IE62844B1 - Apparatus for and method of powerline surveying designing and maintenance - Google Patents

Abstract

Apparatus for powerline surveying comprises means for measuring points off the powerline in addition to points strictly along the route of the line, and means for preparing two and three dimensional representations of the line and the land surrounding it. The apparatus includes one or more of the following means for the two and three dimensional survey of overhead powerlines; means for transfer of chainage, offset and datum, (i.e. height) measurement to an off-line station via a change point and a sighting to a known point; means to establish the position of an inaccessible point by remote location; means to monitor towers with interactive checking against design information; means to reset the offset of on-line observing stations back to zero and reset the horizontal circle orientation through sighting the powerline; means to reset the offset of points on-line to zero if they are within a certain specified distance of the line; and means to log land usage and topographical features. The method of the invention utilises the above apparatus.

Description

APPARATUS FOR AND METHOD OF POWERLINE SURVEYING, DESIGNING AND MAINTENANCE The present invention relates to an overhead powerline survey method and in particular to a survey method for the design and maintenance of overhead power lines, including survey of a line from points off the line so that the route of the line and the local topography in the vicinity of the line may be recorded.

Traditionally, surveying of existing powerlines or of the route of planned powerlines is restricted to exactly following the route of the powerline by sighting from one point on the line to the next, along the route of the line. The traditional methodology allows only very limited account to be taken of local topographical features, e.g. roads, houses and the like. Measurements taken in powerline surveys are generally recorded manually in a logbook and computed at a later time to derive twodimensional co-ordinates for the points measured, i.e. height and distance along the line. These co-ordinates are then plotted using traditional drafting techniques.

If it is required to import this data into a computerised system, the transfer has to be done manually.

The positions of the required support structures for a proposed powerline may then be defined on this plot. Following this the line of the conductor is plotted and ground clearance checked. If sufficient clearance has 9 -'! A J “r '!· been obtained, this design is accepted and the relevant materials ordered so as to construct it.

This paper based system has a number of inherent shortcomings. These are: - The whole design process takes place in two dimensions whereas in reality three dimensional data should be used.

- Modifying a proposed design is time consuming and costly.

The whole process is slow.

- The transcription of data and manual computation of co- ordinates and draughting thereof is prone to error.

- The survey technique requires that a corridor along the proposed route be cleared completely of vegetation, so as to establish a clear line of sight.

- The survey technique does not take full account of features offset from the route of the line.

- The design process takes place in a scaled plot, not at actual scale, thereby introducing errors due to the poor definition of the features plotted.

- The conductors are modelled using fixed parameters. 1 These cannot be easily altered to take account of varying < limits. _ cost of the proposed line is not calculated until the design has been accepted.

It is the object of the present invention to seek to overcome the above difficulties.

According to one aspect of the present invention there is provided a computer arrangement for ground-based powerline surveying comprising means for measuring points off the powerline in addition to points strictly along the route of the line, and means for preparing two and three dimensional representations of the line and the land surrounding it. The ground profile beneath the line may be observed from locations referenced to, but not necessarily lying on, the actual route of the line itself.

Advantageously, the computer arrangement of the present invention includes one or more of the following means for the two and three dimensional survey of overhead powerlines,· means for transfer of chainage, offset and datum, (i.e. height) measurement to an off-line station via a change point (i.e. a point observed from two stations, the position of the second one being established from the observation to the change point) and a sighting to a known point; means to establish the position of an inaccessible point by remote location; means to monitor towers with interactive checking against design information; means to reset the offset of on-line observing stations back to zero and reset the horizontal circle orientation through sighting the powerline; means to reset the offset of points on-line to zero if they are within a certain specified distance of the line; and means to log land usage and topographical features.

According to a second aspect of the present invention, there is provided a method for powerline surveying comprising measuring points off the powerline in addition to points strictly along the route of the line, and preparing two and three dimensional representations of the line and the land surrounding it.

Conveniently, the method of the present invention includes one or more of the following steps; transferring chainage, offset and datum measurements to an off-line station via a change point and a sighting to a known point; establishing the position of an inaccessible point by remote location; monitoring towers with interactive checking against design information; resetting the offset of on-line observing stations back to sero and resetting the horizontal circle orientation through sighting the powerline; resetting the offset of points on-line to zero if they are within a certain specified distance of the line; and logging of land usage and topographical features.

The invention further includes a computer arrangement for handling the data collected in the field, converting the data to a digital data base and representing the geography of the area surrounding a surveyed powerline in digital form compatible with a specified host computer aided design (CAD) system, so that the information collected in the survey may be represented in three dimensional form.

According to another aspect of the invention, there is provided a method for defining a feature or type of object being measured, by calling on a feature library which is common to the system in which the data is initially collected and the system which transforms that data into the form which can be displayed in two or three dimensions.

Conveniently, during the survey, data is collected by a powerline program operating on a hand held or other portable computer.

Advantageously, the data, as collected, enter a totally integrated system which handles the data from the field collection stage to its conversion to a final three dimensional digital database. Computations are done during the survey on a field computer which can also transfer data directly from the field measuring equipment. 2Q Conveniently, computational facilities are provided for measuring off-line stations.

Advantageously, the method of the invention provides for the application of polar co-ordinate and trigonometric heighting methods to powerline surveys. Measurements of polar co-ordinates allows the definition of a point in the horizontal plane by taking a distance and bearing measured from a known point (the observing station). Trigonometric heighting uses a distance and vertical angle to determine the difference between an observing station and the observed point. Using a combination of these two techniques, the three dimensional co-ordinates of any - 6 observed point can be computed.

The means for transfer of chainage, offset and height data to an off-line station via a change point and a sighting to a known point incorporates the traditional technique of passing distance and height via a change point (i.e. a point observed from two stations, the position of the second one being established from the observation to the change point), but additionally permits this technique to be utilised for the computation of the three dimensional co-ordinates of stations lying off the route of the powerline.

The means to establish the position of an inaccessible point by remote location comprises means of lining up two additional temporary points with the point required. These two points are then observed and define the vertical plane in which the required point lies. The horizontal and vertical angles from the observing station to the unknown point define the vector on which the unknown point lies. The intersection of this vector with the defined plane gives the position of the unknown point.

According to yet another aspect of the present invention, there is provided a computer arrangement for powerline designing comprising means for measuring points off the proposed route of a powerline in addition to points strictly along the route of the powerline, means for preparing two and three dimensional representations of the proposed powerline and the land surrounding it, means for defining the conductor design of the proposed powerline in relation to its specific environment,means for comparing and checking the conductor design parameters against industry standards and means for identifying and specifying component requirements.

According to a further aspect of the present invention, there is provided a computer arrangement for use in constructing and maintaining powerlines, comprising 0 means for recording data pertaining to the condition of an existing powerline, means for conducting in-field sag and tension calculations in respect of the powerline conductors and means for determining and specifying 15 repairs or modifications to the powerline.

