I.Power Cable Categories & Analysis of Cable Fault

1.Power Cable Categories

1.1 By rated power.

Low voltage cable : 6KV rated or below

Middle& High power cable:6KV & above,35KV below.

High Voltage Power cable : 66KV & above rated cable.

1.2 By Power cable insulation dielectric materials

Oil immersed paper dielectric： MV or HV Cable

Non drip paper dielectric cable：MV or HV Cable

 (XLPE)Dielectric power cable：MV or HV Cable

Other rubber dielectric cable：MV & HV Cable or LV Cable

Oil filled cable：HV Power Cable

1.3 By construction

No external metal shielding layer of the cable：LV Cable

outer metal shielding layer of the cable：HV &HV Cable.

Mental inner sheath cable：HV Cable

2.Power Cable Fault Categories & The Fault Analysis

2.1 Power Cable Fault categories

By the fault part:

Joint fault；host cable fault

By Performance form：

Closed fault; exposed fault。

By structure：

Main insulation fault；Inner & outer sheath fault.

 2.2 Analysis of cable fault

The open circuit fault: if the cable insulation is normal, and that the conductor cannot normally convey

 Voltage can be considered as the open circuit fault, such as wire or wires seem to break or the non

Breaking and core existing a larger line resistance and core fracture. General simple open circuit fault rarely seen,

 Mainly to coexist with low resistance or high fault resistance

Low resistance fault: if the insulation damage of the cable, can directly use the testing method of low voltage pulse of one class phase or phase to earth fault, called the leakage of low resistance fault, Low resistance fault. The general resistance value is less than a hundred ohm. If the resistance value is zero, it is called short circuit fault, which is a special case of low resistance fault 

Leakage of high impedance fault: if the cable insulating medium has been damaged and fixed channel resistance, but the fault cannot be directly used cable fault tester by "low pressure pulse measurement method” called leakage of high fault resistance, the resistance is usually in the hundreds of ohms or more. When the DC leakage voltage test is done on the spot, the leakage current value increases continuously with the increase of the DC voltage, and exceeds the standard value of the cable itself. Leakage of high resistance and low resistance fault are relatively described and there is no distinctive difference between them.

The flashover of high resistance fault: The flashover of high resistance fault in cable pre test voltage range, when the cable pre test voltage is applied to a certain value, the leakage current value of cable suddenly increased, which greatly exceeds the value of the subjects required cable standard value, this type of failure is called flashover of high resistance fault. Although the cable insulation is damaged, it has not formed a fixed resistance channel。

2.3 Discrimination method of fault characteristics of power cable

     Three of fault characteristics of power cable:

（1） Judged by MΩmeter ,multi meter. ；

（2） Judged by cable pre-testing result;

（3） Judged by HZ-501A power cable pre-locator

  Under normal circumstances, low resistance, open circuit fault can be directly judged by the Ohm meter or HZ-501A Power cable flashover instrument impulse testing wave.

2.4 Power cable fault testing program.

By applying the HZ-501A flashover instrument to locate the cable fault following procedures are generally required:

 ( 1 ) Analyze the cable fault characteristics and learn about the cable rated voltage and the insulation materials.

    （2）Using the HZ-501A Power cable Flashover instrument’s impulse method to detect the cable length, and also to calibrate the radio wave speed in the fault cable.

    （3）By selecting the suitable testing method, applying the HZ-501A Power cable flashover instrument to pre-locate the cable fault.

    （4）to pin point the power cable fault precisely, include the underground cable route, depth and the fault point locating.

（5）Applying the tolerances analysis method to the cable fault testing results(measuring tolerances、transferring speed tolerances、judgments tolerances、instrument tolerances)。

3.The Main Specification Index of System

1) The single chip operational platform, touch-screen operational method:

2）System functions：Fault distance measurement、Fault locating、transmission speed test、fault resistance、Power cable route tracing、buried depth detection etc；

3）Detecting method：Low voltage impulse、Flash over method、Audio frequency method、Acoustic magnetic synchronous method、Valley value method、Peak method、Electromagnetic induction etc；

4）Display control：Flashover instrument：8inchesindustrialgrade LCD ,Battery inside，can workfor6 hours continually； others are Pointer table display；

5）Detection range：testing distance：30km，detection depth：2-5m；

6）Measurement accuracy：Pre-testing tolerances：±10m（absolute value）or 1%（relative value），Precisely detecting tolerances：±0.2m（Locating、route、depth）；

7）sampling frequencies： 80MHz、40MHz、20MHz、10MHz

8）sampling method：automatic continuous sampling， no any discharging wave form can be left out absolutely.

9）low voltage impulse：0.05/0.1/0.2/0.5/1/2/8uS，seven

10）Output power：Route power：100W、Impact power：0～400W

11）Impact high voltage：0～35kV

12）short circuit current：0～320mA

13）Burn through power：0～1225J