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Autotransformers
Published in K.R.M. Nair, Power and Distribution Transformers, 2021
An autotransformer is a transformer in which at least two windings have a common part. In the electric power system, it finds application in place of a two-winding transformer, especially when the interconnection or power transfer is required between two high-voltage systems. The major advantages of an autotransformer are as follows; It has higher efficiency when compared to a two-winding transformer of equal rating.It has lower material cost.It offers better voltage regulation.The excitation current is low.
Motor controllers
Published in Raymond F. Gardner, Introduction to Plant Automation and Controls, 2020
Autotransformer3 starters use single-winding stepdown transformers to supply each motor phase with reduced voltage and reduced starting current during acceleration. Conventional two-winding transformers having separate primary and secondary windings could be used, but the relatively close turns ratio, and the significantly smaller size and weight makes a single-winding autotransformer far more practical. The primary and secondary windings of the autotransformer share some windings and are linked both electrically and magnetically. The autotransformer works on the principle that when line voltage is applied to a coil, a fraction of the line voltage appears at an intermediate tap, whose value is based on the turns ratio to the tap. Taps are usually made at 5:4, 3:2, and 2:1 ratios to produce a choice of 80%, 65%, and 50% reduced-voltage levels for motor starting.
Ideal Transformers
Published in Nassir H. Sabah, Circuit Analysis with PSpice, 2017
The principal disadvantage of the autotransformer is that the input and output sides are directly connected together. That is, there is a conductive pathway between input and output, unlike a two-winding transformer. Thus, if a battery is connected between terminals ‘a’ and ‘d’ of the ideal, two-winding transformer of Figure 10.27a, no current flows (Figure 10.28). This is because the insulation between the two windings is assumed to be perfect in an ideal transformer, just like the insulation between the two plates of an ideal capacitor. Perfect insulation has infinite resistance, so that the dc current IB is VB divided by an infinite resistance between the two windings, which gives IB = 0. In other words, there is no conductive pathway between the two windings. The two windings are said to be electrically isolated from one another. On the other hand, if a battery is connected between terminals ‘a’ and ‘d’ of the autotransformer of Figure 10.27b, the battery is short-circuited by the zero dc resistance of the primary winding between terminals ‘a’ and ‘bd’. Electrical isolation is sometimes required in practice to safeguard against electric shock, or for other reasons, such as having different grounded nodes on the two sides of a two-winding transformer. An autotransformer cannot be used in these cases.
Real Time Implementation of Pollination Based Techniques for Radial Distribution Network Reconfiguration
Published in IETE Journal of Research, 2021
Mariaraja Paramasivam, Manigandan Thathan
As such, a scaled-down multi-phase RDS workstation [41] with 13 buses, 12 branches and several types of loads is built to facilitate physical experiments and real-time research work. The system has a base voltage of 0.11 kV and 0.1 MVA rating. The workstation is integrated with (i) a power station modeled with a 3-phase 440/110 V, 4A, isolation transformer with one 1:1 autotransformer, (ii) four Pi-section panels each of 2 km length, (iii) load control panels with the resistive, inductive, capacitive and motor loads, (iv) numerical overcurrent relay with a current rating of 1A/5A and storage capability of the last 20 events, (v) graphical user interface with data acquisition, (vi) smart meters for remote monitoring where each of which is provided with RS485 communication port, (vi) fault simulator panel to perform different types of power system faults and (vii) transmission line simulator MICRO-II software package.
Development of multilayer perceptron artificial neural network (MLP-ANN) and least square support vector machine (LSSVM) models to predict Nusselt number and pressure drop of TiO2/water nanofluid flows through non-straight pathways
Published in Numerical Heat Transfer, Part A: Applications, 2018
Mostafa Kahani, Mohammad Hossein Ahmadi, Afshin Tatar, Milad Sadeghzadeh
The experimental used set-up is demonstrated in Figure 1. This set-up consists of a tank, bypass, and heat transfer test sections, centrifugal pump, pressure transmitter, data logger, temperature data acquisition, cooling heat exchanger and flow rate measuring section. Two PT100-type thermocouples with precision: ±0.1% were fixed at inlet and outlet of coils to measure the temperatures of water and nanofluids. Same model of thermocouples were placed on the surface of coils at various locations. To apply the constant heat flux over the coils, an electric resistance was considered. An autotransformer was employed to regulate the heat flux by setting the electrical voltage. In addition, two layer of rock wool and fiberglass sheets was applied to the all possible heat transfer sections. Moreover, coils were equipped with a special pressure transmitter to measure the pressure drop. The pump and also cooling heat exchanger were turned on after the reservoir tank was filled with the nanofluid. Then resistance was switched on and the test section's temperature commenced to augment. More detailed information about experimental setup were presented in the previous researches of first author [14,19].
Disturbance Observer Based Power Control of DFIG Under Unbalanced Network Conditions
Published in Electric Power Components and Systems, 2018
Emre Ozsoy, Burak Soner, Fiaz Ahmad, Akhtar Rasool, Asif Sabanovic, Metin Gokasan, Seta Bogosyan, P. Sanjeevikumar
Figure 3 depicts the experimental setup. A back to back inverter topology drives DFIG; rotor side control (RSC) inverter drives the rotor circuit, while grid side control (GSC) inverter keeps the DC link voltage constant at 100VDC. GSC inverter is connected to the grid with an autotransformer (AT1) to generate unbalanced voltage in the stator side of DFIG. A 1.1 kW, 380VAC, 1500 rpm DFIG is used as a generator of which plate data is given in Table 1. A three-phase autotransformer (AT2) is installed to reduce nominal grid voltage for safety reasons. Single-phase autotransformer (AT3) is used to generate unbalanced voltage condition. Two separate inverters are used (Semikron 21f_b6u_e1cif_b6ci_12_v12) for GSC and RSC. Space vector pulse width modulation (SVPWM) method is used with 10 kHz switching frequency.