RO PLANTS

Reverse Osmosis Plants/RO Plants

Reverse osmosis is the process of forcing a solvent from a region of high solute concentration through a membrane to a region of low solute concentration by applying a pressure in excess of the osmotic pressure. This is the reverse of the normal osmosis process, which is the natural movement of solvent from an area of low solute concentration, through a membrane, to an area of high solute concentration when no external pressure is applied. The membrane here is semipermeable, meaning it allows the passage of solvent but not of solute.

To illustrate, imagine a semi permeable membrane with fresh water on one side and a concentrated aqueous solution on the other side. If normal osmosis takes place, the fresh water will cross the membrane to dilute the concentrated solution. In reverse osmosis, pressure is exerted on the side with the concentrated solution to force the water molecules across the membrane to the fresh water side.

The membranes used for reverse osmosis systems have a dense polymer barrier layer in which separation takes place. Since Reverse Osmosis does not occur naturally, it must be created by applying pressure to the high solids water in order to force it through the membrane, with pressures from 8 - 14 bar for fresh and brackish water, and 40 - 70 bar for seawater, which has around 24 bar (350 psi) natural osmotic pressure which must be overcome.

Design Considerations for RO Plant

Fluid Systems RO Plants work on the Crossflow Filtration method, which takes the feed water and uses a percentage of it as a wash or reject stream, removing the solids during the filtration process.

The product flow of an RO Plant is mainly a function of temperature and pressure. System recovery (product divided by feed) is limited by the characteristics of the feed water and can be controlled through the use of recycle stream. Product quality is based on a percentage of dissolved solids fed to the membrane. There should be an economic balance between product quality and system recovery. High recoveries increase concentration of dissolved solids in the system which degrades quality, but high recoveries make the system work more efficiently and decrease waste.

Reverse Osmosis Plants do not deliver to service all of the water that is fed to them. During operation, some of the incoming water is used to wash down the membrane, and only part becomes finished product water. Purified water is referred to as product and wastewater is referred to as concentrate, or reject. The percent of water delivered as product is called the recovery, and depends upon the membrane and on total RO Plant design considerations.

Pretreatment – Reverse Osmosis Plants

The feed water, depending on its source, may contain various concentrations of suspended solids and dissolved matter. Suspended solids may consist of inorganic particles, colloidal particles and biological impurities such as microorganisms and algae. Dissolved matter may consist of highly soluble salts, such as chlorides, and sparingly soluble salts, such as carbonates, sulfates, and silica.

During the Reverse Osmosis process, the volume of feed water decreases, and the concentration of suspended particles and dissolved ions increases. Suspended particles may settle on the membrane surface, thus blocking feed channels and increasing pressure drop across the system. Sparingly soluble salts may precipitate from the concentrate stream, create scale on the membrane surface, and result in lower water permeability through the RO membranes. This process of formation of a deposited layer on a membrane surface is called membrane fouling and results in performance decline of the RO system. The objective of the feed water pretreatment process is to improve the quality of the feed water to the level which would result in reliable operation of the RO membranes. Based on the raw water quality, the pretreatment process for RO Plants may consist of all or some of the following treatment steps:

Clarification followed by Sand Filtration for Turbidity removal
Water disinfection with chlorine
Hardness reduction by Softening
Addition of scale inhibitor
Reduction of free chlorine using sodium bisulfite/ Activated carbon filters
Final removal of suspended particles using cartridge filters

We Offer a wide range of Reverse Osmosis Plants [RO Plants]

Industrial Reverse Osmosis Plants/ Industrial RO Systems

We manufacture a wide Range of industrial Reverse Osmosis Plants to cater the stringent process requirements. Our industrial reverse osmosis Plants are carefully customized and configured to suit the individual requirement of the output water, which varies from normal drinking application to the specific usage, such as food Processing, pharmaceuticals and boiler feeding requirement.

These systems come standard with pre-filters, chemical dosing and Antiscalant dosing. Customization is available on all our units based on individual water application and customer needs.

