Theory of Operation:
1. The principle used in measuring the
earth resistance is based on simple ohm’s law.
2. Four electrodes
A,B,C & D are buried in the earth, the resistance of which is to be tested
at a distance of 20 meter from each other as shown in fig 1.
3.
AC Signal is applied to electrodes A and D and voltage developed across
electrodes B and C due to flow of current through the earth is measured by
ammeter.
4.
If the current is constant, the voltage measured will be directly
proportional to the earth resistance.
Steps to measure earth resistance as
per Digital Earth Resistance Tester Manual:
1. Take work permit and Isolate the
equipment. The Earth electrode C1, whose resistance to be measured must be
disconnected from its connection to the site.
2. To obtain a correct measurement, the
three electrodes must be in straight line and the well aligned.
3. The Auxiliary current electrode C2
is placed at the distance D, it is approximately 30Mtrs from Earth Electrode C1.
4. The potential probe (Reference Probe
P2) is placed in the soil in a straight line-away from the earth electrode
Normally, Spacing of 20Mtr.
5. Now short the C1, P1 terminal of
earth tester and connect that point to earth electrode, P2 to potential probe (Reference
Probe) and the last point C2 is connected to Current Electrode or Auxiliary
electrode. Connect the earth tester as shown in the Fig – 2. Press start and
read out the RE (resistance) value.
6. This is the actual value of the
ground electrode under test.
No comments:
Post a Comment