Electric Locomotives with 3-phase Drives



Till electronics came into the field of traction recently, the best suited drive for traction application was the dc series motor because of its inherent characteristics to give high torque at low speeds and vice-versa. The dc series motor was the best solution found for meeting the actual service as well as control requirements. On a fixed frequency, the asynchronous motor has a characteristic which is not well suited for traction application. However, this motor is of rugged construction when compared to a dc motor and requires much lower inputs for maintenance. Therefore its choice as a traction motor will always be preferred if control of the motor to suit the service requirements is possible. With the development of GTO thyristors, power electronics and micro processor control, controlling of any drive to suit specific requirements has become quite easy. In the circumstances, adoption of 3-phase induction motor for traction application has been tried for the past 10 years and has now become commercially viable proposition. The control is being achieved through variable voltage and variable frequency briefly referred to as WVF. Originally thyristors were used with commutation requirements for cut off. With the advent of GTO, the control has been made much simpler and more efficient thus use of 3-phase asynchronous motors for traction could also become financially viable.

A locomotive with 3-phase asynchronous motor drive has the following advantages :

  • higher power capability due to high power/weight ratio,
  • regeneration capability over a wide speed range,
  • lesser maintenance,
  • unity power factor at pantograph,
  • higher adhesion.

Why 3-phase Drive is used?

The speed/torque characteristic of an induction motor supplied from a 3-phase voltage source of fixed frequency “f” is of the form shown in this figure.


It may be seen that at low speed, the torque is small and the stator current is high. The zone normally usable lies at the extreme from the point of maximum torque, in the vicinity of synchronous speed. For traction applications a high TE is necessary for starting and accelerating the train. Therefore, when constant torque is required, It is necessary to obtain whole series of characteristics curves such as shown in figure given below. This calls for change in synchronous speeds and therefore variable frequency.


The control of the ac induction motor drive in traction application is achieved in 3 stages

Constant torque mode:

The torque developed by a motor is proportional to the product of the magnetic flux in the air gap, and the rotor current. The applied voltage is proportional to the synchronous frequency and the magnetic flux in the air gap. To keep the magnetic flux constant, therefore, the applied voltage to the traction motor is to be made proportional to the synchronous speed.

The rotor current depends upon the slip frequency of the rotor. By keeping this constant, the rotor current is also kept constant. This is possible till the voltage is increased to the rated terminal voltage of the traction motor. Thus in this mode the control is achieved by increasing the voltage and frequency uniformly with respect to the actual speed of the rotation of the rotor and the required slip frequency.

Constant power mode:

In this mode the voltage is already reached to the rated voltage. By increasing the frequency, the magnetic flux in the air gap is reduced proportionately. By keeping the slip frequency constant, the motor current is kept constant. Thus the motor is made to give constant power output till the maximum service speed is reached.

Balancing speed stage:

Once the maximum pre-determined speed is achieved, the same power output from the traction motor may not be required and the output is to be matched to meet the resistance of the train for running at the balancing speed. This is achieved by suitably reducing the terminal voltage of the traction motor.

These functions are performed through micro processor control giving various inputs of parameters like voltage, current and speed.

Converter/Inverters System:

In order to achieve the above control requirements, the converter/ inverters system with a dc link is adopted. The converter rectifies the ac voltage to dc and feeds it to the dc link. The dc link supplies power to the inverters. The converter output power is controlled by controlling the output current keeping the dc link voltage constant. The inverters output power is controlled by varying the terminal voltage initially till the full voltage is achieved. However the motor output current is kept constant.

The control of output current of the converter and output voltage of the inverters is achieved by pulse width modulation control.

The power circuit diagram of a typical 3-phase locomotive fitted with asynchronous motors is shown in figure given below.



