ELECTRIC POWER DISTRIBUTION SYSTEM FOR ACTIVE CATHODIC PROTECTION OF REINFORCED CONCRETE CONSTRUCTIONS

Abstract: Electrical power distribution system for active cathodic protection of reinforced concrete consists of a power supply (A), computational means (B), a cabling system (C) with only few common conductors, electric connection means to the reinforcement iron bars (D), electric connection means (E) to the concrete mass (e.g. by means of drilled-in anodes) and a number of distributing means (F) where the computational means and the distributing means can transmit digitally coded information to each other via the cabling system (C), the purpose of said cabling system primarily being to distribute electric power to the connection means (E).

Description: ELECTRIC POWER DISTRIBUTION SYSTEM FOR ACTIVE CATHODIC PROTECTION OF REINFORCED CONCRETE CONSTRUCTIONS BACKGROUND OF THE INVENTION. Concrete renovation has grown into a very large field that even increases faster and faster due to the enor¬ mous amount of reinforced concrete constructions built after the second world war. The concrete renovations are neccessary as it is extremely difficult to produce concrete constructions of such high guality that rein¬ forcement corrosion is avoided. When the reinforcement corrodes, the concrete construction gradually looses its strength. Reinforcement corrosion typically occurs as a result of the destruction of the highly alkaline environment of concrete, e.g. due to cracks in the concrete cover. The cracks are often so fine that they can not be spotted with the naked eye - but are large enough to allow moisture to penetrate and start the corrosion process. Around the cracks areas emerge emitting iron ions as part of an electric circuit (see fig. 2). Such an area is the anode of the circuit. Electrons which are freed at the anode are consumed elsewhere along the reinforcement - the cathode of the circuit - thus freeing hydroxide ions (OH- ions). Iron ions and OH- ions together create rust. For a long time concrete renovation has consisted of an optical inspection of the surface of the concrete by skilled people, taking out numerous samples of the construction using tubular drills, investigating the samples in laboratories, deciding which areas of the construction that must be renewed, breaking up these areas, sand blasting the reinforcement, priming, pre- watering and filling the holes with repair mortar, possibly supplemented with surface treatment of the concrete. The durability of this kind of repair is not well known. An alternative treatment is cathodic protection. Catho- dic protection can only be used if the corrosion is not yet so advanced that the strength of the construction is critical. Cathodic protection is particularly superior where breaking up the concrete is very inconvenient, i.e. at bridge piers and other constructions carrying heavy weight. Using this method, negative voltage is applied to the reinforcement, binding the positive iron ions to the steel. Typically the reinforcement is held at approxi¬ mately -0,75 volt compared with the potential of the surrounding concrete. The positive pole of the circuit is typically established using drilled-in anodes or wire netting attached to the surface of the concrete. In its simplest version the cathodic protection system consists of a central power supply producing low volta¬ ge direct current, a wire connecting the negative supply outlet to the reinforcement, a cable (normally strongly ramified) that lead the positive voltage to the concrete areas to be protected, simple current distributors and a number of drilled-in anodes (see fig. 3). The distibutor normally only consists of a series resistor for each anode and maybe one or two jumper selectable common series resistors to lower the common supply voltage and current. In practice this type of installation has shown too primitive for most constructions. The system does normally not allow for individual adjustment of the current to each anode and, more important, there is no immediate way that it can be controlled if the anodes functions as intended. The presently most advanced systems has an over- and undervoltage detector for each anode built into the distributor. All the outputs of the undervoltage detec¬ tors are logically ORed and the output of the OR gate is then lead through a separate wire to a control panel near the power supply. The same holds for the over- voltage detectors so that for each distributor two separate wires lead to the control panel where each of them activates a warning light. The system does not tell which anode(s) are malfunctioning only that the malfunctioning anode(s) is(are) connected to a specific distributor. Further more for large concrete constructions an over¬ whelming number of wires must be taken from the many distributors to the control panel. Finally the system does not allow for individual adjustments of voltage/current to each anode. DESCRIPTION OF THE INVENTION. The present invention eliminates all the known draw¬ backs of existing cathodic protection systems and further offers extended security and flexibility. Fi¬ nally the invention forms a basis for gathering new knowledge and experience on controlling cathodic pro¬ tection. A cathodic protection system according to the invention is made up from five elements: 1) Power supply A, centrally positioned, delivers power to both the anodes E and the controlling sections of the distributing means F. 2) A computer B, typically an industrial Personal Computer (PC), whith a computer program that overlook and control the entire installation. 