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Saturday, 31 January 2015

Vacuum Mixing Machine Feeder


 

 

 

 

 

 

 

 

 

 

 

 







Basic Info.

Model NO.:                 ZKJ-2

Spec:                           SUS 304

Type:                           Feeder

Usage:                         Industrial

Conveying Capacity:    600kg/Hour

Voltage:                       380V, 50Hz

Power:                        2.2kw

Dimension:                  1300*420*1200mm


Additional Info.
Trademark:                  XD

Origin:Jiangyin,            Jiangsu, China(Mainland)
HS Code:                   84282000

Production Capacity:  20 Pieces/Month

Product Description

ZKS Vacuum Charging Machine is mainly used for charging the material automatically to V-mixer, twin-cone mixer, three dimensional motion mixer and two dimensional motion mixer. This machine can fulfill the automatic material charging process to various mixers without the aid of any external vacuum generator and lifting equipment.
The whole operation meets the requirement of GMP.
ZKS Vacuum Charging Machine consists of the portable frame, vacuum pump, powder recovery barrel, secondary filtering purifier portable frame. The machine features beautiful appearance and convenient movement.

Technical Specification:

Model
Motor PowerCharging Rate
(KW)(kg/h)
ZKJ-11.5400
ZKJ-22.2600
ZKJ-331200
ZKS-442000
ZKS-55.53000
ZKS-65.54000
ZKS-75.56000

Thursday, 29 January 2015

Automatic Multi Head Screw Capping Machine

Automatic Multi Head Screw Capping Machine


Features:

  • No container no cap arrangement
  • Single motor synchronizes conveyor, star wheel, & platform turret
  • Adjustable height of conveyor belt
  • All contact parts are made out of stainless steel
  • Pick & Place arrangement
  • Torque adjustable
  • Low noise level, low power consumptions

Operation:

The feed container moving on conveyor belt are feed into an in-feed star wheel, bringing the container below the sealing head in the subsequent indexing part, mean while the rotating head pickup a cap from the cap star wheel which is receiving from delivery chute of cap filling bowl, where the body and the neck of the container are positioned below the rotating head, where the sealing head is performing perfect operation of sealing, rotating head is design to seal container according to preset torque.

Other Details:

  • Automatic Screw Capping Machine is versatile, self-supported on stainless steel leg with height adjustable adjustment system.
  • The machine is precision built on sturdy welded steel frame completely enclose in stainless steel sheet and doors are providing to facilitate the servicing of machine.

Utility Requirement:
Electrical supply3 Phase + Neutral + Earthing
Electrical load1.5 KW
Air Pressure: Minimum6 Bar, 0.5 CFM.

Multi Head Ropp Cap Sealing Machine

http://2.imimg.com/data2/TH/BS/MY-2396310/8-250x250.jpg


Features:

  • No container no cap arrangement
  • Single motor synchronizes conveyor, star wheel, & platform turret
  • Adjustable height of conveyor belt, to align with other machine of the line
  • Sealing pressure can be varied to suit different gauges and size of caps
  • Specially designed hopper is provided to increase storage capacity of bowl
  • Low noise level, low power consumptions
  • Self-lubricating UHMW- PE guide profile for low friction wears surface, smooth and noiseless conveying
  • Drain tray around the machine platform
  • SS cladding or hard chrome platting of all exposed parts to ensure long life and resistance against corrosion
  • Synchronized A/C drives to synchronize, Conveyor, Star wheel and Platform turret & capping bowl
  • Universal coupling for quick and easy setting of In-feed worm
  • Adjustable bottle height gauge for easy and quick setting

Other Details:

  • Automatic Multi Head Ropp Cap Sealing Machine is versatile, self-supported on stainless steel leg with height adjustable adjustment system.
  • The machine is precision built on sturdy welded steel frame completely enclose in stainless steel sheet and doors are provided to facilitate the servicing of machine.

