Download Unit ELTK 08 Understanding the electrical principles associated with

Unit ELTK 08
Understanding the electrical principles associated with the design, building, installation and
maintenance of electrical equipment and systems
Unit ELTK 08: Activity Sheet 8.26
Learner:
Date:
Transformer theory
Aims and objectives
At the end of this activity sheet, you should be able to:
●
demonstrate an understanding of transformer theory.
1
Transformers make use of what form of inductance in their operation?
2
Explain using a diagram the operating principle of a single-phase, core type
transformer.
1
© Pearson Education Ltd 2011. Copying permitted for purchasing institution only. This material is not copyright free.
Unit ELTK 08
Understanding the electrical principles associated with the design, building, installation and
maintenance of electrical equipment and systems
3
Although very efficient, no transformer can be 100 per cent efficient. There will
always be power losses. The losses that do occur in transformers can normally
be classed under two main categories. Explain what these are and what their
effects are.
4
Explain what is meant by the term ‘hysteresis’ and draw a diagram of a
‘hysteresis loop’ to support your explanation.
5
Autotransformers have the advantage of being reasonably economical to
manufacture. Give one major disadvantage, and explain your reasoning.
2
© Pearson Education Ltd 2011. Copying permitted for purchasing institution only. This material is not copyright free.
Unit ELTK 08
Understanding the electrical principles associated with the design, building, installation and
maintenance of electrical equipment and systems
6
A transformer having a turns ratio of 3:6 is connected to a 230 V a.c. supply.
Calculate the output voltage.
7
A single-phase transformer with 4000 primary turns and 1000 secondary turns is
fed from a 230 V a.c. supply. Calculate the:
a) secondary voltage
b) volts per turn in both the primary and secondary windings
8
A 100% efficient single-phase transformer with supply voltage Vp = 23 V and a
secondary voltage of 290 V has a power rating of 5 kVA. Calculate the:
a) primary current
b) secondary current
9
A 4.4 kVA transformer has a secondary current of 2.3 A and a primary current of
4.2 A. Calculate the following:
a) the primary voltage
b) the secondary voltage
10 A single phase transformer has a turns ration of 1:33 and a primary current of
16 A. Calculate the:
a) secondary current
b) primary voltage if it is rated at 15 kVA
c) secondary voltage
3
© Pearson Education Ltd 2011. Copying permitted for purchasing institution only. This material is not copyright free.