Railway Production in India

Production of Rolling Stock

  • Indian Railways have set up production units for Rolling stock and Rolling Stock components
  • Apart from production for use of Indian Railways, these production units export Rolling Stock and components to many countries such as Burma, Bangladesh, Sri Lanka, Hungary, East Africa, Central Asian countries, East Asian countries etc.
  • The following are the production units of Mechanical Department for production of different types of Rolling Stock:
List of Production Units
Name of PU Place where situated
Chittaranjan Locomotive Works Chittaranjan
Diesel Locomotive Works Varanasi
Integral Coach Factory Chennai
Rail Coach Factory Kapurthala
Rail Wheel Factory Bangalore
Diesel Loco Modernisation Works Patiala
List of railway workshops under various railways
Railway   Name of Workshop
Central 1 Kurduwadi
  2 Matunga
  3 Parel
Eastern 4 Jamalpur
  5 Kanchrapara
  6 Lilluah
East Central 7 Samastipur
East Coast 8 Mancheswar
Northern 9 Alambagh
  10 Amritsar
  11 Charbagh
  12 Jagadhari
  13 Kalka
North Central 14 Jhansi
North Eastern 15 Gorakhpur
  16 Izatnagar
Northeast Frontier 17 Dibrugarh
  18 New Bongaigaon
  19 Tindharia
North Western 20 Ajmer (Carriage)
  21 Ajmer (Loco)
  22 Bikaner
  23 Jodhpur
Southern 24 Golden Rock
  25 Perambur (Carriage and Wagons)
  26 Perambur (Loco)
South Central 27 Lallaguda
  28 Tirupati
  29 Guntapalli
South Eastern 30 Kharagpur
Southeast Central 31 Raipur
  32 Nagpur
South western 33 Hubli
  34 Mysore
Western 35 Bhavnagar
  36 Dahod
  37 Junagarh
  38 Parel
  39 Mahalaxmi
  40 Pratapnagar
West Central 41 Bhopal
  42 Kota
  • Wagons are manufactured in various Railway workshops as well as some private firms.

Chittaranjan Loco Works, Chittaranjan, West Bengal

Diesel Loco Works, Varanasi

Diesel Modernization Works, Patiala

Parel Workshops, CR

Rolling Stock

Integral Coach Factory, Perambur

Rail Coach Factory, Kapurthala

Jessop & Co.

Burn & Co.

Braithwaite & Co.

Bharat Wagon & Engineering Co. (BEWL)

Titagarh Wagons Ltd.

Axles & Wheels

Wheel and Axle Plant (now Rail Wheel Factory)


Jamalpur Workshop

Alambagh Workshop

Charbagh Workshop

Ajmer Workshop

Liluah Workshops

Golden Rock Workshops

Kharagpur Workshops

Motibagh Workshop, Nagpur

Tindharia Workshop

Coonoor Steam Shed


Rail Spring Karkhana

Fuse, Types and Characteristics


A fuse is a device that protects a circuit from an over current condition only.

It has a fusible link directly heated and destroyed by the current passing through it. A fuse contains a current-carrying element so that the heat generated by the flow of normal current through it doesnot cause it to melt the element; however, when an over current or short-circuit current flowsthrough the fuse, the fusible link will melt and open the circuit.

The Underwriter Laboratories (UL) classifies fuses by letters e.g. class CC, T, K, G, J, L, R, and so forth. The class letter may designate interrupting rating, physical dimensions, and degree of current limitation.

Construction of Fuse:

The typical fuse consists of an element which is surrounded by filler and enclosed by the fuse body. The element is welded or soldered to the fuse contacts (blades or ferrules).

The Element:The element provides the current path through the fuse. It generates heat at a rate dependent on its resistance and the load current.

Filler Materials:

The heat generated by the element is absorbed by the filler and passed through the fuse body to the surrounding air. The filler material, such as quartz sand, provides effective heat transfer and allows for the small element cross-section typical in modern fuses. The effective heat transfer allows the fuse to carry harmless overloads. The small element cross section melts quickly under short-circuit conditions. The filler also aids fuse performance by absorbing arc energy when the fuse clears an overload or short circuit.

Inverse Time Characteristic of Fuse:

When a sustained overload occurs, the element will generate heat at a faster rate than the heat can be passed to the filler. If the overload persists, the element will reach its melting point and open. Increasing the applied current will heat the element faster and cause the fuse to open sooner. Thus, fuses have an inverse time current characteristic: that is the greater the over current, the less time required for the fuse to open the circuit.

