Barbara Kulesz

Multi-phase rectifier transformer and their impact on traction lines voltage quality

To transform power grid three-phase ac voltage into tram traction lines dc voltage, multi-phase rectifier-transformer systems are used. Operation of 18- and 24-pulse systems is investigated in this paper, taking into account different supply conditions. Numerical simulations and laboratory tests have been run in order to check which system is the least sensitive to fall in power grid voltage quality.

Effectiveness of different designs of 12- and 24-pulse rectifier transformers

Investigation of effectiveness of different designs of rectifier transformers of tram traction substations has covered issues such as transformer weight, rated power and efficiency and traction line voltage quality. Mathematical models have been created and time and frequency domain analysis has been run as well as power, voltage and current calculations for steady-state conditions. It is pointed out that transformer weight may constitute the most significant criterion for system selection, since under non-ideal supply conditions rectified voltage quality is comparable for different transformer types.

Impact of Hall sensors positioning on symmetry of BLDC control signals

The paper presents results of investigating symmetry of signals used to determine motor shalt angular position and generated by two different sensors. One group of sensors was built into the motor and consisted of six single Hall sensors placed inside rotor slots. The other group consisted of six Hall sensors positioned in the same way as in the first group with respect to each other, but assembled outside the motor and operating with additional magnet device (independent magnetic field source) mirroring rotor magnets. A special dedicated recorder was constructed, helping to record durations of different shaft positions. Exemplary efficiency curve of the motor is shown, depicting efficiency vs. control angle shift. Investigation of motor efficiency was conducted for wide range of control angles, in the neighbourhood of one particular angle where efficiency is maximum.

Influence of diode commutation processes on rectifier transformers operation

To obtain rectified voltage needed for d.c. traction networks, different types of energy transformation circuits may be used. This paper deals with 6- and 24-pulse transformer-rectified set operation under different supply condition. Commutation issues have been investigated for Yd transformer supplied with sinusoidal and distorted voltage. It has been shown that supply voltage THD factor affecting rectified voltage quality is not sufficient to examine voltage transformation extensively; phase angles of the harmonics have been researched as well and their impact on commutation processes presented. For 24-pulse system it has been shown that transformer windings connection scheme giving the desired phase shifts between secondary side voltages is not sufficient to achieve 24 pulses in rectified voltage. Due to commutation processes in uncontrolled diode bridges, this system produces 6 pulse output voltage only. In order to modernise traction substation, simple switchover from 3-phase to 12-phase transformer with presented windings connection is not, therefore, possible.

RECTIFIER TRANSFORMERS IN ELECTRIC TRACTION SUBSTATIONS - DIFFERENT DESIGNS

Abstract Electric traction in Poland is supplied with dc voltage which is obtained from the power grid via traction substations equipped with transformers and rectifiers. The paper gives the results of the investigation of different designs of these transformer‐rectfier sets ‐ namely, 12‐ and 24‐pulse systems. The comparison of electrical quantities such as ripple content, harmonic content of supply current and output voltage and utilisation of transformer secondary windings is provided.

Minimization of Power Pulsations in Traction Supply – Application of Ant Colony Algorithm

In this paper a particular problem related to transformation of AC voltage into DC voltage used in tram supply is considered. Variable component is always present in rectified voltage. Pulsation of rectified voltage is influenced by different factors. In 12-pulse system, where two secondary transformer windings are used (one delta-connected, the other star-connected), an additional factor increasing the pulsation is the unbalance of the output voltages at these windings. Tap changer may be used to compensate (equalize) those voltages and its setting is optimized here by applying ant colony algorithm. Different supply voltage variants have been considered, with particular attention paid to distorted voltage, containing 5th and 7th harmonic. The effects of applying ACO algorithm are demonstrated.

Capacitance and Resistance of Turn-to-Turn Insulation—Measurements in Transformers

Transformers operating in the power grid are subjected to different types of overvoltages, generated by lightning discharges or by switchings in the network. The overvoltage wave voltage is distributed unevenly across transformer’s winding. The maximum voltage rise rate occurs at beginning of winding. This maximum rate depends on insulation parameters such as insulation to ground capacitance and turn-to-turn insulation capacitance. Measurements of insulation to ground parameters: resistance R g and capacitance C g have been known and conducted for many years, mostly for diagnostic purposes. Capacitance C z and resistance R z of turn-to-turn insulation of transformer windings are used in analysis of voltage wave distribution across the windings during overvoltages and in diagnostics of insulation system. Method of measuring parameters R z and C z is demonstrated in the paper. The measurement is based on recording of dc current course after the winding has been short-circuited and of winding voltage after the dc current (of identical value) has been instantaneously switched off. The procedure is illustrated with example, the test object was a dry-type transformer rated at 160 kVA.