Question 34 CEL02 - Chief Engineer - Limited (Alt)

The Correct Answer is B ### Explanation of Correct Option (B) Option B is correct because it accurately describes the fundamental operating principle of a step-down potential transformer (or simply, a step-down transformer) when considering the relationship between its primary and secondary sides under ideal conditions (or standard operating conditions). 1. **Reduced Voltage:** A step-down transformer is specifically designed to decrease (step-down) the voltage from the primary winding to the secondary winding. This is achieved by having fewer turns in the secondary winding ($N_s$) than in the primary winding ($N_p$). According to the transformer voltage ratio ($V_p/V_s = N_p/N_s$), $V_s$ must be less than $V_p$. 2. **Increased Current:** Transformers operate based on the principle of conservation of power. In an ideal transformer, the apparent power (kVA or VA) on the primary side equals the apparent power on the secondary side ($P_{in} \approx P_{out}$). $$V_p I_p = V_s I_s$$ Since the voltage has been reduced ($V_s < V_p$), to maintain power equality, the current must increase ($I_s > I_p$). Therefore, a step-down transformer delivers **reduced voltage** and **increased current** to the secondary load compared to the primary input. *** ### Explanation of Incorrect Options **A) reduced current and increased voltage** * This describes the operation of a **step-up** transformer. A step-up transformer increases the voltage and consequently reduces the current to maintain power balance. This is the opposite of a step-down transformer. **C) reduced voltage and reduced current** * While the voltage is reduced (characteristic of a step-down transformer), the current cannot also be reduced if power is to be conserved (i.e., if the transformer is operating normally and transforming power). Reducing both voltage and current would mean the power output ($V_s I_s$) is significantly less than the power input ($V_p I_p$), violating the fundamental operational characteristic of a power transformer. **D) reduced power (kVA)** * A transformer is a power transfer device. It transfers power from the primary to the secondary side. It does not actively reduce the power itself (aside from small internal losses). The power (kVA) rating is relatively constant across the transformer (Primary kVA $\approx$ Secondary kVA). The power is determined by the source and the load, not the transformation process itself. If the load demands less power, the transformer transfers less power, but the function of the transformer is voltage reduction and corresponding current increase, not power reduction.