Utility Requirement:
Electrical supply3 Phase + Neutral + Earthing
Electrical load1.5 KW

Wednesday, 28 January 2015

GHL High Speed Mixing Granulator (RMG)





The machine adopts horizontal cylinder structure, its structure reasonable.
Air filled seal shaft for to drive. When washing , it can be changed to water.
Fluidized Granulation, the granule is around ball shape. Its flow ability is good.
Compared to traditional process, 25% of adhesive can be reduced and the drying time is short.
The dry mixing time is 2 minutes and the granulating time is 1-4 minutes. Compared to the traditional process ,
 4-5 times of efficiency is raised.
Dry mixing ,humid mixing and granulating are finished in the same sealed container. 
It is in conformity with the requirements of GMP.
The whole operation has strict safe and protective measures.
Jacket type might be adopted on request.

The powder raw material and adhesive in a cylinder are fully mixed at the bottom to 

become a humid soft material.
 Then it is cut by high-speed cutter and become uniform granules.
itemspecification
nameunit1050150200250300400600
capacityL1050150200250300400600
outputkg/batch3155080100130200280
mixing speedr.p.m300/600200/400180/270180/270180/270140/220106/15580/120
admix powerkw1.5/2.24/5.56.5/89/119/1113/1618.5/2222/30
cuting speedr.p.m1500/30001500/ 30001500/ 30001500/30001500/30001500/30001500/30001500/3000
cuting powerkw0.85/1.11.3/1.82.4/34.5/5.54.5/5.54.5/5.56.5/89/11
compressed air consumptionm3/min0.60.60.90.90.91.11.51.8
weightkg25050080010001300180022002600
spec.ABC × DEF
102707501000×6507451350
503209501250×8009701650
15042010001350×80010501750
20050011001650×94014502050
25050011601650×94014002260
30055012001700×100014002310
40067013001860×110015502410
60075015002000×123017502610

Saturday, 17 January 2015

Electromechanical Relays


Electromechanical Relays1.gif
A few uses for relays are:
1. Control a larger/smaller voltage/current with a smaller/larger voltage/current. 2. Holding or Latch circuit to “capture” a momentary input signal 3. As building blocks in basic logic circuits 4. Isolate the input circuit from the output circuit
The Holding Circuit (or Latch) has commonly been used in MP to turn on a device with a momentary signal. A brief electrical pulse actuates a holding circuit which keeps power applied after the pulse has ended. For discussion, we’ll use a ball rolling into an elevator to be raised to the top of the device. As the ball enters the elevator, it depresses a lever closing normally open contacts of a switch mounted on the floor under the elevator. As the elevator rises, it lifts the ball off the switch, releasing the lever and allowing the contacts to open. The drawing below shows the basic holding/latch circuit. To simplify the diagram, both the relay coil and Device Under Control use the same battery.
Electromechanical Relays2.gif
First Diagram: Electricity cannot flow to the Elevator (Device Under Control) because of the normally open contacts of switch (S1) and the relay. Second Diagram: The ball rolls into the elevator, closing S1, energizing the relay coil and starting the elevator. Third Diagram: The elevator lifts the ball off S1, allowing its contacts to open. Normally this would break the circuit and the elevator would stop; however, the closed relay contacts continue supplying current to both the relay coil and the elevator.
This works great, but sooner or later the elevator reaches the top. If it continues to run, it could cause physical damage or waste energy from the batteries. Our next circuit addresses the problem.
Electromechanical Relays3.gif
In this circuit we’ve added a normally closed switch (S2). Its purpose is to stop the elevator when it reaches the upper limit of its travel.
First Diagram: The ball has just rolled into the elevator closing S1 and starting the elevator. Second Diagram: As the elevator rises, S1 opens, but the latch circuit keeps the elevator on. Third diagram: When the elevator reaches the top, it opens the normally closed switch S2, de-energizing the relay and stopping the elevator. Since the relay contacts are now open, closing S2 will not start the elevator again.
A switch that prevents a device from exceeding specified parameters is called a “limit switch”, regardless of what type it is. Lever switches and magnetic reed switches are particularly well suited in these applications.
The Loop-Back Circuit And finally, the last circuit! Sometimes it’s desirable to have several devices in series. The circuit below shows how each device can turn off the preceding device. This is sometimes called a “loop-back” circuit.
Electromechanical Relays4.gif
Switches S1, S2 and S3 and the normally open relay contacts prevent any of the devices from running.
Electromechanical Relays5.gif
A mechanical action closes switch S1, energizing the 1st latch, starting the 1st device.
Electromechanical Relays6.gif
1st device continues operation, even though S1 has opened.
Electromechanical Relays7.gif

