The present invention relates to monitoring the status of objects, especially to monitoring of condition. The invention especially relates to automatic remote monitoring of objects. The object can be e.g. an electric line or other similar object. Sagging of electric lines and stretching of cables cause problems when the cables sway and contact each other or various obstacles in the terrain. Because of this line sag must be constantly monitored and, when necessary, operations must be carried out to rectify the situation.

Monitoring of condition, service and maintenance of power grid and high voltage distribution network with current methods is very expensive and time-consuming, as the network is located on a geographically wide area, often without access roads. Thus, inspecting electric lines by visiting on the spot is labour-intensive. Traditionally, for example helicopters have been used for monitoring the condition of the lines, which is a very expensive solution and does not allow continuous condition monitoring of the lines. There also is a known solution in which the tension of the electric cable is measured with a force sensor fastened between the cable and the pylon. Another known technique is to measure the inclination of the cable at a certain distance from the pylon. The measurement data allow determining e.g. excessive line sag of the cable. The disadvantage of these is, however, the price of the technique or the fact that the cable will have to be removed from the pylon for the duration of the installation. Thus they are not well suited for monitoring the condition of wide networks or parts of network.

The purpose of the invention is to provide a novel apparatus and method especially for monitoring the condition of electric lines and networks. An especial purpose is to provide a solution having low costs, allowing reliable monitoring and being easy to retrofit. The invention is based on the idea that the line sag of an electric line or other corresponding dynamic object is monitored by means of an apparatus arranged to measure the movement or change of the movement of the object, to derive a parameter describing the status of the object on the basis of the movement data and to further relay the parameter describing the status wirelessly from a data processing unit to outside the apparatus, for example to a control centre. The apparatus according to the invention can be fastened to the movable (dynamic) part of the object, such as an electric cable in the case of an electric line.

More specifically, the invention is characterized by what is disclosed in the characterizing parts of independent claims.

Preferably the object is an object behaving dynamically when influenced on by natural forces, such as an electric line in which a cable, hanging freely between the pylons, oscillates when influenced on by wind. Thus the line sag of the electric line or another comparable parameter can be defined by means of a simple measurement. For example, by measuring the period of swing of a single cable, it is possible to calculate the vertical deviation of the cable from horizontal describing the line sag of the cable using a kinematic or mathematic model.

The kinetic state of the object is preferably monitored by means of an acceleration sensor. Further, the data processing unit of the apparatus is arranged to calculate the period of swing based on the acceleration data measured by the acceleration sensor and/or the vertical deviation according to the pendulum model in the oscillating object. The magnitude of the period of swing and/or vertical deviation further allows determining, for example, whether the line sag of the electric line is excessive. On the other hand, measurement of the kinetic state can also indicate whether the line is contacting obstructions, such as fallen trees or branches or trees preventing normal oscillation of the line.

The system according to the invention for monitoring especially electric lines and other cell- or network-type objects comprises a control centre, a plurality of remote apparatuses of the kind described above fastened to the cells of the object or parts of the network for locally detecting their state and for wirelessly relaying condition information to the control centre.

In a method according to the invention the status of the cell- or network-type objects is monitored by measuring the kinetic state or change of kinetic state of the object, by deriving a parameter describing the state of the object on the basis of the measurement data and by relaying the parameter describing the status of the object at least partially wirelessly to the control centre. The invention provides considerable advantages. The status data of the network available by means of the apparatus according to the invention makes it possible to predictively service the electric network and to flexibly monitor problematic points. By means of realtime monitoring that can further be carried out in a centralized way, the operational and service reliability of the electric network can be considerably increased. As the apparatus according to the invention can also be carried out with low costs and it reduces the need for manual monitoring, its economic effect is very considerable.

The apparatus can also be installed in a line without disconnecting the voltage during the installation, which considerably saves installation costs. As a summary, it can be said that the invention differs from competing technologies in its cost efficiency and its easy installability.

In the following, the embodiments and additional advantages of the invention are described by means of reference to the appended drawings.

Figure 1 is a schematic illustration of an apparatus according to one embodiment of the invention.

Figure 2 is a side view of an electric line with condition monitoring apparatuses according to the invention installed between the pylons.

Figure 3 is an illustration of the operation principle of the invention according to one embodiment. Figure 4 is a flow diagram of the main principle of the method according to the invention.

Figure 1 illustrates a remote monitoring apparatus 10 according to the invention comprising an acceleration sensor 12, a data processing unit 14 and a wireless communication unit 16 operationally connected to each other.

