Two balanced Y-connected loads, one drawing 10 kW at 0.8 power factor lagging and the other 15 kW at 0.9 power factor leading, are connected in parallel and supplied by a balanced three-phase Y-connected, 480-V source.
(a) Determine the source current.
(b) If the load neutrals are connected to the source neutral by a zero-ohm neutral wire through an ammeter, what will the ammeter read?

a.  30.O7A

b.  no reading

Explanation:

for the first load with power factor 0.8, we calculate the reactive power

note the reactive power is calculated as

where p=power

a. for the first load the reactive power is

for the second load the reactive power is

The total reactive power is the summation of both reactive power in he load

and the total real power is 25kw

Hence using Pythagoras theorem to calculate the apparent power we have

Hence we can determine the source current using

b. in a balance 3phase system, there is no neutral current, Hence the ammeter will read zero current