High voltage cable
Encyclopedia
A high voltage cable - also called HV cable - is used for electric power transmission
at high voltage
. High voltage cables of differing types have a variety of applications in instruments, ignition systems, AC and DC power transmission. In all applications, the insulation of the cable must not deteriorate due to the high voltage stress, ozone produced by electric discharges in air, or tracking. The cable system must prevent contact of the high-voltage conductor with other objects or persons, and must contain and control leakage current. Cable joints and terminals must be designed to control the high-voltage stress to prevent breakdown of the insulation. Often a high-voltage cable will have a metallic shield layer over the insulation, connected to earth ground and designed to equalize the dielectric stress on the insulation layer.
High voltage cables may be any length, with relatively short cables used in apparatus, longer cables run within buildings or as buried cables in an industrial plant or for power distribution, and the longest cables are often run as submarine cables
under the ocean for power transmission.
s, high voltage cables have the structural elements of one or more conductors, insulation, and a protective jacket. High voltage cables differ from lower-voltage cables in that they have additional internal layers in the insulation jacket to control the electric field around the conductor.
For circuits operating at or above 2,000 volts between conductors, a conductive shield may surround each insulated conductor. This equalizes electrical stress on the cable insulation. This technique was patented by Martin Hochstadter in 1916; the shield is sometimes called a Hochstadter shield. The individual conductor shields of a cable are connected to earth ground at the ends of the shield, and at splices. Stress relief cones are applied at the shield ends.
Cables for power distribution of 10kV or higher may be insulated with oil and paper, and are run in a rigid steel pipe, semi-rigid aluminum or lead sheath. For higher voltages the oil may be kept under pressure to prevent formation of voids that would allow partial discharge
s within the cable insulation.
Sebastian Ziani de Ferranti
was the first to demonstrate in 1887 that carefully dried and prepared paper could form satisfactory cable insulation at 11,000 volts. Previously paper-insulated cable had only been applied for low-voltage telegraph and telephone circuits. An extruded lead sheath over the paper cable was required to ensure that the paper remained absolutely dry.
Vulcanized rubber was patented by Charles Goodyear
in 1844, but it was not applied to cable insulation until the 1880s, when it was used for lighting circuits. Rubber-insulated cable was used for 11,000 volt circuits in 1897 installed for the Niagara Falls Power Generation project.
Mass-impregnated paper-insulated medium voltage cables were commercially practical by 1895. During World War II
several varieties of synthetic rubber and polyethylene
insulation were applied to cables. Modern high voltage cables use polymers or polyethylene, including (XLPE) for insulation.
is defined as any voltage over 1000 volts. Cables for 3000 and 6000 volts exist, but the majority of cables are used from 10 kV and upward. Those of 10 to 33 kV are usually called medium voltage cables, those over 50 kV high voltage cables.
Modern HV cables have a simple design consisting of few parts. A conductor of copper
or aluminum wires transports the current, see (1) in figure 1. (For a detailed discussion on copper cables
, see main article: Copper wire and cable
.)
Conductor sections up to 2000 mm2 may transport currents up to 2000 amperes. The individual strands are often preshaped to provide a smoother overall circumference. The insulation
(3) may consists of cross-linked polyethylene, also called XLPE. It is reasonably flexible and tolerates operating temperatures up to 120 °C. EPDM is also an insulation.
At the inner (2) and outer (4) sides of this insulation, semi-conducting layers are fused to the insulation. The function of these layers is to prevent air-filled cavities between the metal conductors and the dielectric so that little electric discharge
s can arise and endanger the insulation material.
The outer conductor or sheath (5) serves as an earthed layer and will conduct leakage currents if needed.
Most high voltage cables for power transmission that are currently sold on the market are insulated by a sheath of cross-linked polyethylene
(XLPE). Some cables may have a lead or aluminium jacket in conjunction with XLPE insulation to allow for fiber optics. Before 1960, underground power cables were insulated with oil and paper and ran in a rigid steel pipe, or a semi-rigid aluminium or lead jacket or sheath. The oil was kept under pressure to prevent formation of voids that would allow partial discharge
s within the cable insulation. There are still many of these oil-and-paper insulated cables in use worldwide. Between 1960 and 1990, polymers became more widely used at distribution voltages, mostly EPDM (ethylene propylene diene M-class); however, their relative unreliability, particularly early XLPE, resulted in a slow uptake at transmission voltages. While cables of 330 kV are commonly constructed using XLPE, this has occurred only in recent decades.