3) A bus type cabling system C that primarily dis¬ tributes the electric power to the distributing means F and with these to the anodes E and secondly it carries digitally coded information from the computer B to the 5 distributing means F and from the distributing means to the computer B. 4) Distributing means F, that control and distribute the voltage and or current to one or more anodes. Each distributing means would have a built in micro control- ler 3 that can receive and transmit messages via the cabling system C. Further more the distributing means F has means for sensing and controlling the voltage and current to each anode or group of anodes. 5) Anodes E, either drilled into the concrete or co- vering the surface of the concrete as a wire netting. The power supply A would ideally be connected to the reinforcement in a single point D but if the reinfor¬ cement is not completely interconnected and consists of isolated reinforcement sections, each section must be connected to the power supply, typically to the ground or negative outlet of the supply. The computer B and power supply A would typically be built into the same enclosure also alowing the computer to directly supervise and control the function of the power supply. The cabling system C would ideally be a two-wire-only system, transmitting both power and the digitally coded information on these two wires. Two possibilities are available for the type of power supply: ALTERNATING CURRENT, A/C, in which case the power supply A merely is a transformer possibly with some type of protection and each distributing means must therefore contain both a rectifier and a stabilizing means. This princible alows for a small transformer built into each distributor thereby galvanically isola¬ ting the distributor from the cabling sytem. This would typically reguire that each distributor being connected individually to the reinforcement. DIRECT CURRENT, D/C, in which case the power supply A includes a rectifier, possibly some capacitive or in¬ ductive stabilizing means and possibly some protective circuitry. The negative power outlet is connected directly to the reinforcement sections and the positive and negative outlets are both connected to each dis¬ tributing means by means of the very simple two wire system that may ramify or branch into a typical tree structure. The distributing means F may have a further stabilizing element and directly supplies the anodes E. Ideally each distributing means F has an A/D-converter 16 and a multiplexer 15 so that the micro controller 3 can measure voltage and current to each anode. Further more the micro controller would have controlling means 14 - such as multiplying D/A-converters - for control¬ ling voltage and/or current to each anode. Finally each distributing means F would be given a unigue preset address so that the computer B at any time could address the distributing means and collect information from or give commands to its microcontrol¬ ler. In this way an operator could - from the central computer location - supervise and control the behaviour of every single anode in the system. A special address could be reserved for messages recog¬ nized by all distributors such as reset and self test operations. As the corrosion processes act very slowly - it typi¬ cally takes several years for a concrete construction to reach a critical stage - the digital communication can take place at a very slow transfer rate. For in- stance, sampling the status of each anode once every six hours will normally be sufficient and will allow even very large installations to be controlled from a rather modest computer, in particular if each distribu¬ tors micro controller is capable of recording irregu- larities that occurred since it was last addressed/pol¬ led by the computer. The present invention has a number of advantages when compared to existing cathodic protection systems. Firstly the invention allows for a maximally simple cabling system - only two conductors (possibly bran¬ ching into a tree structure) need to be installed. This in turn allows for a very rational installation pro- cedure where electricians mass-install the cabling, the distributors and the many anodes. Secondly, fully exploiting the invention, the function of each and every anode can be supervised and control¬ led centrally from the computer. This is of cause of particular value if the anodes are mounted at positions difficult to access, such as underneath balconies, on bay bridge piers etc. Thirdly, the computer can log status and changes for each anode over any time period enabling very competent corections to the control of each anode and facilita¬ ting an extension of the professional experince and knowledge in the field. Fourthly, in case of severe errors the computer could easily be arranged to send some kind of alarm, e.g. via the telephone network. Fifthly, if more experience is gained about how voltage and current to each anode is optimized when temperture, wind, direct sunshine etc. changes, by attaching sen¬ sors for these parameters to the computer, the computer will be able to optimize voltage and current to each anode constantly. Finally, if the invention is built into new concrete constructions (typically with sparse concentration of anodes and with the supervisory functions active on- ly) - in particular if built into critical construc¬ tions like underwater tunnels and bridge piers - an early warning can be obtained indicating that the construction is beginning to severely deteriorate and that full cathodic protection should be implemented. DESCRIPTION OF THE FIGURES. Figure 1 