EECE 350-Fund

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EECE 350-Fund.Elect Power

The leakage flux circulates inside the ferromagnetic core

Select one:

a. True

b. False

The magnitude of the series impedance (referred to the primary circuit) of the single phase transformer can be found from the short-circuit test voltage and current.

Select one:

a. None of the above

b. True

c. False

The open circuit test of a single phase transformer gives Open circuit voltage: V oc = 4000V, Open circuit current Ioc = 0.2 A. Active power Poc = 400 W. The resistance Rc (used for modeling the core losses) is:

Select one:

a. None of the above

b. 20000 Ohm

c. 26666 Ohm

d. 80000 Ohm

e. 40000 Ohm

A single phase transformer has Reqs=0.08 Ohm, Xeqs=0.09 Ohm, Vs=220 V, Is=20 A, power factor pf=0.85. Calculate the voltage regulation Vr.

Select one:

a. None of the above

b. 1.049%

c. 2.17%

d. 2.73%

e. 1.6%

The short circuit test of a single phase transformer gives: Short circuit voltage: V sc = 400 V, Short circuit current Isc = 2 A. Active power Psc = 300 W. The series resistance Req1 is:

Select one:

a. 50 Ohm

b. None of the above

c. 25 Ohm

d. 75 Ohm

e. 100 Ohm

In ferromagnetic materials, the permeability varies with the amount of flux already in the material.

Select one:

a. True

b. False

The open circuit test of a single phase transformer gives Open circuit voltage: V oc = 4000V, Open circuit current Ioc = 0.2 A. Active power Poc = 400 W. The reactance Xm (used for modeling the magnetization current) is:

Select one:

a. 11547 Ohm

b. None of the above

c. 46188 Ohm

d. 23094 Ohm

e. 15396 Ohm

The parameters of a single phase transformer are: equivalent resistance referred to its secondary side Req=0.05 Ohm, secondary current Is = 20 A, core losses Pc=50 W, output power Pout=2500 W. The efficiency of the transformer is

Select one:

a. 0.97

b. 0.79

c. None of the above

d. 0.9

e. 0.94