Automatic Railway Gate Control

Automatic Railway Gate Control

INTRODUCTION

Now a days, India is the country which having worlds largest railway network. Over hundreds of railways running on track everyday. As railway has straightway running as well as it has somewhat risky and dangerous as per as general public and traffic concern. As we know that it is surely impossible to stop the running train at instant is some critical situation or emergency arises. Therefore at the places of traffic density, suburban areas and crossings there is severe need to install a railway gate in view of protection purpose. Obviously at each and every gate there must be a attendant to operate and maintain it. In view of that, if we calculate the places of railway crossings and such places where it would to be install and overall expenditure, the graph arises and arises at the extent.

But, India, our country is a progressive country. It has already enough economical problems which are ever been unsolved. So, to avoid all these things some sort of automatic and independent system comes in picture. Now a days automatic system occupies each and every sector of applications as it is reliable, accurate and no need to pay high attention.

So, keeping all these things and aspects and need of such system our project batch tries to make such type of system with the help of various electrical, electronic and mechanical components. The thorough and detail information as per as construction and working is concerned, it is discussed furtherly.

AUTOMATIC CONTROL SYSTEM

An automatic control system is an arrangement of physical components connected in such a manner so as to direct or regular itself or some another system i.e. some controlled condition forming part of the system is maintained in a prescribed manner.

Automatic control system have influenced the current way of life. In recent year automatic control systems have been rapidly increasing importance in all fields of engineering. Its application covers a very wide range from design of precision control devices to design of massive equipments used for manufacture of steel and other industries.

ADVANTAGES OF ATOMATIC CONTROL SYSTEM:

The need of automation is due to or advantages of automatic control system are :

1)It result in economy of operation.

2)Elimination of human error.

3)If frees human beings from mental tasks.

4)Saving in energy requirements.

5)Increases in efficiency.

WORKING of automatic railway gate control

In this project to lift the railway crossing gate D.C. series motor. Gear and belt drive arrangement is used. The relay at two points on the either side of railway crossing gate is used as shown in fig. The relay will complete the circuit when railway will pass through if hence at that first time when rail will be near the gate, the gate will be closed and similarly when the rail will pass through the another relay which is mounted on the other side of gate, the relay will get operated completing the circuit. Hence the motor will operate and with help of belt and gear drive, the gate will get opened. In this way the automatic operation of gate takes place. The gate which is unguarded, at such place the percentage of accidents is more. Therefore to overcome this problem this system is capable. As it is fully automatic there is no chance of failure due to human mistake.

+ -

T1 C

T2 -

Motor 1

LED +

+ -

T1 C

T2 -

Motor 2

LED +

TR1 TR2

Common Common

Connector

_ _

Motor 1 Motor 2

+ +

RELAY

Introduction :

Automatic control of the operation of any installation implies that the installations being controlled is monitored, supervised and protected by it’s own means without manual interference. The relay is a device which control the switching of circuits by receiving an energy to operate itself. In can be considered as remote control switch.

Electromagnetic relays give a from ON to OFF when the coil is energized or deenergized.

Relays can be hermetically sealed to protect them from dust, oxidation etc.

The main feature in a relay is contacts. They close the electric circuit. or open an electric circuit under the control of an electromagnet.

Smaller relays operate faster because the moving parts have to travel a smaller distance. Also the inductance is reduced.

Classification of Relays:

The function of construction of relays are different and they can be classified accordingly. The main difference between switches and relays is, switches are manually operated whereas relays are electrically operated. Relay contacts are categorized into No (normally open) and NC (normally closed) types.

Classification of Relays

Basically relays can be called as light, medium or heavy duty general purpose relays. Mostly they are known by their functions.

