Analysis of DC offset in fault current caused by machines in a medium voltage distribution network

Abstract

This study presents a study on the time when the short-circuit fault current in an MV distribution network will cross the zero point in the presence of DC offset affected by the local synchronous and/or induction machines. The motivation of the study is to examine using thyristors to bypass a series compensator in the network while the subsequent turning-off of the thyristors depends on the zero-crossing of the current. One of the main uncertainties is the DC offset in the fault current due to the machines connected locally, which may defer the thyristor turning-off. This possibility has been examined in this study and the results demonstrate the parameters of the machines that have most influence on the time when the fault current will pass the zero point. It is shown that machines with higher unit ratings usually cause more delays in comparison with smaller units.

Keywords

• distribution networks
• fault diagnosis
• fault currents
• power distribution faults
• thyristors
• short-circuit currents
• fault current
• zero point
• medium voltage distribution network
• short-circuit fault
• MV distribution network
• local synchronous induction machines
• thyristor
• zero-crossing
• induction machines
• DC offset analysis