This work has proposed an innovative technical approach in enhancing the performance of surge arresters to guard the MV transformers towards indirect lightning overvoltages. More typically than not, surge arresters fail after experiencing a thermal runaway as a end result of receiving larger energy than their thermal vitality absorption limit. An simple approach to stop such failures is to utilize a higher rating surge arrester with a desired vitality class, nevertheless, it imposes further prices to the system operator. In this paper, an inductor has been used as a filtering device to restrict the energy pushed into the surge arrester. By controlling the vitality of a surge arrester, the failure is prevented, and a decrease score surge arrester can be utilized as a substitute of the high rating expensive surge arresters.
The filters that have been used to regulate the energy levels are a hundred μH, 250 μH, 500 μH, and 1 mH inductors put in earlier than the surge arrester. Besides contemplating the performance of the proposed filtered surge arrester configuration, the impacts of the spark gap on the efficiency of this configuration have also been studied. An energy-controlled swap has been proposed to monitor the thermal vitality of the surge arrester and to simulate the failure. Results show the effectiveness of equipping surge arresters with an inductor-based filter.
For occasion, equipping a 1 mH filter resulted in a substantial enhancement within the protecting performance of a 12 kV rating surge arrester (i.e., SA-12b). A non-filtered surge arrester SA-12b may only protect the MV transformer in opposition to 100 kV lightning impulses, while a 1 mH filtered surge arrester SA-12b offers correct safety in opposition to 200 kV lightning impulses. Moreover, the surge arrester SA-42b can only lower the overvoltage rigidity to ninety eight.7 kV, whereas a 1 mH filtered surge arrester SA-12b keeps the overvoltage pressure beneath 28.2 kV.
It has also been shown that the spark hole installed in collection with the surge arrester could assist in decreasing the absorbed power by the surge arrester only barely. In inner modifications, the microstructure and electrical properties of surge arresters are optimized to resist different overvoltage situations . When a standard surge arrester is used for safeguarding MV transformers, a number of characteristics must be taken into consideration to prevent undesirable failures or returning to regular working situation after absorbing surge vitality . Among all, the thermal vitality absorption limit performs a vital position in guaranteeing the healthy operation of the surge arrester whereas absorbing surge power. The authors of offered sufficient info on deciding on the surge arresters for residential areas. In a distribution network, the location of surge arresters is a vital problem , where putting in too many surge arresters will increase the likelihood of surge arrester failure, and consequently undesirable outages might occur .
One approach is to decrease the number of surge arresters within the network , whereas strengthening the surge arrester and enhancing its efficiency towards lightning overvoltages may be another various. However, on this work, the thermal power absorption restrict was not thoroughly investigated. Several other combinations of the spark gap and surge arresters have been studied to reinforce the protection quality.
In , consultants advised putting in surge arresters at both the MV and LV terminals, which will impose additional prices to the system operator. Figure 28 compares the absorbed energy by completely different configurations of surge arresters goals at offering proper protection for MV transformers towards the 200 lightning impulse. Note that the surge arrester SA-42b has absorbed 228.1 kJ of power to maintain the overvoltage degree under the specified voltage. This is an unimaginable achievement by which the system operators can save their gear against lightning overvoltages with a lower rating surge arresters, and consequently save a fantastic sum of money.
Preventing the medium voltage transformer fault by protecting transformers against indirect lightning strikes plays an important position in enhancing the continual service to electrical energy customers. Surge arresters, if chosen properly, are efficient units in providing enough protection for MV transformers in opposition to transient overvoltage impulses while preventing undesirable service interruptions. However, in comparison with different protecting units such because the spark hole, their prices are relatively high. The higher the surge arrester ranking and power absorption capability are, the higher the costs go. This paper proposes an inductor-based filter to limit the vitality pushed into the surge arrester, and consequently to stop any undesirable failure.
An energy-controlled change is proposed to simulate the fault of the surge arrester. Furthermore, these surge arresters are equipped with different filter sizes of 100 μH, 250 μH, 500 μH, and 1 mH. Therefore, such configurations not solely improve the protective capability of surge arrester, but additionally cut back the planning and working costs of MV networks. In this part, first we validate the functionality of the proposed energy-controlled change, which is used to mannequin the surge arrester's fault situation due to absorbing vitality greater than the thermal vitality absorption restrict. Then, a quantity of case research are carried out to see the potential of filtered surge arrester compared with the traditional surge arrester and collection connection of surge arrester and spark hole.
