A new thyristor-controlled reactor scheme is presented in this paper, in which the total bank is split into one Δ- and one Y-connected reactor bank with the addition of a low-rating zig-zag autotransformer, instead of the conventional scheme using a Δ-connected reactor bank with a harmonic current filter. This arrangement prevents the triplen harmonics generated by the Y bank from entering into the supply system and at the same time, the combination results in cancellation of some major characteristic harmonics from the source current. Thus, without using any additional filters or phase-shifting two-winding transformer, this scheme facilitates reactive power control over a wide range and also meets the requisite harmonics standards. The scheme is simple and provides a cost-effective solution to the VAr compensation problem. Simulation and experimental results are provided to validate the proposed concept.

A New Harmonic Reduced Three-Phase Thyristor-Controlled Reactor for Static VAr Compensators

A three-phase three-wire thyristor controlled reactor (TCR) topology is presented comprising of two reactor banks, involving simultaneous firing angle control of both banks having maximum kVAr in the ratio of 60:40. The first reactor bank is “ Δ ” connected and has phase switching whereas the second reactor bank is either “ Δ ” or equivalent “ Y ” connected with line switching. Such an arrangement prevents the triplen harmonics from entering into the supply system and some major characteristic harmonics can also be eliminated from the TCR line current due to the selection of the ratings of the two reactor banks. Thus, without using any additional filters or phase shifting transformer, this scheme enables reactive power control with a low current total harmonic distortion (THD) over a reasonable range of control, meeting requisite harmonics standards. Simplicity in construction and operational requirements of the proposed topology makes it a viable and cost effective solution. Its modeling, analysis, and performance assessment are presented. Simulation and experimental results support the theoretical proposition.

Harmonic Cancellation in a Three-Phase Thyristor Controlled Reactor Using Dual Banks

The conventional “Delta” connected thyristor-controlled reactor (TCR) bank used for static var compensation and other applications is proposed to be split into two identical “Delta” banks each having kvar capacity half of the total TCR capacity. The study presented shows that such combination of two identical “Delta” connected reactor banks, one with phase switching by thyristors and the other with line switching thyristor arrangement can effectively reduce the harmonic generation of the TCR. Since both the three-phase banks are connected in delta, the zero sequence triplen harmonics generated due to phase control of thyristors remain trapped inside the delta, thus reducing the harmonic injection into the power system. Further, some other major characteristic harmonics are also minimized in the TCR line current. Thus, the proposed TCR yields a low current THD which meets the requisite harmonics standards and it can therefore be used as an economic solution for reactive power control over a reasonable range in high power grid without using any external harmonic filter or special phase shifting transformer. This paper describes in detail the modeling, analysis, and performance assessment of the proposed scheme. Simulation results are furnished to evaluate the output characteristics of the scheme under varying operating conditions. Finally, experimental results are presented, which proves the theoretical proposition.

Dual Delta Bank TCR for Harmonic Reduction in Three-Phase Static Var Controllers

A thyristor-controlled reactor (TCR) has been investigated and developed for a VAR compensator. Its application to industry is put into practice. This system has, however, inherently a disadvantage of generating many lower-order harmonic currents. Some countermeasures to reduce harmonics have been proposed up to the present day. The TCR based on an asymmetrical firing control (AFC-type TCR) has been already proposed for one of the positive countermeasures by the authors. The paper presents the systematic design procedure of the setting of firing angles which satisfy the design specifications of the TCR; that is, each harmonic, the total content of the harmonics and the capacitances of the thyristor and reactor. The use of computer-aided design (CAD) for the choice of firing angles is developed in accordance with the above procedure. Furthermore, the limit of harmonic reduction of the TCR based on an asymmetrical firing control and the effect of multiplexing units on the harmonic reduction are also discussed for the use of CAD.

Design procedure of firing angles for harmonic reduction in a thyristor-controlled reactor by asymmetrical firing control

A 3-phase 3-wire thyristor controlled reactor topology is presented comprising of two banks, involving thyristor switched and controlled coupled reactors (TSCCR), one bank of which is “Δ” connected and the other being “Y” connected. Each TSCCR comprises of a reactor with two well coupled identical sections, two main thyristor back-to-back switches and an auxiliary thyristor switch such that the two sections can be either connected in parallel or in series. The ratio of the effective reactor values between the “Δ” bank phase and that of the “Y” bank, as well as the condition when and which switch shall be used for phase control, are selected from an optimization process. Such an arrangement prevents the triplen harmonics from entering into the supply system and some major characteristic harmonics are also eliminated from the source current. Thus, without using any additional filters or phase shifting transformer or oversized reactors, this scheme enables reactive power control with a low current total harmonic distortion over a wide range of kVAr control. Simplicity in construction and operational requirements of the proposed topology makes it a viable and cost effective solution. Its modeling, analysis, and performance assessment are presented, supported by simulation and experimental results.

A Wide-Range TCR With Low-Current THD by Optimized Combination of Coupled Reactors and Thyristor Switching and Control

Owing to discontinuous current in a thyristor-controlled reactor (TCR) of a static VAR compensator, harmonic currents are generated in the supply system. The paper presents a new method for reducing these harmonics. In the method used, the TCR is fed through the sequentially controlled transformer taps. Two alternative approaches of sequence control of transformer taps are described. The feasibility of the proposed method has been verified experimentally.

H.K. Patel

Papers

Harmonic reduction in the static VAR compensator by sequence control of transformer taps