Electric traction

Established as per the Section 2(f) of the UGC Act, 1956
Approved by AICTE, COA and BCI, New Delhi
Electrical Power Utilization
Course Code :B19EE4051
School of Electrical and Electronics Engineering,
REVA University
Latha N,
Ass istant Professor
A Y : 2 0 2 0 - 2 0 2 1

COURSE CONTENTS
UNIT – 2a: Introduction to Electric and Hybrid Vehicles Total duration = 12 Hours
Configuration and performance of electrical vehicles
Traction motor characteristics, tractive effort, transmission requirement
Vehicle performance and energy consumption
.

Frenchman
Gustave Trouvé
First electric
vehicle (1881)
ELECTRIC AND HYBRID VEHICLES
Tricycle
0.1 hp DC motor
Lead–acid batteries

•No emission
•High efficiency
•Very robust & less maintenance
•Quiet and smooth operation
•Excellent torque and output characteristics
•Regenerative braking
Advantages of EV over ICEV
Advantages of EV over ICEV

•Limited range
•Charging time
•Electric charging stations is sparse
Disadvantages of EV over ICEV
Disadvantages of EV over ICEV

ICEV EV
Gasoline tank
IC
Batteries
Electric Motor
How EV is made from ICEV?

Modern EV in place of primary EV

Drive Train
Electric
propulsion
system
Energy source
sub system
The auxiliary
sub system
Modern EV in place of primary EV

Electric propulsion
system
Vehicle controller
Power electronic
converter
Electric motor
Mechanical
Transmission
Driving wheels
1. Electric propulsion system

Energy Source Sub
System
Energy Source
The Energy Management
Unit
The Energy Refueling Unit
2. Energy source sub system

3. The auxiliary sub system
The auxiliary sub
system
Power steering unit
The hotel climate
Control unit
The auxiliary supply
unit

1. Electric propulsion system
Power electronic converter regulates the power flow between the electric
motor and energy source
Power electronic converter regulates the power flow between the electric
motor and energy source
Control inputs from the accelerator and brake pedals to vehicle controller
Control signals from vehicle controller to electronic power converter

2. Energy source sub system
Energy management unit (EMU) cooperates with the
vehicle controller to control the regenerative braking and
its energy recovery
EMU also works with the energy refueling unit to control
the refueling unit and to monitor the usability of the
energy source

3. The auxiliary sub system
Provides the necessary power with different voltage
levels for all the EV auxiliaries (climate control
and power steering unit)

EV configurations
C : Clutch
D : Differential
FG : Fixed Gearing
GB : Gearbox
M : Electric Motor

EV configurations
The clutch is used to connect or disconnect the
power of electric motor from the driven wheels
The differential is a mechanical device (usually a set of planetary gears) which
enables both sides to be driven at different speeds when the vehicle runs along
a curved path
The gear box provides a set of gear ratios to
The gear box provides a set of gear ratios to
modify the speed-power (torque) profile to match
the load requirement

EV configurations
An electric motor that has a constant power in a long
range, a fixed gearing can replace the multispeed
gearbox and reduce the need of a clutch
Not only reduces the size and weight of the mechanical transmission, it also simplifies
the drive train control because gear shifting is not required

EV configurations
M,FG and D can be further integrated into a single
assembly while both axles point at both driving
wheels
The whole drive train is further simplified and compacted

EV configurations
D is replaced by using two traction motors
Each of them drives one side wheel and operates at a different speed when
the vehicle is running along a curved path

EV configurations
The drive train and M can be placed inside a
wheel
A thin planetary gear set may be employed to reduce the motor speed
and enhance the motor torque

EV configurations
Mechanical gearing is avoided by connecting a
low speed motor directly to the driving
wheels
The speed control of motor is the speed control of driving
wheel
But this arrangement requires a motor having a higher torque

Performance of EVs
Vehicle’s driving
performance
Acceleration
time
Maximum
speed
Gradeability
Proper motor power rating and transmission parameters are the primary
considerations to meet the performance specification
The design of all these parameters depends on the speed-power (torque)
characteristics of the traction motor

Traction motor characteristics
Variable speed motor
characteristics

The characteristics is usually represented by a speed ratio x, defined as the ratio of
its maximum speed to its base speed
Low speed region
(less than the base speed)
motor has a constant
torque
High-speed region
(Higher than the base speed)
motor has a constant
power

