Kingtronics Blog

Telecommunications installations as well as CATV amplifiers, CB transmitters, home entertainment systems, computers and similar equipment can be exposed to voltage surges conducted via the power network. The combination of a surge arrester and a varistor offers proven protection in these cases. The phase and neutral conductors are connected to ground potential of both protection elements

Surge arresters are an essential aid to insulation coordination in electrical power supply systems. Valuable equipment can be protected against lightning- and switching overvoltages.

If basic rules are kept, modern Metal oxide surge arresters offer complete protection against overvoltages.

Costs of surge arresters in electrical power supply systems are less than 1% of the worth of the equipment they protect.

High availability and low costs of surge arresters facilitate new applications like surge arresters for transmission lines. As a result surge arresters convince with a quality improvement of electrical power supply systems.

The surge arrester is shown in Figure 7. It is built-up of 6 separate mechanical and electrical modules connected in series. The design of each module includes an HTV silicone rubber insulator moulded directly onto the internal structure with the  ZnO block column. The internal cage-style mechanical structure provides high mechanical strength and well controlled short-circuit capability in the event of arrester overloading.

The special location of the  arrester in the tower has required extensive 3D electrical field calculations to determine necessary grading rings to control the voltage distribution along the  arrester. The mass of the  arrester including the grading rings is 128 kg or approximately one third of the mass of an equivalent  arrester with porcelain housing. The creep age distance of 27 mm/kV corresponds to IEC class III.

Gas-filled surge arresters operate on the gas-physical principle of the highly effective arc discharge. Electrically, surge arresters act as voltage-dependent switches. As soon as the voltage applied to the arrester exceeds the spark-over voltage, an arc is formed in the hermetically sealed discharge region within nanoseconds. The high surge current handling capability and the arc voltage, which is almost independend of the current, short-circuit the overvoltage. When the discharge has died down, the arrester extinguishes and the internal resistance immediately returns to values of several 100 MΩ.

The surge arrester thus meets almost perfectly all requirements made on a protective element. It reliably limits the overvoltage to permissible values, and – under normal operating conditions – the high insulation resistance and the low capacitance contribute to the fact that an arrester has virtually no impact on the system to be protected.

The capability of the surge arrester in energy dissipation against switching surge is well expressed by the magnitude of kJ/kV (arrester rated voltage). These values show the dissipated total energy per two shots of switching surge that the surge arresters can withstand thermally with these values. Where the energy capability is inadequate in our standard series.

Typical structure of surge arresters are shown in Figure below .The surge arresters are basically composed of the TNR elements, housing and associated parts with insulating gas filling as shown in figures. The hermetic sealing of the housing is constructed with weather-proof synthetic rubber. The pressure relief diaphragm is structured with special metal plate, which is ruptured when a sudden pressure rise occurs in case of the internal failure.

Surge Arresters conduct lightning surges around the protected insulator so that a lightning flashover is not created. They are designed to be installed functionally in parallel with the line insulator. The arrester conducts the lightning surges around the protected insulator so that a subsequent 60 Hz fault on the circuit is not created. The arrester becomes a low ohmic path for the surge as voltage across it increases. When the voltage returns to normal, the arrester once again returns to a high ohmic device with only microamps of leakage current.

If an arrester experiences a surge higher than it is capable of handling without failure, and it is failure, equipped with an isolating device, it will isolating device, disconnect during the event.

After the surge is over, and fault current starts to flow, the disconnector senses the fault and ignites the powder built into the device.

The disconnecting device is not an interrupter so during this rare event, an interrupting device must clear the circuit.

The valve arrester consists of disks of zinc oxide material that exhibit low resistance at high voltage and high resistance at low voltage. By selecting an appropriate configuration of disk material, the arrester will conduct a low current of a few milliamperes at normal system voltage. During conditions of lightning or switching surge over voltage, the surge current is limited by the circuit; and for the magnitudes of current that can be delivered to the arrester location, the resulting voltage will be limited to controlled values, and to safe levels as well, when insulation levels of equipment are coordinated with the surge arrester protective characteristics.

A typical surge arrester consists of disks of zinc oxide material sized in cross-sectional area to provide desired energy discharge capability, and in axial length proportional to the voltage capability. The disks are then placed in porcelain enclosures to provide physical support and heat removal, and sealed for isolation from contamination in the electrical environment.

Telephone/fax/modem protection

Telephones, faxes and modems are equipped with sophisticated but sensitive electronics. Typical circuits used to protect them with surge arresters are shown in following Fig.

These arresters protect against common-mode interference voltages, i.e. surge voltages that appear in both lines to ground. In the event of an over voltage, the arrester protects both exchange lines by conducting the surge current away to ground.

A transmission line arrester also known as a transmission line surge arrester is any arrester that is applied out on the transmission line to reduce the possibility.

The resulting wave when an electrical variation in a circuit such as a transmission line takes the form of translation of energy along a conductor, such energy being always equally divided between current and potential forms. The traveling waves propagate at close to the speed of light and can generate surges at 2-4 times the initial impulse under certain circumstances.

Impulse protective levels of an arrester

a) Fast front protective level: The highest of either the steep current residual voltage or the front-of-wave impulse spark over voltage.

b) Standard lightning impulse protective level: The highest of the residual voltage at nominal current or 1,2/50 lighting impulse spark over voltage.

c) Switching impulse protective level: The highest of either the maximum residual voltage for the specified switching current or the specified switching impulse spark over voltage.

Application range:

Peace project(police),telecom "global E-eye"(telecom),road monitoring(police), Community Monitoring(building management), monitoring of environment(environment protection),expressway monitoring, etc.

System specification:

The lightning protection of monitoring system of CCTV is relatively complicated firstly we should understand the main reason why the monitoring system was damaged by the lightning and the possible lightning invaded route, specially, the outdoor monotoring equipment suffer from serious damage of lightning. only analysis on basis of the reason of damage, research and discussion on the laying, shield and earthing mode of signal and power line, the lightning protection device of monitoring system device can be selected and used accurately.

The TV monitoring systemis consisting of three parts as below:

1,The former part: composed of monochrome (colour television) vidicon, len, holder, hood , bracket, etc

2, transmission part:coaxial-cable,wire,Multi-core wire,fibre,which transmiss video,audio or control signal by way of overhead in air,burial under ground or wall following laying.

3, computer roomterminal part: composed of matrix, monitoring device, hard disk video recorder,etc.