The present invention relates generally to devices and methods of monitoring devices in electrical power systems, and in particular to remote reading of such monitoring devices that performs intermittent measurements.
The electric power networks of today represent large investments in time and constructions. Unscheduled operational interruptions involve therefore normally very large absent incomes. This is particularly serious when the operational interruption is caused by defect network components, since costs for replacement and/ or repair of constructions are added. Many industry processes are totally dependent on a safe supply of electrical current. In order to meet these demands, different types of equipment are introduced, which are intended for monitoring of different courses of events in the electrical power network. Of particular interest are courses of events that characterise abnormal conditions in the electrical power network. Such transient and/ or intermittent courses of events often constitute the large risks for the function of the electrical power networks. Such transient and/or intermittent courses of events may e.g. be constituted by overvoltages that e.g. can be caused by strokes of lightening or similar, connection or disconnection of large power consumers, reconnections in switch gears etc.
In switch gears, different types of surge arresters are today used in order to protect apparatuses against incoming overvoltages. The surge arresters are connected between live wires and earth. The new generation of surge arresters is a gap-free surge arrester with serially connected zinc oxide varistors. At a too high voltage level, the surge arresters permit that a current is conducted to earth, whereby the overvoltage is reduced. The
current-voltage characteristics of the zinc oxide varistors are such that the diverted current increases very considerably at only somewhat increased voltages. At continuous operational voltage, these surge arresters use currents in the order of magnitude of 1 mA, of which a few percent constitute the resistive component. Even when the very highest occurring lightening currents are discharged through the surge arresters, the voltage is increased only 2 to 2.5 times the normal one.
In plants with surge arresters, it is of great interest to know how often these are put into action. Knowledge of this is achieved by connecting so called surge counters. The surge counter fulfils a double purpose. Partly it gives information about how exposed the installation is for overvoltages, partly it serves as monitoring means for the surge arrester, in that way that abnormally numbers of registrations during a certain time should bring about an overhaul and control of the surge arrester.
The surge counter is provided with a relay that counts the number of surges passing through the surge arrester. The surge arrester current is conducted through a current transformer, which is why a dangerous voltage level can not be achieved, even at passage of a lightening current. The counter is normally sensitive for the energy content of the overvoltage and the counting function is activated when certain values of amplitude and /or duration are exceeded. Surge counters according to prior art often have a display, showing the number of surges.
A monitoring system for a surge counter "Surge arrester monitoring (SAM)" is provided commercially by ABB Hochspannungstechnik AG, Switzerland. This system is in principle built by a current sensor, a sensor cable and a storing unit. The current sensor is placed as a distance block between an insulated surge arrester and earth, and reads the current through the surge arrester.
The read values are transferred via the cable to the storage unit, where the number of surges and possibly present leak current is presented at a
display. A connectable unit can then be used to transfer the read values from the storage unit to an external computer.
There is a general request about making the monitoring systems more and more rational, safe and robust. In the light of this, surge counters according to prior art present a number of annoying disadvantages. On one hand, the sensors are often arranged at positions close to high voltages, which makes a manual reading or connection of external units risky. On the other hand, the surge counters are often arranged at places that are difficult to reach for manual reading, e.g. at high heights. If long cables are used to remove the storage unit from the sensor, problems with guiding the cable in a safe way through e.g. a switch gear, without forming an assignment for voltage flash- over, are instead raised. Furthermore, connection of cables for reading of the content of the storage unit suffers from well-known contact and wear problems. If instead stationary connections are used, the installation costs are instead increasing in the same rate.
The European patent application EP 0 825 577 discloses a system for remote reading of meters for e.g. electrical energy, water, gas etc. A measurement unit collects data and stores these in a memory unit. The measurement unit comprises a transreceiver in the form of a passive, not powered, unit. By a radio signal from a reading unit, the transreceiver can be awakened for transferring stored data to the reading unit. Exactly how this non-powered transreceiver operates is not evident. A problem with such an approach arises if several measurement units should be read from the same reading unit, when all transreceiver units react on the signals and start to send simultaneously.
