Partial discharge is a discharge event that does not bridge the entire insulation system between electrodes. It occurs within cavities in insulation materials under high electric fields. During partial discharge, a plasma channel briefly forms within the cavity, conducting electricity from one side to the other without crossing the entire material. Measurement setups use coupling devices and detectors to monitor the short voltage pulses caused by partial discharge, in order to evaluate insulation condition and detect defects.
EE2353 / High Voltage Engineering - Testing of CablesRajesh Ramesh
Cable testing is important to ensure the long life and high efficiency of cables used for high voltage transmission. There are several types of tests conducted on cable samples including mechanical, thermal, impulse withstand voltage, partial discharge, and dielectric power factor tests. Partial discharge tests are particularly important for determining the life of cable insulation by detecting internal discharges under voltage stress. These tests are conducted at various stages of voltage levels on cable samples to certify them for transmission use.
High voltage technology & insulation testingZeeshan Akhtar
About HV Transmission, distribution, Voltage level classification, Insulation testing.
Part 1
What is High Voltage?
Why Needed
Levels of Voltages
Application of High Voltage
Electrical Insulation and Dielectrics
Part 2
Design & Test Issues for High Voltage
Aircraft Electric Power System
Introduction to the importance of HV in electric actuator systems
Basic review of HV design
Discussion of test methods
Summary
Part 3
Voltage Testing & Partial Discharge Measurement For Power Cable Accessories
Introduction
Ac Test After Installation
Acrf Test System
Schematic Diagram Of Test System
Arallel Operation Mode Of Test System
Artial Discharge Methods & Principle.
Iscussion & Conclusion.
This document discusses power transformer losses. It covers the classification of losses into no-load losses and load losses. No-load losses are mainly due to eddy currents and hysteresis in the magnetic core. Load losses are mainly due to resistive heating of the windings. The document also discusses EU regulations that define maximum loss levels for different power transformer classes. Measurement methods for determining losses through no-load and short-circuit tests are also covered.
Underground cables consist of one or more insulated conductors surrounded by protective layers. They are used to transmit electric power underground, which ensures continuous power supply with less maintenance compared to overhead lines. Common types include low, high, and extra high tension cables. Cables have conducting cores insulated and surrounded by a metallic sheath, bedding, armouring and serving for protection. Screened and belted cables are used for 3-phase underground transmission up to 66kV, while pressure cables are used above 66kV.
As the AIS (Air-Insulated Substation) is having more limitations, More and more people are going for the Gas-Insulated Substation which is environment friendly as well.
In these presentation, We discussed about theoritical and technological advancement and advantages related to GIS as compared to other substations.
We discussed different parts of the GIS as well as their operations and advantages.
By going through this presentation, you will have idea regarding comparative advantages and disadvantages of both substations.
Partial discharge is a discharge event that does not bridge the entire insulation system between electrodes. It occurs within cavities in insulation materials under high electric fields. During partial discharge, a plasma channel briefly forms within the cavity, conducting electricity from one side to the other without crossing the entire material. Measurement setups use coupling devices and detectors to monitor the short voltage pulses caused by partial discharge, in order to evaluate insulation condition and detect defects.
EE2353 / High Voltage Engineering - Testing of CablesRajesh Ramesh
Cable testing is important to ensure the long life and high efficiency of cables used for high voltage transmission. There are several types of tests conducted on cable samples including mechanical, thermal, impulse withstand voltage, partial discharge, and dielectric power factor tests. Partial discharge tests are particularly important for determining the life of cable insulation by detecting internal discharges under voltage stress. These tests are conducted at various stages of voltage levels on cable samples to certify them for transmission use.
High voltage technology & insulation testingZeeshan Akhtar
About HV Transmission, distribution, Voltage level classification, Insulation testing.
Part 1
What is High Voltage?
Why Needed
Levels of Voltages
Application of High Voltage
Electrical Insulation and Dielectrics
Part 2
Design & Test Issues for High Voltage
Aircraft Electric Power System
Introduction to the importance of HV in electric actuator systems
Basic review of HV design
Discussion of test methods
Summary
Part 3
Voltage Testing & Partial Discharge Measurement For Power Cable Accessories
Introduction
Ac Test After Installation
Acrf Test System
Schematic Diagram Of Test System
Arallel Operation Mode Of Test System
Artial Discharge Methods & Principle.
Iscussion & Conclusion.
This document discusses power transformer losses. It covers the classification of losses into no-load losses and load losses. No-load losses are mainly due to eddy currents and hysteresis in the magnetic core. Load losses are mainly due to resistive heating of the windings. The document also discusses EU regulations that define maximum loss levels for different power transformer classes. Measurement methods for determining losses through no-load and short-circuit tests are also covered.
Underground cables consist of one or more insulated conductors surrounded by protective layers. They are used to transmit electric power underground, which ensures continuous power supply with less maintenance compared to overhead lines. Common types include low, high, and extra high tension cables. Cables have conducting cores insulated and surrounded by a metallic sheath, bedding, armouring and serving for protection. Screened and belted cables are used for 3-phase underground transmission up to 66kV, while pressure cables are used above 66kV.
As the AIS (Air-Insulated Substation) is having more limitations, More and more people are going for the Gas-Insulated Substation which is environment friendly as well.
In these presentation, We discussed about theoritical and technological advancement and advantages related to GIS as compared to other substations.
We discussed different parts of the GIS as well as their operations and advantages.
By going through this presentation, you will have idea regarding comparative advantages and disadvantages of both substations.
Power Diagnostix produces versatile instruments for high-voltage diagnostic applications including partial discharge detection. Their ICMseries detectors are used worldwide for evaluating electrical insulation. In addition to partial discharge equipment, they also produce instruments for fiber optic transmission, GIS fault location, and high-voltage test control. The ICMsystem is their flagship partial discharge detector, known for its versatility and ability to evaluate insulation conditions across various frequencies through modular components.
This document discusses transformer overcurrent protection calculations and settings. It provides information on:
1. Coordination principles for transformer protection and examples of typical protection zones for different fault locations.
2. Guidelines for setting instantaneous and time-overcurrent relays to ensure selective coordination, including maintaining coordination intervals.
3. Calculations for determining short circuit currents and relay settings for different transformer configurations, including delta-wye transformers. Thermal and mechanical withstand curves for different transformer categories are also presented.
Test done on Power transformers.
Insulation Resistance test, Winding Resistance test, Ratio Measurements, Magnetic balance test, Tan delta test, DIssolved gas analysis for transformer, Sweep frequency response analysis.
The document provides information about switchyard protection, powerline carrier communication, and SCADA application in substation control from Power Grid Corporation of India. It includes single line diagrams of substation equipment, descriptions of circuit breakers, lightning arrestors, isolators, and other components. It also explains power line carrier communication using PLCC, and line traps to block carrier waves. Finally, it outlines the architecture and functionality of SCADA systems for data collection, transmission, monitoring, control, and network supervision in power grids.
Cables are made up of conductors that transmit electricity surrounded by insulation. Common cable types include fiber optic cables which transmit data using light through glass or plastic fibers, coaxial cables with a copper conductor surrounded by insulating material and a shield, and twisted pair cables which rely on twisting copper wires to reduce interference. Cable components must have appropriate electrical, mechanical, and chemical properties to safely and reliably transmit signals or power. Common conductor materials include copper, aluminum, and alloy-coated steel wires.
Sample calculation-for-differential-relaysRoberto Costa
The document provides calculations for setting differential relays on a power transformer. It includes calculations of currents at different transformer taps to determine relay settings that avoid unwanted operation during tap changes. Currents are calculated for the high voltage side, low voltage side and on the relay at extremes of +/- 10% taps. The differential current at each tap is compared to the relay operating current to set the pickup value to avoid operation during tap changes while maintaining protection.
This document provides an overview of cable fault finding and locating techniques. It describes characteristics of good and bad cable insulation, and various cable faults. Methods are presented for locating faults in buried and above-ground primary cable, including testing the cable, analyzing fault resistance and loop tests, using time domain reflectometry (TDR) and DC hipot testing. Cable route tracers and locators are also discussed. The document details how underground cable problems can be seen using TDR and differential TDR/radar. It presents various localizing and pinpointing methods, and concludes with solutions for cable fault locating equipment.
This guide presents a methodology based on standard PN-IEC 60354 to check overloading capacity of transformers. Main changes versus standard PN-71/E-81000 are discussed and step by step examples are given. An essential advantage of the recommended methods of verification of overloading capacity of transformers is that the size and cooling modes of transformers are considered.
This document summarizes a seminar presentation on transmission line maintenance techniques in India. It provides an overview of extra high voltage alternating current (EHVAC) transmission line maintenance in India, including methods such as predictive maintenance using thermography and insulator testing, as well as preventive maintenance techniques including cold line maintenance (with the line de-energized) and live line maintenance (with the line energized). It describes some of the specific maintenance works that can be done using live line techniques, and discusses the advantages of live line maintenance.