The apparatus 10 also preferably comprises a battery (not shown) from which the parts of the apparatus are supplied with power. According to an advantageous embodiment the apparatus further comprises means for charging the battery (not shown). Such charging means can include, for example, an inductive loop or a coil by means of which the charging power can be received from the electric line to which the apparatus is fastened. The use of the apparatus can sequenced so that the battery can be charged between usage periods. The apparatus can be activated e.g. on the basis of the acceleration sensor when the kinetic state of the line is sufficient for carrying out the measurement. Wind provides the excitation for the movement.

According to an alternative embodiment the charging means can comprise e.g. a solar panel or a wind generator.

Preferably the parts of the apparatus are enclosed as one weather-proof, integrated unit.

With reference to figures 2 and 3, according to one embodiment the apparatus 10A, 10B is designed to be fastened to an electric line. Thus its enclosure can comprise means for grabbing the air cable. The enclosure can comprise e.g. a cable channel, a pincher, a belt or the like for ensuring its reliable fastening to the cable. Preferably the grabbing means allows retrofitting the apparatus to an air cable without cutting the cable or removing it from the pylon.

In figures 2 and 3 the pylons are denoted by reference numerals 20A, 20B and 20C, while the air cables therebetween are denoted by reference numerals 22A and 22B. In order to monitor the condition of the electric line the acceleration sensor is arranged so that it detects essentially horizontal oscillation perpendicular to the electric line as shown in figure 3, because in this direction the oscillation of the cable 22A caused by the wind 24 is greatest and easiest to detect and model. In other words, the acceleration sensor is used for measuring transverse acceleration of the cable, from which the period of swing can then be derived. Vertical deviation (L) in relation to straight line can then be derived from this data using the mathematical pendulum formula.

The kinematic model of a sagging electric line can be simplified to conform to the behaviour of a mathematical pendulum by taking into account interference factors caused by air resistance, elasticity of the cable, location and suspension of the mass. Thus the vertical deviation from vertical (X). i.e. line sag, can be calculated e.g. as follows using a simple mathematical pendulum model: L = g*(T/2 ) ² *x, where g is the acceleration of earth's gravity, T is period of swing, x is coefficient taking the interference factors into account.

Calculation of the period of swing and/or the vertical deviation on the basis of the measurement result is preferably carried out by means of the microprocessor in the data processing unit of the apparatus. However, it should be appreciated that at least a part of the calculations can be carried out in the control centre as well. Most preferably, however, at least period of swing is determined in the remote apparatus in order to minimize the data amount of the data transfer. The remote apparatus can be realized so that it sends data about the condition of the line to the control centre at certain time intervals, regardless of the condition of the line, or only if the parameter describing the condition exceeds a certain allowable value or range.

Figure 4 illustrates the basic principle of the condition monitoring according to the invention. At step 42, the kinetic state of the object is measured. At step 44, a parameter describing the condition of the object is derived on the basis of the measurement of kinetic state. At step 46 the parameter is wirelessly sent to the control centre. In the control centre, the condition of the whole electric network or a part thereof is monitored on the basis of the data relayed by the remote apparatuses.

The wireless connection can be realized with an operator network, such as a cellular phone network or a data communications network. According to another embodiment the connection is carried out by routing along the line via measurement devices. In this case the communication means of the apparatuses are arranged to communicate with another corresponding apparatus for relaying the parameter describing the condition of the apparatus in a chain from one apparatus to another corresponding apparatus, possibly all the way to the control centre. The system can also be realized as a combination of these such as first collecting the condition data of one branch of the network by routing to one apparatus further relaying the data to the control centre via the operator network.

As has become apparent from the above the invention is especially suited for monitoring the condition of electric networks and -lines. Other possible applications include other objects subjected to wind or other natural influences, such as various antennae and link pylons that can also be located at a geographically wide area.

According to one embodiment the line sag of the movable object, especially an electric line, is determined by means of independent position recognition or by means of the dynamic measurement described above. In the embodiment one axis of the 3D acceleration sensor is locked to be parallel with the electric line so that this known axis is always parallel with the cable. The means for fastening the sensor to the cable are known per se. The two other axes of the acceleration sensor are utilized for determining the rotation of the electric line occurring as the length of the line changes. The resultant of the rotation movement is used together with the third axis for estimating the line sag, whereby the first parameter is produced. In other words, the 3D acceleration movement is used for measuring the position, i.e. sag angle so that the direction of the acceleration component produced by the gravity of earth is determined from the measurement data produced by the sensor. The swing amplitude of a certain point between two pylons is measured by estimating the period of swing and acceleration produced by means of a 3D acceleration sensor connected to the line. A separate calculation model giving the second parameter is used for this estimate. A number of measurement apparatuses can be used simultaneously preferably with a wireless network, whereby reliability produced by redundancy is achieved. The wave form of the oscillation thereby produces the third estimate for the line sag analysis.