The 1st device completes, closing S2, energizing the latch, turning off the 1st device and starting the 2nd device.

Electromechanical Relays8.gif
2nd device continues to operate, even though S2 has opened.
Electromechanical Relays9.gif 2nd device completes its action closing S3, energizing the 3rd latch, turning off the 2nd device and starting the 3rd device.
Electromechanical Relays10.gif

3rd device continues to operate, even though S3 has opened.


3rd device completes its action, openings S4, releasing the latch and stopping the 3rd device. Since none of the relays are latched, none of the devices will operate, even if S4 closes again.

Electromechanical Relays11.gif

Medicine Machine: Motor control circuits

Medicine Machine: Motor control circuits: P L C based Process Control   The interlock contacts installed in the previous section's motor control circuit work fine, but the ...

Motor control circuits

P L C based Process Control

 The interlock contacts installed in the previous section's motor control circuit work fine, but the motor will run only as long as each push button switch is held down. If we wanted to keep the motor running even after the operator takes his or her hand off the control switch(es), we could change the circuit in a couple of different ways: we could replace the push button switches with toggle switches, or we could add some more relay logic to "latch" the control circuit with a single, momentary actuation of either switch. Let's see how the second approach is implemented, since it is commonly used in industry:

When the "Forward" push button is actuated, M1 will energize, closing the normally-open auxiliary contact in parallel with that switch. When the push button is released, the closed M1 auxiliary contact will maintain current to the coil of M1, thus latching the "Forward" circuit in the "on" state. The same sort of thing will happen when the "Reverse" push button is pressed. These parallel auxiliary contacts are sometimes referred to as seal-in contacts, the word "seal" meaning essentially the same thing as the word latch.
However, this creates a new problem: how to stop the motor! As the circuit exists right now, the motor will run either forward or backward once the corresponding push button switch is pressed, and will continue to run as long as there is power. To stop either circuit (forward or backward), we require some means for the operator to interrupt power to the motor contactors. We'll call this new switch, Stop:

Now, if either forward or reverse circuits are latched, they may be "unlatched" by momentarily pressing the "Stop" push button, which will open either forward or reverse circuit, DE-energizing the energized contactor, and returning the seal-in contact to its normal (open) state. The "Stop" switch, having normally-closed contacts, will conduct power to either forward or reverse circuits when released.
So far, so good. Let's consider another practical aspect of our motor control scheme before we quit adding to it. If our hypothetical motor turned a mechanical load with a lot of momentum, such as a large air fan, the motor might continue to coast for a substantial amount of time after the stop button had been pressed. This could be problematic if an operator were to try to reverse the motor direction without waiting for the fan to stop turning. If the fan was still coasting forward and the "Reverse" push button was pressed, the motor would struggle to overcome that inertia of the large fan as it tried to begin turning in reverse, drawing excessive current and potentially reducing the life of the motor, drive mechanisms, and fan. What we might like to have is some kind of a time-delay function in this motor control system to prevent such a premature start up from happening.
Let's begin by adding a couple of time-delay relay coils, one in parallel with each motor contactor coil. If we use contacts that delay returning to their normal state, these relays will provide us a "memory" of which direction the motor was last powered to turn. What we want each time-delay contact to do is to open the starting-switch leg of the opposite rotation circuit for several seconds, while the fan coasts to a halt.