illustrates an active cathodic protection system according to the invention. Figure 2 illustrates the reinforcement corrosion pro- cess. Figure 3 is a principal diagram of an active cathodic protection system. Figure 4 shows the functional diagram of a preferred embodiment of the distributing and controlling means F according to the invention. In fig. 1 mains power enters into the main power supply A and is converted into low voltage. Normally the power is rectified and smoothened for instance by means of large capacitors and/or inductors. The result could typically be a DC output of 10 to 30 volts. Somewhere in the concrete construction one or more holes are drilled leading to the reinforcement and a reliable connection D is established from the ground output (or most negative output) of the main power supply A to the reinforcement 1. The cabling system C consist of a minimum of conductors and conducts power from the main power supply A to each of many distributing and controlling means F from which the power is distributed to the anodes E or to anode wire nettings. Ideally the cabling system consists of only two conductors that may branch or ramify in a possibly large number of branching points 17. Preferably located near the mains supply A a computer B is connected to the cabling system C. The computer has means for sending and/or receiving digitally coded information via the cabling system C. A number of distributing and controlling means F are connected locally to the cabling system C near all those sections of the concrete that needs cathodic protection. Each distributing and controlling means supplies one or more drilled in anodes E or one or more wire nettings with electric power. Each anode or wire netting has its own output from a distributing and controlling means F, possibly with an individually set voltage or current value. Each distributing and controlling means F has its own digital controller 3 which will normally be a micro¬ controller or a micro processor. In a typical system according to the invention the computer B will periodically send and receive digitally coded messages to/from each distributing and control¬ ling means F. This can be made possible by giving each distributing and controlling means a unigue address and having the computer perform a polling procedure where each distributing and controlling means receives a message with its own address from the computer and - if necessary - can transmit a reply message to the compu¬ ter. The computer will typically have a controlling status so that all communication activities on the cabling system always are initiated by the compu¬ ter. Figure 2 illustrates the reinforcement corrosion pro- cess which the present invention is entended to stop. A section of concrete 4 can be seen with a reinfor¬ cement iron 1. A crack 5 allow moisture to penetrate and start the corrosion process at the anode areas 6. The anode process is Fe —> Fe-H- + 2e- and the freed electrons are consumed at cathode areas 7 along the reinforcement. The cathode process is 02 + 2 H20 + 4e- —> 40H- Finally the iron ions and hydroxide ions together create rust. In figure 3 a principal diagram of active cathodic protecion is shown. By forcing the reinforcement 1 to a negative potential compared with the (humid) concrete 4, the positive iron ions are bound to the reinforcing steel 1 and thereby causes the corrosion process to stop. In the figure drilled-in anodes, 9a and 9b, are placed near the corrosion area and supplied via series resistors 8a and 8b from a power supply. In figure 4 a distributing means F according to the invention is illustrated. The distributing means F is connected to the cabling system C and would possibly have a fuse 11. The power is stabilized and regulated in the voltage regulator 12 that could be adjustable. A receiver/transmitting means 10 unloads freguency mo¬ dulated signals from the cabling system C and converts these signals into a binary representation compatible with the micro controller/processor 3. The micro con- troller/processor 3 correspondingly can send binary information to the receiver/transmitting means 10 which in turn will convert the information into freguency modulated signals and pass these to the cabling system C. The computer B in fig. 1 would need a similar arran¬ gement to enable communication between the computer and the distributing means. From the voltage regulator 12 the power is taken through a relay 13 so that the micro controller/pro- cessor 3 can interrupt the supply of the anodes thereby enabling a (possibly external) decay measurement of the potentials in the concrete. From the relay 13 the power is split into several output lines each going through a voltage and/or cur- rent controlling means 14 - typically a multiplying D/A converter - and finally leading to output terminals 18a to 18e. More or less output lines could be implemented depending on the particular needs. The voltage/current controlling means 14 are controlled from the micro controller/processor 3 which enables an idividual adjustment of voltage and/or current to each anode. The micro controller/processor 3 has an external or built in analog-to-digital (A/D) converter 16 that can measure the voltage at the output of the voltage regu¬ lator 12 and by means of a multiplexer 15 also the voltage at each of the output terminals 18a to 18e. Knowing the characteristics of the voltage/current controller 14 the micro controller/processor 3 can measure the voltage and calculate the current to each anode. On demand from the computer B these values can now be transmitted to the computer.

