Induction motors performance study under various voltage sags using simulation

Voltage support in industrial distribution systems in presence of induction generator-based wind turbines and large motors

This paper describes the various characteristics of voltage sags experienced by customers within industrial distribution systems. Special emphasis is paid to the influence of the induction motor load on the characterization of voltage sags. During a fault, an induction motor operates as a generator for a short period of time and causes an increase in sag magnitude. Its reacceleration after the fault clearance results in an extended post-fault voltage sag. The influence of the induction motor on the imbalanced sags caused by single line-to-ground faults (SLGFs) and line-to-line faults (LLFs) has been analyzed in detail. For an imbalanced fault, the induction motor current contains only positive- and negative-sequence components. Induction motors create a low impedance path for the negative-sequence voltage due to an imbalanced fault. This causes a small sustained nonzero voltage with large phase-angle jump in the faulted phase and a voltage drop in the nonfaulted phases with a small phase-angle jump. The symmetrical components of the induction motor during the imbalanced sags have been studied. The results show that induction motor behavior is determined by positive- and negative-sequence voltages during the imbalanced sag.

Starting an induction motor causes voltage sag in the industrial grid that may disturb the operation of grid equipment. Direct-on-line starting is the simplest and most cost-effective method for starting induction motors, but also the most problematic. Large industries often use internal power plants with synchronous generators and starting powerful motors may impact the generator operations. The synchronous generators could be operated with the automatic or manual mode of voltage control. As the operation experience proves, the generator voltage control mode has a significant impact on the transient behaviours in the industrial power grid when starting a large induction motor. This article presents a case study of the synchronous generator tripping within a true medium-voltage industrial grid during the direct-on-line starting of a large induction motor driving the feed water pump. An analysis of the generator protection logs after the tripping showed that the synchronous generator was controlled in manual mode and its protection relay settings were exceeded. The transients initiated by induction motor starts were studied for possible configurations and operating conditions of the grid using a model developed on the Matlab/Simulink Software platform. The simulations have shown that concern about starting large motors in industrial grids containing internal synchronous generators needs to be solved considering the grid configurations and the coordination of generator protection and control devices.

Voltage sags and interruption are one of most important of power quality problems. They can influence performance of equipment such as induction motors. They are generally caused by short circuit faults in transmission and distribution systems which propagate in entire of power systems. When their appear at a motor terminal, its effects are the speed and the torque will decrease to a level lower than values of the normal and even the motor become stall if magnitude of the voltage sags and duration exceed certain limit. The voltage can return to nominal voltage after end of the voltage sag and interruption. The motor will experience re-acceleration to normal condition is accompanied by large inrush current. A study on induction motors was carried out to confirm these effects. Single-phase and three-phase of small induction motors were used for investigating the effects caused by symmetrical voltage sags and interruption through experimental and simulation.

Currently, the voltage sag is the major power quality issue in the power system and in an industry, which are occurred due to loss of load, faults, suddenly energization of the load, transformers and capacitors etc. These voltage sags will not be easily identified by the operators. Therefore, there is need to detect and analyze the voltage sag. In this paper, Wavelet Transform and Artificial Neural Network (ANN) are used for evaluating such voltage sag events. Here, ANN is machine tool which is more compatible for the pattern classification, estimation and other operations.

Motors used in industries are mainly induction motors. This is due to their high torque to volume ratio, ruggedness, robustness and low maintenance. Study of reference frames is essential for the analysis of transient behavior of induction machine. Steady state and transient behavior of squirrel cage induction motors is studied in stationary, rotor and synchronous reference frames under normal and fault conditions as well as tested under varying load torque. Voltage, torque and current waveforms are included in the comparison of the induction motor frames. The study concludes the suitability of the reference frames for different applications. Open loop V/f control for induction motor is implemented after selecting suitable reference frame. The study is done using simulation in MATLAB/SIMULINK.

