PQ Capability Curve-Contin....
PQ capability curve can be considered as a boundary within which the operating point of synchronous generator has to be maintained and this boundary should not be crossed during steady state operation though during dynamic disturbances, short term limit violation within permissible band and for short time(mainly determined by thermal limit) is allowed.
Though in theory, generator is rated in MVA at a given pf, however in practcice the nameplate rating is in MW at a given power factor, rated voltage and rated current. The rated operating point(name plate rating) corresponds to the point on PQ capability chart where armature heating connstraint curve and field current limit curve cut each other.
MW rating as pointed out by Himaja is determined by turbine rating, one might just wonder why turbine is the limiting factor of MW though there is always margin from generator side, in other words why we cant have MW rating of turbine same as full capacity(MVA) of generator and why are we underutilising generator but the fact is that generator has to supply reactive power(Q) alongwith active power and this Q has to be genrated most of the time to maintain terminal voltage, though theoritically machine can be operated at unity power factor to use full capacity of generator for MW generation but in practcice it doesnt happen as Q has to be generated to maintain terminal voltage primarily for technical reasons as voltage shouldnt violate the limit and secondarily due to grid code requirements from TSO. So it is not economically viable to have urbine whose MW rating is equal to MVA rating of Genrator as most of the time turbine has to remain underutilised in addition to initial huge additional installation cost.
PQ capability curve can be considered as a boundary within which the operating point of synchronous generator has to be maintained and this boundary should not be crossed during steady state operation though during dynamic disturbances, short term limit violation within permissible band and for short time(mainly determined by thermal limit) is allowed.
Though in theory, generator is rated in MVA at a given pf, however in practcice the nameplate rating is in MW at a given power factor, rated voltage and rated current. The rated operating point(name plate rating) corresponds to the point on PQ capability chart where armature heating connstraint curve and field current limit curve cut each other.
MW rating as pointed out by Himaja is determined by turbine rating, one might just wonder why turbine is the limiting factor of MW though there is always margin from generator side, in other words why we cant have MW rating of turbine same as full capacity(MVA) of generator and why are we underutilising generator but the fact is that generator has to supply reactive power(Q) alongwith active power and this Q has to be genrated most of the time to maintain terminal voltage, though theoritically machine can be operated at unity power factor to use full capacity of generator for MW generation but in practcice it doesnt happen as Q has to be generated to maintain terminal voltage primarily for technical reasons as voltage shouldnt violate the limit and secondarily due to grid code requirements from TSO. So it is not economically viable to have urbine whose MW rating is equal to MVA rating of Genrator as most of the time turbine has to remain underutilised in addition to initial huge additional installation cost.
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