Hipot Tester or ‘Hi- Potential’ test/ dielectric strength test are essential electrical safety testing instruments that are used to verify that the electrical insulation of a product in an electric circuit is adequate to withstand high voltage without breaking down; HIPOT is therefore an essential tool for predictive maintenance of existing electrical utility and equipment assets.
Portable high-voltage test system (HIPOTs) are designed for high-voltage testing of solid dielectrics with low and medium electric capacitance (power cables, switchgear, surge arresters, busbars, insulators, etc.) with DC (rectified*) voltage and high-voltage testing of other objects with AC voltage at industrial frequency (f = 50 Hz).
During the testing stage, voltage of a set magnitude is applied to the Object under test (OuT) connected between the HVU transformer output and the grounding of the System for a predetermined period of time. If the OuT survives without a breakdown, the test is considered to have passed. The leakage current measured directly on the OuT determines whether dielectric breakdown has occurred. Reaching the current limit defined by the selected test parameters’ pre-set is interpreted by the System as a breakdown.
Hipots are Generally used in electrical circuits to:
- find cuts/nicks/ crushes in cable insulation, stray wire strands/ braided shielding
- conductive or corrosive contaminants around the conductors
- Terminal spacing problems as well as tolerance errors in cables
- Inadequate creepage/ clearance distance- pointing at manufacturing defects
Depending on how the DUT (device under test) is powered- selection can be made whether AC or DC Hipot test is to be conducted.
In a DC Hipot test, the voltage is applied in gradual steps, referred to as ramping, pausing after each increase to allow the capacitance of the DUT to absorb a charge and stabilize. If the leakage current suddenly starts to increase over the expected value, an insulation breakdown is likely to occur soon.
In an AC High Voltage test, this ramping time is relatively reduced. AC Hipot testing also has the advantages of checking both polarities of voltage and of not needing to discharge the DUT after testing is complete – which is required in a DC Hipot testing.
Stanlay offers different variants of Hipot testers- including:
Manual Hipot tester HVT 70/50 with DC voltage up to 70 kV and ACV 50kVrms.
Automatic Hipot testers are available in the following variants:
HVTS 70/50, with DC Voltage up to 70kV and AC Voltage up to 50kVrms.
HVTS HP-100kV with DC and AC Voltage up to 100kV and 100kVrms.
and HVTS HP-140kV (with DC voltage up to 140 kV)
All of the above automatic variants can be operated in manual test mode as well. These Hipot testers are AC/DC high voltage testers and have the highest safety standards such as over-voltage tripping, over-current tripping, automatic grounding bar, thermal overload warning & low-pressure warning.
The benefit of using an Automatic AC/DC Hipot for dielectric strength test is that they allow setting voltage and current limits and regulating voltage ramp rate. In AUTO control mode there is a shortcut to further limit the test voltage within the boundaries of the selected pre-set. Ramp up can be set in range 0.5 … 4.0 kV/s, step 0.5 kV/s- thereby finding accurate voltage of breakdown, thereby making it a much precise & accurate high voltage test instrument. The High potential test/ Hipot Test is, much more than a pass/fail test- as it is a versatile test that can find several faults within electric and manufacturing field.
* The System performs half-wave voltage rectification on the output. When connected to a capacitive load, the voltage on the output closely resembles direct. Thus, in this document direct voltage stands for half-wave rectified voltage (in the case of an idle run).
