Line Traps for A.C. Power Systems
|Publication Date:||1 April 2002|
|ICS Code (Telecontrol. Telemetering):||33.200|
|ICS Code (Power transmission and distribution lines):||29.240.20|
Line traps may be designed with or without a tuning device. A critical condition for the application of line traps designed with a tuning device is the high reliability of the tuning device when exposed to dielectric stresses due to lightning strokes, circuit breaker operations and disconnector switching operations.
The basis of the requirements for the dielectric strength of the tuning device is the protective level of the line trap's surge arrester. The voltage withstand levels of the tuning device's capacitor units shall be coordinated, on a worst case basis, for either single unipolar voltage impulses (related to lightning strokes) or repetitive bipolar voltage impulses (related to disconnector switching operations) with the arrester's protective level.
The protective level is defined for the selected metal-oxide (MO) arrester by the residual voltage UP1 based on an arrester surge current of 20 kA peak and a waveshape of 8/20 μs.
In this annex, the dielectric requirements for the tuning device are based only on gapless MO arresters, which provide a protective level with negligible dependency on the surge waveshape.
For line traps with tuning devices protected by surge arresters with series gaps the time delay of the breakdown voltage of the spark gaps shall be taken into consideration.
NOTE The time delay of the breakdown voltage of surge arresters with series gaps is a function of the front-ofwave rate of rise of the impulse voltage. Thus, the protective level for the system is determined by the breakdown voltage of the spark gaps.
This annex refers in total to four tuning circuits which are predominantly in use.
These circuits are:
• single frequency tuning, figure C.1,
• double frequency tuning, figure C.2,
• damped single frequency tuning, figure C.3 and
• wide band tuning, figure C.4.
The inductor and resistor components of a tuning device are usually protected by an auxiliary spark gap and voltage endurance is therefore not an issue.
This annex only covers the voltage endurance qualification of tuning device capacitor elements. This is a component qualification test only and is not a tuning device type test