A Hipot test (also called a Dielectric Withstand test) verifies that the insulation of a product or component is sufficient to protect the operator from electrical shock. In a typical Hipot test, high voltage is applied between a product’s current-carrying conductors and its metallic chassis. The resulting current that flows through the insulation, known as leakage current, is monitored by the tester. The theory behind the test is that if a deliberate over-application of test voltage does not cause the insulation to break down, the product will be safe to use under normal operating conditions — hence the name, Dielectic Withstand test.

Dielectric breakdown Test
The test voltage is increased until the dielectric fails, or breaks down, allowing too much current to flow. The dielectric is often destroyed by this test so this test is used on a random sample basis. This test allows designers to estimate the breakdown voltage of a product’s design.

Dielectric Withstand Test
A standard test voltage is applied (below the established Breakdown Voltage) and the resulting leakage current is monitored. The leakage current must be below a preset limit or the test is considered to have failed. This test is non-destructive and is usually required by safety agencies to be performed as a 100% production line test on all products before they leave the factory.

Insulation Resistance Test
This test is used to provide a quantifiable resistance value for all of a product’s insulation. The test voltage is applied in the same fashion as a standard Hipot test, but is specified to be Direct Current (DC). The voltage and measured current value are used to calculate the resistance of the insulation.

Ground Bond Test
A high current (usually 25-30A AC) is applied to the product under test to verify that all conductive parts of said product (exposed to the user) are connected to power line ground.

The most important specifications to consider when searching for hipot testers include AC and DC output voltage, AC and DC output current, resistance range, insulation limit, and test time. Output voltage can either be AC or DC. The type of test will determine what level of voltage will be supplied. For example: in hipot testing the output voltage is usually very high. Output current can either be AC or DC. The type of test will determine what level of current will be supplied. For example: in hipot testing the output current is usually very low. Testers can also measure the resistance range. The insulation limit specification determines the voltage range the insulator can withstand. Many tests performed for electrical safety have a test time requirement. This is the overall time of the test.

The testing method for hipot testers can be automatic, semi-automatic, and manual. Some test instruments are fully automated to store and perform testing from a program. They may also have the ability to perform a series of electrical safety tests. Semi-automatic is a combination of automatic and manual testing capability. Manual testing requires that an operator be present to make physical changes to the test parameters.

Displays and interfaces are also important to consider when searching for hipot testers. Display choices include analog meters, digital meters, and LED indicators. Interfaces include GPIB, RS232, printer ports, scanner ports, and printouts. Safety agency ratings that can be applied to hipot testers include CE conformity marks, CSA, IEC, IPC, TÜV Rhineland (US, C, US & C), UL listing, and VDE. Common features for hipot testers include built-in calibration, buzzer or annunciator, front panel lockout, memory or storage, multiple test setup, PLC interface, rapid cutoff, remote control, selectable output frequency, and warning indicator lights.

What makes an Operator Qualified?

NFPA 70E defines qualified persons in the following manner:

“A qualified person shall be trained and knowledgeable of the construction and operation of equipment or a specific work method, and be trained to recognize and avoid the electrical hazards that might be present with respect to that equipment or work method. Such persons shall also be familiar with the proper use of special precautionary techniques, personal protective equipment, insulating and shielding materials, and insulating tools and test
equipment.”

It is the employer’s responsibility to provide safety related work practices, maintain a safe working environment and train the employees implementing those practices. One way an employer can help ensure a safe working environment is by using electrical safety testers with safety agency listings. Recognizing this, OSHA requires that electrical instruments used in the workplace be listed by a Nationally Recognized Testing Laboratory (NRTL). There are a total of 18 NRTLs recognized by OSHA. To ensure that the hipot testing being performed is safe, and to comply with OSHA requirements, it is best to use a safety tester that is listed by one of these recognized testing labs.
The degree of training required for the operators performing the product safety test is highly dependent upon the set up of the
product safety testing workstation. Whenever possible, the workstation should be constructed so that there are no exposed energized circuits and so that it employs some positive means to protect the operator from coming in contact with the device under
test (DUT). When the electrical testing workstation does not employ positive protection, the operator must be trained to recognize and avoid the potential hazards. Figure 1 is an example of a workstation that employs automatic protection against direct contact with the DUT. The hooded enclosure is interlocked to the hipot.

