Coefficient of Voltage Energy Efficiency

Abstract

The reduction of greenhouse gas emissions is a major contemporary challenge. This has prompted the requirements concerning energy efficiency for ships, among other things. Improvement in efficiency of ship operations could be achieved by reducing unnecessary power consumption by induction motors. Specifically, the occurrence of power quality disturbances, such as frequency and voltage deviations, voltage unbalances, and voltage harmonics, can cause an extraordinary increase in the power losses occurring in induction motors, as well as an unnecessary increase in the output power. Furthermore, excessive power quality disturbances are often interconnected with failures of on-board equipment, and in extreme cases, these may even pose a threat to safety at sea. Consequently, strict power quality monitoring of on-board microgrids can also contribute to improving safety while afloat. In this study, a dedicated tool for power quality monitoring is proposed, namely the coefficient of voltage energy efficiency, which has a value proportional to the power losses occurring in induction motors under power quality disturbances. INDEX TERMS Energy efficiency, induction motors, marine technology, power systems, power quality.

Power Quality and Energy-Efficient Operation of Marine Induction Motors

“…This example demonstrates that the impact of PQ disturbances on electric motors depends on the motor load characteristics as well as the disturbance itself. This justifies the proposed mathematical model of cvee coefficient [16]. The calculated value of the coefficient is presented in Fig.…”

“…For the limited values, the coefficient cvee is up to 1.13. It should be noted that the mathematical description of the coefficient considers an increase in the load torque due to an increment in the rotational speed [16]. At the same time, the requirements given in [25] concern motors working with constant torque.…”

“…As a result, even PQ disturbances within the limit prescribed by [9]- [12] exert a deleterious effect on various elements of ship power systems, including induction motors. In induction motors, they cause, among other things, an increase in power losses and overheating [13]- [16]. According to the authors' investigations, PQ disturbances may even result in about a 50% increase in power losses in comparison to the nominal supply.…”

“…Under these new circumstances, now is good time to consider a power quality-related index, to complete the EEDI idea. In a previous study [16], a tool dedicated to assessment of PQ from the point of view of energy-efficient operation of induction motors was proposed and experimentally verified-namely a coefficient of voltage energy efficiencycvee (its mathematical description is presented in the Appendix). The cvee coefficient is a synthetic PQ factor, whose value is proportional to power losses occurring in induction motors due to PQ disturbances.…”

“…For purely sinusoidal, balanced voltage of the rated value and frequency, the coefficient takes the value cvee = 1.00. An increase in power losses in induction motors due to PQ disturbances is reflected by the value of the cvee coefficient [16]. It is worth mentioning that the increase in mechanical output power due to PQ disturbances significantly affects ohmic power losses in a motor, and consequently is also reflected by the value of the coefficient of voltage energy efficiency [16].…”