Where are the variable resistors wired in the DC generator field circuit to regulate output?

Where are the variable resistors wired in the DC generator field circuit to regulate output?

• A. In series with the magnetic field
• B. In parallel with the field
• C. In parallel with the armature
• D. Across the load

Answer: (A)

The key idea is that a DC generator’s output is governed by how much current flows in the field winding, i.e., the excitation. The generated voltage is roughly proportional to the magnetic flux, which depends on the field current. Putting a variable resistor in series with the field winding lets you control that current for a given terminal voltage. Increasing the series resistance lowers the field current, reducing flux and output voltage; decreasing the resistance raises the field current, increasing flux and output voltage. If the resistor were placed in parallel with the field or across the load, it wouldn’t properly regulate the field current, so the output wouldn’t be reliably controlled.

The key idea is that a DC generator’s output is governed by how much current flows in the field winding, i.e., the excitation. The generated voltage is roughly proportional to the magnetic flux, which depends on the field current. Putting a variable resistor in series with the field winding lets you control that current for a given terminal voltage. Increasing the series resistance lowers the field current, reducing flux and output voltage; decreasing the resistance raises the field current, increasing flux and output voltage. If the resistor were placed in parallel with the field or across the load, it wouldn’t properly regulate the field current, so the output wouldn’t be reliably controlled.