If the motor has been running in the forward direction, both M1 and TD1 will have been energized. This being the case, the normally-closed, timed-closed contact of TD1 between wires 8 and 5 will have immediately opened the moment TD1 was energized. When the stop button is pressed, contact TD1 waits for the specified amount of time before returning to its normally-closed state, thus holding the reverse push button circuit open for the duration so M2 can't be energized. When TD1 times out, the contact will close and the circuit will allow M2 to be energized, if the reverse push button is pressed. In like manner, TD2 will prevent the "Forward" push button from energizing M1 until the prescribed time delay after M2 (and TD2) have been DE-energized.
The careful observer will notice that the time-interlocking functions of TD1 and TD2 render the M1 and M2 interlocking contacts redundant. We can get rid of auxiliary contacts M1 and M2 for interlocks and just use TD1 and TD2's contacts, since they immediately open when their respective relay coils are energized, thus "locking out" one contactor if the other is energized. Each time delay relay will serve a dual purpose: preventing the other contactor from energizing while the motor is running, and preventing the same contactor from energizing until a prescribed time after motor shutdown. The resulting circuit has the advantage of being simpler than the previous example:

REVIEW:
  • Motor contactor (or "starter") coils are typically designated by the letter "M" in ladder logic diagrams.
  • Continuous motor operation with a momentary "start" switch is possible if a normally-open "seal-in" contact from the contactor is connected in parallel with the start switch, so that once the contactor is energized it maintains power to itself and keeps itself "latched" on.
  • Time delay relays are commonly used in large motor control circuits to prevent the motor from being started (or reversed) until a certain amount of time has elapsed from an event.

Friday, 16 January 2015

Medicine Machine: LDO regulator / low dropout regulator

Medicine Machine: LDO regulator / low dropout regulator: LDO regulator / low dropout regulator LDO regulator means low dropout regulator. An LDO voltage regulator is just a DC linear voltage ...

Wednesday, 14 January 2015

LDO regulator / low dropout regulator

LDO regulator / low dropout regulator

LDO regulator means low dropout regulator. An LDO voltage regulator is just a DC linear voltage regulator which can be operated with a very small input-output voltage differential. This input output voltage differential is called dropout voltage. In simple words dropout voltage is the voltage dropped by the regulator circuitry alone for its working. For example, an LM2941 LDO voltage regulator has a dropout voltage of only around 0.5V, which means that in order to get 5 volts at the output you need to input only 5.5 volts where an ordinary 7805 linear voltage regulator has a dropout voltage of around 2V. This means that, in order to get 5V at the output of 7805 you need to input at least 7V.

LDO regulator working.

LDO regulator block diagram
Schematic of a LDO regulator
The image shown above is the schematic of a typical LDO voltage regulator. The working principle of LDO regulator is just like that of an ordinary linear voltage regulator. The essential components of an LDO voltage regulator are a reference voltage source, error amplifier and series pass element (BJT or MOSFET). The voltage drop across the series pass element is controlled by the error amplifiers output in order to control the output voltage. For example, suppose the load current decreases and as results the output voltage tends increase. This increase in output voltage will increase the error voltage (VERR).The output of the error amplifier will increase, making the series pass element ( P-Channel MOSFET) less conducting, which results in the reduction of the output voltage and the output voltage is brought back to the original level.
As I said above the working of a LDO voltage regulator is similar to the working of an ordinary linear voltage regulator and the only difference is in the schematic topology of their internal circuitry. Ordinary linear regulators (7805, LM117, LM317 etc) uses a common collector scheme while the LDO regulators use an open collector (termed as open drain if a MOSFET is used as the series pass element) scheme.

Common collector scheme.

Common collector scheme is one of the three basic transistor configurations. Here base is the input terminal, emitter is the output, and supply voltage is applied to the collector terminal. The series pass transistor inside an ordinary linear voltage regulator is wired in this configuration. Fig A shows the common collector scheme (also termed as emitter follower scheme).
emitter follower scheme and open drain scheme
Common collector and open collector scheme

Open collector scheme.