The international patent application WO 95/27272 describes a remote reading system, where a reading unit establishes communication with a number of measurement units, in order to extract measurement data therefrom. The measurement units comprise a transferring unit, which is responsible for all communication therewith. The measurement units are
awakened from a "sleeping" low-power state to an active state by that the reading unit sends a request. The transmission unit is during the low power state not completely inactive, but checks occasionally if there is any request for reading. This activity implies a certain energy consumption, which during a longer time of use demands relatively large batteries or network connection of the measurement units, which is of disadvantage according to the above discussion.
Other problems with surge counters according to prior art are that only very limited information is available, normally only the number of pulses. At handling of a multitude of surge counters in the same plant, there is also a large risk for confusion of data from the different units.
An overall object with the present invention is to achieve an improved remote reading and remote manoeuvring of monitoring equipment, in particular such equipment that is used for measurement of intermittent courses of events. A more specific object is to provide methods and devices where exposure for high voltage is avoided at transfer of data. An additional object with the present invention is to make the monitoring equipment less energy consuming. Another object is to remove confusion risks between different equipment. A further object is to facilitate maintenance of monitoring equipment, such as e.g. zero setting, restarting, fault identification and so on.
The above objects are achieved by methods and devices according to the present patent claims. In general words, the present invention provides a monitoring device comprising a collecting unit and a reading unit. A reading unit should be able to operate together with several collecting units, but only with one at the time. The collecting unit comprises a registration means, a control means, a memory means and a communication means for data transmission via radio waves and is characterised by an activation detector,
separate from the communication means. The reading unit comprises a control means and a communication means for data transmission via radio waves and is characterised by an activation means, separate from the communication means. The activation detector consists of a photo-cell and the activation means consists of a laser diode. The communication means preferably comprises units with an AM- or FM-radio transceiver, which provides bi-directional communication of data and/ or instructions. The collecting unit preferably further comprises an identification code stored in a permanent manner in the hardware. The energy supply of the collecting unit is preferably provided by means of a solar cell and an energy- storing medium. The reading unit preferably further presents also an interface for computer communication with a processor unit.
The invention further provides a method for control of a monitoring device. The method comprises to register parameters concerning the operation of the electric power system, to store measurement data in the collecting unit. At suitable occasions, the collecting unit is activated by light in order to initiate a transmission of data to the reading unit via radio waves. After the transmission, the transmission functions of the collecting means returns to an inactive state. The method may preferably also comprise transmission of the identification code of the collecting unit. Furthermore, the method may also comprise transmission of instructions concerning different maintenance measures for the collecting unit.
The invention further provides a system for monitoring of electrical power plants. The system comprises at least one reading unit and at least one activatable collecting unit, which communicate transmitting data and control signals between each other via radio waves, and where the activation of the collecting unit is performed by light signals.
The present invention is according to one aspect useful at electrical power systems. The invention is generally applicable on different types of monitoring devices at electrical power systems, and in particular for
monitoring devices that operate with measurement of transient or intermittent signals. A particularly suitable device for the present invention is a surge counter for surge arrester equipment.
SHORT DESCRIPTION OF THE DRAWINGS
The invention and further objectives and advantages that are achieved thereby is best understood by reference to the below description and the enclosed drawings, in which: Fig. 1 is a block diagram showing a monitoring device according to the present invention;
Fig. 2 is a flow diagram illustrating a method for collection and transmission of data according to the present invention;
Fig. 3 is a circuit diagram for an embodiment of a collecting unit in a surge counter according to the present invention;
Fig. 4 is a circuit diagram for an embodiment of a reading unit in a surge counter according to the present invention;
Fig. 5 is a block diagram illustrating the data flow during a collection phase according to the present invention; Fig. 6 is a block diagram illustrating the instruction and data flow during a reading phase according to the present invention;
Fig. 7 is a block diagram illustrating the instruction flow during a resetting procedure according to the present invention; and
Fig. 8 is a block diagram illustrating an embodiment of a system according to the present invention.
The present invention can be used in connection with different types of electrical apparatuses that are present in electrical power systems. The showed detailed embodiments relate to surge counters for use at surge arrester devices. However, the scope of the invention is solely defined by the
wording of the enclosed patent claims, and should not in any way be limited by the detailed descriptions of the embodiments.
