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Hi-Po t te st is a co ntractio n fo r hig h p o te ntial HV te sting .

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What is HIPOT Testing (Dielectric Strength Test)?

Hipot Test is short name of high potential (highvoltage) Test and it is also known as DielectricWithstand Test . A hipot test checks f or goodisolation.

Hipot test makes surety of no current will f low f romone point to another point.

Hipot test is the opposite of a continuity test.

Continuity Test checks surety of current f lows easilyf rom one point to another point while Hipot Testchecks surety of current would not f low f rom onepoint to another point (and turn up the voltage reallyhigh just to make sure no current will f low).

Importance of HIPOT TestingThe hipot test is a nondestructive test that determines the adequacy of electrical insulation f or thenormally occurring over voltage transient. This is a high-voltage test that is applied to all devices f or aspecif ic t ime in order to ensure that the insulation is not marginal.

Hipot tests are helpf ul in f inding nicked or crushed insulation, stray wire strands or braided shielding,conductive or corrosive contaminants around the conductors, terminal spacing problems, and toleranceerrors in cables. Inadequate creepage and clearance distances introduced during the manuf acturingprocess.

The production- line hipot test, however, is a test of the manuf acturing process to determine whether theconstruction of a production unit is about the same as the construction of the unit that was subjected totype testing. Some of the process f ailures that can be detected by a production- line hipot test include, f orexample, a transf ormer wound in such a way that creepage and clearance have been reduced.

Such a f ailure could result f rom a new operator in the winding department.

HIPOT test is applied af ter tests such as f ault condition, humidity, and vibration to determine whether anydegradation has taken place.

Other examples include identif ying a pinhole def ect in insulation or f inding an enlarged solder f ootprint.As per IEC 60950, The Basic test Voltage f or Hipot test is the 2X (Operating Voltage) + 1000 VThe reason f or using 1000 V as part of the basic f ormula is that the insulation in any product can besubjected to normal day-to-day transient over voltages.

Experiments and research have shown that these over voltages can be as high as 1000 V.

Video: HIPOT Test After Repair Generator

Test method for HIPOT TestHipot testers usually connect one side of the supply to safety ground (Earth ground). The other side ofthe supply is connected to the conductor being tested. With the supply connected like this there are twoplaces a given conductor can be connected: high voltage or ground.

When you have more than two contacts to be hipot tested you connect one contact to high voltage andconnect all other contacts to ground. Testing a contact in this f ashion makes sure it is isolated f rom allother contacts.

If the insulation between the two is adequate, then the application of a large voltage dif f erence betweenthe two conductors separated by the insulator would result in the f low of a very small current. Although thissmall current is acceptable, no breakdown of either the air insulation or the solid insulation should takeplace. Theref ore, the current of interest is the current that is the result of a partial discharge or breakdown,rather than the current due to capacitive coupling.

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Time Durat ion for HIPOT TestThe test duration must be in accordance with the saf ety standard being used. The test t ime f or moststandards, including products covered under IEC 60950, is 1 minute.

A typical rule of thumb is 110 to 120% of 2U + 1000 V f or 12 seconds.

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Current Sett ing for HIPOT TestMost modern hipot testers allow the user to set the current limit. However, if the actual leakage current ofthe product is known, then the hipot test current can be predicted.

The best way to identif y the trip level is to test some product samples and establish an average hipotcurrent. Once this has been achieved, then the leakage current trip level should be set to a slightly highervalue than the average f igure.

Another method of establishing the current trip level would be to use the f ollowing mathematical f ormula: E(Hipot) / E(Leakage) = I(Hipot) / 2XI(Leakage)

The hipot tester current trip level should be set high enough to avoid nuisance f ailure related to leakagecurrent and, at the same time, low enough not to overlook a true breakdown in insulation.

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Test Voltage for HIPOT TestThe majority of saf ety standards allow the use of either ac or dc voltage f or a hipot test.

When using ac test voltage, the insulation in question is being stressed most when the voltage is at itspeak, i.e., either at the posit ive or negative peak of the sine wave.

Theref ore, if we use dc test voltage, we ensure that the dc test voltage is under root 2 (or 1.414) t imesthe ac test voltage, so the value of the dc voltage is equal to the ac voltage peaks.

For example, f or a 1500-V-ac voltage, the equivalent dc voltage to produce the same amount of stress onthe insulation would be 1500 x 1.414 or 2121 V dc.

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Advantages and Disadvantages of use DC Voltage for Hipot TestOne of the advantages of using a dc test voltage is that the leakage current trip can be set to a much lowervalue than that of an ac test voltage. This would allow a manuf acturer to f ilter those products that havemarginal insulation, which would have been passed by an ac tester.