However, before validating the model and performing profound analyses, the lightning impulses must be generated. Table 2 presents the optimum parameters of the double exponential mannequin , obtained by solving –. Most indirect lightning strikes have an overvoltage amplitude of less than 300 kV .
Table 2 can be used as a fast source for interested readers to generate the desired indirect lightning impulses. Therefore, the proposed filter, by boosting the efficiency of surge arresters, prolongs its lifetime by limiting the vitality pushed into the surge arrester and stopping any unwanted failure. Above all, installing low rating surge arresters instead of excessive score surge arresters ends in considerable financial savings for the system operator. Figure 31a–f offers a comparison among the safety mechanisms of the filtered surge arrester and joint filtered surge arrester and spark gap against a 200 kV lightning impulse.
In this figure, the stable curves current the measurements made at the presence of filtered surge arresters, while the dashed curves stand for the measurements made on the presence of a filtered surge arrester and spark gap. Note that Figure 31f presents the protection mechanisms of protecting units with standard (non-filtered) surge arrester SA-42b. However, the spark has a small influence on reducing the absorbed power by surge arrester that increases the functionality margin against larger lightning impulses, though negligible.
As an instance, in Figure 31a, the energy pushed into the surge arrester when no spark gap is taken into account is ~59.33 kJ, while for the case with the spark gap, the power is decreased to ~57.65 kJ, which reveals 2.83% enhancement. Moreover, for lower ranking surge arresters connected with spark gaps, the working time is a bit less than the time required by using solely surge arresters (see Figure 31a–c). Such a state of affairs just isn't valid for greater score surge arresters (see Figure 31d–f).
Table 3 presents the impacts of contemplating totally different filter sizes on the performance of surge arresters in opposition to indirect lightning overvoltages. This desk accommodates the very best degree of lightning impulses, among the many impulses listed in Table 2, against which the surge arrester supplies correct protection for MV transformers. From Table 3, it can be seen that by contemplating a 1 mH inductor to SA-12a, its performance is enhanced such that it provides similar protection as the non-filtered surge arresters SA-12b, SA-18b, and SA-30a. By considering a 1 mH filter for SA-12b, a 100 percent enhancement in its protecting performance is achieved. In different phrases, as an alternative of utilizing an costly class-b surge arrester with an energy class-b forty two kV ranking surge arrester, a a lot lower score surge arrester with the same power class (i.e., SA-12b) can be utilized.
First, the surge arrester SA-12a, which is the bottom ranking surge arrester with power class a is taken into account. Figure 24 a–d presents the efficiency of filtered surge arrester SA-12a beneath the 100 kV oblique lightning impulse at the presence of the aforementioned inductors. However, because the energy pushed into the surge arrester is larger than the thermal absorption restrict, a failure, and consequently, an interruption occurs. Moreover, through the use of the 100 μH inductor, it takes ~43 μs until the vitality pushed into the surge arrester passes the thermal absorption restrict , while for the case without the inductor, the time to failure is ~6.1 μs.
Similarly, by rising the inductor dimension in Figure 24b,c, the time to failure, in contrast with Figure 24a, is elevated. Eventually, as depicted in Figure 24d, by using an applicable filter, i.e., 1 mH, the surge arrester SA-12a properly protects the MV transformer against the one hundred kV lightning impulse. That is, by rising the filter size, the absorbed vitality is lowered till which the filtered surge arrester begins functioning correctly and guarantees the continual service to the electrical energy shoppers. The di/dt of the surge arrester underneath the conventional situation, Figure 24d, is ~0.03 kA/μs. As could be seen from this determine, by utilizing a conventional surge arrester , a voltage sag happens firstly of lightning.
After attenuating the voltage to ~30 kV, the surge arrester, due to absorbing more energy than its thermal absorption limit, is pushed into a failure and acts as a brief circuit. Then, though even the overvoltage peak is much lower than one hundred twenty five kV (~66 kV), all in all, the surge arrester isn't suitable for guaranteeing a steady service to customers. On the opposite hand, it can be seen that when the surge arrester is provided with an inductor, this newly fashioned filtered surge arrester offers proper safety towards the a hundred twenty five kV lightning surge. That is, first, the voltage sag is eliminated, and second, there shall be no interruption in the supply service. Moreover, it may be deduced that by rising the size of the filter, the peaks of the measured voltages are decreased, whereas the working times of surge arrester are increased. For instance, by rising the inductor size from 100 μH to 250 μH, the height voltage is decreased from 28.seventy two kV to 27.60 kV, while the working time is elevated from ~195 μs to ~243 μs.