In low-speed operations, voltage supply to the motor increases with the increase
of the speed through the electronic converter while the flux is kept constant
After the base speed, the motor voltage is kept constant and the flux is
weakened, dropping hyperbolically with increasing speed. Hence, its torque also
drops hyperbolically with increasing speed
At the point of base speed, the voltage of the motor reaches the source voltage

Speed- Torque
characteristics different
speed ratios x (x=2,4,6)

With a long constant power region, the maximum torque of the motor can be
significantly increased, and hence vehicle acceleration and gradeability
performance can be improved and the transmission can be simplified

Vehicle performance
Vehicle’s driving
performance
Acceleration
time
Maximum speed Gradeability

Vehicle performance
Acceleration time
Acceleration performance of a vehicle is evaluated by the time used to
accelerate the vehicle from a low speed to a higher speed (100km/h for
passenger cars)
For passenger cars, acceleration performance is more important than max.
cruising speed and gradeability, since power rating of motor drive
depends on acceleration performance

Vehicle performance
Maximum speed
The maximum speed of a vehicle can be easily found by the intersection point of the
tractive effort curve with the resistance curve

Vehicle performance
Gradeability
It is defined as the highest grade a vehicle can ascend maintaining a particular speed
The maximum grade that a fully laden vehicle combination is capable to maintain the
forward motion on an uphill road at a certain constant speed at a certain friction level
OR
It is determined by the net tractive effort of the vehicle
The gradeability at mid and high speeds is smaller than at low speed

Tractive effort
𝒕
𝒎 𝒈 𝟎 𝒕
𝒅
𝒎 𝒅
𝒈 𝟎
The tractive effort developed by a traction motor on driven wheels
And the vehicle speed
Tm and are the motor torque output
Nm speed in rpm
ig is the gear ratio of transmission
i0 is the gear ratio of final drive
ηt is the efficiency of the whole driveline from the motor to the driven wheels
and rd is the radius of the drive wheels

The use of a multigear or single gear depends mostly on the motor speed-torque
characteristics
At a given rated motor power, if the motor has a long constant power region, a
single gear transmission would be sufficient for a high tractive effort at low
speeds, otherwise a multigear (more than two gears) transmission has to be used
Transmission requirement

x=2, 3 gears, 3 speed
regions

x=4, 2 gears, 2 speed
regions

x=6, 1 gear, 1 speed
regions

Energy consumption
Energy consumption

The energy consumption is an integration of the power output at the battery
The energy consumption is an integration of the power output at the battery
terminals
Energy consumption
Energy consumption
For propelling, the battery power output is equal to the resistance power
and power losses in transmission and motor drive, including power losses in
the electronics
The efficiency of a traction motor varies its operating points on the speed-
time curve (speed-power) plane, where the most efficient operating area exists

The architecture of a hybrid vehicle is defined as the connection between the
components that define the energy flow routes and control ports
HYBRID VEHICLES

Classification of Hybrid vehicles
Classification of Hybrid vehicles
HEVS
Series hybrid
Parallel hybrid
Series–parallel hybrid
Complex hybrid

HYBRID VEHICLES
HYBRID VEHICLES

HYBRID VEHICLES
HYBRID VEHICLES
Configuration of a series hybrid electric drive train
Configuration of a series hybrid electric drive train

Operation modes
Pure electric mode
Pure engine mode
Hybrid mode
Engine traction and battery charging mode
Regenerative braking mode
Battery charging mode
Hybrid battery charging mode
Operation modes of a series hybrid electric drive train

Pure electric mode
The engine is turned off and the vehicle is propelled only by the
The engine is turned off and the vehicle is propelled only by the
batteries
Pure engine mode
 The vehicle traction power only comes from the engine-generator, while the
batteries neither supply nor draw any power from the drive train.
 The electric machines serve as an electric transmission from the engine to
the driven wheels

Hybrid mode
The traction power is drawn from both the engine generator and the batteries
Engine traction and battery charging mode
The engine-generator supplies power to charge the batteries and to propel
The engine-generator supplies power to charge the batteries and to propel
the vehicle

Regenerative braking mode
Battery charging mode
 The engine-generator is turned off and the traction motor is operated as a
generator
 The power generated is used to charge the batteries
The traction motor receives no power and the engine-generator charges the
batteries

