Category Archive for: «Low Voltage»

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10 Important Precautions When Working On Low Voltage Energized Equipment

Have eyes in the back of head… For most work, the electrical equipment must be de-energized because there is a high risk of injury to workers if they work on energized equipment. It may be possible to schedule such work outside of normal work hours to limit the inconvenience. Sometimes it is not practicable to completely disconnect low-voltage […]

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Harmonic Distortion and High Frequency Applications

Distortion of the fundamental sine wave The presence of harmonic frequencies in addition to the fundamental 50Hz, bring about distortion of the fundamental sine wave. Considerable problems may arise dependant upon the level of this distortion. Sources of harmonic distortion can be: Variable Speed Drives UPS equipment Non linear load (switch mode power supplies) Special […]

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What affects the operating temperature within LV switchgear

Maximum ambient condition BS EN 60439 states a maximum indoor ambient temperature of 40ºC, a maximum daily average of 35ºC and a minimum ambient of -5ºC. As a general guidance rule, the temperature within the low voltage switchgear should not exceed 50/55ºC. If Switchroom/Plant room ambients are typically considered to be up to 25°C this […]

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Example of MV/LV network structure with dual fed main MV switchboard

Connected to article: Example of standard MV/LV network structure Network structure: MV consumer substation; The main MV switchboard can be backed up by a generator set and it feeds two MV/LV transformers; MV switchboard can be GIS or AIS and consist of following cubicles: – two incoming feeders (from utility) – two transformer cubicles – […]

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Switching contactor and effect of long control lines

Voltage drop In accordance with IEC 60947-4-1 and IEC 60947-5-1, the normal control voltage range of power and control contactors lies between 85 … 110 % of the rated control voltage. Within these limits contactors pull-in perfectly. Frequently contactors are offered with an extended control voltage range, thus for example with contactors with electronic coil […]

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Using AC switchgear in DC applications

Skin effect Switchgear designed for alternating current can carry at least the same rated continuous operational DC current. With direct current the skin effect in the circuits disappears and none of the specific effects associated with alternating currents such as hysteresis or eddy current losses occur. DC devices that are operated at low voltage can be […]

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Defining Size and Location of Capacitor in Electrical System (2)

Continued from part 1: Defining Size and Location of Capacitor in Electrical System (2) Content Size of circuit breaker (CB), fuse and conductor of capacitor bank: A. Thermal and magnetic setting of a circuit breaker B. Fuse selection C. Size of conductor for capacitor connections Size of capacitor for transformer no-load compensation: Fixed compensation Sizing […]

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Differences Between Earthed and Unearthed Cables

Introduction In HT electrical distribution, the system can be earthed or unearthed. The selection of unearthed or earthed cable depends on distribution system. If such system is earthed, then we have to use cable which is manufactured for earthed system. (which the specifies the manufacturer). If the system is unearthed then we need to use cable […]

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Generalities and Discrimination Between RCDs

Generalities on Residual Current Circuit-Breakers The operating principle of the residual current release is basically the detection of an earth fault current, by means of a toroid transformer which embraces all the live conductors, included the neutral if distributed. In absence of an earth fault, the vectorial sum of the currents IΔ is equal to […]

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Lighting Circuits Connections for Interior Electrical Installations (2)

Continued from first part: Lighting Circuits Connections for Interior Electrical Installations Introduction In modern internal electrical installations, domestic and professional, there is a need for lighting installations in staircases and installation of emergency lighting that will operate in the event of interruption of electricity supply from the grid. The automatic staircase timer abolished Aller – Retour […]

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