This condition is essentially the most correct design for a collection connection of a surge arrester and a spark gap, where the spark hole supplies the first protection, and after that, the surge arrester prevents any unwanted interruption. Figure 20 presents the proper protection of MV transformers under the one hundred fifty kV lightning impulse by connecting surge arresters SA-24b with the spark hole. The spark gap is triggered at level when the voltage reached to about 149 kV in less than zero.82 μs. Then, the voltage drops quickly to ~134 kV by discharging present through the protecting gadgets. At level , the surge arrester begins its lively role in defending the transformer, and as could be seen, the absorbed power reaches to about 161 kJ, which is beneath the utmost absorption limit for this surge arrester .
Consequently, no service interruption occurs, while on this case, the di/dt is about 9.8 kA/μs. Figure 15 presents the performance of the 36 kV score surge arresters under failure condition. In practice, typically spark gaps are used to guard the transformers in MV networks in opposition to lightning impulses . Although spark gaps are somewhat cheap protective devices, their operation yields a service interruption as a result of voltage chop and such voltage chopping imposes steep voltage stress across the transformer terminal . Besides, transients may also happen as a result of energization of the transformer after the observe current interruption as a result of spark hole operation. On the other hand, surge arresters, by their charming nonlinear habits in addition to surge energy capabilities, can present enough safety towards lightning impulses whereas stopping any unwanted service interruption .
However, utilizing a surge arrester as the protecting gadget may not at all times protect the MV transformers in opposition to lightning . A report by the Cigre Study Committee A2.37 on the failure rate of MV transformers lists the failure rate of surge arrester-protected transformers due to lightning as ~3% . This case investigates the influence of a joint filtered surge arrester and spark hole on the safety in opposition to oblique lightning impulses. It is worth mentioning that the same situations introduced in Case 2 (see Section three.three.2) are additionally legitimate for this case.
However, the focus of this case is to show the impression of the spark gap on enhancing the overvoltage stress and absorbed vitality by surge arrester, in comparison with Case three (see Section three.3.3). To this finish, the performances of surge arresters presented in Figure 26 are studied on the presence of a joint filtered surge arrester and spark gap. Figure 26 reveals a comparability amongst all the surge arresters that may provide proper protection against the 200 kV lightning impulse. As may be seen from this figure, the surge arresters with lower rankings decrease the overvoltage amplitude to a larger extent than the upper score surge arresters. For instance, the 1 mH filtered SA-12b lowers down the overvoltage stress at the MV terminal of the transformer to about 26.9 kV , which is ~85.8% lower than the peak voltage stage at the presence of 100 μH filtered SA-36b.
However, by utilizing the lower score filtered surge arresters, it takes more time to soak up the surplus energy and attenuate the overvoltage. As an occasion, in case of utilizing the a hundred μH filtered SA-36b, it only takes ~380 μs to eliminate the overvoltage stress, while for the 1 mH filtered SA-12b, it takes ~505 μs. Furthermore, this figure reveals that the only conventional surge arrester (i.e., non-filtered surge arrester) that can protect the MV transformer against 200 kV lightning impulse is the SA-42b. This surge arrester, firstly of lightning, does not work properly, and a voltage sag with an amplitude of 174.4 kV is reached the MV terminal of the transformer.
This downside of surge arrester SA-42b could be addressed by using a a hundred μH filter , whereas, from Table three, it can be seen that the correct protection towards lightning amplitudes is enhanced by 50 kV . As an instance, the residual voltage of SA-42b is ninety eight.7 kV, while a 500 μH filtered surge arrester SA-18b supplies a residual voltage of 35.three kV . However, for greater overvoltage amplitudes, it does not have a optimistic effect on providing higher protection for the transformer. Therefore, it's required to find a higher method to control the input vitality pushed right into a surge arrester and thereby prolong its lifetime. Figure 12 exhibits that just like the 12 kV surge arresters, surge arresters SA-18a and SA-18b expertise failures underneath the a hundred kV and a hundred twenty five kV lightning impulses, respectively. However, in contrast with Figure eleven, the times to failure are a bit longer, which is due to greater energy absorption ranges of 18 kV rating surge arresters .