This characteristic is desirable because it parallels the characteristics of conductors, motors, transformers, and other electrical apparatus. These components can carry low-level overloads for relatively long periods without damage. However, under high-current conditions, damage can occur quickly. Because of its inverse time current characteristic, a properly applied fuse can provide effective protection over a broad current range, from low-level overloads to high-level short circuits.

Types of Fuse:

A fuse unit essentially consists of a metal fuse element or link, a set of contacts between which it is fixed and a body to support and isolate them. Many types of fuses also have some means for extinguishing the arc which appears when the fuse element melts. In general, there are two categories of fuses.
(1) Low voltage fuses.
(2) High voltage fuses.

Usually isolating switches are provided in series with fuses where it is necessary to permit fuses to be replaced or rewired with safety.

In absence of such isolation means, the fuses must be so shielded as to protect the user against accidental contact with the live metal when the fuse is being inserted or removed.

(1) Low Voltage Fuse:

Low voltage fuses can be further divided into two classes namely

a) Semi enclosed (Rewireable Type Fuse / Kit Kat Fuse):

The most commonly used fuse in ‘house wiring’ and small current circuit is the semi-enclosed or rewire able fuse. (Sometime known as KIT-KAT type fuse). It consist of a porcelain base carrying the fixed contacts to which the incoming and outgoing live or phase wires are connected and a porcelain fuse carrier holding the fuse element, consisting of one or more strands of fuse wire, stretched between its terminals.

The fuse carrier is a separate part and can be taken out or inserted in the base without risk, even without opening the main switch. If fuse holder or carrier gets damaged during use, it may be replaced without replacing the complete unit.

The actual fusing current will be about twice the rated current. When two or more fuse wire are used, the wires should be kept apart and a derating factor of 0.7 to 0.8 should be employed to arrive at the total fuse rating.

The specification for re wire able fuses are covered by IS: 2086-1963. Standard ratings are 6, 16, 32, 63, and 100A.

A fuse wire of any rating does not exceeding the rating of the fuse. We use 80 A fuse wire in a 100 A fuse, but not in the 63 A fuse. On occurrence of a fault, the fuse element blows off and the circuit is interrupted. The fuse carrier is pulled out, the blown out fuse element is replaced by new one and the supply can is resorted by re-inserting the fuse carrier in the base.


Easily removal or replacement without any danger of coming into the contact with a lie part.
Negligible replacement cost
Unreliable Operations.
Lack of Discrimination.
Small time lag.
Low rupturing capacity.
No current limiting feature.
Slow speed of operations.

b) Totally Enclosed(Cartridge Type Fuse)

The fuse element is enclosed in a totally enclosed container and is provided with metal contacts on both sides. These fuses are further classified as

I) D- Type Cartridges Fuses

It is a non interchangeable fuse comprising fuse base, adapter ring, cartridge and a fuse cap. The cartridge is pushed in the fuse cap and the cap is screwed on the fuse base. On complete screwing the cartridge tip touches the conductor and circuit between the two terminals is completed through the fuse link. The standard ratings are 6, 16, 32, and 63 amperes.

Breaking or rupturing capacity: 4k A for 2 and 4 ampere fuses the 16k A for 63 A fuses.

Ratings of D Type Cartridge fuses: 2, 4, 6, 10, 16, 25, 30, 50, 63

D-type cartridge fuse have none of the drawbacks of the re wire able fuses. Their operation is reliable. Coordination and discrimination to a reasonable extent and achieved with them.

II) Link type Cartridge or High Rupturing Capacity (HRC)

Where large numbers of concentrations of powers are concerned, as in the modern distribution system, it is essential that fuses should have a definite known breaking capacity and also this breaking capacity should have a high value.

High rupturing capacity cartridge fuse, commonly called HRC cartridge fuses, have been designed and developed after intensive research by manufactures and supply engineers in his direction.

The usual fusing factor for the link fuses is 1.45. The fuses for special applications may have as low as a fusing factor as 1.2.

Knife Blade Type HRC Fuse:

It can be replaced on a live circuit at no load with the help of a special insulated fuse puller.