CPC100 + TD12 Tan Delta Test Report for 132kV CT.SARAVANAN A
This document summarizes the results of three tan delta tests performed on a cable sample using a CPC test device with serial number FC628G. Each test was performed on February 16, 2021 at different times and measured capacitance, dissipation factor, and other parameters at voltages of 2 kV, 5 kV, and 10 kV. All tests showed similar results and passed without overload or other issues.
Future Meshed HVDC Grids: Challenges and Opportunities, 29th October 2015, Po...Francisco Gonzalez-Longatt
This document provides a brief history of HVDC transmission systems from the late 19th century to modern applications. Some key points:
- Early systems in the late 1800s used DC transmission over long distances but were inefficient due to the need for rotating machinery.
- In the 1930s, mercury arc valves were used in experimental HVDC systems in the US and Germany.
- The first modern HVDC system using thyristor valves went into service in Sweden in 1950, transmitting 20MW over 98km.
- Major projects in the 1960s included the first cross-channel link between England and France and a 750MW, 450km overhead line in Russia.
This document provides information on underground power cables. It discusses the construction of underground cables including conductors, insulation materials like rubber, paper and PVC. It classifies cables based on voltage level and describes common cable types used for different voltages like screened and pressure cables. It also discusses cable insulation materials, laying of cables, types of cable faults and compares underground and overhead power systems.
This document provides an introduction to medium voltage (MV) equipment, including key concepts such as:
- Voltage levels including operating voltage, rated voltage, insulation levels, and derating factors
- Current levels including operating current, short circuit current, and thermal withstand current
- Frequency standards of 50Hz and 60Hz
- Types of MV switchgear including air insulated switchgear, metal enclosed, compartmented, and block types
- Standards that MV switchgear must comply with such as IEC 62271
- Main functions of switchgear including protection, isolation, and control
- Comparison of SF6 and vacuum circuit breaker technologies
The document concisely covers the essential electrical concepts and specifications
GIS – Necessary for Extra HV & Ultra HV
Some important areas to be studied include:
More conservative design.
Improved gas handling.
Decomposition product management techniques.
Achieving & maintaining high levels of availability require – more integrated approach to quality control by both users and manufactures.
This document discusses testing of transformers. It provides an overview of transformers and their functions in transmission and distribution of electrical energy. It then describes various routine, type, and special tests performed on transformers, including winding resistance measurement, voltage ratio measurement, no-load loss measurement, load loss measurement, insulation resistance measurement, and dielectric tests. It also discusses short-circuit testing procedures and criteria. Temperature rise testing and its limits are also summarized.
The document provides information about ABB's medium voltage V-Contact VSC contactors. It describes the contactors' permanent magnet drive system and vacuum interrupter breaking mechanism. It lists the available contactor versions and their technical specifications, including voltage ratings, short circuit ratings, switching times, and environmental compliance standards. Installation and application information is also provided.
30, 31st July 2012 - The India Blackoutgiridaran123
The document summarizes power blackouts that occurred in India on July 30-31, 2012. It provides background on India's power grid system and describes how planned line maintenance and failures of other lines led to overloading and eventual tripping of multiple transmission lines, resulting in the first blackout on July 30th affecting 8 states. Efforts to restore power are also outlined. The second larger blackout on July 31st affecting 21 states is also summarized, including impacts like trapped miners. Technical recommendations to prevent such widespread outages are mentioned.
This document discusses optimal power flow (OPF) analysis, which determines optimal settings for control variables like generator outputs and transformer taps to minimize objectives like power losses while satisfying operating constraints. The key aspects covered include: the differences between standard load flow and OPF; examples of optimization problems; common objective functions and control variables used in OPF; and the use of an OPF study case editor to set up optimization problems.
This document discusses procedures for locating cable faults and types of cable testing. It describes why cable testing is important to determine the condition of power cables and systems. The main types of cable testing discussed are high voltage DC withstand testing, partial discharge testing using acoustic equipment, and dielectric response testing measuring factors like dissipation factor, DC leakage current, and recovery voltage. The document also outlines procedures for locating cable faults, including fault indication, insulation testing, cable route tracing, and precise fault location. Various cable testing methods and their purposes are explained.
DIGITAL TESTING OF HIGH VOLTAGE CIRCUIT BREAKERRitesh Kumawat
1. The document discusses the testing of high voltage circuit breakers. Digital testing employs software to simulate circuit breaker performance based on characteristic measurements from standard tests.
2. High resolution current and voltage measurements are made around current zero crossing to characterize breaker behavior. An empirical arc model is validated and used to predict test outcomes.
3. The software can be used to study the influence of system components on breaker performance and determine critical line lengths for short line faults by simulating different test circuits digitally.
Power Diagnostix produces versatile instruments for high-voltage diagnostic applications including partial discharge detection. Their ICMseries detectors are used worldwide for evaluating electrical insulation. In addition to partial discharge equipment, they also produce instruments for fiber optic transmission, GIS fault location, and high-voltage test control. The ICMsystem is their flagship partial discharge detector, known for its versatility and ability to evaluate insulation conditions across various frequencies through modular components.
This document discusses transformer overcurrent protection calculations and settings. It provides information on:
1. Coordination principles for transformer protection and examples of typical protection zones for different fault locations.
2. Guidelines for setting instantaneous and time-overcurrent relays to ensure selective coordination, including maintaining coordination intervals.
3. Calculations for determining short circuit currents and relay settings for different transformer configurations, including delta-wye transformers. Thermal and mechanical withstand curves for different transformer categories are also presented.
Test done on Power transformers.
Insulation Resistance test, Winding Resistance test, Ratio Measurements, Magnetic balance test, Tan delta test, DIssolved gas analysis for transformer, Sweep frequency response analysis.
The document provides information about switchyard protection, powerline carrier communication, and SCADA application in substation control from Power Grid Corporation of India. It includes single line diagrams of substation equipment, descriptions of circuit breakers, lightning arrestors, isolators, and other components. It also explains power line carrier communication using PLCC, and line traps to block carrier waves. Finally, it outlines the architecture and functionality of SCADA systems for data collection, transmission, monitoring, control, and network supervision in power grids.
Cables are made up of conductors that transmit electricity surrounded by insulation. Common cable types include fiber optic cables which transmit data using light through glass or plastic fibers, coaxial cables with a copper conductor surrounded by insulating material and a shield, and twisted pair cables which rely on twisting copper wires to reduce interference. Cable components must have appropriate electrical, mechanical, and chemical properties to safely and reliably transmit signals or power. Common conductor materials include copper, aluminum, and alloy-coated steel wires.
Sample calculation-for-differential-relaysRoberto Costa
The document provides calculations for setting differential relays on a power transformer. It includes calculations of currents at different transformer taps to determine relay settings that avoid unwanted operation during tap changes. Currents are calculated for the high voltage side, low voltage side and on the relay at extremes of +/- 10% taps. The differential current at each tap is compared to the relay operating current to set the pickup value to avoid operation during tap changes while maintaining protection.
This document provides an overview of cable fault finding and locating techniques. It describes characteristics of good and bad cable insulation, and various cable faults. Methods are presented for locating faults in buried and above-ground primary cable, including testing the cable, analyzing fault resistance and loop tests, using time domain reflectometry (TDR) and DC hipot testing. Cable route tracers and locators are also discussed. The document details how underground cable problems can be seen using TDR and differential TDR/radar. It presents various localizing and pinpointing methods, and concludes with solutions for cable fault locating equipment.
This guide presents a methodology based on standard PN-IEC 60354 to check overloading capacity of transformers. Main changes versus standard PN-71/E-81000 are discussed and step by step examples are given. An essential advantage of the recommended methods of verification of overloading capacity of transformers is that the size and cooling modes of transformers are considered.
This document summarizes a seminar presentation on transmission line maintenance techniques in India. It provides an overview of extra high voltage alternating current (EHVAC) transmission line maintenance in India, including methods such as predictive maintenance using thermography and insulator testing, as well as preventive maintenance techniques including cold line maintenance (with the line de-energized) and live line maintenance (with the line energized). It describes some of the specific maintenance works that can be done using live line techniques, and discusses the advantages of live line maintenance.
CPC100 + TD12 Tan Delta Test Report for 132kV CT.SARAVANAN A
This document summarizes the results of three tan delta tests performed on a cable sample using a CPC test device with serial number FC628G. Each test was performed on February 16, 2021 at different times and measured capacitance, dissipation factor, and other parameters at voltages of 2 kV, 5 kV, and 10 kV. All tests showed similar results and passed without overload or other issues.