4" & 8" TFC spiral wound membranes
FRP membrane housings
Epoxy painted steel frame
SS High Pressure Piping
Stainless steel High Pressure Multi-stage pumps
20 & 5 micron cartridge filter
Low & High pressure switches
Glycerin filled pressure gauges
Permeate & concentrate flow meters
PLC/Microprocessor based Controllers
Outlet Conductivity meter

These Industrial RO Systems are available in the Flow Ranges from 1 M3/Hr Product Water Capacity and above. Standard Ranges are available in Multiples of 1 M3/Hr up to 10 M3/Hr.

Higher flow Rates from 10 M3/Hr to 100 M3/Hr and above are custom-built as per Customers requirement with extensive pre-filtration units to suit the most aggressive waters.

Commercial RO Systems / Institutional RO Systems

One of our most popular series, the Commercial RO usually comes in standard Models. These Commercial RO Systems can be customized to add Multimedia Filters & Activated carbon Filters, Water softeners, Antiscalant Dosing Systems, and UV sterilizers.

These systems are used to purify water and remove salts and other impurities. It is also capable of rejecting bacteria The Main features of these RO Plants are

Powder coated frame
20 & 5 micron sediment pre-filter
Stainless Steel Multistage High pressure pump
FRP pressure vessel
Product and Reject Flow Meters
Low & High pressure switch
High rejection TFC membranes
Heavy duty high pressure tubing

These Commercial/Institutional RO Systems are available in following Flow Ranges:

50 LPH RO Plants
100 LPH RO Plants
200 LPH RO Plants
500 LPH RO Plants
750 LPH RO Plants

Electrical Circuit Diagram;

Containerized RO Plants

Containerized Reverse Osmosis Plants / Containerized Desalination Plants/Containerized Ultra filtration Plants Fluid Systems supplies a host of water treatment in a containerized version. From ultra filtration to brackish water plants to Desalination Plants. Fluid Systems provides an affordable, plug-and-play desalination solution that can be commissioned in a short period. Our ready-to-use containerized desalination plants can produce up to 1000 m3/day of drinking water.

The Plant is housed in a standard 20 or 40 ft container. The containers can be insulated on request. The Plant comes with pre-piped and pre cabled connections [plug and play]. Remote Monitoring Option also available with GSM connectivity Benefits of Fluid Systems Containerized Plants

Plug and Play Unit
Minimum civil construction required
Small footprint
High quality components
High recovery
High TDS Rejection
Easy Spare parts availability as standard Components are used
Modular in design
Low energy and chemical consumption
Quick Installation

Applications

Off shore Applications
Armed Services Camps
Construction Sites
Mining Operations
Resorts

Mineral Water Plants/Packaged Drinking Water Plants

As people become more health conscious, the demand for bottled water is increasing at a rapid rate. Bottled water provides easy transportability and assured water quality.

With our several years of experience in the Water Treatment Field, we have developed comprehensive, economically viable packages, such that the capital outlay is optimized. Our packages are offered in modules so that they can be upgraded at a later date as the demand increases. Typically a Packaged Drinking water Plant may consist of:

Water Treatment Plant
Packaging Plant

The Water Treatment Plant consists of One or All oft the below mentioned pocess:

Chlorine/Hypochlorite Dosing System
Chlorine/Hypo chlorite dosing system is done in the raw water for disinfection / oxidation of iron and manganese (if present) in the water before filtration. sodium hypo chlorite reacts with water to form hypo chlorite acids which acts as disinfecting agent.

PRESSURE SAND FILTER Raw Water is first filtered by filtration unit in series prior to feeding the RO Plant. Pressure Sand Filter unit is provided for removal of Suspended Matters & Turbidity from raw water.

ACTIVATED CARBON FILTER
Basic Natural water may contain Colour, Odour, Chlorine & Organics in different proportion, which is undesirable for potable application, and hence, it is necessary to remove the same from water. The Activated Carbon Filter removes Chlorine, Odour, & Colour, Pesticides, Organics and In organics Impurities while passing the water through Carbon Bed.

