Cable Fault Location by Baur (Connecting Measurement Technology) - Part 2 of 3

By Chris Dodds on 22nd February, 2016

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Cable Fault Location On Low, Medium & High Voltage Cable Networks by Baur

Baur cable fault locators, cable sheath testers and cable/phase identification systems cover the entire cable fault location process from pre-location to pinpointing - T&D are Baur Distributors, contact us with your requirements.

In the second of a series of Guest Blogs by Baur we learn in depth all about connection measurement technology.

Part 1: Introduction to Cable Fault Location by Baur (Sources, Types & Pre-location Methods)

• About the process
• Fault sources and types
• Pre-location methods

Part 2: Cable Fault Location by Baur (Connecting Measurement Technology)

• Connecting the most varying systems
• Earthing
• Safety aspects

Part 3: Cable Fault Location by Baur  (TDR Time Domain Reflectometry)

• Method and prerequisites
• Reflection factor
• Tracing low-resistive faults

Perfect Measurement With Safety

Before commencing the actual cable fault location, you should connect the measurement technology.

Regardless of the type of cable fault location, it is absolutely necessary to already work diligently and with care at this stage.

The exact connection of the measuring devices and proper earthing prevent accidents and provide loadable, reproducible and, in particular, precise measurement results.

Whether locating low, medium or high voltage cable faults the following tips are useful.

Outdoor Connections

If the end of the cable to be measured is at a transmission pole, first clean the cable ends. Only this way can perfect measurement be guaranteed.

The safety and operational earthing is carried out together at the earthing point of the pole.

Enclosed Substations and Substation Buildings

In enclosed substations and substation buildings you will typically find different types of cable ends.

Use only the most suitable connection accessory and check if this accessory is safe. Also check if the distance to adjoining cables or conductors is big enough to prevent a flashover. In addition, you must erect danger signs for personal safety and block the work area.

Precision and an accurate procedure are absolutely essential while connecting the measurement technology.

Earthing Unused Cores

If only one phase is measured in a three-phase cable or three one-phase cables, you should earth the other two. If all three phases are measured simultaneously, ensure that they are connected properly.

Earthing For Safety

Both the protective earthing as well as the operational earthing should be on the same earthing bar and at the same earthing point.

Exclusively use clean, blank metal for the earthing. Any existing paint or corrosion should be removed carefully before connecting the ground terminals.

Connecting To Low Voltage Systems

For the cable fault location at low voltage, the device is typically connected to the conductor with the defect or earth fault. Consequently, it can result in rise in the earth potential, even with the protective earth.

This potential rise causes a higher voltage between the (earthed) neutral conductor and phase, which can damage the voltage source.

An isolation transformer can be used as remedy here. It can help adjust the supply voltage in such a way that no damaging overvoltage occurs at the mains input of the measuring device.

If only one phase is measured, you need to earth the other two.

An isolation transformer is also helpful in case of poor earthing in substations.

During the measurement, it ensures a stable voltage even with earthing-related potential shifts.

Earthing Systems and Cable Test Vans Under Normal Conditions

High voltage devices should be earthed before use. With a normal, good earthing, this can be done without special additional measures. For additional safety, provide for:

• An isolation transformer
• The earth monitoring system in the cable test van. The system ensures that there is no potential rise between operational earth (OE) and protective earth (earth resistance) and checks that the earth terminals are fixed properly.
• The earth monitoring of the cable test van. This auxiliary system monitors the earth potential at the cable test van and at the earth point of the substation. In addition, the connection between the safety earth and substation earth is monitored.

Steps for Earthing A Cable Test Van

Earthing At High Earthing Resistance

Sometimes, you might not be able to provide proper earthing. At an earthing resistance of over 4 Ohm, it is very important to place the operational earth (OE) and the protective earth on the earthed screening of the cable to be tested.

In addition, an earth spike should be connected close to the connection point. If you need to insert this earth spike in a poorly conductive ground, such as dry and sandy earth, ensure that the earth spike is of adequate length.

Otherwise, the transition resistance between the earth spike and the ground would be too high. In addition, an isolation transformer is also highly recommended for protection of the devices.

Safety For Good Results

It’s better to be on the safe side by follow the aforementioned tips and carry out the connections and the removal of the system in compliance with the rules.

On one hand this will help avoid personal and property damages, and on the other hand, careful connection of the measurement technology leads to “clean” i.e. precise and reproducible - measurement results.

 

Thorne & Derrick Specialist Electrical Distributor

Established since 1985, T&D distribute the most extensive range of LV, MV & HV Cable Jointing, Terminating, Fault Location & Installation Equipment - contact us today for a competitive quotation.

Key Products : MV Joints & Terminations, Cable Fault Locators, Cable Cleats, Duct Seals, Cable Transits, Underground Cable Protection, Jointing Tools, Feeder Pillars, Cable Duct, Earthing & Lightning Protection, Electrical Safety, Cable Glands, Arc Flash Protection & Fusegear.

Distributors for : Baur, 3M, Pfisterer, Nexans Euromold, Elastimold, Catu Electrical, Roxtec, Emtelle, Centriforce, Lucy Zodion, Alroc, Hivotec, Cembre, Prysmian, Ellis Patents, ABB & Furse.

 

 

• Further reading :

Video Tutorial Masterclass - PD Partial Discharge & Electrical Cable Breakdown

Condition Assessment of HV Cables - Guest Blog by EA Technology

"Reducing Failure Rates and Better Management of Underground Cable Networks"

Portable Partial Discharge Diagnostics - Baur PD-TaD 60 PD Diagnostics System

 

Invitation

Thorne & Derrick are inviting you to join LinkedIn’s fastest growing Discussion Group : Low & High Voltage Power, Cabling, Jointing, & Hazardous Area Electricals (LV-HV).

Discussion subjects include cable installations, cable jointing, electrical substation, overhead line and electrical construction at LV, 11kV, 33kV and EHV.

Network, engage and promote your profile, company or products with over 10,000 influencers.

 

Baur - Cable Fault Locators & Location Specialists (LV MV HV Cables)

Category:  HV Cable Jointing & Terminating

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