Therefore, although the surge arresters SA-18a and SA-18b, compared with the surge arrester SA-12a and SA-12b, have larger vitality absorption capability, their performance towards lightning overvoltages is comparable. Both the class-a surge arresters failed in opposition to a one hundred kV lightning impulse, while both the class-b surge arresters could not present correct protection towards a one hundred twenty five kV lightning impulse. It should be noted that the spark gap can play an essential function through the failure of the surge arrester. Each surge arrester, if not deteriorated beneath overvoltage stress, wants approximately forty five to 60 min for cooling down , and virtually it behaves as a brief circuit.
Therefore, the spark hole can protect the MV transformers in opposition to the lightning impulses during this cooling down period, although by interrupting the continual service to the electrical energy customers. Figure 31f reveals the mechanism of the non-filtered surge arrester and spark hole in opposition to the 200 kV lightning impulse. Unlike Figure 31a–e, during which at the presence of the filtered surge arresters , no voltage sag was occurring , in Figure 31f, and at the presence of non-filtered surge arrester SA-42b, voltage sag is noticed. To see this phenomenon extra clearly, Figure 32 presents the performance of SA-42b for the primary 5 μs of lightning impulse. As could be seen from this determine, the spark gap is triggered at ~0.5 μs after the lightning strike, and this ends in even sharper voltage sag than the case with solely surge arrester. Although triggering the spark gap decreases the power pushed into the surge arrester , the overvoltage tendencies for each safety approaches (i.e., surge arrester and joint surge arrester and spark gap) after ~14 μs are comparable .
In order to check the efficiency of joint surge arrester and spark gap safety in opposition to lightning overvoltages, the right operation of such mixture is investigated. The first class supplies correct protection for transformers only underneath the a hundred kV lightning impulse. Figure 14 presents the first measurements of the 30 kV score surge arresters experiencing failures. Figure 13 presents the performance of the 24 kV ranking surge arresters beneath failure condition.
As could be seen in Figure 13b, surge arrester SA-24b provides correct protection for the MV transformers under the a hundred kV, one hundred twenty five kV, and a hundred and fifty kV lightning impulses, and the failure occurs under the one hundred seventy five kV lightning impulse. Therefore, its efficiency is much better than the efficiency of previous surge arresters in the same energy class, i.e., surge arresters SA-12b and SA-18b . However, the failure of surge arrester SA-24a, like earlier type-a surge arresters (i.e., SA-12a and SA-18a in Figure 11a and Figure 12a, respectively), happens underneath the 100 kV lightning impulse. The fault for the surge arrester SA-24a occurs after ~17.9 μs, which takes eleven.8 μs and 7.9 μs longer than the failure occurrence for surge arresters SA-12a and SA-18a, respectively. The performance of the forty two kV ranking surge arrester, namely, SA-42b, has been presented in Figure eight. However, when the 250 kV lightning impulse is applied, after ~28 μs, a failure occurs.
Moreover, it can be seen from Figure eight that by increasing the utilized impulse, the time to fault is decreased while the overvoltage stress is increased. To perform in-depth analyses on the protecting performances of surge arresters towards overvoltage surges, a number of case studies are performed. In this work, and so as to achieve the aforementioned objectives, the following case research are carried out. Table 3 can be used as a lookup table for a system operator for choosing the right surge arrester in addition to to adjust the inductor dimension aiming at acquiring the required safety for the MV transformers. For instance, if the operator decides to guard the MV transformer against a 200 kV lightning impulse, Table 3 exhibits a quantity of appropriate designs. To see what's the distinction among these totally different configurations, the overvoltage stress on the MV terminal of the transformer and the absorbed vitality by surge arresters are in contrast.
Lira et al. proposed two on-line monitoring strategies based mostly on feature extraction of the harmonic content of the whole leakage current. These do not require separation of the resistive com- ponents thus eliminating the need for voltage measurements. From the extracted features, methodology one builds a characteristic database that relates the harmonic parts to the arrester working standing. Then the database is utilized in training of a situation classification system based mostly on artificial neural networks .
Method two organizes the options into patterns to be utilized to the classification system based on self-organizing maps . Both methods claim an accuracy of 98\% for proper prediction. Our electronics provider database is a comprehensive record of the key suppliers, producers, wholesalers, trading companies in the electronics business. Import electrical products from our verified China suppliers with aggressive costs.
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