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Nôi dung của tài liệu GENERATOR CAPABILITY CURVE bao gồm: - Giới thiệu về Reactive Capability Curves - Giới thiệu về Armature current limit - Giới thiệu về Field current limit - Giới thiệu về End region heating limit - Giới thiệu về Generator Characteristics
GENERATOR CAPABILITY CURVE By Prof. C. Radhakrishna 10/17/2010 10:20 AM 2 CONTENTS GENERATOR CAPABILITY CURVE Reactive Capability Curves Armature current limit Field current limit End region heating limit Generator Characteristics 10/17/2010 10:20 AM 3 GENERATOR CAPABILITY CURVE Reactive Capability Curves • Synchronous generators are rated in terms of the maximum MVA output at a specified voltage and power factor (usually 0.85 or 0.9 lagging) which they can carry continuously without overheating. • The active power output is limited by the prime mover capability to a value within the MVA rating. • The continuous reactive power output capability is limited by three considerations: armature current limit, field current limit, and end region heating limit. Armature current limit • One of the limitations on generator rating is the maximum current that can be carried by the armature without exceeding the heating limitations. 10/17/2010 10:20 AM 4 Figure 1 Armature current heating limit Armature current limit The per unit complex output power is where φ is the power factor angle. Therefore, in the P-Q plane the armature current limit, as shown in Figure 1, appears as a circle with centre at the origin and radius equal to the MVA rating. * ~ ~ tt IEjQPS )sin(cos jIE tt 10/17/2010 10:20 AM 5 Because of the heat resulting from the power loss, the field current imposes a second limit on the operation of the generator. The constant field current locus may be developed by the steady-state equivalent circuit developed earlier. With X d =X q =X s , the equivalent circuit of Steady-state model gives the relationship between E t , I t and E q (equal to X ad i fd ). The corresponding phasor diagram, with R a neglected, is shown in Figure 2. . Field current limit 2 fdfd iR 10/17/2010 10:20 AM 6 Field current limit 10/17/2010 10:20 AM 7 Field current limit cos sin ad tt tfd i s X PEI Ei X 2 sin cos ad t tt tfd i ss X E QEI Ei X X (1) 10/17/2010 10:20 AM 8 The relationship between the active and reactive powers for a given field current is a circle centred at ( ) on the Q-axis and with as the radius. Therefore, the effect of the maximum field current rating on the capability of the machine may be illustrated on the P-Q plane as shown in Figure 3. Field current limit st XE / 2 fdtsad iEXX )/( In any balanced design, the thermal limits for the field and armature intersect at a point A, which represents the machine nameplate MVA and power factor rating. Figure 3 Field current heating limit 10/17/2010 10:20 AM 9 End region heating limit 10/17/2010 10:20 AM 10 • The localized heating in the end region of the armature imposes a third limit on the operation of a synchronous machine. • This limit affects the capability of the machine in the under excited condition. • This is illustrated in Figure 4, which also includes the limit imposed by the armature current heating effects. • The field current and armature current heating limits when plotted on a P-Q plane depend on the armature voltage. End region heating limit Figure 4 End region heating limit . GENERATOR CAPABILITY CURVE By Prof. C. Radhakrishna 10/17/2010 10:20 AM 2 CONTENTS GENERATOR CAPABILITY CURVE Reactive Capability Curves Armature current limit Field. 3 GENERATOR CAPABILITY CURVE Reactive Capability Curves • Synchronous generators are rated in terms of the maximum MVA output at a specified voltage and power factor (usually 0.85 or 0.9 lagging) which. The active power output is limited by the prime mover capability to a value within the MVA rating. • The continuous reactive power output capability is limited by three considerations: armature