Question

b) An 80MVA, 11kV synchronous generator with a sub transient reactance j0.125pu is connected to each of three busbars labelled A, B and C in Figure 2. Three equal current limiting reactors (100MVA, 11kV) are connected in series with the feeders. The main busbars supply secondary busbars (E, F and G) through a line of reactance j2.70 and 100MVA, 11kV/33kV j0.06pu transformers at both ends Busbar D is commected at the 33kv side of the transformer at G to facilitate the connection of distributed generation A 5MVA, 6.6kV biomass generator with a sub transient reactance j0.02pu is introduced on the network. It is connected through a 10MVA, 6.6kV/33kV j0.05pu transformer and a line of reactance j0.120 to busbar D. Draw the equivalent circuit in pu, assuming a base of 100MVA i) (8 marks) i) Detemine the minimum value (in pu) of current limiting reactors required to limit the current for a symmetrical fault at D to 2.0pu when the biomass generator is disconnected. 11 (6 marks) i) Calculate the symmetrical fault current at D when the biomass generator is connected. Consider the same value of current limiting reactor obtained in () (5 marks) B A Figure 2

Answer 1

So2 Given Ger ersatos 12SPu Reactuss oo mVA, 11kv, x Ple (Let) Smeseactoames Transfosmers: eiomar at generabors sids Jonerates: SonvA, 6.6Kv, TF : 6.6Ku/33 kv amol f7e seactene- JO-12 N Base VA = 3 3 Kv (332 Base Reactgne = .Reactam Qs o LCre muA-\ oDmvA. X hao (muA) -jo- I562A Rascroas Line reacteme X . Transfromeo {= joa06 Au t abmo gonasator deneratrs Pu -02X hoa T So.aPu jo.12 10. g9 TF No. o11 Pu ama

So aui valent ol2 o.S62 Reochs X rgrs feener joo6 Frano .OG Sy etne feult at D:- egwivetat difem jo.299 ewi

Curosent Pault InvA . S-O-36 X+o-26) reactrs C en crcui Xes Zio-01 1es 0.I562 +0.1440.06 -+0.24 79 1=14t6 e 4+o.05to011jo.la es

o o4 Pu . eg nos fault muA = -11.90 Pu feuttmuA- i1.90 Pu faut mA= 19 0 mvA ehicafauit ureut 119ox penlt rent = 20.81q KA.