Question 8

The Correct Answer is B ### Why Option B is Correct Option B ("non-reversing squirrel cage induction motor with reduced voltage autotransformer starting") is correct based on the typical components and configuration found in an electrical control diagram utilizing an autotransformer starter (also known as a compensator). 1. **Motor Type (Squirrel Cage Induction Motor):** Standard industrial motors used in fixed-speed applications (like pumps, fans, compressors) are almost universally three-phase squirrel cage induction motors. The control diagram will typically show three lines (L1, L2, L3) going to the motor (M), confirming a three-phase AC motor. 2. **Starting Method (Reduced Voltage Autotransformer Starting):** The presence of an **autotransformer** (T1, T2, T3) in the power circuit, often labeled with multiple taps (e.g., 50%, 65%, 80% voltage taps) and controlled by specialized contactors (usually labeled S for Starting and R for Running, or 1A, 2A, 3A), is the defining characteristic of this type of reduced voltage starting. This method applies a lower voltage to the motor during startup to limit inrush current and starting torque. 3. **Direction (Non-Reversing):** A reversing starter requires additional components—specifically, a second main contactor (usually labeled REV) and interlocks—to swap two of the three phases (L1, L2, L3) going to the motor. If the diagram shows only a single set of main contactors and thermal overloads leading to the motor, it is a **non-reversing** starter. ### Why Other Options Are Incorrect **A) reversing squirrel cage induction motor with reduced voltage autotransformer starting:** * **Incorrect:** The starter does not feature the necessary second main contactor and associated control logic required to swap phases and reverse the motor direction. It is non-reversing. **C) non-reversing squirrel cage induction motor with reduced voltage primary reactor starting:** * **Incorrect:** Reduced voltage primary reactor starting uses large series **reactors** (coils, or large resistors if resistor starting) placed in series with the motor during startup, which drop the voltage. It does not use an autotransformer to step down the voltage. Since the diagram specifically features an autotransformer (T1, T2, T3), this option is wrong. **D) reversing squirrel cage induction motor with across-the-line starting:** * **Incorrect:** * **Across-the-line starting** (full voltage) uses only a single main contactor (M) and no specialized components (like autotransformers, reactors, or resistors) to reduce voltage during startup. This illustration uses an autotransformer, meaning it is reduced voltage starting. * **Reversing** is incorrect, as the necessary reversing contactor is absent.