A one-machine system is shown in Figure 1. Data for the system is as follows:

f = 60 Hz, MVA = 100 MVA, HG= 3 MJ/MVA

G: x" x= x=j0.25 pu, xº =j0.1 pu

T₁ & T2: x= x= xº =j0.1 pu

L₁ & L₂: x = x = j0.4 pu, xº =j1.2 pu

Figure 1

ELEC 3207 Power Systems 2 Assignment

T₁

(c)

L₁

L₂

T₂

Initially, EG=E; = 1.0 pu and Po=1.0 pu.

Consider a single line-to-ground (a-g) fault at point A and the following switching operations:

1. The a-g fault occurs at t=0.

2. Circuit breakers of all the three phases at both ends of Line 2 open at 8:1-60°, stay open

while 8 advances 10°, and then reclose.

3. Since the fault is not cleared, the circuit breakers reopen at 8.2 after 8 advances another 20°,

and then remain open.

(a)

(b)

Study the stability of the system for this operation.

Determine the maximum angle 8c at which the circuit breakers can reopen at Operation

3 above so that the system is stable.

It is required to set the reopening time of the circuit breakers for part (b), calculate the

critical clearing time tec