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This paper deals with the design methodology for cascaded multilevel converter (CMC)-based transmission-type STATCOM(T-STATCOM) and the development of a +/- 12MVAR, 12 kV line-to-line wye-connected, 11-level CMC. Sizing of the CMC module, the number of H-bridges (HBs) in each phase of the CMC, ac voltage rating of the CMC, the number of paralleled CMC modules in the T-STATCOM system, the optimum value of series filter reactors, and the determination of busbar in the power grid to which the T-STATCOM system is going to be connected are also discussed in this paper in view of the IEEE Std. 519-1992, current status of high voltage (HV) insulated gate bipolar transistor (IGBT) technology, and the required reactive power variation range for the T-STATCOM application. In the field prototype of the CMC module, the ac voltages are approximated to sinusoidal waves by the selective harmonic elimination method (SHEM). The equalization of dc-link capacitor voltages is achieved according to the modified selective swapping (MSS) algorithm. In this study, an L-shaped laminated bus has been designed and the HV IGBT driver circuit has been modified for the optimum switching performance of HV IGBT modules in each HB. The laboratory and field performances of the CMC module and of the resulting T-STATCOM system are found to be satisfactory and quite consistent with the design objectives.

In this research work, the design and implementation of a 154-kV +/- 50-Mvar transmission static synchronous compensator (T-STATCOM) have been carried out primarily for the purposes of reactive power compensation and terminal voltage regulation and secondarily for power system stability. The implemented T-STATCOM consists of five 10.5-kV +/- 12-Mvar cascaded multilevel converter (CMC) modules operating in parallel. The power stage of each CMC is composed of five series-connected H-bridges (HBs) in each phase, thus resulting in 21-level line-to-line voltages. Due to modularity and flexibility of implemented HBs, each CMC module has reached a power density of 250 kvar/m(3), thus making the mobility of the system implementable. DC-link capacitor voltages of HBs are perfectly balanced by means of the modified selective swapping algorithm proposed. The field tests carried out at full load in the 154-kV transformer substation where T-STATCOM is installed have shown that the steady-state and transient responses of the system are quite satisfactory.

The variable frequency operation of the coreless induction melting furnace has been investigated in detail both theoretically and experimentally. The time variations of the operational impedance value of the induction melting furnace, owing to the time-varying resonance frequency and crucible conditions, have been derived for typical melting cycles by using a variable, parallel RLC model derived from extensive field measurements. The work coil and its crucible is supplied at variable frequency from a multi-pulse rectifier and a current-fed, load resonant inverter cascade. Uncharacteristic current harmonics caused by cross modulation phenomenon across the AC-DC-AC link have been derived theoretically, and verified by field tests. These theoretical results and extensive field measurements on a sample induction melting furnace installation have shown that i. the major power quality problem of an induction melting furnace as a load on the power system, is the injection of various characteristic and uncharacteristic current harmonics to the grid, ii. line currents on the supply side are nearly balanced, iii. flicker contribution is below the limits specified in the standards, iv. reactive power demand is relatively low and the variations in the magnitude and rate of change of active power are not drastic, and v. no voltage sag and swell phenomena arising from furnace operation occur.

Electrical power quality (PQ) data is one of the prevalent types of engineering data. Its measurement at relevant sampling rates leads to large volumes of PQ data to be managed and analyzed. In this paper, an extensible database architecture is presented based on a novel generic data model for PQ data. The proposed architecture is operated on the nationwide PQ data of the Turkish Electricity Transmission System measured in the field by mobile PQ monitoring systems. The architecture is extensible in the sense that it can be used to store and manage PQ data collected by any means with little or no customization. The architecture has three modules: a PQ database corresponding to the implementation of the generic data model, a visual user query interface to enable its users to specify queries to the PQ database and a query processor acting as a bridge between the query interface and the database. The operation of the architecture is illustrated on the field PQ data with several query examples through the visual query interface. The execution of the architecture on this data of considerable volume supports its applicability and convenience for PQ data. (C) 2009 Elsevier Ltd. All rights reserved.

In this research work, design and implementation of a 154 kV, +/- 50 MVAr Transmission STATCOM (T-STATCOM) has been carried out primarily for the purposes of reactive power compensation and terminal voltage regulation, and secondarily for power system stability. The implemented T-STATCOM consists of five 10.5 kV, +/- 12 MVAr Cascaded Multilevel Converter (CMC) modules operating in parallel. The power stage of each CMC is composed of five series connected H-Bridges (HB) in each phase, thus resulting in 21-level line-to-line voltages. Due to modularity and flexibility of implemented HBs, a CMC module power density of 250kVAr/m(3) is reached, thus making the mobility of the system implementable. DC link capacitor voltages of HBs are perfectly balanced by means of the Modified Selective Swapping Algorithm proposed. The field tests carried out at full load in the 154 kV transformer substation where T-STATCOM is installed and put into service have shown that the steady-state and transient responses of the system are quite satisfactory.

This paper deals with the development and implementation of a current-source-converter-based static synchronous compensator (CSC-STATCOM) applied to the volt-ampere-reactive (VAR) compensation problem of coal mining excavators. It is composed of a +/- 750-kVAR full-bridge CSC with selective harmonic elimination, a low-pass input filter tuned to 200 Hz, and a Delta/Y-connected coupling transformer for connection to medium-voltage load bus. Each power semiconductor switch is composed of an asymmetrical integrated gate commutated thyristor (IGCT) connected in series with a reverse-blocking diode and switched at 500 Hz to eliminate 5th, 7th, 11th, and 13th current harmonics produced by the CSC. Operating principles, power stage, design of dc link, and input filter are also described in this paper. It has been verified by field tests that the developed STATCOM follows rapid fluctuations in nearly symmetrical lagging and leading VAR consumption of electric excavators, resulting in nearly unity power factor on monthly basis, and the harmonic current spectra in the lines of CSC-STATCOM at the point of common coupling comply with the IEEE Std. 519-1992.