Megger DET2/2 Guia Del Usuario página 19

Ocultar thumbs Ver también para DET2/2:
Tabla de contenido

Publicidad

This is the 61,8% Rule and strictly applies only when
the earth electrode and Current and Potential spikes lie
in a straight line, when the soil is homogeneous and
when the earth electrode has a small resistance area
that can be approximated by a hemisphere. Bearing
these limitations in mind this method can be used, with
care, on small earth electrode systems consisting of a
single rod or plate etc. and on medium systems with
several rods.
61,8% of EC
Electrode
under test
Connections for the 61,8% Rule.
For most purposes the Current spike should be 30
metres to 50 metres from the centre of the earth
electrode under test. The Potential spike should be
inserted in the ground 61,8% of this distance, between
and in a straight line with, the Current spike and the
earth electrode. The distance is measured from the
earth electrode. If the earth electrode system is of
38,2% of EC
Potential
Current
spike
spike
medium size containing several rods, then these
distances must be increased. The following table gives
a range of distances that agree with the rule. In the first
column 'Maximum dimension' is the maximum
distance across the earth electrode system to be
measured.
Maximum
Distance to Potential
spike in metres from
dimension
centre of earth
in metres
system
5
62
10
93
20
124
For greater accuracy an average reading can be
calculated by moving the current spike, say 10 metres,
towards and then away from its first position and
making further resistance measurements. (Remember
that the Potential spike must also be moved in
accordance with the 61,8% Rule). The average of the
three readings can then be calculated.
Distance to Current
spike in metres from
centre of earth
system
100
150
200
19

Hide quick links:

Publicidad

Tabla de contenido
loading

Tabla de contenido