IEC60034.1 and NPS Voltage

[Vegemite]

We have a distribution system which, with some active harmonic filters, can be made to meet all of the harmonics limits of IEC61000.2.4 (Class 2) & IEC61000.3.6.

When the negative phase sequence components of voltage are geometrically added, however, we get a negative phase sequence voltage 2 or 3 times greater than the 1% limit imposed for normal types of induction motors by clause 7.2.1.1 (or 8.2.1.1) of IEC60034.1 Form and symmetry of voltages and currents - AC motors.

When adding the negative phase sequence components, we take the square root of the sum of the squares of harmonic orders 2, 5, 8, 11, 14, 17 etc. The various harmonic voltages were obtained by network analysis of the harmonic currents provided by the VVVF drive manufacturer's software.

Could it be that manufactures are building motors to withstand higher levels of negative phase sequence voltage than the 1% specified in IEC60034?

Could it be that our analysis is flawed?

 

[bacon4life]

In rural areas 3 phase motors seem to often survive larger than rated voltage imbalances (i.e. negative sequence 60 Hz component). I assume whether or not the additional heat from negative sequence voltage causes a motor to fail largely depends on whether other factors already have the motor operating near its thermal limits.