Many integrated circuits like LDO voltage regulators this scheme for wiring the series pass element (BJT or MOSFET). The input signal (which comes from the previous stage inside the IC) is coupled to the base of the BJT (or gate of the MOSFET), collector is left open and it is connected to a pin of the IC while the emitter is connected to the IC ground. This configuration makes it easy to saturate the series pass element and hence the dropout voltage is minimized.Fig B shows the open collector / drain scheme.

Practical LDO regulator circuit.

practical LDO regulator circuit
LDO regulator using LM2941

The circuit shown above is of a practical LDO regulator circuit using IC LM2941 from National semiconductors. LM2941 is an integrated LDO voltage regulator IC whose output can be adjusted. The IC has many good features like thermal shutdown, transient protection, short circuit protection etc. The reverse polarity protection feature makes this IC very applicable in automotive applications. The output voltage can be adjusted from 5V to 20V and the dropout voltage is 0.5V at 1A output current.
In the circuit the voltage divider network comprising of R1 and R2 sets the output voltage. Capacitor C2 is the input filter which is very essential if the regulator circuitry is situated away from the rectifier+filter module. Capacitor C1 is the output filter while S1 is the ON/OFF switch. Resistor R3 is used to ensure the necessary 300mA pull up current which is necessary for proper shutdown when the switch S1 is made open.

Notes.

  • The circuit must be assembled on a good quality PCB.
  • A heat sink is required for application above few hundred milli amps.
  • Vout = 1.275 ((R1 + R2)/R1)
  • During calculation select R1=1K and solve for R2.
  • Selecting R1 = 1K will make the input bias current error of the adj pin negligible.
  • Reducing the value of C1 below 22uF will induce instabilities and also this capacitor must be placed as close as possible to the IC on the PCB.

Monday, 12 January 2015

Sunday, 11 January 2015

Medicine Machine: Direct On Line Starter

Medicine Machine: Direct On Line Starter: Direct On Line Starter Different starting methods are employed for starting induction motors because Induction Motor draws more start...

Medicine Machine: STAR DELTA connection Diagram and Working principl...

Medicine Machine: STAR DELTA connection Diagram and Working principl...: STAR DELTA connection  Descriptions:   A Dual starter connects the motor terminals directly to the power supply . Hence, the motor is ...

STAR DELTA connection Diagram and Working principle

STAR DELTA connection 

Descriptions:

 A Dual starter connects the motor terminals directly to the power supply. Hence, the motor is subjected to the full voltage of the power supply. Consequently, high starting current flows through the motor. This type of starting is suitable for small motors below 5 hp (3.75 kW)


Reduced-voltage 

starters are employed with motors above 5 hp. Although Dual motor starters are available for motors less than 150kW on 400 V and for motors less than 1 MW on 6.6 kV.
Supply reliability and reserve power generation dictates the use of reduced voltage or not to reduce the starting current of an induction motor the voltage across the motor need to be reduced. This can be done by 1. Autotransformer starter, 2. Star-delta starter or 3. Resistor starter. Now-a-days VVVF drive used extensively for speed control serves this purpose also.


In dual starter the motor is directly fed from the line and in star delta starter then motor is started initially from star and later during running from delta. This is a starting method that reduces the starting current and starting torque. The Motor must be delta connected during a normal run, in order to be able to use this starting method.
The received starting current is about 30 % of the starting current during direct on line start and the starting torque is reduced to about 25 % of the torque available at a D.O.L start.

More: 

Star/Delta starters are probably the most common reduced voltage starters in the 50Hz world. (Known as Wye/Delta starters in the 60Hz world). They are used in an attempt to reduce the start current applied to the motor during start as a means of reducing the disturbances and interference on the electrical supply.

Component: 
  
The Star/Delta starter is manufactured from three contactors, a timer and a thermal overload. The contactors are smaller than the single contactor used in a Direct on Line starter as they are controlling winding currents only. The currents through the winding are 1√3 = 0.58 (58%) of the current in the line. this connection amounts to approximately 30% of the delta values. The starting current is reduced to one third of the direct starting current.

