The article deals with arresters type metal-oxide with serial clearance. It briefly describes the advantages EGLA, working principle and purpose of implementation of a research object.
Arresters type metal-oxide with serial clearance (EGLA) optimizes the positive characteristics of old components in the construction fuses — Serial arrester — and the newest component in the design of fuses, called metal-oxide varistor (MOV). This combination can significantly improve the security and reliability of the line utilities. However, due to a negative opinion on using fuses in series with the previous arresters based on silicon carbide (SiC), sometimes there are problems with perception EGLA.
Most often these types of arresters are used for protecting lines. When used on a transmission line, they may be designed so as not to operate at switching, but only when a lightning strike.
When used on a shielded line (upper grounded conductor), and where spark gaps are used primarily for reverse mitigate overlapping insulators (for supporting a wire), they can be very small, as are required not to be as stringent as in unshielded lines. When using unshielded lines in their size which are considerably larger so that they could skip 100 percent of the lightning current. In any case, the dimensions depend on the fuses in application.
EGLA has two main components: MOR and the spark gap. MOR is the metal oxide non-linear resistor having approximately the same characteristics as the standard MOV arrester. Spark gap — the unit is typically an air gap in series.
Strengths of EGLA
Section fuses previous generation SiC consisted of hundreds of components, including many spark gaps in parallel resistors, inductors, etc. These were high-tech elements, always enclosed in a casing. In contrast, surge EGLA are only two conclusions, and nothing more.
The design of the previous generation SiC arresters section dischargers to function as a switch that turned on at the time of discharge, and then turns off when the voltage across it becomes close to zero. In this case, the gap is used for switching and to turn off the discharger.
Arrester EGLA, on the contrary, is only used for the operation — not till the end. Instead, MOR assumes the function of stopping the discharge. Thanks to its excellent non-linear characteristics, MOR overcomes very negative properties of the sequence of the arrester, known as adherence to current aging due to changes in the frequency of the supply current.
In older SiC arresters, MOR consisted of blocks of silicon carbide, which were used to limit the current supply frequency, following the discharge through the gap after the pulse. These limited levels of current arresters are protected from excessive damage and it is possible to complete the operation at low voltage to a low level. However, they also allow sufficiently large currents to pass through the gap, which causes deterioration of fuses and a gradual change their characteristics.
Design Advantages consecutive fuses
1. The smaller creepage distances MOR
Since MOR connected in series with the arrester, a voltage drop across it in steady state is close to zero. Therefore, the casing does not need in such a strict requirements like standard fuses and creepage MOR can be reduced. Since the isolation of MOR is effective only after 100 microseconds discharge, awnings are not needed.
2. Fewer MOV disks
Another significant advantage of the sequential spark gap is that the reference voltage MOR may be 20–30 percent less than the direct connection of arresters. The reference voltage must still be large enough to carry out its functions off after the passage of the discharge. This means that the inclusion MOR voltage may be only a few percent above the system voltage, it will be observed whenever a short circuit during discharge of the spark gap. Minimal voltage reference reduces the number of disks MOV or at least reduce consumption of materials.
The second advantage is a smaller reference voltage that decreases disc stack finite residual voltage will be less. This means that a long and difficult goal to achieve the lowest possible residual stress per unit length MOV disk gets closer. Without prejudice to the total amount of protective discs may be used with a higher residual stress per unit length.
3. Less body
Due to 30 percent smaller creepage and 30 percent less material consumption, the volume of the housing can be reduced by 50 percent compared with conventional arresters without series gaps.
4. Less wear body
Another positive aspect of the inclusion of a spark gap in series with body MOR is that the aging of the body due to electrical discharges becomes insignificant. Due to the fact that there is no resistive path for the arc discharge on the surface of the housing, it is practically negligible to wear.
5. Less wear material MOV
Metal-oxide unit employed in the newest generation of dischargers are resistant to wear due to the modern technology of their production. Although their manufacture is relatively expensive. Perhaps varistor blocks for EGLA can effectively influence their value.
6. Zero power loss
These aspiration parameters of high voltage equipment were made in EGLA. We fuses metal-oxide with successive gaps may have both internal and external leakage. Even if the losses are small, in the presence of millions of service fuses amount of these losses will be impressive.
