EN Caratteristiche della tensione fornita dalle reti pubbliche di distribuzione utilizzare un registratore conforme alla CEI EN In questo. Power quality has many meanings depending on what the power is used for. • Measuring PQ is all about deviations from normal state. • USERS. of European Norm Some countries have used EN as the basis for their national quality of supply regulations. But the standard’s statistical models.
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Studies in the field of Power Dn have become increasingly important in recent years. International standards establish the limits of the main disturbances that can compromise the quality of electricity. All voltage values outside these tolerances do not correspond to GOST and can be hazardous to appliances and equipment in one form or another. The RDF node for measuring basic parameters of power quality which allows connecting to the central computer which can detect the direction of sag events has been developed.
The project is related to the development of a sensors’ network to measure Power Quality with the ability to connect it both wirelessly and by wiringfor the analysis of a low-voltage grid. Power Quality; smart sensors; low-voltage grid; EN standard; voltage sags measurement; disturbances of power quality.
Electricity is the main “raw material” for industry and service sectors, and it is an example of the philosophy of “Just in time”, according to which the components are delivered from a trusted supplier to the production line only when it is used, without making any preventive control, which ensures their quality before use.
In fact, electricity is very different from any other product: To ensure the quality of the energy supplied to the point of delivery is not easy, and there is no way to rn electricity. From the user point of view the problem is even more complex, since it can reveal inefficiencies, such as the complete 501660, which can last from several seconds to several hours, or sags, during which the voltage drops for a short time at a level lower than nominal.
A cause of troubles is not only long interruptions.
Some processes are profoundly affected even by very short breaks, for example:. This happens for example in managing actions, and currency exchange. Each of the problems related to the quality of energy is caused by distinct phenomena. Some problems come from sharing the power supply network by 501160 users, others are born in facilities eb the users themselves and may or may not propagate through the network with 550160 against other customers.
The concept of quality of energy is not easy to define there is not a single parameter, which can describe the complete em immediate change in it. The problem arises when it dn necessary to apply such a general definition to a particular product such cdi electricity. It is possible however to define the “energy quality” as a perfect supply of it, which can ensure continuity of service, within certain tolerances of voltage and frequency, and can be characterized by a voltage with undistorted sinusoidal waveform.
The acceptability of the deviations from the nominal characteristics of the energy depends on the type of use by the user, the equipment installed and its needs. The quality of electricity that a typical user considers necessary for his activity is not therefore an absolute concept, but will depend on the users’ sensitivity to noise technical aspect and the consequences of disruption economic fn being thus variable from case to case.
In conclusion, the disturbances that affect the user depend on the characteristics of the distribution network, and on the behavior and the sensitivity of their loads. In Table 1, 500160 are reported both disturbances aforesaid, with their tolerances compared to standard EN [2, 3]. Voltage distortion depends on the distance from the transformer and on the line impedance.
In short, the voltage distortion affecting the grid at a certain location depends on the value of the short-circuit current of that point. Also, once the grid voltage is distorted, a linear load absorbs a distorted current. The presence of such harmonics on the grid is responsible for detrimental effects. Moreover, at higher frequencies, iron losses hysteresis losses and eddy current losses as well as the losses in the cables increase.
Finally, electronic equipment may experience failures due to the presence of harmonics. Another aspect, which should not be neglected, is the resonance issue related to the presence of harmonics in electrical networks. In fact, in this case the amplitude of a specific harmonic may increase sn times as much of normal operation.
Consequently this high-value current may seriously damage capacitors and equipment connected to the grid.
In order to prevent this kind of event, the resonance frequency of the grid at a certain point has to be known and, additionally, the insertion of wellfitted ci coils may be considered to damp the oscillatory phenomena. The purpose of the project is to create a network that can monitor systematically the power quality cie a site. Intelligent sensors are used in a growing number of industrial applications in which, with the development of innovative architectures, the transducer participates in the elaboration of the overall data, which in these new configurations can be divided between all the elements [4, 6].
The structure of a smart sensor includes, therefore, an cdi that should be able to convert the value of the physical quantity to be detected in information of an electrical nature, which is converted into numerical form in order to facilitate the management and processing by the microcontroller.
At the point of measurement it is necessary that the instrument detects the following parameters: In this 50106, data processing complies with the requirements of IEC cfi. And so on for the other measured quantities, the goal was to create a device belonging to the class S. To identify the source of a voltage dip it is first necessary to evaluate the intensity of the event through its features and unambiguously define its duration, depth and instant start.
This latter fact is important to investigate other parameters monitored and perform a matching. The starting instant of the event is the. With regard to xei classification requirements of the sag we followed the industry cri IEC On the measurement point the operating characteristics of the node you are monitoring are acquired in real time: The calculation of the phase follows the same logic of the frequency detector of the PLL VCO where the samples were replaced by the current samples measured: Having the phase it is particularly easy to derive various values of active, reactive and apparent power.
Once the event has been identified, it is possible to analyze the variation of reactive power in transit. This change should be assessed by comparing the value of reactive power in the system, i. This method has been implemented within a network of sensors for a distributed measurement, and it will be illustrated in more detail in the following paragraphs.
