Smart Transformer-Based Single Phase-To-Neutral Fault Management

Abstract

The Smart Transformer, with its high control capability, offers new features for optimizing the management of the distribution grid. The ST, controlling the voltage in each phase independently, is able to manage the operations during grid faults, and in particular in the single-phase ones. The ST, when a single-phase to ground fault occurs, can rapidly reduce the voltage in the phase under fault. Thus, it guarantees system safety and operates with the remaining two healthy phases to avoid unnecessary interruption in the healthy lines. However, the two-phase asymmetrical operation challenges the system performances due to the high power 2 nd harmonic ripple in the DC voltage, that reduces the capacitors lifespan, and the high current flowing in the neutral conductor. These issues would force the grid operator to increase the ST maintenance, in order to avoid unplanned faults in the ST hardware, due to failure of aged capacitors. This paper presents a flexible control strategy, based on the phase-shift angle control between two healthy-phase voltages, that reduces the impact of the power 2 nd harmonic oscillation and thus can delay the maintenance intervention. The proposed strategy aims to improve system performances by avoiding neutral-line current overload and attenuating AC side active power (low voltage DC-link voltage) oscillation. Depending on the grid conditions (small DC link capacitance or low ampacity of neutral cable), the voltage angle can be adapted, minimizing the impact of the two-phase operation system in the ST-fed grid. The effectiveness and feasibility of the proposed approach have been validated experimentally with a simplified microgrid setup.

Research on eigenparameters and detection methods for single‐phase‐to‐ground faults in non‐effectively grounded distribution systems

“…According to the strong injectionrelated methods, the resistances could be parallelled at the neutral point or a resistive current could be injected for detection (Master's thesis of Liu Jian). Such methods can effectively enhance the fault detection by amplifying the fault characteristics detection and have an important impact on fault detection and systematic protection for the power distribution system [11][12][13][14][15][16][17]. However, these improvements are only effective for SGF detection in systems detection with low transition resistance.…”

Methodology for Assessment of the Impact of Smart Transformers on Power System Reliability

“…This has been used to reduce the active power which is transferred through the ST to avoid the overcurrent [11]. Application of a 4-leg inverter structure [12] at this side allows for voltage control in each phase independently, which can reduce the common-mode harmonics [13], manage the fault [14,15] and minimize the energy losses in the distribution system [16,17].…”