Ideal Site of Shunt FACTS Devices for Power Flow Control in Long Transmission Line

A Power flow control, in an existing transmission line, plays an imperative role in Power System. This study makes use of the Shunt Attached Compensation (STATCOM) FACTS device for the manipulation of voltage and the power flow in a transmission line. The proposed devices are used in different sites such as sending end of the, middle and receiving end of the transmission line. Simulations were carried out using MATLAB SIMULINK software. The apposite location and the performance of the proposed model were examined. In this study a STATCOM is cast off to standardize voltage in a power system. The STATCOM more proficiently boost the voltage stability and upsurge transmission size in a power system. In this study a semblance is also performed between SVC and STATCOM under burden state and it is shown that STATCOM have the adeptness to take care for more capacitive power during a slip over SVC. It is also shown that STATCOM revelations accelerated retort than SVC.


INTRODUCTION
The growth of power electronics brings into operation FACTS devices in power systems.FACTS devices are adept for monitoring the network settings in a very profligate manner and this unique feature of FACTS devices can be put upon to titivate the stability of a system.Power compensation is a critical concern in electrical power systems.For that shunt FACTS devices play a crucial starring role in controlling the reactive power flow to the power network.Hence the system voltage fluctuations and stability remains un-affected.SVC and STATCOM are adherents of FACTS family that are coupled in shunt with the system (Panda and Patel, 2006).Even though the prim devotion of shunt FACTS devices is to support bus voltage by pump out or suck up reactive power, they are also adept of improving the transient stability by increasing or decreasing the power transfer capability when the machine angle increases or decreases, which is realized by operating the shunt FACTS devices in capacitive or inductive mode in a transmission line.
The efficacy of SVC and STATCOM of the identical mark for the augmentation of power flow, they have focused on two or more VSCs are coupled to a DC link modeling converter-based controllers and in their approach they allowed efficient implementation of several VSC in force bounds, where one or more VSCs are loaded to their rated capacity (Hingorani and Gyugyi, 2006).The shunt FACTS devices give supreme benefit from their alleviated voltage backing when seated at the intermediate of the transmission line.The proof of maximum increase in power transfer ability is based on the cut down model of the line being incurred for resistance and capacitance of the line.However, for long transmission lines, when the definite model of the line is considered, the ravages may deviate think through from those found in the abridged model.
This study consists of the comparison of various results found for the different sites on the shunt FACTS device in a long line in view of the tangible models of the line for a stability study.Computer simulation ravages under a lop off ruckus condition three phase defect for different fault clearing times and different sites of FACTS devices are evaluated.It is felt that for the actual long transmission line model with a predefined direction of real power flow, shunt FACTS device needs to be located slightly off-center.Further the site of these devices hangs down on the amount of local load and through the load (Haque, 2000;Tan, 1999).In this study performance strategy were conducted on SVC and STATCOM at different locations such as sending end, middle and the receiving end of the long distance line.In every part of the location the power flow is tested through and devoid of compensation tactics.A mathematical modeling style and check design are presented in the proposed work.The SIMULINK model of the prevailing system is established and tested using MATLAB SIMULINK environment.The firing angle regulation of the thyristor bank firmly decides the peer shunt admittance turned out to the power system (Chandrakar and Kothari, 2003;Masood et al., 2010).

