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Tutorial Week 7

1.1 If v (t ) = 160 cos 50 t V and i(t ) = - 20 sin (50t - 30) A, calculate the average o!er"

1"2 #efer to the circuit de icted $elo!" %ind the average o!er a$sor$ed $& each ele'ent"

1"3 Assu'ing that v s = cos(2 t - 0) V in the circuit sho!n $elo!, find the average o!er delivered to eachof the assive ele'ents"

1" A rela& coil is connected to a 210-V, 50-*+ su l&" If it has a resistance of 30 and an inductance of 0"5*, calculate the a arent o!er and the o!er factor"

1"5 $tain the o!er factor for each of the circuits $elo!" ecif& each o!er factor as leading or lagging"

1"6 A source delivers 50 .VA to a load !ith a o!er factor of 65 ercent lagging" %ind the load/s averageand reactive o!ers"

1" he voltage across a load and the current through it are given $&

v (t ) = 20 60 cos 100 t V

8/9/2019 Electrical Power and Machines- Tutorial

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i (t ) = 1 0"5 sin 100 t A

%ind4 (a) the r's values of the voltage and of the current

($) the average o!er dissi ated in the load"

1" %or the entire circuit $elo!, calculate4

(a) the o!er factor

($) the average o!er delivered $& the source

(c) the reactive o!er

(d) the a arent o!er

1" #efer to the circuit sho!n $elo!"(a) hat is the o!er factor7(b) hat is the average o!er dissi ated7(c) hat is the value of the ca acitance that !ill give a unit& o!er factor !hen connected to the

load7

1"10 An 0-VA, 220-V, 50-*+ load has a o!er factor of 0" lagging" hat value of arallel ca acitance!ill correct the load o!er factor to unit&7

1"11 An 0-. induction 'otor, !ith a lagging o!er factor of 0" 6, is su lied $& a 120-V r's 60-*+sinusoidal voltage source" %ind the ca acitance needed in arallel !ith the 'otor to raise the o!erfactor to4

(a) 0" lagging(b) 1"0"