This chapter gives an overview of overvoltage protection to industrial contraptions. To commence with, the overvoltage definition and its causes have to be known in order to understand what kind of overvoltage sensing should be assessed farther in this undertaking. Furthermore, it is of import to analyze the significance of the overvoltage sensing circuit in overvoltage protection devices that are presently available in market. Further analysis in overvoltage sensing circuit is helpful to develop this undertaking, run intoing the circuitry demands, as to do this undertaking worthwhile.
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Industry, public establishments and place contraptions largely depend on electrical and electronic informations technology. As the information recording devices at the production installations are connected to office terminuss and computing machines, electromotive force supplied to them should be hold dependability and stableness. High supply dependability, which is the cardinal significance, may do major nuisance to the client if there is any break. Furthermore, it can take to life endangering state of affairss, for industrial client or make terrible proficient and production jobs. Therefore, the dependability of the supply is of import to avoid any amendss or losingss due to devices malfunctioned.
Electrical power supply of good quality is provided by the regulated and defined electromotive force degrees with low fluctuations, regulated value of frequence with low fluctuations and low harmonic current. To guarantee a high quality of electrical supply, two basic methods can be used which are the proper usage of automatic electromotive force and frequence control methods ; by using big interrelated power systems which by their very nature, are less susceptible to lade fluctuations and other perturbations. [ 2 ]
An electronic insurance company in Germany reported that the costs of compensation for over electromotive force harm due to electromagnetic perturbations on electronic system and equipment, such as computing machines, mensurating devices and communicating systems have quadrupled within a period of 10 old ages. The amendss largely caused by rush and electromotive force supply instability [ 1 ] .
Surge harm analysis has shown that lightning discharges are the chief perturbations, followed by due to exchanging operations in proficient system and by electrostatic discharge. In malice of the lightning is the chief perturbation, indirect harm caused by electromagnetic lightning perturbations is far higher than those due to direct lightning. In this instance, the hardware harm is merely little part of the entire impact ; eventful harm is the dislocation of computing machine systems and malfunctioning of mensurating and command systems do the extreme proportion of loss [ 1 ] .
In general, overvoltage occurs when the electromotive force in a circuit or portion of it exceed the upper preset electromotive force. Overvoltage is one of the electromotive force unbalance status, in which the three stage electromotive forces differ in amplitude or displaced from their normal 120 degree stage relationship or both. The nature of imbalance includes unequal electromotive force magnitudes at the cardinal system frequence, either undervoltage or overvoltage and cardinal stage angle divergence [ 3 ] . Overvoltage may do by transeunt overvoltage, which is a electromotive force extremum with a maximal continuance of less than one msec.
There are two possible causes of overvoltages on electrical webs which are natural causes and other cause due to equipment or exchanging devices.
Natural Caused Over electromotive force
Natural overvoltages on low electromotive force webs are caused by lightning work stoppages. The high electromotive force potency contained in direct lightning work stoppage on a lightning music director leads to considerable harm of the installing. Surges of this atmospheric cause can be divided by two, which are direct work stoppage and remote work stoppage.
Lightning current in a lightning way causes a electromotive force bead at the impulse Earth opposition of the grounding system, which so induces rush electromotive forces and currents in cringles inside the construction ‘s installing circuit. The lightning work stoppage causes the induced electromotive forces, hence rush currents in installing cringles particularly due to its magnetic interfering radiation. Consequently, if lightning work stoppages a feeding overhead line, there will be increased electromotive forces on the incoming power lines. However, it can be presume that 50 % of the lightning current flows into earthing system and the other 50 % is distributed every bit to the surpassing remote- earthed supply systems, which are the four wires of power overseas telegram or informations line [ 3 ] .
In the instance of remote work stoppages, going rushs either propagate along the lines or lightning work stoppages in the locality of the protected systems, thereby bring forthing electromagnetic Fieldss which affect the system. Damage due to rushs of natural cause has shown that electronic installings, up to a distance of approximately 2km from the lightning point of work stoppage, are susceptible to induced rushs. When this partial of the lightning currents flow in overseas telegrams, it generates cross electromotive forces. Therefore, the cross electromotive force generated between the wire and the metal overseas telegram creates emphasis on the insularity of the affiliated device between its input terminuss and Earth. Within a radius up to several kilometers, the electromagnetic field caused by lightning in clouds besides create sudden addition in electromotive force [ 1 ] .