Hybrid battery charging mode
Both the engine-generator and the traction motor operate as generators to
charge the batteries

Series hybrid electric drive train
Advantages
Advantages
Because electric motors have near-ideal torque–speed characteristics, they
Because electric motors have near-ideal torque–speed characteristics, they
do not need multigear transmissions. Therefore, their construction is
greatly simplified and the cost is reduced
Simple control strategies may be used as a result of the mechanical
decoupling provided by the electrical transmission

Series hybrid electric drive train
Disadvantages
Disadvantages
in
 The energy from the engine is converted twice (mechanical to electrical in
the generator and electrical to mechanical in the traction motor)
 The inefficiencies of the generator and traction motor add up and the
losses may be significant
The generator adds additional weight and cost
The traction motor must be sized to meet maximum requirements since it is
the only power plant propelling the vehicle

Thank You
Name : Latha N
Department: School of Electrical and Electronics Engineering
Contact : Email ID: latha.n@reva.edu.in
Mobile No. : 9743994095

COURSE CONTENTS
UNIT – 2b: Electrolytic process Total duration = 12 Hours
Fundamental principles
Extraction, refining of metals and electroplating
Factors affecting electro deposition process
Power supply for electrolytic process
Numerical

ELECTROLYTIC PROCESS
The process in
which electrical
energy is used
to produce
chemical
changes
.
.

Copper
Zinc
Aluminium
Magnesium

Gold
Silver
Copper
Nickel

Manufacturing
of chemicals
Caustic soda
Potassium permanganate
Chlorine

Electrotyping

Chemical
Metallurgical

Electrolysis
 Electrolysis, process by which electric current is passed through
a substance to effect a chemical change
 The chemical change is one in which the substance loses or
gains an electron (oxidation or reduction)

Electrolysis
CuSO4
Cu++
SO4
--
𝟒 𝟐 𝟐 𝟒 𝟐
𝟐 𝟒 𝟒 𝟐

Faraday’s laws of Electrolysis
The mass of the substance liberated during electrolysis is directly proportional to
quantity of electricity flowing through the electrolyte
First Law
First Law
Where, m = mass of the substance liberated in kg
Z = a constant know as the electro-chemical
equivalent of the substance in Kg/C
I = current flowing in amperes
t = time for which flows in seconds

First Law
First Law
The electrochemical equivalent Z of a substance is defined as the amount of the
substance deposited , when a current of 1A flows through the electrolyte for 1
second
If, And
Then,
Unit is in kilogram per coulomb (kg/C)

When same quantity of electricity is passed through several electrolytes, the mass
of the substances liberated are proportional to their respective chemical
equivalents or equivalent weights
Second Law
Second Law

Definitions
Electrochemical equivalent (Z)
ECE of a substance is the mass of it liberated in a process of electrolysis by the
passage of unit quantity of electricity, i.e. by unit current (ampere) for unit time
(second)
The SI unit of ECE (Z), is the kg/Coulomb
Atomic weight
Atomic weight of an element is a number, which is the average of the masses of
its various isotopes (protons=electrons, no. of neutrons different)

Definitions
Formula weight
Formula weight of a chemical entity (atom, radical, molecule, ion) is the sum of
the atomic weights of its constituents
Example:
The formula weight of water (H2O) is two times
the atomic weight of hydrogen plus one times
the atomic weight of oxygen
Numerically, this is
(2×1.00797)+(1×15.9994)
= 2.01594+15.9994=18.01534

Definitions
Valency
The Valency of an atom or radical (a group of atoms) is the no. of hydrogen
atoms with which it will react chemically
Valency is always an integer (i.e. 1,2,3..) but for a given atom or radical, it
can have different values in different chemical reactions
Example:
Valency of Aluminium is 3

Definitions
Equivalent weight
It is defined as the mass of an element/compound/ion which combines or
displaces 1 part of hydrogen or 8 parts of oxygen or 35.5 parts of chlorine
by mass
Example:
Atomic weight of Silver is 107.88 and Valency is 1
Then , Equivalent weight is 107.88

Current efficiency
Current efficiency is defined as “ The ratio of the actual quantity of
substances liberated to the theoretical quantity”
Definitions
It is usually between 90 to 98%, for Chromium plating only about 12 to 15%