Figure 1 is a block diagram illustrating the units that are included in a monitoring device according to the present invention. The device consists of two main parts, a collecting unit 1 and a reading unit 2. One and the same reading unit 2 should be functional in turn together with a number of collecting units 1. The collecting unit 1 is connected to an electrical power system 14 in order to read parameters therefrom that concern the operation of the electrical power system. A registration means 4 is connected to the electrical power system 14 in order to carry out necessary measurement measures. The registration means 4 is connected to a control means 3 for controlling the operation of the collecting unit. The control means 3 comprises preferably a processor. The control means 3 is also responsible for the control of the other means in the collecting unit 1.
The collecting unit 1 further comprises a memory means 5 for storage of collected data. Input and writing to the memory means is controlled by the control means 3. In the collecting unit 1 is preferably also an identification means 8 present. This identification means 8 comprises an identification code for the collecting unit 1 stored in a permanent way. The identification code can be read upon request by the control means 3, but is not possible to change or replace during operation. The collecting unit 1 further comprises a current supply means 9, which is responsible for the current supply to the collecting unit and its part means. Preferred embodiment of the current supply means is described further below.
The collecting unit 1 is often placed in an inaccessible manner, and often in the vicinity of high electrical voltages. The collecting unit 1 is therefore according to the present invention provided with two separate means for communication with the surroundings, where the communication takes place via different transfer means; radio waves and light, respectively. An activation detector 6 is arranged in order to receive light signals from outside
to start certain predetermined processes in the control means 3, which is described more in detail below. The activation detector 6 is preferably of a totally passive type that does not demand any power to monitor the entering of signals. The activation detector is a photocell, which is described further below. A communication means 7 is arranged for wireless transferring of data via radio waves to the reading unit 2.
According to prior art, the same communication links are used both for the awakening of a measurement unit and for transmission of data. This takes place via radio waves. Even if there in other places within prior art are used communication via light signals, it is not obvious for one skilled in the art that from unitary communication units separate an activation communication function and perform this by a second separate transmission method. The advantage with such a separation is that the main communication unit can be put in a completely inactive state, in order to reduce the energy consumption of the collecting unit. An activation detector based on light signals demands less energy for operating, which is why the energy in e.g. laser light is enough in order to get it to operate. In this way, both parts can be left turned-off in the collecting unit, until activation occurs.
The reading unit 2 is electrically totally released from the collecting unit 1 , and comprises also a control means 10 that is responsible for the controlling of the reading unit 2 and its included means. A separate activation means 1 1 is arranged for emitting light signals to the activation detector 6 of the collecting unit. This means is a photodiode for suitable wavelengths. The operation for the activation means is controlled by a switch unit 15. A communication means 12 is also included in the reading unit 2. This communication means 12 corresponds to the communication means 7 of the collecting unit, and is thus arranged for wireless radio transferring of data from the communication means 7 of the reading unit 2. However, this communication is preferably bi-directional and arranged to be able to transfer both data and instructions between the control means 3 and 10,
respectively. The reading unit 2 is preferably further provided with an interface 13 for communication with external processor units.
Figure 2 illustrates a flow diagram, which schematically represents a method for a monitoring unit according to the present invention. The process starts in step 100. In step 101 measurement parameters are registered, which are associated with the electrical power system, to which the monitoring unit is connected, in a collecting unit. Here, a processing of measurement data can possibly take place. In step 102 measurement data is stored in the collecting unit. The steps 101 and 102 are repeated at need, e.g. when something unusual occurs, or according to a predetermined scheme. These steps can even take place continuously. When one then wishes to read out the inputted measurement data, the collecting unit is activated in step 103 by transferring light signals from a reading unit. The transferring functions of the collecting unit are revived and stored measurement data is transferred wireless via radio signals to the reading unit in step 104, whereupon the collecting unit again is allowed to be deactivated in step 105. The process returns at continuous operation to step 101 and 102, but may otherwise be finished in step 106.
In the case of a surge counter, the register means 4 is responsible for the detection of present overvoltage pulses in the connected surge arrester device. Such overvoltage pulses occur only at certain irregular occasions, which is why the collecting unit during the larger part of the time is inactive. During such inactivity periods, many functions in the control means, the
, registration means and the communication means may be turned off, i.e. the means are put into an inactive state. This procedure reduces the need of current supply to a minimum. At transient or intermittent courses of events, such as e.g. overvoltage pulses, the occurrence of the event is used as start signal for the registration functions. The measurement and/ or registration of the voltage pulses are carried through and stored in the memory means. The registration of the surges can be performed as a simple counting of the numbers.
