This paper produced by Schneider Electric USA

explores the affect of various short-circuit current ratings (SCCR) values to Altivar ATV 61 and ATV 71 inverter drives. It considers potential equipment damage at low (5kA) and high (100kA) short-circuit currents and compares the impact of adding a 3% line reactor and Adding a DC Choke with an Impedance Equivalent to the 3% Line Reactor.

In particular, what happens to the line current when a drive with a 6-diode rectifier section is combined with different power systems and different types of added inductance.1 This application note applies to Altivar® 61 drives and Altivar® 71 drives, as well as other variable frequency drives with a 6-pulse rectifier circuit. It does not apply to Altivar® 21 devices as they have a greatly reduced amount of DC bus capacitance.

Findings

Running a drive, without additional inductance, on a power system with a short-circuit current greater than the published SCCR of the drive severely reduces the life of the drive. Using an appropriately sized input line reactor or DC choke reduces both the input line current peaks and the heating in the DC bus capacitors, bringing the drive’s life expectancy back to specified levels. Attention must be paid to the manufacturer’s specified over-current protective devices and the enclosure type used with the recommended reactor or choke at the UL Listed higher SCCR in order to properly apply the adjustable speed drive power converter.

Open the full PDF document here The Effects of Available Short-Circuit Current on AC Drives

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