The Dielectric Voltage Withstand Or Hipot Test

The dielectric voltage withstand or hipot test is a routine production line test that can be hazardous if theoperator is not aware of the potential hazards of the higher voltages that he/she is working with. The hipot test is the deliberate application of an excessive amount of voltage intended to stress the insulation of a DUT.

Here are 10 examples of the knowledge of a test operator should have as it pertains to hipot testing with exposed energized circuits:

1. A test operator should have a basic understanding of electricity, voltage, current, resistance, and how they
   relate to each other. A test operator should also understand conductors, insulators and grounding systems.
2. A test operator should have a working knowledge of the test equipment, the tests that are being
   performed, and the hazards associated with the tests, as well as the circuits that are being energized.
3. A test operator should understand the approach distances and corresponding voltages to which they may be exposed.
4. A test operator should be trained to understand the specific hazards associated with electrical energy.
   They should be trained in safetyrelated work practices and procedural requirements as necessary to provide protection from the electrical hazards associated with their respective job or task assignments. Employees should be trained to identify and understand the relationship between electrical hazards and possible injury.
5. A test operator should understand the three primary factors that determine the severity of electric shock, namely:
   A. The amount of current flowing through the body
   B. The path of the electrical current through the body
   C. The duration or length of time the person is exposed
6. A test operator should know that the human body responds to current in the following manner:
   A. 0.5 to 1 mA: perception level
   B. 5 mA: a slight shock is felt, a startle reaction is produced
   C. 6 -25 mA for women and 9 -30 mA for men: produces the inability to let go
   D. 30 – 150 mA: extreme pain, respiratory arrest, ventricular fibrillation and possible death
   E. 10 amps: cardiac arrest and severe burns can occur
7. A test operator working on or near exposed energized electrical conductors or circuit parts should be trained in methods of release of victims from contact with exposed energized conductors or circuit parts.
8. A test operator should understand that the test instrument is a variable voltage power source and the current will flow to any available ground path. A test operator should be aware that contacting the device under test (DUT) during the test can result in a dangerous shock hazard under certain conditions.
9. A test operator should understand that, if the return circuit is open during the test, then the enclosure of
   the DUT can become energized. This can occur if the return lead is open or the operator lifts the return lead from the DUT while a test is in process.
10. A test operator should be made aware of the importance of discharging a DUT. Lifting the high voltage lead from the DUT before the test is complete can leave the DUT charged. When you are performing a hipot test, you are testing the insulation between two conductors which is essentially a capacitor. This capacitor can act as a storage device and hold a charge
    even when performing an AC test. If  the circuit is opened at the peak of the applied voltage, the DUT could hold a charge, even under an AC test. When the test is allowed to finish and the voltage is reduced to zero, the charge is dissipated through the impedance of the high voltage transformer. Most DC hipot testers today employ an output shorting device to discharge the DUT, but the hipot must remain connected to the DUT throughout the test cycle.

This is just a partial listing of the knowledge required for a test operator  to be able to safely perform a hipot test. Many product safety testing workstations are set up for maximum productivity rather than safety. If the test station is not set up with positive
protection against direct contact, then a potentially hazardous situation can result. Even the placement of the test equipment can create a potential shock hazard. For instance, if the operator has to look away from the DUT to observe the test equipment, he/she could inadvertently contact an energized circuit, or a return probe could accidentally slip off resulting in an energized chassis.

Performing a hipot test on a DUT with exposed energized circuits can be much safer when a tester is used that offers the latest technology and safety features. Many testers today have multiple shut down circuits to disable high voltage. These testers use both
adjustable high limit and low limit current sense circuits. The high limit circuit will shut down the hipot within 0.5 seconds if the adjustable current threshold is exceeded. This commonly occurs when there is a breakdown of the DUT’s protective insulation.

A second sensing current is the low limit current sense circuit. During a normal hipot test, the enclosure of the DUT is at or near ground potential (see Figure 2). The low limit circuit monitors the test for a minimum current draw and will shut down the circuit if a minimum current flow through the DUT is not detected. This most often is the result of an open lead or the operator not making a good contact with the return lead (see Figure 3). In either of the above cases, the DUT chassis could become energized present a shock hazard for an operator coming in contact with the chassis.

Increasing Hipot Testing Safety

To offset this potentially dangerous situation, there have been many developments made to increase the safety of hipot testing. One example is the recent development of a GFI circuit into electrical safety testers. This provides operators with an even greater
level of protection from electrical shock. The GFI circuit reduces the risk of the operator receiving an electrical shock when testing an ungrounded DUT, and it can also protect operators who come into direct contact with the high voltage output of the electrical
safety tester. Most GFIs will shut down the high voltage if excess leakage current of 450:A is detected through the ground circuit. This is a high-speed shutdown circuit that disables the high voltage in less than 1 millisecond.

