Math Problem Statement

A machine requires 10 kW of electrical power when operating at 100V.

[2 marks] If power is delivered through a cable with resistance 100, how much power is lost to the cable’s resistance?

[2 marks] In order to reduce the power loss, a transformer is used between the cable and the machine. What ratio of turns is required on the transformer in order to reduce power loss on the cable by a factor of 104?

Solution

Part 1: Power loss due to cable's resistance

The machine requires 10 kW of electrical power, and it operates at 100 V. First, we can calculate the current II flowing through the cable using the formula for power:

P=V×IP = V \times I

Where:

  • PP is the power (10 kW = 10,000 W),
  • VV is the voltage (100 V),
  • II is the current.

Rearranging the formula to find II:

I=PV=10,000100=100AI = \frac{P}{V} = \frac{10,000}{100} = 100 \, \text{A}

Now, the power lost due to the resistance in the cable can be found using the formula for power loss in a resistor:

Ploss=I2×RP_{\text{loss}} = I^2 \times R

Where:

  • PlossP_{\text{loss}} is the power lost in the cable,
  • II is the current (100 A),
  • RR is the resistance of the cable (100 Ω).

Substituting the values:

Ploss=(100)2×100=10,000×100=1,000,000W=1,000kWP_{\text{loss}} = (100)^2 \times 100 = 10,000 \times 100 = 1,000,000 \, \text{W} = 1,000 \, \text{kW}

Thus, the power lost to the cable’s resistance is 1,000 kW.


Part 2: Transformer turns ratio

To reduce the power loss by a factor of 104, the voltage supplied to the cable must be increased (while reducing the current). A transformer is used for this purpose. The power loss is proportional to I2I^2, so to reduce the power loss by a factor of 104, the current must be reduced by a factor of:

10410.2\sqrt{104} \approx 10.2

The transformer increases the voltage and reduces the current proportionally. The turns ratio nn of the transformer (primary to secondary) is related to the voltage and current as:

n=VsecondaryVprimary=IprimaryIsecondaryn = \frac{V_{\text{secondary}}}{V_{\text{primary}}} = \frac{I_{\text{primary}}}{I_{\text{secondary}}}

Since we want the current reduced by a factor of 10.2, the turns ratio of the transformer must also be 10.2:1.


Summary:

  • The power lost to the cable’s resistance is 1,000 kW.
  • The required turns ratio for the transformer is 10.2:1.

Would you like a further breakdown of these steps or more detailed explanations?


Here are 5 follow-up questions for further exploration:

  1. How is power loss affected if the resistance of the cable is halved?
  2. What would the power loss be without a transformer if the operating voltage was increased to 200 V?
  3. How does increasing the transformer’s turns ratio affect the machine's operation?
  4. If the transformer is 95% efficient, how does this affect the overall system power loss?
  5. Can you explain how transformer efficiency impacts the power delivered to the machine?

Tip: Transformers allow voltage transformation to reduce current and minimize power loss in transmission systems, which is why they are essential in long-distance power delivery.

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Math Problem Analysis

Mathematical Concepts

Electric Power
Ohm's Law
Power Loss in Resistors
Transformers

Formulas

P = V × I (Power equation)
P_loss = I^2 × R (Power loss in a resistor)
n = V_secondary / V_primary (Transformer turns ratio)

Theorems

Ohm's Law
Power Transmission Theorem
Transformer Law

Suitable Grade Level

College Level (Physics or Electrical Engineering)