Future Meshed HVDC Grids: Challenges and Opportunities, 29th October 2015, Po...Francisco Gonzalez-Longatt
This document provides a brief history of HVDC transmission systems from the late 19th century to modern applications. Some key points:
- Early systems in the late 1800s used DC transmission over long distances but were inefficient due to the need for rotating machinery.
- In the 1930s, mercury arc valves were used in experimental HVDC systems in the US and Germany.
- The first modern HVDC system using thyristor valves went into service in Sweden in 1950, transmitting 20MW over 98km.
- Major projects in the 1960s included the first cross-channel link between England and France and a 750MW, 450km overhead line in Russia.
This document provides information on underground power cables. It discusses the construction of underground cables including conductors, insulation materials like rubber, paper and PVC. It classifies cables based on voltage level and describes common cable types used for different voltages like screened and pressure cables. It also discusses cable insulation materials, laying of cables, types of cable faults and compares underground and overhead power systems.
This document provides an introduction to medium voltage (MV) equipment, including key concepts such as:
- Voltage levels including operating voltage, rated voltage, insulation levels, and derating factors
- Current levels including operating current, short circuit current, and thermal withstand current
- Frequency standards of 50Hz and 60Hz
- Types of MV switchgear including air insulated switchgear, metal enclosed, compartmented, and block types
- Standards that MV switchgear must comply with such as IEC 62271
- Main functions of switchgear including protection, isolation, and control
- Comparison of SF6 and vacuum circuit breaker technologies
The document concisely covers the essential electrical concepts and specifications
GIS – Necessary for Extra HV & Ultra HV
Some important areas to be studied include:
More conservative design.
Improved gas handling.
Decomposition product management techniques.
Achieving & maintaining high levels of availability require – more integrated approach to quality control by both users and manufactures.
This document discusses testing of transformers. It provides an overview of transformers and their functions in transmission and distribution of electrical energy. It then describes various routine, type, and special tests performed on transformers, including winding resistance measurement, voltage ratio measurement, no-load loss measurement, load loss measurement, insulation resistance measurement, and dielectric tests. It also discusses short-circuit testing procedures and criteria. Temperature rise testing and its limits are also summarized.
The document provides information about ABB's medium voltage V-Contact VSC contactors. It describes the contactors' permanent magnet drive system and vacuum interrupter breaking mechanism. It lists the available contactor versions and their technical specifications, including voltage ratings, short circuit ratings, switching times, and environmental compliance standards. Installation and application information is also provided.
30, 31st July 2012 - The India Blackoutgiridaran123
The document summarizes power blackouts that occurred in India on July 30-31, 2012. It provides background on India's power grid system and describes how planned line maintenance and failures of other lines led to overloading and eventual tripping of multiple transmission lines, resulting in the first blackout on July 30th affecting 8 states. Efforts to restore power are also outlined. The second larger blackout on July 31st affecting 21 states is also summarized, including impacts like trapped miners. Technical recommendations to prevent such widespread outages are mentioned.
This document discusses optimal power flow (OPF) analysis, which determines optimal settings for control variables like generator outputs and transformer taps to minimize objectives like power losses while satisfying operating constraints. The key aspects covered include: the differences between standard load flow and OPF; examples of optimization problems; common objective functions and control variables used in OPF; and the use of an OPF study case editor to set up optimization problems.
This document discusses procedures for locating cable faults and types of cable testing. It describes why cable testing is important to determine the condition of power cables and systems. The main types of cable testing discussed are high voltage DC withstand testing, partial discharge testing using acoustic equipment, and dielectric response testing measuring factors like dissipation factor, DC leakage current, and recovery voltage. The document also outlines procedures for locating cable faults, including fault indication, insulation testing, cable route tracing, and precise fault location. Various cable testing methods and their purposes are explained.
DIGITAL TESTING OF HIGH VOLTAGE CIRCUIT BREAKERRitesh Kumawat
1. The document discusses the testing of high voltage circuit breakers. Digital testing employs software to simulate circuit breaker performance based on characteristic measurements from standard tests.
2. High resolution current and voltage measurements are made around current zero crossing to characterize breaker behavior. An empirical arc model is validated and used to predict test outcomes.
3. The software can be used to study the influence of system components on breaker performance and determine critical line lengths for short line faults by simulating different test circuits digitally.
This document discusses various methods for testing and locating faults in power cables, including DC hipot (high potential) testing and AC hipot testing. It provides details on the types of cables, their typical designs and insulation faults. DC hipot testing can effectively detect insulation faults but may accelerate deterioration in aged cables. AC hipot testing is commonly used for new cable installation testing but the equipment is large and expensive. Other methods like VLF hipot testing are better for maintenance testing on cables in service. The document compares the advantages and limitations of different cable testing methods.
Brugg Kabel AG uses silicone insulation for high voltage cable accessories up to 400kV. Routine partial discharge (PD) testing is done on prefabricated joints to ensure quality and detect defects. On-site PD measurements after installation can accurately detect PD above 5pC and localize faults. Directional coupler sensors allow sensitive PD detection and localization in unscreened environments. PD testing is important for ensuring reliability of joints and avoiding premature failures during operation.
1. There are three main tests used to validate the function of vacuum interrupters: contact resistance testing, high potential withstand testing, and leak rate testing.
2. Contact resistance testing measures the resistance of the closed contacts and compares it to design values. High potential testing applies a high voltage to open contacts to measure any leakage current.
3. Leak rate testing uses the Penning discharge principle - applying a high voltage and magnetic field to contacts to determine the internal gas pressure based on the amount of current, indicating the leak rate. A high leak rate can shorten the life of vacuum interrupters.
03 partial discharge theory cutler-hammerprasadkappala
This document discusses partial discharge theory and its applications for monitoring electrical systems. Partial discharge monitoring is an effective online predictive maintenance tool for motors, generators, and other electrical equipment operating at 4160 volts or above. Understanding partial discharge theory and how it relates to early detection of insulation deterioration is important for properly evaluating this technique. The document presents simplified models of partial discharge voids and insulation systems to promote understanding of partial discharge technology.
Underground Cable Fault Detection Using IOTIRJET Journal
This document discusses a system to detect faults in underground cable lines using IoT. It proposes using a microprocessor, LCD display, fault sensing circuit module, LoRa module, and power supply to detect the location and type of fault (single line to ground, double line to ground, or three phase faults). The system measures voltage changes across series resistors when a short circuit occurs to determine the fault location. It can display the fault location and phase on the LCD and transmit the data over WiFi. The document reviews literature on condition monitoring of underground cables, current transformer saturation effects, and comparing optical and magnetic current transformers.
ESDEMC_PB2014.08 An Ethernet Cable Discharge Event (CDE) Test and Measurement...ESDEMC Technology LLC
This document describes a test and measurement system for cable discharge events (CDEs) on Ethernet cables. A CDE occurs when a charged Ethernet cable discharges to a connector. The system aims to reproduce real-world CDE conditions in the lab to test hardware immunity. It consists of a controller to set cable charge levels and control discharges, charge modules representing different cable types, and a failure test monitor. The controller controls each cable wire separately and measures discharge currents. Calibration with defined loads validated the system's functionality and output parameters.
An Ethernet Cable Discharge Event (CDE) Test and Measurement SystemESDEMC Technology LLC
This document describes a test system for measuring Cable Discharge Events (CDEs) on Ethernet cables. CDEs occur when charged Ethernet cables are connected to devices and can damage electronics if not properly handled. The proposed test system aims to reproduce real-world CDE scenarios in the lab by controlling cable charge levels, cable types, contact sequences and timings, and electrical characteristics of the discharge path. This will allow engineers to test designs under repeatable CDE conditions and improve immunity. Key parts of the system include a controller to set test parameters, a charge module representing different cable types, and monitors to check for failures.
1) The document discusses the application of Australian standards for routine testing of high voltage switchgear, specifically AS 62271.200 for metal enclosed switchgear between 1kV and 52kV.
2) It outlines the various routine tests required by the standard, including dielectric tests on the main circuit and auxiliary circuits, measurement of resistance of the main circuit, and tightness checks.
3) The dielectric tests involve applying power frequency voltage to verify no disruptive discharge occurs, with test voltages specified in the standard based on the rated voltage of the switchgear.
DC testing has been accepted for many years as the standard field method for performing high-voltage tests on cable insulation systems. Whenever DC testing is performed, full consideration should be given to the fact that steady-state direct voltage creates within the insulation systems an electrical field determined by the geometry and conductance of the insulation, whereas under service conditions, alternating voltage creates an electric field determined chiefly by the geometry and dielectric constant (or capacitance) of the insulation.