Switch overing Over Voltage
Switch overing over electromotive forces linked to a web ‘s equipment create over electromotive forces linked to a web ‘s equipment. Even though the overvoltages much lower than natural causes, it occur much more frequent, therefore causes premature ripening of the equipment. The exchanging overvoltages can be caused by disjunction of an open- circuit power line. It occurs when the switch opens, therefore the instantaneous value of the supply electromotive force on the line consequences in a high possible difference between the system and the staccato line. The possible difference can do a flash back between the switch contacts that are yet to shut. The line electromotive force so balances at a degree equal to the instantaneous value of the supply electromotive force and the discharge between the switch contacts is quenched.
Switch overing overvoltage excessively can be caused by the disjunction of an unfastened circuit transformer, where its ego electrical capacity is loaded by energy of the magnetic field. Therefore, the inductive capacitive circuit now oscillates until all of the energy in the ohmic opposition of the circuit is converted into heat. These overvoltages can make amplitudes of several times the value of the nominal supply electromotive force.
Equipment incorporating electronic constituents is besides likely to bring forth electrical perturbations comparable to overvoltages. The effects of which on sensitive equipment, although non seeable, are no less harmful: premature ageing and unpredictable dislocations.
Significance OF OVERVOLTAGE PROTECTION
Recently, there has been an increasing figure of incorporate circuit on bit that support embedded maps such as CPU, logic Gatess, memory and etc. In such an incorporate circuit device, different power supply electromotive forces are needed for each internal circuit. Thus this innovation relates to incorporate circuit devices, in peculiar, an integrated circuit device with a power- supply electromotive force sensing circuit to observe that a power supply electromotive force goes out of preset ordinance.
The intent of an overvoltage protection circuit is to protect sensitive electronic circuitry from harm or emphasis that may ensue from the application of a electromotive force that exceeds a preset acceptable scope. Frequently, electronic devices such as telecastings, stereos, or Personal computers are plugged into such overvoltage protection circuits which are connected straight to a wall socket. During operation, if the walls socket electromotive force rises above preset value ( e.g 230V ) due to an electrical spike, the sensing circuit will observe the overvoltage, hence send signal to the control circuit, which so clamp or short the extra electromotive force to land, forestalling the line electromotive force from lifting above preset value. Therefore, it will protect the affiliated devices from harm.
2.4 OVERVOLTAGE PROTECTION REVIEW
In general, the electronic devices are configured in Figure 2.1. By mentioning to Figure 2.1, an electronic device comprises a power supply system an electronic circuit. The power supply system comprises an AC to DC power supply and DC to DC power supply. The power supply system receives commercial power, from a power having terminus. The AC to DC power supply is used to change over the AC received power to DC power while DC to DC power supply used to bring forth a coveted degree of DC electromotive force.
Figure 2.1: Electronic device.
Furthermore, by mentioning to calculate 2.2, DC to DC power supply comprises a power circuit, a control circuit and overvoltage sensing circuit. The power circuit receives power from input terminuss and outputs a coveted degree, stabilized DC electromotive force to end product terminuss. The overvoltage sensing circuit, which connected to the end product terminuss, senses any electromotive force anomalousnesss. When the end product electromotive force becomes abnormally high or low, the overvoltage sensing circuit outputs the stop signal to the control circuit. The control circuit turns on or off the power circuit harmonizing to the signal received via the control terminal [ 4 ] .
From the general block diagram of electronic devices shown, the overvoltage sensing is of import to look into if the electromotive force across terminuss is equal or higher than predetermined value, hence send signals for farther action to the control circuit.
Figure 2.2: District of columbia to DC power supply
In add-on, overvoltage protection besides can be equipped with monitoring device, in order to supervise the statistics of the imbalance electromotive forces. The overvoltage protection device excessively may includes an electro-optical relay unit, that may be optically- linked to overvoltage protection device. The electro- optical relay unit has a digital information port for puting system conditions, metering and event coverage. The end product may include a problem dismay or index every bit good as dismaies at different set points of over electromotive force [ 5 ] .
