Altivar Process 600 Variable Speed Drives Page 24 Application Information

24 Altivar Process 600 variable speed drives Motor cable length Application Information Motor Cable Length Impact of Long Motor Cable Lengths Long motor cable lengths between a drive and motor may cause over current conditions, causing the drive to trip on short circuit or ground fault errors or cause over voltage conditions that cause premature wear on the motor. These phenomenon are often underestimated at the design and installation stage. Left un-checked, this neglect can lead to motor breakdown and unexpected down time. Over current conditions may be caused by capacitive coupling between motor cables, generating enough current flow to ground, which causes the drive to trip on ground fault errors. Also capacitive coupling between motor cable may cause the drive to detect and trip on short circuit errors. Over voltage conditions may be caused by the mismatched impedance of the cable and the motor. This mismatch of impedences causes the switching frequency pulsed output voltage from the drive to reflect back from the motor terminals. The result can be voltages at twice the level of the DC bus or higher, which can stress the drive, cable, motor windings and motor bearings. Generally, longer motor cables yield higher voltages. This effect is amplified when by using shielded cable. Preventative Measures There are several steps provided below, beginning with the least costly, that can be taken to reduce nuisance trip errors and improve the life of the motor. Reduce the switching frequency of the drive to 2.5kHz or less. Use un-shielded motor cables. Specifiy a drive, like the Altivar Process, that has software functionality to help manage voltage wave reflection. Specify motors that are NEMA MG1 Part 31 or IEC60034-25 compliant. Specify output load reactors (also known as motor chokes) to limit voltage rise time Specify dV/dt filters to further limit voltage rise time Specify Sine wave filters (also known as sinus filters) that allow a smooth, lower voltage output wave form to the motor Recommendations Additional Filters The following table provides guidelines when to specify additional filters Motor Cable Length (unshielded cable) Motor Conforming to NEMA MG1 Part 31 Motor Not Conforming to NEMA MG1 Part 31 1 m (3.3 ft.) < Lm <50 m (164 ft.) Filter not required dV/dt filter 50 m (164 ft.) < Lm < 100 m (328.1 ft.) Filter not required Sinus filter 100 m (328.1 ft.) < Lm < 300 m (984.3 ft.) Filter not required Sinus filter 300 m (984.3 ft.) < Lm < 500 m (1640.4 ft.) dV/dt filter Sinus filter 500 m (1640.4 ft.) < Lm < 1000 m (3280.8 ft.) Sinus filter Note: When calculating cable lengths for the purpose of guarding against these overvoltage situations, a shielded cable should count as twice the length of an unshielded cable. For example, if a shielded cable is 100 meters in actual length, it should be considered to be equal to a 200 meter length standard cable in the calculation. Note: In applications where one drive is used to power multiple motors in parallel, the appropriate cable length should be calculated based on the sum of all the cables. For example, if three motors in parallel are connected to a single drive, each with a 20 meter (66 foot) cable, the total length that should be calculated in not 20 meters, but should be 60 meters (197 feet). Precautions must be taken to protect the VSD from any unexpected tripping.

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