Transformers and Transformer Calculations Flashcards
7 cards from real Licensed Electrical Contractor practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 Transformers and Transformer Calculations flashcards as text
A transformer has 480 primary turns and 120 secondary turns. What is the turns ratio?
Answer: 4:1
The turns ratio is primary turns divided by secondary turns: 480 / 120 = 4:1.
A transformer has a primary voltage of 480V and a turns ratio of 4:1. What is the secondary voltage?
Answer: 120V
Secondary voltage = Primary voltage / turns ratio = 480V / 4 = 120V.
Which type of transformer provides electrical separation between its primary and secondary windings with no direct electrical connection?
Answer: Isolation transformer
Isolation transformers separate primary and secondary windings to prevent direct electrical connection, protecting equipment from power line disturbances.
What does the kVA rating on a transformer nameplate represent?
Answer: The transformer's apparent power capacity
The kVA rating indicates the apparent power (kilovolt-amperes) the transformer can continuously deliver without exceeding its temperature rating.
In an ideal transformer, when voltage is stepped up from primary to secondary, what happens to the current?
Answer: Current decreases proportionally
In an ideal transformer, apparent power in equals apparent power out; as voltage increases, current must decrease proportionally to maintain constant power.
What is the primary purpose of dielectric oil in a liquid-filled transformer?
Answer: To insulate windings and dissipate heat
Transformer oil serves dual functions: it acts as an electrical insulator between windings and as a cooling medium to transfer heat away from the core and coils.
Which NEC article governs the installation requirements for transformers, including guarding, clearances, and overcurrent protection?
Answer: Article 450
NEC Article 450 covers all transformer installation requirements including protection, location, grounding, and construction standards.