According to yet a further asepct of the present invention, there is provided a method of powerline designing comprising measuring points off the proposed route of a powerline in addition to points strictly along the route of the powerline, producing two and three dimensional representations of the proposed powerline and the land surrounding it, defining the conductor design of the proposed powerline in relation to its specific environment, comparing and checking the conductor design parameters against industry standards and identifying and specifying component requirements.

The powerline program is a specialised program module that runs within any suitable program development environment such as that described in the invention - 8 disclosed in U.K. Patent Application No. 2202871A, entitled Method and Apparatus for Survey Datalogging, hereinafter referred to as Autograd (Trade Mark).

The PowerLine survey system is a suite of computer programs produced to assist in the design and maintenance of overhead power lines. It covers all aspects of the design process from the measurement of the initial ground profile under the proposed route through the definition of the exact support structure positions and conductor types, taking into account the predicted cost and the relevant safety standards and industry guide-lines, to ordering of the actual fittings required and checking the tension of the line at the final construction stage. An important feature of this suite of programs is that it does not finish on completion of the construction stage but also provides facilities whereby constructed lines may by subsequently checked both by visual inspection of the various fittings for depreciation or damage and also by re-survey if so required. Furthermore, it is not restricted to newly constructed lines but also provides facilities whereby existing lines may be surveyed and the existing support structures monitored, thereby bringing them into the system. All these functions are available within a single integrated suite of programs and are all referenced to a single data-base.

As well as being innovative overall in providing a fully intregated system, there are included within these - 9 programs a number of very significant specific innovations.

The field survey program permits the route of the line to be surveyed not only from positions actually on that route itself but also from other places remote from but referenced to the route of the line. This has not however prevented implementation of the traditional survey technique of passing height and distance information via a change point but rather has supplemented it by now permitting the full three dimensional position of the observing station to be computed in this manner. Further flexibility is given in that the traditional traversing technique of passing three dimensional position information directly from one station to the next is provided as an alternative method.

During field surveys the position of totally inaccessible points may be easily established utilising a technique new to powerline surveys of defining a vertical plane containing the required point using two easily accessible points and then sighting directly to the required point and computing its position.

For refurbishment surveys of existing powerlines the facility has been provided in the field survey programs of monitoring existing support structures and checking them £ against design data-base information while the surveyor is - 10 still in the field.

All positional data is recorded as three dimensional co-ordinates, unlike the traditional method in which only two dimensional information is collected and plotted. Two dimensional output may still be obtained however so as to provide compatibility with existing work practices and formats.

The survey data gathered using a field computer may be passed either directly or via a storage medium to an office based design system. Each data point is incorporated in a data string and referenced to a specific feature type. This means that when it is passed across to the office design system, the reception program can read this information and define it appropriately using database information. The reception program thus creates a data file appropriate to the specified Computer Aided Design (CAD) system.

The support structure positions and types may then be added to this design file. These support structures are drawn from a library referenced directly to the data-base. This means that the exact dimensions, loadings, components and cost of each type of structure are immediately available.

Once the support structure have been planted the actual conductors may be strung. To do this a special program has been written which takes the complex mathematical equations of the curves defined by the conductors and plots their positions. A shadow may also be plotted defining the minimum clearance line thereby enabling ground clearance to be quickly checked. Some features (i.e. roads) require a greater clearance than this minimum distance. These clearances may be checked by the design engineer using the minimum distance function provided as standard by the host CAD system.

The conductor program holds data on all the conductor types available and permits the design engineer to select the most appropriate one. The design engineer may also alter the equivalent span (related to the distance between tension points), operational temperature, ice loading and wind conditions thereby checking the ground clearance even in extreme conditions.

The next stage in the design process is to check that the designed line meets all the required safety standards. To do this a special analysis program has been written. This takes the designed line (together with all the related data-base information on the support structures and conductors used) and checks it against internationally recognised safety standards.

The designed line may then be costed on the basis of the fittings required and the estimated construction - 12 costs. A list of the required fittings may then be produced so that they may be ordered.

If at any time during the design or checking procedure a change is made this is immediately reflected in the displayed plot and can quickly be checked for n ground clearance, accordance with safety standards and costs. ί A hard copy of the form of a fully annotated and properly presented drawing may be obtained at any time using the standard CAD system plot facility.

This plot may be passed to the engineer in charge of the construction process. The support structures may then be placed on this basis. The conductors may then be strung. In order to check that the required tension is being correctly applied the conductor computations are also provided on the hand-held field computer. This enables the engineer to determine how far the line should sag (taking into account the currently existing temperature conditions) for the tension applied.

If at some later stage it is required to update the ground profile to take account of any changes in the local geography since it was constructed this may be quickly done using the same field survey system. The new survey may then be passed to the head office and overlaid over the original showing immediately any changes which have - 13 occurred. The effect of these changes are immediately revealed. Any resultant modifications may then be quickly determined and costed, A further feature is that if at some stage a change 5 is planned in the local geography (i.e, a new road is to be built or a local householder desires to build an extension) the effect of these changes may be determined prior to the actual construction taking place, and the proposed construction or the route of the line modified accordingly if this is significant.

For the continued maintenance of the line a Line Patrol program has been written for the field computer which permits updated information resulting from a visual inspection to be gathered. This data is added to the data-base as soon as it is returned to head office. The relevant repairs or points for further inspection or survey may then not only be listed but their position may also be shown on an attached plot or plan saving substantial time at the repair stage.

Finally it is possible at the time of a re-survey to check the tension of the line on the spot using the Sag ft Tension module. The clearance between any observed point (either at ground level or at some other height e.g. the top of a tree) may be checked without having to observe the line at all. A further benefit of this module is that where ground clearance is tight the clearance may be checked not only for the currently prevailing weather conditions but also for worst case situations.

The PoleLine and TowerLine suite of programs running on an office computer give the overhead line engineer all the tools needed to design and maintain overhead lines under one environment. The system is sufficiently open to allow the completed design to be passed to other departments for their modifications to be incorporated. θ The package runs under a host CAD environment and Poleline/Towerline data and drawings can be transferred amongst individuals with no conversation processes necessary and with no loss of information providing they have access to a computer running the same CAD package, 15 irrespective of hardware.

This is a novel solution. There are current automated systems available to the overhead line engineer in certain specific tasks he has to perform, but the bulk of his existing workload is still manual drawings and manual calculations. Current methods are inaccurate and their scope limited. Current methods rely on a 2D profile scaled at lOsl and thus proper 3D clearance checks often require the building of a scaled model. Poleline/ Towerline is full 3D, full sized and hence exact measurements and design are possible.

Another advantage of using a CAD base is that the designer can annotate and tailor his drawing precisely, as well as being able to invoke other external processes to operate on his drawing.

Towerline/Powerline consists of four processes 1. Ground Modeller The ground modeller takes the survey data and produces a fully annotated 2D profile and/or 3D model.

The appearance of each feature is user customisable. Surveys done at a later date can be appended to the model for instance to reflect a new road built. 2. Conductor programmes This is the second stage of the design. Once the surveyed data has been modelled, the poles/towers are strung with conductor curves.

