Application of 'Line Drop Compensation' to improve voltage of 33 kV distribution network

Abstract

Leanthy Medium Voltage lines are typical in Rural Electrification implementations. The voltae of ends of such lines varies drastically from the time of peak loading to mid-night owing to drastic difference i line loaing in Sri Lanka. Therefore consumers at end of long feeders experience very low voltage during peak loading times. Although distribution transformers come with off-load tap adjustments to buck/boost LV voltage, effective use of the full range of this tap setting is restricted due to high variation of voltage drop during the day day night. Hence these off-load tap adjustment may not fully resolve the low voltage problem of some consumers. However, if voltage at the Grid Substained Medium Voltage bus is dynamically adjusted such that voltage at some mid location of the line is maintained constant irrespective of the line load, deviation of voltage along the line can be minimized, The 'Line Drop Compensation' feature available in MK20 Voltage Regulator provides this feature. Voltage of MV lines of polonnaruwa and suburbs are badly affected due to long distance from Habarana Grid Substation. As a remedy, implementation of LDC in Habarana GSS has been studied. The MV network was modeled and load flow study was carried out with and without LDC for peak and \off-peak times. The voltage profiles so obtained were used for selection of optimum off-load tap of distribution transformers. The study indicates that the line end voltage is greatly improved, particularly in Polonnaruwa and suburbs, with the implementation of LDC. Hence LV terminal voltage of distribution transformers can be improved to provide customers with better voltage. Therefore, the study recommends suitable parameters of LDC for implementation at Habarana GSS. The study also established a methodology for determining LDC parameters and verifying LDC implementation ina GSS having more than one distribution feeder.