Voltage unbalance has been interpreted in a number of ways based on the conditions and complexities that are involved. This paper takes the widely used expression of voltage unbalance factor (VUF) and puts forward the various ambiguities that arise due to voltage variation and unbalance when applied to a test case. If the results are not properly interpreted, they affect decision making with regard to motor derating and protective system settings. It is also shown that various voltage combinations are possible for a particular VUF. By fixing an upper limit so as to signify the upper limit, a simple solution by way of conceptual interpretation is suggested to overcome the same. The discussion that is put forward is supported by a test case.

A Novel Approach Toward Interpretation and Application of Voltage Unbalance Factor

Centrifugal pumps are the most widely used ac-motor-driven pump systems mainly for water pumping applications. Due to increasing and varying load demand, voltage variation and unbalance is a reality and has to be dealt with carefully. Studies on motor-driven systems under conditions of voltage unbalance have either neglected or maintained constant magnitude of the rotational loss component and focused only on the motor performance while system side performances have not been discussed generally. This paper presents the experimental results of a three-phase induction motor-pump system subjected to voltage and load variations with a view to justify that knowledge of voltage and load variations are very much essential for better result analysis.

Effect of Voltage and Load Variations on Efficiencies of a Motor-Pump System

The air gap torque (AGT) method is a well established technique for determining the efficiency of an induction motor, yet there are still discrepancies in the literature when applying the method. Additionally, the AGT method is known to be highly accurate, however, it is considered to be too intrusive for industry applications. To resolve this, the efficiency of an induction machine can be estimated non-intrusively by implementing the non-intrusive air gap torque (NAGT) method. The NAGT method combines various estimation techniques to determine the stator resistance, rotor speed and losses non-intrusively. However, due to the various estimation techniques associated with this method, the accuracy of the method is compromised. This paper assesses the various methods for estimating these parameters. It proposes a technique for improving the estimation of SLLs and addresses the discrepancy, as seen in literature, in interpreting the AGT method. Efficiency results from the NAGT method are compared to the IEC Std 34-2-1 and direct methods. The effects of voltage supply unbalances on efficiency estimation using the NAGT method are also examined. Lastly, an error analysis is conducted on experimental data to investigate the effects of instrumental errors on efficiency determination using the IEC Std 34-2-1, direct and NAGT methods.

Considerations for improving the non-intrusive efficiency estimation of induction machines using the air gap torque method

This paper investigates factors which influence the power quality performance of the Dhofar Power Grid, based upon the first 50MW wind farm project connection. The wind farm consists of 20×2.5 MW wind turbines and will be integrated into the 132kV Dhofar network which is connected with the Maim Interconnected System via the Petroleum Development of Oman grid. As this is the first wind farm project in Oman, a review of fundamental aspects which influence power quality for connecting the wind farm is presented, as well as an initial view on Grid Code performance. The power quality assessment is required as part of the license obligation for a transmission operator and is vital to a wind farm developer for their filter design and compensation sizing. The paper addresses power quality topics such as voltage unbalance, flicker and harmonic compliance, in relation to network changes and potential future non synchronous connections. Simulation studies are carried out in DIgSILENT software and are presented in the paper.

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Power quality of Dhofar network with 50 MW wind farm connection

Globally, there is a drive toward ensuring energy efficiency in all aspect of production operations and power supply systems. Industries are the backbone of our modern word, and a significant percentage of industrial operations are motor driven. Three Phase Induction Motor is massively deployed in industries due to its ruggedness, reasonable cost and ease of maintenance. The energy efficiency of the induction motor is affected by the internal configurations of the motor and the nature of the supply. Power supply fluctuations result in power quality issues and its attendant negative effects on equipment operation. This research, studies the cost and performance implication of the effects of balanced over voltage, balanced voltage, balanced under voltage and unbalance voltage on the operation of the three phase induction motor using the peculiarities of Nigeria. The result shows that, there is an increase in operational cost due to increased energy loss in the windings as a result of voltage variations from the balanced state, with balanced over voltage operation showing more cost severity among the voltage variations considered.

Cost implication of Line Voltage variation on Three Phase Induction Motor operation

Availability of quality power has become an important issue for industrial utilities due to frequent performance variations in process industries. Increase in the generating capacity has not kept up pace of power demand, which results into shortage of power supply and power system network is normally subjected to varying and unequal loads across the three phases. Continuous variation of single-phase loads on the power system network leads to voltage variation and unbalance, most importantly; the three-phase voltages tend to become asymmetrical in nature. Application of asymmetrical voltages to induction motor driven systems severely affects its working performance. This paper presents the effects of voltage variation and unbalance on the performance of an induction motor driven centrifugal pump with a case study.

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Giridhar P Kini

Papers

Impact of voltage unbalance on the performance of three-phase induction motor