Should the survey be a 69green field55 survey i.e. there are no existing poles/towers, or should the surveyor not have surveyed the towers and merely made a note of the tower actually there, it is first necessary to insert them.

The insert pole/tower facility is a powerful tool.

All known poles/towers are stored in a symbol/cell library and can be called out and drawn as required. The degree of detail is determined by the user who customises these libraries. For instance the engineer is merely interested - 16 in the attachment points and his tower would be simply a T shape to connect the conductors onto. The wayleaves offices would use a full 3D image to demonstrate to grantors (landowners) that the design is aesthetic.

There are several programmes available to produce conductor curves. There is a user customisable database containing all the current and historic conductors and for $ each conductor are stored the relevant physical constants; weight, weight when buffeted by the elements, Young“s modulus, surface area, diameter, coefficient of termal expansion, maximum tension allowed and the relevant temperature, the places where aeolian vibration is dangerous and the necessary counterbalances.

These values are essentially fixed for good by the user. Every time a conductor is drawn, the user has to specify the temperature it will be at in order to calculate the corresponding sag (i.e. on a cold day it will not sag as much as on a hot day). The user also specifies the scale he is working at. Traditionally, designers have worked at an exaggerated scale in order to fit the drawing onto a manageable sheet of paper. In some instances, he may specify the basic span. This quantity is a preset value that guarantees the resultant tension in the conductor will not be excessive.

Another programme matches one conductor to another.

That is should an existing line have been strung with conductor A and the designers want to replace it with conductor B (typically for sending more voltage down), they want to make sure the sag is the same so that the heavier conductor B will not violate the safety limits guaranteed by the previous conductor.

Another programmes produces templates. These can be plotted on acetate and used by draughtsmen on the existing manual drawings. The ability to draw these templates at any size and scale (by altering the span and temperature) is a novel feature of the present invention. In the past, the extreme cost of laboriously calculating the ordinates, drawing them and cutting out has meant that draughtsmen had a limited set and used the nearest template available.

Thus precise curves are now feasible.

Two other programmes are downleads for drawing the conductors as they come down from a tower to the substation and jumpers, the short pieces of conductor connecting sections of lines connected to different insulator sets. Traditionally these processes could only be designed using scaled physical models.

Where the conductor programmes are different and unique from existing programmes in existence is that the full catenary equations are used in their construction.

Displaying them graphically is also novel. In the past, - 18 people have been content to print out ordinates at fixed points along the curve. The ability to draw them swung out at any angle is new.

The interaction with the CAD system allows accurate 5 measurement and dimensioning of critical clearances and rapid redesign should these clearances infringe legal obligations. 3» Pole/Tower analysis There are a set of analysis packages to check the design of the overhead line. The checking done for the conductor programmes is to check the interaction of the conductors with surrounding features. These analysis programmes check that the resultant design does not infringe safety rules for the operating parameters of the equipment. For instance on a cold day when the sag is reduced, the tension in the wire increases. Regulations decree the maximum loadings any particular piece of equipment can tolerate.

The analysis used primarily for poles is what is known as 43/40, the draught standard required to be implemented by all electricity companies in England and Wales as a result of the earlier regulations and the October 1987 storms. For towers, there are existing regulations, but a standard similar to 43/40 is being draughted. For poles there are previous regulations still - 19 in force and for some time (to check on existing designs) these will still have to be used.

All these standards are set by the ESI (Electrical Standard Industry) and indeed every electricity company has computer programmes to implement them. Where the method of the present invention is superior is that the design checks are done automatically on the CAD drawing, rather than at present having to type into a computer programme all the details laboriously arrived at on the drawing board. In fact some electricity companies have different interpretations of the regulations; the regulations say that stays should come out at 45 degrees. This is acceptable in rural areas, but in semirural/London areas, land usage is at such a premium that this is impracticable. Hence the implementations of these regulations are customised for each electricity company. 4. Scheduler The final stage of the design is the building of it. After checking the clearance and engineering details, the designer will need to know what components are needed to implement his design. He may even iterate again to find another design satisfying all the constraints but being cheaper to build using smaller/fewer poles/towers.

Furthermore stores requisitions notices have to be issued telling the stores what components are required, - 20 where and when to deliver them. A scheduler would do all this.

Every electricity company has a system to do this. They are all different and the format of the information they require is different again. The system according to the invention may be readily tailored to adapt to the particular needs of different electricity companies.

Most companies work as follows? the designer would write down a list of the towers/poles he has used in his design as well as their location and the conductors used. This would be given to a secretary to type into a mainframe computer programme which would start the relevant machinery rolling. In the first instance, a programme can be modified to produce the relevant input required by the mainframe and put it on a medium readible by it.

Further to this is the information required by the builders. When the engineer has designed his plan, he has decided what sag/tension should be in the conduct at the critical temperatures (freezing to check the maximum likely tensions will not snap the wire or pull over the tower/pole, and very hot to check the maximum likely sags will not interfere with ground objects). Unfortunately, when the builders put up the conductor the temperature will be about room temperature. Thus the programme has the ability to inquire of the design what the corresponding tension and sag will be at the temperature of the day so that the builders can tension the wire accordingly. The necessary engineering form is printed out giving the relevant details.

Other features of the invention will become apparent in relation to the figures, in which; 1 Figure 1 is the Autograd (Trade Mark) Pull-down menu; & Figure 2 is the Autograd (Trade Mark) Main menu; Figure 3 is the Autograd (Trade Mark) administration flow chart; Figure 4 is a general overview of the geo-processing program; Figure 5 is the flow chart for the program for establishing an initial instrument position; Figure 6 is the flow chart for the program for establishing subsequent instrument positions; Figure 7 is the flow chart of the program for the measurement of a point; Figure 8 is the flow chart for measuring inaccessible points; Figure 9 is the feature library selection flow chart; Figure 10 are the tower monitoring and pole recording * program flow eharts; Figure 11 is a general overview of the date flow of the tower design file; Figure 12 is the benchmark comparison program flow chart; Figure 13 is the chainage; offset and datum display program,Figure 14 is the input-output flow chart; Figure 15 is the file management flow chart; Figure 15 is the flow chart showing the initial menu flowchart of the overhead line profile modelling program; Figure 17 is a flow chart of the data processing in the overhead line profile modelling program; Figure 18 is the flow chart of the program controlling the plotting of data points in the overhead line profile modelling program; Figure 19 is the data flow diagram for the feature library; Figure 20 is an overview flow chart showing the flow of data between the programs; Figure 21 is an isometric projection of a sample powerline survey produced by a CAD system; Figure 22 is a schematic overview depicting powerline survey, design and maintenance system in its entirity; Figure 23 is an example of a template plot produced in the system; Figure 24 shows a sample section of line with the conductor strung; Figure 25 is an illustration of a typical incoming - 23 line terminating on high voltage switchgear overhead gantry showing jumpers and downleads; Figure 26 is an overview flow chart of the integrated line patrol program; and Figure 27 is a flow chart showing the integrated line patrol program in detail. ' Figure 1 shows the nrogram module for selecting a pulldown menu option in the Autograd (Trade Mark) master program. As shown in Figure 2, upon selection, the standard Autograd (Trade Mark) menu is displayed, giving four options, i.e. administration (Figure 3), geo-processing (Figure 4), input/output (Figure 15) and file management (Figure 16).

