12/3/2009 | 71-022 V6
D30R
39
6
Principles and theory of Surge
testing
Principles of Surge testing
Surge testing is performed to detect insulation damage between turns within a motor’s
winding. This type of insulation problem cannot be found any other way than by surge testing.
The surge test consists of applying a short, fast rise time, high current impulse to a winding.
This high rise time impulse will induce, via Lenz’s Law, a voltage difference between adjacent
loops of wire within the winding. If the insulation between the two loops of wire is damaged
or somehow weakened, and if the voltage difference between the wires is high enough there
will be an arc between the wires. The arc is detected by observing a shift in the surge
waveform.
The Surge test is performed with an impulse generator and an oscilloscope type display to
observe the “surge waveform” in progress. The surge waveform is a representation of the
voltage present across the test leads of the Baker tester during a test. The indication of a
turn-to-turn fault is a shift to the left, and/or a decrease in amplitude of the surge test
waveform as the test voltage is increased.
Surge testing theory
As mentioned above very short high current pulses are applied to the coil during a Surge test
to create a voltage gradient (or potential) across the length of the wire in the winding. This
gradient produces a momentary voltage stress between turns.
The coil will respond to the surge pulse with a ringing or damped sinusoidal waveform
pattern. Each coil has its own unique signature ringing or wave pattern, which can be
displayed on a CRT display screen as shown below.
The wave pattern observed during a Surge Test is directly related to the coil’s inductance.
(There are other factors influencing the wave pattern but inductance is the primary one.) The
coil becomes one of two elements in what is known as a tank circuit – a
LC-type
circuit made
up of the coil’s inductance
(L)
and the surge tester’s internal capacitance
(C).
Inductance (L)
of a coil is basically set by the number of turns in a winding and the type of
iron core it rests in. The frequency of the wave pattern is determined by the formula:
LC
Frequency
π
2
1
=
Summary of Contents for D30R
Page 6: ...Table of Contents 12 3 2009 71 022 V6 D30R 6...
Page 12: ...Safety precautions CE compliance 12 3 2009 71 022 V6 D30R 12...
Page 24: ...Coil Resistance Testing 12 3 2009 71 022 V6 D30R 24...
Page 28: ...Principles of High Voltage DC Testing 12 3 2009 71 022 V6 D30R 28...
Page 38: ...High Voltage DC Testing 12 3 2009 71 022 V6 D30R 38...
Page 50: ...Surge Testing 12 3 2009 71 022 V6 D30R 50...
Page 70: ...Data Recording Retrieving 12 3 2009 71 022 V6 D30R 70...