How it works?

There are two contactors that are close during run, often referred to as the main contactor and the delta contactor. These are AC3 rated at 58% of the current rating of the motor. The third contactor is the star contactor and that only carries star current while the motor is connected in star. The current in star is one third of the current in delta, so this contactor can be AC3 rated at one third of the motor rating.
In operation, the Main Contactor (KM3) and the Star Contactor (KM1) are closed initially, and then after a period of time, the star contactor is opened, and then the delta contactor (KM2) is closed. The control of the contactors is by the timer (K1T) built into the starter. The Star and Delta are electrically interlocked and preferably mechanically interlocked as well. In effect, there are four states:
  1. OFF State.
      All Contactors are open
  2. Star State. 
    The Main and the Star contactors are closed and the delta contactor is open. The motor is connected in star and will produce one third of DOL torque at one third of DOL current.
  3. Open State. 
    The Main contactor is closed and the Delta and Star contactors are open. There is voltage on one end of the motor windings, but the other end is open so no current can flow. The motor has a spinning rotor and behaves like a generator.
  4. Delta State.
     The Main and the Delta contactors are closed. The Star contactor is open. The motor is connected to full line voltage and full power and torque are available.

This type of operation is called open transition switching because there is an open state between the star state and the delta state.






Direct On Line Starter

Direct On Line Starter

  • Different starting methods are employed for starting induction motors because Induction Motor draws more starting current during starting. To prevent damage to the windings due to the high starting current flow, we employ different types of starters.
  • The simplest form of motor starter for the induction motor is the Direct On Line starter. The DOL starter consist a MCCB or Circuit Breaker, Contactor and an overload relay for protection. Electromagnetic contactor which can be opened by the thermal overload relay under fault conditions.
  • Typically, the contactor will be controlled by separate start and stop buttons, and an auxiliary contact on the contactor is used, across the start button, as a hold in contact. I.e. the contactor is electrically latched closed while the motor is operating.

Principle of DOL:

  •  To start, the contactor is closed, applying full line voltage to the motor windings. The motor will draw a very high inrush current for a very short time, the magnetic field in the iron, and then the current will be limited to the Locked Rotor Current of the motor. The motor will develop Locked Rotor Torque and begin to accelerate towards full speed.
  • As the motor accelerates, the current will begin to drop, but will not drop significantly until the motor is at a high speed, typically about 85% of synchronous speed. The actual starting current curve is a function of the motor design, and the terminal voltage, and is totally independent of the motor load.
  • The motor load will affect the time taken for the motor to accelerate to full speed and therefore the duration of the high starting current, but not the magnitude of the starting current.
  • Provided the torque developed by the motor exceeds the load torque at all speeds during the start cycle, the motor will reach full speed. If the torque delivered by the motor is less than the torque of the load at any speed during the start cycle, the motor will stops accelerating. If the starting torque with a DOL starter is insufficient for the load, the motor must be replaced with a motor which can develop a higher starting torque.
  • The acceleration torque is the torque developed by the motor minus the load torque, and will change as the motor accelerates due to the motor speed torque curve and the load speed torque curve. The start time is dependent on the acceleration torque and the load inertia.
  • DOL starting have a maximum start current and maximum start torque. This may cause an electrical problem with the supply, or it may cause a mechanical problem with the driven load. So this will be inconvenient for the users of the supply line, always experience a voltage drop when starting a motor. But if this motor is not a high power one it does not affect much.

Parts of DOL Starters:

(1)   Contactors & Coil.
  • Magnetic contactors are electromagnetically operated switches that provide a safe and convenient means for connecting and interrupting branch circuits.
  • Magnetic motor controllers use electromagnetic energy for closing switches. The electromagnet consists of a coil of wire placed on an iron core. When a current flow through the coil, the iron of the magnet becomes magnetized, attracting an iron bar called the armature. An interruption of the current flow through the coil of wire causes the armature to drop out due to the presence of an air gap in the magnetic circuit.

