(a) A grid-connected micro-hydro scheme has the following characteristics: Synchronous motor/generator: 3-phase; 0.8 MVA: 0.7MW; 11...

  

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(a) A grid-connected micro-hydro scheme has the following characteristics: Synchronous motor/generator: 3-phase; 0.8 MVA: 0.7MW; 11 kV; star-connected Synchronous impedance = 0.05 +j 1.2 pu; Hydro Turbine rating = 0.7 MW (reverse power is not allowed) Rated field current = 2.0 pu; Note: 1 pu field current is defined as the current that would generated an emf of 1pu at rated speed. Draw, to scale, the capability diagram showing the safe operating area. Allow for a stability margin of 0.1 pu of active power below the theoretical steady state stability limit. [20 marks] (b) A grid-connected pumped micro-hydro scheme has the following characteristics: Synchronous motor/generator: 3-phase; 0.8 MVA; 0.7MW; 11 kV; star-connected Synchronous impedance = 0.05 +j 1.2 pu; Hydro Turbine rating = 0.7 MW (reverse power is not allowed) Pump rating = 0.3 MW Rated field current = 2.0 pu; Note: 1 pu field current is defined as the current that would generated an emf of 1 pu at rated speed. Draw, to scale, the capability diagram showing the safe operating areas. Allow for a stability margin of 0.1 pu of active power below the theoretical steady state stability limit. [20 marks] (c) A three phase bolted fault occurred at the terminals of the generator in part (a). Just before the fault the terminal voltage was 1 pu and the generator was on-line but unloaded. That is both the active power and the reactive power was zero. The generator circuit breaker operated normally. The sequence of events data showed that the peak value of the instantaneous fault current in one of the generator phases reached a value that was significantly more than 1.18 pu. Please explain. Restrict your explanation to about 100 words. [10 marks] This question assesses your understanding of the synchronous machine equivalent circuits and their applications. The equivalent circuits are used in computer software that models electricity supply networks. (a) A grid-connected micro-hydro scheme has the following characteristics: Synchronous motor/generator: 3-phase; 0.8 MVA: 0.7MW; 11 kV; star-connected Synchronous impedance = 0.05 +j 1.2 pu; Hydro Turbine rating = 0.7 MW (reverse power is not allowed) Rated field current = 2.0 pu; Note: 1 pu field current is defined as the current that would generated an emf of 1pu at rated speed. Draw, to scale, the capability diagram showing the safe operating area. Allow for a stability margin of 0.1 pu of active power below the theoretical steady state stability limit. [20 marks] (b) A grid-connected pumped micro-hydro scheme has the following characteristics: Synchronous motor/generator: 3-phase; 0.8 MVA; 0.7MW; 11 kV; star-connected Synchronous impedance = 0.05 +j 1.2 pu; Hydro Turbine rating = 0.7 MW (reverse power is not allowed) Pump rating = 0.3 MW Rated field current = 2.0 pu; Note: 1 pu field current is defined as the current that would generated an emf of 1 pu at rated speed. Draw, to scale, the capability diagram showing the safe operating areas. Allow for a stability margin of 0.1 pu of active power below the theoretical steady state stability limit. [20 marks] (c) A three phase bolted fault occurred at the terminals of the generator in part (a). Just before the fault the terminal voltage was 1 pu and the generator was on-line but unloaded. That is both the active power and the reactive power was zero. The generator circuit breaker operated normally. The sequence of events data showed that the peak value of the instantaneous fault current in one of the generator phases reached a value that was significantly more than 1.18 pu. Please explain. Restrict your explanation to about 100 words. [10 marks] This question assesses your understanding of the synchronous machine equivalent circuits and their applications. The equivalent circuits are used in computer software that models electricity supply networks.

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a and b THE BOLTED FAULT OCCUR AS THE THREE PHASES ARE SHORT CIRCUITED TOGETHER AND SO THE ZERO IMPE... View the full answer