Megger DELTA 4000, Справочное руководство

Страница: 6 / 48

6 DELTA 4000 ZM-AH02E
1 INTRODUCTION
1
I
ntroduction
Principle of operation
Most physical test objects can be accurately represented as
a two or three-terminal network. An example of a two-
terminal capacitor is an apparatus bushing without any test
tap. The center conductor is one terminal and the mount-
ing flange (ground) is the second terminal. An example of
a three-terminal capacitor is an apparatus bushing which
has a power factor or capacitance tap. The center conduc-
tor is one terminal, the tap is the second terminal, and the
mounting flange (ground) is the third terminal.
It is possible to have a complex insulation system that
has four or more terminals. A direct measurement of any
capacitance component in a complex system can be made
with this test set since it has the capability for measuring
both ungrounded and grounded specimens.
Figure 1 shows a simplified measuring circuit diagram of
the DELTA 4000 test set measuring a two-winding trans-
former
in UST test mode. The test voltage is connected to the HV
terminal and the current is measured at the LV terminal.
Voltage and current are accurately measured in amplitude
and phase and CHL capacitance, dissipation factor, power
loss etc are calculated and displayed.
Figure 1: UST-R test setup for a 2-w transformer
Dissipation factor measurements can generally be per-
formed with two different configurations, UST (Unground -
ed Specimen Test) where the ground act as natural guard
or GST (Grounded Specimen Test) with or without guard.
Figure 2 shows a guarded UST measurement. The current
flowing through CHL is measured but the current paths
through CH and CL is guarded/grounded and not mea-
sured. Figure 3 shows a guarded GST measurement where
the CH current to ground is measured but the current
through CHL is guarded and measured.
General
The intention of this reference-application manual is to
guide the operator in the appropriate method of making
capacitance and dissipation factor/power factor measure-
ments on power apparatus and to assist in the interpretation
of test results obtained. It is not a complete step-by-step
procedure for performing tests.
Before performing any test with this apparatus, read the
user manual and observe all safety precautions indicated.