Under ideal, homogeneously uniform insulation conditions, the mathematical formulas governing the steady-state stress distribution within the cable insulation are of the same form for DC and for AC, resulting incomparable relative values; however, should the cable insulation contain defects in which either the conductivity or the dielectric constant assume values significantly different from those in the bulk of the insulation,the electric stress distribution obtained with direct voltage will no longer correspond to that obtained with alternating voltage.
Underground Cable Fault Detection Using ArduinoIRJET Journal
This document describes a project to detect faults in underground cables using an Arduino. It contains the following key points:
1. The project uses a circuit of resistors connected to an Arduino to represent the length of an underground cable. Switches placed at 1 km intervals can induce faults manually.
2. When a fault occurs, the Arduino and its ADC convert the analog current readings to digital data to determine the precise location of the fault in kilometers.
3. The document reviews related work on cable fault detection and discusses cable types, common fault types like earth faults and short circuits, and methods like Time Domain Reflectometry that have been used.
IRJET - A Review of an Investigation of Partial Discharge Sources and Loc...IRJET Journal
This document reviews methods for detecting partial discharge (PD) sources and locations along high voltage transformer windings. PD occurs due to dielectric breakdown within cracks or voids in insulating materials under high voltage stress, degrading insulation over time. The document discusses several PD detection methods including conventional electrical measurements of apparent charge, ultra-high frequency measurements of electromagnetic emissions from PD, and ultrasonic acoustic measurements to locate PD sources based on differences in signal arrival times at sensors. It provides details on the principles, advantages, and limitations of each method for both offline and online PD monitoring and diagnosis in transformers.
1) Tan delta testing uses a very low frequency AC voltage to measure the dissipation factor of insulation to determine its quality and condition. A higher loss angle indicates more contamination.
2) The cable or winding is disconnected and the test voltage is applied and increased in steps while tan delta measurements are taken. A straight trend line indicates healthy insulation while a rising line indicates contamination.
3) Routine maintenance of bushings includes inspecting the porcelain for cracks, metal parts for corrosion, oil levels, and cleaning surface contamination which can cause flashovers. Leaks should be repaired to prevent moisture issues.
This document is the Indian Standard specification for PVC insulated electric cables with working voltages from 3.3 kV up to and including 11 kV. It outlines the key materials and construction requirements for single-core unscreened, single-core screened, single-core armored, and three-core armored PVC insulated cables. The standard specifies requirements for conductors, insulation, screening, fillers, inner sheaths, armorings, and outer sheaths. It also provides thickness requirements for insulation and inner sheaths. The purpose is to specify standards for PVC insulated electric cables to ensure safe and reliable performance when used for electricity supply purposes in India.
The document discusses various types of tests conducted on isolators, bushings, cables, and circuit breakers. Key tests include:
1. Power frequency and impulse voltage withstand tests to check the insulation strength of isolators, bushings, and cables.
2. Partial discharge and tan delta tests to evaluate insulation condition and dielectric losses.
3. Short circuit tests on circuit breakers to check their ability to safely interrupt fault currents under different voltage and current conditions.
4. Other tests include temperature rise, mechanical endurance, and measurement of electrical characteristics.
The document provides information on cable cleats, including:
- What cable cleats are and why they are necessary to restrain cables and prevent movement from fault currents.
- International standards that specify cable cleats must withstand electromagnetic forces from faults and be rated for cable size and current.
- Short-circuit testing is outlined as the best way to test cable cleats' ability to withstand fault conditions, and the IEC standard's methodology is described.
- A formula from the IEC standard is presented to calculate cable cleat spacing based on fault level and cable size.
This document provides a review of insulation materials, designs, and testing procedures for high voltage direct current (HVDC) extruded cable system joints. It discusses the different types of joints, including factory joints made in controlled conditions and pre-molded field joints assembled on-site. The main insulation materials for joints are silicone rubber (SiR) and ethylene propylene diene monomer (EPDM) rubber. While SiR has better electrical and mechanical properties, EPDM is often used for HVDC joints to reduce space charge accumulation at dielectric interfaces under high DC voltages. The document identifies that joints are critical components that require reliable testing to evaluate insulation quality and lifetime. It proposes that partial discharge measurements may be a
This document discusses sheath voltage limiters (SVLs), which are surge arresters used to protect the outer jacket of underground high voltage cables. SVLs limit the voltage stress across the cable jacket during transient overvoltage events like faults, switching surges and lightning strikes to prevent puncture and moisture ingress. The document provides guidelines for selecting the proper rating for SVLs, including calculating the voltage that could appear on the cable sheath during faults based on cable characteristics, and ensuring the SVL's voltage rating is above this level so it does not conduct during faults. It also discusses using simulations and margins of protection to determine if the SVL can adequately protect the cable jacket from other transient overvoltages.
Similar to Sheath Fault Location On Power Cables - Sheath Testing, Sheath Fault Location & Location Of Earth Faults - SEBA KMT (20)
Isolation Procedures for Safe Working on Electrical Systems and Equipment by the JIB | solation Procedures for Safe Working on Electrical Systems and Equipment
This chart shows the safe isolation procedure that you should use when working on electrical systems and equipment.
You'll receive a printed copy of this from your Training Provider, but it's also here as a handy reference to keep electronically.
THE RULES OF SAFE ISOLATION ARE:
Obtain permission to start work (a Permit may be required in some situations)
Identify the source(s) of supply using an approved voltage indicator or test lamp
Prove that the approved voltage indicator or test lamp is functioning correctly
Isolate the supply(s)
Secure the isolation
Prove the system/equipment is DEAD using an approved voltage indicator or test lamp
Prove that the approved voltage indicator or test lamp is functioning correctly
Put up warning signs to tell other people that the electrical installation has been isolated
Once the system/equipment is proved DEAD, work can begin
Uploaded by THORNE & DERRICK LV HV Jointing, Earthing, Substation & Electrical Eqpt | Explosive Atmosphere Experts & ATEX IECEx.
Thorne & Derrick International are specialist distributors of low, medium, and high voltage cable installation, jointing, substation, and electrical equipment. They have over 30 years of experience and stock over 100,000 products from over 100 brands. Their product range includes cable joints, terminations, tools, accessories, distribution equipment, and safety products for voltages up to 132kV.
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2. 2010-07-13 2
Table of Contents
1. Introduction.............................................................................................................3
2. Why Sheath testing ................................................................................................3
2.1 Sheath test devices ..........................................................................................4
2.2 Norms and regulations for sheath testing.........................................................5
2.3 User definitions.................................................................................................5
2.4 Conducting the test...........................................................................................6
2.5 Safety ...............................................................................................................7
3. Sheath fault prelocation..........................................................................................8
3.1 Prelocation with the comparison or voltage drop method.................................9
3.1.1 Bipolar Measurement of the voltage drop ................................................11
3.1.2 Advantages and disadvantages of the voltage drop method ...................11
3.2 Prelocation with a measuring bridge...............................................................12
3.2.1 Prelocation...............................................................................................12
3.2.2 Prelocation with MVG 5 ...........................................................................12
3.2.3 Two wire measurement according to Murray ...........................................13
3.2.4 Three wire measurement according to Graaf...........................................13
3.2.5 Advantages and disadvantages of bridge methods .................................14
4. Sheath fault pinpointing........................................................................................15
4.1 The different methods.....................................................................................15
4.2 Voltage gradients............................................................................................15
4.3 The DC Method ..............................................................................................16
4.3.1 Pulsed DC and current limits....................................................................18
4.3.2 Power.......................................................................................................18
4.3.3 Specialties of the DC - Method ................................................................19
4.3.4 Influences ................................................................................................19
4.3.5 Advantages and disadvantages of the DC - Method................................19
4.4 Surge Method.................................................................................................20
4.5 Localisation of earth contacting faults in LV plastic insulated MV systems.....20
4.6 Audio frequency methods...............................................................................21
4.7 Equipment combination FL 50 with Step voltage Probe DEB 3-10.................22
4.8 Audio Frequency Method with 4,8 Hz and SFL2 A-Frame .............................22
4.9 Localisation of earth contacting faults in LV and illumination systems............24
5. Wording................................................................................................................25
3. 2010-07-13 3
1. Introduction
Since many years the main reason of faults in cables with plastic insulated outer
sheath is the damage of this sheath. This permits the penetration of water into
the cable and as a consequence it enhances the growth of „Water Trees“ and
other corrosion based damages in power cables. Water trees are one of the
primary reasons of cable faults.
In communication cables the ingress of water significantly reduces the
transmission quality which is in today’s high performance data transmission
requirements almost equal to a loss of the line.
In cables, which are not protected against longitudinal water migration there is
the additional danger of joint faults due to water spreading though the
conductors into the joints.
The following article describes the different test procedures for plastic insulated
and the prelocation and pinpointing of sheath faults.
