Abstract
The phenomenon responsible for the different apparent powers measured in a subsystem of a three-phase star-configured system, based on the voltage reference point, was identified in this paper using specific components of the instantaneous powers, as a result of applying the conservation of energy principle to the entire system. The effects of the phenomenon were determined using a proposed apparent power component referred to as the neutral-displacement power, whose square is the quadratic difference between the apparent powers of a subsystem, measured using two voltage reference points. The neutral-displacement power is a component of the apparent power, which is determined using the values of the zero-sequence voltages and the line currents in that subsystem. Expressions of the proposed power were derived using the Buchholz apparent power formulations. The validation of the derived expressions was checked in the laboratory and in a real-world electrical network, using a well-known commercial analyzer and a prototype developed by the authors.
Highlights
In electrical power instrumentation, the apparent power measured by a power analyzer placed at the point of common coupling (PCC) of two subsystems of a three-phase power system (Figure 1)generally varies with the selected voltage reference point, a neutral point (N) of subsystem 1, a neutral point (n) of subsystem 2, or a grounding point (G)
8, the the apparent apparent powers powers measured. It should the neutral point of the load (n) was used as the voltage reference point (58,385.30 VA) were slightly higher than the apparent powers measured at the PCC using the source neutral point (N) as the the voltage reference reference point point (58,382.40 VA)
The phenomenon associated with the apparent power differences measured in each subsystem of a three-phase star-configured power system, depending on the point used as the voltage reference, was examined in this paper
Summary
The apparent power measured by a power analyzer placed at the point of common coupling (PCC) of two subsystems of a three-phase power system (Figure 1). Generally varies with the selected voltage reference point, a neutral point (N) of subsystem 1, a neutral point (n) of subsystem 2, or a grounding (earthing) point (G). This phenomenon is relevant when measuring, for example, the apparent power of one of the subsystems and the corresponding neutral point (N or n) is not accessible, such as may occur in a star-connected three-phase motor with only three terminals, or when the neutral points are far from the measurement point
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