Lesson 21 - Three-Phase Circuits

The neutral current will be ___ amperes where two-phase conductors and the neutral conductor of a three-phase, wye-connected system supply 20-ampere phase-to-neutral connected resistance loads. Select one: a.20 b.0 c.17 d.28.28

a.20

There will be a voltage drop of ___ volts across each of three wye-connected 200-ohm resistors connected to a 480-volt, three-phase circuit. Select one: a.277 b.480 c.240 d.120

a.277

To solve for power in a 3-phase system, you would use the formula __________. Select one: a.E × I × 1.73 for wye b.E × I × 3 for delta c.E × I × 0.58 for delta d.E × I × pf for wye

a.E × I × 1.73 for wye

It is an advantage to rectify 3-phase power sources compared to single-phase sources because _______. Select one: a.the 3- phase produces less DC ripple b.the AC voltage peaks are greater with 3-phase c.3-phase requires fewer rectifiers d.the AC component of the DC voltage is higher

a.the 3- phase produces less DC ripple

To find the line current in a 3-phase delta connected system, multiply the phase current by ______ to get line current. Select one: a.2 b.1.73 c.1.58 d.1.27

b.1.73

To supply the same kVA load with three phase system, as compared with a single phase system would require _______________ conductors . Select one: a.20% less copper b.62.5% of the copper c.the same amount of copper d.20% more copper

b.62.5% of the copper

The voltages of a three-phase system are ___ degrees out of phase. Select one: a.90 b.60 c.120 d.180

c.120

Total kVA of a balanced 3-phase power system with 25A and 480 volts would be _________. Select one: a.12,000 VA b.36,000 VA c.20,760 VA d.17,300 VA

c.20,760 VA

The voltage to ground on the high leg of a 240/120V, 4-wire delta system is ___ volts. Select one: a.240 b.120 c.208 d.277

c.208

A power of ___ kilowatts is used by a resistive load that draws 42 amperes line current at 480 volts, three-phase. Select one: a.20.16 b.11.64 c.34.92 d.53.43

c.34.92

Line voltage and coil current are the same in a __________ 3-phase system. Select one: a.3-wire delta b.4-wire delta with center tap c.4-wire wye connected d.2-wire wye

c.4-wire wye connected

The input kilovolt-amperes to a 480-volt, three-phase Delta, phase-to-phase connected load of 14 ohms is ___. Select one: a.28.5 b.85.5 c.49.4 d.16.5

c.49.4

To find the voltage to the "high leg" of a 4-wire delta multiply the center tap voltage by _______. Select one: a.1.58 b.0.58 c.2 d.1.73

d.1.73

Three 25-ohm resistors wye-connected to a 480-volt, three-phase circuit will draw ___ amperes. Select one: a.19.2 b.14.3 c.25 d.11.1

d.11.1

The voltage across the phase windings of a 480-volt, three-phase delta alternator is ___ volts. Select one: a.277 b.120 c.208 d.480

d.480