The administration feature, as shown in the flow chart of Figure 3, is a standard Autograd (Trade Mark) feature used for the selection of any of nine different jobs and the inputting of job identity information for the selected one, consisting of project number, surveyor, title, location, client and start date.

Figure 4 shows a general overview flowchart of the geo- processing program. This is a program for the establishment of instrument positions relative to the powerline or proposed route thereof and the recording and / processing of the measurements taken from these positions.

This is the central core of the program which will now be described in greater detail. - 24 Referring now to Figures 5 and 6, flow charts for the establishment of initial and subsequent instrument positions respectively are shown. Each section of line, between two changes in direction is treated as a separate entity and output independently of all other sections of line. For a given section of line the initial instrument fc u position has to be either under the first tower/pole of the section of line or may alternatively be established from sightings to the first tower/pole. Thereafter new positions may be established either by sighting them from a previous instrument position or alternatively sighting a pre-established change point. The horizontal circle orientation may be set on either the earth line, the previous station or another known point i.e. the previous tower/pole.

Figure 7 shows the program steps involved in point measurement. Once the instrument position and the orientation of the horizontal circle of the instrument have been established any point may be co-ordinated simply by observing the horizontal angle, zenith angle and slope distance from the station to that point.

Points which are vertically above or below previously observed points may be co-ordinated simply by measuring > zenith angle. In this case the height difference between the two points is displayed. - 25 As shown in the Figure 8 flow chart, inaccessible points may be co-ordinated by selecting the 'Remote Location’ option from the menu and then observing two points colinear with the required point and measuring the horizontal and vertical angles to the required point.

Points are measured sequentially, the most recently measured always appearing at the bottom of the logging sheet. Previous points may be reviewed either through scrolling up the logging sheet, using the cursor control keys, or alternatively moving the display directly to a specified point using the ’Point Find’ option from the pull-down menu.

Figure 9 shows the flow chart for the features library selection. Feature names are used to define the type of object being measured. They consist of alpha/numeric text. A specific object is defined by a series of points having the same feature name and string number. Within both the field collection/computation and the office based graphic processing modules there resides a common feature library. This library holds information pertaining to each feature which may be observed.

When collecting data in the field the user may select a feature from this library. Associated with this feature will be a connection code (usually either 'S' (Straight), 'C' (Curved), 'G11 (Gap) or ’V' (Vertical Straight)), a - 26 string number (either an absolute number or an increment on the string number associated with the previous feature of the selected type observed during the current job), and a code indicating whether the elevation of points on this feature should be used to form a digital terrain model and associated contoured drawing. When a feature is chosen r from the library these associated codes are placed in the appropriate fields. They may however be overwritten at the users discretion. If the user inputs a feature name directly it is pulled automatically from the feature library. (If it does not exist in the feature library a warning is given.) Alternatively the user may return to an incomplete feature by selecting the relevant feature name and string number combination using a feature recall facility. Selection of a feature from the library (or feature recall memory) is done through inputting the first character of the required feature (this moves the display to the features starting with this character) and then scrolling through the displayed features using the cursor control keys and/or the space bar until the required one is displayed. The displayed feature may be selected using the enter key.

The contents of the feature library are; \ Common Data :25 Feature Name - 27 Field Specific Data;Default Connection Code Default String Number (or 1' to increment from previous number) Office Specific DatasColour Line Thickness Colour of Gaps Line Thickness of Gaps (can be set to zero) Text to be displayed? (All points, First Point on Feature, None) Symbol (If any) Direction of connection (Up, Down, Left, Right) 3D Connection Representation, the current options are as follows (These will be expanded as the need becomes evident)»Horiztonal Splined Best Fit Curve/Straight Straight Vertical Line Single Point Dip/Rump (Straight Sides’,· - 28 Dip/Hump (Rounded) if % Vertical Lines Connected at Top · Vertical X.ines Connected at Bottom y * # * — ifr - Vertical Lines Connected ——* Top δ * --— 1 i fr - - — .ill.- -- . -· <) 3D Curve (Left/Right of Line).

The option is given within the field system to add new features to the library.

An eight character feature code may be entered in order to identify the object being observed. This feature code has an equivalent in the feature code library in the overhead line profile modelling program which indicates how this particular feature is displayed and plotted. The required feature may be pulled from a library held in the computer memory using the ’Feature Recall5 or ’Feature 20 Library option in the pull-down menu.

A feature number is also given for each point to differentiate between points on similar features i.e. Wall 1 and Wall 2.

Each point may be given a link code indicating how 25 that point is linked to the next point with the same feature name and number. These codes and their meanings may be displayed by choosing an option from the pull-down menu.

By selecting an option from a pull-down menu the 5 current land usage may be logged. This land usage remains active until another land usage is logged.

An offset code indicates whether a point being observed is on the route of the power line or not. This influences whether an offset value is computed. If a point on line would have an offset value of greater than one metre a warning is given. An 51’ code excludes the current point. The permissible codes may be displayed by choosing the relevant option from the menu.

The flow chart for the tower monitoring section of the geo-processing program is shown in Figure 10, while Figure 11 shows a general overview of the data flow route for the tower design file. The field survey program is divided into two distinct modules, one for surveying high voltage lines (generally supported by steel towers) known - as TowerLine and one for surveying low voltage lines (generally supported on wooden poles) known as PoleLine.

As shown in Figure 10a and 10b, towers along the route of the powerline may be logged, recording their name and type, chainage and datum. Their height above stub level may also be measured and compared with the design height - 30 for towers of that type. The difference is displayed.

The recorded details are written to a separate file which may be output from the Input/Output section of the program.

The contents of the Tower Design file ares Tower Type Design Height above Stub.

* Cross-Arm Length (Left) Cross-Arm Length (Right) Angle of Deviation In order to facilitate low voltage lines, an alternative to the Tower Monitoring function has been provided. This new function, the Pole Recording function, is shown in Figures 10c and lOd. This new Pole Recording 15 function basically permits the pole number and type to be recorded, the pole height to be measured, and seven lines of details to be input. The headings on these seven lines are configurable by the end user. These poles are not checked against design information.

Another modification made in order to facilitate low voltage lines is the facility to observe a number of sections of line in a single job. The termination points are now defined by the positions where the line changes v direction (Angle Poles or Angle Towers). The facility is also given to measure the angle of deviation at these points.

The PoleLine and TowerLine modules are kept separate right throughout the system. The are downloaded to two different reception programs, are displayed differently, are strung with different conductors, are referenced with different data-bases and are checked against different safety standards. However although these differences occur the overall approach to both types of poweline are the same. Essentially they are two aspects of a single program.

Referring now to Figure 12, the benchmark comparison flow chart is shown. Anywhere along the line a benchmark may be observed. The height difference between the computed height for this point and its given value is 1 5 displayed.