Electromagnetic Relay

Relays can further be divided as :

(1)General purpose relay

(2)Current relay

(3)Power & voltage relay

(4)Reactance relay

(5)Impedance relay

(6)Gas pressure relay

(7)Acoustic relay

(8)Optical relay

(9)Chemical relay

(10)Time delay relay

(11)Sequence relay

(12)Stepping relay

(13)Interlock relay

(14)Latch in relay

(15)Rotary relay

(16)Telephone relay

(17)Polarized relay

(18)Differential relay.

General Purpose Relay :

They can be further classified as sealed and unsealed.

The sealed general-purpose relay is relatively simple in design. When a d.c. current is passed through a coil, the iron core gets magnetized attracting armature towards it. The moving contact is attached to the armature therefore switches can be operated with the help of this make contact.

Instrument control, control of light industrial loads like motors etc. are the applications of this relay.

The typical switching capacities are :-

Normal duty contacts5 amp,24 Vdc.

1 amp,250 Vdc.

Heavy duty contacts10 amp,24 Vdc.

5 amp250 Vac.

The sealed relays are hermetically sealed. Coils which are wound on bobbins are covered with varnish and are sealed inside containers with leads brought out through seals.

Miniature relays are also enclosed in metal cans with typical dimensions of 1”  ¾”  ½” and are known as ‘Crystal Can’ relays or ‘Postage Stamp’ relays. Typical contact rating for miniature relay is 1 amp at 28 V dc.

Microminiature relays are still smaller with dimensions of 8 mm x 10 mm x 12 mm. They are normally used for printed circuit. boards where the leads can be directly mounted. Rating is 0.5 amp at 28 v dc for resistive load.

AC operated Relay :

The application of these relays is well known. They are used for switching on 50 HZ equipments like motors and industrial loads. When a. c. flux passes through the armature gap due to nature of a.c. it passes through Zero and chatter is observed.

Hum and chatter are actually the well known problems of this relay and it is reduced by keeping the tolerance close.

Differential Relay :

As shown in the fig., the two windings operate the relay only when there is difference in voltage or current. This relay is ideal for comparing.

We have seen the bimetal type of thermal relay, similarly there are relays that work on the principle of expansion.

A special steel wire is wound between two bobbins that are insulated. When switched on, heat is produced due to current which expands the wire. This expansion causes lever operation and contact is closed.

Telephone relays :-

These can be used for d.c. as well as a.c. operation for a.c. operations laminated cores are used to reduce losses. The telephone relay has L shaped frames which holds armature & coil. The contacts are normally interleaved and are separated by spaces which are made up of insulating material.

D.C.SERIES MOTOR

A D.C. Motor is a machine which converts electrical energy into mechanical energy. Its location is based on the principal that when a current carrying conductor is placed in the magnetic field, it experiences a mechanical force whose direction is given by Fleming’s left hand rule.

Fig. shows a multipolar D.C. Motor. When its field magnets are excited & its armature conductors are supplied with current from the supply mains, they experience a force tending to rotate the armature. Armature conductors under N-pole are assumed to carry current downwards (plus) & those under S-pole are assumed to carry current upwards (minus). By applying Fleming’s left – hand rule, the direction of the force on each conductor can be found. It is shown by small arrow placed above each conductor. It will be such that each conductor experiences a force which tends to rotate the armature in anti-clockwise direction. These forces collectively produce a driving torque which sets the armature rotating.

Characteristics of series motor

Characteristic curve of a motor are those curves which shows relationship.

1) Electrical Characteristics :- i.e. Torque and armature current characteristics i.e.T/Ia characteristic.

We know that Ta  Ia, as field winding also carry the armature current,  Ia upto the point of magnetic saturation, hence by saturation

Ta  Ia & Ta  Ia2

At light load, Ia and hence  is small. But as Ia increases, Ia increases as the square of the current. Hence Ta/Ia curve is a parabola as shown in fig. 01. After saturation,  is almost independent of Ia, hence Ta  Ia only. So the curve becomes a straight line. The shaft torque Tsh is less than armature torque due to stray losses. It is shown by dotted line.

