1. High-Impedance Fault Detection with the F60 Universal Relay
Bruce Buxkemper
Optima Systems, Inc.
College Station, Texas
Consultant to GE Power Management

2. Agenda Definition of a high-impedance (HiZ) fault Theory of operation
Security and sensitivity analyses
Settings
Field tests to date

3. Optima Systems, Inc. Specialize in software and embedded systems
Designed research prototypes for Texas A&M
Designed first GE HiZ product
Consultant to GE for integrating HiZ in UR
Located in College Station, Texas (

4. Definition
A high-impedance (HiZ) fault is one that draws too little current to operate conventional overcurrent protection (fuses, relays, etc.).

5. Feeder Currents
10,000
1,000
AMPS
100 10 1
HiZ Fault Load Bolted Fault

6. Typical Fault Current Behavior

7. Causes Contact with tree limb or other object
Broken hardware allowing primary to sag
Contaminated or failing equipment (insulators, etc.)
Broken line on ground

8. Misconception #1
Misconception: Properly set, overcurrent protection will clear all faults.
Reality: HiZ faults often draw less current than loads, making overcurrent protection impossible.

9. Misconception #2
Misconception: Sensitive ground protection will clear HiZ faults.
Reality: Unbalanced loads limit sensitivity of ground protection.

10. Misconception #3
Misconception: Over time, fault current will increase and operate protection.
Reality: In most cases, fault current decreases as conductor burns, moisture evaporates, sand fuses, etc. O/C protection seldom operates after first minute or so.

11. Misconception #4 Misconception: Faults always clear on my system.
Reality: Engineering staffs believe HiZ fault rate is low, but line crews report many downed conductors are still hot when they arrive on scene.

12. Misconception #5
Misconception: TAMU/GE technology will solve all my HiZ problems.
Reality: This technology will detect many faults that overcurrent technology cannot, but no known technology can detect all HiZ faults reliably and securely.

13. Primary Protection Philosophies
Overcurrent protection – Protect power system
HiZ protection – Protect people and property

14. Research History EPRI targeted problem in late 1970s
Constraint: Passive, substation monitoring
Texas A&M University looked at non-fundamental frequency current
Seven patents
GE licensed technology in early 1990s

15. Detection Requirements
Driven by utility workshops
High speed operation not desired
Allow conventional protection to operate
Distinguish arcing on pole from downed conductor
Don't false operate!

16. Characteristics of Arcing Faults
Little effect on voltage
Small fault current
Current not steady state
Significant harmonic and non-harmonic current
No single parameter uniformly responsive

17. Detection Concepts Monitor multiple parameters simultaneously
Use multiple detection techniques
Use time to distinguish arcing from transients

18. Detection Parameters Odd harmonics (3rd, 5th, …)
Largest increase
Smallest relative increase
Even harmonics (2nd, 4th, …)
Small ambient level
Affected by inrush
Non harmonics (1/2, 1-1/2, 2-1/2, …)

19. Normal System Behavior

20. Normal System Behavior

21. Fault Behavior

22. Fault Behavior

23. Basic Arc Algorithms Energy algorithm Randomness algorithm
Monitor parameter continuously
Look for sudden sustained increase
Randomness algorithm
Look for sudden increase in variability

24. Expert Arc Detector Algorithm
Monitor outputs of basic arc algorithms
Increase confidence level…
Based upon multiple algorithms' indications
Based upon persistent indications
Operate on per-phase basis

25. Load Pattern Analyzer Algorithm
Monitor output of Expert Arc Detector
Monitor load flags
Overcurrent
High rate of change
Three-phase events
Perform coordination
Require continued arcing
Distinguish downed conductor from arcing

26. Simplified Block Diagram
1/0 % Ia
Parameter
Processing
(DSP)
Energy
Algorithm
Expert
Arc
Detector
Load
Pattern
Analyzer % Ib 12 12
Arcing Ic
Randomness
Algorithm % In 12 12
Downed
Conductor %
Overcurrent
High Rate of Change
Loss of Load
Three-phase Event
Coordination Timeout
Even Harmonic Level
Voltage

27. High-Level Logic Behavior

28. High-Level Logic Behavior

29. Sensitivity Tests Texas A&M University's facility
12.47/7.2 kV multi-grounded wye, overhead
2000+ amps available fault current
30K fuse to coordinate with upstream protection
Substation monitoring point
1-3 MVA nominal load
UR connected to existing CTs, PTs
UR installed long-term

30. Sensitivity Tests (cont'd)
Three sets of tests to date
September 27, 2000
October 5, 2000
October 26, 2000
Tests remaining (tentative dates)
November 1, 2000
November 8, 2000

31. Sensitivity Test Summary (Three-Day Totals)
Total Tests
Blew 30K Fuse Quickly (17)
No Fault Current (2)
Total Detectable 15
Total Detected (73%)

32. Test Surfaces Used Grassy ground Bared ground Reinforced concrete
Non-reinforced concrete

33. Response Procedure Factors suggesting tripping
Heavily populated areas (especially schools, etc.)
Highly flammable conditions
Reasons to delay tripping
Need written procedure

34. Response Procedure Factors suggesting tripping
Reasons to delay tripping
Loss of traffic signals, etc.
Personal injuries (darkened stairways, etc.)
Hospitals
Location difficulty when circuit not energized
Need written procedure

35. Response Procedure Factors suggesting tripping
Reasons to delay tripping
Need written procedure
IEEE Power System Relay Committee WG D15 (

36. Levels of Alarms Downed Conductor Arcing Alarm Arcing Suspected Alarm
Arcing following O/C or loss of load
Most serious
Arcing Alarm
Arcing Suspected Alarm

37. Levels of Alarms Downed Conductor Arcing Alarm Arcing Suspected Alarm
May indicate tree contact, failing equipment, etc.
May indicate downed conductor on lightly loaded lateral
Arcing Suspected Alarm

38. Levels of Alarms Downed Conductor Arcing Alarm Arcing Suspected Alarm
Possible intermittent tree contact, etc.
Least serious

39. HiZ User Settings Arcing Sensitivity
OC Protection Coordination Timeout
Phase/Ground OC Min Pickup
Phase/Ground Rate of Change
Loss of Load Threshold
3-Phase Event Threshold

40. HiZ User Settings (cont’d)
Phase/Ground Event Count
Event Count Time
Voltage Supervision Threshold
Even Harmonic Restraint

41. Arcing Sensitivity Setting
Range 1-10 (10 = most sensitive)
Determines arc confidence threshold
Determine how many times to confirm
Indirectly affects speed of operation

42. OC Coordination Timeout Setting
Determines minimum operating time
Arcing must continue after timeout
Need to balance speed with reliability
Long enough to allow conventional protection to sectionalize
Fault current often decreases over time, so timeout must be short enough that significant arcing still exists

43. O/C Min Pickup Setting Used to recognize downed conductor
Determines current at which to inhibit arc detection (temporarily)