The flow chart for the chainage, offset and datum program is shown in Figure 13» The chainage, offset and datum from any selected point may be displayed using a pull-down menu option. From this option the values for the previous, next or any specified point may be subsequently displayed.

Referring still to the geo-processing program « (Figures 4 to 13), observed points are numbered sequentially. The storage capacity of the powerline γ surveying program is only limited by the memory capacity - 32 of the computer on which it is being operated. The remaining space can be reviewed at any time (in terms of the number of points which may still be added) by choosing a pull-down menu option. If the available capacity drops below 50 points a warning is given.

Observations may be edited freely. However, measurements downloaded from an automatic instrument may only be edited by overwriting them with other values following the choosing of the 'Overwrite1 option from the pull-down menu.

A remark of up to 20 characters may be logged for each point immediately after the measurements have been logged.

The flow chart of the program controlling input and output of data is shown in Figure 14. This is a program 9θ for interfacing with a portable disk drive, printer and external computer. Specific routines are included to output data in a suitable format for use by a program running within the overhead line profile modelling program for designing and analysing overhead lines.

This may be selected from the Autograd (Trade Mark) main menu. It has four standard Autograd (Trade Mark) options:«jl Λ 1. Communications. This is a standard Autograd (Trade Mark) feature used to a) Enter terminal emulation mode. b) Set communications parameters for interfacing with a - 33 printer, computer, plotter or digitser. c) Set device control codes for printouts. d) Set time and date. 2. Disk Operations. This is also a standard Autograd (Trade Mark) feature for interfacing with a portable disk drive. It provides the following facilities:a) Directory of disk currently in drive. b) Save data from any Autograd (Trade Mark) module to disk. The particular data to be saved is selected after 'Save file to Disk' is selected. c) Load data for any Autograd (Trade Mark) module from disk. d) Delete a file from disk. e) Format a Disk. 3. Printouts. This permits a hard copy of the powerline data to be output to a printer or computer. The powerline 2θ surveying program outputs the following data:Administration Information Point Number Feature Code Feature Number Link Code Chainage Offset ] For each point - 34 Datum ] Remark ] Land Usage (when there is a change in Land Usage) al Observation Number ] Tower Number ] Tower Type ] Chainage of Tower Centre ] Datum of Stub ] Height of Tower ] For each Tower Copyright message 4„ System Xnput/Output. This permits the recorded powerline data to be output to an external computer either in ASCII format or a format suitable for reception by a special program operating in the overhead line profile modelling program. The same data is output as is included in a standard printout.

A new interface has been written to permit downloading of PoleLine data, including the seven lines of pole details which are displayed as text on the final plot. They are included in a distinct layer within the CAD system so that they may be easily excluded using the - 35 { standard CAD function of switching off a specific layer. Referring now to Figure 15, the file management program is a standard autograd feature used for erasing data and controlling which program modules are currently resident within the computer. Program modules may be erased and reloaded from a portable disk-drive.

Turning now to Figures 16, 17 and 18, the means for representing the geography of the area surrounding a powerline will now be described. There is provided a program for receiving data collected in the course of a field survey of an overhead line, which program converts the geographical data of the surveyed area into digital form compatible with a specified host CAD system. The data is initially collected, at the time of a survey, by the powerline program operating on a hand held computer.

It is then transferred to the overhead line profile modelling program in a standard data interchange format shown in Figure 16. The transfer of data is via a specially written interactive communications program consisting of an output facility in the powerline program which has been mated with an input facility to the overhead line profile modelling program. Handshaking between the two programs takes place on the basis of exchanged codes.

The following field data may be transferred? - 36 HeadersClient Name Measurement Date Job Title Location Job Number Surveyor Data for each point measured;Sequential Point Number Feature Name String Number Connection Code Chainage Offset Datum Remark (If any) Land Usage start (If any) The Feature Library and Tower Design Dimension files may be transferred if required.

Referring now to Figure 17, in order to process the received data appropriately the program requests any additional information required i.e. two dimensional, three dimensional or combined representation. It also accesses a library file holding the required - 37 ( representation for each type of feature encountered. This file may be edited by the operator as required. The program is invoked from a customised menu that may be activated during the operation of the host CAD system.

Among the options given are the loading of field data, processing of data, selection of general parameters, activation of HELP messages, display of errors encountered, editing of data, editing of the library file, exit to the host CAD system, activation of associated programs and various other appropriate options specific to the CAD system involved.

Figure 18 shows the flow chart relating to processing of the data and plotting it in two or three dimensions, as specified. Processing of the data takes place on a copy of the original data file held internally within the program memory. Prior to general processing all points lying on the route of the powerline are extracted from the field data and are plotted as a separate distinct feature irrespective of the associated feature names or tag codes.

The feature names are however used to indicate the connection between one point and the next along the line.

Points lying on the route of the powerline are sorted in order of ascending chainage and are connected appropriately. Points on all other features are linked sequentially in the order they are encountered within the - 38 field data file.

During processing the feature names associated with the observed data are matched with those held in the library and the surveyed features presented accordingly.

The data held internally is scanned for all occurrences of the first feature and string number combination encountered. All points lying on this feature are extracted from the file and processed. This procedure is then repeated until all the data has been processed.

Each individual feature is identified through a combination of the associated feature name and number.

Therefore a number of features of the same type can be processed as separate units.

Points associated with a particular feature name and string number combination are connected together in accordance with a TAG code collected during the survey.

The most common connections are a straight or curved horizontal line, a verti'cal line or a gap. The program may add an additional or alternative connection or symbol as specified in the library file. The colour and thickness of the connecting lines are defined in the library file.

Gaps within a feature are represented using a gap line the existence of which (together with its colour and thickness) is specified in the library file. - 39 If a curved connection is specified all points relating to a feature (including those on gap lines) are used to define the best fit curve. The degree of curve smoothing applied may be set from the initial menu.

In order to represent the collected three dimensional information on a two dimensional plane any features lying off the route of the power-line are represented by dashed lines. These dashed lines are only created if a two dimensional representation is required. All other connections are made using solid lines.

If there is insufficient or incorrect data associated with a specific feature, or a feature associated with the field data does not occur in the library, this is noted in the record of errors which may be reviewed from the initial menu.

The observed points are plotted at actual size so as to maintain the integrity of the original data. They may be viewed through using the panning facilities of the host CAD system.

Any text associated with the field data (remarks or land usage information) is scaled (in accordance with an input scale factor) and placed in the appropriate annotation field. The feature name, chainage, offset and datum values are treated similarly if so indicated in the library file. This scaling is done in order to maintain the legibility of the text as the scale of the full plot is reduced.

There are five distinct annotation fields.

Annotation is displayed vertically within the relevant field at a position corresponding to the chainage of the point to which is refers, with the exception of land use which is written horizontally commencing at the relevant start point. Land uses which occur in close proximity to each other are slightly offset vertically so as to prevent them from overwriting each other.

The five annotation fields and the survey model are displayed vertically one above the other (separated by horizontal lines) in the following order (top to bottom):Survey Model Description - Remarks - Feature Name Datum Value Chainage Value Offset Left Offset Right Lane Usage Text describing the job being processed is read from the field data file and placed in a title block at the top left hand corner of the plot. The input scale factor is also applied to this text.

