Propagation of voltage unbalance from HV to MV power systems

The recently released IEC Technical Report IEC/TR 61000-3-13 for voltage unbalance allocation requires quantitative measures of the propagation of voltage unbalance from higher voltage to lower voltage power systems in terms of transfer coefficients. IEC/TR 61000-3-13 indicates a method for estimating the MV to LV transfer coefficient giving it a value of unity for passive loads in general. This value has been seen to be conservative in the presence of commonly prevailing constant power loads. As a continuation of the work that has been carried out to develop an improved method which overcomes the above limitation for estimating the MV to LV transfer coefficient, this paper addresses the propagation of voltage unbalance from HV to MV power systems. Paper reports on a systematic method for estimating the HV to MV transfer coefficient in terms of system and load characteristics and downstream load composition, which could be considered in future updates of IEC/TR 61000-3-13.