Energy efficiency
Energy efficiency is defined as ratio of the theoretical energy required for
depositing a certain quantity of the substance to the actual value of the energy
required
Definitions

Electrode Potential
A potential difference exists between the anode and electrolyte and also
between cathode and electrolyte, this potential difference is called
electrode potential
Depends on temperature and concentration of electrolyte

Calculation of current required
From the ECE(kg/C) it is possible to calculate the theoretical value of current
required to deposit any given quantity of metal or alternatively the amount of
metal which should theoretically be deposited by a given current

A sheet of iron having a total surface area of 0.36m2 is to be electroplated
with copper to a thickness of 0.0254mm.Estimate the time required for the
process? The iron will be made cathode and immersed, together with an
anode of pure copper, in a solution of copper sulphate. Given density of
copper as 8.96e+03kg/m3 , ECE of copper as Z=32.9e-08 kg/C, current
density is 330A/m2
Numerical - 1

 Surface area = a = 0.36m2
 Thickness = t = 0.0254mm
 Density of copper = D = 8.96e+03kg/m3
 ECE of copper = Z = 32.9e-08 kg/C
 Current density = δ = 330A/m2
Data Given:
To find:
Time required=T=?
Numerical - 1

Solution - 1
Mass of the copper deposited = 9.144 x 10-6 m3 x 8.96e+03 kg/m3
Volume of the Iron Sheet = Surface Area of the Iron sheet x Thickness of sheet
Volume of the Iron Sheet = 9.144 x 10-6 m3
Volume of the Iron Sheet = 0.36m2 x 0.0254mm
Mass of the copper deposited = Volume of the Iron Sheet x Density
Volume of the Iron Sheet = 0.36 x 0.0254 x 10-3
AH = 69.233 kg
Mass of the copper deposited = 0.081930 kg = 0.082kg

Solution - 1
Current = I = 0.36m2 x 330A/m2
T = 0.585 Hrs
Current = I = Surface Area x Current Density
Current = I = 118.8 A

Calculate the Ah required to deposit a coating of silver 0.1mm thick on a
sphere of 10cm radius. Assume ECE of silver = 0.001118 g/C and density
of silver to be 10.5 g/cm3. Assume that the energy efficiency is 95%.
Numerical - 2

 Thickness = t = 0.1mm
 Radius of sphere = r = 10cm
 Density of silver = D = 10.5 g/cm3
 ECE of silver = Z = 0.001118 g/C
 energy efficiency = 95%
Data Given:
To find:
AH required = ?
Numerical - 2

Solution - 2
Volume = Surface Area of Sphere x Thickness
Volume = 12.5664 cm3
Mass of the silver deposited = Volume x Density
Surface Area of Sphere = 4𝜋𝑟
Surface Area of Sphere = 1256.64𝑐𝑚
Surface Area of Sphere = 4𝜋 ∗ 10
Volume = 1256.64𝑐𝑚 x 0.1 x 10
Mass of the silver deposited = 12.5664 cm3 x 10.5 g/cm3
Mass of the silver deposited = 131.94 g

Solution - 2
AH = 32.78 g Theoretical Value of AH
Actual AH = 34.50 g

If 96500C of electricity liberate 1g equivalent of any substance, how long
will it take for a current of 0.15A to deposit 20mg of Cu from a solution of
copper sulphate? Chemical equivalent of Cu is to be taken as 32.
Numerical - 3

 Current = I = 0.15A
 Mass of copper deposited = 20mg
 ECE of copper = Z = 32/96500 g/C
Data Given:
To find:
Time required = T = ?
Numerical - 3

Solution - 3
AH = 0.01675
T = 402s
T = 0.11168Hrs

A rectangular plate 20 x 10cm is to be coated with Nickel with a layer of
0.2mm thickness. Determine the quantity of electricity in Ah and time
taken for the process. Current density is 190A/m2 and current efficiency is
90%. Specific gravity (density) of nickel is 8.9g/m3. ECE of Nickel =
0.0010954kg/Ah
Numerical - 4

A 20cm long portion of a circular shaft 10cm diameter is to be coated with
a layer of 15mm Nickel. Determine the quantity of electricity in Ah and time
taken for the process. Assume a current density of 195 A/m2 and current
efficiency of 92%, Specific gravity (density) of Nickel is 8.9g/m3, ECE of
Nickel = 1.0954kg/1000Ah
Numerical - 5

