# Power Quality Impact and Its Assessment: A Review and a Survey of Lithuanian Industrial Companies
## 2 Literature Review
### Social Impact
Flicker severity is calculated according to IEC 61000-4-15:2011 based on the simulation of the response of the lamp-eye-brain chain. The procedure consists of five parts--input voltage adaptor, squaring multiplier, weighting filters, squaring and smoothing, and statistical analysis: (1) Block 1 prepares the input signal--mains frequency voltage--for further processing by scaling it to an internal reference level; (2) Block 2 extracts the voltage fluctuation by squaring the input voltage scaled to the reference level, thus simulating the behavior of a lamp; (3) Block 3 consists of three filters--the low-pass filter with a cutoff frequency of 35 Hz (50 Hz power supply) or 42 Hz (60 Hz power supply) removes the double mains frequency ripple components, the high-pass filter with a cutoff frequency of 0.05 Hz can be used to eliminate any DC voltage component, and the bandpass filter with a center frequency of 8.8 Hz simulated the frequency response of the human visual system to sinusoidal voltage fluctuations of a coiled filament gas-filled lamp (60 \(W\)); (4) Block 4 is composed of a squaring multiplier and a first order low-pass filter, the output of which represents instantaneous flicker sensation; (5) Block 5 performs statistical processing of the instantaneous flicker severity values to calculate the short-term and long-term severity values. According to the requirements of EN 50160:2010, long-term flicker severity must be less than or equal to 1 during 95% of the time in one week; however, the standard admits that the response to flickering is subjective, thus in some cases the same severity may have a serious impact, while in other cases it may not. Voltage harmonics and inter-harmonics measurement techniques are defined in IEC 61000-4-7:2002. The first step, as usual for any digital signal, is the computation of discrete Fourier transform, usually using a fast Fourier transform algorithm. As has been already mentioned in [1; 8], the calculation result of the supplied electricity spectrum depends on a number of factors, particularly on window function and width. For full compliance with IEC 61000-4-7:2002, the rectangular window with a width of 10 (50 Hz power supply) or 12 (60 Hz power supply) periods shall be used and synchronized to power system frequency (the Hann window is allowed only in the case of loss of synchronization). Then, harmonic levels are extracted by performing two additional artificial steps--grouping and smoothing. The grouping is the summation of the squares of the spectral lines between two adjacent harmonics according to the formula given in the standard. Since the Fourier transform analysis assumes that the signal is stationary, but the actual signals of a continuous power supply are not necessarily stationary, the standard provides additional instructions to improve the assessment accuracy. After the grouping, the smoothing shall be performed by using the given first-order low-pass filter with a time constant of 1.5 s.  
On the other hand, the question that may arise is whether it is more important to focus on the quantity (characteristics) of PQ events or on the problems caused regardless of the quantity. For example, although the quantity of rapid voltages changes, voltage sags, voltage swells, and voltage transients (as well as their measurement process) are not currently regulated by the PQ standards, some Lithuanian insurance companies as well as independent electricity suppliers (which emerged after the initiation of electricity market liberalization process) offer insurance against voltage variations.