Abstract
The compensation of an electrical system from passive compensators mainly focuses on linear systems where the consumption of charges does not vary significantly over time. In three-phase three-wire systems, when the network voltages are unbalanced, negative-sequence voltages and currents appear, which can significantly increase the total apparent power supplied by the network. This also increases the network losses. This paper presents a method for calculating the compensation of the positive-sequence reactive power and unbalanced powers caused by the negative-sequence line currents using reactive elements (coils and/or capacitors). The compensation is applied to three-phase three-wire linear systems with unbalanced voltages and loads, which are connected to an infinite power network. The method is independent of the load characteristics, where only the line-to-line voltages and line currents, at the point where compensation is desired, need to be known in advance. The solution obtained is optimal, and the system observed from the network behaves as one that only consumes the active power required by a load with a fully balanced current system. To understand the proposed method and demonstrate its validity, a case study of a three-phase three-wire linear system connected to an infinite power network with unbalanced voltages and currents is conducted.
Highlights
At present, it is practically impossible to achieve balanced low-voltage distribution systems as these systems, to a greater or lesser degree, are unbalanced
This paper proposes a procedure for compensation by passive compensators formed by reactive elements, to compensate for the positive-sequence reactive power, and the unbalanced powers caused by the negative-sequence currents
The proposed method is valid for systems that are fed with unbalanced voltages, and does not require the characteristics and values of the loads connected to the bus or measurement point
Summary
It is practically impossible to achieve balanced low-voltage distribution systems as these systems, to a greater or lesser degree, are unbalanced. Passive compensators are used to compensate for the reactive and unbalanced power resulting from the negative-sequence current of any three-wire system. Gyugyi et al [25] studied compensation through passive compensators for a three-wire linear system with unbalanced load and balanced voltages For this purpose, they categorised the line currents into symmetric component values, and proposed two delta-connected compensators: one for compensating the imaginary part of the positive-sequence current and the other for compensating the negative-sequence current. Jeon and Willems [30], based on [28], presented a procedure to compensate for only the reactive power through passive compensating circuits, both in star and delta connections This system applied three wires and multi-phase to unbalanced three-phase systems.
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