High Voltage PFT Series, Safety, Operation, And Procedure Instructions

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9
Using the Guarded Return
The use of the GUARD/GROUND return feature of this test set provides for very accurate leakage current
measurements if certain conditions exist allowing for the GUARD circuit to be employed. The following
explanation will detail different test samples and methods that lend themselves to the use of this circuit. The
same setup precautions such as proper grounding still apply to the test but the grounds will be manipulated to
accomplish the test requirements.
1.
Grounded Return- With the output return in the grounded mode, the current meter reads all
current to ground, internal and external to the test set. This current might include corona, surface
tracking, and any shunt resistance. The typical diagram for grounded return operation is shown
in Figure 2 below.
2.
Guarded Return- With the output return in the guarded mode, the current meter will only read
currents through the test sample. The test sample must be isolated from ground on the low side
as shown in Figure 3 below.
Figure 2, Grounded Return Diagram
Test
Sample
High
Voltage
From Test
Set
Current flow through
return includes all
current to ground
Meter
GUARD GROUND
RETURN
POST
GROUND
POST