In general, a detector is used to feel external measures and frequently being called as transducers. A transducer is a device that converts one physical measure into another, plus different transducers convert a broad scope of physical measures. Transducers of a 3rd category take an parallel input measure and generate from it a digital end product. In some cases the end product is a simple binary representation of the input, as for illustration in thermoregulator, which produces one of two end product values depending on whether temperature is above or below a certain threshold [ 6 ] . Therefore, this illustration excessively can be applied to overvoltage detector. However, stand foring linear measure by agencies of a digital measure is, by necessity, an estimate. Indeed, in many instances, the mistake caused by this estimate is little compared with the noise or other mistakes within the system therefore can be ignored. When depicting detectors, it is of import to quantify their features and public presentations [ 6 ] .
This defines the upper limit and minimal values of the measure that the detector is designed to mensurate.
This is the smallest discernable alteration in the mensural measure that the system is able to observe
This is the difference between a measured value and its true value. Mistakes can be divided by two which are random mistakes and systematic mistakes.
It describes the maximal expected mistake associated with a measuring and may be expressed as an absolute value or scope.
It is a step of the deficiency of random mistakes produced by a detector. Devicess with high degrees of preciseness will bring forth repeated end product with less discrepancy.
In overvoltage protection device, the overvoltage detector plays of import function in observing the input electromotive force within or beyond the preset electromotive force. Therefore, the top demand for overvoltage detector should be able to compare the input electromotive force to the electromotive force mention set earlier.
To get down with, the overvoltage detector should consist two comparing circuits. The first comparing circuit is for the overvoltage sensing circuit. This circuit may dwell of electromotive force spliting resistance, comparator and electromotive force mention beginning. The electromotive force mention is set to upper bound of the normal electromotive force scope ; hence if the input electromotive force supplied exceeds the electromotive force bound, the comparator will be activated.
On the other manus, the 2nd comparing circuit excessively comprises electromotive force spliting resistances, comparator and electromotive force mention beginning. However, the electromotive force mention here is set to take down bound of the normal electromotive force scope. Thus, whenever the input electromotive force supplied much lower than the electromotive force bound, the comparator will be activated [ 4 ] .
The detector should exactly observe either overvoltage or undervoltage exactly with really minimal false dismay. The nominal stage electromotive force input supply is followed under the Malaysia Grid codification, which are 230 Vrms +10 % -5 % [ 7 ] . Besides truth and stableness, the detector excessively should be runing relevantly with speedy clip response, in order to observe anomalousnesss from damaging the electronic circuits for farther development.
CASE STUDIES/ AVAILABLE PRODUCTS.
Nowadays, there is advanced AC Voltage Transducers manufactured in the market. Most of merchandises are improvised by equipped by broad scope of electromotive force and frequence, temperature compatibility, high truth and efficiency. One of them is the MiltiTek AC Voltage Transducer. Its theoretical account M100 series electromotive force transducers are designed to mensurate AC electromotive force in individual and three stage system. They convert the AC signal input electromotive force to a DC end product which is straight relative to the input signal. For the M100 VA1 1 stage, it is self powered, which is no subsidiary calibrated electromotive force is required. This merchandise used to mensurate electromotive force in energy direction systems, patchboards, generator and telemetry controls [ 8 ] .
Other merchandise, which is CR4500 Series, besides the true RMS electromotive force transducers are designed for applications where AC electromotive force wave forms may non strictly sinusoidal. It is much precise and accurate than other devices. Therefore, its applications largely used in rapidly changing electromotive force supplies and for harmonic electromotive forces. It has highest preciseness and the end products are isolated from inputs. From its datasheet, it is noted that its operating temperature is 0 & A ; deg ; C to 60 & A ; deg ; C. Furthermore, its response clip to be 250ms [ 9 ] .
Based on the patents and merchandises reviewed, most of the electromotive force transducer or detector is a common application that used to supervise the feature of the electromotive force respective to clip. It is besides of import for the detector to observe any alterations or varies in electromotive force with less clip response. The detector may fit with bespeaking visible radiations or sound qui vives to bespeak user if there is any electromotive force abnormalcies. Furthermore, some of the detector excessively may supply the relay for farther protection, which is stumbling the circuit whenever major anomalousnesss that may damage the equipment occurred.
Therefore, electromotive force detector and indicant design is put into precedence to be studied in this undertaking. Furthermore, it is an nonsubjective to plan a electromotive force detector that is cheaper than in the market.