power quality means

Power Quality is a measure of closeness to a perfect sine wave at the correct amplitude. See Wikipedia Power Quality for detailed explanation.

Hi,

Power Quality is the combination of voltage quality and current quality. It is defined according to its effect on different parts of the power system. It is defined as the reliability of the system from the electric utility point of view. Equipment manufacturers defined it as the changes in the characteristics of the power supply. The customers, who are most affected by power quality issues, defined it as any power problem manifested in voltage, current, or frequency deviations that results in the failure or misoperation of their equipment.

IEEE std. 100-1996: "Power Quality is the concept of powering and grounding sensitive equipment in a matter that it is suitable to the operation of that equipment"

IEC 61000-4-30: "characteristics of the electricity at a given point on an electrical system, evaluated against a set of reference technical parameters"

The Council of European Regulation uses the term Quality of Service in Electricity Supply which considers three dimensions:1. Commercial Quality concerns the relationship between the network company and the customer, 2. Continuity of Supply concerns long and short interruptions, and 3. Voltage quality which includes the following disturbances: frequency, voltage magnitude and its variation, voltage dips, temporary and transient overvoltages, and harmonics.

Let me try to simplify this for the semi-layman a bit.

The perfect ideal load for a AC sinewave is a pure resistor. The current and the voltage waveform rise and fall together. This is called Unity power factor or 1:1 power factor. But if the load is inductive (a big industrial motor or transformer for instance) or capacitive (switch-mode power supplies like those used in computers), the voltage and current phases can get out of sync with each other. There are devices on the market that actively change their input impedence to correct for these shifts. These are called power factor correction circuits. These phase differences can wreak havoc on some sensitive equipment and they can even damage distribution networks if they get too large.

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What is good Power Quality on 3 – phase AC supply system: •* Good Voltage Stability for large variations in Load Currents. * No Voltage Harmonics on supply point of every connected Load. * Power Factor is 1.00 (Unity) (Reduction in T&D losses) * All the three phases are equally Loaded. Neutral current is zero. * No transient (fast changing) Voltage at supply point of every connected Load. (No high dV/dt component) * Supply System Contract Demand is never exceeded. (Electrical charges related) * Supply System Contract Demand is not too high as compared to average Maximum Demand. (Electrical charges related) * All the appropriate points in supply system are earthed. This should ensure the finite limit on maximum Voltages w.r.t. reference earth. (Human safety angle) * Supply frequency remains stable at rated value and does not change.