GB2080958A - Apparatus for testing insulators - Google Patents
Apparatus for testing insulators Download PDFInfo
- Publication number
- GB2080958A GB2080958A GB8120998A GB8120998A GB2080958A GB 2080958 A GB2080958 A GB 2080958A GB 8120998 A GB8120998 A GB 8120998A GB 8120998 A GB8120998 A GB 8120998A GB 2080958 A GB2080958 A GB 2080958A
- Authority
- GB
- United Kingdom
- Prior art keywords
- insulator
- conductors
- support
- successive
- test
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Granted
Links
Classifications
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
- G01R31/12—Testing dielectric strength or breakdown voltage ; Testing or monitoring effectiveness or level of insulation, e.g. of a cable or of an apparatus, for example using partial discharge measurements; Electrostatic testing
- G01R31/1227—Testing dielectric strength or breakdown voltage ; Testing or monitoring effectiveness or level of insulation, e.g. of a cable or of an apparatus, for example using partial discharge measurements; Electrostatic testing of components, parts or materials
- G01R31/1245—Testing dielectric strength or breakdown voltage ; Testing or monitoring effectiveness or level of insulation, e.g. of a cable or of an apparatus, for example using partial discharge measurements; Electrostatic testing of components, parts or materials of line insulators or spacers, e.g. ceramic overhead line cap insulators; of insulators in HV bushings
Abstract
Apparatus for testing a cap and pin insulator assembly comprises a plurality of flexible conductors 12 spaced apart on an insulating support or supports 10, 11 and arranged so that the various conductors can be put against the successive metal elements in the insulator assembly between the successive insulator elements to effect electrical connection thereto. Permanent magnets 13 may be provided to hold the flexible conductors against the metal elements of the insulator assembly. A test unit 26 including insulation resistance measuring means is provided together with a switching device located in the test unit or on the insulating support 10, 11 arranged for connecting the measuring means in succession across the successive insulator units so that the resistance of the various units in the insulator assembly may be measured.
Description
SPECIFICATION
Apparatus for testing insulators on high voltage electrical supply lines
This invention relates to apparatus for testing insulators on high voltage supply lines.
The invention is particularly concerned with the testing of cap and pin insulators. Insulators of this type are widely used throughout the world because they have certain significant advantages compared with other types of insulators, such as long rod insulators. Their performance under conditions of pollution is better than long rod insulators. Also, shattering of the insulating material in any one unit of a high voltage cap and pin insulator string will not cause mechanical failure. With a toughened glass cap and pin insulator, mechanical damage will cause the glass to shatter and visual inspection indicates that a unit should be replaced. However, glass insulators are more vulnerable to spark damage than porcelain insulators and sometimes shatter for reasons which are not fully understood.Hence porcelain cap and pin units are widely used throughout the world for insulating overhead lines.
The present invention is concerned with the problem of detecting faulty units in a cap and pin insulator assembly. If enough individual units in a string are faulty, the effective length of the string will be reduced until either on over-voltage produces flashover or the weather conditions and pollution deposits are such as to cause flashover at the working voltage. When flashover takes place, the arc current will often fiow through the defective insulator rather than around it, particularly if moisture has penetrated any cracks within the cap. An insulator through which an arc passes will usually disintegrate and hence the conductor will fall unless there is an additional supporting string. If a string has one or more defective units, not only are flashovers more likely but the resulting faults are often persistent rather than transient.However, a fallen conductor may be held by the adajcent insulators at a reduced height without making contact with earth and may inadvertently be re-energised and thus present a hazard to the public.
It is known to check cap and pin insulators, in situ, with the line live. The detection of faulty units, in this case, is usually effected by means of a test stick having two probes on the stick arranged for making contact across a single unit of an insulator chain and the voltage across this unit has been indicated by an electrostatic voltmeter which made up one arm of a capacitive divider across the probe. The probe is used to measure the voltage across the various insulator units in a chain when the insulators are dry and any unit with an indicated voltage less than some predetermined value is considered suspect. An alternative technique has been to use a small sphere gap connected across two probes and set to spark over at a suitable voltage. Such a device will produce a high frequency signal which can be detected on the ground.Failure to obtain a signal indicates a possibly defective unit. Test sticks, particularly at higher voltages such as 275 and 400 kV are very cumbersome and hence the testing rate is slow.
Also for live line working, an instrument has
been developed which can be fitted to the earth end of the string which is moved, either by a batterydriven motor or by a gravity down the string, successively shorting out units of the insulator chain, applying direct voltage to the unit and sending the measured resistance by coded audio frequency to a remote recorder. Such an instrument is complex and has certain limitations, namely that it is only suitable for single suspension or half "V" or double tension insulator strings, and that a linesman on a crossarm employing the equipment would in many cases infringe safe clearances.