  • Line-voltage magnetic motor starters are electromechanical devices that provide a safe, convenient, and economical means of starting and stopping motors, and have the advantage of being controlled remotely. The great bulk of motor controllers sold are of this type.
  • Contactors are mainly used to control machinery which uses electric motors. It consists of a coil which connects to a voltage source. Very often for Single phase Motors, 230V coils are used and for three phase motors, 415V coils are used. The contactor has three main NO contacts and lesser power rated contacts named as Auxiliary Contacts [NO and NC] used for the control circuit. A contact is conducting metal parts which completes or interrupt an electrical circuit.
  • NO-normally open
  • NC-normally closed
(2)   Over Load Relay (Overload protection).
  • Overload protection for an electric motor is necessary to prevent burnout and to ensure maximum operating life.
  • Under any condition of overload, a motor draws excessive current that causes overheating. Since motor winding insulation deteriorates due to overheating, there are established limits on motor operating temperatures to protect a motor from overheating. Overload relays are employed on a motor control to limit the amount of current drawn.
  • The overload relay does not provide short circuit protection. This is the function of over current protective equipment like fuses and circuit breakers, generally located in the disconnecting switch enclosure.
  • The ideal and easiest way for overload protection for a motor is an element with current-sensing properties very similar to the heating curve of the motor which would act to open the motor circuit when full-load current is exceeded. The operation of the protective device should be such that the motor is allowed to carry harmless over-loads but is quickly removed from the line when an overload has persisted too long.
  • Normally fuses are not designed to provide overload protection. Fuse is protecting against short circuits (over current protection). Motors draw a high inrush current when starting and conventional fuses have no way of distinguishing between this temporary and harmless inrush current and a damaging overload. Selection of Fuse is depend on motor full-load current, would “blow” every time the motor is started. On the other hand, if a fuse were chosen large enough to pass the starting or inrush current, it would not protect the motor against small, harmful overloads that might occur later.
  • The overload relay is the heart of motor protection. It has inverse-trip-time characteristics, permitting it to hold in during the accelerating period (when inrush current is drawn), yet providing protection on small overloads above the full-load current when the motor is running. Overload relays are renewable and can withstand repeated trip and reset cycles without need of replacement. Overload relays cannot, however, take the place of over current protection equipment.

  • The overload relay consists of a current-sensing unit connected in the line to the motor, plus a mechanism, actuated by the sensing unit, which serves, directly or indirectly, to break the circuit.
  • Overload relays can be classified as being thermal, magnetic, or electronic.
  1. Thermal Relay: As the name implies, thermal overload relays rely on the rising temperatures caused by the overload current to trip the overload mechanism. Thermal overload relays can be further subdivided into two types: melting alloy and bimetallic.
  2. Magnetic Relay: Magnetic overload relays react only to current excesses and are not affected by temperature.
  3. Electronic Relay: Electronic or solid-state overload relays, provide the combination of high-speed trip, adjustability, and ease of installation. They can be ideal in many precise applications.

Wiring of DOL Starter:

(1)   Main Contact:
  • Contactor is connecting among Supply Voltage, Relay Coil and Thermal Overload Relay.
  • L1 of Contactor Connect (NO) to R Phase through MCCB
  • L2 of Contactor Connect (NO) to Y Phase through MCCB
  • L3 of Contactor Connect (NO) to B Phase through MCCB.
  • NO Contact (-||-):
  • (13-14 or 53-54) is a normally Open NO contact (closes when the relay energizes)
  • Contactor Point 53 is connecting to Start Button Point (94) and 54 Point of Contactor is connected to Common wire of Start/Stop Button.
  • NC Contact (-|/|-):
  • (95-96) is a normally closed NC contact (opens when the thermal overloads trip if associated with the overload block)
(2)   Relay Coil Connection:
  • A1 of Relay Coil is connecting to any one Supply Phase and A2 is connecting to Thermal over Load Relay’s NC Connection (95).
(3)   Thermal Overload Relay Connection:
  • T1,T2,T3 are connect to Thermal Overload Relay
  • Overload Relay is Connecting between Main Contactor and Motor
  • NC Connection (95-96) of Thermal Overload Relay is connecting to Stop Button and Common Connection of Start/Stop Button.

