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Safety tests are mandatory and are part of every final inspection of your electrical product.
Learn the most important facts about high voltage test DC in a nutshell.
We explain the WHY, WHERE, HOW, and also the potential dangers!
And if you want to learn even more, you can download more detailed information at the bottom of this page for free!
RIso or HV-DC?
The basic approach of the high voltage test very similar to the insulation resistance test. This is because both test methods focus on the quality of the insulation.
This can be done by measuring the insulation resistance or by testing the dielectric strength with high voltage and simultaneously measuring the leakage current. So what is the main difference between the two test methods? It is the TEST VOLTAGE the Test current. Both are high voltage test significantly higher in high voltage test . In addition, the quality of the TEST VOLTAGE is not subject to such high TEST VOLTAGE .
Basically, the high voltage test DC is quite similar to the insulation resistance test. Provided that the voltage quality is high in terms of low residual ripple, it can also be used to measurement insulation resistance in MΩ or GΩ. At SCHLEICH , however, we consistently refer to SCHLEICH test as an insulation resistance test.
With HV-DC, the evaluation is based on the flowing current. This corresponds to the same evaluation as with HV-AC.
The WHY?
Safe insulation is the key protective measure for ensuring electrical safety. It ensures that the operator touch operator live conductors and that no short circuit can occur between the conductors or to the housing of the equipment. If this were to happen, a life-threatening current could operator through the operator if they touched the housing. Of course, the protective earth conductor ensure that this does not happen. But in the worst case, it could also be defective. And it would only prevent the effect and not the cause.
to ensure all this, the insulation must function perfectly! And this must high voltage test proven and documented by you before delivery of the electrical product by means of a high voltage test .
This test is not mandatory for all electrical appliances. However, it may be required for the certification of the electrical appliance in the type test. If it is required during manufacture, it is a unit test. This means that every unit, i.e., every single electrical product you place on the market, must undergo a high voltage test DC.
The WO?
As a general rule, there must be good insulation between live conductors or between these and housing components. Typically, electrical conductors are insulated against dangerous contact, i.e., they are covered with insulating material. However, this protective covering must be removed at the latest when the electrical conductor is connected to other electrical components. At these points, insulation is ensured by maintaining a safe distance. This involves safety distances through air and creepage distances.
In addition, live conductors can also be insulated from each other using casting compounds, insulating films, or solid materials, for example.
When is which type of insulation used?
This always depends on the design of the electrical product and the type of requirements, such as high temperatures or mechanical stress, etc.
It is certainly understandable that insulation in a light fixture, an iron, an electric motor a high-voltage insulator in a power plant has very different requirements and designs.
This diversity therefore results in quite complex electrical insulation structures on a case-by-case basis.
The HOW?
Since the insulation has "something to do with voltage, voltagethe test is performed with a defined test voltage level. This can be device under test to the device under test in a ramp-shaped increase or directly at full level.
The aim is to measurement the current through the insulation measurement breakdown detect a breakdown . This is because it is the evaluation criterion for the insulation. It must not exceed a specified maximum current.
The upper limit of the current can vary greatly from product to product. There is little to nothing to be found in the standards regarding this limit. And there is a good reason for this – because the amount of current depends heavily on the capacitive component in the insulation. With HV-DC, the polarity is not changed 50 or 60 times per second as with HV-AC, but the Capacitance test object must first be charged.
Depending on the design of the product and its use in different regions/continents, the standards specify the TEST VOLTAGE, the minimum power required from the high-voltage source, and the test duration. They also specify whether the high voltage must be potential-free.
High voltage resistance is often measured sequentially between all conductors involved. These can be combined groups of conductors as well as individual conductors and, of course, the housing or housing parts. It quickly becomes apparent that, depending on the complexity of the electrical product, the test run at a wide variety of locations.
This could be done by scanning the test points with a test probe – an approach that can quickly prove to be time-consuming and costly.
For this reason, complex tests have been carried out automatically and freely programmable at any test points using the SCHLEICH matrix for 25 years:
SCHLEICH switch flexibly in 2- and 4-wire technology. The 4-wire technology is particularly important in automated systems and plants. It guarantees reliable contact control of the TEST VOLTAGE thus process reliability.
| test parameters | typical values | SCHLEICH Standard to customized |
| Minimum required TEST VOLTAGE | 1,000–3,000 V DC | 50 to 100,000 V DC |
| maximum permissible Test current | 1–10, 50, 100 mA | 0.1 – 5,000 mA |
| minimum test duration | 1 s | from 0.1 seconds to 1 month |
| start-up ramp | off; 1 s – 1 min | from 0.5 seconds to 1 month |
| descent ramp | off; 1 s – 1 min | from 0.5 seconds to 1 month |
| voltage profiles | out; in 5 stages | from; in any number of steps with any profile curve |
| . |
With such a wide range of requirements, it is of course ideal to use a testing device that covers as many of the global standards as possible.
That is our strength.
The Test current
Does insulation always consist of insulation resistance a capacitor? Why a capacitor? It wasn't even installed? ...
The test always takes place between two electrical conductors/poles. In abstract terms, these two poles form two opposing metal plates. The insulation is located between them. This structure corresponds to that of a capacitor. As a result, the entire insulation structure also behaves in a highly capacitive manner. This effect is particularly noticeable in electric motors, generators, and transformers.
These are physical conditions that have nothing to do with the good or poor insulating properties of the test object. They, and of course the standard, specify the maximum permissible current.
The decisive factor now is the power of the high-voltage source. It must be able to supply the charging current required to charge the Capacitance the time you require. The required level is therefore determined by your time requirements for the test. After charging, the Test current drops back Test current almost zero. Advantage of HV-DC: The test voltage source does not need to be nearly as powerful as with HV-AC.
Low-end – In the simplest and most cost-effective case, the high voltage test is performed with a rectified AC voltage. However, this means that Capacitance after charging, a current continues to flow in the Capacitance , which TEST VOLTAGE on the residual ripple of the TEST VOLTAGE .
High-end – In most cases, SCHLEICH HV-DC test devices with highly stable DC voltage for demanding requirements. And this with a residual ripple of less than 1 V in some cases! This makes it possible to measure insulation resistance at high test voltages again.
The DANGER?
If a direct current of less than 12 mA flows through the human body, it is classified as harmless.
If a high-voltage DC source can only supply a maximum of 12 mA, it is therefore considered to be safety-current-limited and harmless. Special protective measures are then not necessary.
However, the charge in device under test also device under test taken device under test account. Here, a maximum charge of 250 mJ is permissible without safety measures. This is quickly exceeded in electric motors and generators. Appropriate protective measures are then absolutely necessary.
These include:
- electrically isolated high voltage
- Barricading of the test site
- Safety test guns
- Two-hand start with corresponding safety relays
- Test cage or test cabin – monitored by two circuits with approved safety relays and, if necessary, a secure interlock
- Compliance with performance level PL e, SIL 3, Cat. 4 ...
Performance Level PL e, SIL 3, Cat. 4 …
The safety technology requirements are correspondingly high for a Test current 12 mA. The relevant international standards must be complied with worldwide.
SCHLEICH testers meet these requirements!
It should be noted that there are various testing devices on the international market that may appear to be a bargain, but do not comply with the legally required safety regulations of EN50191/VDE0104!
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Our mission – knowledge, knowledge, knowledge ... Those who have a sound technical and normative understanding of testing methods will get the most out of their testing equipment.
– Dipl. Ing. Martin Lahrmann
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