2. Why Sheath testing
A perfect, non disturbed operation of a cable system requires in addition to the stated
requirements for data transmission and energy transfer, good insulation values
between the conductors as well as between conductors and shield. Prerequisite for
this is also the intact outer sheath (Jacket), which is today mostly consisting of PE.
The damage statistics of cable faults published in the recent years, especially for
medium voltage cables, indicated a significant amount of sheath faults, which were
obviously the triggering cause for a breakdown of the cable.
Resulting the sheath testing permits in a certain context also a diagnostic information
about the condition, resp. the expectable state of the cable
Additionally the sheath test is one oft he most important tools in combination with all
diagnostic technologies, since a diagnostic evaluation of a cable requires that the
cable to be tested has to be in a good and faultless condition
A diagnose without a
combined sheath test is a
relatively unreliable
valuation of the cable
condition, since entering
water as a result of a
sheath fault and the
following damages result
in a fast decrease of the
condition quality.
This again will decrease
the value and reliability of
any diagnostic evaluation
Fig 1: Cable with sheath faults
4. 2010-07-13 4
The test of the integrity of the outer sheath provides almost the ideal condition for the
early detection of damages and provides the possibility of an early elimination of
beginning cable faults.
With a simple insulation and voltage breakdown test between cable shield and outer
soil, it is already possible to conduct a commissioning
test directly after laying and to confirm the integrity
of the outer plastic sheath.
With regular tests, especially in areas with high
construction activities, it is possible to detect
damages of the outer sheath at an early stage,
where an immediate repair will prevent further
damages, and where it is still possible to locate
the cause of the damage and to claim an
according compensation.
A sheath damage, if not associated with a direct
damage of the cable insulation, will seldom lead to
a fast breakdown and failure of the cable installation. Fig 2: Cable construction details
From the moment of damage until the appearance of
the real breakdown, many months or even years can pass
If the sheath is damaged by a manual impact or a by penetrating stone, the shield
beneath can be driven more or less through the semiconducting layer into the
insulation. In this location the homogenous field distribution is distorted and partial
discharge sources develop. This partial discharge will then, depending on its intensity,
destroy the insulation and lead to a breakdown
2.1 Sheath test devices
For the testing of the cable sheath High voltage generators with an adjustable voltage
of 0 to 5 resp. 0 to 20 kV can be used. The commonly available insulation testers,
which are sometimes recommended for this purpose by some local regulation are not
usable for such a measurement, since they do not provide a current measurement and
the measured insulation values are not based on sufficient criteria, like current and
voltage. Most likely an insulation test with 1 kV will not reveal a problem!
The test voltage should be applied continuously for a test duration of 10 minutes,
which is not possible for a normal insulation tester. There should be an adjustable
limitation of output power / current, or at least a possibility to control this, to avoid an
over current during a sudden breakdown of an insulation fault, which could result in
further damages of the cable and especially its semiconducting layer.
On the other side, the output power of the HV Test Generator has to be sufficient, to
serve the high cable capacity as it exists in long cables, because in this case the high
leakage current may lead to a breakdown of the test voltage due to an overload.
As Sheath test generators, there are models which can deliver several milliamps test
current. The supply of these unit happens through integrated rechargeable batteries as
well as from mains supply. For the field use in new, un-commissioned systems, a
battery operated, mains independent system is certainly the better choice, since a
mains supply is seldom available. Combination units, which are capable to deliver a
test current of several 100 mA will normally also provide the possibility of prelocation
and pinpointing of sheath faults.
Sheath
Shield
Insulation
Semicon layer
Semicon layer
Conductor
5. 2010-07-13 5
2.2 Norms and regulations for sheath testing
The testing of cable sheaths is regulated in different norms, IEEE, IEC 60229, VDE 0276 part
620 and part 632, also their Harmonised document HD 60602 and 60632
The VDE specifies the following details:
Voltage tests at the cable sheath
Test Voltage Test Level Test Duration
DC at cables acc. to VDE 0276 Part 620
(Extruded cables from 6 to 36 kV)
PVC–Sheath 3 kV
PE – Sheath 5kV
Not specified
DC at cables acc. to VDE 0276 Part 632
(Extruded cables above 36 to 150 kV)
5 kV 1 min
2.3 User definitions
Several local power utilities have already defined own regulations for sheath testing, where the
main idea was to define measuring criteria.
Connected with this test is a „quality test“, which has to be proven by external contractors.
This factory norm operates outside the normal regulations and defines more details, that are
shown in the following table below. The test duration for this test is defined with 10 minutes.
Cable length Leakage current Leakage current
Metres Feet PVC PE
50 164 0,04 mA 0,001 mA
100 328 0,08 mA 0,002 mA
250 820 0,2 mA 0,005 mA
50C 1640 0,4 mA 0,01 mA
750 2460 0,6 mA 0,015 mA
1000 3280 0,8 mA 0,02 mA
2000 6560 1,6 mA 0,04 mA
5000 16400 4,0 mA 0,1 mA
Fig. 3: Permitted leakage current for new installations
Here it has to be observed, that an increased amount of joints, the ageing and other influences
will have a direct impact on the measured current. This means the values shown in [Fig 3.] are
to be considered for a new installation, with typically one joint per 500 m.
For aged installations, the condition must be considered in the evaluation of the current.
Requirement for a sheath test is a continuous insulation of the shield through the sheath
against the surrounding soil. Earth contacting joints and armatures are not permitted, since
these will conduct the test voltage to earth.
The insulation condition or the electric strength of a shield resp. sheath against earth is easily
determined and requires no extensive test instruments. Depending on the insulation material
of the cable, but also according to the above described factory rules, DC voltages from 3 to 5
kV (partially 10 kV and more) are connected between the metallic shield and operational earth
and the measured leakage current or the insulation resistance is evaluated
In many international applications, voltages up to 10 kV are already standard.
This value depends also on the construction of the cable sheath, where in some cases, for
example in HV Cables with a thick sheath, the common 5 kV are insufficient to bridge the thick
outer sheath of high voltage cables.
6. 2010-07-13 6
2.4 Conducting the test
The test voltage is connected in such a way, that the negative potential is connected to the
shield, and the positive will be connected to earth. Even if polarisation effects are rather rare it
is recommended, to maintain this polarity to enable the reproducibility of the measurements.
An exception is the bipolar measurement of the new MFM 10.
The typical recommended test duration is 10 minutes. Are the measured current values above
the described values, and resulting, the insulation resistance values below the permitted limits,
the cable should be investigated more detailed or at lest tested in sorter, regular intervals to
check for changes.
After the connection oft he sheath test set, the test voltage is slowly (maximum 1 kV per
second) increased to the typical test end value of 3 resp. 5 kV.
During the increase, it is very important to observe the charging current of the shield. Sudden
changes or just one single fast increase of the current are a clear indication of a sheath fault
After reaching the nominal test voltage level, single flashovers during the 10 minutes test
duration are not always detected, since the observation of an analogue measuring instrument
requires a lot of concentration
Some of the flashovers happen only once, due to the fact that one single flashover will already
interrupt the fault or will dry it up, causing it to appear like an intact cable sheath. This will
happen especially in long cables where the charged cable capacity contains sufficient energy,
to dry up the fault during the flashover.
Here sheath test systems are preferable, which indicate a single flashover also in the case,
where the unit discharges the shield and switches off after the preset test duration.
For this purpose, the new MFM 10 will automatically record and indicate all these events in the
test protocol
7. 2010-07-13 7
2.5 Safety
The discharge and grounding of the sheath test system and the connected shield should
receive special attention.
The shield capacity, fully charged, contains a dangerous energy and can provide a high
personal hazard.
A shield capacity of app. 1200 pF / m results for a cable lengths of 1000 m in a complete
shield capacity of 1.2 µF. This is a charge of 15 Joules, an energy amount that has to be
considered as highly dangerous when touched.
[ 1 ]
2
2 C
UP = J or Ws
On the other side, this charge is too small to cause further damages at the fault position.
Also for operation within these specific applications, there is the same potential danger and
resulting the same safety rules as for any operation will apply.
For the sheath testing, prelocation or pinpointing of sheath faults it is required to disconnect
the cable shield on all ends of the cable. Since a cable shield may carry a dangerous voltage
potential, it is important to perform the connection (As well as the disconnection) only on a
discharged and grounded shield.
The sheath tester must be only powered up, after all connections have been performed!
Like for any other operation in high voltage environment the 5 safety rules apply!
1. Disconnect power
2. Secure against reconnection
3. Check that there is no voltage
4. Make an earth connection and a short circuit
5. Cover or block access to adjacent components which are energised
8. 2010-07-13 8
3. Sheath fault prelocation
To avoid a long time duration for the pinpoint location procedure, especially on longer cables
and solid surfaces, it is always recommended to do a prelocation. Without prelocation the time
for the location can consume quite some time, thus also extending the thermal load by on the
fault which includes the risk of drying it op, before it has been located.