In order for the GFI circuit to properly work in electrical safety testing applications, the safety tester’s return lead needs to be ungrounded or floating. Having the return lead floating means that the case of the DUT, to which the return lead is normally
connected, must also be isolated from earth ground. If the return lead is disconnected or is open, then there is no path for the current to return to its source. If an operator were to come in contact with the DUT case, then he/she could complete the return path. The GFI is designed to eliminate this situation.

A GFI in an electrical safety tester works in the following manner. One point of measurement senses the current returning from the DUT through the return, while the other point of measure is return current combined with current coming back through earth ground. With a good DUT that is floating, these measurements should be almost identical since very little current should return through the ground connection. If there is a condition whereby the operator comes into contact with the high voltage circuit and completes a path to ground, the GFI will sense an excessive differential between these two points and shut down. However, if the DUT is grounded, all the current returns directly through the ground point thereby bypassing the other leg of the GFI. This results in a difference in measurement between these two points, causing a false GFI failure indication. If  you have to test a grounded DUT that will require the return to be grounded, then the GFI circuit must be manually disabled.

There are also some GFI circuits on the market that integrate so-called “smart” technology. In cases where the DUT is earth grounded, such devices will allow the “return ground sense” circuit to automatically disable the GFI circuit and the instrument operates in a grounded return mode of operation. This mode allows the user to perform their tests normally without the operator
having to manually change the instrument’s configuration. When test conditions change from grounded return back to a floating return, these “smart” GFIs will automatically enable themselves, allowing the tester to monitor the return condition of the
DUT itself without manipulation of the GFI circuits by the test operator.

Many testing applications are very versatile and production lines can quickly be re-configured to manufacture and test a wide range of different products. In some cases, these products might be grounded via a production roller platform, requiring the return of
the electrical safety tester to be grounded and on others the return may be floating. Smart GFIs ultimately provides the most effective safety protection since it is an active circuit monitoring the configuration of the return connection which automatically
sets itself accordingly. By eliminating the operator from the equation, such devices work as an effective safety circuit because they do not require human interaction that could invite operator error.

Other Steps Toward Safe Testing

The test operator should be trained in the care, use and inspection of any personal protective equipment and insulating tools required to do the job. The test operator should also perform a daily visual and functional verification test on the test equipment. This is done to certify that the equipment is functioning properly and to verify that the equipment will detect a fault condition. A common way of performing functional verification tests is the use of an external verification box or external resistor bank. While these verification procedures do perform their intended purpose, they also represent an extra piece of equipment that must be
hooked up to the safety tester.

In order to help satisfy this requirement, some companies like HARREXCO offer safety testers with a built-in self verification feature, since today’s safety testers contain microprocessor-controlled technology and software driven circuits that allow for verification to be built-in to the instrument. If available on your instrument, this verification test should be performed at
every shift change. Likewise, if personal protective equipment such as high voltage gloves are in use, then they must be
inspected before each use and electrically tested at a minimum of every 6 months. Any defects must be reported immediately
and the defective item must not be used.

Summary

Preventing against the risk of injury while performing hipot tests should be a primary concern of any manufacturer.

Fortunately, through the use of engineering and work practice controls, this risk can be greatly reduced. These controls should be automatically in place and enacted each time a hipot test is performed. A secondary precaution that can be taken is the use of safe and up-to-date electrical safety testers. Safety agency listed hipot testers ensure that the test equipment and workstation being used is safe. In addition, technology has been developed that enhances safe testing. GFI circuitry has greatly reduced the risk of operator shock, and maintaining functional checks and calibration schedules of the hipot tester are now being built into safety testers themselves. These developments, coupled with operator training and a proper work station set-up, have made performing electrical
safety tests much easier and safer for manufacturers.

Reference: www.conformity.com

Hipot Test Theory

In order to understand what a Hot Hipot test is and how it is performed, it is first necessary to discuss the theory of the Hipot test itself. The Hipot test, sometimes called a Dielectric Withstand test, is used to verify the strength of the insulation between a product’s current-carrying components and its chassis or enclosure. This is done by applying a high voltage from the mains-input lines to the chassis of the product and measuring the resulting leakage current flowing through its insulation. The theory: if a voltage much higher than the product would normally see is applied across the insulation without a breakdown (which results in an excessive amount of leakage current flow), the product will be able to operate safely when run under nominal operating conditions.