It is an object of the invention to provide an improved form of test apparatus for testing cap and pin insulator chains on a dead line, enabling rapid checking to be effected on each insulator assembly.
According to this invention an apparatus for testing a cap and pin insulator assembly comprises a plurality of flexible conductors, the conductors being spaced apart on a rigid insulating support such that the various conductors can be put against the successive metal elements in the insulator assembly between the successive insulator elements to effect electrical connection to the respective conductors, a test unit comprising insulation-resistance measuring means, and a switching device for connecting the measuring means in succession across the successive insulator units in the insulator assembly. Preferably each conductor has one or more permanent magnets to hold the conductor against the metal element (which is normally steel) in the insulator assembly.
The main physical problem in in situ testing is to get access to each unit. It will be seen that, with the above-described apparatus, all the electrical contacts are made at one time thereby avoiding any necessity of, after each application of a voltage to an insulator unit, getting access to the next unit and making connections thereto.
The switching device may comprise relays; such relays conveniently are located on said rigid insulating bus. In this case a high voltage bus system may be employed with high voltage relays to permit the application of the test voltage to selected insulator units. Means may be provided to program the relays to scan automatically in sequence the insulator units or to allow a particular unit to be inspected on demand.
Instead of having the switching device on said rigid insulating support, it may be located in said test unit. In this case, a multi-lead connector may be provided between the insulating support and the test unit, this connector having separate leads electrically connected to each of said flexible conductors.
Thus, in one form of this invention, an apparatus for testing a cap and pin insulator
assembly comprises a plurality of flexible
conductors, the conductors being spaced apart on
a rigid insulating support such that the various
conductors can be put against the successive
metal elements in the insulator assembly between
the successive insulator elements to effect
electrical connection to the respective conductors,
a multi-lead connector extending between the
insulating support, and a test unit, the connector
having separate leads for each of the
aforementioned flexible conductors and the test
unit comprising insulation-resistance measuring
means with a switching device for connecting the
measuring means in succession across the
successive insulator units in the insulator
assembly.
The insulation-resistance measuring means
conveniently comprises a test voltage source and
current indicator. The test voltage might be from
500 V to 50 kV and may be a.c. or d.c. This test
source must be of low enough impedance to
detect a low resistance such as would occur if a
crack or puncture hole in the insulator unit is filled
with moisture and/or discharge products. The test
voltage preferably however is high enough to
break down the air in a crack through the insulator
head so that a clean crack of puncture hole can be
detected; such a crack might typically be about
30 mm thick and hence a voltage of 2 to 30 kV is preferred. It has been found that a voltage of 5 to
10 kV is adequate for most types of defect. A d.c.
voltage is convenient. Any crack eventually fills
with dirt and moisture and presents the
characteristics of a resistor rather than an air gap.
It has been found that a measured insulator
resistance of less than 10 M.ohms almost
invariably indicates a defective unit and a value
greater than 100 M.ohms indicates a sound one.
The surface resistance of the insulator is in parallel
with the internal resistance and a low surface
resistance can be misinterpreted as that of a
defective insulator. Hence testing is preferably
carried out in dry conditions, say with a relative
humidity less than 70%, to avoid problems of a
wet surface on the insulator. If an insulator is very
dirty or is visibly wet, it may be necessary to clean
and dry it. It has been found that such a procedure
enables the vast majority of defective insulators to
be detected using a test voltage of 10 kV d.c.
The use of a rigid support with flexible
connectors which are magnetically attached to the
insulator chain enables an operator, holding the
support at one end, to position it on or against the
insulator assembly. It thus enables rapid and easy
access to be obtained to test insulator assemblies
which may be hanging down or outwards from, for
example, tower cross-arms 50 to 200 ft above the
ground.
The above-described apparatus thus enables
the insulators in an insulator chain to be tested
very rapidly. The testing can be effected in situ on
overhead lines for suspension insulators and
tension insulators with the line made dead and
earthed only for the necessary time to effect the
testing.
in one form of construction, the aforementioned flexible conductors are formed of copper braid. In apparatus for testing tension insulators, which extend in a generally horizontal direction, the various conductors of copper braid may be arranged to extend between two rigid elongate insulating elements forming said supports with at least one magnet attached to each length of braid intermediate its ends, preferably at or near the centre of its length. With this construction, the two rigid insulating elements, conveniently tubes, enable the flexible conductors to be put over the insulator assembly with the rigid insulating elements spacing the conductors apart along the assembly, the insulating elements hanging down, one on each side of the insulator assembly. With the linesman sitting on the string, the apparatus can readily be correctly positioned.No further positioning means is required. Long strings of insulators can be tested in sections. One or both of the insulating supports may be a hollow tube of insulating material and the connections to the braid may be taken through the tube to a multi-way connector at one end of the tube. If two support tubes are used alternate connections may be taken through the separate tubes so as to avoid any risk of interlead insulation breakdown within the tubes.
