High Voltage Insulation / Continuity / Earth
Glossary - HV Insulation Diagnostics PI - Polarization Index
As a voltage is applied to an insulating material, the particles inside the mate- rials line up and become polarized. The more atoms that become polarizes, the resistance of the material increases. In an insulating material, the quicker the particles polarize, the better the insulat- ing material is. PI is defined in the IEEE Std 43-2000 as the ratio between two insulation resistances readings, during the test, the first is taken after 1 minute and the second is taken after 10 minutes of continuous insulation measurement.
DAR - Dielectric Absorption Ratio The principle behind an insulating mate- rial is to keep two conductive materials separated. If an insulating material be- comes contaminated (e.g. through dirt, grease, etc.) leakage current can be ab- sorbed by the insulating material. This leakage current reduces the resistance of the material which results in less power can be delivered to the load. DAR is defined as the ratio between two in- sulation resistances measured after 30 seconds and after 60 seconds (1 min) of continuous insulation measurement.
IR - Insulation Resistance of Insulator According to IEV 151-15-43 IR is the re- sistance under specified conditions be- tween two conductive elements, sepa- rated by insulating materials.
DD - Dielectric Discharge
After the power is turned off to a high voltage appliance, the built-up charge needs time to dissipate away before the appliance is safe. Typically the insu- lation material is left connected to the test voltage for 10 ... 30 min and then discharged before DD test is carried out. After 1 minute, the capacitance, voltage and discharge current is measured and the DD can be calculated.
Step voltage
Step voltage test involves insulation re- sistance measurement at different test voltages. Good insulation will show very
little deviation between particular read- ings. In case of microcracks, dirt or hu- midity in insulation system the insulation resistance decreases with rising test voltage. When performing a step volt- age test, it is important to start with the lowest test voltage and then move to a higher voltage level. Typical test duration is 60 seconds.
Withstanding voltage test
This function offers withstanding volt- age test of insulation material. It covers two types of tests:
a) Breakdown voltage test of high volt- age devices, e.g. transient suppressors; b) DC withstanding voltage test for insu- lation coordination purposes. Both functions require breakdown cur- rent detection. The test voltage increas- es step by step from the Start up to the Stop value over a predefined time and it is kept at the Stop value for a predefined test time.
Guard terminal
The purpose of the GUARD terminal is to lead away potential leakage currents (e.g. surface currents), which are not a result of the measured insulation mate- rial itself but of the surface contamina- tion and moisture. Guard terminal is to be used in conjunction with shielded test leads when measuring insulation re- sistances in GΩ and TΩ range.
R(t) graphs
Sometimes a simple value does not show the full picture about the quality of an insulating material. R(t) graphs illus- trate how resistance (on the Y or vertical axis) changes in relation to time (on the X or horizontal axis).
Leakage
Leakage current is an AC or DC current that flows trough or on the insulation’s surface.
Part No.
MEASUREMENTS Test voltage range Voltage steps
Insulation resistance measuring range Calculation of DD, DAR, PI Withstanding voltage test Voltage ramp test
Leakage current measurement Capacitance measurement Short circuit / charge current Voltage measurement AC / DC OTHER FEATURES Programmable timer
Automatic discharge after test Graph R(t) Bar graph
Auto adjustment function Auto ranging Audible warnings Guard terminal Shielded test leads COMMUNICATION PORTS USB
RS232 MEMORY, SOFTWARE Memory
Number of memory locations Software
GENERAL DATA Display type Backlight
Safety category
Rechargeable batteries Built-in battery charger Low battery indication Battery life (no load connected) Weight
Dimensions (mm)
2. 2
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