With the increase in the scale of demand side management (DSM) activities, the load characteristic of power system at the load reduction and recovery times will experience significant changes due to DSM actions and hence affect the dynamic performance of power systems. This paper proposes a methodology to assess the effect of DSM actions on power system network performance — small signal stability of transmission network. A case study of shifting of different type of load from one hour to the other is tested and investigated to what extent the impact of these DSM activities can have on grid performance. A generic 295 bus distribution network and the IEEE standard 9-bus transmission network are used to demonstrate this effect. In the proposed methodology, different types of load sectors (domestic, commercial, industrial) with corresponding mix of load categories (small and large induction motors, constant power, constant impedance and constant current load) in each of them are modelled in DigSILENT/PowerFactory based on typical structure and composition of demand in distribution network. The paper demonstrates and quantifies the impact of the DSM actions on transmission network performance and establish the extent to which DSM can contribute, or otherwise, to power system stability. It will pave the way to development of optimal DSM that will ensure that not only total demand is managed but also the way how it should be managed in order not to endanger network performance in case of disturbances.

Recent power quality (PQ) research shows that the most common types of power quality disturbances are voltage sags and swells in medium and low-voltage distribution grids. This paper shows how to improve two significant power quality disturbances: sags and swells voltage. To find out what effect these two PQ issues have in real life, a study case based on real nonlinear loads data from large induction motors at Beshai Company in Sadat City in Egypt is investigated. The dynamic voltage restorer (DVR) has been suggested as a solution to the voltage swell and voltage sag issues. The point of common coupling (PCC) is linked with the dynamic voltage restorer to mitigate the PQ problems that have been found. The power network, loads, and DVR may all be modeled using the MATLAB/Simulink platform. The jellyfish search optimizer (JFS) is used to get the gain settings of the proportional and integral (PI) controller for the proposed DVR. MATLAB/Simulink's results show that the proposed device is effective, reliable, and has low latency.

Problem statement: ANRPC is a refinery based in Alexandria, Egypt. The plant was subjected to several shutdowns due to tripping of large induction motors, either by under voltage or by over current relays, sometimes by the mechanical protection. The main cause for such unplanned shutdowns was voltage sags. The Dynamic Voltage Restorer (DVR) has recently been introduced to protect the industrial facilities from voltage sags and other voltage disturbances. Existing configurations and control techniques for the DVR aim at protecting industries of high-tech, loads with adjustable speed drives and other power-electronic based loads. Industries with induction motors loads require a complete different approach for the design and control of a suitable DVR. Owing to the inherit inertia of the induction motors and their capability to withstand short-duration, shallow sags, in addition to its tolerance to phase jumps, a DVR with low cost, fast response and simple controller could be configured to fulfill the voltage restoration requirements. Approach: In this study, a simple DVR was proposed, which utilized the classical Fourier Transform (FT) for sag detection and quantification, a controller based on feed-foreword technique which utilized the error signal (difference between the reference voltage and actual measured voltage) to trigger the switches of an inverter using a Pulse Width Modulation (PWM) scheme. The proposed DVR utilized energy from other available feeder or from energy storage unit through a rectifier. Modeling and simulation of the proposed DVR was implemented in the Matlab/Simulink workspace. Results: Simulation results showed that the proposed DVR was efficient in mitigating balanced, unbalanced, multistage and consecutive sags, as well as swells (over-voltages). The main shortcoming of the DVR, being a series device, is its inability to mitigate complete interruptions. Conclusion: The DVR should be configured with respect to the load requirements. With respect to induction motors loads with inherit inertia and insensitivity to phase jumps, the proposed DVR would be of lower cost, simpler controller and faster response.

Large induction motors can have a high inrush and run-up current during starting, often up to ten times the rated current. In weak supplies, this could be a problem, causing system stability issues and the voltage to dip below acceptable levels. In islanded systems, the capacity could be pulled below its maximum. There are several different starting methods possible, but they are often only suitable for smaller machines. One method not investigated is the use of parallel capacitor compensation during the starting because large induction motors are very inductive during the starting sequence, so that supplying reactive power may be more effective than supplying energy. This paper first investigates several different induction motors with increasing size and assesses their compensation requirements in terms of the reactive power requirement during starting. It is shown that they do generally become more inductive as they increase in size. It is illustrated, using simulations, that using parallel capacitors during starting can significantly reduce the starting current. The concept is tested using a small experimental motor. Series inductors are added to the motor to make it more inductive and look more like a larger machine. The experimental results confirm that the method works. It is also found that the parallel capacitors require series filters to prevent harmonic current, and these can be realized using inductors in series with the compensation capacitors. Point-on switching using solid-state relays was tested, and these can reduce the transient switch-on current over the first voltage cycle.

