I. Analysis of malfunction nature of electric cables

1. Type of electric cables

1.1 Classification according to withstand voltage level:

Ø LV cable:6kV and lower voltage level:

Ø MV cable:6KV to 35kV voltage level

Ø High voltage leve:66kV and above voltage level

1.2 Classification according to insulation medium:

Ø Oil impregnated paper cable: cable for medium high voltage level

Ø Non drip paper dielectric cables: most is medium and high voltage cables

Ø Cross linked polyethylene (XLPE) dielectric cables: most is medium and high voltage and low voltage levels of cables

Ø Other media for cable rubber cable, most is medium, high voltage and low voltage level

Ø Oil filled cables: most cables with high voltage levels

1.3 Classification according to structural model:

Ø Cable without outer metal shield layer: most is low voltage cable

Ø Cable with outer metal shield cables: most is medium and higher voltage levels.

Ø Metallic sheathed cables: most is high voltage levels

2. Malfunction type of electric cables

2.1：Malfunction classification of electric cables

Classification according to wave measurement theory

Connector fault ;body fault

Classification according to display type:

Closed faults; exposed faults

Classification according to structure

Main insulation fault; Internal and external fault

2.2 Analysis of cable malfunction nature

Open route malfunction: Once the cable insulation is under normal condition, yet it can not transmit voltage due to conductor, it refers to open route malfunction such as seemingly broken core wire or ground wire, large wire resistance in a certain area of core wire and broken core. The pure open route malfunction is seldom seen; it is often co-existent with low or high resistance malfunction. 

Low resistance malfunction: The phase-to-phase or phase-to-ground malfunction featuring that cable insulation medium is damaged and can be directly tested through “low voltage pulse method” is called leakage low resistance malfunction – generally, it is called low resistance malfunction. The resistance is below several hundred ohms. Once the resistance is zero, it is called short circuit malfunction – it is an exception of low resistance malfunction.

Leakage high resistance malfunction: The malfunction featuring that cable insulation medium is damaged and has formed fixed resistance tunnel, yet it can not be directly measured through “low voltage pulse method” of cable malfunction tester is called leakage high resistance malfunction – generally, the resistance is above several hundred ohms. During DC leakage voltage resistant test to cables, the leakage current increases continuously with the increase of added DC voltage and can exceed the required standard value of cable. The leakage high resistance malfunction is relative to the low resistance malfunction and there is not any strict difference.

Flashover high resistance malfunction: Once the cable pre-test voltage is increased to a certain value within the pre-test voltage scope, the leakage current will suddenly increase and greatly exceed the required standard value of test cable – it is called flashover high resistance malfunction. Although the cable insulation is damaged in the malfunction point, yet it has not formed fixed resistance tunnel.

2.3 Judgment methods of malfunction nature of electric cables

 Generally speaking, there are 3 methods to judge the cable malfunction nature:

(1) Through MΩ meter;

(2) Through cable pre-test result;

(3) Through “HZ-501B series cable malfunction flash tester”.

Generally speaking, the low resistance and open route malfunction can be directly judged through “resistance test” function or “pulse method” test wave shape of “HZ-501 series cable malfunction flash tester”; the leakage high resistance and flashover high resistance malfunction can be judged through megameter or pre-test result; the malfunction can also be judged through “resistance test” function of “HZ-501 series cable malfunction flash tester”.

2.4 Test methods and equipment preparation of cable malfunction

Brief introduction of test methods

(1)Analysis of the fault characteristics of the cable and know the voltage level of the fault cable and insulation medium

(2) By pulse method to test all phase length of fault cable and the calibrate the wave transmission speed of fault cable.

(3)Select the appropriate test method, using the "HZ-501B cable malfunction flash tester " for cable fault pre-location.

(4) Pin-pointing the cable faults, and tracing the direction and the depth of the buried cable.

(5)Analysis of cable fault test results error(measurement error, transmission speed error, interpretation error, instrument error).

3 The main technical parameter

1) SCM operation, button operation mode, micro printer integrated design, can be printed the test waveform and related content at any time;

2) System function: measure the distance of fault, fault location, transmission speed test, fault resistance and cable route search and buried depth detection;

3) Test methods: low voltage pulse, flashover method, audio frequency method, acoustic magnetic synchronous method, the valley value method, the peak method, the electromagnetic induction method and so on;

4) Display control: HZ-501B: 5.7”industrial grade LCD, built-in 24V/7Ah DC power supply, can work continuously for 6 hours;

5) Test range: test distance: 60km, detection depth: 6-7m;

6) Measurement accuracy: Pre-location accuracy: + 10m (absolute value) or 1% (relative value), precision measurement accuracy: + 0.2m (pin-pointing, path, depth);

(7) Sampling frequency: 100MHz, minimum resolution 0.5m (100m/us)

8) Sampling methods: automatic continuous sampling, never miss any discharge waveform

9) Low voltage pulse: width: 0.1uS and 2uS amplitude: 100Vpp

10) Output power: path power: 100W, impact power: 0 ~ 400W

11) Surge high voltage: 0 ~ 35kV

12) Short circuit current: 0 ~ 320mA

13) Surge energy: 0 ~ 1225J

II.Cable Fault Flash Tester(Cable fault pre-locator)

Measure the power cable of different sections, different media of various materials, can detects the low resistance faults, short, open faults, high resistance leakage and high resistance flashover faults of underground power cables, high frequency Coaxial cable, Street light cables.

1、Main technical parameters

1) Industrial grade 5.7 ”LCD display---Angle view>160,Working conditions: temperature: -10 ℃ ~ +45 ℃

2) 2,SCM centralized control, push button operation mode, with strong anti -interference ability;.

3) 3. With distance, speed and resistance measurement function.

4) 4. With Micro-printer can print out the wave form and measuring results

5) 5. Automatic continuous sampling and never lose any discharge waveform.

6) 6. Testing method: flashover sampling, low-impulse method.

7) 7. Pulse amplitude: about 100VP-P.

8) 8. Impulse Width:0.1/2us

9) 9. Measure distance: Smax:60km……Smin:15m.

10) 10. Pre-locating accuracy: ±1%;DL/T849.1-2004 provides no more than + (1%L+20) m ,of which: L for the length of the cable

               11).Built-in DC power 24V/7Ah, can continuous working 6 hours.also with an external AC 220V±10% power supply