Bolted Type HRC Link Fuse:

It has two conducting plates on either ends. These are bolted on the plates of the fuse base. Such a fuse needs an additional switch so that the fuse can be taken out without getting a shock.

Ratings of HRC fuses: 2, 4, 6, 10, 16, 25, 30, 50, 63, 80, 100, 125, 160, 200, 250, 320, 400, 500, 630,800, 1000 and 1,250 amperes.


Types of Relays

An electrical relay is a switch that is used for controlling circuits. Today you’ll learn about different types of electrical relays.

Electromagnetic attraction type

The magnetic force produced by undesired current attracts the armature of the relay. Electromagnetic attraction type relays can operate on either a.c or d.c quantities. They are further divided into three types:

  1. Attracted armature type
  2. Solenoid type
  3. Balance beam type
Induction type relay

The working of Induction type relays relies on the electromagnetic induction phenomenon. They are only used for a.c quantities. They are further classified into two groups:

  1. Induction cup relay
  2. Induction disc relay
Directional type relay

Directional type relays operate on the direction of current and power. They are classified into two groups:

  1. Reverse current
  2. Reverse power
Time relays

The tripping instant in time-based relays can be controlled. Such relays are classified into three classes:

  1. Instantaneous type relays
  2. Definite time lag type
  3. Inverse time lag type
  4. Capacitor type
  5. Electronic type
Distance type relay

Distance type relays contain two coils. One of which is energized using current and another one with voltage. The voltage to current ratio is measured and working of distance relays is based on this voltage to current ratio. They are further classified into three distinctive groups:

  1. Admittance
  2. Impedance
  3. Reactance
Differential relay

A differential relay compares the difference of quantity entering and leaving the system. They are also classified into two groups:

  1. Differential current
  2. Differential voltage
Thermal Relay

The relay operates when the temperature rises above certain limit due to current.

Rectifier relay

The sensed quantities are first rectified and then provided to relay coil.

PMMC Relay

It is a permanent magnet d.c relay in which he coil is free to rotate.

Gas actuated relay

In such relays, the gas pressure is adjusted in a manner so as to trip the relay coils.

Numerical/Microprocessor based relay

Microprocessor based relays are the most advanced type of programmable relays.

Reed switch relays

These are simple and compact relays. The basic reed relay is simple reed switch which has a winding wrapped around the relay. They are manufactured in many DIP and SIP packages as well as winding free reeds are also available.

Static relays – Solid State Relays

Static relays are composed of electronic components. Such relays are composed of transistors, diodes, integrated circuits, resistors and other electronic components. An essential part of such relays is a comparator which takes two or more current/voltages as input and provides an output.

Frequency Monitoring relays

The frequency of voltage plays key role in electrical power networks. The working of various electrical machines, generators, and mechanisms heavily relies on frequency. Frequency relays continuously monitor the operating frequency of system and trip on the variations.

Thermal relays

As the name indicates, the working of thermal relays depends on the temperature of the equipment. They can either directly detect the temperature or can detect the current overloading conditions.

Motor load monitoring relays

Such relays monitor the load condition and operate under specified conditions. These relays can be based on current measurement or on cosφ based.

Insulation monitoring relays

Insulation monitoring relays continuously monitor the insulator. Whenever insulation fault occurs it immediately trips when the voltage drops behind specified threshold value.

Liquid monitoring relays

They are used to monitor regulator and control of liquid fluids.

Hybrid Relays

One part of such relays in electro-mechanical while another part is solid state electronics.

General purpose relays

These are different types of relays whose working principle is based on either of above types.

General Application of Induction Motors

The induction motor is the most popular machine that is widely employed in process and manufacturing industries. Alongside manufacturing facilities, it is the most popular machine for domestic purposes.

Deep Well Water Pumps

Deepwater wells use a special type of induction motor with a compact diameter and longer length.

Refrigerator and Compressors

Refrigerators and other compressuse split type induction motors in their working principle.

Small water pumps

Small water pumps use single phase induction motors.

Ceiling fan

Ceiling fans use single phase induction motors in their working.
The video below displays repairing of a single phase induction motor:

Washing machines

Many washing machines utilize single phase ac machines in their working.