The Hipot tester is used to indicate whether or not a dielectric breakdown of the insulation has occurred by monitoring the leakage current resulting from the applied test voltage. Even under normal operating conditions, some leakage current will be present in any device under test (DUT), but at minute and safe levels; however, when the insulation breaks down or is damaged an excessive amount flows to the chassis. This can present a substantial shock hazard to anyone that comes into contact with the product.

The Hipot test is so crucial because it is the best way to uncover workmanship and assembly defects in an electrical product that can lead to insulation breakdown. Mistakes during assembly or faulty/damaged components exist to an extent in any manufacturing environment, and the Hipot test can uncover units that are unfit and dangerous to sell. Some of the defects which could result in insulation breakdown include: pinched insulation, pinholes, and poorly crimped wiring. In order to detect for breakdown in electrical products, this test is usually performed during the manufacturing process on 100% of all manufactured units, as well as during routine repair and maintenance.

Hipot Test Specifications

Hipot tests can be performed using either an AC or a DC voltage. Manufacturers may or may not be required to perform a specific type of Hipot test depending on the product and the standard to which it is being tested. Both AC and DC Hipot tests have inherent advantages and disadvantages that become evident depending on the characteristics of the DUT. Basic Advantages of each type of test:

AC Hipot Advantages

• Slow ramping of the test voltage isn’t necessary due to the changing polarity of the applied waveform.
• It is unnecessary to discharge the DUT after AC testing
• AC testing stresses the insulation alternately in both polarities.

DC Hipot Advantages

• The test can be performed at a much lower current level, saving power and with less risk to the test operator.
• Leakage current measurement is a more accurate representation of the real current
• DC testing is the only option for some circuit components: diodes, capacitors, ect.

These differences between AC and DC waveforms necessitate a variation in Hipot test procedures. Although the test is basically the same, the test operator needs to take into account the relationship between a DC waveform and its equivalent AC waveform. AC waveforms are often listed as RMS (root mean squared). This RMS value, known as the
effective value, provides a load with the same amount of energy as a DC waveform of the same voltage: a 25 volt DC source provides the same amount of effective energy as a 25 volt rms AC source.

The actual quantitative value of the RMS AC waveform is much higher at the peaks of the sine wave. In fact, the difference between a peak AC waveform measurement and the RMS measured value is 1.414. The calculation is as follows:

Volts rms * 1.414 = Volts peak

Since a Hipot test stresses the insulation of a DUT with a high voltage, the applied test voltage must be the same value whether it is AC or DC. It is unnecessary to worry about the effective RMS value since the energy delivered to the DUT is of no importance; the peak (maximum) voltage is what we are concerned with.

A good rule of thumb for determining the test voltage during an AC Hipot test is to multiply the nominal input voltage (usually from a wall outlet given as an RMS voltage) by 2 and add 1000 volts.

AC Hipot test voltage = Nominal input voltage * 2 + 1000

For a DC test use the following procedure to assure that the DC voltage is the same value as the peak of the AC waveform: multiply the calculated AC voltage by 1.414.

DC Hipot test voltage = AC Hipot test voltage * 1.414

By performing this operation, the DC voltage is applied at the same level as the peak of the AC voltage waveform.

The amount of time high voltage must be applied during testing is also specified in many safety agency standards. The most common test durations are 1 second for production tests and 1 minute for design tests. Further, agencies such as UL require that Hipot testers meet certain output voltage regulation specifications to ensure that the DUT is stressed at the correct voltage. Contact your local safety agency for more information about test duration and voltage requirements.

The Hipot test is set up by connecting the two output leads of the tester to the device under test. Follow the steps below to ensure that your tester is properly connected.

1. For products terminated in a three-pronged line cord (known as Class I products) or a two-pronged line cord (known as Class II products), connect the hot lead of the Hipot tester to both the line and the neutral inputs to the DUT.
2. Place the DUT’s power switch to the ON position.
3. Connect the return lead of the Hipot tester to the metal chassis or enclosure of a Class I DUT.
4. For a Class II product, connect the return lead of the tester to a piece of aluminum foil that is wrapped around the chassis of the DUT. The aluminum foil is necessary to create a conductive material around the insulation which comprises the chassis of a Class II product.