When a user wishes to remotely read the content of the memory 5 of the collecting unit 5, the reading unit is used. The switch unit 15 is activated and the photodiode 11 becomes active and emits light of suitable wavelength. Laser light within the visible range is normally most appropriate
(about 660 nm), since one then by a simple visual control easily can decide if the light reaches the photocell 6 of the collection unit. Maybe, a confocal combination of a visible light wavelength and another wavelength can be used, where the visible wavelength is used to direct the alignment of the reading unit, but where the other wavelength activates the actual detector.
When the photocell 6 detects incoming laser light, a transfer sequence starts in the control means 3. At use of laser light in the above mentioned wavelength range, the light contains enough energy in order to that should be no need for any active component as detector. This reduces the need of inactivity power. The reading unit is preferably also provided with functions that turn off the activation means, when the transfer of data starts, or after a certain time.
In a typical case, the identification code of the collecting unit 1 is transferred followed by the measurement data that is stored in the memory 5. The control means 10 of the reading unit controls that the received data is correct and sends it preferably further to a connected computer unit, where an evaluation takes place. The external computer unit may e.g. comprise a database with existing identification codes. When the transferring sequence is finished, the collecting unit returns to the inactive state, where the current
, use is minimised.
Since the collecting unit 1 for most of the time is in an inactive or low power state, where the power consumption can be as low as 5 μA, the mean power consumption is of the same order of magnitude. The current supply means 9 can therefore e.g. consist of a simple lithium battery, which would get an approximate life of 10 years. However, a preferred embodiment of the current supply means 9 comprises instead a small solar cell together with an energy
storing medium, e.g. a large supercapacitor ELNA DYNACAP DLC (Double Layer Capacitors) available from ELNA America, Inc. (>= 1 F). Such a solution gives a system that is free from maintenance and environment friendly. The charging can with the solar cells of today take place relatively fast even at moderate light intensities, and the energy consumption is normally not larger that that a fully charged capacitor is enough to give the collecting unit current during several days.
The communication means 7 and 12, respectively, is preferably an AM- or FM radio transceiver, whereby known radio transfer techniques and protocols can be used. Since standard components can be used, the cost for the communication means, the activation means and the activation detector becomes very low.
In figure 3, an embodiment of a collecting unit in a surge counter according to the present invention is shown. This embodiment corresponds in large to a tested prototype construction. Parts that are presented earlier (in figure 1) have been given the same reference numbers and are therefore not explained further. The registration means 4 is connected to a surge arrester device according to prior art, via connection terminals 20 and 21. The registration means 4 according to the present embodiment comprises a rectifier bridge LBR1 connected in series with a resistor RIO over the connection terminals 20, 21. The outputs of the rectifier bridge LBR1 are connected in parallel over a capacitor C4, a resistor R12 and a diode Dl, via a resistor Rl l, and further over a resistor R13 to a diode D2 to feed voltage and a resistor R15. Incoming voltage pulses over a certain level will thereby give a voltage pulse of constant and non-harming size, that is fed further to the control means 3.
The control unit 3 comprises substantially a RISC -microcontroller U 1 of the type PIC 16F84, available from Microchip Technology Inc. The microcontroller
Ul is conventionally connected to a crystal oscillator XI , a number of resistors R1-R6, R8, R9, capacitors C 1-C3 and switches S 1-S3. The switches are in this prototype used for manual emptying of the memory means and
resetting operations. A clock circuit U4 of the type DS1602, available from Dallas Semiconductors Corp. is used together with a crystal oscillator X2 and a resistor R7 as an internal clock unit 22. The microcontroller Ul sends the pulses from the registration means 4 for storage in the memory means 5. The memory means 5 comprises in this embodiment an EEPROM U3 of the type 24LC256, available from Microchip Technology Inc.
A photo transistor PT of the type BPX 81-3 from Siemens is used for detection of an incoming activation laser signal, and gives as a response thereon a signal to the microcontroller Ul, to start an read-out procedure.