In another arrangement, more particularly for suspension insulators, a single support tube is used and the aforementioned flexible conductors may be spring arms, e.g. phosphor bronze arms, each arm having a permanent magnet to hold it in contact with the metal part of the cap and pin insulator.
Particularly in apparatus having a single support member and used for testing suspension insulators, it may be convenient to form the aforementioned support tube with positioning means, e.g. an adjustable fork which can be positioned on an overhead conductor or on an arcing horn to locate the lower end of the support member. The support member (e.g. tube) may be made rotatable about its axis with respect to the positioning means so that the various arms can be swung into position against the insulator caps to make contact with the metal parts of the insulator chain.
The following is a description of a number of embodiments of the invention, reference being made to the accompanying drawings in which:
Figure 1 illustrates a test apparatus for a nineunit cap and pin tension insulator;
Figure 2 illustrates how the apparatus of Figure
1 is located on an insulator assembly;
Figure 3 illustrates diagrammatically the electrical connection for an eleven-unit tester; and
Figures 4 and 5 illustrate another construction of test apparatus arranged for testing suspension
insulators.
Referring to Figure 1 there is shown diagrammatically part of a test apparatus for a nine-unit cap and pin insulator assembly used as a tension insulator on a 132 kV overhead line. This test apparatus comprises two rigid insulating tubes 10, 11, typically formed of polyvinylchloride, between which tubes extend ten lengths of flexible copper braid 12. Each length of copper braid has a permanent magnet 1 3 attached at the centre of the length. The lengths of copper braid are spaced apart a distance corresponding to the distance between the caps of the units in the insulator assembly.The test apparatus is arranged so that the flexible braid conductors can be located on an insulator assembly, as shown diagrammatically in Figure 2, with the magnets 13 holding the braid 12 in electrical contact with the metal portions 20 of an insulator assembly having porcelain insulator units 21.
The two tubes 10, 11 form, in effect, a laddershaped unit which can be put over an insulator by a linesman holding the unit at one end. The flexible braids are put in contact with the metal parts of the various units forming the insulator assembly and the tubes 10, 11 allowed to hang down so that the unit remains in position without any further fixing. The magnets ensure that the braids 1 2 remain in contact with the metal portions of the insulator assembly.
In the particular embodiment illustrated in
Figure 1, measurement leads are taken from each length of braid 12, where it is attached to the tube 11, and extend through a small hole in the tube near the point of attachment of the braid and along the length of the tube to a multi-lead flexible connector 24 which is connected, for example by a pin and socket connector 25 or plug box, to a test unit 26. This test unit is an insulation tester, conveniently battery-powered, arranged to produce an output d.c. voltage adjustable in the range of 2 to 10 kV and having a current meter for reading the resultant current when the voltage is applied to a high resistance.As shown in Figure 3, two linked selector switches 30, 31 enable the resistance measuring device comprising the voltage generator 32 and meter 33 to be selectively connected across any one of the units of the insulator assembly to check the insulation resistance of that unit. Operation of the switches 30, 31 enables the successive units in the chain to be checked in turn.
By operation of the two switches 30,31, which are mechanically interlinked, each unit of the insulator chain is tested in turn and the meter 33 indicates whether or not the resistance is satisfactory. Instead of a meter, it may in some cases be preferred to use indicator lamps, for example to indicate a resistance greater than 100 M.ohms, or less than 10 M.ohms or an intermediate value. Thus by having a set of lights for each insulator unit connected to the tester, and an automatic switch, it is possible to carry out the testing automatically once connection is made to the insulator units.
Automatic data recording means may be provided for recording the measured data.
Figures 4 and 5 illustrate another construction of test apparatus, arranged in this case more particularly for use on a suspension insulator. As shown in Figure 4 an insulating support tube 40, typically formed of resin-bonded-glass fibre, is rotatable about its axis with respect to a supporting metal fork 41 which is adapted to rest on the conductor suspended by the insulator or on an arcing horn. Between the forks 41 and tube 40 is a threaded adjustment 42 enabling the position of the fork to be adjusted axially with respect to the tube. This fork is made of metal and is electrically connected via the adjusting screw and flexible conducting braid 43 to one of the leads in a multi-core connector cable 44. Along the length of the tube 40 are a plurality of arms 45 of spring material, e.g. phosphor bronze strips.Each of these arms 45, as shown in Figure 4, is bolted onto a metal clamp 46 around the tube 40, the tube having a locating spine 47 of insulating material which locates the clamp to prevent rotation thereof about the axis of the tube. Each arm 45 is connected by a flexible copper braid 49 to a connector 50 which extends into the inside of the tube 40 and is connected to an appropriate conductor in the multi-core connector cable 44.