*By connecting the tester in this way, all of the internal current-carrying conductors are raised to the same potential with respect to the chassis. This connection scheme ensures that the high voltage waveform is applied directly across the insulation of the product.

Hipot Test Shortcomings

The Hipot test has long been considered the most important electrical safety test; as such it is usually specified by safety agencies to be performed on all consumer and industrial products terminated in three- or two-pronged line cords. Historically this test has been effective on the gamut of electrical products due to a dependence on single-pole
relays and mechanical switches. Yet products that operate off of a 220 volt input often incorporate double-pole relays that open both sides (line and neutral) of the input line. Further, with the dawn of the digital age we now find that many products incorporate electronic switches. Often these switches and relays cannot be closed manually without
powering-up the product under test. In these cases a standard Hipot test becomes ineffective.

With both sides of the line open the Hipot tester cannot energize all the current-carrying conductors within the DUT and the test results become invalid. The only way to perform a valid Hipot test on products that contain these types of relays or electronic switches is to energize the product while the Hipot test is being performed. Yet in order to Hipot test a powered product, special steps must be taken since under normal conditions the line and neutral inputs of the DUT would be shorted together. This modified setup is commonly called a “Hot Hipot test.”

Hot Hipot Test Procedure

A Hot Hipot test is performed in the same fashion as a standard Hipot test. The primary difference is the addition of 1 piece of equipment, an isolation transformer. This transformer is used to isolate the input power to the DUT from earth ground. Without the use of this type of transformer, the chassis of the DUT, which is usually grounded, would be directly connected to the return of the Hipot tester (which is also referenced at or near ground potential). The return of the Hipot tester usually sees current in the milliamp range; however, without an isolation transformer the Hipot tester could be exposed to several amps of line current flowing back through its return. This could cause damage to
the tester as well as create a possible shock or fire hazard during a Hot Hipot test.

The isolation transformer creates the necessary isolation between the input lines of the DUT and the Hipot tester. Of course, an AC test voltage is necessary for this test since DC waveforms don’t work with transformers. It is also important to verify that the isolation transformer is rated to handle the applied Hipot test voltage; this will prevent
damage to the transformer.

1. In order to set up the test correctly, the primary side of the isolation transformer should be plugged into the power source used to provide the input power to the device under test.
2. The secondary side of the transformer should then be connected to the input of the DUT.
3. Once connected, the Hipot tester may then be plugged into a standard wall outlet.
4. The hot lead of the Hipot tester should then be connected to the output of the secondary side of the isolation transformer. By doing this, you are connecting the hot lead of the Hipot in between the isolation transformer output and the line side input of the DUT.
5. The return lead of the Hipot tester should then be connected to the chassis of the DUT.
6. Once the setup is completed, you may turn on the Hipot tester and the DUT.
7. Perform the test as you would a standard Hipot test.

Summary

With the advancement of the electronics industry Hot Hipot testing is becoming more and more common during routine production line testing. Products that were once operated solely through the use of mechanical relays and switches are now being controlled via electronic circuits that can only be energized while the product is running. Still other products that use 220 volt inputs contain relays that open both sides of the line, rendering a standard Hipot test ineffective. Whatever the reason, a working knowledge of the Hot Hipot test makes good sense of anyone working in the quality assurance or safety testing fields.

Although the Hot Hipot test has long been considered a mysterious and complex safety test, in actuality it isn’t much more difficult to perform than a standard Hipot test. With an understanding of the basic test procedure involved in performing a Hipot test and possession of the right equipment, a Hot Hipot test can be performed safely and efficiently. Paying attention to careful setup and implementation, a test operator, quality assurance supervisor, or engineer alike can feel comfortable performing a Hot Hipot test on a variety of products.

Reference: www.asresearch.com

Most people know what a continuity test is. A continuity test checks for good connections. Continuity tests are done by seeing if currents flow from point to point. If the currents flows easily the points are connected. “Hipot” is short for high potential => high voltage. Hipot testing checks that isolation is good. A hipot test is done to ensure that no current will flow from point to point.

Contnuity test = ensure current does flow from point to point.

Hipot test = turn up the voltage to ensure current does not flow from point to point.

Why test using high voltage?

A  hipot test is done to ensure that isolation is secure ie that no current is leaking out of the circuit. Good isolation guarentees safety to the user of electrical products.

Obviously this safety is a requirement in photovoltaic technology as well.

Common high voltage tests

1. Dieelectric Breakdown Test
2. Dieelectric Withstanding Test
3. Insulation Resistance Test