In the process of fulfilling a desired function, electronic products consume power. This process will influence the system supplying the power by virtue of what are called ‘conducted emissions’ which include Harmonic Distortion of consumed current and Voltage disturbance, most commonly Flicker. The process of converting energy may also result in ‘radiated emissions’, where electromagnetic interference is generated.
Since conducted emissions can affect other devises connected to the same supply network and radiated emissions can affect the function of devices nearby, limits defined within standards are applied to electronic products so that emissions and susceptibility fall within internationally agreed levels.
Outside the scope of emissions but now an area of increasing regulatory attention, is standby power, where devices connected to the low voltage AC supply and consuming power in a standby mode when not carrying out their primary function, must fall within defined power limits.
Most standards to which we refer originate from the International Electrotechnical Commission (IEC). The international nature of the commission and associated committees reflects a global move toward standards equivalence and standardisation.
Limits to the harmonic current drawn or what is sometimes described as being ‘injected’ into a public low voltage supply system, focus on products that consume up to 16Arms per phase, or between 16Arms and 75Arms per phase. The standards are called IEC61000-3-2 and IEC61000-3-12 respectively.
Limits to voltage changes, voltage fluctuations and Flicker that a product connected to a public low voltage supply may produce are also applied on the basis of phase current, with devices up to 16Arms per phase required to meet IEC61000-3-3 and those between 16Arms and 75Arms required to meet IEC61000-3-11.
Given clear and measurable harmonic and voltage flicker limits, fully compliant level testing requires measurement equipment with accredited calibration for all defined functions
For immunity testing, no measurement or test limits are involved. A device under test is exposed to defined power variations or interruptions and the behaviour of the device is observed.
Standards again fall into phase current categories, where devices consuming up to 16Arms per phase are tested to IEC61000-4-11 and those above 16Arms are tested to IEC61000-4-34.
Low Power Standby
In recognition of the considerable total power consumed by the sum of all electronic devices that continue to draw power from the low voltage public supply when in standby mode, low power or standby power standards define limits on power level consumed.
Associated standards are IEC62301 & EN50564, where a power limit must be proven by a measurement instrument that meets defined accuracy and resolution criteria.
Since the standby mode of some devices involves low duty cycle current pulses, the standards also require that low power measurements are accumulated and averaged over time, with confirmation that voltage THD and Crest Factor remain within defined limits during the test period.
Power Transformer standards
As a large, complex, expensive and service critical part of a power distribution network, power transformers are manufactured and tested in accordance with standards that specify manufacturing processes and electrical testing.
With respect to electrical testing, IEC60076-1 defines terms and methodology such as load and no-load loss testing with specific computational algorithms and multiple measurement techniques, for example both mean and rms computation when most applications require one or the other, or very specific equations to derive voltage and current harmonic content.
Also associated with power transformers, ANSI/IEEE C57.110 addresses the capability of transformers to supply non-sinusoidal load currents, without loss of normal life expectancy.