IEC 60052:2002 pdf download

IEC 60052:2002 pdf download.Voltage measurement by means of
standard air gaps.
The spheres shall be carefully made so that their surfaces are smooth and their curvature is as uniform as possible.
The tolerances on size and shape need usually only be checked when the spheres are first supplied and any suitable Instrument (e.g. spheron,eter) may be used.
The diameter of each sphere shell not differ by more than 2 % from the nominal value The spheres shall be reasonably free from surface irregularities in the region of the sparking point A medium grade mechanical surface finishing (roughness R below 10 m) is considered to be adequate. The region of the sparking point is defined by a circle such as would be drawn on the spheres by a pair of dividers set to an opening of 0,3 1) and centred in the sparking point.
When the sphere-gap Is used, it will normally be sufficient to examine the surface by touch and visual inspection.
NOTE Any minor damage on the non-adjacent henisphenai surfaces does not alter the sphere-gap performance
4.2 General arrangement of a sphere-gap for measurement
4.2.1 Vertical gap
When the spheres are arranged vertically, the shank of the high-voltage sphere shall be free from sharp edges or corners and the diameter of the shank shall not exceed 0.2 L) over a length 0. This requirement is made in order to reduce the influence of the high-voltage shank on the disruptive discharge voltage. If a stress distributor (corona shield) is used at the end of the shank, its greatest dimension, perpendicular to the axis of the spheres, shall not exceed 0,5 0 and shall be at least 2 1) from the sparking point of the high-voltage sphere.
The earthed shank and the operating gear have a smaller effect and their dimensions are therefore less Important.
Figure 1 gives the limits of size of the components of a typical vertical sphere-gap The sphere shanks should be visually in line.
4.2.2 Horizontal gap
When the spheres are arranged horizontally, the limiting dimensions of a typical sphere-gap are given in figure 2, They are the same for both sides of the gap.
The sphere shanks should be visually in line.
4.2.3 Height of the spheres above the horizontal earth plane
The height A of the sparking point of the high-voltage sphere above the earth plane of the laboratory floor shall be within the limits given in table 1.
If the sphere-gap is mounted with the earthed sphere nearest to the ceiling, and if other surfaces such as walls and the floor are at a considerably greater distance, then the ceiling shall be regarded as the horizontal plane, from which the distance . is measured downwards.
4.3.2 HIgh-voltage conductor
The high-voltage conductor, including any series resistor not in the shank itself, shall be connected to a point on the shank at least 2 1) away from the sparking point of the high-voltage sphere.
Within the region where the distance to the sparking point of the high-voltage sphere is less than H, the high-voltage conductor (including the series resistor, if any) must not pass through the plane normal to the axis of the sphere-gap and situated at a distance 2 D from the sparking point of the high-voltage sphere. See figures 1 and 2 where the plane is shown.
4.3.3 Prot.ctiv. resIstor for measurement of alternating and direct voltages
Precautions should be taken to minimize pitting of the spheres and to prevent superimposed oscillations, which may cause erratic disruptive discharges. For this purpose, a resistance of 0.1 to I Mfl shall be connected In series with the sphere-gap. This range of resistance values applies to measurements of direct voltages and of alternating voltages at power frequencies, because the values of the resistance results in a negligible voltage drop.
The protective resistor should be placed as near as possible to the shank of the sphere and connected directly to it.
When streamer discharges are present in the test circuit, series resistance is particularty important in order to reduce the effect of the consequent transient over-voltage on the operation of the sphere-gap When these discharges are not present either in the test circuit or in the test specimen, the value of resistance may be reduced to a value which prevents excessive burning of the spheres by disruptive discharges.
4.3.4 Protective series resistor for measurement of impulse voltages
Series resistance is needed with large diameter spheres to eliminate oscillations In the sphere- gap circuit which may cause a higher voltage to occur between the spheres and, If connected, across the test object. This phenomenon is usually of minor importance for smaller spheres. unless they are used with long connecting leads. Series resistance may also be needed to reduce the steepness of the voltage collapse which might introduce undesirable stresses in the test object.