TEST & COMPLIANCE FEATURE FLASH, AHHH! Flash testing new electronic products
As components and machinery are made obsolete at a faster rate, it is for distributors like Test-Meter to provide testing equipment for ensuring optimal safety and effectiveness. Flash testing is one such safety test
F
lash testing might not be a glamorous test for new electronic appliances,
but it is important in determining how insulation performs in rated electrical conditions. The potential consequences of electrical breakdown, irreparable damage and risk to human life, make it an essential test on new or refurbished electrical items.
WHAT IS A FLASH TEST? A flash test, also known as a dielectric withstand test, or ‘hipot’ (high potential test), is the application of a high voltage across a product’s insulation. As standard, a voltage of 1.5kV is used for class one appliances and 3kV for class two appliances, although many instruments offer further options with increased AC and DC voltages. This is typically ramped up to its full voltage, depending on appliance class, for a 60-second period. Flash testing devices will have a probe that applies this voltage to the product. This should be employed between conductors and earth for class one appliances, contrasted to class two appliances, harnessing the voltage between conductors and the outer insulation. The tester will then produce a touch/earth leakage current reading, according to the class. Any significant current indicates an electrical breakdown.
WHAT DOES A FLASH TEST TELL ITS USER ABOUT THE PRODUCT? A dielectric withstand test is essential because high voltages applied to electrical insulation can result in ‘electrical breakdown’, where large amounts of electrical current flow through because of unequal potential from one side to the other. This applies equally to solid insulation, and insulation through air gaps, where an electrical arc forms through the space. This can result in damaging currents running throughout a product, creating a risk of fire, damage, and even a risk
of electric shock to users, both at the time of the test and later on, due to the degradation of insulation. As a proposed resolution, a flash test will detect increased leakage current if there is a problem such as inadequate clearance between conductors or cracks/ damage to insulation, sustained during manufacturing. This shows that the product is not fit for use and that there has been a fault at either the design or manufacturing stage.
FLASH TESTING SENSITIVE, POTENTIALLY UNSAFE ELECTRONICS It has long been noted that AC flash testing can damage sensitive electronics in perfectly assembled products, so alternatives have been developed to prevent this from reoccurring. Principally, DC flash testing can be used, as long as the test voltage is multiplied by 1.414 to achieve the peak AC wave voltage. But to prevent further damage, there are the possibilities of ramp testing, where the voltage is gradually increased to full voltage as described earlier, and the inclusion of a trip limit.
WHAT ARE THE REQUIREMENTS SURROUNDING FLASH TESTING? With all of the technical requirements for dielectric withstand testing, the most relevant ones for electronics designers and manufacturers are BS EN 60950 and BS EN 60335. These respectively cover IT equipment with a rated voltage of 600V or under, domestic appliances with
The flash test covers all kinds of equipment, ensuring it performs at its optimal standard
a rated voltage of 250V for single phase equipment, and 480V for everything else. Whilst a small current is permissible, any signs of breakdown are unacceptable. Flash testing is also required to follow several standards for the protection of users and equipment from dangerous electric current. With correct implementation, through sufficient clearance and insulation, safety is ensured, reducing the risk of damage within the production process.
Currents are a health and fire hazard: a flash test could prove the difference between a workplace accident and a successful day
FLASH TESTING INSTRUMENTATION There are many flash testing options on the market, from advanced PAT testers such as the Megger PAT350, Metrel OmegaPAT Plus or Seaward Supernova Elite, to industrial, electrical safety testers such as the Clare HAL and Metrel MI3321, and dedicated flash testers including the Clare Sentinel and Metrohm ranges.
Some offer more advanced flash tests and/or a variety of other functions, so choosing a tester largely depends on the equipment already available and the user’s individual requirements. Specifically, PAT testers might have a very low trip current limit of 2.5mA for safety, whilst an electrical safety tester may go up to 100mA, to facilitate CE and type testing.
Test-Meter
www.test-meter.co.uk
/ ELECTRONICS ELECTRONICS | MAY 2019 25
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44
