72A-1230 Rev. F 1-1
July 22, 2005
1. Introduction
The M4000 Insulation Analyzer is used to determine the insulation quality of
high-voltage power apparatus in the field. This portable test set incorporates
automated Doble Testing with high accuracy and sensitivity, over a wide range
of values, and with minimal susceptibility to electrostatic interference and
noise.
Measurement Principles
The M4000 generates a 0-12 kV test signal with an internal sine wave
generator, a 3 kVA power amplifier and a step-up isolation transformer. The
M4000 then measures the voltage and current of the specimen and a reference
impedance by periodically sampling instantaneous values with an A/D
converter. The M4000 then calculates and reports test results by converting the
sampled data into vector (magnitude and phase) quantities and applying
conventional ac circuit theory. All reported results – including power loss,
power factor and capacitance – are derived from the vector voltage and
current.
The M4000 rejects interference through the judicious application of shielding,
line-synchronized reversal, and line frequency modulation (FM). The first two
techniques are similar to those employed in the earlier Doble M2H product
line. The FM technique involves running tests at sinusoidal frequencies 5% (or
even 10%, if necessary) above and below the line frequency and averaging the
results. The choice is user configurable.
The inevitable interference current component is removed from the sampled
data set before test results are calculated using synchronous detection. This is
a mathematical process that separates out a single frequency component in a
given signal. It is analogous to a bandpass filter centered at the test frequency.
Synchronous detection is also useful for removing harmonic distortion and
random noise in the test signal itself.
Safety
The M4000 is designed to drive grounded and ungrounded specimens at lethal
voltages and high power levels. Conventional ground-fault and current-
limiting schemes cannot be used to protect the operator under these test
conditions. Therefore, the M4000 implements special safety techniques to
minimize risk to the equipment operator.
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