Part 1: Checkbox tasks - only one is right at a time!

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You have to connect a motor to a 400V 3-phase power supply. Which statement is not correct?

 In Delta the phase voltage is 400V.

 In Star connection, the neutral line is voltage-free if all three phase resistances are of the same size.

 The voltage between L1 and N is 230V.

 In Star the line-voltage is 400V.

 In Delta the phase voltage is 230V.

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What voltage can be measured on a 400 V TN-C-S system?

 Between two phases: U = 400 V

 Between two phases: 230 V

 Between phase and neutral line: U = 400 V

 Between phase and PE: U = 0 V

 Between neutral line and PE: U = 400 V

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An industrial furnace is switched from Star to Delta. How does the power behave?

 The power increases four times.

 The power increases by the factor √3 .

 The power doubles.

 The power triples.

 The power increases by the factor 1.5 .

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Part 2: Work orders

Work order 1:

3 Phase Voltage - work order 1

Three resistors are connected to a three-phase power supply.

1.1 In which type of circuit are these resistors connected to each other?
1.2 What is the current I_L in the supply line ?
1.3 What is the size of a phase resistor if the total power of the circuit is 10 kW?

Work order 2:

Three resistors are connected together to Delta.

3 Phase Voltage - work order 2

2.1 What is the current flowing through a resistor?
2.2 How large is the conductor current I_L?
2.3 Calculate the total power of the circuit!
2.4 The fuse S1 blows. How large is the conductor current I_L2? Draw the equivalent circuit díagram!

Work order 3:

3 Phase Voltage work order 3

Three equal-sized 80 Ω heating resistors of a three-phase heater are connected as shown. The string current is 5 A.

3.1 Which connection is shown here?
3.2 To which line voltage must these resistors be connected? Justify by calculation!
3.3 What is the supply current I₁?
3.4 What is the rated power of the heater?
3.5 What is the current in the supply line if a fuse blows?

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