High Voltage Wine

Applying a high voltage electric field can shorten the ageing process of wines. Research has been underway for ten years. Taste tests by a panel of experts indicate that this works.

The best results appear to occur with a field strength in the range from 300Vac/cm to 600Vac/cm. Details of the plug-in ageing process have been reported in New Scientist magazine. ''Not only can it shorten a wine's normal storage time, it can also improve some lower-quality wines,'' according to the New Scientist article.

Ultra-High Voltage Transformer

A new transformer developed for the world’s first ultra high-voltage DC transmission systems (UHVDC) has successfully completed final testing. It is the first transformer for the new 800 kilovolts (kV) HVDC in China. Today’s HVDC transmission systems normally operate at a standard transmission voltage of 500 kilovolts. HVDC systems can transmit power over much greater distances and at considerably reduced loss than is possible with AC systems.

To achieve this 60-percent increase in peak voltage capacity, Siemens had to develop a range of entirely new technical solutions for the new 800-kilovolt HVDC transmission system. One of several major challenges facing the company’s development engineers in Nuremberg was a lack of any defined standards for this scale of system. Due to the very high operating voltage, for example, they had to design exceptionally effective insulation systems. Therefore, in order to achieve the needed insulating clearances in air, the two valve bushings through which the current flows from inside the transformer to the converters are 14 meters in length. To construct the 800 kV transformers, a new, specially air-conditioned production hall had to be built to prevent the insulation from absorbing moisture from the atmosphere during final assembly. Similarly, the test facility in the Nuremberg factory had to be adapted to accommodate the tremendous increase in voltage when carrying out final acceptance testing on the new transformer.

High Voltage Curve Tracer

Agilent Technologies Inc. recently introduced the industry's first power device analyzer/curve tracer able to characterize semiconductor devices at up to 3,000 volts and 20 amps.

Power devices, including power management ICs (PMIC) and power MOSFETs and motor control ICs used in cars, are a growing device category that requires both high-power and high-accuracy test. In order to meet emerging standards for low-carbon emissions and improved energy efficiencies, power devices must function more efficiently even as they continue to become more complex, smaller and faster. New devices using wide band gap materials such as silicon carbide (SiC) or gallium nitride (GaN) have been widely studied in order to achieve high efficiency. To enable the careful and precise testing to meet performance and safety requirements, these studies require high-voltage measurement capabilities greater than 1,000 volts. In addition, for those power-device developments, on-wafer testing becomes very important for reducing development turnaround times.

Featuring a curve tracer mode, the Agilent B1505A can replace curve tracers used in failure analysis, as well as in circuit design or power module development of electronic equipment makers.

Key Features of the Agilent B1505A Power Device Analyzer/Curve Tracer usful to high voltage engineers:
-- Accurate measurement of breakdown voltage and leakage currents at high voltage.
-- Sub picoamp level measurement capability at high voltage.
-- Capacitance-Voltage (CV) measurement with up to 3,000 V bias.
-- Device characterization at 3,000 volts and 20 amps in a single instrument.

High Voltage DC Leakage Tester

The newly introduced Model PT-5000W High Voltage DC Leakage Tester from HC Electric is a general purpose dual voltage leakage tester designed to test equipment for faults or high leakage currents. The test voltage can be set by the user to either 500 VDC or 5,000 VDC.

The handheld PT-5000W can be used to check for leakage on cables, transformers, capacitors, joints, terminations, insulators, etc.

Key Features:
• Portable unit tests de-energized and discharged capacitors, transformers, terminations and insulators

• Use in overhead or underground systems

• User selectable - test 500 VDC or 5,000 VDC

The PT-5000W can only be used on cables or equipment that has been verified to be de-energized and discharged. primary distribution voltage or secondary voltage. For further info, see http://www.hdelectriccompany.com/pt5000w.htm

Insulation Testing

Insulation testing is often seen as the third core test and is usually preceded by an earth bond and a flash test.

The insulation test measures the resistance of a product's insulation protection by applying a DC voltage between phase and neutral to the earth conductor for Class I equipment and between phase and neutral to the outer case for Class II equipment. This will show a reading of resistance in Mohms.

The test ensures protective insulation is good enough to form a barrier to make sure people aren't electrocuted and to ensure other manufacturing systems and machinery are not affected.

Legislation such as the low voltage directive (LVD) requires evidence of due diligence and the results of this and the in-service test can be used as well.

The test can be applied to both Class I and Class II equipment and should be carried out using probes or insulated clips and without the equipment being connected to a power supply.

Test voltages vary between standards - although 500V DC is the most common application - and the voltage is applied for a maximum of three seconds.

However, electrical safety testing specialists Clare Instruments has designed test equipment for supplying up to 1000V where greater protection is called for (for example in automotive industry ignitions).

Equipment has also been supplied with voltage as low as 100V where higher voltages may cause damage (for example in motor industry switches).

In general, pass/fault limits for Class I equipment is a resistance greater than 2Mohms and for Class II equipment is a resistance greater than 7Mohms.

There are differences in the flash/hipot tests - flash testing detects gaps or clearance between conductive parts and earth, pin holes in insulation and other degradation that may be the result of production processes and/or wear and tear, while insulation resistance testing is designed to provide a quantitative measurement of the quality of insulation.

If a wire was positioned 0.5mm from exposed metal, an insulation test conducted in dry air could provide a pass reading.

However, a flash test is more likely to detect if this situation was dangerous.

Similarly, if insulation is somehow contaminated, a flash test would produce a pass, but an insulation test would highlight the deficiency.

For example, the normal minimum insulation resistance value for Class I appliances is 2Mohm, but with a 1,500V AC flash test, the current would be 0.75mA and would not be detected by the 5mA trip, which has to accommodate the capacitive losses that occur.

A DC flash test with a leakage meter can provide insulation resistance monitoring, as the capacitive component is leveled out after the initial switch-on surge.

The test time of two to three seconds does not generally pose a problem on the production line, but some practicalities need to be addressed.

For example, the use of a conductive foam nest can aid the testing of Class II products, and this nest can be integrated with test enclosures and probes.

Typical causes of insulation test failure include poor quality insulating materials, material that has been over-stressed either mechanically or electrically, poor maintenance and cleaning procedures, ingress of fluids and dust, and assembly faults.

For more information, request a free brochure from Clare Instruments, where this article is from.

Isolated High Voltage DC-DC converters

Two isolated dc-to-dc converters with high isolation voltage have come to our attention recently. Providing low voltage power that floats at a high voltage can be tough to implement. However, these products can do just that, and they do in in compact packages.

One is a 1W single or dual output unit with 15kVdc isolation. It is supplied in a DIP package. Very handy. For more information on this, please contact us at fred@highvoltageinfo.com

The other is a 0.5W single output unit with 2.5kVac isolation. It is the Analog Devices ADUM5000 Isolated DC/DC Converter. Note that this product is not yet released to manufacturing, so it it worth checking further into availability of this announced part.

High Voltage, Low Noise DC/DC Converter Circuit Designs

Have you seen the Linear Technology application note on high voltage, low noise DC/DC converters? Ap notes don't get any better than this one. It includes circuits for high voltage power supplies rated from 200V to 1000V. It also addresses noise issues, and the effects of various voltage feedback techniques on transient response.

The ap note describes resonant Royer topologies (which produces power by utilizing sinusoidal waveforms instead of switched waveforms) and also flyback converters. It also describes methods of measuring output noise.

If you are planning to design a high voltage power supply for photomultipliers (PMT's) or other applications requiring low noise, low power in the range of hundreds of volts, you might want to peruse the ap note. It is Linear Technology Application Note 118.