When using a dc hipot tester, the capacitors in the circuit could be highly charged and, theref ore, a saf e-discharge device or setup is needed. However, it is a good practice to always ensure that a product isdischarged, regardless of the test voltage or its nature, bef ore it is handled.

It applies the voltage gradually. By monitoring the current f low as voltages increase, an operator can detecta potential insulation breakdown bef ore it occurs. A minor disadvantage of the dc hipot tester is thatbecause dc test voltages are more dif f icult to generate, the cost of a dc tester may be slightly higher thanthat of an ac tester.

The main advantage of the dc test is DC Voltage does not produce harmf ul discharge as readily occur inAC.

It can be applied at higher levels without risk or injuring good insulation. This higher potential can literallysweep-out f ar more local def ects.

The simple series circuit path of a local def ect is more easily carbonized or reduced in resistance by the dcleakage current than by ac, and the lower the f ault path resistance becomes, the more the leakage currentincreased, thus producing a snow balling ef f ect which leads to the small visible dielectric puncture usuallyobserved. Since the dc is f ree of capacitive division, it is more ef f ective in picking out mechanical damageas well as inclusions or areas in the dielectric which have lower resistance.

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Advantages and Disadvantages of use AC Voltage for Hipot TestOne of the advantages of an ac hipot test is that it can check both voltage polarit ies, whereas a dc testcharges the insulation in only one polarity. This may become a concern f or products that actually use acvoltage f or their normal operation. The test setup and procedures are identical f or both ac and dc hipottests.

A minor disadvantage of the ac hipot tester is that if the circuit under test has large values of Y capacitors,then, depending on the current trip setting of the hipot tester, the ac tester could indicate a f ailure. Mostsaf ety standards allow the user to disconnect the Y capacitors prior to testing or, alternatively, to use a dchipot tester.

The dc hipot tester would not indicate the f ailure of a unit even with high Y capacitors because the Ycapacitors see the voltage but dont pass any current.

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Step for HIPOT Test ingOnly electrically qualif ied workers may perf orm this testing.Open circuit breakers or switches to isolate the circuit or Cable that will be hi-pot tested.Conf irm that all equipment or Cable that is not to be tested is isolated f rom the circuit under test.The limited approach boundary f or this hi-pot procedure at 1000 volts is 5 ft . (1.53m) so placebarriers around the terminations of cables and equipment under test to prevent unqualif ied persons

f rom crossing this boundary.Connect the ground lead of the HIPOT Tester to a suitable building ground or grounding electrodeconductor. Attach the high voltage lead to one of the isolated circuit phase conductors.Switch on the HIPOT Tester. Set the meter to 1000 Volts or pre decide DC Voltage. Push the Testbutton on the meter and af ter one minute observe the resistance reading. Record the reading f orref erence.At the end of the one minute test, switch the HIPOT Tester f rom the high potential test mode to thevoltage measuring mode to conf irm that the circuit phase conductor and voltage of HIPOT Tester arenow reading zero volts.Repeat this test procedure f or all circuit phase conductors testing each phase to ground and eachphase to each phase.When testing is completed disconnect the HIPOT Tester f rom the circuits under test and conf irm thatthe circuits are clear to be re-connected and re-energized.To PASS the unit or Cable under Test must be exposed to a minimum Stress of pre decide Voltagef or 1 minute without any Indication of Breakdown. For Equipments with total area less than 0.1 m2,the insulation resistance shall not be less than 400 M. For Equipment with total area larger than 0.1m2 the measured insulation resistance times the area of the module shall not be less than 40Mm2.

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Safety precautions during HIPOT TestDuring a HIPOT Test, There may be at some risk so to minimize risk of injury f rom electrical shock makesure HIPOT equipment f ollows these guidelines:

1. The total charge you can receive in a shock should not exceed 45 uC.2. The total hipot energy should not exceed 350 mJ.3. The total current should not exceed 5 mA peak (3.5 mA rms)4. The f ault current should not stay on longer than 10 mS.5. If the tester doesnt meet these requirements then make sure it has a saf ety interlock system that

guarantees you cannot contact the cable while it is being hipot tested.

For Cable:

1. Verify the correct operation of the safety circuits in the equipment every time you calibrate it.2. Dont touch the cable during hipot testing.3. Allow the hipot testing to complete bef ore removing the cable.4. Wear insulating gloves.5. Dont allow children to use the equipment.6. If you have any electronic implants then dont use the equipment.

What is HIPOT Testing (Dielectric Strength Test)?Importance of HIPOT TestingVideo: HIPOT Test After Repair GeneratorTest method for HIPOT TestTime Duration for HIPOT TestCurrent Setting for HIPOT TestTest Voltage for HIPOT TestAdvantages and Disadvantages of use DC Voltage for Hipot TestAdvantages and Disadvantages of use AC Voltage for Hipot TestStep for HIPOT TestingSafety precautions during HIPOT Test