METREL TeraOhm User Manual

TeraOhm 5kV
12
5. Measurements
5.1. Generally about DC High voltage testing
(FURTHER INFORMATION CAN BE FOUND IN METREL’S HANDBOOK
“INSULATION MEASURING TECHNIQUES”)
The purpose of insulation tests
Insulating materials are important parts of almost every electrical product. The material’s
properties depend not only on its compound characteristics but also on temperature,
pollution, moisture, ageing, electrical and mechanical stress, etc. Safety and operational
reliability require the regular maintenance and testing of the insulation material to ensure
it is kept in good operational condition. For testing the insulation materials high voltage
test methods are applied.
DC vs. AC testing voltage
Testing with DC voltage is widely accepted as being useful as well as AC and / or
pulsed. DC voltage can be used for breakdown tests especially where high capacitive
leakage currents interfere with measurements using AC or pulsed voltage. It is mostly
applied for measurement tests of the insulation resistance. The voltage in this type of
test is defined by the appropriate product application group. It is lower than the voltage
for the withstanding test so the tests can be applied more frequently without stressing
the tested material.
Typical insulation tests
In general, insulation resistance tests consist of the following possible procedures:
- Simple insulation resistance measurement also called spot test;
- Measurement of voltage dependence of the insulation resistance;
- Measurement of time dependence of the insulation resistance;
- Test of recovered charge after the dielectric discharge.
The results of this test can indicate whether the replacement of the insulation system is
needed.
Typical examples, where testing insulation resistance and its diagnosis are
recommended, are transformer and motor insulation systems, cables and other electrical
equipment.
Electrical representation of insulating material
The following figure represents the equivalent electrical circuit of insulating material
Riso
Cpi
Rpi
Ciso
Riss1
Riss2
material
surface
Itest
+
-
Guard
I
PI
I
Ci so
I
Ri so
I
Ri ss
Itest

METREL TeraOhm Specifications

General

Brand	METREL
Model	TeraOhm
Category	Test Equipment
Language	English