Three single-phase two-winding transformers, each rated 25MVA , 54 . 2 / 5 . 42 kV , are connected to form a three-phase Y-Δ bank with a balanced Y-connected resistive load of 0 .6 Ω per phase on the low-voltage side. By choosing a base of 75 MVA (three phase) and 94 kV (line-to-line) for the high-voltage side of the transformer bank, specify the base quantities for the low-voltage side. Determine the per-unit resistance of the load on the base for the low-voltage side. Then determine the load resistance R L in ohms referred to the high-voltage side and the per-unit value of this load resistance on the chosen base.
Three single-phase two-winding transformers, each rated 25MVA , 54 . 2 / 5 . 42 kV , are connected to form a three-phase Y-Δ bank with a balanced Y-connected resistive load of 0 .6 Ω per phase on the low-voltage side. By choosing a base of 75 MVA (three phase) and 94 kV (line-to-line) for the high-voltage side of the transformer bank, specify the base quantities for the low-voltage side. Determine the per-unit resistance of the load on the base for the low-voltage side. Then determine the load resistance R L in ohms referred to the high-voltage side and the per-unit value of this load resistance on the chosen base.
Three single-phase two-winding transformers, each rated
25MVA
,
54
.
2
/
5
.
42
kV
,
are connected to form a three-phase
Y-Δ
bank with a balanced Y-connected resistive load of
0
.6
Ω
per phase on the low-voltage side. By choosing a base of 75 MVA (three phase) and 94 kV (line-to-line) for the high-voltage side of the transformer bank, specify the base quantities for the low-voltage side. Determine the per-unit resistance of the load on the base for the low-voltage side. Then determine the load resistance
R
L
in ohms referred to the high-voltage side and the per-unit value of this load resistance on the chosen base.
A 1200-ampere service was installed, consisting of three sets of 600 kcmil THHN/THWN copper conductors per phase. The electrical contractor was careful to cut theconductors the same length. When the utility crew made up the connections at theservice heads, they cut the conductors to different lengths to make their connectionssimpler. The actual lengths of the service-entrance conductors in a given phase ended up being20 ft (6.1 m), 22 ft (6.7 m), and 24 ft (7.3 m). The maximum ampacity of a 600-kcmilTHHN/THWN copper conductor is 420 amperes using the 75°C column of Table310.16. This is more than adequate for the calculated 1200 amperes when three conductors are run in parallel. Determine how the load of 1200 amperes would divide in each of the three paralleledconductors in a phase.
Determine the conductor sizes for a feeder to a panelboard. It is a 120/240-volt,single-phase system. The OCPD has a rating of 100 amperes. The calculated load is15,600 VA. All the loads are 120 volts.
Calculate the neutral current in a 120/240-volt, single-phase system when the current inphase A is 20 amperes and the current in phase B is 40 amperes. The load is resistive.
Calculate the neutral current in a 208Y/120-volt, 3-phase, 4-wire system when thecurrent in phase A is 0, in phase B is 40, and in phase C is 60 amperes. The load isresistive
Chapter 3 Solutions
MindTap Engineering, 1 term (6 months) Printed Access Card for Glover/Overbye/Sarma's Power System Analysis and Design, 6th
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