Voltage sag is considered to be the most serious problem of power quality. It is caused by faults in the power system or by the starting of large induction motors. Voltage sag causes about 80% of the power quality problems in power systems. One of the main reasons for voltage sag is short circuit fault, which can be compensated for by a distribution static compensator (DSTATCOM) as an efficient and economical flexible AC transmission system (FACTS) device. In this paper, compensation of this voltage sag using DSTATCOM is reviewed, in which a sliding mode control (SMC) technique is employed. The results of this control system are compared with a P+Resonant control system. It will be shown that this control system is able to compensate the voltage sag over a broader range compared to other common control systems. Simulation results are obtained using PSCAD/EMTDC software and compared to that of a similar method.

With increasing number of inverter-based resources (IBRs) being incorporated into the bulk energy system, their influence on planning and operation of the bulk power system cannot be neglected. Over the past few years, their impact on inertia and frequency response has received a lot of attention. This has been related to the resource's tendency to operate at maximum power point and thus inherently linked to its active power response. However, their large-scale impact on system voltage recovery following a fault has only been minimally studied. Specifically, since inverters are current restricted devices, their impact on slow voltage recovery brought upon by the behavior of induction motors is important to be identified to be able to determine expected interconnection requirements for future inverter resources. In this work, using a large realistic power network, the effect of large-scale integration of IBRs on Fault Induced Delayed Voltage Recovery is studied.

Adjustable-frequency drives have not been widely used with single-phase induction motors. Computations show that, unlike the three-phase induction motor, the single-phase induction motor's slip is not constant with changes in frequency at a constant load torque. A constant volts-per-hertz law is found to provide nearly rated torque over a portion of the upper speed range, but the maximum available torque decays rapidly below about 50% of the base frequency. The behavior of the single-phase induction motor under variable-frequency operation is studied, providing insights to possible scalar control laws for optimizing performance at all speeds. Several possible open-loop control strategies are examined using computer simulations on a 0.5-hp single-phase induction motor. Experimental results show excellent agreement with the analysis and simulation. These experiments provide proof that an adjustable-frequency power supply can be used for speed control of the single-phase induction motor if the motor's unique operating characteristics are accounted for. >

Dynamic voltage restorer (DVR) is conventionally utilized in the electrical distribution system to mitigate the voltage sag and swell on point of common coupling of sensitive consumers. In this paper, a novel DVR based on power electronic transformer (PET) is proposed to mitigate the symmetrical and asymmetrical voltage sag and voltage swell. PET is connected between DC power supply and multilevel inverter to provide transitive DC voltage for DC-link of DVR. PET has effectually and flexibly created relevant DC voltage with required magnitude and low distortion. The performance of suggested DVR based on PET has been evaluated under occurrence of different disturbances in the electrical distribution system. Ultimately, the simulation results have confirmed that DVR-PET can significantly mitigate the symmetrical and asymmetrical voltage sag and voltage swell on sensitive consumers.

This paper proposes a new stray-load loss (SLL) formula for small and medium induction motors (IMs) based on tests data of a 182, 60 Hz IMs in the range of 1-500 hp (0.75-375 kW). They are all tested in accordance with IEEE Std 112-Method B. The proposed formula is validated by recalculating the efficiency of the same number of motors by using the proposed formula, as well as the IEEE Std 112 and the IEC 60034-2-1 standards. Another validation was done on testing 17 additional IMs that are independent of the 182-motor data. In both validations, the new formula demonstrates better accuracy. This formula shows the potential to replace the existing SLL estimation formula for this horsepower range.