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Regulation/legislation High time for New Measurement Standards Higher Harmonics in the Grid By Pavel Mihatsch Briefly put: As more elements are added into the grid, power quality standards and measurement need to be reassessed to take into consideration the necessity of more refined standards. The situation on the low voltage grid has significantly changed over the past few years. This comes as a result of the arrival of new appliances – lights, electronics with switched-mode power supplies – and due to the changes at supply/generator sites. Power supplies – a lot of small players In the past, big generators (rotating machines) were predominantly used. Their construction led to the direct generation of a sinus curve. Their distortion came as a result of technical (electric and mechanical) imperfections, and was very small. Today, large amounts of small, non- rotating generators are in the field – they are switched-mode inverters/converters. In order to generate pseudo sinusoid curves, pulse-width modulation (PWM) with low-pass filter is used. Modulation frequency reaches several kHz. Principally, PWM generates plenty of higher harmonics, which should be filtered from the final signal. However, filtration of these harmonics brings higher financial costs, and it is thus, in most cases, tolerated. The higher power generated supplied, the more complicated and expensive the filtration (coil and capacitor) to be used. Subsequently, this leads to a power supply quality aggravation. Appliances – no reason for satisfaction In the past, household appliances operating on a resistance basis (bulbs, heating, water boilers…) prevailed. They consisted of simple regulators, their electronics were supplied from linear supplies. Rotating machines were controlled through classic linear regulators. Harmonics appeared very rarely, and were insignificant in size. Appliance were also well compensated at power factor. That is why it was not necessary for final customers – households – to measure reactive energy or watch the power quality of supplied energy. This quality was monitored by big customers only, as well as at distribution transformers where it made sense to do so. 52 Today’s situation is quite different. Compact fluorescent lamps, and LED bulbs prevail among light sources. They are supplied from switched-mode changers, and with poor compensation for power factor and none for disturbance. Sometimes the compensation is totally missing in order to keep prices low. Capacitors are used for limiting impedance for LED bulbs. As a result, a decrease of active power consumption by tens of percent occurs while the influence of reactive, and higher frequency power, increases. We save on the active power, while the power factor is significantly deteriorated. Nowadays, almost all appliances use switched-mode power supplies, or other synchronised changers controlled/ switched-mode by zero crossing. These sources have relatively high efficiency and they are small in size, but if we use them, a large amount of higher current harmonics (and secondary to that, voltage) appears. The picture shows an example of harmonics on the grid. Today, standards are broken without exception. METERING INTERNATIONAL ISSUE - 1 | 2014