First, the introduction of the semiconducting layers. These layers must be absolutely smooth, without even protrusions as small as a few microns. Further the fusion between the insulation and these layers must be absolute; any fission, air-pocket or other defect - of the same micro-dimensions as above - is detrimental for the breakdown characteristics of the cable.
Secondly, the insulation must be free of inclusions, cavities or other defects of the same sort of size. Any defect of these types shortens the voltage life of the cable which is supposed to be in the order of 30 years or more.
Cooperation between cable-makers and manufacturers of materials has resulted in grades of XLPE with tight specifications. Most producers of XLPE-compound specify an “extra clean” grade where the number and size of foreign particles are guaranteed. Packing the raw material and unloading it within a cleanroom
environment in the cable-making machines is required. The development of extruders for plastics extrusion
and cross-linking has resulted in cable-making installations for making defect-free and pure insulations.
Many HVDC cables are used for DC submarine
connections, because at distances over 30 km AC can no longer be used. The longest submarine cable today is the NorNed
cable between Norway and Holland that is almost 600 km long and transports 700 megawatts, a capacity equal to a large power stations.
Most of these long deep-sea cables are made in an older construction, using oil-impregnated paper as an insulator.
Equipotential lines
are shown here which can be compared with the contour lines on a map of a mountainous region: the nearer these lines are to each other, the steeper the slope and the greater the danger, in this case the danger of an electric breakdown. The equipotential lines can also be compared with the isobars on a weather map: the denser the lines, the more wind and the greater the danger of damage.
In order to control the equipotential lines (that is to control the electric field) a device is used that is called a stress-cone, see figure 3. The crux of stress relief is to flare the shield end along a logarithmic curve. Before 1960, the stress cones were hand made using tape—after the cable was installed. These were protected by pothead
s, so named because a potting compound/ dielectric was poured around the tape inside a metal/ porcelain body insulators. About 1960, preformed terminations were developed consisting of a rubber
or elastomer
body that is stretched over the cable end. On this rubber-like body R an shield electrode is applied that spreads the equipotential lines to guarantee a low electric field.
The crux of this device, invented by NKF in Delft
in 1964, is the fact that the bore
of the elastic body R is narrower than the diameter of the cable. In this way the (blue) interface between cable and stress-cone is brought under mechanical pressure so that no cavities or air-pockets can be formed between cable and cone. Electric breakdown in this region is prevented in this way.
This construction can further be surrounded by a porcelain
or silicone insulator for outdoor use, or by contraptions to enter the cable into a power transformer under oil, or switchgear
under gas-pressure.
in 1965 by introducing a device called bi-manchet.
Figure 4 shows a photograph of the cross-section of such a device. At one side of this photograph the contours of a high voltage cable are drawn. Here red represents the conductor of that cable and blue the insulation of the cable. The black parts in this picture are semi-conducting rubber parts. The outer one is at earth potential and spreads the electric field in a similar way as in a cable terminal. The inner one is at high-voltage and shields the connector of the conductors from the electric field.
The field itself is diverted as shown in figure 5, where the equipotential lines are smoothly directed from the inside of the cable to the outer part of the bi-manchet (and vice versa at the other side of the device).
The crux of the matter is here, like in the cable terminal, that the inner bore of this bi-manchet is chosen smaller than the diameter over the cable-insulation. In this way a permanent pressure is created between the bi-manchet and the cable surface and cavities or electrical weak points are avoided.
Installing a terminal or bi-manchet is skilled work. Removing the outer semiconducting layer at the end of the cables, placing the field-controlling bodies, connecting the conductors, etc., require skill, cleanness and precision.
or any other HV device in scientific equipment. They transmit small currents, in the order of milliamperes at DC
voltages of 30 to 200 kV, or sometimes higher. The cables are flexible, with rubber or other elastomer
insulation, stranded conductors, and an outer sheath of braided copper-wire. The construction has the same elements as other HV power cables.
One needs to distinguish between cable testing and cable diagnosis.
While cable testing methods result in a go/no go statement cable diagnosis methods allow judgement of the cables current condition.
In some cases it is even possible to locate the position of the fault in the insulation.
One of the favorite testing methods is VLF cable testing. Using a very low frequency voltage with frequencies in the range of 0.1 to 0.01Hz protects the device under test from deteriorating due to the test itself, as it used to be with DC testing methods in the older days.
Depending on the sort of treeing in the insulation two cable diagnostics methods are common. Water trees can be detected by tan delta measurement. Interpretation of measurement results yield the possibility to distinguish between new, strongly aged and faulty cables and appropriate maintenance and repair measures may be planned.
