USES OF ELECTRICAL& INSTRUMENT IN CONVEYING SYSTEM

 E & I ASPECTS BELT CONVEYORS

A Conveyor Belt consists of two or more pulleys, with a continuous loop of material that rotates about them. One or both of the pulleys are powered, moving the belt and the material on the belt forward. The powered pulley is called the Drive Pulley while the unpowered pulley is called the Idler. 

ELECTRIC MOTOR ATTRIBUTES:

TYPE:  SCIM , WRIM or DC Shunt/Compound motors.

  Mainly SCIM is used.

ENCLOSURE: Open  Drip Proof Type (ODP) 

  (A)  It gives protection from falling water 

  (B)  Splash Protection

  (C)  Forced Ventilation design

SPEED: Normally 1800 rpm or 1200 rpm.

VOLTAGE: Common conveyor AC motor application voltages are 230, 460, 575, 950, 2300, 4160 & 6600V AC. DC Motor application voltages are 250, 500, 600, 700, 750V DC.

BEARINGS:

vConveyor rotating motors are available in Ball, Roller & Sleeve Bearings.

vCommonly bearings are deep groove ball bearings with grease lubrication.

vChoice & availability depends upon speed, size and local practices.

MOTOR PROTECTION

vWINDING TEMPERATURE: In conveyor environments heavy duty Pt100 RTD’s are most common choice for temperature measurement.

v

vBEARING TEMPERATURE: Pt100 RTD’s are best choice. By embedding a RTD sensor within bearing housing, the belt control system may monitor the bearing temperature.

v

vVIBRATION: Vibration control system generates alarm but does not shut down the motor on belt conveyors.

vBELT OVERLOAD PROTECTION

BELTPROTECTION CONTROLS

BELT ALIGNMENT :

vBelt alignment sensors are positioned along the edges of the conveyor fabric.

vThey are generally at discharge and at loading zones of conveyor but can be  distributed along the conveyor at intervals.

BELT OVERLOAD:

vThe belt conveyor system is protected from belt overload by the motor overload.

vThe motor over load can be bi-metallic strip type protection.

vThe overload protection can be by belt weigh scales also.

BIN LEVEL:

  When conveyor discharges into bins or hoppers, bin level sensor provides protection to belt conveyor.

SIDE TRAVEL SWITCH/ DRIFT SWITCH/BELT SWAY SWITCH

vUsed to detect if a belt conveyor has moved too far away from its’ center line in either direction.

vA fault is then displayed, or the equipment is shutdown in order to prevent damage to the Belt Conveyor structure.

v

PULL CHORD SWITCHvPull Cord switch also known as Rope Operated Emergency Switch is used as a safety switch to stop the belt conveyor belt in case of an emergency.

vPull Cord switches are housed in a dust and weatherproof enclosure.

v These switches have got an operating handle with  steel rings at both ends for fixing the rope.

vThe switch is designed with manual reset type of mechanism.

OPERATION:

  Pull Chord switch is mounted on the walkway side of the conveyor belt, preferably at About 20 Meters. When the rope is pulled from any side, the switch gets operated.  Unless and until the handle is reset manually to normal position, the switch remains in operated condition.

LOCATION OF PULL CHORD SWITCH

NOTE:

vFor walkway on one side of the belt the location of pull chord shall be on one side only.

vThe pull chord shall be located as per the above options either above the belt or below the nip points depending on the location of the walkway. Two pull chords are not required.

ZERO SPEED SWITCH(ZSS):Speed Switches are devices which are shaft or pulse driven and can indicate or control the rotary motion of the equipment they are attached to. Zero speed switches are widely used as interlocks on conveyor systems of all types. When driven from a critical shaft, a zero speed switch can be electronically connected to:

v Actuate a signal or alarm device

v Break a circuit to a motor

v Make a circuit to start aux. equipment

v Make or break  to other electrical devices

v Signal a control station PLC

ZSS IN VARIOUS CONVEYING SYSTEMS

SEQUENCE OF OPERATION OF CONVEYOR BELTS:

vConveyors are switched on in opposite direction of  transport.

vThe opposite sequence is followed while switching off.

BELT PROTECTION INTERLOCKING:v

Conveyor control strategy that shuts down all upstream conveyors in event of a fault.

vPrevents loading onto Static Conveyor.