STATCOM:
The STATCOM has a characteristic as shown in Fig. 2. The structure of a STATCOM is shown in Fig. 1b.Typically, a STATCOM consists of a coupling transformer, an inverter and a DC capacitor (Johnson, 2004).In such an arrangement, in ideal steady state analysis, it can be assumed that the active power exchange between the AC system and the STATCOM can be neglected and only the reactive power can be exchanged between them.Have a high regard to bus voltage STATCOM can operate in inductive region or capacitive region from Fig. 2 (Sode-Yome and Mithulananthan, 2004).Fig. 3: Real power at B1, B2 and B3 without compensation Fig. 4: Reactive power at B1, B2 and B3 without compensation is set back to 1 Pu.And also the flaw breaker at bus B 1 will not function during the bus B 1 will not carry out during the simulation.The ravages were attained through and lacking recompense and also the numerical results were tabulated in Table 1. Figure 3 and 4 highlights the real and reactive power control at the three stages when the STATCOM and SVC is not connected i.e., without compensation.B1, B2 and B3 and also tabulated the result in Table 1.The circuit diagram when SVC is connected at the sending end of the long transmission line.Similarly the connections are made when the SVC is connected at the middle and receiving end of the long transmission line.The Real power across buses B1, B2 and B3 with STATCOM at middle end, is shown in Fig. 7.The Real power is occurring at sending end B1 (940.1 MW), Middle end B2 (820.5 MW) and receiving end B3 (806.5 MW) buses, as indicated in Fig. 7.
The Reactive power across buses B1, B2 and B3 with STATCOM at middle end, is shown in Fig. 8.The reactive power is occurring at sending end B1 (-79.97MVAR), Middle end B2 (-37.43MVAR) and receiving end B3 (56.36 MVAR) buses, as indicated in Fig. 8.
The Real power across buses B1, B2 and B3 with SVC at middle end, is shown in Fig. 9.The Real power is occurring at sending end B1 (940.1 MW), Middle end B2 (820.4MW) and receiving end B3 (806.5 MW) buses, as indicated in Fig. 9.
The Reactive power across buses B1, B2 and B3 with SVC at middle end, is shown in Fig. 10.The reactive power is occurring at sending end B1 (-79.95MVAR), Middle end B2 (-37.39MVAR) and receiving end B3 (56.34 MVAR) buses, as indicated in Fig. 10.
The results were getting along and default of compensation.The simulation ravages reveal that the reactive power spawned is outdo at the middle of the transmission line when contrast by means of the further terminates of the line and also the voltage is controlled at the middle of the line.So, the location of SVC is optimum when connected in the middle of the line.SVC performs at the middle end of transmission line.The numerical results of the system analysis were elaborated in the Table 1.

CONCLUSION
To improve the power transfer capability and to control the power flow in the power system network shunt FACTS devices, connect with long distance transmission lines.In this study STATCOM is employed as the shunt FACTS device.SVC is connected at several locations like sending end, middle and receiving end of the transmission line.The ravages were attained through and devoid of compensation.The replications ravage reveals that the reactive power spawned and the voltage control is better in the middle of the line when contrasted with the other ends of the transmission line.The statistical analysis of the system was elaborated in the Table 1 and 2. The Hardware implementation of the optimum location of the shunt FACTS devices for power flow control in long transmission line was done and the results are presented.

Fig. 1 :
Fig. 1: (a) SVC coupled to the line, (b) STATCOM coupled to the line METHODOLOGY Shunt facts devices in power system: Shunt FACTS devices are differentiated into two kinds, namely flexible impedance type and switching converter type.SVC: The SVC uses conventional Thyristors to attain fast check of shunt coupled capacitors and reactors.The structure of the SVC is shown in Fig. 1a, which comes right down with a Capacitor (C) and a TCR.The SVC makes adequate smoother and clear-cut check.It improves the stability of the network and it can be adapted instantaneously to new situations.The main applications in transmission, distribution and industrial networks are: • Keeping of contractual power exchanges with balanced reactive power • Compensation of Thyristor converters e.g., In conventional HVDC lines • Improvement of static or transient stability

Fig. 2 :
Fig. 2: Equivalent circuit of STATCOM with its VI characteristics RESULTS AND DISCUSSION Description of STATCOM and SVC: The power grid made up of two 500 KV counterparts, individually 3000 MVA and 2500 MVA, associated with a 600 km long line.When the STATCOM is not in maneuver, the normal power flow on the line is 925.8MW from bus B1 to B3.The device has a mark of +/-100 MVA.This STATCOM is a phase model of a typical three-level PWM STATCOM.STATCOM is coming up through a DC link nominal voltage of 40 KV through a parallel capacitance of 375 µF(Sharma et al., 2007) On the AC side, its total corresponding impedance is 0.22 Pu on 100 MVA.This impedance typifies the transformer trickle reactance and the phase reactor of the IGBT Bridge of a definite PWM STATCOM(Salemnia et al., 2009;Garg and Kumar Agarwal, 2012).

Fig. 5 :
Fig. 5: Voltage V m of SVC and STATCOM at middle end

Table 1 :
Comparison of P and Q at B1, B2 and B3 with SVC Simulation results: Initially V ref is set to 1 Pu; at t = 0.2 sec, V ref is decreased to 0.97 Pu; then at t = 0. 4 sec, V ref is increased to 1.03; and finally at 0.6 sec, V ref

Table 2 :
Comparison of P and Q at B1, B2 and B3 with STATCOM

Table 2 .
The numerical results of the system analysis were elaborated in the Table1 and 2.