China
Africa
Explore chapters and articles related to this topic
Principles of Energy Conversion
Published in Hamid A. Toliyat, Gerald B. Kliman, Handbook of Electric Motors, 2018
Hamid A. Toliyat, Gerald B. Kliman
A synchronous machine, being a doubly excited device, can be designed to operate at any power factor, lagging or leading. Furthermore, the voltage regulation of a generator or the pullout torque for a motor depends on the synchronous reactance of the machine. With modern solid-state devices, used in variable speed motors, the commutation reactances of the machine and hence the sibtransient reactances of the machines are also of critical importance. A synchronous machine is therefore designed for a given power rating, power factor, the synchronous reactances Xsd,Xxq, and the substransient reactances Xsd'',Xxq''.
Short Circuit of Synchronous and Induction Machines
Published in J.C. Das, Power System Analysis, 2017
Synchronous reactance is the steady-state reactance after all damping currents in the field windings have decayed. It is the sum of leakage reactance and a fictitious armature reaction reactance, which is much larger than the leakage reactance. Ignoring resistance, the per unit synchronous reactance is the ratio of per unit voltage on an open circuit divided by per unit armature current on a short circuit for a given field excitation. This gives saturated synchronous reactance. The unsaturated value of the synchronous reactance is given by the per unit voltage on air-gap open circuit line divided by per unit armature current on short circuit. If 0.5 per unit field excitation produces full-load armature current on short circuit, the saturated synchronous reactance is 2.0 per unit. The saturated value may be only 60%–80% of the unsaturated value.
Electric Power Production
Published in J. Lawrence, P.E. Vogt, Electricity Pricing, 2017
A generator’s ability to produce both real and reactive power is limited by thermal heating effects caused by the i2R current flows in the field and armature conductors. Figure 6.2 exemplifies the capacity output or loading capability of a synchronous generator designed to operate at an 85% lagging power factor. Below 85% power factor, i.e., at higher overexcitation states, the generator’s output is limited by the heating of the field windings (Point A to Point B). Above an 85% lagging power factor, through unity, and into a slight leading power factor condition (about 98% in this example), the output is limited by the heating of the armature windings (Point B to Point C). For higher underexcitation states (Point C to Point D), power output is constrained by the machine’s steady-state stability limit, which is primarily a function of the generator’s synchronous reactance (XS) and the equivalent reactance of the connected system (XE). In addition, heating of the iron components of the machine caused by eddy current induction provides constraints to the generator’s output in this area. As shown in Figure 6.2, the range of operation for underexcitation is much less than for overexcitation.
A Millman based alternate to symmetric component methods for fault level calculations in marine power systems
Published in Journal of Marine Engineering & Technology, 2022
The active internal voltage (E) driving the generator’s sustained fault current is calculated based on the generator’s stated sustained fault current (Ikd) at its terminals. Ikd is largely defined by the ability of the generator’s Automatic Voltage Regulator (AVR) to supply field current under fault conditions. For a PP fault the sustained fault current (Ik2) at the generator’s terminals can be taken to be if Ik2 is not stated on the generator’s data sheet. If a fault occurs at the generator terminals then its terminal voltage (Vt) is equal to zero. Under sustained PP fault conditions the active internal voltage (E2) must therefore be entirely dropped across the generator’s steady-state phase impedance made up of the armature resistance (Ra) and synchronous reactance (Xd). Therefore:
Harmonic Electromagnetic Torque Analysis of Turbo-Generators by a Novel Lumped Magnetic Parameter Method and Finite Element Method
Published in Electric Power Components and Systems, 2021
Pin Lv, Xiaojie Wu, Xunwen Su, Ying Yang, Xianhui Zhu, Peng Lin
Here, a is the complex factor (a=ej120º), Xs and Ra are the synchronous reactance and armature resistance respectively, E+, U+ and I+ are the fundamental positive sequence electromotive force, voltage and current effective value respectively, X+, R+ and Z+ are the positive sequence reactance, resistance and impedance respectively, U− and I− are the fundamental negative sequence voltage and current effective value respectively, X−, R− and Z− are the negative sequence reactance, resistance and impedance respectively, uA, uB and uC are the stator fundamental instantaneous voltage of phase-A, phase-B and phase-C respectively, and iA, iB and iC are the stator fundamental instantaneous current of phase-A, phase-B and phase-C respectively. The parameter Z−can be viewed as a constant and it is decided by the turbo-generator structure and material. All the parameters are displayed in the Figure 1. Instantaneous voltage and current in positive sequence network can be shown as
Maiden Application of Fuzzy-2DOFTID Controller in Unified Voltage-Frequency Control of Power System
Published in IETE Journal of Research, 2021
Satish Kumar Ramoji, Lalit Chandra Saikia
The AVR system consists of amplifier, excitation mechanism, generator field circuitry, and sensor, etc. The sensor be installed to predominantly calculate terminal voltage (ΔV) and equate this with an error voltage. The amplifier recapitulates the insufficient voltage accordingly regulates the voltage of the generator. Thus, the excitation voltage (Ev) is affected by the core controller of the AVR, which will have a significant impact on the actual power (Pa), i.e. given by (2) Where the terminal voltage is (V), the synchronous reactance is (Xsr), and the rotor angle is (δ). So, the real power is affected, which creates an impact on the ALFC loop. As a result, during the minimal load change, the frequency varies from its nominal values [32]. The frequency disparity creates a substantial