SMBS DOSING SYSTEM
The Chlorinated water may oxidize the membrane and to avoid the same precautionary we provide Sodium Meta BiSulphite dosing system

ANTI SCALANT DOSING
The hardness salts of Calcium & Magnesium are likely to be precipitated if concentration exceeds its solubility limit & it may faults the membranes resulting into scaling which ultimately leads to poor treated water quality from RO System. To prevent this Antiscalant dosing (scale inhibitor) dosing system is provided.

MICRON CARTRIDGE FILTER
Micron Cartridge Filter having Series of filtration with the 20 Micron, 10 Micron, 5 Micron, 1 Micron, 0.45 Micron & 0.2 Micron Cartridge. This is a Consumable Cartridge and should replace it after Days of operation. This for Extra Safety of Product water as it comes through series of filtration and there are some chances of slippages of particles, which can be arrested through the Cartridges

HIGH PRESSURE PUMP
For Reverse Osmosis Process to take place feed pressure of water need to be raised. For this purpose a Vertical Multistage Centrifugal High Pressure Pump in S.S construction is provided R.O. System requires operating pressure of about 14-16 kg/cm^2 . High-pressure pump is fitted with S.S. discharge pipe work with necessary control valves. Necessary instruments like a High Pressure Switch, Pressure Gauge and re-circulation valves are provided for safer operation of system.

REVERSE OSMOSIS SYSTEM
Reverse Osmosis System rejects 97 – 99 % of total dissolved solids by the principle of `Osmosis’. This system consists of a R.O. Module assembly mounted on Structural Skid. High pressure rating FRP Pressure Vessel (Pressure Tubes) are fitted on the skid which houses spirally wound membrane elements in series.

In RO System feed soften water is divided into two streams viz Product & Reject water. Product water is treated water having lesser TDS. Reject water is highly concentrated water, which is not to be used for any purpose but drained. Followed Filtered water at elevated pressure is first feed to Pressure Vessel; treated water is collected in center core tube. Treated water from each membrane is collected jointly in a common product water storage tank and reject is drained.

For safe operation of system following instruments are provided on the Panel.

Feed & Reject Pressure Gauge: to indicate respective pressure of R.O.System.
Feed & Reject Flow Indicator: to indicate respective flow of R.O.System.
T.D.S Meter: to measure TDS of Raw & Treated water.
High Pressure Switch: for tripping HPP in case of excessive feed pressure
Time Totaliser: for counting working hours of H.P Pump/ R.O.System.

PRODUCT WATER STORAGE TANK
Treated water from R.O. System are collected in S.S. constructed storage tank of appropriate capacity. The tank is fitted with S.S. pipe work & isolation valves and suitable type of level indicator.

ABSOLUTE MICRON CARTRIDGE FILTERS: (MCF) - Removing the Micro Biological Growth
During storage, atmospheric or any other contamination may take place in treated water. Hence, after passing water from R.O. System & after Storage, water is once again passed through a micron cartridge filters. This is a S.S.316 Vessel, internally Electro polished fitted with internally with P.P Pleated micron cartridge elements having absolute ratings of 1.0 micron & 0.2 microns which removes all bacterial impurities present in the water and make the water free of particulates.

ULTRA VIOLET STERILIZER
With follow treatments treated water is free from all the micro-biological impurities like Bacteria, Virus, etc. it may redevelop again in water during prolonged storage. For dis-infection of water is essential for Reverse Osmosis Application before Filling & Sealing in bottle. Hence, a online Ultra Violet Sterilizer is require for disinfections of Treated water before filling in pre-cleaned PET Bottles. The water to be disinfected, is passed through U.V.System, which consists of U.V.Tubes which radiates high intensity Ultra Violet Rays, which in turn kills the micro organisms. This systems consists of a S.S finished surface housing with Ultraviolet Lamps fitted in it. The water to be treated is surroundings this tubes during treatment. An electrical system is provided for production of high voltage required for U.V.Rays generation and Operating Life of U.V.Lamps.

