Survey of Methods for Reactive Power Injection to Sub-transmission Voltage Level by MV Shunt Capacitor Banks

In the African country of Niger, as a different method, the shunt capacitor banks are installed at distribution voltage levels (۲۰ kV and ۳۳ kV) for reactive power injection to the sub-transmission voltage levels (۶۶ kV and ۱۳۲ kV). This is due to some economical and technical reasons, such as low short-circuit level of the electrical grid and the small size of capacitor banks, ease of operation, repair and maintenance. These banks are connected to the sub-transmission voltage bus via power transformers. In ۱۳۲/۳۳-۲۰ kV Dosso substation in Niamy (the capital of Niger), the mentioned arrangement is applied. The aforesaid substation is now under construction according to the general single-line diagram of the project's employer, NIGELEC. In this substation, considering the features of connecting the capacitor banks to the ۱۳۲ kV switchgear (via a power transformer), there are two methods for power factor control of ۱۳۲ kV bus which one is by means of generating constant reactive power (holding constant number of energized capacitor banks in each specified condition) and transferring the reactive power via On Load Tap Changer (OLTC) of power transformer and the other one is generating variable reactive power via capacitor banks switches (interrupters). In this paper, three criteria including voltage change value, the harmonic resonance occurrence probability and the ferro-resonance occurrence probability are applied for comparing two above mentioned methods and the optimized control procedure is suggested.