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The ride through voltage disturbance of an induction motor (IM) reduces the unscheduled shutdown from processes, and the discriminatory protection allows industries to save time, protect machines and to increase the mean time before breakdown. This paper discusses the analyses of the stability performance of an induction motor under disturbance from voltage sags and short interruptions. The work also addresses the challenge associated with the operation of induction motors of power rating from 3 to 100 kW, during voltage dips, brief interruptions, transient overcurrent, and how to select the induction motors protection for a maximum operating time under such circumstances. The study aims to look for the corrected delay time and peak transient of stator current that protection scheme can handle. It is found that the rising stator current during a voltage disturbance (due to voltage sag and short interruption) can reach the per unit value of stator current up to 18 times, and it is recommended that the delay time should be settled between 100 and 200 msec. Therefore, this study is of great significance to the manufacturing industry where IMs are commonly used as it can avoid damage to the motor. [ABSTRACT FROM AUTHOR]

Let-through energy (LTE) refers to the I2t or Joule energy that a conductor is exposed to during a fault on the feeder. This energy is influenced by the magnitude of the fault current and time it takes for the protection system to clear the fault. If the LTE exceeds the conductor thermal energy limit, the conductor will get damaged. This concept of LTE evaluation is applied to the inverse definite minimum time (IDMT) current based back-up protection elements on a multisource high-voltage feeder in a hypothetical and actual network. Another method to calculate the relay operating time for IDMT relays was developed based on an average disk speed of electromechanical over-current relay and the proportionality of its speed to the magnitude of the fault current. This method was incorporated into a software application to generate results. These results allow the user to evaluate the conductor LTE exposure, total fault time exposure, the effect of instantaneous fault clearing and the application of autoreclose cycles. An energy-area evaluation was applied to quantify and evaluate small protection settings changes. The conclusion is that LTE analysis on back-up protection should be considered for high-voltage feeders to ensure that the conductors are protected. [ABSTRACT FROM AUTHOR]

Methods of accurately determining the efficiency of motors in situ without costly plant downtime are required to implement online motor management strategies that can lead to energy and cost savings. An ideal method must perform in practical power system conditions where there is variation in the supply voltage. An improved non-intrusive compensated slip technique utilising vibration signature analysis has been proposed for accurately estimating induction motor efficiency. The performance of this technique is evaluated through experimental data under ideal and non-ideal supply voltage conditions. The proposed method of estimating motor efficiency is found to be accurate and easy to implement. The proposed technique is robust in under-voltage and over-voltage power supply conditions. [ABSTRACT FROM AUTHOR]

The effectiveness of phase over-current protection cannot be evaluated by using time-current graphs alone. This article develops a method to evaluate and optimize the phase over-current protection on a radial medium-voltage distribution feeder, which can reduce the risk at the point of fault and improves the overall reliability of the feeder. The method is based on the evaluation of protection operating time, let-through energy, pickup sensitivity, and extent of the voltage dips experienced at the point of common coupling due to network faults under high- and low-source impedance conditions. A Microsoft Excel-based software application (Microsoft, Redmond, WA, USA) is developed that incorporates the four evaluation measures under user-definable network criteria. The application illustrates the results in unique, special forms across the analyzed path and allows the benefits of small changes in protection settings to be quantified. The method and software applications are applied in two case studies on an actual distribution network. The results confirm that it is possible to evaluate the effectiveness of the phase over-current protection philosophy using the aforementioned criteria. [ABSTRACT FROM PUBLISHER]

This review paper is focused on common protection challenges related to the integration of distributed generation (DG) into medium voltage (MV) distribution power systems. Protection challenges, as indicated by the general scientific community, are explained and discussed. Based on these challenges, several alternative centralized and decentralized protection alternatives are explained and critically evaluated. Photovoltaic (PV) based distributed generators are connected to the utility grid through inverters, which are able to control active and reactive parts of their output and also limit their fault current contribution. Research is proposed to quantify the risks to protection in conventional power systems with increasing presence of distributed generation. Since the positive, negative and zero sequence current output from PV inverters can be controlled, conventional overcurrent protection using negative and zero sequence current is proposed to increase the protection reliability and maintain coordination in the presence of distributed generators. [ABSTRACT FROM AUTHOR]