Insulation condition is the key factor of operational safety and correct operation of electrical devices and systems, and in addition, it is a protection against direct contact. Systematic examination of insulation condition is necessary in order to detect any deterioration of insulation and is a permanent element of inspection and measurement works. In the case of measurements of industrial equipment, the tendency of resistance value changes is of key importance, because it can indicate gradual deterioration of insulation condition. Basic elements influencing deterioration of insulation are: electrical and mechanical exposures, chemical aggression, thermal exposures and environmental pollution; as a result of their influence during normal operation of electrical equipment, its insulation is subjected to ageing. Insulation resistance measurements are performed with direct current in order to eliminate the influence of capacitance.
The method for performing insulation resistance measurements and the required measurement voltages are defined in the standards: HD 60364-6, E-04700, EN 61557-2. After applying measurement voltage, physical phenomena occur in insulation, causing the flow of current. During resistance measurement, the following components of the current flowing through insulation (1) can be distinguished:
The capacitance charging current (2) – depending on the capacitance (e.g. the length of measured cable), the absorption current (3) – resulting from charge and dipole movement in the electric field, the insulation leakage current (4) – the sum of currents flowing through and on the surface of the material.
Due to the nature of current flowing through insulation, the measured value is influenced by the time of measurement, as well as humidity, temperature, measurement voltage and Cleanness of the insulation material surface.
The three-lead method, used in all advanced instruments, allows for eliminating the influence of the surface leakage current. In the case of cables, the core insulation must be wrapped in a metal foil connected to the shield terminal of the instrument – only the leakage current flowing through insulation is measured. Measurement with the three-lead method is recommended for large surfaces exposed to pollution (large diameter cables, transformers, HV switches):
- MIC10K1 – Insulation resistance meter which has a high Noise immunity to work in 765KV substation
- Newly launched model with the special feature of having the capacity to work even in high induction substation namely 765KV.
- High test current upto 6mA makes the test procedure easy to get the better result.
Resistance measurement upto 40 T?.
- Large LCD graphic display 5.6-inch
- Test Voltage range – 50V to 10KV (50 to 1000V with 10 steps, 1KV to 10KV with 25V steps)
- Adjustable measuring time from 0.01-inch to 99.59-inch
- Real time on screen graph printing during resistance measurement.
- Automatic measurement of multiple core cables with the use of the additional Auto ISO-5000 adaptor.
- Ability to work with wireless Bluetooth keyboard.
- Digital filter function for measurements in high noise environment (10s, 30s, 60s).
Sonel Instruments India Pvt Ltd
1B, Block IV, Natwest Vijay,
Velachery Main road,
Pallikaranai, Chennai – 600 100