At the graphic processing end the way each type of feature should be displayed is defined in the library.

The points making up a feature may be connected or symbolised in different manners as appropriate» This enables single points, linear vertical objects, horizontal objects or three dimensional objects to be logically represented in the final graphic output. When a feature name is encountered in the field data the associated data is read from the feature library. This data consists of colour, line width, symbol (if any), whether to display associated text or not, whether to display gaps in the feature and if so the colour and line thickness to be used and how to connect points together. The feature library may be edited from within the graphic processing module.

The contents of the feature library may be transferred freely between the field and office based modules.

The final product is the data for a full drawing (in two and/or three dimensions as specified) which is passed into the host CAD data management/ground modelling system from which interactive screen editing may be done, the data analysed and a graphical plot produced.

Figures 19 and 20 are general overview flow charts showing the data flow between the field and office computers with respect of the features library and general - 42 data flow respectively.

Figure 21 is an isometric projection of a sample powerline survey produced by a CAD system.

Figure 22a to i is a schematic overview depicting the 5 entirity of the system according to the invention.

Figure 22a is an overview of the data collection area of the system, as described above, while Figure 22b shows the previously described data processing.

Figures 22c to g relate to the design aspects of the 10 scheme. In Figure 22c the number, type, position, etc. of support structures may be specified and passed to the cell library, which then indicates how the structures are displayed and cross-references them with the data-base.

A schematic view of the conductor program is shown in 15 Figure 22d. This conductor program is one of the most significant innovations of the system. In order for the clearance between the ground profile and the existing or designed line to be checked the position of the actual line itself must first be defined. The Conductor program does this precisely using mathematical equations. The defined conductor is then plotted on the same drawing as the ground profile enabling clearance checks to be quickly carried out. To facilitate this a clearance line the specified minimum clearance distance from the defined line may also be plotted showing graphically where sufficient - 43 clearance has not been obtained.

Traditionally, this whole procedure was carried out in a number of stages. The ground profile was plotted on paper. This was usually done at a scale of l;10 so as to fit it on a sheet of paper. Reducing the scale however also reduced the accuracy of the determined clearances so a substantial margin of safety had to be left. The line was then designed and the relevant support structures overlaid on the original plot. Following this the positions and types of the support structures used, together with the type of conductor used, its normal operating temperature and the maximum and minimum environmental temperatures were fed into a computer program. This program computed the coordinates of a number of points on two lines (hot and cold). Curves were then fitted to these points and cut out so as to form two templates. These templates could then be used to draw the hot and cold conductor curves on the plot. Because of the length of time and cost of producing these templates, the tendency was to use similar templates which had already been produced. The chances of this template actually being correct however are very small as there are a large number of variables used in defining these curves. One of the more significant variables is the weight and type of the conductor used. If a new improved conductor type was - 44 introduced a completely new set of templates had to be produced. If after all this it was found that sufficient ground clearance had not been obtained the line would have to be re-designed and the whole procedure repeated.

Because of the great cost and inconvenience involved in doing this the line was designed so that any great possibility of this happening was avoided. This margin of safety however in most situations resulted in a much more expensive design being implemented so as to give the exaggerated clearances required.

If a rare or awkward situation were encountered an actual scaled model had to be built to determine the relevant curves. This scaled model however still had the limitations of scale inaccuracy and could not take account of extreme conditions. It was also very difficult to modify it.

The conductor program removes the uncertainity over the exact position of the conductor. All calculations are undertaken at actual scale as the process is no longer paper based. It is now possible to scale down the plot so as to fit it on a sheet of paper.

The slow and expensive process of producing templates has been completely by-passed as the curves are drawn by the program. These curves are exact as they are related to a specific curve with specific variables rather than being best fit curves.

If any of the variables are changed the curve is also changed. This means that different conductor types, weights, tensions, temperatures, etc. may be tested and the most suitable selected. Furthermore, whereas the traditional system could only show the conductor line at extreme temperatures the conductor program can model it under a wide range of conditions the most important of these being normal, extremely cold, extremely hot, very windly, icy and construction conditions.

The conductor program, so as to facilitate users who may still wish to follow traditional methods or who are fitting new conductors to an existing line on the basis of existing plots also gives the facility of simply producing the relevant template, given the relevant details.

Figure 23 is an example of a template plot produced in the system. For conventional conductor placement templates can be plotted for any loading conditions, temperature and exact equivalent span. Catenary calculations are used throughout and templates can be plotted at any scale in both metric and imperial units. Figure 24 shows a sample section of line with the conductor strung. The inset box shows a typical clearance check. The conductor loading parameters are listed to the left. Because it can do this instantly the curve can simply be plotted on acetate and overlaid on the drawing. An exact curve can thereby be produced for each span. The slow and expensive process of making plastic templates is bypassed.

The conductor program also has facilities to cope with rare and awkward situations. It can model the downleads from an initial support structure to a substation or a short stretch of line between two different insulator sets. Figure 25 is an illustration of a typical incoming line terminating on high voltage switchgear overhead gantry. For clarity the towers are only shown in outline form. In using Microstation level control all internal bracing and detail could be shown. Downleads can be strung at any reduced tension with Microstation providing full phase to phase clearance checks. Downleads can also be strung under any swing conditions. Each conductor can be strung under any loading conditions and all relevant sag/tension data is accessible. Jumpers can also be strung under any swing conditions„ The conductor program can model two or more different conductors in the same model. Where one powerline crosses the route of another or two lines are in close proximity to one another the clearance between the two can therefore be quickly and precisely determined. Complex situations - 47 such as usually occur in close proximity to substations can be simply and quickly resolved.

The design checking scheme is depicted schematically in Figure 22e. A selection of powerline has to conform to a number of pre-set safety conditions. In the UK these conditions are set out in a document issued by the Electricity Supply Industry (CEGB). This is one of a series outlining Electricity supply Industry (ESI) standards. It is referenced by the title ’ESI STANDARD 43 -40'. These conditions include such items as maximum and minimum equivalent spans, maximum and minimum distances between supports, maximum and minimum tension, spacer requirements etc. Compliance with these conditions must be checked for both normal and extreme (temperature, wind, snow and ice) weather conditions. Obviously these extreme conditions vary from one place to another.

Once a section of powerline has been designed it must be checked that it conforms to these standards. When these standards were first developed this involved lengthy calculations. Since then computer programs have been developed which, once the support structure details are fed into it, check the proposed line for compliance. A major disadvantage of these systems is that the support structure details have to be input manually taking considerable time and leaving plenty of scope for errors.

By integrating this checking procedure with the graphic design system this interim stage is overcome. The data for the designed line is read directly from the design file, which is displayed graphically on screen, and may be plotted out at will. Each support structure is stamped with a data-base tab cross-referencing it with its full details and dimensions.

