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An analytical method for voltage sag profile estimation of a power system with STATCOMs
Published in Rodolfo Dufo-López, Jaroslaw Krzywanski, Jai Singh, Emerging Developments in the Power and Energy Industry, 2019
Qingbin Wang, Ri Cai, Yun Yang, Hui Huang, Xiongkeng Zhan, Chuangdao Li, Gai Li, Rongqin Huang
Voltage sag is defined as a short-duration reduction of the root mean square value of the voltage that is mostly caused by faults in the power system (Bollen 2000). The voltage sag profile is defined as the voltage sag performance of all system buses during a given fault event, and short-circuit calculation is commonly used for voltage sag profile estimation (Cruz et al. 2015). In order to assess the impact of STATCOM installation on voltage sag and allocate STATCOM reasonably, including a STATCOM model in the voltage sag profile estimation is essential. Many studies has been conducted for power flow (Kazemtabrizi & Acha 2014), optimal power flow (Zhang et al. 2001), and stability analysis of a power system with STATCOMs (Zhang et al. 2006), but few studies addressed the voltage sag profile estimation problem. In the past, electromagnetic transient model simulation was often used to assess the voltage sag in the system with STATCOM (Ramamurthy et al. 2018). Although a detailed electromagnetic transient model can provide an accurate voltage waveform during both the transient and steady state of power system, it is unnecessary and impractical for voltage sag profile estimation of a large system because of the time-consuming process of build electromagnetic models Milanovic and Zhang (2010) is a pioneer work that modeled STATCOM and included it in short-circuit calculation equations. However, the method may not be feasible in the case of multiple STATCOMs connected in the system situation because the injected current of STATCOM needs to be calculated beforehand.
Customers: Electric Service Requirements
Published in J. Lawrence, P.E. Vogt, Electricity Pricing, 2017
Transients and surges are extremely short duration voltage excursions. High impulse voltages can destroy sensitive electrical and electronic components. Other momentary events include sags or dips in the voltage, as shown in the upper graph of Figure 4.4. Voltage sags are commonly caused by system short circuits or by switching on a large magnitude of load. When a large induction motor is energized, the starting or inrush current causes a momentary voltage sag. Such voltage irregularities can be noticed as flicker, a fluctuation in the output of a light connected to the same electrical source. The supply voltage may also momentarily swell above its nominal rating as a result of system fault current (i.e., short circuit) conditions, as shown in the lower graph of Figure 4.4. Generally, short duration voltage aberrations last less than a minute and often less than a second.
Power Quality in Buildings
Published in Moncef Krarti, Energy-Efficient Electrical Systems for Buildings, 2017
The voltage sag occurs when the root mean square (rms) voltage value decreases over a limited time period before it settles and returns to its average value. There are several types of sags including (Caramia et al., 2009)Instantaneous sags lasting typically from 0.5 to 30 cyclesMomentary sags that can last 30 cycles to 3 sTemporary sags that last 3 s to 1 minIf the sag lasts for more than a minute, it is then classified as an undervoltage. A voltage sag is generally caused by a short-circuit fault or by a sudden change in the characteristics of a load, such as the case during the starting of a motor. If the voltage does sag, some equipment may not be supplied with the amount of voltage they require and their performance may be affected (Kusko and Thompson, 2007). Figure 11.1 provides a typical time variation of voltage during a sag event.
Identification of the Area of Vulnerability to Voltage Sags Based on Galerkin Method
Published in Electric Power Components and Systems, 2019
Yongzhi Zhou, Hao Wu, Boliang Lou, Hui Deng, Yonghua Song, Wen Hua, Yijun Shen
Voltage sag is defined as a decrease in rms voltage to between 0.1 pu and 0.9 pu from 0.5 cycles to 1 min in IEEE-1159 standard [1]. The voltage sag occurs when interruptions take place in power systems, which may be caused by power system faults, equipment failures, or control malfunctions. For sensitive equipment, the voltage reduction will cause abnormalities or trips, which may result in huge financial losses. Moreover, the system interruptions may be preceded by the response of sensitive equipment to voltage sags, posing threaten to the safety of system operation. For example, the line-commuted-converter (LCC) based high-voltage direct-current (HVDC) systems may suffer commutation failure faults, when voltage sag occurs at the bus to which the HVDC system is connected [2, 3]. To establish countermeasures effectively, it becomes an increasingly important issue to assess the performance of system voltage sag problems.
Discriminatory Protection Analysis of Three-Phase Asynchronous Motors During Power Disturbances
Published in Electric Power Components and Systems, 2019
Nsilulu Tresor Mbungu, Ramesh C. Bansal, Raj M. Naidoo, Mandangi Jean-Pierre Bazolana
The guidelines for calculating the cost of the disturbances are provided by IEEE standard 1346–1998, which describes losses resulting from unplanned breakdowns, lost production and damage to equipment. The potential costs have to be carefully evaluated before consigning a particular stakeholder business case. The devices and equipment in all areas may be affected by the different magnitudes of voltage sags. Moreover, the voltage sag can be evaluated case-by-case according to each event and the disturbance costs [5]. The performance evaluation of induction motors during and after voltage sags can reduce any damage due to unplanned breakdowns through voltage disturbance [31]. However, the improvement of voltage disturbances depends on the usage by end-users as well as their operating costs [7].
An improved sag detection approach based on modified Goertzel algorithm
Published in International Journal of Electronics, 2019
Ehsan Najafi, A.H.M. Yatim, Amin Mirzaei
Sag can be defined as a decrease between 0.1 and 0.9 pu in RMS voltage or current at the power frequency for durations of several milliseconds to 1 min (IEEE Recommended Practice for Monitoring Electric Power Quality, 1995). The value of voltage sag is defined by the magnitude of actual voltage during the disturbance. There are many causes for voltage sag such as grid faults, inrush currents and starting of large motors. These problems arise from utility of customer side. Lightning may also lead to a voltage sag (Naidoo & Pillay, 2007; Polajz, Rtumberger, & Dolinar, 2015). Although there are many methods nowadays to mitigate this power quality problem such as dynamic voltage restorer (DVR) (Kassarwani, Ohri, & Singh, 2017) and STATCOM (Deben Singh, Mehta, Singh, & Meng, 2016), the key part in these equipments is sag detection algorithm. Some algorithms face some constraints and are sophisticated for implementation, while others may lack precision or speed of detection (Jian, Cao, Jintao, & Yinge, 2017).