7. Energy processing
Since MOR is connected in series with a spark gap in the steady state voltage on or offline. This means that in case of instantaneous discharge EGLA, MOR does not withstand all required system voltage fuses as in the case of the metal-oxide with successive gaps. Since there is no powerful exposure voltage on MOR, then there is no need to achieve a thermal stability, as in the designs without fuses. Number of processed energy is determined only by the ability to withstand a single pulse, without limiting thermal stability. It follows that, if we ignore the thermo stability this embodiment can use smaller wheels.
8. Insensitive to rolls on the line
Historical disadvantage of MOV arresters without spark gaps was their sensitivity to strong fluctuations in frequency. It was not so much for the early generation of SiC arresters, because their domestic dischargers were often set to off in excess of the system voltage is greater than one and a half times. This capability is available again for EGLA type fuses, and consequently, adjustment of the arrester can make them insensitive to most electric voltage surge on the line.
9. A choice of surge
Unique and useful properties of the structure EGLA is that they do not respond to voltage spikes during switching, but only on a bolt of lightning. This has never happened in previous design fuses (except for structures with external arresters). Since only discharger responsible for their work, only the clearance of a gap determines at what voltage it happens. If it is set at a level just above the maximum roll when switching, it works only when there is a lightning strike. This effect, in turn, and checks the test plan, as now a audio switching surges or TLD type tests are not necessary.
Due to the fact that the external surge arrester acts as an insulator from the system after a failure, the probability of disconnection of the arrester constant as it glitches practically to zero. Indeed, in the short-term a failure of MOR system near the faulty unit will be limited to setting the level of the spark discharge by EGLA arrester. However, this is not a problem with guaranteed open failure, which means that no permanent system is closed due to a fault or overload protector.
Another advantage of this open mode failure is that the pendants isolating any of the discharger are required. Isolating suspension is used in fault-tolerant polymer arresters. When such a surge fails, it essentially fails briefly. This means that without disconnecting any type and isolating suspension system shutdown occurs undesirable.
The transition from SiC arresters to MOV arresters at the end of the 80s led to a significant reduction in weight and size of these components. EGLA design allows for even greater weight loss, although not such a significant. This reduction in weight allows dischargers to change their configuration that has not been practiced in the past, and provides unlimited opportunities for this.
If you look at modern air network in the United States, you can be surprised to find the distribution lines emergency surge protectors, established over 50 years ago. And, interestingly, almost all of these 'ancient' arresters have external dischargers and represent an era of 'excluding fuses' when external arresters were needed. It seems that a new generation of SiC arresters of direct connection to the distribution system will be replaced by MOV arresters. Although devices with external arresters are probably still used. Due to the relatively low dielectric material load, the expected lifetime EGLA is very large — comparable to the lifetime of the insulator.
Two questions need to pay further attention.
The first — a fault indication.
Without isolation devices is difficult to find the faulty arrester. A possible solution is built-in fault indicator. An example of this is shown in Figure 6. In this configuration, the display device is activated (as all modern circuit breakers) current error Overload EGLA and part or all of the electrodes of the arrester may fall off or fall on the ground.
The second question, which requires a permit for this type of fuses, involves setting up a discharger. All instructions require EGLA make adjustments arrester on the spot. In this case, the responsibility is not based on the manufacturer, and a tuner. Fortunately, a placing surge line has a relatively wide range, and does not affect the performance of the system.
It is known that the use of the line arresters can alleviate or eliminate off line due to lightning strikes. We also know that the in calculation the reliability and dependability of dischargers must be taken into account. Naturally, the ideal would be dischargers with zero probability of failure. It offers arresters EGLA.
Number fuses also affect the reliability of the system. Generally, the larger fuses, the more likely are blackouts due to overloading. However, in the case EGLA, a zero probability of false trips, the number of installed fuses does not affect the reliability of the overall system.
Thus, we can conclude that the arresters EGLA obviously a step forward in the constant search of ways to protect the distribution lines and transmission lines from lightning strikes. Having a good ecological potential, lower cost with high reliability, longer life and lower life-cycle costs, we can expect that they will arresters lines of the.
References:
1. Wikipedia, the free encyclopedia [electronic resource] / American non-profit organization «Fund of Wikipedia». — United States, 2001. Access: www.wikipedia.org