The detection of the laser signal also lights the light-emitting diode D4, which thus is used as a hit indicator. The software coded identification code, in this embodiment comprised in a memory chip U2 of the type DS2402, available from Dallas Semiconductors Corp. is read-out, followed by data stored in the memory means 5. The memory chip U2 comprises a 64-bit serial number. The communication means 7 is activated. In this embodiment, the communication means 7 comprises a transmitter circuit U5 of the type RFH433 MHz, available from RF Monolithics, Inc. and antenna belonging thereto. The identification code and read-out data is sent to the transmitter circuit U5 and is transferred by radio waves to the reading unit.
In figure 4, an embodiment of a reading unit in a surge counter according to the present invention is shown. This embodiment corresponds in large to a tested prototype construction. Parts that are presented earlier (in figure 1)
, have been assigned the same reference numbers and are therefore not further explained. The communication means 12 comprises a receiver circuit
U6 of type RXIOOO, available from RF Monolithics, Inc., conventionally connected to capacitors C9-C11 and an antenna. An output signal is sent to the control unit 10. The control unit 10 is substantially based on a microcontroller PIC16F84 available from Microchip Technology Inc., controlled by a crystal oscillator X3 and connected to capacitors C5-C7. A laser control section 23 is constituted by of a switch S4, two resistors R16,
R17 and a capacitor C8. This section 23 provides a time limitation function for the activation means 1 1. The light-emitting diode D5 indicates when the activation means 1 1 is active. A switch S5 here constitutes the switch unit 15. When the switch S5 is closed, a voltage is applied over the diode D6 and the laser diode D7, whereby the latter emits laser light. A received data transfer or the time limitation of the laser control section 23 can turn out the laser diode D7.
Data received from the communication means 12 is forwarded via the computer interface 13 to an external computer unit. The computer interface in this embodiment is constituted by a serial interface built by a DS275 circuit U8 available from Dallas Semiconductors Corp.
It is obvious for one skilled in the art that the embodiments in Fig. 3 and 4 easily can be developed further according to earlier indicated lines of thought. The communication means in Fig. 3 and 4 can be exchanged to circuits supporting bi-directional communication, whereby also an instruction exchange can take place. This enables a more flexible control of the collecting unit and enables a remotely controlled reset, fault detection, control of the current supply level etc.
An embodiment of a system 30 for monitoring of an electrical power plant according to the present invention is illustrated in Fig. 8 and comprises at least one collecting unit 1 and at least one reading unit 2. The collection unit 1 is activatable by light for wireless radio transferring of measurement data stored therein. One and the same reading unit 2 is by advantage used for several collecting units 1. The reading unit 2 then uses the identification code in order to distinguish data from the different collecting units 1. The system 30 preferably also comprises at least one processor unit 31 for processing of the collected data.
In earlier analogous systems, a surge counter had e.g. a certain recovery time, within which no new surges could be registered. Such a recovery time
could easily amount to quite a number of seconds, due to that it often was based on charging of capacitors. By the introduction of the digital technology according to the present invention, the recovery times are reduced. Overvoltages following closely to each other can thereby be registered without problems.
The above problems are usual also in other types of monitoring devices in electrical power systems. Current measurement by current transformers, in particular measurements of transient courses of events, voltage measurement by voltage transformers and state monitoring of electrical switches are examples of areas of technology where similar types of problems can be believed to arise. Corresponding solutions are therefore applicable also within these areas of technology.
Also temperature measurement on rails, cables an other apparatuses can be of interest, in particular monitoring of whether a certain temperature is exceeded. A possible configuration would be to use e.g. a temperature sensing reed relay MTS-A from Midwest Components Inc. which waken the registering unit up when a certain temperature is reached. Since the switch is open during normal operation, no power is consumed at "sleeping" state.
At the wakening-up, either a registering, in analogy with the surge counter case, can be made, or the registering unit can initiate a read-out from a connected accurate temperature sensor, in order to follow a temperature course.