OZONE GENERATOR: (OZONE) - Generate the Ozone Gas
Though R.O. System rejects all the micro – organisms like bacterial & virus and even after passing through MCF & U.V.System it may redevelop in packed bottles over a period of time. Hence, it is necessary to disinfect R.O.Product water prior to bottling filling. This is very much essential to ensure good Mineral Water Quality as per the standards. This Ozone Generator use for the Final Treated Water to make Oxygen Rich water and it removes the Bacteriological growth and also provide you the Shelf Life of your Packed Bottle water unless it open for some period of time. Also this Ozonated water can add some taste in to your Treated water.

RO PLANTS Reverse Osmosis Plants/RO Plants

RO PLANTS

Reverse Osmosis Plants/RO Plants

Design Considerations for RO Plant

Pretreatment – Reverse Osmosis Plants

Clarification followed by Sand Filtration for Turbidity removal
Water disinfection with chlorine
Hardness reduction by Softening
Addition of scale inhibitor
Reduction of free chlorine using sodium bisulfite/ Activated carbon filters
Final removal of suspended particles using cartridge filters

We Offer a wide range of Reverse Osmosis Plants [RO Plants]

Industrial Reverse Osmosis Plants/ Industrial RO Systems

4" & 8" TFC spiral wound membranes
FRP membrane housings
Epoxy painted steel frame
SS High Pressure Piping
Stainless steel High Pressure Multi-stage pumps
20 & 5 micron cartridge filter
Low & High pressure switches
Glycerin filled pressure gauges
Permeate & concentrate flow meters
PLC/Microprocessor based Controllers
Outlet Conductivity meter

Commercial RO Systems / Institutional RO Systems

Powder coated frame
20 & 5 micron sediment pre-filter
Stainless Steel Multistage High pressure pump
FRP pressure vessel
Product and Reject Flow Meters
Low & High pressure switch
High rejection TFC membranes
Heavy duty high pressure tubing

These Commercial/Institutional RO Systems are available in following Flow Ranges:

50 LPH RO Plants
100 LPH RO Plants
200 LPH RO Plants
500 LPH RO Plants
750 LPH RO Plants

Electrical Circuit Diagram;

Containerized RO Plants

Plug and Play Unit
Minimum civil construction required
Small footprint
High quality components
High recovery
High TDS Rejection
Easy Spare parts availability as standard Components are used
Modular in design
Low energy and chemical consumption
Quick Installation

Applications

Off shore Applications
Armed Services Camps
Construction Sites
Mining Operations
Resorts

Mineral Water Plants/Packaged Drinking Water Plants

Water Treatment Plant
Packaging Plant

Feed & Reject Pressure Gauge: to indicate respective pressure of R.O.System.
Feed & Reject Flow Indicator: to indicate respective flow of R.O.System.
T.D.S Meter: to measure TDS of Raw & Treated water.
High Pressure Switch: for tripping HPP in case of excessive feed pressure
Time Totaliser: for counting working hours of H.P Pump/ R.O.System.

Explanation of the working and operation of Star Delta Automatic Starter with Timer Wiring Installation:

From the left you have the main contactor with the pneumatic timer because your main contactor is always energized, in the Middle you have the Delta contactor with a thermal overload for motor protection in case the motor exceeds the ampere rating set on the thermal overload, on the right you have the Star contactor which is the first contactor to be energized with the main contactor then when the timer reaches its time limit the Star contactor de-energizes and the Delta contactor energizes and the Motor is running at full load.

