23
method refers to 6.2.1.2. if the laying path is narrow, the straight line method can be used,
otherwise, the angle method can be used. a) straight line method. Usually the current
pole C the straight line distance from the edge of the tower foundation dco take 3 D~4 if
the soil around the earthing device is more
Uniform, dcc can take 2 D. The linear
distance P the potential pole from the base edge of the tower dpoa 0.6 dca.
b) angle
method. Usually dco take 3 D~4 D,d slightly less than the dc,0 usually 30°D~45; if the soil
around the earthing device
The resistivity is uniform, dco can take 2 D, current line and
potential line 30 angle, dco=dko. 7.2.3 Notes
Attention to testing grounding impedance
of tower grounding device by three-pole method
∶
as follows
a) should avoid placing
the test potential and current poles on the radiation of the grounding device and should
not be extended with the radiation of the grounding device
The line is wired in the same
direction.
b) when it is found that the measured value of grounding impedance
increases or decreases significantly compared with the previous test results, the layout
direction of current pole and potential pole should be changed, or the distance of laying
line should be increased, and the test should be carried out again.
When c) test with the
three terminal grounding resistance tester shown in figure 7, the C2 and P2 of the
grounding terminal should be shortened as far as possible
length of lead between
devices.
7.3 Backward impedance
7.3.1 Conditions of application
Circuit impedance method applies to
∶
following conditions
a) there is no electrical connection between the tower and its earthing device.
b) there is a parallel circuit of multi-base tower in the distance, that is, the lightning
protection line of the transmission line is well connected with the tower at this level, and it
has been connected with the multi-stage tower in the distance all the time
The tower and its grounding device are well connected. For the number of parallel towers
on lightning lines requiring direct grounding in the line section of the test tower, see Table
1 in the DL/T887—2004.
Summary of Contents for HZDW-DB
Page 27: ...25...