In figure 5, a block diagram is illustrated, showing the data flow through the collecting unit during a collection phase. Corresponding parts as in figure 1 has achieved corresponding notations and are not further discussed. At registration or measurement, a current of data 201 corresponding to a parameter associated with the electrical power network flows, normally in the form of analogous signals, from the electrical power network 14 to the registering means 4. The registering means 4 attends to register and /or measure these parameters and sends measurement data 202 further onto
the control means 3. These measurement data can be in analogous or digital form. The control means 3 processes these measurement data 202 and adapts data for storage. Data 203 in digital form is then sent to the memory means 5 for storage. During this procedure, the activation detector 6, the identification means 8 and the communication means 7 are totally inactive, whereby these may be put in an energy-saving inactivity state. Remaining functions are only active during a short period of time at data collection and storage.
In figure 6, a block diagram is illustrated, showing the instruction and data flow through the collecting and reading unit during a reading-out phase. Corresponding parts as in figure 1 has been given corresponding notations and are not further discussed. The switch means 15 is activated, whereby a signal 210 is sent to the activation means 1 1. The activation means 1 1 sends out a signal 21 1 , preferably in the form of laser light, which is detected by the activation detector 6. The detection gives in turn rise to a signal 212 to the control means 3 for initiating a reading-out procedure. These information signals concerning activation of the control means 3 are shown with broken arrows in Fig. 6.
When the control means 3 is activated, it sends out signals 213 and 214 to the memory means 5 and the identification means 8, respectively, that implies a demand for transferring of data. The signals 213 and 214 concerning the initiation of reading-out of data are depicted by full arrows in the figure. These signals can also be sent directly from the activation
• detector 6 in connection with the creation of the signal 212.
The memory means 5 and the identification means 8 respond to the signals 213 and 214, respectively by transferring respective data 215 to the control means. Data flows are denoted by unfilled arrows in figure 6. The control means 3 compiles received data 215 and sends a data stream 216 to the communication means 7. The communication means converts the data stream 216 according to conventional principles and transmits the data
wireless via radio waves 217 to the communication means 12 of the reading unit. The communication means 12 of the reading unit forwards achieved data 218 to the control unit 10 and further over the computer interface 13 as a data stream 219 to an external computer unit. During this procedure, the registration means 4 is normally inactive.
If the communication means is used for bi-directional communication, additional special points and advantages can be achieved. If the memory means 5 is filled with data, it must be possible to be emptied and restarted in a simple way. Possibly, this can be connected to a restart of the clock function in the collection unit. This would, not least at the installation, facilitate the management. The collecting unit is installed and is allowed to reach normal operation. The collecting unit is activated in a common way by irradiating it with laser light. This can, instead of directly starting a reading- out sequence, prepare the communication means 7 of the collecting unit for reception of instructions, sent by the reading unit. These instructions can e.g. consist of a demand for reading-out, whereby earlier sketched procedures are followed. The instruction may, however, also e.g. consist of a demand for resetting or restarting of the collecting unit.
In the figure 7, a block diagram is illustrated, showing the information flow through the collecting unit during a resetting procedure. Corresponding parts as in figure 1 has been given corresponding notations and are not further discussed. The switch means 15 is activated, whereby a signal 230 is sent to the activation means 1 1. The activation means 11 sends out a signal
• 231 , preferably in the form of laser light, which is detected by the activation detector 6. The detection gives in turn rise to a signal 232 to the control means 3 for initiating 233 the communication means 7 for reception of instructions. These information signals concerning activation of the communication means 7 are shown with broken arrows in Fig. 7.
The control unit of the reading unit sends resetting instructions 234 to its communication means 12, which forwards these instructions in the form of
radio waves 235 to the communication means 7 of the collecting unit, which now is prepared for reception. The resetting instructions are sent 236 to the control means 3, where the message is interpreted and intended measures are performed, whereby e.g. the clock function is reset and instructions about emptying the memory 237 are sent out.
If the reading unit 2 at the same time is provided with the identification code of the collecting unit, this can automatically be stored. In this way, the collecting unit can be manufactured totally without external contacts and if solar cell current supply is used, without need for battery change possibilities. The entire construction can thus be manufactured totally embedded, which makes it more robust and cheaper to manufacture.
One skilled in the are realises that also other maintenance measures can be performed via the communication means 7 and 12, respectively. This can e.g. comprise fault detection of circuits, measurement of battery status or charge level etc., calibration of the registration means etc.
One skilled in the art realises that different modifications and changes can be made to the present invention without departing from the scope of the invention, which is defined by the enclosed patent claims.