Related Motor Control & Power Diagrams:

STAR/DELTA Starter Without Timer Power, Control Diagrams & Wiring Diagrams
Control 3-Phase Motor from more than Two Places – Power & Control Diagrams

Operation & Working of Automatic Star Delta Starter

From L1 The phase current flows to thermal overload contact through fuse, then OFF push button, On push button Interlocking contact 2, and then C3. This way, the circuit is completed, as a result;

Contactor coil C3 and timer coil (I1) is energized at once and the motor winding then connected in Star. When C3 is energized, its auxiliary open links will be closed and vice versa (i.e. close links would be open). Thus C1 Contactor is also energized and Three Phase Supply will reach to the motor. Since winding is connected in Star, hence each phase will get √3 times less than the line voltage i.e. 230V. Hence Motor starts safely.
The close contact of C3 in the Delta line opens because of which there would be no chance of activation of contactor 2 (C2) .
After leaving the push button, Timer coil and coil 3 will receive a supply through Timer contact (Ia) , Holding contact 3 and the close contact 2 of C2.
When Contactor 1 (C1) is energized, then the two open contact in the line of C1 and C2 will be closed.
For the specific time (generally 5-10 seconds) in which the motor will be connected in star, after that the Timer contact (Ia) will be open (We may change by rotating the timer knob to adjust the time again) and as a result;

Contactor 3 (C3) will be off, because of which the open link of C3 will be close (which is in the line of C2) thus C2 will also energize. Similarly, When C3 off, then star connection of winding will also open. And C2 will be closed. Therefore, the motor winding will be connected in Delta. In addition, Contact 2 (which is in the line C3) will open, by which, there would not be any chance of activation of coil 3 (C3)
Since the motor is connected in Delta now, therefore, each phase of the motor will receive full line voltage (400V) and the motor will start to run in full motion.

Star Delta Starter Power Diagram

Click image to enlarge

Star Delta starter Power Circuit Diagram

Control Diagram of Star Delta Starter with Timer

Abbreviations: ( FOR Control Wiring of Three Phase Star Delta Starter with Timer)

R , Y, B = Red, Yellow, Blue ( 3 Phase Lines)
C.B = General Circuit Breaker
Main = Main Supply
Y = Star
Δ = Delta
1a = Timer
C1, C2, C3 = Contactors (For Power & Control Diagram)
O/L = Over Load Relay
NO = Normally Open
NC = Normally Closed
K1 = Contactor (Contactor coil)
K1/NO = Contactor Holding Coil (Normally Open)

Advantages & Disadvantages of Star Delta Starter with Timer

Advantages:

Simple Design and Operation
Comparatively cheaper than other voltage controlling methods
Torque and Current performance of the Star delta starter is well.
It draws two times starting current of the FLA (Full Load Ampere) of the connected motor.
It reduced the starting current to one-third (approximately) as compared to DOL (Direct ON Line Starter.

Disadvantages

Starting Torque is also reduce to one-third because starter reduce the starting current to one-third of the rated current [as Line voltage also reduced to 57% (1/√3)]
It required Six leads or terminals Motor (Delta Connected)
For Delta connection, the supply voltage must be same as the rated motor voltage.
At switching time (From Star to Delta), if the motor does not reach at least 90% of its rated speed, then the current peak may be equally high as in Direct ON Line starter( D.O.L), thus it may cause harmful effects on the contactors contacts, so it would not be reliable.
We may not use star delta starter if the required (application or load) torque is more than 50% of the three phase induction motors rated torque

Characteristics & Features of Star-Delta Starter

The starting current is 33% of full load current for star delta starter.
The peak starting torque is 33% of full load torque.
The peak starting current is 1.3 to 2.6 of full load current.
Star-Delta Starter can be used only for low to high power three phase induction motors.
It has reduced starting current and torque.
The 6 connection cables are needed for motor terminal box.
In Star Delta starter, Current peak and mechanical load on changeover from star delta

Applications of Star Delta Starter

As we know the main purpose of star delta starter is to start the three phase induction motor in Star Connection while run in Delta Connection.

