Transient torque and load angle of a synchronous generator following several types of system disturbance

Mehta, D.B.; Adkins, B.

doi:10.1049/pi-a.1960.0015

Cited by 29 publications

(11 citation statements)

References 1 publication

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“…As both aperiodic and alternating components of current and flux exist following synchronisation, then both alternating and aperiodic components of torque will occur [7,23,24].…”

Section: Shaft Torquementioning

confidence: 99%

Effect of loading, voltage difference and phase angle on the synchronisation of a small alternator

Best

Morrow

Crossley

2009

IET Electr. Power Appl.

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Synchronisation of small distributed generation, 30 kVA -2 MVA, employing salient-pole synchronous machines is normally performed within a narrow range of tolerances for voltage, frequency and phase angle. However, there are situations when the ability to synchronise with non-ideal conditions would be beneficial. Such applications include power system islanding and rapid generator start-up. The physical process and effect of out-of-phase synchronisation is investigated both through simulation and experimental tests on a salientpole alternator. There are many factors that affect synchronisation, but particular attention is given to synchronisation angle, voltage difference and, as generators will be loaded during islanding, the load angle. The results suggest that it would be acceptable for the maximum synchronisation angle of distributed generation to exceed that of current practice. Interesting observations on the nature of out-of-phase synchronisation are made, including some specific to small salient-pole synchronous machines. Furthermore, recommendations are made for synchronisation under different system conditions.reactance a angular acceleration u sync synchronisation angle d load angle t time constant F magnetic flux C flux linkage v angular speed Subscripts and superscripts a armature bus power system bus d direct axis (armature) e electrical f field k d direct-axis damper k q quadrature axis damper m mechanical m d direct-axis mutual m q quadrature-axis mutual

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“…As both aperiodic and alternating components of current and flux exist following synchronisation, then both alternating and aperiodic components of torque will occur [7,23,24].…”

Section: Shaft Torquementioning

confidence: 99%

Effect of loading, voltage difference and phase angle on the synchronisation of a small alternator

Best

Morrow

Crossley

2009

IET Electr. Power Appl.

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“…For this last case, the agreement between the calculated and test results is excellent during the first 50 ms, and the errors thereafter are attributed by the present author to an overestimate of the magnitude of the unidirectional electrical torque by about 30%. This contradicts the findings of Mehta and Adkins, 5 who sought an explanation of the difference between their calculated and test results by assuming an underestimate of the magnitude of the unidirectional electrical torque.…”

Section: Micromachine Testmentioning

confidence: 57%

“…Since that time, a pause or back swing of generator rotors has been seen in other system test results 3 -4 and also in micromachine studies. 5 Fig. 1 demonstrates typical variations of the total electrical torque on the rotor when a generator is subjected to a 3-phase fault, which is applied simultaneously to all three phases.…”