The to
The worn out part of a circular shaft 0.15m in diameter and 0.3m long is to
be repaired by depositing on it 1.6mm of Nickel by electro-deposition
process. Estimate the quantity of electricity required and the time taken, if
the current density is 215A/m2. The energy efficiency of the process may be
taken as 95%. The density of Nickel is 8.9e+03kg/m3 and ECE of Nickel is
30.349e-08kg/C
Numerical - 6

Nickel coating of 1mm thickness is to be built on a cylindrical surface 15cm
diameter and 20cm long in 1 ½ Hrs. Calculate the electrical energy needed
if ECE of nickel is 0.3043 mg/C. Specific gravity (Density) =8.9g/m3 and
voltage used in electroplating is 10V.
Numerical - 7

Estimate the current required to produce 10g of caustic soda in 5min from a
solution of sodium chloride given that ECE of sodium is 0.0002388g/C and
atomic weights of sodium=23, Oxygen=16 and Hydrogen=1
Numerical - 8

A weighed copper plate is made as cathode in a copper sulphate
voltammeter (electrolytic cell). At the end of two hours a weight of 50g was
deposited on it. The current during the operation time was kept constant
and the ammeter indicated 20A. Did the ammeter read correctly; if not
what is the %age error?. Given atomic weight of copper=63.5; Hydrogen
= 1; Silver = 108 and ECE of Silver=0.001118g/C, Valency of Copper=2,
Valency of Silver=1
Numerical - 9

Extraction of metals
Ore is treated with
strong acid
Ore is available in
molten state

Metal Treatment of ore Solution
Consumption
kwh/t (approx.)
Aluminium -
Fused cryolyte (combustible matter
for firing mines)
20,000-25,000
Copper
Roasted and leached (to
moisten) with sulphuric
acid
Copper sulphate 2000-2500
Magnesium -
Fused magnesium chloride or
carnallite
17,000-20,000
Sodium -
Fused sodium hydrate or sodium
nitrate and sodium chloride
10,000-20,000
Zinc Leached with sulphuric
acid
Zinc chloride and zinc sulphate 3000-5000

Extraction of Zinc
The ore, consisting largely of zinc oxide, treated with strong sulphuric acid, roasted
and passed through various chemical processes to precipitate cadmium, copper
and any other impurities; the resulting zinc sulphate solution is passed to the
electrolytic cells
The electrolytic cells consists of large lead-lined wooden boxes, each containing a
no. of aluminum cathodes and lead anodes and carrying a current of several
hundred and thousand Amperes, according to the size

Extraction of Zinc
The current density on the cathodes is about 1100A/sq. m
The potential drop in each cell is about 3.5V, so that 100 or 150 of them in
series
The zinc is deposited on the cathodes, which are removed once or twice a day
for stripping (To peel)
The energy consumed is of the order 3000 to 5000kWh per tonne

Extraction of Aluminium
An example of the fused electrolyte process is the extraction of aluminium from
its ores, bauxite and cryolite
The bauxite is first treated chemically to reduce it to aluminium oxide and this is
then dissolved in fused cryolite and electrolyzed
The furnace in which the fusion and electrolysis take place consists of a shallow
rectangular bath lined with carbon

Carbon anodes project downwards into the bath and the bottom of the bath
forms the cathode
The high temperature (1000 degree) necessary to keep the ores in a fused state
is maintained by the Ohmic losses of the current passing through the electrodes
and electrolyte

A furnace having an area of 13.6 sq.mt will require a pressure of 5 or 6V and a
current of 40,000A
Aluminium is deposited at the cathode and settles at the bottom of the bath, from
which it is tapped off as required

Refining of metals
Highly concentrated mixture of metals is subjected to electrolysis for recovering of
metal in its purest form
Recover precious metals like gold, silver, bismuth

Refining of metals
Metal Solution Consumption
kWh/tonne
Copper Copper sulphate 150-300
Gold Chloride of gold 300-350
Iron Iron ammonium sulphate 1000-1500
Lead Lead fluosilicate 100-120
Nickel Nickel-chloride and
sulphate
2500-4000
Silver Nitric acid and silver
nitrate
400-420

