October 2015

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Tools not provided

Some companies do not always provide you with tools required to complete your task quickly and efficiently. I do not truly understand this company philosophy. Even if they will provide the tools, it does not…


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Circuit Breaker Utilization Categories (IEC 60947-2)

Utilization category (for a switching device or a fuse) is defined in IEC 60947-1 as the combination of specified requirements related to the conditions in which the switching device or the fuse fulfills its purpose,…


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System Voltage Classes (ANSI)

In ANSI C84.1-2011, Clause 3, system voltage classes were explained Low Voltage (LV) A class of nominal system voltages 1000 volts or less. Medium Voltage (MV) A class of nominal system voltages greater than 1000…


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Inverter Topologies – Variable Speed Drives

Voltage-source inverter has a configuration where rate of change of voltage (dv/dt) in the inverter is limited by a large capacitor connected in parallel across the DC link. Current-source inverter has a configuration where rate…


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Modes of Operation – Variable Speed Drives

Variable speed drives are capable of operating in 4-quadrant modes of operation. When energy is transferred from the electric motor to the mechanical load, it is operating in motoring mode. These modes take place in…


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Effect of Air Density on Equipment Physical Size

IEEE C57.13 Clause 4.2 states that the dielectric strength of air decreases as altitude decreases. The dielectric strength on air should be multiplied by the altitude correction factor provided in Table 1. Dieletric strength is…


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