Section: Introductionmentioning

confidence: 99%

Effect of oscillatory torques on the movement of generator rotors

Shackshaft

1970

Proc. Inst. Electr. Eng. UK

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The paper discusses the process whereby some of the kinetic energy stored in a generator rotor is converted to magnetic energy when a generator is short circuited. This gives rise to oscillatory electrical torques at fundamental frequency which, hitherto, have not been recognised as an important factor in the initial angular movement of a generator rotor and have usually been ignored; this is shown to be a serious omission which, when corrected, will influence future studies of generator stability. The effect of these oscillatory torques is to cause a back swing of the rotor when a generator is faulted. This phenomenon has been noticed during several system tests, and the results of such tests are used in the paper to support the theory which is presented. The practical system conditions necessary for the existence of these torques is discussed. Since these torques are of fundamental frequency, the exact calculation of them in digitalcomputer programs is time consuming, and thus a simple approximate method for simulating their effect on rotor movement is presented. 1 List of symbols x d = direct-axis synchronous reactance, p.u. x' d = direct-axis transient reactance, p.u. x'y -subtransient reactances in direct and quadrature axes, respectively, p.u. H = inertia constant, kWs/kVA V = terminal voltage, p.u. T e = electrical torque, p.u. T m = prime-mover torque, p.u. T s = magnitude of oscillatory torque, p.u. r a = armature time constant, s r' d = transient time constant, s T'J = subtransient time constant, s OJQ = rated speed, rad/s /o = rated frequency, Hz 6 = change of rotor angle, deg IntroductionThat generator rotors, when subjected to close-up 3-phase faults, tend to pause or even swing backwards* prior to accelerating under prime-mover action, is now a recognised and accepted phenomenon. It was first noticed in the results of field tests which were held at Cliff Quay 1 in 1956, and Powell 2 made the first attempt to quantify the observed back swing. Based on experience, he chose to delay the forward movement of the rotor by 0 06 s in his calculation, and was then able to obtain satisfactory agreement with the test result. Since that time, a pause or back swing of generator rotors has been seen in other system test results 3 -4 and also in micromachine studies. 5 Fig. 1 demonstrates typical variations of the total electrical torque on the rotor when a generator is subjected to a 3-phase fault, which is applied simultaneously to all three phases. The prefault torque (curve a) represents the generator with full load and the postfault torque (curve b) has two components; one is a unidirectional torque (curve c) which is due to resistive losses in the set, and the other is an oscillatory torque which is almost entirely of fundamental frequency and which is much larger than the prefault torque. 6 The resistive losses during the initial period of a fault (say, the first 50ms) can be quite high, and there is no doubt that these do influence the movement of the rotor. The resulting

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“…The first (highest ) amplitude is derived from power dissipation by the resistance of the generator, and then subsequent oscillations are due to system frequency imposed on the oscillatory torque of the generator rotor due to unilateral direction components to the machine [56].…”

Section: Fault Analysis On Single Line Diagrammentioning

confidence: 99%

Dynamic analysis of Southern Africa power pool (SAPP) network

Mludi

Davidson

2017

2017 IEEE PES PowerAfrica

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Synchronous generators have been connected through overhead transmission lines and interconnected to a regional power system network to improve reliability, enhance the security of supply, trade electricity and share the available natural resources for energy fuel supply. The interconnected power system experiences disturbances during normal operation such as load variations and faults, causes stress on the generators to control and remain in synchronism. This dissertation analyses the natural damping oscillations that will emanate during a disturbance in the interconnected power system and provide understanding to the system operator to monitor and operate effectively the Southern African Power Pool (SAPP). It is required to carry out the performance analysis and characteristics of the generators during the disturbances in order to identify the synchronizing and damping torque in respect of rotor angle and speed deviations. In power system control, the frequency is monitored continually since the speed of the generators is synchronized into the transmission lines. Any small variation on the interconnected system will affect the others machines. The effect can either be the system maintaining its stability or loss of synchronism. The latter can be avoided by identifying the nature and behaviour of oscillations and determining effective means to minimize them in interconnected power pool. It can also notify the system operator of an impending power outage. In this research investigation, a simplified model of the Southern African Power Pool is modeled using DIgSILENT Powerfactory power systems analysis software tool, using input data of the primary plant (synchronous generators) and associated interconnected power system network. Nodal and modal analysis tools were used to determine the dynamic status of the interconnected power network. A dynamic analysis will enable participating members of the power pool understand the nature of oscillations when affected by different types of events with continuous monitoring of the modes and eventually assist in re-tuning of secondary control equipment to improve the service delivery of electricity of a pool such as of the Southern African region.The study has identified the focal points of power oscillations in the modelled SAPP grid through simulations that affects the behaviour of system voltages during a disturbance and require to control damping oscillations on the synchronous generators.

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Transient torque and load angle of a synchronous generator following several types of system disturbance

Cited by 29 publications

References 1 publication

Effect of loading, voltage difference and phase angle on the synchronisation of a small alternator

Effect of loading, voltage difference and phase angle on the synchronisation of a small alternator

Effect of oscillatory torques on the movement of generator rotors

Dynamic analysis of Southern Africa power pool (SAPP) network

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