Kỹ Thuật Điện Cuối Kỳ

Given a branch as shown in the figure. Find the correct statement.

• u_ab = R.i1 + L.di2/dt

• u_ab = Ri1 - Li2

• i1 + i2 + i3 = 0

• i1 + i2 + i3 > 0

A linear inductor. If the current flowing through decreases by 2 times. Find the correct statement?

• Magnetic flux increases by 4 times

• Energy in the magnetic field decreases by 4 times

• Energy in the magnetic field increases by 4 times

• Energy in the electric field increases by 4 times

The voltage and current of an electrical circuit have the following values. Determine the property of the load. Find the incorrect statement?

• U̇ = U.e^(j60°) (V); İ = I.e^(j30°) (A) → The load has inductive properties

• U̇ = U.e^(-j60°) (V); İ = I.e^(-j30°) (A) → The load has capacitive properties

• U̇ = 50 + 50j (V); İ = 5 - 5j (A) → The load has purely capacitive properties

• U̇ = 40 - 30j (V); İ = 12 + 16j (A) → The load has purely capacitive properties

The current through an ideal coil with inductance L has the form: i_L(t) = I_m sin(ωt). Find the incorrect statement?

• u_L(t) = L.di(t)/dt = L.I_m.d(sin(ωt))/dt

• L.ω.I_m = U_m

• u_L(t) = L.ω.I_m.sin(ωt - π/2)

• X_L.I = U_L; X_L = ωL = 2πfL

Given u(t) = 100√2sin(314t + 80°) (V) and i(t) = 10√2sin(314t - 10°) (V). Find the total active power P of the circuit:

• 308W

• 616W

• 1000W

• 0W

Find I, knowing X_L = X_C = R = 20Ω; U = 200V

• 10A

• 15.4A

• 10√2 A

• 5.75A

For a 3-phase asynchronous motor with a wound rotor Y/Δ – 380/220V. R1 = 0.36Ω; X1 = 0.955Ω; R2' = 0.245Ω; X2' = 0.94Ω; p = 2; f = 50Hz; U1 = 380V. When starting, if the voltage drops by 20% U_dm, what is the maximum torque M_c?

• M_c < 36.6Nm

• M_c < 40Nm

• M_c < 56.6Nm

Determine P, Q of the entire circuit and currents I1, I. Know that

What is the maximum value of M?

• Mc <36.6Nm

• Mc <40Nm

• Mc <56.6Nm

Determine P, Q of the entire circuit and current I. Given Ud = 380V, symmetrical 3-phase load with P1 = 35540W, cosφ=0.6. Load Z2 has P2 = 10000W. What is the power factor of the entire circuit cosφ=?

• P=35540W

• I1=100A

• Q=22056VAr

• I=125A