Download THREE–PHASE SYSTEMS 1. A balanced Y–connected source with

THREE–PHASE SYSTEMS
1. A balanced Y–connected source with
supplies power to a
balanced Y–connected load with a per–phase impedance of
. If
, find the per–phase impedance of the power–distribution line.
2. The power–distribution line of a balanced Y–Y system has a per–phase impedance of
. If the per–phase load impedance is
and the per–phase power
loss on the line is 60 W, find the per–phase power absorbed by the load as well as the
per–phase complex power supplied by the source.
3. A balanced, positive–phase–sequence Y–connected source with
is connected by four perfect conductor lines to an unbalanced Y–connected load having
,
,y
. Find the current on the neutral line.
4. If the neutral line in the Y–Y system of Problem 3 is removed, find
the load neutral node referenced to that of the source neutral node.
, the voltage of
5. A balanced, negative–phase–sequence Y– system has a per–phase distribution–line
impedance of
and a per –phase load impedance of
. If
, find the line currents and the phase voltages at the load.
6. A balanced Y– system has
and
. If the load absorbs
400W per phase with a lagging power factor of 0.875 and the distribution line absorbs
20W per phase, find
,
, ,y
.
7. A balanced load draws a complex power of
kVrms, 60Hz.
at a line voltage of 4
a. Assuming a –connected load, find a simple parallel equivalent for its phase
impedance.
b. Assuming a Y–connected load, find a simple series equivalent for its phase
impedance.
8.
a. What –connected capacitor bank must be connected in parallel with the load of
Problem 7 to achieve pf = 1? Assume the line voltage remains unchanged
b. Repeat, but for a Y–connected bank
9. A balanced load absorbs 360kW at pf = 0.8, lagging. If the load is fed by a balanced
source via a power–distribution line with a per–phase impedance of
and
the line voltage at the load es 660Vrms, find the power factor at the source.
10. A balanced source supplies power to three balanced loads via a power–distribution line
having a per–phase impedance of
. Load 1 absorbs 100kVA at pf = 0.85,
lagging; Load 2 absorbs 25kVAR at pf = 0.75, leading; Load 3 dissipates 20kW at pf =
1. If the line voltage at the load is 240Vrms, find the line voltage and pf at the source.
11. A balanced Y–connected load is powered by a balanced source and draws a total of
120kW at pf = 0.8, lagging. The line voltage at the load is 208Vrms, 60Hz.
a. If three 5mF capacitances are connected in parallel with the load in a Y
configuration, find the power factor of the combined load.
b. Repeat, but with the capacitances connected in a
comment.
configuration. Compare and