Advantages And Disadvantages Of Voltage Sag

In 1980s the Electric Power Research Institute (EPRI) has introduced a new technology program known as Flexible AC Transmission System (FATCS).

Skin and proximity effects are part of formula to calculate cable ampacity known as Neher-McGrath (NM) method in 1957 (Blackledge, O'Connell, Barrett& Sung, 2012, 2012). However this method, according to the authors, could not handle a range of harmonic frequencies. In 1991, Ajit Hiranandani (AH) introduced a way to calculate temperature and ampacity of a cable using generalised finite difference model (Hiranandani, 1991). Hiranandani (1995) produced a paper which tackles the problem of size selection for cable under harmonic condition. In this paper, he introduced term such as harmonic signature (HS), with reference to

Modelling of the series transformer, VSC and LC filter is presented in this section. A time-varying threephase

It is observed that the power factor is maintained closer to unity when the input voltage is reduced from 230V to 110Vrms. Figure 11 (a) and (b) shows the power factor correction of controller for various load condition such as 20% (60W) and 75% (230W). The power factor for the system is found to be 0.84 for light load condition and 0.99 for full load condition. The THD of input current at full load with predominant third and fifth harmonic components are shown in Figure 12(a) and (b).Third harmonics is found to be 4.8% and fifth harmonic component is 4.9% which are well within IEC 61000-3-2 standard during wide range of load variations. The variation in power factor with load is shown graphically in Figure 13(a). It can be inferred from the graph that improved resettable control operates at high power factor for all load condition whereas the conventional PI control has poor power factor under light load conditions. Figure 13(b) shows the comparison between the efficiency of the converter for varying load conditions with the conventional control method and the resettable integrator control. The converter’s efficiency is maintained at 92% for light load conditions and 96% for fully loaded condition with integrator control technique. Thus the improved resettable integrator controller provides a very simple and reliable solution for power factor correction and

The electrical power grid is a network of electrical transmission lines connecting a multiplicity of generating stations to loads over a wide area. The power sent across the network of power lines are used to power everything from homes to automobiles. This is a very challenging process. The most challenging aspect of the operation is that electricity must be generated at the same moment as it used due to the current inability to store it effectively.

Present power system is in need of a high level of redundancy and reliable protection devices along with the periodic maintenance to keep the system healthy. In these circumstances, there is a need for an efficient protection

Fig. 5.12. Control of the dc–dc converter with FLC to produce less power under voltage sag: grid voltages, related grid currents, related dc-link

So, the above issues can be applied to distributed power systems similarly, and the recent research focuses are summarized as follows:

The DVR is one of the most common and effective solutions for protecting critical load against voltage sags [10] [11]. The DVR is a power electronic device used to inject three-phase voltages in series and in synchronism with the distribution feeder voltages in order to compensate for voltage sags. Moreover, it can be efficiently used to augment the fault ride through capability in wind applications. Detection time is an important factor in the voltage restitution process. Fast detection

Problem statement: As the characteristics of the distribution network and high volume power electronics penetration into the network are significantly different from the conventional power system, several issues are raised. Some of the issues, which are a promising field for future research, are described shortly below:

3.1.2 Active Filters: It inject equal and opposite harmonics onto the power system to cancel those generated by other equipment. Remarkable advances in the field of power electronics had sparked interest in APF for harmonic distortion mitigation. The basic technology of APF is to use power electronics technologies to produce the harmonic current components such that the source will supply only the fundamental part of

HVDC transmission may also be selected for other technical benefits. HVDC can transfer power between separate AC networks. HVDC powerflow between separate AC systems can be automatically controlled to support either network during transient conditions, but without the risk that a major power system collapse in one network will lead to a collapse in the second. HVDC improves on system controllability, with at least one HVDC link embedded in an AC grid—in the deregulated environment, the controllability feature is particularly useful where control of energy trading is needed.

The aging of the available infrastructure and increased demand has caused the power supply voltage to become unstable. As a result, there is a need to implement emergency control actions, to prevent blackout (a country-wide power system trip) (Eskom).

In recent years, conversion of ac line voltages from utilities has been dominated by using a single-phase diode rectifier followed by a single switch boost stage. Designers have embraced the usefulness of this topology since it draws a sinusoidal input current and maintains a unity input power factor under varying load

The increase of electronic equipments has caused the increase in the nonlinear loads and due to these loads power quality is being deteriorated. The supply voltage is distorted due to harmonic currents drawn from the supply by nonlinear loads. Distorted currents and voltage cause the user’s equipment to not work properly, conductors will overheat and may decrease the efficiency and life of the equipment. Usually a passive LC power filter is employed to wipe out the current harmonics