
Problem 
Answer 
1 
A group of Yconnected resistors is connected in parallel with a group of Δconnected resistors to a 230volt line, as shown in the accompanying diagram. Calculate the line currents.
 I_{L1} = 116.5 A I_{L2} = 123.6 A I_{L3} = 106.3 A 
2 
As indicated in the diagram at the left, an induction motor drawing 50 amp at 220 volts with 50% power factor, lagging, from a threephase line has connected in parallel with it between two line wires a singlephase electric furnace which draws from the line 25 amp at 100% power factor. Calculate the total active power. Calculate the current in each line.

I_{L1} = 50 A I_{L2} = 72 A I_{L3} = 56 A 
3 
If, in Problem 2, the motor power only be measured by the twowattmeter method, what would be the reading of each wattmeter? 

4 
By use of a given size of wire, a load of 1000 kilowatts can be delivered over a twowire singlephase line with a loss of 750 watts per wire. How much power could be delivered over a threephase line through the same distance with the same weight of copper and with the same power loss in the line? 
1155 kW 
5 
A balanced threephase, Yconnected load of three singlephase impedances each of which is 5+j6 ohms is connected to a 230volt line. Determine the line current and the power in the load. Draw the vector diagram. 

6 
Three impedances Z_{AB} = 4+j0.5, Z_{BC} = 5j6, and Z_{CA} = 10j0 are connected in delta across a 230volt threephase line whose voltage sequence is V_{AB}, V_{CA}, V_{BC}. Calculate the line currents and the total power in the load. Draw the vector diagram of voltages and currents. 

7 
Calculate the line currents in Problem 6 for the condition of reversed phase rotation. 

8 
A balanced threephase load at 60% power factor is being metered by the twowattmeter method. The total power is 4000 watts. What is the power indicated by each meter? 

9 
Calculate the reactive voltamperes in Problem 8. 

10 
A balanced load of three hundred 75watt lamps on a threephase system is measured by the twowattmeter method. What will be the reading on each wattmeter? 

11 
An induction motor draws from a threephase line 5000 watts at 70% power factor. If a singlephase wattmeter is connected with its current coil in line A and with its potential coil across lines B and C, how much will be the reading of the wattmeter and what will it measure? 

12 
A threewire line of No. 1 conductors 200 ft long with TypeSN insulation (see Appendix) supplies a 120/240volt singlephase load with maximum permissible current. What per cent of load increase would be permissible if the system voltage were changed to threephase 240 volts at the load? 
73.2% 
13 
If three 5ohm resistors connected in wye draw 10 amp per phase from a threephase line, how much power will they draw from the same line if they are connected in delta? 
4500 W 