RRB JE Electrical One Liner Questions and Answers series Part -3 (Power System)

 In previous article we learned questions about light and household appliances applications. In this article we will learn about power system questions which will be helpful for RRB JE exam

101. Service mains are the conductors, which connect the consumer's terminals to the distribution.

102. The underground system can not be operated above 66 KV.

103. Overhead system being used in India is upto 765 KV.

104. Kevin 's law is used for conductor cost calculations.

105. The wooden poles well impregnated with creosite oil or any preservative compounds have life 25 to 30 years.

106. Galvanised steel wire is generally used as stay wire, earth wire and structural component.

107. The usual spans with RCC poles are 80 to 100 meter.

108. Corona depends on size of conductors, shape of conductors and surface condition of conductors.

109. The formula for voltage regulation of transmission line is 


Where Vs = Sending end voltage and Vr = Receiving end voltage 

110. The phenomenon of rise in voltage at receiving end of the open circuit or lightly loaded line is called the Ferranti effect.

111. Low voltage cable is upto 6.6 KV, super tension cable 33KV, extra high tension cable 66 KV, and  High voltage cable 11KV. 

112. Direct laying,  draw in system and solid method are used for underground cables.

113  Radial distribution system is the simplest and lowest in cost.

114. The distributors for residential areas employee 3 phase 4 wire system.

115. Distribution lines in India generally use RCC poles.

116. In Overhead lines generally ACSR (ALUMINIUM CORE STEEL REINFORCED) conductors are used.

117. Transmission line insulators are made of porcelain. Composition of porcelain is Feldspar,  Kaolin, Bone Ash, Quartz,  Petuntse, and Alabaster.

118. The minimum clearance between the ground and 220 KV line is about 7.0 meter.

119. The spacing between phase conductors of a 220 KV line is approximately equal to 6.0 meter.

120. Large industrial consumer's are supplied electrical energy at 66 KV.

121. For an overhead line surge impedance is taken as 100 to 200 ohm.

122. The presence of ozone due to corona is harmful because it corrodes the material.

123. A feeder in a transmission line feeds power to distributors.

124. 3 phase 4 wire system is called secondary distribution system.

125. Mho relay is used for long transmission line.

126. Impedence relay is used for medium transmission line.

127. Reactance relay is used for short transmission line.

128. Ring main system is most reliable distribution system.

129. Transmission voltage 11KV, 33 KV, 66KV, 132 KV, 220 KV and 400 KV is used for 15 - 30 KM, 30 - 60 KM, 60 - 100 KM, 100 - 200 KM, 200 - 300 KM  and 300 - 400 KM length respectively.

130. Skin effect is proportional to square of conductor diameter.

131. String efficiency can be improved by using a guard ring, grading of insulators and using long cross arm.

132. For isolators current rating is not necessary as they break line when uncharged.

133. Corona occurs on 30 KV/CM electrostatic stress.

134. Aluminium specific gravity is 2.7

135. The frequency of generated voltage can be changed by adjusting the governor.

136. Number of conductors in an ACSR wire can be calculated by 3 -3m +1. where m= layer

137. Diameter of ACSR conductor is calculated by (2m-1)×d, where m= layer, d=diameter of stranded wires.

138. Main consideration for designing feeder is current carrying capacity.

139. Main consideration in Distributer design is voltage drop.

140. Different type names are given to ACSR conductor according to voltage and current 

Rabbit type ACSR  -  11 KV, 157 Ampere, 2 layers, 7 conductors, 1 steel, 6 aluminium, d = 3.35 mm, A = 50 mm2, Breaking Load = 18.25 KN

Dog type ACSR  -   33 KV - 66 KV, 300 Ampere, 6 aluminium strands of 4.72 mm diameter, 7 steel strands  1.57 mm  diameter, A = 100 mm2, Breaking Load = 32.41 KN

Panther type ACSR - 66 KV - 132 KV, 480 Ampere, 4 layers, d= 3 mm, 37 conductors, 30 aluminium,  7 steel,  A = 200 mm2, Breaking Load = 89.67 KN

Zebra type ACSR  - 220 KV, 735 Ampere, 5 layers, d=3.18 mm, 61 conductors , 54 aluminium,  7 steel, Breaking Load = 130 KN

Moose type ACSR  - 400 KV, 800 Ampere , 5 layers, d= 3.53 mm,  61 conductors, 54 aluminium, 7 steel, 

Bundle 8 or 4 Moose type ACSR   -   765 KV

141. Basic terminology for over head lines

Low Voltage       0 - 250 V

Medium Voltage       250 V - 650 V

High Voltage       650 V - 33 KV

Extra high Voltage     33 KV - 132 KV

Super High Voltage      132 KV and beyond 

Modern Extra High Voltage      400 KV

Ultra High Voltage      765 KV and beyond 

142. Human body current bearing limit is 30 mili ampere per second.

143. Basic terminology for underground cable 

Low Tension Cable   upto 1000 V

High Tension Cable   upto 11 KV

Super Tension Cable   22 KV to 33 KV.

Extra High Tension Cable  33 KV to 66 KV.

Extra Super Tension Cable  beyond of 132 KV.

144. Minimum clearance of HV lines from ground across street is 6.1 meter.

145. Minimum depth of laying from ground surface to the top of cable is 1.0 meter at railway crossings and road crossings.

146. 765 KV transmission line is installed at Solapur-Raichur on 31 December 2013 under One Nation - One Grid - One frequency scheme.

147. Bundled conductors are used in EHV transmission to decrease corona loss.

148. Ground clearance for 220 KV transmission line is 7.0 meter. Where as for 400 KV and 765 KV it is 8.84 meter and 12.40 meter respectively.

149. Permissible Voltage variation in transmission and distribution system is +- 10 %.

150. Some important formulas used in power system 

Demand Factor = Max demand / Total Connected load

Load Factor = Average Load / Max Demand or Peak Load

Where Average Load = Total Energy Consumed / Total Time

Plant Capacity Factor = Average Load / Plant Capacity 

Reserve Capacity = Plant Capacity  -  Max Demand 

Where Max Demand = Max sustained demand more than 30 minutes 

Diversity Factor = Sum of individual Max demand  / Co- incident Max demand 


1. Diversity Factor is define only on distributed loads and have value more than Unity.

2. Load Factor and Demand Factor both have value less than Unity.

Author:- Amarjeet Singh Jamwal authored articles on Basic Electronics EngineeringElectric Traction, and Electronics Practical for INFO4EEE Website

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