Electrical Energy Systems 1st. Edition by Mohamed E. El-Hawary | 9780849321917 | 849321913 | Holooly

Electrical Energy Systems

43 SOLVED PROBLEMS

Question: 7.6

For the system of Example 7.5 find the voltages and currents at the fault point for a double line-to-ground fault. Assume Zf=j0.05 p.u. Zg=j0.033 p.u. ...

Verified Answer:

The sequence network connection is as shown in Fig...

Question: 7.7

For the system of Example 7.5, find the voltages and currents at the fault point for a line-to-line fault through an impedance Zf = j0.05 p.u. ...

Verified Answer:

The sequence network connection is as shown in Fig...

Question: 7.10

Consider the 11-kV radial system shown in Figure 7.42. Assume that all loads have the same power factor. Determine relay settings to protect the system assuming relay type CO-7 (with characteristics shown in Figure 7.43) is used. ...

Verified Answer:

The load currents are calculated as follows: [late...

Question: 7.4

Obtain the sequence networks for the system shown in Figure 7.17. Assume the following data in p.u. on the same base. Generator G1: X+ =0.2P.u. X- =0.12 P.u. X0 = 0.06 P.u. Generator G2: X+ = 0.33 P.u. X- = 0.22 P.u. X0 =0.066 P.u. Transformer T1: X+ = X- = X0 = 0.2 p.u. Transformer T2: X+ =X- = X0 ...

Verified Answer:

The positive sequence network is as shown in Figur...

Question: 7.9

Consider a Δ/Y-connected, 20-MVA, 33/11-kV transformer with differential protection applied, for the current transformer ratios shown in Figure 7.37. Calculate the relay currents on full load. Find the minimum relay current setting to allow 125 percent overload. ...

Verified Answer:

The primary line current is given by

I_{P} ...

Question: 7.8

For the system of Example 7.5, find the short-circuit currents at the fault point for a balanced three-phase fault through three impedances each having a value of Zf = j0.05 p.u. ...

Verified Answer:

I_{A_{sc} }=I_{+}=\frac{1\angle 0}{j\left(0...

Question: 7.5

Consider a system with sequence impedances given by Z+ = j0.2577, Z- = j0.2085, and Z0 = j0.14; find the voltages and currents at the fault point for a single line-to-ground fault. ...

Verified Answer:

The sequence networks are connected in series for ...

Question: 7.2

Given that V0=100 V+=200∠ 60° V-=100∠ 120° find the phase voltage VA, VB, and VC. ...

Verified Answer:

V_{A}=V_{+}+V_{-}+V_{0}

=200...

Question: 7.1

The following currents were recorded under fault conditions in a three-phase system:IA=150∠45° A IB=250∠150° A IC=100∠300° A Calculate the values of the positive, negative, and zero phase sequence components for each line. ...

Verified Answer:

I_{0} =\frac{1}{3} \left(I_{A}+I_{B}+I_{C}\...

Question: 6.7

A single-phase induction motor takes an input power of 490 W at a power factor of 0.57 lagging from a 110-V supply when running at a slip of 5 percent. Assume that the rotor resistance and reactance are 1.78 Ω and 1.28 Ω, respectively, and that the magnetizing reactance is 25 Ω. Find the resistance ...

Verified Answer:

The equivalent circuit of the motor yields

...

Loading...