So, we conclude that on heavy loads, a series motor exerts a torque proportional to the square of armature current. Hence in cases where huge starting torque is required for accelerating heavy masses quickly, series motors are used.

Tsh

Torque 

Ia 

Fig. 01

2) Speed and armature current i.e. N/Ia characteristics

Variations of speed can be calculated by

Change in Eb for various load currents is small and hence can be neglected for time being with increased Ia,  also increases. Hence speed varies inversely as armature current as shown in fig. 02.

When load is heavy, Ia is large. Hence, speed is low. But when load current decreases and hence Ia falls to a small value and speed becomes very high. Hence, series motor should never be started without some mechanical load on it otherwise it may develop excessive speed and get damaged due to heavy centrifugal forces so produced. It is clear that series motor is a valuable speed motor.

N 

Fig. 02

Ia 

3) Mechanical i.e. N/Ta characteristic

It is seen from the above two characteristics that when the speed is high, torque is low and vice-versa. Hence the relation between speed and torque is shown in fig. 03.

N 

Ta 

Fig. 03.

Which qualities should a D.C. series Motor have / why it is preferred ?

Relatively high starting torque, which is required characteristic for traction.
Motor should have relieving property .
Due to relieving property, at high loads the speed of motor is low, hence reactance voltage induced is low, hence trouble of commutation is less.
Its speed should be controlled by different methods.
It should have good accelerating torque.
As torque is dependent upon current, slight variation of voltage should not affect the working of motor.
It should have load speed at high loads and vice – versa.

Uses or Applications of D.C. series motor.

1)It is used whose high starting torque is required such as for driving hoists, cranes, trains etc.

2)It is used where the motor can be directly coupled to load such as fan, where torque increases with speed.

3)It is used where the speed has to be maintained approximately constant i.e. from no load to full load.

4)It can be used to drive load at various speed.

Gear arrangement

Belt drive

This type of drive is practically used in majority of cases but with in certain limits. Leather belt is a most economical form of drive. The maximum power which can be conveniently transmitted by means of belt is about 200 to 300 H.P. For motor upto 30 to 40 H.P. Speed ratio is 6 to. The slip of belt 3 to 4 percent.

Shaft Load

Driven

Machine

Belts used are

1)Solid woven cotton belt.

2)Rubberised cotton ply belt.

3)Leather belt.

4)Nylon belt.

5)Terylene belt.

Important Factor

1) Dia. of motor pulley > 6

Driven pulley 1

2)Center distance between shafts of driving and driven machine should not be less than four times the diameter of larger pulley. Electric Motor shaft and driven motor shaft. The belt is run the pulley and hence power is transmitted from motor shaft to the machine shaft

Disadvantages

1)Efficiency is less

2)Belt slipping problem exits.

Advantages

1)Variable speed or torque is possible

2)It provides flexible coupling between the driving and driven machine.

3)By changing the dia. of pulley variable speed torque o/pn is possible.

Gear Drive

Advantages

1)Compact drive

2)Very high transmission efficiency

3)No slip problem

4)Simple gear changing mechanism.

Disadvantages

1)High initial cost

2)Proper alignment of gears required.

Conclusion

From the above discussion and information of this system we, upto now surely comes to know that it is highly reliable effective and economical at dense traffic area, suburban area and the route where frequency of trains is more.

As it saves some auxiliary structure as well as the expenditure on attendant it is more economical at above mentioned places than traditional railway crossing gate system. We know that though it is very beneficial but it is also impossible to install such system at each and every places, but it gives certainly a considerable benefit to us, thereby to our nation.

REFERENCES

1)Instrumentation and Control

- CTP Publication

2)EMCDT ( Everest Publication )

- Mrs. A. Kalavar

3)Electrical Technology – vol. 2

- B.L. Theraja

4)Utilization System – Vrinda Publication.

- A.S. Zope, B.P. Patil

5)Utilization System – Nirali Publication.

- M.P. Vader

Govt. Poly. Washim.