For the prelocation of sheath faults on cables, high voltage measuring bridges of different type
in varying connections can be used. But these measuring bridges and their methods require
voltage proof technologies, because the measurement can go up to 10 kV.
Usual bridges operate with voltages up to a maximum of some 100 Volts, a voltage level,
which is for the location of sheath faults only seldom sufficient. Another method is the
comparison of the ratio measurement, which evaluates the current, voltage and resistance
before and after the fault position and converts this ratio to the cable length
For this method, the voltage drop of both cable parts and its according partial test current is
measured.
Due to the very high resistive Measurement, the measuring current can be comparatively low,
which makes the complete measurement almost independent from resistances in the
measuring path. Due to this low current, the risk of changing the fault or drying it up is
negligible.
The following described Voltage-Drop-Method in a specific circuit version proved its
performance in many thousands of measurements during the past years.
This method does not require any complex measuring instruments or technologies and
characterises itself by a most simple calculation process. A modern version determines the
fault distance already automatically as soon as the cable length is entered.
Fig. 4: Comparison of ratio method
Definition of details as shown in the above Fig. 4.
Characters like L describe the according value in respect to the complete length, while the
appendix N stands for the distance from near end to the fault position and F represents values
in the section from the fault position to the far end.
L
UN UF
IN
RN
LN
IF
RF
LF
9. 2010-07-13 9
G
!!
!! !!
White
Green
Black
Yellow
L
Rfault
Faulty Sheath
LN , UN , IN , RN LF , UF , IF , RF
!!
3.1 Prelocation with the comparison or voltage drop method
According to Figure 5, a constant current source G is connected between shield and ground.
For this procedure, the shield at both ends of the cable to be tested must be disconnected!
The current flow is though the fault resistance Rfault via the surrounding soil back to the
generator ground.
The current flowing in the route part LN (Cable begin to Fault position) results in a voltage UN in
the size of some millivolts on the shield resistance.
For “test leads” it is possible to use the core of the “faulty” cable and/or core and shield of a
second cable of the same system.
Fig. 5: Principle of prelocation
The voltage drops on the resistance of these” test leads” and the contact resistances of the
connection points are negligible, since the measurement system has a high resistive
measuring input, and do not need to be included into the calculation of the fault distance.
This one of the major advantages of the voltage drop method in comparison with bridge based
procedures.
In a second measurement, the constant current source is now connected though one of the
auxiliary lines through the shield at the far end and the fault resistance Rfault via the
surrounding soil back to the generator ground. The voltage UF is now measured at the shield
resistance of the route part LF. The two partial voltages have the same ratio as the two
distances LN to LF.
According to the following equation [ 2 ] the fault distance LN can be calculated as follows.
[ ]
FN
N
N
UU
U
LL
+
=...2
10. 2010-07-13 10
The only requirement of the voltage drop method is a constant, identical current for both
measurements. Small deviations between the two test currents will reduce the accuracy
For this there are two solutions available.
The first is solved with the state of the art electronic supply, which provides an accuracy of the
regulated constant currents, much higher than required for the stated accuracy.
The second additional solution is the use of calculated resistance values instead of the voltage
drop only. By converting the voltage drop into resistance by simultaneous measuring of current
and voltage at the shield of the cable, the resistances of the partial sections can be calculated.
The equation for this process is as follows.
[ ]
FN
N
N
RR
R
L
+
=...3
A requirement for small measuring deviations are low resistive connection at the cable ends,
since contact resistances will add to the line resistances and may cause deviations in the
measuring results.
In case of several sheath faults at the same cable, error measurements are likely, but
field test have shown that a careful increase of the test voltage locates the fault with the lowest
breakdown voltage first. After the location of this fault the further increase of the voltage will
then allow a second sheath fault location. In this case the result will show the distance
between the two faults, which very often is an average of the complete cable length.
Therefore, special attention is required if the measured fault distance is similar to 50% of the
complete cable length.
Fig. 6: Multiple faults
G
!!
!! !!
White
Green
Black
Yellow
Rfault1
Virtual Fault Spot
!!
Rfault2
11. 2010-07-13 11
Fig. 7: Multiple Faults – Trend of the display to low resistive faults
3.1.1 Bipolar Measurement of the voltage drop
To increase the accuracy of the voltage drop method, the MFM 10 provides the possibility of a
bi-polar measurement. This bi-polar measurement is used to eliminate thermo-electrical and
galvanic effects
Thermo-electrical effects are a result of temperature differences in the conductor and will
result in a polarised offset voltage on top of the real measured voltage and may falsify the test
results. Galvanic effects appear by chemical elements, which are included as metallic ore or
as salt in the soil that functions as return for the current. In combination with humidity and the
flowing current, they will also generate a voltage which may have an influence on the
measured results
With the bi-polar measurement, these effects can be detected and then eliminated by an
according correction of the results.
3.1.2 Advantages and disadvantages of the voltage drop method
Advantages of the voltage drop method are:
- Much less error-sensitivity compared to the bridge-based methods resulting in
significantly higher accuracy of the prelocation results.
- High sensitivity
- Independency from the resistance of the supplementary wires.
- Independency from the difference in sheath and core conductor resistance.
- No need for manual and tedious corrections using equations and a pocket
calculator.
- Fast measurements – no moving parts. No need for time-consuming bridge
balancing adjustment using a high precision and motor-driven potentiometer and
corresponding readout facilities, which cause significant efforts.
- No sensitivity to contact resistance of the test leads
Disadvantages:
- No direct detection of multiple faults
A B C
10R
R
10
R
A B C
10
1
R2
1
21 RR = 10
R
R
100
10
1
0,1
0,01
10
10
1
0,1
0,0
A B C
100
10
1
0,1
0,01
10
10
1
0,1
0,0
R
R
R1
R2
A B C
Rfault1 Rfault2
2
1
12. 2010-07-13 12
3.2 Prelocation with a measuring bridge
3.2.1 Prelocation
In opposition to the voltage drop method, in bridge measurements the resistance value is used
for the evaluation.
For plain resistance measurements it is required to eliminate any external influence. Important
is a very good contact between measuring bridge and test object. The contacts points have to
be carefully cleaned and the contact itself should be done with screw clamps, and not with
clips.
The bridge technology requires a very homogenous line resistance, meaning that the
resistance per length unit has to be a constant parameter. For older cables, water ingress and
the resulting changes of the cross section due to corrosion of the cable shield may result in
resistance in-homogenities.
Similar problems appear, if the cable shields of several segments are jointed inside the joint by
a wire with a smaller cross section. Here it has to be as well expected, that the measuring
result is of lower accuracy.
In the case of cables with graphitized outer sheath, (semiconduction sheath) the fault
resistance is typically lower. The return current flow happens primarily via this layer, and not
through the soil.
3.2.2 Prelocation with MVG 5
The prelocation of sheath faults can also be done with a HV Fault location bridge. In this case
a good shield of the system is used for the bridge circuit. The according circuit setup is shown
in the following fig. 8.
In this case the supply for the high voltage can be delivered from any suitable external high
voltage supply.
Fig. 8: Principle of a measuring bridge
After the bridge adjustment, the distance is evaluated from the percentage according to the
equation [ 4 ].
[ 4 ]
100
[%]
2
M
ll gX =
!
!
!
!
!
! !
MMG 5
0 - 5 kV DC
MVG 5
Faulty shield
Reference shield
13. 2010-07-13 13
3.2.3 Two wire measurement according to Murray
For longer three phased, single core cables in the kilometre range, the two wire measurement
according to Murray can be used. Strict requirement is, that the specific resistance of the
“good” shield is equal to the on of the fault shield. And the good shield must undamaged
without any sheath faults, which due to practical experience rather seldom.
3.2.4 Three wire measurement according to Graaf
If no good shield is available or if the prelocation is done on three cored cables, the three wire
measurement according to Graf has to be used. In this case the insulation resistance of the
good wire (Help Line) has to 1000 times higher than the faulty line resp. sheath.
Fig 9: Principle of a Graaf bridge
A difference of diameter or resistance parameters between good and faulty line is permitted.
In case of short cables, the test leads will influence the measurement
Three measurements have to be done with:
Earth at the begin of the faulty sheath Mk1
Earth to ground: Mk2
Earth at the begin of a good line: Mk3
13
12
KK
KK
X
MM
MM
LL
−
−
⋅=
If no zero adjustment is possible, the result can be corrected by switching the connections for
Measurement Mk2 or MK3.
