EEB 326 – 2020
ELECTRICAL MACHINES 1
ASSIGNMENT #: 1
ANSWER ALL QUESTIONS
EACH QUESTION CARRIES 20 MARKS
Question 1
Table 1: Dimensions for Magnetic Circuit
𝐴𝑔 = 26𝑐𝑚2
𝐴1 = 40𝑐𝑚2
𝐴2 = 12𝑐𝑚2
𝐴3 = 25𝑐𝑚2
𝐴4 = 25𝑐𝑚2
𝑙𝑔 = 25 ∗ 10−3 𝑐𝑚
𝑙1 = 40𝑐𝑚
𝑙2 = 24𝑐𝑚
𝑙3 = 𝑙4 = 26𝑐𝑚
𝐻1 = 150𝐴𝑡/𝑚
𝐵2 = 1.34𝑇
𝐻3 = 120𝐴𝑡/𝑚
𝐻4 = 120𝐴𝑡/𝑚
Figure 1: Magnetic Circuit
On figure 1, above is a parallel magnetic structure with an air gap on the right wing. The structure
has 500 turns as shown and sets up a flux of 2 ∗ 10−3 𝑊𝑏. The dimensions and relevant
information are shown on table 1.
a. Draw a labelled equivalent circuit
b. Calculate the mmf required in the air gap
c. Calculate the magnetic field strength and the relative permeability of the central limb
(𝐻2 𝑎𝑛𝑑 𝜇𝑟2 )
d. Current flowing in the coil
Question 2
a. A 24kVA, 2400/240V, 50Hz transformer has a primary winding impedance of 𝑍1 = 0.8 + 𝑗2Ω
and secondary winding impedance of 𝑍2 = 0.008 + 𝑗0.025Ω.
i.
Compute the transformer equivalent resistance and reactance referred to the primary
and secondary winding
ii.
Compute the equivalent voltage drops (active and reactive) referred to primary and
secondary winding
iii.
Compute the equivalent power losses referred to primary and secondary windings
iv.
Sketch a labelled phasor diagram for the equivalent circuit of a transformer referred to
the primary
Submission deadline: 6th March 2020 @ 1200hrs
Venue: Block 248 Office 220