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MCQ in Transformers Part 3 | REE Board Exam

This is the Multiple Choice Questions Part 3 of the Series in Transformers as one of the Electrical Engineering topic. In Preparation for the REE Board Exam make sure to expose yourself and familiarize in each and every questions compiled here taken from various sources including but not limited to past Board Exam Questions in Electrical Engineering field, Electrical Engineering Books, Journals and other Electrical Engineering References.

Continue Practice Exam Test Questions Part 3 of the Series

Choose the letter of the best answer in each questions.

101. REE Board Exam October 1997

What is the main use of a zigzag transformer?

A. to step down voltage

B. to provide path to zero sequence currents

C. to stabilize transformer sequence currents

D. to step down current

Solution:

102. REE Board Exam October 1997

A power transformer is rated at 50,000 kVA, 34.5 kV/13.8 kV is connected wye-wye, what are the line currents at full-load?

A. 525.2 amperes, 1,725 amperes

B. 836.7 amperes, 2,092 amperes

C. 483.1 amperes, 1,207.7 amperes

D. 1,449.3 amperes, 3,623.2 amperes

Solution:

103. REE Board Exam October 1996

A three-phase transformer has a primary voltage rating of 34.5 kV, wye-connected with two 2.5% taps above and two 2.5% taps below the rated voltage. The secondary winding is rated 460 volts and is delta connected. If it has 100 turns, what will be the effective number of turns in the primary winding if voltage tap us set at minus 2.5%?

A. 7,133 turns

B. 7,312 turns

C. 4,222 turns

D. 4,333 turns

Solution:

104. EE Board Exam April 1988

Two single-phase transformers each rated 75-kVA are connected in V-V or open-delta, to serve a three-phase load of 120 kW at 0.80 power factor lagging. To prevent the overloading of transformers, determine the size of the capacitor in kVAR.

A. 50

B. 40

C. 30

D. 20

Solution:

105. ECE Board Exam April 2001

A transformer composed of two or more coils which are wound around a non-metallic core

A. Metallic core transformer

B. Free core transformer

C. Iron core transformer

D. Air core transformer

Solution:

106. ECE Board Exam April 1999

An autotransformer contains how many coils?

A. None

B. One

C. Two

D. Three

Solution:

107. ECE Board Exam April 2000

Find unloaded output of a power supply having a transformer regulation of 11.10% and 900 V load output.

A. 99.99 V

B. 90 V

C. 999.9 V

D. 900 V

Solution:

108. ECE Board Exam April 1998

A transformer consists of the following?

A. An inductance and resistance

B. A parallel resonant circuit

C. A capacitor and an inductor

D. Two coils wound on a common core

Solution:

109. ECE Board Exam April 2001

How much is the secondary voltage of a power transformer whose parameters are as follows, primary voltage is 240 Volts, 140 turns in the primary and 7 turns in the secondary.

A. 12 V

B. 24 V

C. 6 V

D. 36 V

Solution:

110. ECE Board Exam April 2000

It is a transformer with two or more windings on a laminated iron core used to supply stepped up or stepped down values of voltages to various circuits of an equipment.

A. RF transformer

B. Power transformer

C. Autotransformer

D. AF transformer

Solution:

111. ECE Board Exam April 1999

A transformer with 100 turns in the primary winding and 25 turns in the secondary winding is which of the following?

A. A step-up transformer

B. An isolation transformer

C. A step-down transformer

D. An autotransformer

Solution:

112. ECE Board Exam November 2001

Find the primary voltage of a power transformer under the following conditions 3 turns for primary, 6 turns for secondary and 120 volts for secondary voltage.

A. 8 volts

B. 60 volts

C. 6 volts

D. 12 volts

Solution:

113. ECE Board Exam April 1999

The current that flows in the primary of a transformer with the secondary open (or no load is attached).

A. Source current

B. Exciting current

D. Coupling current

Solution:

114. ECE Board Exam April 1996

What type of transformer that is used to protect technicians and operates from deadly electrical shock?

A. Absorber transformer

B. Step down transformer

C. Step up transformer

D. Isolation transformer

Solution:

115. ECE Board Exam November 2000

Components of the transformer which receives energy from the primary winding and delivers it to the load.

A. Enclosure

B. Core

C. Secondary winding

D. Primary winding

Solution:

116. ECE Board Exam November 1998

Which of the following does not contribute to losses in a transformer?

A. Leakage resistance

B. Self-inductance

C. Stray capacitance

D. Iron losses

Solution:

117. ECE Board Exam April 2001

A transformer composed of two or more coils which are wound around a non-metallic core

A. Metallic core transformer

B. Free core transformer

C. Air core transformer

D. Iron core transformer

Solution:

118. A transformer will work on ____.

A. a.c. only

B. d.c. only

C. a.c. as well as d.c.

D. none of these

Solution:

119. The primary and secondary of a transformer are ____ coupled.

A. electrically

B. magnetically

C. electrically & magnetically

D. none of these

Solution:

120. A transformer is an efficient device because it ____.

A. is a static device

B. uses capacitive coupling

C. uses inductive coupling

D. uses electric coupling

Solution:

121. A transformer transfers electrical energy from primary to secondary usually with a change in ____.

A. frequency

B. power

C. voltage

D. time period

Solution:

122. The voltage per turn of the primary of a transformer is ____ the voltage per turn of the secondary.

A. more than

B. less than

C. the same as

D. none of these

Solution:

123. The winding of the transformer with greater number of turns will be ____.

A. high-voltage winding

B. low-voltage winding

C. either high or low voltage winding

D. none of these

Solution:

124. A transformer does not possess ____ changing property.

A. impedance

B. voltage

C. current

D. power

Solution:

125. The iron-core is used to ____ of the transformer.

A. increase the weight

B. provide tight magnetic coupling

C. reduce core losses

D. none of these

Solution:

126. If a transformer core has air gaps, then ____.

A. reluctance of magnetic path is decreased

B. hysteresis loss is decreased

C. magnetizing current is greatly increased

D. eddy current is increased

Solution:

127. The maximum flux produced in the core of a transformer is ____.

A. directly proportional to supply frequency

B. inversely proportional to supply frequency

C. inversely proportional to primary voltage

D. none of these

Solution:

128. The flux in the core of a single-phase transformer is ____.

A. purely alternating one

B. purely rotating one

C. partly alternating and partly rotating

D. none of these

Solution:

129. A transformer is so designed that primary and secondary have ____.

A. high leakage flux

B. large resistance

C. tight magnetic coupling

D. good electric coupling

Solution:

130. When the primary of a transformer is connected to a d.c. supply, ____.

A. primary draws small current

B. primary leakage reactance is increased

C. core losses are increased

D. primary may burn out

Solution:

131. An ideal transformer is one which ____.

A. has no losses and leakage reactance

B. does not work

C. has the same number of primary and secondary turns

D. none of these

Solution:

A. 3 โ 5%

B. 15 โ 30%

C. 30 โ 40%

D. above 40%

Solution:

133. The no-load p.f. of a transformer is small because ____

A. iron losses component of Io is large

B. magnetizing component of Io is large

C. magnetizing component of Io is small

D. none of these

Solution:

134. The no-load input power to a transformer is practically equal to ____ loss in the transformer.

A. iron

B. copper

C. eddy current

D. none of these

Solution:

135. Two things which are same for primary and secondary of a transformer are ____.

A. ampere-turns and voltage per turn

B. resistance and leakage reactances

C. currents and induced voltages

D. none of these

Solution:

136. A transformer operates poorly at very low frequencies because ____.

A. permeability of core is increased

B. magnetizing current is abnormally high

C. primary reactance is too much increased

D. none of these

Solution:

137. If a power transformer is operated at very high frequencies, then ____.

A. primary reactance is too much increased

B. primary will draw large power

C. core losses will be excessive

D. none of these

Solution:

138. The primary leakage flux links ____.

A. primary winding only

B. secondary winding only

C. both primary and secondary winding

D. none of these

Solution:

139. The effect of leakage flux in a transformer is to ____.

A. increase copper losses

B. decrease copper losses

C. cause voltage drop in the windings

D. none of these

Solution:

140. Leakage flux in a transformer occurs because ____.

A. iron core has high permeability

B. air is not good magnetic insulator

C. applied voltage is sinusoidal

D. transformer is not an efficient device

Solution:

141. The mutual flux in a transformer remains constant at all loads because ____.

A. applied voltage and frequency are constant

B. leakage flux is small

C. iron-core is used

D. losses are small

Solution:

142. Cores of large

transformer are built up to nearly circular crosssection in order to reduce ____.

A. leakage reactance

B. iron losses

C. eddy current loss

D. copper loss

Solution:

Unsolved problems

143. REE Board Exam September 2002

A 20 kV/7.87 kV autotransformer has 200 A current in the common winding. What is the secondary line current?

A. 143.52 A

B. 200 A

C. 56.48 A

D. 329 A

Solution:

144. REE Board Exam April 2004

Instrument transformers are used in indicating and metering and with protective devices, they are used for

A. measuring

B. detecting

C. relaying

D. sensing

Solution:

145. REE Board Exam October 2000

The CT ratio and PT ratio used to protect a line are 240 and 2000 respectively. If the impedance of each line is 10 ฮฉ, what is the relay impedance to protect the line from fault?

A. 83.33 ฮฉ

B. 1.2 ฮฉ

C. 48,000 ฮฉ

D. 12 ฮฉ

Solution:

146. REE Board Exam October 2000

Two single-phase transformers operate in parallel. Transformer 1 is rated 100 kVA with 4% reactance while transformer 2 is rated 75 kVA with 3% reactance. The transformers have secondary voltages of 220 volts and same voltage ratio. If the common load is 125 kVA at 80% p.f. lagging, determine the kVA sharing of each transformer.

A. 71.43 kVa and 53.57 kVA

B. 75 kVa and 50 kVA

C. 62.5 kVA and 62.5 kVA

D. 82.5 kVA and 42.5 kVA

Solution:

147. REE Board Exam April 2004

A transformer rated 2,000 kVA, 34,500/240 volts has 5.75% impedance. What is the per unit impedance?

A. 0.0635

B. 0.0656

C. 0.0575

D. 34.2

Solution:

148. REE Board Exam April 2001

A 69 kV/13.8 kV, 7.5 MVA transformer has 8% impedance. What is its impedance at 100 MVA base?

A. 0.6%

B. 8%

C. 800%

D. 106.7%

Solution:

149. REE Board Exam October 1997

A 3-phase transformer is rated 30 MVA, 115ฮ/13.8Y kV and 2% impedance, the resistance is negligible compared with the reactance. Determine the percent (%) voltage drop at the secondary at 80% load and at 75% power factor.

A. 4.1%

B. 2.26%

C. 1.05%

D. 3.15%

Solution:

150. Which of the following connection is best suited for 3-phase, 4- wire service?

A. โ

B. Y โ Y

C. โ Y

D. Y โ

Solution:

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