On each of the spring arms 45, in this particular embodiment, there are two permanent magnets 51, 52 for holding the arm in electrical contact with the metal part of the insulator cap. The spacing between the arms 45 (which can be adjusted) is made in accordance with the insulator dimensions. This device is used by putting the fork 41 on the conductor or arcing horn and then rotating the tube 40 about its axis, conveniently making use of pivoted arms 53, 54 on one end of the tube 40 as handles, to set the various arms 45 in contact with the metal parts of the various insulator units along the chain. The multi-core connector 44 is connected to a test set, as described with reference to Figure 3, enabling the insulation resistance of the various units in the chain to be checked.
One arm of the fork 41 has a hook portion 55 on its end. In some circumstances, it is possible for a linesman to stand on a crossarm of a tower and to apply the tester to an insulator string suspended from another higher arm; the hook 55 enables the test device to be hooked over the toparcing fitting on this higher insulator string to be supported thereby whilst the various arms 45 are set into contact with the metal parts of the insulator units along the chain.
For very high voltage insulators, e.g. 400 kV insulators, it may be convenient to make the support tube, e.g the tube 40 in Figure 4, of jointed construction so that it may be carried in two parts, a spring loaded hole and plug latch being used to hold the tubes together in their correct relative positions with a jointing piece of insulating material fixed in one length of tube end and a free fit in the other length of tube. Instead of forming the support in two parts with a connector, the two parts might be hinged together.
The arms 45 may be hingedly connected to the tube 40 for ease of carrying. In this case, a simple insulating rod or filament arrangement may be provided to push or pull the arms into their operating position.
During testing, for safety. the line end of the insulator string to be tested and the test instrument case are both earthed. For ease of working, a single switching operation from one pair of measuring leads to the next is desirable, but, since both ends of the insulator string are earthed, such a system requires the test voltage polarity to be reversed during the test sequence. It will be noted that the switching arrangement shown in Figure 3 makes provision for this, the contacts E and F on the selector switch 31 being common and the switch connections are arranged so that the high voltage can only be applied to intermediate points along the insulator chain and not to the two ends thereof. This switch can be used for any number (n) between 6 and 11 insulator units without modification to the circuit provided that the plug connections are made in sequence and start from the end (i.e. A, B, C... n).
A similar switch on the same principle can be designed for any number of insulator units.
For safety reasons, the test apparatus may be provided with an interlock which prevents switching on of the tester until it has been earthed, e.g. to a supporting tower. Also an interlock may be provided which prevents testing until both the test set operator and the operator handling the unit to be put on the insulator assembly are simultaneously pressing appropriate buttons.
Conveniently the apparatus includes a means for monitoring the ambient humidity so that data about local humidity may be recorded with the insulator resistance data.
Claims (22)
1. Apparatus for testing a cap and pin insulator assembly comprising a plurality of flexible conductors, the conductors being spaced apart on a rigid insulating support such that the various conductors can be put against the successive metal elements in the insulator assembly between the successive insulator elements to effect electrical connection to the respective conductors, a test unit comprising insulation-resistance measuring means, and a switching device for connecting the measuring means in succession across the successive insulator units in the insulator assembly.
2. Apparatus as claimed in claim 1 wherein the switching device comprises relays.
3. Apparatus as claimed in claim 2 wherein said relays are located on said rigid insulating support.
4. Apparatus as claimed in claim 1 wherein the switching device is located in said test unit.
5. Appparatus as claimed in claim 4 wherein a multi-lead connector is provided between the insulating support and the test unit, the connector having separate leads electrically connected to each of said flexible conductors.
6. Apparatus for testing a cap and pin insulator assembly comprising a plurality of flexible conductors, the conductors being spaced apart on a rigid insulating support such that the various conductors can be put against the successive metal elements in the insulator assembly between the successive insulator elements to effect electrical connection to the respective conductors, a multi-lead connector extending between the insulating support and a test unit, the connector having separate leads electrically connected to each of the aforementioned flexible conductors, and the test unit comprising insulation-resistance measuring means with a switching device for connecting the measuring means in succession across the successive insulator units in the insulator assembly.