OPERATION & APPLICATION OF LIMIT SWITCHES

The equipment pushes the switch roller/ lever  actuating the switch  contacts.  The  heavy  duty  actuating  mechanism  is  designed to absorb hits of heavy machinery without damaging the internal mechanism. Limit  switches  are  enclosed  in  heavy  duty  weatherproof  enclosure. 

  Heavy duty limit switch are extensively used on EOT Cranes,  Conveyors,  Transfer  Cars,  Elevators,  Steel  Mills  &  Mobile  Material  Handling  Equipments  for  sensing  of  end  limits  and position sensing.

OPERATION & APPLICATIONS OF PROXIMITY SENSORSv

Proximity Switches are mainly used in Belt Conveyor Protection.

vIt is used as an interlocking for the protection of personnel & machinery.

vSafe Guarding of machinery is provided with the Proximity Sensors. If guarding is opened then Belt Conveyor would stop automatically.

LIQUID RESISTANCE STARTER TESTING OF SODA WATER

THUMB RULE

1 LITRE WATER CONTAINS 10 gm SODA.

Method to test resistance of the soda water.

Soda is basically mixed with water to lower the resistance of water. Now the method to check the resistance of soda water is as follows,

 Let the rotor voltage is 1600V.

Now, the resistance needed is 2.4Ω(say)

We know, I=KV/R,

Therefore, I=5 amp.

Take 12V from secondary of a transformer, connect one terminal with the star connected moving electrode, the other terminal with one terminal of the fixed electrode. An ammeter is connected according to the fig above. As we go on adding soda, check the reading of the ammeter. When the reading shows 5 amp, it will mean that the resistance has reached 2.4 ohm.

The fixed and moving electrode must be shorted within 30 sec.

CALCULATION TO DETERMINE TYPE OF CARBON BRUSHES

CALCULATION TO DETERMINE TYPE OF CARBON BRUSHES

Passing of current between brush and slip ring is called electrical greasing.

Types of Brushes

Group	% Cu	Current Density(A/cm2)
1(metal graphite )	85	20
2(metal graphite )	75	17
3(metal graphite )	65	12
4(electro graphite )	0	8

DIMENSIONS OF DIFFERENT BRUSHES

TR ₅ – 38X32X22

NGEF-1> 315R-40X40X20

           2>280-40X32X16

TR₄ – 38X32X16

Let us take example of NGEF 315R GROUP 3.

Area touching the slip ring- 40x20=8cm²           

Capacity of a brush= 12x8=96A

Let us take a motor whose secondary current is 260A

 2 brushes needed, so capacity of one brush will be 130A

So 3 Group brush will not work, we take Group 2 brush.

For group 2, capacity of each brush will be 17x8=136A

We can use this brush.

Therefore, to order a brush we will tell the vendor specifications as follows:

NGEF 315R brush, Group 2.

Calculation of Spring Tension of Brush

Range available- 180-200 gm/cm²

                               200-220 gm/cm²

For NGEF 315R Group3, area=8cm²

Let’s take 200 range.

So, tension will be 200x8= 1.6KG

Coefficient of Friction

 

                                                           12 A, 120°C

At the point 12 A coefficient of friction is 0.1 which is lowest, here heat developed will be minimum, so an increase or decrease in temperature will result in an increase in coefficient of friction, which  is undesirable.

Electric motor control damper actuator

Electric motor control damper actuator – it has 3 phase induction motor its operate the lever this actuator has primary and secondary gear secondary gear also known as worm gear at front side there is indicator which shows the position of damper at the back side wheel and handle is given if we want to operate the actuator manually then push the handle clockwise this thing bypasses the motor now we can easily set the position of damper as per requirement through the wheel in this actuator there is an advantage that we can adjust the damper at 30% , 40% etc but in most pneumatic actuator(with single solenoid coil) we operates only either fully open or fully close condition

Electric motor damper actuator has 6 limit switch as described further

2 limit switch for full open (1 for retendency in case failure)

2 limit switch for full close condition (1 for retendency in case failure)

1 for open torque (when we open the damper for flow if there is obstruction like material jamming or some material struck around)

1 for close torque (when we close  the damper if there is obstruction like material jamming or some material struck around foreign material coming