This integration removes the possibility of transcription errors thereby ensuring that the analysed line and the designed line are identical. It also speeds up the whole process. Non compliance with the standards is thereby changed from being a major catastrophe, requiring a new line to be designed, drawn and analysed (taking a number of days), to a minor inconvenience as with this new system the line can be edited in a matter of minutes. Obviously when non compliance was so critical a substantial margin of error was left - incurring substantial excess construction costs. With this new system this margin of error may be eliminated resulting in substantial savings.

The design costing and distribution areas of the program may be understood by reference to Figure 22f and g. Major considerations in the design of a new section of powerline are the construction cost and time and fittings required. The powerline suite of programs provides the - 49 tools whereby the engineering may minimise these using his own skill and training. The fittings required need to be precisely listed so that they can be ordered before construction commences. The fittings scheduler gives a total listing of all the fittings required for a proposed section of line and the total cost thereof.

The electricity generating boards are currently using their own programs to compute these requirements and costs. These programs however have the disadvantage that they are not integrated with the design system. This means that the details of all the support structures and conductors must first be input into the program. This takes time and leaves openings for mistakes to be made.

At present the line is first designed, then costed and the required fittings ordered. This means that, although the estimated cost is a major factor in the whole design process, the testing of a number of different designs and selecting the most economical is not really practical.

The new powerline fittings scheduler performs exactly the same function as the currently existing programs. However because it is integrated within a total system the details of the support structures and conductors used are read directly from the design drawing. This removes any possibility of mistakes (which may result in substantial expense) being made. It also means that any potential - 50 f changes can be implemented and costed within a few minutes (compared with at least a number of hours with even the most efficient system currently available). The end result is that quite a number of different designs may be tested and the most economical quickly selected.

Line construction and line quality control and maintenance are depicted in Figure 22h and i respectively. It is impossibl actually measure the tension of a conductor. Instead this is done by measuring the amount it sags and from this computing its tension. As a line gets older it tends to stretch thereby causing the tension to lessen and the line to sag further. An important part of line maintenance is therefore to monitor how much a conductor sags and what tension it is under. Obviously a conductor under a different tension from its design tension will react in a different way than predicted under extreme conditions. It will also effect the amount of clearance between the line and its local geography.

The Sag δ Tension program uses similar catenary calculations to the conductor program. It reads the data concerning the type of conductor used from a data-base held in computer memory. However as it is run on a handheld computer it has completely different application areas. It can be used during the construction of a new section of line, or when an existing line is being re- 51 strung so as to check that it is being strung at the required tension. Previously this was done by computing in advance the amount the line should sag and constructing it so that it did in fact sag by this amount. One disadvantage of this system was that the design sag was computed using an estimated air and conductor temperature. If this differed significantly from the actual temperature on the day the line was being strung errors were introduced. Furthermore the process of computing the sags and checking them is very slow and cumbersome. It is also critical to the whole line construction process.

The Sag & Tension program overcomes these problems as all the computations are done immediately. Therefore as it is not necessary to compute in advance the sag positions the actual temperature at the time the measurement is being taken is used in the calculations.

In addition to removing this source of error the whole process is speeded up and simplified.

Another application area for the Sag & Tension program is in the determination of clearances during routine line maintenance.

Traditionally the height difference between the highest point and the line was measured. This dimension was used to determine whether clearance tolerances were being met. This procedure however only checks for the - 52 currently existing conditions. A significant margin of error must be left in order that this tolerance would also be met under extreme conditions. Additionally as the clearance was only determined on the basis of two dimensional information the point selected as being closest to the conductor may in fact be in error.

The Sag & Tension program overcomes these difficulties as it can model the line not only under existing conditions, but can also predict its position under extreme conditions. It works on the basis of full three dimensional conditions. It also simplifies the whole process as only the. attachment points must be measured. From these positions and the input variables the position of the conductor is modelled. There is therefore no longer a requirement to measure the height of the actual conductor for this purpose.

The other application of the Sag & Tension program is in the determination of the tension applied to an existing conductor. This can change over time as the conductor stretches. At present it is computed by measuring the sag on the line and the environmental temperature. These measurements are then used at a later date to compute the actual tension. The Sag & Tension program computes this information immediately. This can be particularly critical after extreme conditions have occurred and the - 53 line is being monitored to determine the extent of the damage.

The quality control and maintenance facility includes an integrated Line Patrol Program which has been produced to enable the collection of data relating to the condition of a section of powerline and the poles or towers supporting it. Figure 26 is an overview flow chart of the integrated line patrol program. The various subsections are shown in more detail in Figure 27. The I.D. information component is shown in Figure 27a, tower components in Figure 27b, insulators in Figure 27c, circuit fittings in Figure 27d and span observations in Figure 27e. The data is generally collected by a person walking along the route of the line inspecting all the relevant items. In most cases the data is recorded on a paper logging sheet which would be returned to head office where the logging sheet would be copied into a standardised format and the logging sheet filed. A planning engineer would then review this data and the necessary repairs would be authorised. In some areas this data collection process has already been automated using a simple hand-held computer.

The main feature which differentiates this product from any previously produced is the fact that this process ? 5 will now be integrated into a total systems solution - 54 10 covering all aspects of powerline maintenance. The data may be transferred (either directly or via an intermediate storage device) from the hand-held collection device to a geographical data-base, holding a full description of the supporting structures involved including their exact position. This new data is cross referenced with any existing data on the basis of the route name and the support structure numbers.

Advantages of an automated systems are: 1. Standardised methodology. 2. Standardised output format. 3. Check against individual items not being investigated. 4. No transcription of results necessary.

Advantages of the system according to the invention are? 1. The data goes directly into the main office data-base from whence it may be accessed immediately by any authorised person. 2. The data may be transferred from the field collection unit without returning to head office. 3. When the collection data is being examined all the information available on the relevant structure is easily accessible.

The maintenance facility also encompasses the - 55 interactive tower monitoring facility described above (and see Figures 10a and 10b) and includes the possibility of carrying out refurbishment surveys on pre-existing power lines .

It will of course be understood that the invention is not limited to the specific details described herein, which are given by way of example only, and that various modifications and alterations are possible within the scope of the invention.

Claims (38)

1. . A computer arrangement for ground-based powerline surveying comprising means for measuring points off the 5 route of a powerline in addition to points strictly along the route of the powerline, and means for preparing two and three dimensional representations of the line and the land surrounding it, whereby the ground profile beneath 1θ the powerline may be observed from locations referenced to, but not necessarily lying on, the actual route of the line itself.

2. A computer arrangement for powerline surveying as claimed in Claim 1, including means for the two and three dimensional survey of overhead powerlines.

3. A computer arrangement for powerline surveying as claimed in any one of the preceding claims, including means for transferring chainage, offset and datum 25 measurements to an off-line station via a change point (i.e. a point observed from two stations, the position of the second one being established from the observation to the change point) and a sighting to a known point.

4. A computer arrangement for powerline surveying as claimed in any one of the preceding claims, including means for establishing the position of an inaccessible - 57 point by remote location.

5. A computer arrangement for powerline surveying as claimed in any one of the preceding claims, including means for monitoring towers with interactive checking against design information.

