Answered: The maximum size overcurrent device for…

The maximum size overcurrent device for primary only protection of a three-phase 45 kVA transformer with a 480V primary and a 120/208V secondary is

Power System Analysis and Design (MindTap Course List)

6th Edition

ISBN:9781305632134

Author:J. Duncan Glover, Thomas Overbye, Mulukutla S. Sarma

Publisher:J. Duncan Glover, Thomas Overbye, Mulukutla S. Sarma

Chapter3: Power Transformers

Section: Chapter Questions

Problem 3.21MCQ: In order to avoid difficulties with third-harmonic exciting current, which three-phase transformer...

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Concept explainers

Single Phase Transformer

A single-phase transformer is a type of power transformer. It is an electrical device that accepts converts the single phase alternating power into single phase alternating power. In this power conversion the voltage is stepped up or down. If the voltage is stepped up, the current will be stepped down and if the voltage is stepped down, the current will be stepped up.

Question

The maximum size overcurrent device for primary only protection of a three-phase 45 kVA transformer with a 480V primary and a 120/208V
secondary is
O
a. 50A
Ob.60A
Oc. 70A
Od.90A

Expert Solution

Step 1 Definition

Transformer is a static device which transfers power from one circuit to another circuit without change in frequency.

As transformer does not change the frequency of the system, it can be treated as constant frequency device.

As transformer transfers almost same amount of power from one circuit to another circuit, it can be treated as constant power device.

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