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V. The Principle and Application of Detection
1. Testing Principle.
Built-in Non-Contact Grounding Resistance Online Detector’s
fundamental is measuring return circuit resistance. firstly Sensor
send out a drive pulse signal to be measured ground return circuit,
then measured ground return circuit responses a pulse electromotive
force E, under the influence of electromotive force E there will gen-
erate current I in the be measured ground return circuit. Sensor
measures E and I, and immediately gets resistance of be measured
ground return circuit through the formula: R=E/I.
2. Return Circuit Resistance Definition.
As picture: return circuit is a composite value includes A spot
grounding resistance, grounding down lead metallic conductor’s
resistance, metal overhead line’s resistance, connection re-
sistance(contact resistance)between grounding down lead and metal
overhead line, B spot grounding resistance. For the formative
above-mentioned return circuit’s grounding system, Detector can be
installed directly for monitoring, if the grounding system not form a
return circuit, it need adding auxiliary grounding electrode to form a
return circuit, further install the Detector, see the after-mentioned
single point grounding system. If the Detector measured out return
circuit’s composite value of grounding network A and grounding
network B is 5.0
Ω
, that is: R
A
+R
B
+R
C
+ R
D
=5.0
Ω
(R
C
and R
D
re-
spectively represent resistance of metal overhead line and grounding
down lead ), actual grounding resistance value of grounding network
A and grounding network B’s in parallel resistances less than or
equal to 2.5
Ω
, accordingly judge actual grounding resistance value
of grounding network A and grounding network B parallel connec-