Arcing horn design presentation
Arcing horn known as the angle gap is overhead electric transmission line insulator protection fittings.In IEC publications, arcing horn is listed as insulator string attachment (hardware)
About the use of arcing horn,there is no precedent ofdomestic overhead transmission line, transmission lines and abroad especially in recent years in our country, the tender, such as Bangladesh, Malaysia, Nepal under 275 kv line is installed on the arcing horn.May be affected by this, recently some new lines in our country, such as nanjing pass across the early running lines of 220 kv and 132 kv transmission line in guangdong has already started to design and install arcing horns on the transmission lines.
Second,function and scope of arcing horns
Transmission line is located in the wilderness, vulnerable to lightning strike.Direct lightning overvoltage caused by lightning strike lines and lightning line accessories caused by induction voltage of the thunder and lightning on the ground, the so-called infusion atmospheric overvoltage often appear on a line.It caused by the insulator flashover, line tripping and thunder electric wave invasion damage electrical substation equipment in power grid accident always occupies a large percentage in the accident.
In order to prevent these accidents caused by atmospheric over-voltage power lines and substations have installed lightning line (overhead ground wire), as well as different forms of lightning arrester and so on.Earth wire to wire shielding protection Angle is generally not more than 25 °, if the main role is to prevent the lightning conductor, the external phase conductors, especially the induction lightning overvoltage protection is more dependent on used with other forms of lightning arrester.Arcing horns as one of effective lightning protection devices, at a certain Angle of arcing gap installation at the end of insulator string (as shown in figure 8), its structure is simple, easy maintenance, used with automatic reclosing in the system, as well as the lightning current grounding in time, and uninterrupted power supply to the customer, so as to prevent the surface of the insulator flashover, protect the normal operation of electrical equipment, maintain the normal operation of the role of the line.
Arcing horn, installed in the ground wire insulator string equivalent to pass through the small gap of insulation wire, only arcing horn breakdown when struck by lightning, lightning arrester grounding, which reduces the line that is running the current in Ground Wire additional losses, but also cater to the lightning-line communications lines.
Due to the terminal Angle of arcing general installation between the first and the second piece of insulator, it also greatly improve the voltage distribution on the insulator string, play a role in equalizing , improve the lightning impulse discharge voltage of insulator string.
According to an example, the atmosphere caused by lightning over-voltage amplitude up 500-600KV, lightning current amplitude up to 100KI.So for more than 330 kv line (voltage) lines due to its high insulation level, generally do not cause flashover accident, and below 220 kv for especially below 110 kv lines caused certain flashover accident.So the arcing horn is only applicable to below 330 kv lines installed on insulator string.Moreover, even the heavy minefield of 330 kv lines, because there are equalizing ring has been installed, it has both the function of arcing horns, so don't install.
Three, the structure of the arcing horns forms
According to the current design and has data show that the structure of the arcing horns form generally has the following five kinds:
(1) Bar. As shown in figure (1) using two 8 to 20 mm diameter electrodes made of round steel bar, meantime keep a certain distance to form a discharge gap. But every time the gap discharge, electrode will burn out, can't even use, commonly used on 69 kv line.
figure (1) Bar arcing horn
(2) Spherical. As shown in figure (2) to reduce bar defects of the electrode ,on the rod end installed two metal ball to form spherical clearance, but still can't completely ruled out electrode burns. Commonly used on below 220 kv line.
figure (2) Spherical arcing horn
(3)Claw shape.As shown in figure (3), (4) the electrode to make double claw shape or single claw shape.Arc discharge gap, the electrodes are separated by recent form, then the upper claw shape gap arc was quickly stretched, consisting of the arc generally easy to go out, even if not in time out, also because of arc, the electrode was burned at the end of the claw clearance, and minimum clearance distance does not burn, so as to ensure the next right action.The clearance under 330 kv lines are available applications, nanjing recently closed across the 220 kv lines on ground trailer with this kind of arcing horns.
figure (3) single claw shape arcing horn
figure (4) double claw shape arcing horn
(4) ring or tennis racket shape.As shown in figure (5) and (6), it is generally used in φ28x3 steel tube bending, and equalizing of long insulator string have obvious effect, improve the lightning impulse discharge voltage, commonly used on the 220 kv-330 kv line,recently Nanjing dashengguan held 220 kv line wire suspension and tension on the string is used in this form.
figure (5) ring arcing horn
figure (6)tennis racket shape arcing horn
(5) the clearance can be adjusted form. As shown in figure (8), (4), the main characteristic is that the Angle of gap clearance can be adjusted, reduce product design specifications, the purposes of standardization, in order to meet the design requirements and installation area.