Mk2 = 200 - Mk2´ (connection white lead – red lead switched)
Mk3 = 200 - Mk3´ (connection black lead – red lead - 2. help line switched)
1. Help Line
2. Help Line
Faulty Line / Shield
Mk1
Mk2
Mk3
Ln
L
Lf
L
13
12
KK
KK
X
MM
MM
LL
−
−
⋅=
100%
[%]M
L
x
L =
14. 2010-07-13 14
In this case the following equation is valid:
13
12
200
200
KK
KK
X
MM
MM
LL
−−
−−
⋅=
3.2.5 Advantages and disadvantages of bridge methods
Advantages are:
Disadvantages are:
Bridge measurements are directly influenced by:
- The amount of the current flowing in the bridge circuit
- a. The accuracy of the measurement depends on the size of the
measuring current.
- b. Sheath faults require some voltage and current to overcome the
insulation and galvanic and resistive influences of the soil.
- The loop resistance
- The matching for power transfer of the internal impedance of the
galvanometer to the bridge resistance
- The sensitivity of the galvanometer
- Linearity of measuring potentiometer
- The contact resistance of all test leads will influence the measurement accuracy.
- No detection of multiple faults
15. 2010-07-13 15
4. Sheath fault pinpointing
4.1 The different methods
For the exact pinpointing, there are four different technologies available
- DC Impulse-Method
- Surge Impulse Method
- Audio Frequency method with direct or capacitive coupling
- Audio Frequency method with modulated frequency 4.8 Hz
All methods are based on the evaluation of the voltage gradients within the fault position,
which can be measured with these different methods and their probes. The different methods
have specific advantages as well as disadvantages, which are not so much a question of
quality and accuracy, but more related to the fault area situation, as underground and surface
condition, and the thermal stability of the fault itself and resulting the ability to manage these
influences
4.2 Voltage gradients
The voltage gradients in the area around the fault consist basically of concentric circles. The
correct interpretation of there gradients is the base of a successful location of the earth fault.
The circles indicate areas of equal potential, and are
called equipotental lines. The closer to the fault, the
higher is the measured step voltage potential. If an
earth fault probe is inserted into the ground in a way,
that both earth electrodes (earth spikes) are on the
same equipotental line, the probe will not see any
potential difference. As result, the indication will be
Fig 10: Voltage gradients around the fault zero. This happens also, if the fault is directly between
the electrodes. But it will also happen if the electrodes
are above the centre of the fault, or half way between fault and ground connection. Similar
effects can also be observed around the earth rod which is used to provide the ground
connection at the connection point of the transmitter. There the return signal produces the
voltage gradients.
If the earth fault probe is moved away from this earthing point towards the fault, the displayed
signal will decrease until the midpoint between earth rod and fault is reached.
At this point the signal amplitude will have
the absolute minimum.
Continuing to move further towards the fault will increase the signal.
70% of the signal are measured at
the last third of the distance.
The measured signal strength Fig: Voltage gradients between connection and fault
is proportional to the amount of
voltage gradients between the earth
spikes. The maximum signal is
displayed, when the spike is directly
on to of the fault.
Fig 11: Voltage gradients between the two earth contacts
16. 2010-07-13 16
4.3 The DC Method
The DC source in this case is like for the sheath fault prelocation, a small DC burner down unit
with adjustable current limitation. The maximum output voltage range can be set to1, 2, 5 or 10
kV, depending on the required or allowed test parameters.
The fault location is done as follows
The sheath test device is connected to the screen of the faulty cable and to the operational
earth / ground.
As described in the Fig 13, the output
voltage of the sheath tester forces a
current through the shield via
the fault and back through the ground
to the ground connection of the tester.
The resulting voltage gradients at the earth
contact of the fault resistance RFault are
then detected and measured with
two earth rods, which measure the value of
the voltage as well as its polarity.
For the localisation of the voltage
gradients, the earth rod a stuck into
the soil, and the voltage is measured.
Fig. 12: Principle of the pinpointing with voltage gradients
For a higher sensitivity, the distance between the two earth rods can be multiples of 10 m at
the start of the location. Close to the fault the step voltage increases to a maximum with a
defined polarity. Here the distance can be reduced to some decimetres or centimetres. If both
earth rods are inserted in the same distance to the fault, the different polarities of the voltages
compensate each other, resulting in a zero Volte display, indicating, that the fault is exactly in
the centre between the two rods. Then the procedure is repeated in a 90°angle to the cable
route, and by the same procedure a second zero point is measured. The crossing point of
these two measurements is directly on top of the fault. The accuracy of this method is in the
centimetre range, and no other technology can reach this accuracy.
17. 2010-07-13 17
! !
R
Fault resistance
At the earth contact
V
0
+-V
0
+-V
0
+
! !!
Fault
V
0
+-V
0
+-V
0
+
ESG 80
Fig. 13: Pinpointing
There is not always the possibility to measure directly on top of the cable route, since the road
surface is often insulating, and the earth rods cannot provide a solid earth contact.
(The drilling of holes to make contact is not always permitted and will increase the time for the
locating process).
In this case it is also possible to shift the whole measurement sideways to the unpaved area of
the road, due to the fact, that the significant voltage gradients have range some ten metres.
At the side of the road, there is always chance to use the free accessible soil, gaps between
stones or between plates to determine the centre of the voltage gradients. The longitudinal
coordinate can then be determined by normal tracing with audio frequency locators.
RF
V
0
+
V
0
+
V
0
+
-
V
0
+
-
V
0
+-
RF
V
0
+
V
0
+
V
0
+
V
0
+
V
0
+
-
V
0
+
-
V
0
+
-
V
0
+
-
V
0
+- V
0
+-
Fig. 14: Determination of the crossing point
18. 2010-07-13 18
4.3.1 Pulsed DC and current limits
When using the DC Method, a periodical interrupt of the current flow has a very positive
effect on the location procedure. External influences of currents in the underground, e.g.
resulting from railway, tram, cathodic protection systems or similar sources will influence the
operation with a straight DC. With a pulsed Signal however, the pointer of the earth fault
probe will show only the capacitive decoupled change of the pulsed signal as a short but
clear directional deflection.
Instead of a zero point, the real fault position will be shown by a change of the polarity. The
pointer can be at any value of the display scale.
The pulsing or duty cycle of the signal, is typically 3 seconds on and 1 second off.
The duty cycle can also be used for receivers without capacitive decoupling, to compensate
for the stray currents and for possible electrolytic effects, which may build up at the probe tips.
For the pinpointing of sheath faults the rule “less is more” applies as well. Large currents will
logically produce larger, better detectable voltage gradients, but the current for the location of
sheath faults performs better between 10 and 100 milliamps. The sheath tester should also
provide the possibility of an automatic current limitation. Both of these limitations have the
purpose to avoid a drying up of the sheath fault due to thermal effects, and will protect other
cable system in the vicinity of the fault. Lower currents will also limit the damage of the sheath
fault which will then allow an easier repair since the inner conductors remain undamaged.
A current limited location procedure has the advantage, that the full power of the sheath tester
is only applied during a short moment, during the change of the fault from high to a low
resistance.
4.3.2 Power
The actual sheath fault location happens only with a low power of some 10 watts. Exact
Details can be taken from the table below. A further reduction of the thermal stress is caused
by the pulsing, which also reduces the duration and following the thermal stress effect of the
current flow through the fault.
Fig. 15: Power diagram MFM 10
19. 2010-07-13 19
4.3.3 Specialties of the DC - Method
For multiple sheath faults, each conductive fault will generate its own voltage gradients.
This will result in so called phantom faults, which cause false measurements
The following Fig. 16 shows such a situation. The correct observation of the polarity changes
during the pinpointing procedure will easily reveal phantom faults by wrong polarity indications
and behaviour.
Fig. 16: Phantom fault
4.3.4 Influences
DC currents in the underground, e.g. resulting from railway, tram, cathodic protection
systems or similar sources will influence the operation with a straight DC. By a capacitor in
series with the input, the DC influence will be blocked, the input signal is differentiated and
the display shows the correct information. An important point is, that always the according
first deflection only indicates the correct direction towards the fault.
4.3.5 Advantages and disadvantages of the DC - Method
Advantages of the DC method are
Prelocation of the fault position
No Error measurements by capacitive coupling
No distortion by 50 Hz or by short switching impulses
No influence to the fault by the location process
Low distorting by external DC
High resistive fault break down
Small loss of sensitivity in case of multiple faults
Disadvantages are:
Low sensitivity
Low sensitivity in case of multiple faults and in some case no breakdown
Difficult location on solid surfaces
RF
!! !!
RF
+
-
+
-
+
-
+
-
+
-
+
-
Phantom fault
20. 2010-07-13 20
4.4 Surge Method
The application of this method is identical to the DC Method, but is based on the discharge of
a surge generator. The output of a surge generator delivers a signal, which is virtually identical
to a pulsed DC.
Warning!