One of the objectives pursued in the design was to obtain the flexibility of the module, in order to be used for different measurements. It is possible, by changing a few lines of code, to implement functions that return a set of parameters than those currently produced. The prototype realized at an early stage allowed us to perform the first steps and check the feasibility of some points.
It is currently being developed on a DSP-based device that allows a performance improvement in terms of computational and considerable possibility of miniaturization also allowing the use of a single processor. If you need to store a greater amount of data, for non-real time query, you can add an external. EEPROM to the device this requirement has already been incorporated in the target of the second prototype in development.
The design of the power supply is surely one of the most delicate aspects to be taken into account when developing a measurement circuit. The voltage stability is critical both for all those devices which for their proper functioning requires a stable operating point, as the operational amplifiers that constitute the part of signal conditioning, or regarding to the sampling, as voltage variations influence the amplitude quantization, and then the entire measurement would be altered.
In this case, in addition to stability, a high immunity to all line disturbances is required, disturbances which presumably will be the ones that the sensor must detect and analyze.
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For cie acquisition of voltage and current signals, we used two Hall effect sensors. Due to their characteristics, the input signal is faithfully reproduced, also ensuring excellent insulation from the network. The acquired signals are processed to be adapted to the input levels of the processor, as shown in the diagram Fig.
Schematic diagram of the circuit for the treatment of the voltage signal implemented with the program CircuitMaker. The next stage of processing is handled by 18F microcontroller. Here all the signal processing is performed, pre-treated and sampled at a frequency of 4 kHz, which is necessary for the study up to the 40th harmonic, as indicated by the CEI EN For communication between two microcontrollers a serial 550160 has been implemented between pin 25 tx of the processing pic, and pin 26 rx of the network management pic.
The protocol is very simple: The first byte is a start byte, then, there are 40 bytes that represent the data.
Finally a parity byte is sent. It has also added a switch between the two serial outputs of the pic so you can monitor via the 5060 the. The serial communication to the PC is made possible according to the standard that describes the RS specifications.
The transmission stage consists of a dedicated pic of the same family of the processing picwhich is implemented by the transmission protocol of ZigBee. In the study of consumption of the smart-sensor the three phases of measurement, the processing and the transmission of the data packet were analyzed separately. The following are the most interesting values Table 2.
The sensors and the RF card parts are more expensive to manage. Even if this prototype is powered by the network you are trying to reduce consumption considerably by working on the sensors, in order to be independent from the network supply. The router is connected directly to a PC via cable, but in the next phase of the project a different connection, for example GSM, will be implemented to send warnings to the control stations.
This single device realizes the SPQ block of the network shown in Fig. The router is a device consisting only of much smaller processor that manages the ZigBee protocol and the RF card.
The prototype has been used to perform some measurements within the university network. The tests were done in order to verify the parameters of robustness and reliability of the measuring instrument. Among the various tests that have been performed, the. As you can see the first node F brings the values of the network at the point of measurement, and the variables related to the load from which it is possible to obtain a complete characterization: As you can see the network parameters are constantly measured and the required parameters are calculated.
Among the most significant disturbances, due to the frequency with which they occur and the economic consequences that may result in, it is possible to recognize the phenomenon of voltage sags. The sags may affect one or more stages depending on the phenomena that cause them. It is possible to ascribe the voltage drops to two main categories of. The main cause of voltage sags in a public network is represented by faults and in some cases by the transients overloads occurring at start up of large motors or during the insertion of large loads.
These latter types of sag are usually due to the supplied loads while faults are associated with the interruption of the network. All the events mentioned above, at a certain instant, cause an increase in the current in the network.
Because of the longitudinal impedance of the transmission line or distribution, the circulating current produces a voltage drop which can lead to voltage sags more or less important for the user.
Also, a ruined or defective wiring increases the impedance of the system and therefore it amplifies the phenomenon. Overcurrents contribute to eh lowering of the voltage level because the latter is a function of the voltage drops through the components cek the network.
The effects of voltage sags are the malfunction of the devices connected to the network or the termination of the operation, depending on the extent of the event, in terms of depth and duration, and the limits of susceptibility of loads.
It is therefore essential to locate the origin of the disturbance in order to allocate responsibilities, and possibly proceed with the correction of the causes. Starting from the scientific literature and regulations it has been possible to define a simple and effective method for the localization of the sags in a low-voltage grid, with a commitment to produce an algorithm 500160 a wireless sensor network with low cost and low impact .
The starting method is the study of the flow of reactive power . The method of monitoring the reactive power flows tries to locate the origin of a voltage dip, indicating whether this is upstream or downstream relating to the point of observation.
An event may be defined caused downstream, if set the direction of the active power flow, it is detected in the side to which the power flows, compared with the monitoring point, conversely, an event could be said to be originated upstream, if it is detected in the side from which the active power is supplied.
For a large part of the phenomena voltage drops correspond to an increase in the current in transit within the system. In these cases if the event takes place downstream of the measurement point, this will correspond to an increase in the current in transit and also to the increase in the product I sin p, and then also to an increase in the instantaneous power associated to the current component in quadrature with the voltage, whose peak value eb with the.