Fourth, the installation position of arcing horns
Arcing horn as the insulator umbrella attached to the insulator string ends with a specific installation location has two kinds:
(1) ball head hanging ring or bowl head hangs hanging strip arcing horn, as shown in figure (7), (8), general installation in single overhang on both sides or tension string.
(2)Split conductor arcing horns installed on board. As shown in figure (9), (10), generally installed on the trailer or tension chain more on both sides of the board.
It is worth noting that: (1)In order to play the arcing horn equalizing effect ,terminal arcing horn is generally higher than that of the first disc insulator 36 mm (Japanese NGK company standards).(2) the arcing horn is generally installed in pairs, but also have to end truncation arcing horns and online only end the installation of the so-called high insulation gap arcing horn, as shown in figure (7), (8).(3) the tension string just above the insulator string on one side of the installation, lower side is not installed.
Five,arcing horn clearance design
The size of the angle of arcing discharge gap, mainly by the grounding system operation requirements to determine the circuit design personnel, the protection of lightning discharge gap voltage should be lower than the impact strength of insulator string, and the discharge power frequency voltage should be higher than that of the system operating overvoltage.Specific follow the relevant provisions of the "over-voltage protection of electrical equipment design order".
According to the current foreign bidding line data and the design of the current domestic existing, arcing horn clearance flash-over rate (as shown in figure (11) B/C) generally take between 75% ~ 85%, shown in figure (11), also does not exceed the reasonable configuration of effective area.
figure (11) The reasonable configuration of arcing horn
In the Japan NGK company ,standard design of induction in a simple design method, main is: (1) Arcing Angle gap 178 mm shorter than full length in detail.(2) Terminal arcing horn higher than the ball at the end of a piece of insulator under 36 mm. and chart can be directly to find out the impact of the Angle of gap discharge voltage , wetand dry power frequency flash discharge voltage .
Six, arcing horn electrical test requirements
According to the function and design requirements of arcing horn, the following electrical type test items should be done.
(1) Dry frequency lightning impulse withstand voltage test or 50% full-wave impulse flashover voltage test.
The experiment is mainly to determine angle of arcing gap for lightning over-voltage electric strength, to protect the insulator, its electric strength must be less than the impulse flashover voltage of insulator string, under the test voltage shall not occur along the insulator surface flashover in whole or in part.
According to IEC standards, the use of 1.2/50 standard shock wave form lightning impact simulation.Commonly used summarized the impact of the 50% flashover voltage values for its dry lightning frequency withstand voltage, when the test method may be inserted or lifting method, the numerical conversion to standard atmospheric conditions generally 6 ~ 7 times in line phase voltage.
(2)The wet power frequency flashover voltage test
According to IEC standards, On the angle of gap with standard artificial and measured cause of arithmetic mean power frequency flashover voltage, can also access the probability of 50% flashover voltage.
The purpose is the inspection angle gap under the condition of the line running resistance working voltage and the ability of operating overvoltage. Its value is usually 4 to 4.5 times the line phase voltage.
(3) the wet power frequency withstand voltage
Running test shows that 1 min ac withstand voltage test of electrical equipment generally can ensure safe operation.Typically take in 75% of IEC standard design is scheduled to test voltage, and then for the test voltage per second 2% speed up a voltage grade, lasts 1 min no flashover or breakdown, is desirable.But also at 95% of the wet flashoverpower frequency voltage lasts 1 min for beginning point, flashover if still fall another 2% generally can accept.
(4) Radio interference test
Arcing horns installed on the insulator string, it is bound to increase its radio interference.According to the requirement of the tender in Malaysia 275 kv insulator string is less than 46 db, test voltage to test according to IEC standard.
(5) Corona initial voltage test
About the corona arcing horns for the analogous to the other with the same voltage grade and elevation corona, also no longer here.According to the requirement of the tender in Malaysia 275 kv insulator string, corona initial voltage not less than 190 kv.