Damages to the insulation and electrical treeing
may be detected and located by partial discharge measurement. Data collected during the measurement procedure is compared to measurement values of the same cable gathered during the acceptance-test. This allows simple and quick classification of the dielectric condition of the tested cable.
Electric power transmission
Electric-power transmission is the bulk transfer of electrical energy, from generating power plants to Electrical substations located near demand centers...
at high voltage
High voltage
The term high voltage characterizes electrical circuits in which the voltage used is the cause of particular safety concerns and insulation requirements...
. High voltage cables of differing types have a variety of applications in instruments, ignition systems, AC and DC power transmission. In all applications, the insulation of the cable must not deteriorate due to the high voltage stress, ozone produced by electric discharges in air, or tracking. The cable system must prevent contact of the high-voltage conductor with other objects or persons, and must contain and control leakage current. Cable joints and terminals must be designed to control the high-voltage stress to prevent breakdown of the insulation. Often a high-voltage cable will have a metallic shield layer over the insulation, connected to earth ground and designed to equalize the dielectric stress on the insulation layer.
High voltage cables may be any length, with relatively short cables used in apparatus, longer cables run within buildings or as buried cables in an industrial plant or for power distribution, and the longest cables are often run as submarine cables
Submarine power cable
Submarine power cables are major transmission cables for carrying electric power below the surface of the water. These are called "submarine" because they usually carry electric power beneath salt water but it is also possible to use submarine power cables beneath fresh water...
under the ocean for power transmission.
Construction
Like other power cablePower cable
A power cable is an assembly of two or more electrical conductors, usually held together with an overall sheath. The assembly is used for transmission of electrical power...
s, high voltage cables have the structural elements of one or more conductors, insulation, and a protective jacket. High voltage cables differ from lower-voltage cables in that they have additional internal layers in the insulation jacket to control the electric field around the conductor.
For circuits operating at or above 2,000 volts between conductors, a conductive shield may surround each insulated conductor. This equalizes electrical stress on the cable insulation. This technique was patented by Martin Hochstadter in 1916; the shield is sometimes called a Hochstadter shield. The individual conductor shields of a cable are connected to earth ground at the ends of the shield, and at splices. Stress relief cones are applied at the shield ends.
Cables for power distribution of 10kV or higher may be insulated with oil and paper, and are run in a rigid steel pipe, semi-rigid aluminum or lead sheath. For higher voltages the oil may be kept under pressure to prevent formation of voids that would allow partial discharge
Partial discharge
In electrical engineering, partial discharge is a localised dielectric breakdown of a small portion of a solid or fluid electrical insulation system under high voltage stress, which does not bridge the space between two conductors...
s within the cable insulation.
Sebastian Ziani de Ferranti
Sebastian Ziani de Ferranti
Sebastian Pietro Innocenzo Adhemar Ziani de Ferranti was an electrical engineer and inventor.-Personal life:...
was the first to demonstrate in 1887 that carefully dried and prepared paper could form satisfactory cable insulation at 11,000 volts. Previously paper-insulated cable had only been applied for low-voltage telegraph and telephone circuits. An extruded lead sheath over the paper cable was required to ensure that the paper remained absolutely dry.
Vulcanized rubber was patented by Charles Goodyear
Charles Goodyear
Charles Goodyear was an American inventor who developed a process to vulcanize rubber in 1839 -- a method that he perfected while living and working in Springfield, Massachusetts in 1844, and for which he received patent number 3633 from the United States Patent Office on June 15, 1844Although...
in 1844, but it was not applied to cable insulation until the 1880s, when it was used for lighting circuits. Rubber-insulated cable was used for 11,000 volt circuits in 1897 installed for the Niagara Falls Power Generation project.
Mass-impregnated paper-insulated medium voltage cables were commercially practical by 1895. During World War II
World War II
World War II, or the Second World War , was a global conflict lasting from 1939 to 1945, involving most of the world's nations—including all of the great powers—eventually forming two opposing military alliances: the Allies and the Axis...
several varieties of synthetic rubber and polyethylene
Polyethylene
Polyethylene or polythene is the most widely used plastic, with an annual production of approximately 80 million metric tons...
insulation were applied to cables. Modern high voltage cables use polymers or polyethylene, including (XLPE) for insulation.
