Name: Craig Goodwin Company Name: HV Diagnostics Inc

Trip Out of Cable Circuit: Over Current , Ground Fault, Differential protection or Fuse blows. Try to establish if the cable has in fact failed or has the failure occurred upstream or downstream of the cable section - electrical apparatus – Motors, Xfrs, Switchgear etc.

Remember that Cables can store energy and the longer the cable, the greater capability of the cable to store energy.

Energy = ½.C.V2

Do not recommend using a DC Hipot – potentially damaging to the cable and not effective in locating many types of defects. Caution against using a typically lower voltage Mega-ohmmeter to perform the test – no assurance that cable has in fact not faulted – false positives.

Apply a AC VLF withstand test to the cable at the IEEE400 test voltage levels. Duration: 15 to 30 minutes. Typically the first few cycles of AC are sufficient to identify the faulty cable circuit.

It is Not Recommended to: To use the “Utility Power Grid” approach where you reclose onto the cable. To use a smaller or larger fuse and reclose

Not Recommended to: To start cutting up the cable in half and retesting each section, cutting in half again and retesting etc etc.

The "Salami Method"

Cable fault location is often more of an art learned from experience than a pure science. Methods used include Arc Reflection, Simultaneous Impulse, Impulse Current, Voltage Decay, TDR, Bridge, Voltage Gradient, Surge testing /thumper, Acoustic and Magnetic detection, Twist Method, others etc.

It is Important to keep the voltage to a minimum !

What is the exact VOP ?

What is the exact Cable Route

Use the VLF AC tester to condition the fault and bring the resistance down and try stabilize it. The injected current is small - < 100mA from the test equipment.

Type of fault Construction of cable

Some methods simply do not work on certain types of cables.

TDR: Detection of Reflections to Locate Abnormalities is Difficult.

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EPR 5kV Cable (~2000 ft) -100nS pulse of about 12V injected - shows no reflection from far end. This is a “Tsunammi “ in magnitude and pulse width when compared to a typical PD pulse. No Reflection !

HF attenuation on aged Tape shielded cables – limits the use and viability of HF Diagnostic techniques – like Partial Discharge Detection and TDR (Time Domain Reflectometry - CFL)

• Large 5nC Calibration Pulse Injected into a 2000ft/610m run of cable.

• One TDR Trace shows a open end and the other a manual installed ground to help identify the end of the cable.

Large 5nC Manually Injected PD Pulse

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5kV EPR Tinned Taped Shield Cable from Nuclear Power Plant

PD Detection Difficult, PD Location not possible.

- PD Pulse

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100nS and 25nS TDR Pulses

5kV Cable Fault 2011/2012 EPR Cable, 7 Cables per phase, 500MCM 3 Core Armored Tape Shielded Cable

Congested Terminations, trenches and Manholes.

Ground Fault Trip / Alarm Technicians Meg the cable phase bus (7 cables) – get bad reading on one phase. Perform VLF-TD Test – cannot get the voltage to come up. Separated all 7 cables on C phase to isolate.

Tried an available on-site TDR for about 2 days – could not locate the defect. Decided to cut pothead off the end of the cable. Megaohm tested the Pothead and found a ground in it !

Hallelujah !!

Retested VLF/TD the cable and cable still could not hold voltage. Called out T&D group to find the fault using traditional methods used in T&D. None of these methods worked. The cable then experienced the salami method and was cut at RP building and in roadway at an easy access main hole.

Performed fault pre-locate using modified bridge from both ends. Located the area where defect was believed to be located – At Turbine Building / Aux Building Performed high energy low voltage surge test Did Audible / Visual Locate of Fault Site Location

Fault was in the low level cable trough under many other cables. Decided to cut the cable on adjacent accessible sides of trough . Performed Cable ID to identify the correct cable to cut. Cut the Cable to isolate the faulted section. Retest the remaining sect. Run new cable from cut point.

1985 XLPE CN Cable 35kV Jacketed 345Mil At nuclear power plant. Cable had failed in one phase in a splice and during the same failure the cable had a insulation failure on second phase. A HV TDR test was performed on the cable the defect sites were located.

No two cable faults are completely the same. The best method to use can vary based on the cable type and construction AND the type of cable fault. A tool chest of test equipment options should be on-hand to ensure a successful and an expedient fault location exercise. Experienced cable fault location testing personnel