Claims: P A T E N T C L A I M S CLAIM 1 Electric power distribution system for active catho¬ dic protection of reinforced concrete constructions being composed of A - means for converting mains supply to low voltage supply, B - computational means preferably located near the converting means A, C - a cabling system leading electric power from the converting means A to those parts of the reinforced concrete construction that needs active cathodic pro¬ tection, D - means for providing electrical contact from the converting means A to the reinforcing iron, E - means for providing electrical contact with the concrete mass (e.g. drilled-in anodes or wire netting), and F - means for locally distributing electrical energy to one or more contact means E, C H A R A C T E R I Z E D I N H A T said cab¬ ling system only has a few conductors that are common to all of or large groups of said distributing means F, said computational means B is capable of sending and receiving digitally coded information via the cabling system C, said distribution and controlling means F has a built in digital control section and said digital control section is also capable of sending and recei¬ ving digitally coded information via the cabling system C. CLAIM 2 Electric power distribution system according to claim 1 C H A R A C T E R I Z E D I N T H A T said dis- tributing means F includes measuring means for measur- ing voltage and/or current to each of or groups of said contact means E. CLAIM 3 Electric power distribution system according to claim 1 C H A R A C T E R I Z E D I N T H A T said dis¬ tributing means F includes controlling means for adjusting voltage and/or current to each of or groups of said contact means E. CLAIM 4 Electric power distribution system according to claim 1 C H A R A C T E R I Z E D I N T H A T said dis¬ tributing means F includes BOTH supervisory means for measuring voltage and/or current AND controlling means for adjusting voltage and/or current to each of or groups of said contact means E. CLAIM 5 Electric power distribution system according to claims l to 4 C H A R A C T E R I Z E D I N T H A T said cabling system essentially is a two wire system combining power distribution and transmission of said digitally coded information on these two wires that may ramify. CLAIM 6 Electric power distribution system according to claims l tθ 4 C H A R A C T E R I Z E D I N T H A T said cabling system essentially has three or more wires distributing the power on separate wires and trans¬ mitting said digitally coded information on separate wires, possibly sharing one wire and possibly having the cabling system ramify. CLAIM 7 Electric power distribution system according to claims 1 to 4 C H A R A C T E R I Z E D I N T H A T power is distributed via separate wires and said digi- tally coded information is transmitted via one or more optical fibres, possibly having both wires and optical fibres ramify. CLAIM 8 Electric power distribution system according to claim 5 C H A R A C T E R I Z E D I N T H A T said digi¬ tally coded information is superimposed on the two power supply lines using an inductive coupling, viz. a transformer, as the coupling element. CLAIM 9 Electric power distribution system according to claim 5 C H A R A C T E R I Z E D I N T H A T said digi¬ tally coded information is superimposed on the two power supply lines using a capacitive coupling as the coupling element. CLAIM 10 Electric power distribution system according to claims 1 to 9 C H A R A C T E R I Z E D I N T H A T said computational means B acts as a master device and has controlling status, and said distributing means F acts as slave devices, so that the computational means B at any time can control the communication between the computational means B and any of many distributing means F. CLAIM 11 Electric power distribution system according to claims 1 to 10 C H A R A C T E R I Z E D I N T H A T said digital coding uses a freguency modulation (FM) principle. CLAIM 12 Electric power distribution system according to claims 1 to 10 C H A R A C T E R I Z E D I N T H A T said digital coding uses a freguency shift keying (FSK) 5 modulation principle. CLAIM 13 Electric power distribution system according to claims 1 to 12 C H A R A C T E R I Z E D I N T H A T said distributing means F includes one or more discon¬ necting means, such as relays, for disconnecting one or more annodes from the supply thereby enabling a (possi¬ bly external) measurement of the decay of the potential in the concrete near the disconnected annodes. CLAIM 14 Electric power distribution system according to claim 13 C H A R A C T E R I Z E D I N T H A T said distributing means F has means that, after said power supply temporarily and locally has been disconnected from a number of anodes, is capable of measuring poten¬ tial and/or resistance in the same areas of the rein¬ forced concrete, as the disconnected anodes are mounted in. CLAIM 15 Electric power distribution system according to claims 1 to 14 C H A R A C T E R I Z E D I N T HA T each of said distributing means F can be given one or more unigue, digital address(es). CLAIM 16 Electric power distribution system according to claim 15 C H A R A C T E R I Z E D I N T H A T said digital information is transmitted as digitally coded packages that includes an address part and an infor¬ mation part.

Inventors: SCHULTZ ERIK, WESTERMANN SOEREN ERIK, SCHULTZ, ERIK, WESTERMANN, SOEREN, ERIK
Applicants: CYBERDAN AS, CYBERDAN A/S
Application year: 1992
Main classification: C23F13
IPC codes: C23F13, E04G23, H02J4, H03C1, H04L27