AC power cable
High voltageHigh voltage
The term high voltage characterizes electrical circuits in which the voltage used is the cause of particular safety concerns and insulation requirements...
is defined as any voltage over 1000 volts. Cables for 3000 and 6000 volts exist, but the majority of cables are used from 10 kV and upward. Those of 10 to 33 kV are usually called medium voltage cables, those over 50 kV high voltage cables.
Modern HV cables have a simple design consisting of few parts. A conductor of copper
Copper wire and cable
Copper has been used in electric wiring since the invention of the electromagnet and the telegraph in the 1820s. The invention of the telephone in 1876 proved to be another early boon for copper wire....
or aluminum wires transports the current, see (1) in figure 1. (For a detailed discussion on copper cables
Copper wire and cable
Copper has been used in electric wiring since the invention of the electromagnet and the telegraph in the 1820s. The invention of the telephone in 1876 proved to be another early boon for copper wire....
, see main article: Copper wire and cable
Copper wire and cable
Copper has been used in electric wiring since the invention of the electromagnet and the telegraph in the 1820s. The invention of the telephone in 1876 proved to be another early boon for copper wire....
.)
Conductor sections up to 2000 mm2 may transport currents up to 2000 amperes. The individual strands are often preshaped to provide a smoother overall circumference. The insulation
Dielectric
A dielectric is an electrical insulator that can be polarized by an applied electric field. When a dielectric is placed in an electric field, electric charges do not flow through the material, as in a conductor, but only slightly shift from their average equilibrium positions causing dielectric...
(3) may consists of cross-linked polyethylene, also called XLPE. It is reasonably flexible and tolerates operating temperatures up to 120 °C. EPDM is also an insulation.
At the inner (2) and outer (4) sides of this insulation, semi-conducting layers are fused to the insulation. The function of these layers is to prevent air-filled cavities between the metal conductors and the dielectric so that little electric discharge
Electric discharge
Electric discharge describes any flow of electric charge through a gas, liquid or solid. Electric discharges include:*Electric glow discharge*Electric arc*Electrostatic discharge*Electric discharge in gases*Leader *Partial discharge...
s can arise and endanger the insulation material.
The outer conductor or sheath (5) serves as an earthed layer and will conduct leakage currents if needed.
Most high voltage cables for power transmission that are currently sold on the market are insulated by a sheath of cross-linked polyethylene
Polyethylene
Polyethylene or polythene is the most widely used plastic, with an annual production of approximately 80 million metric tons...
(XLPE). Some cables may have a lead or aluminium jacket in conjunction with XLPE insulation to allow for fiber optics. Before 1960, underground power cables were insulated with oil and paper and ran in a rigid steel pipe, or a semi-rigid aluminium or lead jacket or sheath. The oil was kept under pressure to prevent formation of voids that would allow partial discharge
Partial discharge
In electrical engineering, partial discharge is a localised dielectric breakdown of a small portion of a solid or fluid electrical insulation system under high voltage stress, which does not bridge the space between two conductors...
s within the cable insulation. There are still many of these oil-and-paper insulated cables in use worldwide. Between 1960 and 1990, polymers became more widely used at distribution voltages, mostly EPDM (ethylene propylene diene M-class); however, their relative unreliability, particularly early XLPE, resulted in a slow uptake at transmission voltages. While cables of 330 kV are commonly constructed using XLPE, this has occurred only in recent decades.
Quality
During the development of the HV insulation, which has taken about half a century, two characteristics proved to be paramount.First, the introduction of the semiconducting layers. These layers must be absolutely smooth, without even protrusions as small as a few microns. Further the fusion between the insulation and these layers must be absolute; any fission, air-pocket or other defect - of the same micro-dimensions as above - is detrimental for the breakdown characteristics of the cable.
Secondly, the insulation must be free of inclusions, cavities or other defects of the same sort of size. Any defect of these types shortens the voltage life of the cable which is supposed to be in the order of 30 years or more.
Cooperation between cable-makers and manufacturers of materials has resulted in grades of XLPE with tight specifications. Most producers of XLPE-compound specify an “extra clean” grade where the number and size of foreign particles are guaranteed. Packing the raw material and unloading it within a cleanroom
Cleanroom
A cleanroom is an environment, typically used in manufacturing or scientific research, that has a low level of environmental pollutants such as dust, airborne microbes, aerosol particles and chemical vapors. More accurately, a cleanroom has a controlled level of contamination that is specified by...
environment in the cable-making machines is required. The development of extruders for plastics extrusion
Plastics extrusion
Plastics extrusion is a high volume manufacturing process in which raw plastic material is melted and formed into a continuous profile. Extrusion produces items such as pipe/tubing, weather stripping, fence, deck railing, window frames, adhesive tape and wire insulation.-Process:In the extrusion of...
and cross-linking has resulted in cable-making installations for making defect-free and pure insulations.
