-rural area.

Downloading Fault Data Into TELUS
The first step is to download the event log from the RC Cubicle on the pole. Connection is via RS232 to a laptop PC. The data is automatically transferred when the connection is first made and may take a few minutes to complete. The data is broken up and displayed in TELUS under five categories:

• Close/Open Operations and Fault Records
• Change Messages
• Load Profile
• Event Log
• Counters

The RC Cubicle also records up to 50cycles of pre-fault history. This pre-fault history was used by TELUS to produce the two graphs above.

An extract of the event log is shown below:

It can be seen that the fault was picked up by a number of protection elements: Overcurrent (OC1+), Earth Fault (EF1+ and EF3+), and Sensitive Earth Fault (SEF+). Although the initially fault rose above the EF3+ element's settings, it then fell back below 600A as the fault progressed. This left the OC1+ and EF1+ elements showing a two phase fault between A, B and Earth. The recloser proceeded to trip and lockout in accordance with the protection philosophy employed by the utility.

The current profile graph shows A and B phase currents rising to 2.3kA while the earth current initially rises to 1.1 kA then drops back down to 600A. The voltage profile graph shows the voltage between A and B phases dramatically dropping. The single phase voltages on A and B also drop while the C phase voltage rises.

Due to the location of this feeder, it can be assumed the fault was most likely caused by a tree or branch falling across A and B phases while still touching earth.

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