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On 22 July 2010, a 24.9-kV distribution feeder

experienced a series of faults at 9.18 pm. A digital

relay (intelligent electronic device) at the

substation reclosed twice but failed to clear the

fault. A total of five event reports were recorded

which provides a snapshot of the distribution

feeder at the time of the fault. The relay eventually

locked out causing all 743 customers to experience

a sustained interruption. Maintenance crew found

a burned jumper cable at 4.43 miles which was

reported as the actual fault location.

The University of Texas at Austin

Swagata Das

Analysis of Distribution Faults using Intelligent Electronic Device Data

What Happened?

WHERE?System Response?

Why and Where did it Happen? Action Items?

1. Trim trees near 4.48 miles and increase conductor

spacing, remove slack, or choose shorter spans

near 5.20 miles to prevent recurring faults.

2. Monitor the future trip times of the relay to

ensure that the relay is not out of tolerance.

3. Download and analyze event reports before

re-energizing the system after a fault. For

example, if event reports on 22 July 2010 were

reviewed in details, the fault on 9 August 2010

could have been prevented. The burned jumper

cable was the failure effect and not the root cause

of the fault.

SHOT 1

Expected Operate Time: 0.8177 – 0.9914 seconds

Actual Operate Time: 0.941 seconds

Relay operated as expected.

SHOT 2

Expected Operate Time: 0.7426 – 0.8995 seconds

Actual Operate Time: 1.037 seconds

Relay has operated slower than expected.

Event 7: BC Fault at 5.46 miles Event 5: BC Fault at 5.22 miles Event 4: B-G Fault at 4.51 miles Event 3: BC-G Fault at 5.34 milesEvent 6: B-G Fault at 4.48 miles

Fault Event Log from the Digital Relay

Intermittent tree contact at 4.48 miles

Intermittent Conductor Slapping at 5.20 miles

Intermittent Tree Contact at 4.48 miles

Intermittent Conductor Slapping at 5.20 miles

Thunderstorms on the day of the event