Megger ADX15, User Manual

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Megger Baker ADX User Guide
49
Test Configuration
Ramp HiPot
— Applies a DC voltage at a slower linear ramping rate to the machine’s windings. As the test runs,
the software monitors the charging current. This higher current is sustained longer due to the slower ramp rate. If it
remains linear with the voltage, the winding is in good condition. This test provides a linear assessment of charging
current and is faster than step test.
HiPot Step Test —A succession of equally-divided voltage levels are applied to the asset to allow the tester to analyze
linearity of leakage current. Step test provides the linearity of leakage current with the most controlled approach of
test voltage. If step durations are different, the linearity assessment becomes invalid; the software cannot accurately calculate
delta T (time) if the times (step durations) are different.
Table 4: DC Tests; HiPot Test sub-section field descriptions.
Field/Control Description
HIpot Test Toggle switch Slide right = test enabled.
Hipot Ramp Rate A slider used to set the rate at which voltage will ramp to the defined level for HiPot tests.
The scale is 1–10 from left to right, with 1 being the slowest rate.
Hipot Voltage Level [V] Refer to “Appendix D — Recommended Test Voltages” to determine the proper voltage
level for your Asset.
Hipot Duration [s] Typical duration is 60 seconds. Applies to standard and ramp HiPot testing.
Step Duration [s] The duration of each step in a HiPot Step Test. Because a standard HiPot test duration
needs to be 60 seconds (default), and the point of step testing is to examine linearity, all
steps must also be 60 seconds.
Hipot Type Select the type of HiPot test you want to run by using the radio buttons.
Hipot Steps Voltage level of each step in a Step HiPot Test. Step tests should have at least four steps
above the IR test voltage. (HiPot Test Voltage - IR Test Voltage) / 4
(For example, 2000 - 500 = 1500 / 4 = 375 per step
Because the DC Test starts at the Asset operating voltage (IR Voltage Level; set at 500 in
this example) the first step in a Step HiPot test will ramp to the next target level for the
Asset (875 volts in this example).
Current Trip Level [µA] Current trip level trips by default at 1200 µA, but you can specify a lower threshold if you
want to provide a larger measure of protection for your assets.
Min Resistance [MΩ] The minimum resistance (in megohms).
Max Res Change [%] During ramping, voltage increases to a charging current value defined by several factors
including ramp rate and circuit capacitance.
When test voltage is reached and ramping reduces to zero, the current drops to a value
that represents the sum of polarization current, surface leakage current, and internal
leakage current.
Max Res Change % compares the summed leakage currents from step to step. If the
insulation system is weak, then as voltage increases near its breakdown point it will cause
resistance to decrease. The reduction in resistance results in an increase in current, and the
change will be seen.
Default is commonly around 50%.
If the Stop on Fail box is checked, the test will stop immediately; otherwise, the test will
complete and then flag the test as a failure.
Min DA/PI Ratio The PI test is typically performed on assets of 100 HP or greater. Per IEEE 43, the ratio
should be set 1.5 for NEMA class A insulation, and 2.0 for class B, F, and H insulation.
The DA test is performed on insulation systems that polarize very quickly—usually motors
< 100Hp.
These suggested ratios assume that you are testing clean dry insulation systems. In high
humidity environments, consider setting lower ratios even for class B, F, or H insulation
systems.