Chapter A General rules of electrical installation design

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L26 © Schneider Electric - all rights reserved L - Power factor correction and harmonic filtering (1) Minimum cross-section not allowing for any correction factors (installation mode, temperature, etc.). The calculations were made for single-pole cables laid in open air at 30 °C. 10 Implementation of capacitor banks Fig L34 : Cross-section of cables connecting medium and high power capacitor banks (1) Voltage transients Schneider Electric - Electrical installation guide 2008 Bank power Copper Aluminium (kvar) cross- section cross- section 230 V 400 V (mm 2 ) (mm 2 ) 5 10 2.5 16 10 20 4 16 15 30 6 16 20 40 10 16 25 50 16 25 30 60 25 35 40 80 35 50 50 100 50 70 60 120 70 95 70 140 95 120 90-100 180 120 185 200 150 240 120 240 185 2 x 95 150 250 240 2 x 120 300 2 x 95 2 x 150 180-210 360 2 x 120 2 x 185 245 420 2 x 150 2 x 240 280 480 2 x 185 2 x 300 315 540 2 x 240 3 x 185 350 600 2 x 300 3 x 240 385 660 3 x 150 3 x 240 420 720 3 x 185 3 x 300 High-frequency voltage and current transients occur when switching a capacitor bank into service. The maximum voltage peak does not exceed (in the absence of harmonics) twice the peak value of the rated voltage when switching uncharged capacitors. In the case of a capacitor being already charged at the instant of switch closure, however, the voltage transient can reach a maximum value approaching 3 times the normal rated peak value. This maximum condition occurs only if: b The existing voltage at the capacitor is equal to the peak value of rated voltage, and b The switch contacts close at the instant of peak supply voltage, and b The polarity of the power-supply voltage is opposite to that of the charged capacitor In such a situation, the current transient will be at its maximum possible value, viz: Twice that of its maximum when closing on to an initially uncharged capacitor, as previously noted. For any other values of voltage and polarity on the pre-charged capacitor, the transient peaks of voltage and current will be less than those mentioned above. In the particular case of peak rated voltage on the capacitor having the same polarity as that of the supply voltage, and closing the switch at the instant of supply-voltage peak, there would be no voltage or current transients. Where automatic switching of stepped banks of capacitors is considered, therefore, care must be taken to ensure that a section of capacitors about to be energized is fully discharged. The discharge delay time may be shortened, if necessary, by using discharge resistors of a lower resistance value.
2 3 4 5 6 7 8 Chapter M Harmonic management Contents The problem: why is it necessary to detect M2 and eliminate harmonics? Standards M3 General M4 Main effects of harmonics in installations M6 4.1 Resonance M6 4.2 Increased losses M6 4.3 Overloads on equipment M7 4.4 Disturbances affecting sensitive loads M9 4.5 Economic impact M10 Essential indicators of harmonic distortion M and measurement principles 5.1 Power factor M11 5.2 Crest factor M11 5.3 Power values and harmonics M11 5.4 Harmonic spectrum and harmonic distortion M12 5.5 Total harmonic distortion (THD) M12 5.6 Usefulness of the various indicators M13 Measuring the indicators M 4 6.1 Devices used to measure the indicators M14 6.2 Procedures for harmonic analysis of distribution networks M14 6.3 Keeping a close eye on harmonics M15 Detection devices M 6 Solutions to attenuate harmonics M 7 8.1 Basic solutions M17 8.2 Harmonic filtering M18 8.3 The method M20 8.4 Specific products M20 Schneider Electric - Electrical installation guide 2008 M © Schneider Electric - all rights reserved
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General rules of electrical install
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Chapter A General rules of electrical installation design

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