Analysis, Modeling, and Simulation of the Phase-Hop Condition in Transformers: The Largest Inrush Currents

Abstract

Inrush currents in transformers can have very disruptive effects, such as voltage sags, false tripping of the protective devices, and mechanical stresses in the transformer windings. This paper shows that there are operating situations that may cause a transformer to draw abnormally high inrush currents. Examples include the normal operation of offline uninterruptible power-supply (UPS) systems, interruptions, voltage sags, and notching. These conditions may produce inrush-like currents of more than twice the value of the "normal" maximum inrush caused by energizing at voltage zero-crossing. For this condition, the term "phase-hop" is used in this paper. Laboratory experiments were performed on four different transformers (1 kVA) with varied characteristics and show the impact of phase-hop in the magnitude of inrush currents. The experiments are also used to validate the Electromagnetic Transients Program model used for the analysis of multiple cases. In addition, the behavior of the magnetic flux in a transformer under phase-hop is investigated and compared with different operating conditions using finite elements. The results of this paper have implications in transformer design and in the operation and design of UPS systems to prevent the damaging effects of phase-hop.

In-Rush Current Mitigation on Toroidal Transformers with Composite Cores

“…Inrush current is a transient scenario, where the high saturation of the transformer core originates high inrush current at the point of energization. Basically the input voltage applied to the transformer will be the driving force for the inrush current and that will force the flux to build up double the steady state flux plus the remanence flux [4]. Therefore, the transformer drives into deep saturation condition resulting a high energization current [12].…”

“…As a result, the overcurrent protection reacts for these high currents and trips the device from the source more often, resulting in inability to energize the equipment. Also the inrush current will result in significant voltage drops, and thus affect the power quality, reliability, and stability [2] [4].…”

ADRC Performance in Power Control of DFIG used in Wind Turbine During Grid Voltage Fault

“…If the variation of voltage wave is more important, the functioning of some electrical machines connected to the grid such as wind turbines, production plants, domestic appliances, industrial machines, may be disturbed. In the most extreme cases, this can range from the impossibility of operating during the duration of the disturbance [5], to longterm material damage or, more rarely, to instantaneous material damage. To sum-up we can distinguish the following grids default type, each disturbance has a specific effect on the network or on the electrical device:…”

A Novel Transient Current Limiter Based on Three-Phase Thyristor Bridge for Y-yg Transformers

“…By explaining the lessened request mathematical statement, i(t) can be communicated by the accompanying comparison and t 1 is the beginning moment. In this circumstance, substituting the i max in i (t), (18) is communicated as [10] …”