6. A computer arrangement for powerline surveying as claimed in any one of the preceding claims, including means for resetting the offset of on-line observing stations back to zero and resetting the horizontal circle orientation through sighting the powerline.

7. A computer arrangement for powerline surveying as claimed in any one of the preceding claims, including means for resetting the offset of points on-line to zero if they are within a certain specified distance of the line.

8. A computer arrangement for powerline surveying as claimed in any one of the preceding claims, including means for logging land usage and topographical features.

9. A method of powerline surveying comprising measuring points off the route of the powerline in addition to points strictly along the route of the powerline, and preparing two and three dimensional representations of the - 58 line and the land surrounding it.

10. A method of powerline surveying as claimed in Claim 9, including transferring chainage, offset and datum measurements to an off-line station via a change point and a sighting to a known point.

11. A method of powerline surveying as claimed in either Claim 9 or Claim 10, including establishing the position of an inaccessible point by remote location.

12. A method of powerline surveying as claimed in any one of Claims 9 to 11, including monitoring towers with interactive checking against design information.

13. A method of powerline surveying as claimed in any one of Claims 9 to 12, including resetting the offset of online observing stations back to zero and resetting the horizontal circle orientation through sighting the powerline.

14. A method of powerline surveying as claimed in any one of Claims 9 to 13, including resetting the offset of points on-line to zero if they are within a certain specified distance off the line.

15. A method of powerline surveying as claimed in any one - 59 of Claims 9 to 14, including logging land usage and topographical features.

16. A method of powerline surveying as claimed in any one 5 of Claims 9 to 15, including converting the data to a digital data base and representing the geography of the area surrounding a surveyed powerline in digital form compatible with a specified host computer aided design (CAD) system, so that the information collected in the survey may be represented in three dimensional form.

17. -. A method of powerline surveying as claimed in any one of Claims 9 to 16, including defining a feature or type of object being measured, by calling on a feature library which is common to the system in which the data is initially collected and the system which transforms that data into the form which can be displayed in two or three dimensions. 25

18. A method of powerline surveying as claimed in any one of Claims 9 to 17, including collecting data by a hand held or other portable computer.

19. A method of powerline surveying as claimed in Claim 18, including entering data, as collected into a totally integrated system which handles the data from the field collection stage to its conversion to a final three dimensional digital database whereby computations are done during the survey on a field computer which can also transfer data directly from the field measuring equipment. 5 20. A method of powerline surveying as claimed in any one of Claims 9 to 19, including applying polar co-ordinate and trigonometric heighting methods to powerline surveys whereby measurement of polar co- ordinates allows the definition of a point in the horizontal plane by taking a distance and bearing measured from a known point (the observing station) and whereby trigonometric heighting uses a distance and vertical angle to determine the 15 difference between an observing station and the observed point so that using a combination of these two techniques, the three dimensional co-ordinates of any observed point

20. Can be computed.

21. . A method of powerline surveying as claimed in any one of Claims 9 to 20, wherein the method of transferring 25 chainage, offset and height data to an off-line station via a change point and a sighting to a known point incorporates the technique of passing distance and height via a change point (i.e. a point observed from two stations, the position of the second one being established from the observation to the change point), but additionally permits this technique to be utilised for the computation of the three dimensional co-ordinates of stations lying off the route of the powerline.

22. A method of powerline surveying as claimed in any one of Claims 9 to 21, wherein the method of establishing the position of an inaccessible point by remote location, comprises means of lining up two additional temporary points with the point required, whereby said two points are then observed and define the vertical plane in which the required point lies and whereby the horizontal and vertical angles from the observing station to the unknown point define the vector on which the unknown point lies and thus the intersection of this vector with the defined plane gives the position of the unknown point.

23. A computer arrangement for powerline designing comprising means for measuring points off the proposed route of a powerline in addition to points strictly along the route of the powerline, means for preparing two and three dimensional representations of the proposed powerline and the land surrounding it, means for defining the conductor design of the proposed powerline in relation to its specific environment,means for comparing and checking the conductor design parameters against industry standards and means for identifying and specifying component requirements.

24. A computer arrangement for powerline designing as - 62 claimed in Claim 23, in which the means for defining the conductor design includes means for checking the position of the actual line and determining the clearance between the ground profile and an existing or proposed powerline and means for modelling design factors such as conductor type, conductor weight, conductor tension, ambient temperature and the like.

25. A computer arrangement for powerline designing as claimed in Claim 23 or Claim 24 in which the means for comparing and checking the conductor design parameters and the means for identifying and specifying component requirements include reference data libraries containing data relating to industry standards, regulations for powerlines and specifications of available components and their properties, and means for accessing said reference data libraries.

26. A computer arrangement according to any of Claims 1 to 8 or 23 to 25 for use in constructing and maintaining powerlines, comprising means for recording data pertaining to the condition of an existing powerline, means for conducting in-field sag and tension calculations in respect of the powerline conductors and means for determining and specifying repairs or modifications to the powerline.

27. A computer arrangement for use in constructing and - 63 maintaining powerlines as claimed in Claim 26, including means for storing the original design data and means for comparing the original design data with the recorded data to ascertain the repairs or modifications required to restore the powerline to its design parameters.

28. A method of powerline designing comprising measuring points off the proposed route of a powerline in addition to points strictly along the route of the powerline, producing two and three dimensional representations of the proposed powerline and the land surrounding it, defining the conductor design of the proposed powerline in relation to its specific environment, comparing and checking the conductor design parameters against industry standards and identifying and specifying component requirements.

29. A method of powerline designing as claimed in Claim 28, in which defining the conductor design includes checking the position of the actual line and determining the clearance between the ground profile and an existing or proposed powerline and modelling design factors such as conductor type, conductor weight, conductor tension, ambient temperature and the like.

30. A method of powerline designing as claimed in Claim 28 or Claim 29 in which comparing and checking the conductor design parameters and identifying and specifying - 64 component requirements includes providing reference data libraries containing data relating to industry standards, . regulations for powerlines and specifications of available components and their properties, and accessing said 5 reference data libraries.

31. A method as claimed in Claim 9 for use in constructing and maintaining powerlines, comprising 1 θ recording data pertaining to the condition of an existing powerline, conducting in-field sag and tension calculations in respect of the powerline conductors and determining and specifying repairs or modifications to the powerline.

32. A method for use in constructing and maintaining 2q powerlines as claimed in Claim 31, including storing the original design data and comparing the original design data with the recorded data to ascertain the repairs or modifications required to restore the powerline to its 25 design parameters.

33. A computer arrangement for ground-based poweline surveying or powerline designing substantially as herein described.

34. A method of powerline surveying substantially as herein described. - 65

35. A computer arrangement for ground-based powerline surveying substantially as herein described with reference to and as shown in the accompanying drawings.

36. A method of powerline surveying substantially as herein described with reference to the accompanying drawings.

37. A computer arrangement for ground-based powerline surveying, designing and maintenance substantially as herein described with reference to and as shown in the 15 accompanying drawings.

38. A method of powerline surveying, design and maintenance substantially as herein described with reference to the accompanying drawings.