While keep in mind that Star Delta starter can only be used for low to medium voltage and light starting torque induction motors. In case of direct on line (D.O.L) start, the receiving current at motor is about 33% while the starting torque reduced about 25-30%. This way, Star Delta Starter can be only used for light load during starting the motor. Otherwise, the heavy load motor wont start due to low torque which need to accelerate the motor to rated speed while converting to the Delta connection.

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Star Delta Starter: Circuit Diagram, Working Principle & Theory

Explanation of the working and operation of Star Delta Automatic Starter with Timer Wiring Installation:

Related Motor Control & Power Diagrams:

STAR/DELTA Starter Without Timer Power, Control Diagrams & Wiring Diagrams
Control 3-Phase Motor from more than Two Places – Power & Control Diagrams

Operation & Working of Automatic Star Delta Starter

From L1 The phase current flows to thermal overload contact through fuse, then OFF push button, On push button Interlocking contact 2, and then C3. This way, the circuit is completed, as a result;

Contactor coil C3 and timer coil (I1) is energized at once and the motor winding then connected in Star. When C3 is energized, its auxiliary open links will be closed and vice versa (i.e. close links would be open). Thus C1 Contactor is also energized and Three Phase Supply will reach to the motor. Since winding is connected in Star, hence each phase will get √3 times less than the line voltage i.e. 230V. Hence Motor starts safely.
The close contact of C3 in the Delta line opens because of which there would be no chance of activation of contactor 2 (C2) .
After leaving the push button, Timer coil and coil 3 will receive a supply through Timer contact (Ia) , Holding contact 3 and the close contact 2 of C2.
When Contactor 1 (C1) is energized, then the two open contact in the line of C1 and C2 will be closed.
For the specific time (generally 5-10 seconds) in which the motor will be connected in star, after that the Timer contact (Ia) will be open (We may change by rotating the timer knob to adjust the time again) and as a result;

Contactor 3 (C3) will be off, because of which the open link of C3 will be close (which is in the line of C2) thus C2 will also energize. Similarly, When C3 off, then star connection of winding will also open. And C2 will be closed. Therefore, the motor winding will be connected in Delta. In addition, Contact 2 (which is in the line C3) will open, by which, there would not be any chance of activation of coil 3 (C3)
Since the motor is connected in Delta now, therefore, each phase of the motor will receive full line voltage (400V) and the motor will start to run in full motion.

Star Delta Starter Power Diagram

Click image to enlarge

Star Delta starter Power Circuit Diagram

Control Diagram of Star Delta Starter with Timer

Abbreviations: ( FOR Control Wiring of Three Phase Star Delta Starter with Timer)

R , Y, B = Red, Yellow, Blue ( 3 Phase Lines)
C.B = General Circuit Breaker
Main = Main Supply
Y = Star
Δ = Delta
1a = Timer
C1, C2, C3 = Contactors (For Power & Control Diagram)
O/L = Over Load Relay
NO = Normally Open
NC = Normally Closed
K1 = Contactor (Contactor coil)
K1/NO = Contactor Holding Coil (Normally Open)

Advantages & Disadvantages of Star Delta Starter with Timer

Advantages:

Simple Design and Operation
Comparatively cheaper than other voltage controlling methods
Torque and Current performance of the Star delta starter is well.
It draws two times starting current of the FLA (Full Load Ampere) of the connected motor.
It reduced the starting current to one-third (approximately) as compared to DOL (Direct ON Line Starter.

Disadvantages

Starting Torque is also reduce to one-third because starter reduce the starting current to one-third of the rated current [as Line voltage also reduced to 57% (1/√3)]
It required Six leads or terminals Motor (Delta Connected)
For Delta connection, the supply voltage must be same as the rated motor voltage.
At switching time (From Star to Delta), if the motor does not reach at least 90% of its rated speed, then the current peak may be equally high as in Direct ON Line starter( D.O.L), thus it may cause harmful effects on the contactors contacts, so it would not be reliable.
We may not use star delta starter if the required (application or load) torque is more than 50% of the three phase induction motors rated torque

Characteristics & Features of Star-Delta Starter

The starting current is 33% of full load current for star delta starter.
The peak starting torque is 33% of full load torque.
The peak starting current is 1.3 to 2.6 of full load current.
Star-Delta Starter can be used only for low to high power three phase induction motors.
It has reduced starting current and torque.
The 6 connection cables are needed for motor terminal box.
In Star Delta starter, Current peak and mechanical load on changeover from star delta

Applications of Star Delta Starter

As we know the main purpose of star delta starter is to start the three phase induction motor in Star Connection while run in Delta Connection.