7. Apparatus as claimed in any of the preceding claims wherein each flexible conductor has one or more permanent magnets to hold the conductor against the metal element.
8. An apparatus as claimed in any of the s preceding claims wherein the insulationresistance measuring means comprises a test voltage source and current indicator.
9. Apparatus as claimed in claim 8 wherein the test voltage source provides a direct voltage in the range between 2 and 30 kV.
10, An apparatus as claimed in claim 8 wherein the test voltage source provides a direct voltage between 5 and 10 kV.
11. An apparatus as claimed in any of claims 8 to 10 wherein the test voltage source provides an adjustable voltage.
12. An apparatus as claimed in any of claims 8 to 11 wherein the test voltage source provides a voltage with respect to earth and wherein the switching device is arranged so that the test voltage with respect to earth is applied only to a selected intermediate one of said conductors, and an adjacent conductor is earthed.
13. Apparatus as claimed in any of the preceding claims wherein said flexible conductors are formed of copper braid.
14. Apparatus as claimed in claim 1 3 wherein the conductors of copper braid are arranged to extend between two rigid elongate insulating elements forming said support, with at least one magnet attached to each length of braid intermediate the ends thereof.
1 5. Apparatus as claimed in claim 14 wherein said magnets are attached to the centres of each length of braid.
1 6. Apparatus as claimed in either claim 14 or claim 1 5 wherein said insulating elements are each a hollow tube of insulating material and wherein connections to the braid are taken through a tube to a multi-way connector at one end of the tube.
17. Apparatus as claimed in claim 16 and having two support tubes with alternate connections taken through the separate tubes.
1 8. Apparatus as claimed in any of claims 1 to 12 wherein the flexible conductors are spring arms, each arm having a permanent magnet to hold it in contact with the metal part of the cap and pin insulator.
19. Apparatus as claimed in claim 18 and - having a single rigid support, wherein said support has positioning means for locating the support on an overhead conductor or on an arcing horn.
20. Apparatus as claimed in claim 1 9 wherein said rigid support is a tube rotatable about its axis with respect to the positioning means so that the various arms can be swung into position against the insulator caps to make contact with the metal parts of the insulator chain.
21. Apparatus as claimed in any of the preceding claims wherein the insulationresistance measuring means includes means for setting in adjustable resistance limits and visual indicator means for indicating whether a measured valve is above or below such a limit.
22. Apparatus for testing a cap and pin insulator assembly substantially as hereinbefore described with reference to Figures 1 to 3 or with reference to Figures 4 and 5 of the accompanying drawings.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB8120998A GB2080958B (en) | 1980-07-08 | 1981-07-07 | Apparatus for testing insulators |
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB8022355 | 1980-07-08 | ||
| GB8120998A GB2080958B (en) | 1980-07-08 | 1981-07-07 | Apparatus for testing insulators |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| GB2080958A true GB2080958A (en) | 1982-02-10 |
| GB2080958B GB2080958B (en) | 1984-04-11 |
Family
ID=26276150
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB8120998A Expired GB2080958B (en) | 1980-07-08 | 1981-07-07 | Apparatus for testing insulators |
Country Status (1)
| Country | Link |
|---|---|
| GB (1) | GB2080958B (en) |
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN112485177A (en) * | 2020-11-19 | 2021-03-12 | 贵州电网有限责任公司 | Detection method and application of composite insulator core rod through hole |
| RU203898U1 (en) * | 2020-12-11 | 2021-04-26 | федеральное государственное бюджетное образовательное учреждение высшего образования "Национальный исследовательский университет "МЭИ" (ФГБОУ ВО "НИУ "МЭИ") | BREAKDOWN AND OVERLAPPED INSULATOR INDICATOR |
-
1981
- 1981-07-07 GB GB8120998A patent/GB2080958B/en not_active Expired
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN112485177A (en) * | 2020-11-19 | 2021-03-12 | 贵州电网有限责任公司 | Detection method and application of composite insulator core rod through hole |
| CN112485177B (en) * | 2020-11-19 | 2023-06-06 | 贵州电网有限责任公司 | Method for detecting through hole of composite insulator core rod |
| RU203898U1 (en) * | 2020-12-11 | 2021-04-26 | федеральное государственное бюджетное образовательное учреждение высшего образования "Национальный исследовательский университет "МЭИ" (ФГБОУ ВО "НИУ "МЭИ") | BREAKDOWN AND OVERLAPPED INSULATOR INDICATOR |
Also Published As
| Publication number | Publication date |
|---|---|
| GB2080958B (en) | 1984-04-11 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| PCNP | Patent ceased through non-payment of renewal fee |