Asynchronous Operationand Resynchronization

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BÁO CÁO: MÔN QUÁ ĐỘ TRONG HỆ THỐNG ĐIỆN ĐỀ TÀI : Asynchronous Operation and Resynchronization ĐẠI HỌC SƯ PHẠM KỸ THUẬT TPHCM KHOA ĐIỆN-ĐIỆN TỬ

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Transcript of Asynchronous Operationand Resynchronization

  • BO CO: MN QU TRONG H THNG IN TI : Asynchronous Operation and ResynchronizationI HC S PHM K THUT TPHCMKHOA IN-IN T

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    OBJECTknowing about Asynchronous Operation and Resynchronization and Transition to Asynchronous Operationknowing about Inuence of the Voltage Regulator to Possibility of Resynchronization factors affecting Resynchronization

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    CONTENTSAsynchronous Operation and ResynchronizationTransition to Asynchronous Operation Asynchronous Operation Possibility of Resynchronization Inuence of the Voltage RegulatorOther Possibilities of Resynchronization

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    1. Asynchronous Operation and ResynchronizationThe synchronizing switch is closed the resulting electromagnetic torque will attempt to pull the rotor into synchronization with the power system by either slowing down or accelerating the rotor until eventually the generator reaches its nal equilibrium position dened by the steady-state rotor angle s=0 and the rotor speed =s

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    1. Asynchronous Operation and Resynchronizationthe turbine static characteristic Pm() is a straight line of droop which crosses the axis in Figure 6.29 at point Pm0 and the horizontal speed deviation axis at point s.PDav( ) As the average value of synchronous power PE over each asynchronous rotation is zero.The intersection between the static turbine characteristic and the damping power characteristic will dene the generator operating point during asynchronous operation

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    1.2 . Transition to Asynchronous OperationNow assume that a three-phase fault occurs on line L2 and is then cleared by tripping the faulted line (without auto-reclosing) after a time such that the acceleration area 1234 shown in Figure 6.30a is larger than the available deceleration area 456. The effect of the synchronous power PE is to produce speed deviation oscillations around the mean value as shown in the lower part of Figure 6.30

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    1.2. Transition to Asynchronous Operation

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    1.3. Asynchronous OperationAssuming that the generator is allowed to settle at the asynchronous operating point, then typical variations in some of the electrical quantities are as shown in Figure 6.31.

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    1.3. Asynchronous OperationThe voltage drop V across the equivalent reactance xd, the stator current is seen to change as the rotor angle changes, with its maximum value being when = and its minimum when =0

    As the armature current changesinducing large uctuations in the internal emf Eq , and smaller variations in E , as shown in Figure 6.31b. As the transient emf E is almost constant, the synchronous power P E is varies as sin (Figure 6.31c). The average value of the asynchronous damping power PDav is shown in Figure 6.31c and can be added to the synchronous power to obtain the resulting air-gap electrical power P e=PE+P Dthe average speed deviation av is determined by the intersection between the turbine characteristic Pm( ) and the average asynchronous damping power characteristic PDav( ). However, due to the sinusoidal changes in the synchronous power PE, the actual speed deviation will oscillate around av in the way shown in Figure 6.31d.

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    1.4. Possibility of ResynchronizationIn order to resynchronize with the system, the generator must full the normal requirements for synchronization, that is its speed deviation and power angle must be small

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    1.4.1 Inuence of the Voltage Regulator

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    1.4.1 Inuence of the Voltage RegulatorBy increasing the excitation voltage, the AVR increases the amplitude of the PE() characteristic and so produces larger changes in the speed deviation. This increases the chance of the speed deviation reaching a zero value as shown in Figure 6.33b. Moreover, as the amplitude of the synchronous power increases, the available deceleration area in Figure 6.32b increases and the range of rotor angles which are acceptable for resynchronization also increases

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    1.4.2 Other Possibilities of ResynchronizationSuccessful resynchronization depends on the action of the AVR and the turbine governing system . Turbine governors can be equipped with supplementary control loops which allow the turbine power tobe quickly reduced after a fault in order to protect the generator from loss of synchronism and /or assist in resynchronization . This is referred to as fast valving. If a generator is not equipped with such a governor, the operating staff may try to resynchronize the asynchronously rotating generator by manually reducing the turbine power to reduce the average speed deviation value. However, in order to avoid large power swings in the system, and possible damage to the generator, generators are usually tripped after a few asynchronous rotations.

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    concludeThe intersection between the static turbine characteristic and the damping power characteristic will dene the generator operating point during asynchronous operationreducing the turbine power to reduce the average speed deviation valueThe effect of the synchronous power PE is to produce speed deviation oscillations around the mean value as shown in the lower part of Figure 6.30b In order to resynchronize with the system, the generator must full the normal requirements for synchronization, that is its speed deviation and power angle must be small Successful resynchronization depends on the action of the AVR and the turbine governing systemincrease in the amplitude of the synchronous power oscillations and the speed deviation oscillations as a result of voltage regulation

  • Khi cc chuyn i ng b ha c ng ca cc m-men xon in kt qu s c gng ko rotor vo ng b ha vi h thng in bng cch hoc lm chm xung hoc tng tc rotor cho n khi cui cng my pht in t n v tr cn bng thc ca n c xc nh bi cc trng thi n nh rotor gc ca = 0v tc rotor = s

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