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DOL Starter (Direct On Line Starter) Diagram And Working Principle

What is DOL Starter?

A DOL starter (also known as a direct on line starter or across the line starter) is a method of starting a 3 phase induction motor. In a DOL Starter, an induction motor is connected directly across its 3-phase supply, and the DOL starter applies the full line voltage to the motor terminals. Despite this direct connection, no harm is done to the motor. A DOL motor starter contains protection devices, and in some cases, condition monitoring.

In this article, we will discuss DOL starter (Direct Online Starter) - Working Principle and Construction, DOL Starter Diagram, control diagram, power circuit, and wiring, Single & 3 Phase starter

Direct On-Line is the simplest and cheapest method used for starting three-phase motor. Dol is used for up to 5 HP motor. dol starter is more popular due to the low price.

DOL starter connects the motor directly to supply without a reduction in supply voltage and apply full line voltage to 3 phase motor. This is the main disadvantage of dol starter.

Small HP motor can be started simply plugging into the power supply. But large HP motor required special unit called a motor starter.

Direct online starter for 3-phase induction motor contain parts like miniature circuit breaker (MCB) for motor protection purpose, overload relay, power contactor, fuse unit, start button, stop button.

Small size dol starter is operated manually but for larger HP motor, dol motor starter are operated using electromechanical contactor (relay) to switch motor ON and OFF.

DOL Motor Starter can be used, if high starting current cannot cause an excessive voltage drop in the motor circuit.

D O L starter use for starting the small motor, compressor, small water pumps, industrial conveyor belts. Fans, air curtains, exhaust fan, blower, etc.

A reversing starter can connect the motor for rotation in either direction. Such a starter contains two DOL circuits—one for clockwise operation and the other for counter-clockwise operation, with mechanical and electrical interlocks to prevent simultaneous closure.

For three phase motors, this is achieved by changing the wires connecting any two phases. Single phase AC motors and direct-current motors require additional devices for reversing rotation

In the case of three phases asynchronous motor, draws very high starting current up till achieving full speed. This starting current up to 6 to 7 time of full load current.

To reduce this starting current larger motor has starting methods like star delta starter or variable frequency drive.to reduced voltage dips on the power supply.

The demerits of dol starter is that gives the highest possible current to motor. Which is 6 to 7 time of rated current of the motor.

Besides then DOL starter draws the starting current there also exists a current peak that can rise up to 14 times the rated current since the motor is not energized from the first moment when starting.

So, here the question arises what is dol motor starter and how dol starter work. Explanation of direct online motor starter with control and power circuit diagram is given below.

Table of Contents

Direct online starter (DOL starter) control diagram :

Fig. direct online starter dol control circuit diagram

DOL starter control circuit diagram consist components like Main power contactor, start button, stop push button and overload relay is connected in series this circuit is called control circuit of dol motor starter. All controlling of starter are controlled by this circuit.

DOL starter power circuit diagram :

Direct Online starter power diagram has fuse unit (F1), Main power contactor (K1), overload relay (F2). Also, we can connect MCB for protection purpose in direct On-Line motor starter.

DOL Starter power circuit diagram

Direct online starter circuit Wiring diagram:

Direct online starter DOL diagram

DOL starter of three phase induction motors control and power circuit consist MCB or fuse unit which connected in series with the supply. Power contactor, thermal Overload relay for protection and stop and start push button.