When using this method, highest caution is required. When using the surge method the
current can reach much higher values even with small pulse widths than for the DC method. A
step voltage of 60 V must not be exceeded. The surge energy should be limited to a maximum
of 100 J.
Advantages of the surge method are
Higher sensitivity
Low distortion by external DC
Break down of high resistive fault
Relatively low loss of sensitivity in case of multiple faults
Disadvantages are:
Error measurements by capacitive coupling
Changes to the fault spot by high energy (drying)
High safety requirements
4.5 Localisation of earth contacting faults in LV plastic insulated MV systems
Short circuits (0 Ohms) between core and shield cannot be localised by means of an acoustic
pinpointing method. Sometimes it is possible to locate the fault because the magnetic pick-up
for the Digiphone sees the magnetic signal rapidly reduce on cables with armoured shields.
But 95 % of short circuit faults inside cables with no steel armour are also earth contacting. By
disconnecting the shield on both ends, these faults can be pinpoint located by the DC step
voltage method. This method in combination with reflectometer or voltage drop prelocation has
also performed very well for the fault location on very long cables, for example wind farm
feeders.
Fig 22: Combined earth faults
!RF
RSoil
V
0
+-V
0
+-V
0
+
ESG
!! !RF
Fault – Core – Shield - Ground
V
0
+-V
0
+-V
0
+
21. 2010-07-13 21
4.6 Audio frequency methods
Instead of a DC generator, a powerful audio frequency transmitter is connected between the
faulty cable shield and earth. Audio frequency units are typically used for cable location,
tracing and for the location of low resistive faults and are therefore in most situations available.
The use of the audio frequency method instead of the DC method has some advantages
despite the limited distance.
Audio Frequency can be selectively amplified by the receiver, which permits a very efficient
suppression or filtering of many types of distortions, for example as a result of electrolytic
voltage sources or from stray currents. Additionally the Audio frequency technology allows the
use of a capacitive voltage measurement. The capacitive voltage measurement provides the
possibility to locate sheath faults in case of solid, poor conducting or insulating surfaces which
prevent the use of a conventional step voltage measurement with earth rods, which have to be
inserted into the ground.
Due to the high capacity of the shield towards earth, the supplying audio frequency generator
has a capacitive load. This may result in a low output voltage in the case of an automatic
impedance matching. In this case it is likely that flash over faults may not ignite and the fault
remains undetectable. The capacitive resistance of the shield and the resulting output voltage
of the generator can be calculated by the following equation.
[ 5 ]
C
RC
ω
1
=
[ 6 ] CPRU =
The following table shows the output voltages in respect to different generator power ratings
and frequencies.
To reduce the effect of the capacitive resistance
of the shield and to have the voltage at the sheath
fault position as high as possible, it is strongly
recommended to keep the frequency for the
capacitive step voltage measurements as low as
possible.
Fig 17: Power dependent on Frequency
An according step voltage probe, for example DEB 3-10,
consists of a light frame that carries two capacitive plates in
approximately 0.8 m distance and is easily handled by one
person. Due to its construction it can be used with capacitive
plates or with earth spikes for direct galvanic applications. Like
for the DC Method, the location is done along the cable route
and the voltage gradients around the sheath fault are evaluated. Fig18: Capacitive Probe
50 Watt @ 480 Hz 117 V
50Watt@ 1450 Hz 68 V
50 Watt @ 9820 Hz 26 V
500 Watt @ 480 Hz 370 V
500 Watt@ 1450 Hz 213 V
500 Watt @ 9820 Hz 82 V
22. 2010-07-13 22
4.7 Equipment combination FL 50 with Step voltage Probe DEB 3-10
Fig. 19: Audio Frequency – Step voltage
To increase the sensitivity, the capacitive plates can be exchanged by earth spikes. In this
case, the sensitivity of the receiver has to be adapted.
Capacitive plates allow fault location over all ground surfaces. Spikes require good ground
contact so are best on soft ground, and not hard surfaces unless the condition is improved by
wetting the spike contact areas.
4.8 Audio Frequency Method with 4,8 Hz and A-Frame
The SFL2 A frame is a stand alone unit and can be used alongside a locator to follow the
cable route. The Locator transmitter is connected between the isolated conductor and the
earthing point. The signal generator transmits a low frequency AC 4.8Hz signal and also a
location frequency of 9.82 or 83kHz which is used to locate and trace the conductor.
This causes voltage gradients in the area of
the earth fault which are then detected by the
earth spikes of the A-Frame. The A-Frame
display guides the operator direct to the
correct fault position.
The A frame displays voltage gradient by a
bargraph. At the start of the survey the voltage
gradient is checked and then the reference is
noted. Then tests are made at regular
intervals along the cable.
Where there is no fault, hence no voltage
gradient across the spikes, the active display
shows 0 or low values. When a fault is detected,
the direction to fault is indicated by blinking
arrows, active numbers and bargraph signal
strength increase.
Fig. 20: Audio Frequency with earth spikes (vLoc Pro with A-frame)
max min max
RSoil
! !
R
! !!
Fault
23. 2010-07-13 23
Beyond the fault the direction blinking arrow is reversed and active numbers and bargraph
signal strength decreases.
The exact point of the fault is determined by blinking arrows changing direction and minimum
active value, as the voltage between spikes is minimum. The fault is directly under the centre
of the A frame.
Very close to the fault the active number will be almost the same as the reference value. If it is
substantially less, then more than one fault exists.
If this is the case, the best approach is to dig up and clear the fault and resurvey using shorter
interval between measurements.
Fig. 21: Audio Frequency – Step Voltage with frequency modulation using SFL
The Metrotech SFL and i5000 transmitters are ideal for high resistance faults where a higher
current is needed to pass current to ground. Low resistance sheath faults are better located
with the Vloc Pro system.
Bargraph: The arrow indicates the direction toward the fault and the bargraph shows the
signal strength.
Active: Shows the numerical value of the potential difference along the cable route.
(Maximum on top of the largest fault)
Reference: Shows the maximum potential difference that was measured during
synchronisation.
Like for the DC Method, the principle is the same. The display indicates the direction towards
the sheath fault, by measuring the voltage gradients. Also the crossing measurement to
determine the exact location is done the same way.
24. 2010-07-13 24
Fig. 21: Audio Frequency with earth spikes (vLoc Pro with A-frame)
The fault location technique using the Vloc system is similar to SFL system above. The
transmitter is connected across the isolated cable and a grounding point. The transmitter
signal transmits a 4.8Hz low frequency AC and 8 kHz location signal. The Vloc A frame has no
display, so is connected by a cable to the Vloc pro locator, and automatically sets the locator
display to the faultfinding display.
The contact spikes of the A frame are provided with green and red markings, and green and
red arrows on the locator display indicate direction to fault and signal strength dB numbers.
The locator also provides left/right arrows to indicate the cable route.
The fault pinpointing procedure is similar to SFL2 A frame operation.
4.9 Localisation of earth contacting faults in LV and illumination systems
The pinpointing of earth contacting faults in LV and street illumination systems is a low cost
alternative measuring principle and has spread fast after the introduction of plastic insulated
LV cables. It is made easy and effective using audio frequency A frame types. The
requirement is a plain plastic insulated network without earthing contacts. Old streetlight
systems using T connections to streetlight and armoured cables are not applicable. The
protective earth must be disconnected from the common ground at the feeding point, in the
distributions and as well in the house connection. If the common earth connections and
earthing in house connections cannot be disconnected then the method is not applicable
Especially in the so called secondaries, as the are used in the US Typical LV distributions, the
used cables are mostly single, unshielded conductors.
Due to the short lengths, and the single cores, a TDR based fault location method is almost
impossible.
But especially here, any fault has also earth contact, which permits the easy use of an
A-Frame for the fault location
Final comments
The regular and early testing, detection and location of sheath faults will reduce the amount of
faults, especially in medium voltage cables with extruded outer insulation.
Cable faults can also be located indirectly, since external damages of a cable will often lead
consequentially to real cable faults.
25. 2010-07-13 25
5. Wording
Due to the fact, that especially the area of sheath fault location deals with a huge amount of
different terms, also partially based on local use, we would like to list these words to avoid
confusion among the readers
PILC, Paper Insulated Lead Cable The outer lead sheath will prevent the typical
Sheath fault location due to its continous earth contact.
XLPE, Crosslinked polyethylene Insulation material, also used for the sheath
PVC, Poly vinyl chloride Insulation material, also used for the sheath
Sheath, Jacket, Sleeve Outer cable insulation
Shield, Screen Outer conductor
can be of copper, aluminium, lead
Sometimes made of steel as armour
Semicon Semiconducting filling material between conductors
Insulation, Dielectric The insulating material that insulates the different
conductors from each other
URD Underground Residential Distribution
Secondaries LV Distribution
Primaries MV Distribution