Refining of Copper
Copper is usually mined from its coal known as blister copper. It is about 98 to 99
per cent pure. Electro-refining process can easily make it 99.95% pure which makes it
a good product
A block of impure copper is taken as an anode or positive electrode
Copper sulphate which is acidified with sulphuric acid is used as a graphite-coated
electrolyte along with pure copper tubes, as a cathode or negative electrode

Refining of Copper
In this phase of electrolysis copper sulfate divides into a positive ion of copper (Cu++)
and a negative ion of sulphate (SO4—)
The positive copper ion (Cu++) or cations travel towards the negative electrode
made of pure copper where it absorbs the electrons from the cathode
Cu atom is deposited on the cathode’s graphite layer

Electro deposition
Electrolytic process in which one metal is coated over another metal or non metal
in its pure form
This process is used in electro-plating, electro-forming, electro-typing, electro-
facing, electro-metallization , electro-deposition of rubber

Electro deposition
Nature of electrolyte
Current density
Temperature
Conductivity
Electrolytic concentration
Additional agents
Throwing power
Polarization
Factors governing electro-
deposition process

Electro deposition
Nature of electrolyte
 The electrolyte from which complex ions can be obtained, such as
cyanides, provides a smooth deposit

Electro deposition
Current density
 The deposit of metal will be uniform and fine-grained if the current
density is used at rate higher than that at which the nuclei are formed
 The deposit will be strong and porous if the rate of formation of nuclei is
very high due to very high current density

Electro deposition
Temperature
 A low temperature of the solution favours formation of small crystals
of metal; and at high temperature, large crystals

Electro deposition
Conductivity
 The solution of good conductivity is important from the standpoint
of view of economy in power consumption and also because it
reduces the tendency to form trees and rough deposits

Electro deposition
Electrolytic Concentration
 Higher current density, which is necessary to obtain uniform and
fine-grain deposit, can be achieved by increasing the concentration
of the electrolyte

Electro deposition
Additional Agents
 The addition of acids or other substances to the electrolyte reduces
its resistance
 additional agents are glue, gums, dextrose, dextrin, gelatin, agar,
alkaloids, albumen, phenol, glycerin, sugar, glucose, rubber
influence nature of deposit
 The crystal nuclei absorb the additional agent added in the
electrolyte
 This prevents it to have large growth and thus deposition will be
fine-grained

Electro deposition
Throwing power
 It is the ability of electrolyte to produce uniform deposit on an
article of irregular shape
 Due to unequal distance, the resistance of the current path
through the electrolyte for various portions of the cathode will be
different
 But the potential difference between the anode and any point on
the cathode will be the same
 And the result will be that the current density will be more on the
portion nearer to anode and it will cause uneven deposit of the
metal

Electro deposition
Polarization
 The rate of deposition of metal increases with the increase in
electroplating current density up to a certain limit
 after which electrolyte surrounding the base metal becomes so much
depleted that the increase in current density does not cause increase
rate of deposition
 Increase in current density beyond this limit causes electrolysis of water
and hydrogen liberation on the cathode
 This hydrogen evolved on the cathode blankets the base metal which
reduces the rate of metal deposition

Electro Plating
Electroplating is electrolytic process in which superior or noble metal is
deposited on an inferior or base metal
Purpose of Electroplating
To protect the metals against corrosion
To give reflecting properties to the
reflectors
To give a shiny appearance to articles
To repair the worn-out materials

Electro Plating
 Electrolytic deposits are crystalline in nature and the
crystals deposited must be very fine, coherent and
uniform deposition
 Proper current density value
 Proper temperature level
Example:
For 1000 CC solution,
150-200gms of copper sulphate
25 – 35 gms of sulphuric acid
Current density 150 – 400A/m2
Temperature 25 – 500C

Power supply required for electrolytic process is low voltage DC supply
For electro-deposition a power supply of 10 to 12 volts which can give 100
to 200 amperes is adequate
Power Supply
Using a Motor-Generator Set
Using a metal Oxide Rectifier

Using a Motor-Generator Set
 The motor is an ordinary three phase induction motor and the
generator is a heavy current, low voltage DC generator
 The generator should preferably be separately excited
 DC voltage can be controlled by controlling the excitation of the
generator

Using a metal Oxide Rectifier
 Better efficiency at low voltages especially at low loads, occupies
less space, has low maintenance cost
 Recently the solid state rectifying devices employing germanium
and silicon diodes have been developed for use

Electric traction

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