Wiring Diagram of DOL Starter:


Working of DOL Starter:

  • The main heart of DOL starter is Relay Coil. Normally it gets one phase constant from incoming supply Voltage (A1).when Coil gets second Phase relay coil energizes and Magnet of Contactor produce electromagnetic field and due to this Plunger of Contactor will move and Main Contactor of starter will closed and Auxiliary will change its position NO become NC and NC become (shown Red Line in Diagram)  .
  • Pushing Start Button:
  • When We Push the start Button Relay Coil will get second phase from Supply Phase-Main contactor(5)-Auxiliary Contact(53)-Start button-Stop button-96-95-To Relay Coil (A2).Now Coil energizes and Magnetic field produce by Magnet and Plunger of Contactor move. Main Contactor closes and Motor gets supply at the same time Auxiliary contact become (53-54) from NO to NC .
  • Release Start Button:
  • Relay coil gets supply even though we release Start button. When We release Start Push Button Relay Coil gets Supply phase from Main contactor (5)-Auxiliary contactor (53) – Auxiliary contactor (54)-Stop Button-96-95-Relay coil (shown Red / Blue Lines in Diagram).
  • In Overload Condition of Motor will be stopped by intermission of Control circuit at Point 96-95.
  • Pushing Stop Button:
  • When we push Stop Button Control circuit of Starter will be break at stop button and Supply of Relay coil is broken, Plunger moves and close contact of Main Contactor becomes Open, Supply of Motor is disconnected.

 Motor Starting Characteristics on DOL Starter:

  • Available starting current:    100%.
  • Peak starting current:           6 to 8 Full Load Current.
  • Peak starting torque:            100%

Advantages of DOL Starter:

  1. Most Economical and Cheapest Starter
  2. Simple to establish, operate and maintain
  3. Simple Control Circuitry
  4. Easy to understand and trouble‐shoot.
  5. It provides 100% torque at the time of starting.
  6. Only one set of cable is required from starter to motor.
  7. Motor is connected in delta at motor terminals.

Disadvantages of DOL Starter:

  1.  It does not reduce the starting current of the motor.
  2. High Starting Current: Very High Starting Current (Typically 6 to 8 times the FLC of the motor).
  3. Mechanically Harsh: Thermal Stress on the motor, thereby reducing its life.
  4. Voltage Dip: There is a big voltage dip in the electrical installation because of high in-rush current affecting other customers connected to the same lines and therefore not suitable for higher size squirrel cage motors
  5. High starting Torque: Unnecessary high starting torque, even when not required by the load, thereby increased mechanical stress on the mechanical systems such as rotor shaft, bearings, gearbox, coupling, chain drive, connected equipments, etc. leading to premature failure and plant downtimes.

Features of DOL starting

  • For low- and medium-power three-phase motors
  • Three connection lines (circuit layout: star or delta)
  • High starting torque
  • Very high mechanical load
  • High current peaks
  • Voltage dips
  • Simple switching devices

DOL is Suitable for:

  • A direct on line starter can be used if the high inrush current of the motor does not cause excessive voltage drop in the supply circuit. The maximum size of a motor allowed on a direct on line starter may be limited by the supply utility for this reason. For example, a utility may require rural customers to use reduced-voltage starters for motors larger than 10 kW.
  • DOL starting is sometimes used to start small water pumps, compressors, fans and conveyor belts.

DOL is not suitable for:

  • The peak starting current would result in a serious voltage drop on the supply system
  • The equipment being driven cannot tolerate the effects of very high peak torque loadings
  • The safety or comfort of those using the equipment may be compromised by sudden starting as, for example, with escalators and lifts.