Hydroelectric Plants in India


Hydroelectric power is a major electrical power generation source.

Clean Fuel

The only fuel required for hydroelectric power generation is water. It is clean resource, has no pollutants, burning, or any sort of chemical reactions associated with it.

Small running charges

Compared to coal, gas, diesel power station and power stations, the hydroelectric station has very small running charges.


Power generation through hydroelectric stations relies on the water cycle. Water comes through the reservoir, flows through penstock, passes through turbines, exits the station and joins some river. In fact, this water is renewable and it is never wasted.


Simple in construction

Unlike complex nuclear, steam, and diesel auxiliaries the hydro dams are simple in construction and operations.

Less maintenance

Equipment requires little to none maintenance.

Supplementary benefits

Alongside power generation, the reservoir has supplementary benefits. Entire list comprises flood control, irrigational water, drinking water.

Longer life

The expected life of a hydroelectric station is around 30 – 35 years after which it demands an upgradation. The actual process of renovation depends on the individual plant.

List of Hydro Power Plants in India

1. Tehri Dam

Operator: THDC Limited, Uttarakhand

Location: Uttarakhand

2. Koyna Hydroelectric Project

Operator: MAHAGENCO, Maharashtra State Power Generation Co Ltd.

Location: Maharashtra

3. Srisailam

Operator: APGENCO

Location: Andhra Pradesh

4. Nathpa Jhakri

Operator: Satluj Jal Vidyut Nigam

Location: Himachal Pradesh

5. Sardar Sarovar Dam

Operator: Sardar Sarovar Narmada Nigam Ltd

Location: Navagam, Gujarat

6. Bhakra Nangal Dam (Gobind Sagar)

Operator: Bhakra Beas Management Board

Location: Sutlej River, Bilaspur – Himachal Pradesh

7. Chamera I  

Operator: NHPC Limited

Location: Himachal Pradesh

8. Sharavathi Project

Operator: Karnataka Power Corporation Limited

Location: Karnataka

9. Indira Sagar Dam

Operator: Narmada Valley Development Authority

Location: Madhya Pradesh

10. Karcham Wangtoo Hydroelectric Plant

Operator: Jaypee Group

Location: Himachal Pradesh

11. Dehar (Pandoh) Power Project

Operator: Bhakra Beas Management Board

Location: Himachal Pradesh

12. Nagarjuna Sagar Dam Guntur

Operator: Andhra Pradesh Power Generation Corporation Limited

Location: Andhra Pradesh

13. Purulia Pass

Operator: West Bengal Electricity Distribution Company

Location: West Bengal

14. Idukki

Operator: Kerala State Electricity Board

Location: Kerala

15. Salal I & II  

Operator: NHPC Limited

Location: Jammu & Kashmir

16. Upper Indravati

Operator: Odisha Hydro Power Corporation

Location: Orissa

17. Ranjit Sagar Dam

Operator: Punjab State Power Corporation Limited

Location: Punjab

18. Omkareshwar

Operator: Narmada Hydroelectric Development Corporation

Location: Madhya Pradesh

19. Belimela Dam

Operator: Odisha Hydro Power Corporation

Location: Orissa

20. Teesta Dam

Operator: NHPC Limited

Location: Sikkim


Types and Classification of Faults on Electrical Power Systems

Question: How many types of faults exist on the power system and how they are classified?

Answer: Generally four types of faults exist and are classified into two categories.

Symmetrical faults: They give rise to symmetrical equal currents having a displacement of 120°.

Unsymmetrical faults: They gave rise to unsymmetrical currents having unequal displacements.

List contains:

  1. Line to line to line fault
  2. Line to ground
  3. Line to line
  4. Double line to ground

Types of Fault


Severity of Fault

3 Line


Most Dangerous

Line to Line

Unsymmetrical Fault

More Dangerous

Line to Ground

Unsymmetrical Fault

Least Dangerous

Double Line to Ground

Unsymmetrical Fault

Dangerous than Line to Line and Line to Ground Fault

Power in DC and AC Circuits

Formulas of Power in DC, AC Single Phase and AC Three Phase Circuits


Back to basic, below are the simple Power formulas for Single Phase AC Circuit, Three Phase AC Circuits and DC Circuits. You can easily find electric power in watts by using the following power formulas in electric circuits.