Working Principle of Direct online starter (DOL Starter ) :

1) To start the motor, start push button is pressed. After that, the main power contactor coil energized due to electromechanical action and this latch contactor pole.it applies full line voltage to the motor terminals. and the motor starts running. The motor will draw a very high inrush current for a short time.
2) As the motor accelerates and head toward the full speed, current begins to drop but it will not drop significantly till motor achieved full speed, about 85% of synchronous speed.

3) The motor load will affect the time taken for the motor to accelerate to full speed and therefore the duration of high starting current, but it will not affect the magnitude of starting current.

4)the torque developed by motor exceeds the load torque at all speeds during the start cycle, the motor will reach full speed. If the torque developed by the motor is less than the torque of load at any speed during the start period. the motor stops accelerating.
5) If motor torque developed by DOL Motor starter is less for load, then the motor must be replaced by the motor which can develop high starting torque.

DOL starter working :

1)When start push button on the direct online motor starter is pressed, contactor coil gets energized and it latches contactor pole due to electromagnetic action. 3 phase supply get applied to the induction motor terminal and motor start running

2) after that start push button get released and supply to contactor coil continued through latching contact provided to the main contractor of D O L starter.

3) At time of stopping the motor we need to pressed stop push button on dol starter circuit, this disconnect supply to the coil and contactor coil get de-energized, and it releases contactor latched pole and motor supply get disconnected.

Component of direct online starter(DOL Starter):

1)Contactor :

A contactor is a heavy duty relay with the high current rating, used for power up electrical motor. Current rating for contactor varies from 10 amps to several hundred amps. High current contactor is made from an alloy containing silver. Arcing during the switching operation of contactor causes contact to oxidize. However, silver oxide still good conductor.

Overload protection is provided along with the contactors to start the motor. Contactor is not used to interrupt a short circuit current, Unlike the circuit breaker used. Contactor size varies from small to large for high current appliances.

Contactor creates noise while switching operation. If when requires silent operation solid state relay used. A contactor is an electromechanical switch which operates on energization and de-energized of the coil.

The contactor has 3 NO contact which connects a motor to the power supply and one additional contact refer as Auxiliary contact, which is act as hold on contact when start push-button release. To maintain energization of contactor coil.

If some time power fails abruptly due to this contactor coil get de-energized, it open contactor terminal and motor get disconnected from the supply.

2) Over load relay (overload protection ):

Most of motor winding failure occurs due to overload. Motor overload tends to the heating of motor winding that results in the weakening of winding insulation. A minor overload does not cause a motor failure immediately but it will eventually shorten the expected lifetime.

To prevent this situation thermal overload relay is provided into a direct online starter circuit.

Thermal overload relay has a bimetallic strip that bends because of overheating caused by overcurrent.

This disconnect motor from supply and prevent further motor winding damage also insulation failure.

3) Miniature circuit breaker (MCB) :

To protect the motor from short circuit condition and avoid damage to motor winding MCB is used in DOL circuit.

4 ) Push buttons :

There are two push buttons are used in dol motor starter, one is a green color for the start button and other is red for the stop push button.

Switching of power supply carried out by using electromechanical contactor which has 3 to 4 pole

Start push button:

this is normally open type push button, to start motor, this push button need to press and supply get applied to motor through power contactor.

Stop push button:

This is NC type push button we need to press to stop motor from running condition. after pressing stop button contactor coil get de-energized with the opening of contacts. Due to this switching operation motor get disconnected from supply and motor stops rotating.

Advantages of DOL Starter(direct online starter)

Direct On-Line motor starter is Cheapest motor Starter.
DOL is the simplest motor starter to design and maintain.
100% starting torque.
D O L starter used up to 5HP motor depending upon insulation class of motor.

Disadvantages of DOL Starter

High starting current
typically 7 to 8 time rated current applied at starting
due to high current stress applied on motor winding.
not suitable for high rating motor.
create a voltage dip on the power system
High starting torque.

DOL Starter(Direct On Line Starter)