HVDC cable
A high voltage cable for HVDC transmission has the same construction as the AC cable shown in figure 1. The physics and the test-requirements are different. In this case the smoothness of the semiconducting layers (2) and (4) is of utmost importance. Cleanliness of the insulation remains imperative.Many HVDC cables are used for DC submarine
Underwater
Underwater is a term describing the realm below the surface of water where the water exists in a natural feature such as an ocean, sea, lake, pond, or river. Three quarters of the planet Earth is covered by water...
connections, because at distances over 30 km AC can no longer be used. The longest submarine cable today is the NorNed
NorNed
NorNed is a long HVDC submarine power cable between Feda in Norway and the seaport of Eemshaven in the Netherlands, which interconnects both countries' electricity grids. It is the longest submarine power cable in the world. Budgeted at €550 million, and completed at a cost of €600m, the...
cable between Norway and Holland that is almost 600 km long and transports 700 megawatts, a capacity equal to a large power stations.
Most of these long deep-sea cables are made in an older construction, using oil-impregnated paper as an insulator.
Cable terminals
Terminals of high voltage cables must manage the electric fields at the ends. Without such a construction the electric field will concentrate at the end of the earth-conductor as shown in figure 2.Equipotential lines
Contour line
A contour line of a function of two variables is a curve along which the function has a constant value. In cartography, a contour line joins points of equal elevation above a given level, such as mean sea level...
are shown here which can be compared with the contour lines on a map of a mountainous region: the nearer these lines are to each other, the steeper the slope and the greater the danger, in this case the danger of an electric breakdown. The equipotential lines can also be compared with the isobars on a weather map: the denser the lines, the more wind and the greater the danger of damage.
In order to control the equipotential lines (that is to control the electric field) a device is used that is called a stress-cone, see figure 3. The crux of stress relief is to flare the shield end along a logarithmic curve. Before 1960, the stress cones were hand made using tape—after the cable was installed. These were protected by pothead
Pothead
A pothead is a type of insulated electrical terminal used for transitioning from overhead to underground high voltage cable or for connecting overhead wiring to equipment like transformers. Its name comes from the process of potting or encapsulation of the conductors inside the terminal's...
s, so named because a potting compound/ dielectric was poured around the tape inside a metal/ porcelain body insulators. About 1960, preformed terminations were developed consisting of a rubber
Rubber
Natural rubber, also called India rubber or caoutchouc, is an elastomer that was originally derived from latex, a milky colloid produced by some plants. The plants would be ‘tapped’, that is, an incision made into the bark of the tree and the sticky, milk colored latex sap collected and refined...
or elastomer
Elastomer
An elastomer is a polymer with the property of viscoelasticity , generally having notably low Young's modulus and high yield strain compared with other materials. The term, which is derived from elastic polymer, is often used interchangeably with the term rubber, although the latter is preferred...
body that is stretched over the cable end. On this rubber-like body R an shield electrode is applied that spreads the equipotential lines to guarantee a low electric field.
The crux of this device, invented by NKF in Delft
Delft
Delft is a city and municipality in the province of South Holland , the Netherlands. It is located between Rotterdam and The Hague....
in 1964, is the fact that the bore
Bore
Bore may refer to:* Bore , the diameter of a cylinder in a piston engine* Bore , the interior chamber of a wind instrument* Bore , a district of Ethiopia that includes the town of Bore* Boré, Mali...
of the elastic body R is narrower than the diameter of the cable. In this way the (blue) interface between cable and stress-cone is brought under mechanical pressure so that no cavities or air-pockets can be formed between cable and cone. Electric breakdown in this region is prevented in this way.
This construction can further be surrounded by a porcelain
Porcelain
Porcelain is a ceramic material made by heating raw materials, generally including clay in the form of kaolin, in a kiln to temperatures between and...
or silicone insulator for outdoor use, or by contraptions to enter the cable into a power transformer under oil, or switchgear
Switchgear
The term switchgear, used in association with the electric power system, or grid, refers to the combination of electrical disconnects, fuses and/or circuit breakers used to isolate electrical equipment. Switchgear is used both to de-energize equipment to allow work to be done and to clear faults...
under gas-pressure.