Power Formulas in DC Circuits

P = V x I

P = I2 x R

P = V2 / R


P = Power in Watts

V = Voltage in Volts

I = Current in Amperes

R = Resistance in Ohms (Ω)

Power Formulas in Single Phase AC Circuits

P = V x I x Cos Ф

P = I2 x R x Cos Ф

P = V2 / 2 (Cos Ф)


P = Power in Watts

V = Voltage in Volts

I = Current in Amperes

R = Resistance in Ohms (Ω)

Cos Ф = Power Factor

Power Formulas in Three Phase AC Circuits

P = √3 x VL x IL x Cos Ф

P = 3 x VPh x IPh x Cos Ф

P = 3 x I2 x R x Cos Ф

P = 3 (V2 / R) x Cos Ф


P = Power in Watts

V = Voltage in Volts

I = Current in Amperes

R = Resistance in Ohms (Ω)

Cos Ф = Power Factor

Basic Electrical Engineering Laws and Theorems

Ohm’s Law

Statement: The current flowing through any resistor is directly proportional to the voltage applied to it.

Mathematically, V = IR

Kirchhoff’s Current law

We all know that current is a basic feature of circuits which exists due to flow of charges. Kirchhoff’s current law explains the behavior of current at any junction.

Statement: The current flowing towards any junction (node) is equal to the current flowing away from that node.

Mathematically, ∑ Current In = ∑ Current out.

In other words, this law is also called the law of conservation of charge.

Kirchhoff’s Voltage law

Like Kirchhoff’s first law is focused on current at any junction, the voltage law explains the behavior of voltage around a loop.

Statement: The sum of voltage rise along a closed loop is equal to the sum of voltage drops around that loop.

Mathematically, ∑ Voltage rise = ∑ Voltage drop

In other words, this law is also called the law of conservation of energy.

Superposition principle

Many electrical circuits contain a single source powering different resistors. Sometimes a circuit contain multiple current and voltage sources. A superposition principle is applied to all circuits having multiple sources.

Statement: The voltage or current appearing across any component is equal to the sum of individual voltage or current of all independent sources.

Thevenin’s Theorem

Statement: Any complex electrical circuit can be reduced to a single voltage source having a single series resistor.

Practically, the Thevenin’s and Norton’s theorems are used in analysing the properties of electrical and electronic systems. They are employed in modelling transmission lines and large complex systems.

Norton’s theorem

Statement: Any complex electrical circuit can be reduced to a single current source having a single parallel resistor.

Maximum Power Transfer Theorem

Statement: if the value of load resistor is equal to the single resistor ( as calculated from Norton or Thevenin theorem) the load resistor will receive the maximum power.

Substitution Principle

Statement: Any electrical branch can be substituted with an equivalent electrical branch provided that current and voltage of both branches are same.

Millman’s Theorem

The Millman’s theorem is applied to the circuits which have several voltage sources in the parallel configuration. According to this theorem, the voltages source in parallel branches can be replaced by equivalent current sources and parallel resistors which can then be reduced to a single voltage source and a series resistors. The same is also true for several current sources in series configuration.

Transformer Rating in kVA, and not in kW or kVAR. Why?

Question: Why transformer rating is expressed in kVA instead of kW or kVAR?

Answer: At the time of manufacturing, the nature of load to be connected is not known. (i.e it is resistive, reactive, R, RL, RC, RLC or of any other type). Therefore it is beneficial to express power in terms of voltage and amps. This V & A represents the overall power delivered to any sort of load.

The power supplied to a resistive load is the product of voltage times current flowing through it.

In case of ac loads, the case is not same. Here the load is the sum of resistance and reactance. The power delivered to an AC load is neither real nor reactive, it is the apparent power which is expressed in terms of kVA.

Furthermore, two types of losses exist in Transformers:

  • Copper loess → They depend on current
  • Iron losses → They depend on the voltage

Since these losses depend on V & I only, a transformer is rated in terms of VA.