Cable joints
Connecting two high-voltage cables with one another poses two main problems. First, the outer conducting layers in both cables shall be terminated without causing a field concentration, similar as with the making of a cable terminal. Secondly, a field free space shall be created where the cut-down cable insulation and the connector of the two conductors safely can be accommodated. These problems have been solved by NKF in DelftDelft
Delft is a city and municipality in the province of South Holland , the Netherlands. It is located between Rotterdam and The Hague....
in 1965 by introducing a device called bi-manchet.
Figure 4 shows a photograph of the cross-section of such a device. At one side of this photograph the contours of a high voltage cable are drawn. Here red represents the conductor of that cable and blue the insulation of the cable. The black parts in this picture are semi-conducting rubber parts. The outer one is at earth potential and spreads the electric field in a similar way as in a cable terminal. The inner one is at high-voltage and shields the connector of the conductors from the electric field.
The field itself is diverted as shown in figure 5, where the equipotential lines are smoothly directed from the inside of the cable to the outer part of the bi-manchet (and vice versa at the other side of the device).
The crux of the matter is here, like in the cable terminal, that the inner bore of this bi-manchet is chosen smaller than the diameter over the cable-insulation. In this way a permanent pressure is created between the bi-manchet and the cable surface and cavities or electrical weak points are avoided.
Installing a terminal or bi-manchet is skilled work. Removing the outer semiconducting layer at the end of the cables, placing the field-controlling bodies, connecting the conductors, etc., require skill, cleanness and precision.
X-ray cable
X-ray cables are used in lengths of several meters to connect the HV source with an X-ray tubeX-ray tube
An X-ray tube is a vacuum tube that produces X-rays. They are used in X-ray machines. X-rays are part of the electromagnetic spectrum, an ionizing radiation with wavelengths shorter than ultraviolet light...
or any other HV device in scientific equipment. They transmit small currents, in the order of milliamperes at DC
Direct current
Direct current is the unidirectional flow of electric charge. Direct current is produced by such sources as batteries, thermocouples, solar cells, and commutator-type electric machines of the dynamo type. Direct current may flow in a conductor such as a wire, but can also flow through...
voltages of 30 to 200 kV, or sometimes higher. The cables are flexible, with rubber or other elastomer
Elastomer
An elastomer is a polymer with the property of viscoelasticity , generally having notably low Young's modulus and high yield strain compared with other materials. The term, which is derived from elastic polymer, is often used interchangeably with the term rubber, although the latter is preferred...
insulation, stranded conductors, and an outer sheath of braided copper-wire. The construction has the same elements as other HV power cables.
Testing of high voltage cables
There are different causes for faulty cable insulations. Hence, there are various test and measurement methods to prove fully functional cables or to detect faulty ones.One needs to distinguish between cable testing and cable diagnosis.
While cable testing methods result in a go/no go statement cable diagnosis methods allow judgement of the cables current condition.
In some cases it is even possible to locate the position of the fault in the insulation.
One of the favorite testing methods is VLF cable testing. Using a very low frequency voltage with frequencies in the range of 0.1 to 0.01Hz protects the device under test from deteriorating due to the test itself, as it used to be with DC testing methods in the older days.
Depending on the sort of treeing in the insulation two cable diagnostics methods are common. Water trees can be detected by tan delta measurement. Interpretation of measurement results yield the possibility to distinguish between new, strongly aged and faulty cables and appropriate maintenance and repair measures may be planned.
Damages to the insulation and electrical treeing
Electrical treeing
Within the field of electrical engineering, treeing is an electrical pre-breakdown phenomenon. It is a damaging process due to partial discharges and progresses through the stressed dielectric insulation, whose path resembles the form of a tree....
may be detected and located by partial discharge measurement. Data collected during the measurement procedure is compared to measurement values of the same cable gathered during the acceptance-test. This allows simple and quick classification of the dielectric condition of the tested cable.
External Links
- Tan delta measurement of medium and high voltage cables
- Partial discharge measurement to detect and locate electrical trees
Sources and notes
This article is based on:- [1] F.H. Kreuger, Industrial High Voltage, Delft University Press, 1991, ISBN 90-6275-561-5. Parts 1, 2 and 3 in one Volume.
- [2] ibid, Industrial High Voltage, Delft University Press, 1992, ISBN 90-6275-562-3. Parts 4, 5 and 6 in one Volume.
- [3] E. Kuffel, W.S. Zaengl, High Voltage Engineering, Pergamon Press, Oxford; later edition 2004, Butterworth-Heinemann, ISBN 0-7506-3634-3.