11212015 StarshyDelta Motor Starter | EEP

httpelectricalshyengineeringshyportalcomstarshydeltashymotorshystarter 113

StarshyDelta Motor Starter

Starshydelta motor starter panel

Introduction to StarshyDelta motor starter

Starshydelta starter panel

11212015 StarshyDelta Motor Starter | EEP

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Most induction motors are started directly on line but when very large motors arestarted that way they cause a disturbance of voltage on the supply lines due to largestarting current surges To limit the starting current surge large induction motors arestarted at reduced voltage and then have full supply voltage reconnected when theyrun up to near rotated speed

Two methods used for reduction of starting voltage are Star delta startingand Auto transformer starting

Working Principle of StarshyDelta StarterThis is the reduced voltage starting method Voltage reduction during starshydeltastarting is achieved by physically reconfiguring the motor windings as illustrated in thefigure below During starting the motor windings are connected in star configurationand this reduces the voltage across each winding 3 This also reduces the torque by afactor of three

Scheme ndash Working Principle of StarshyDelta Starter

After a period of time the winding are reconfigured as delta and the runsnormally StarDelta starters are probably the most common reduced voltage startersThey are used in an attempt to reduce the start current applied to the motor duringstart as a means of reducing the disturbances and interference on the electricalsupply

Traditionally in many supply regions there has been a requirement to fit areduced voltage starter on all motors greater than 5HP (4KW) TheStarDelta (or WyeDelta) starter is one of the lowest cost electromechanicalreduced voltage starters that can be applied

motor

11212015 StarshyDelta Motor Starter | EEP

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The StarDelta starter is manufactured from three contactors a timer and a thermaloverload The contactors are smaller than the single contactor used in a Direct on Linestarter as they are controlling winding currents only The currents through the windingare 1root 3 (58) of the current in the line

There are two contactors that are close during run often referred to as the maincontractor and the delta contactor These are AC3 rated at 58 of the current ratingof the motor The third contactor is the star contactor and that only carries star currentwhile the motor is connected in star

The current in star is one third of the current in delta so this contactor can be AC3rated at one third (33) of the motor rating

Starshydelta Starter Consists following units

1 Contactors (Main star and delta contactors) 3 Norsquos (For Open State Starter) or4 Norsquos (Close Transient Starter)

2 Time relay (pullshyin delayed) 1 No3 Threeshypole thermal overcurrent release 1 No4 Fuse elements or automatic cutshyouts for the main circuit 3 Nos5 Fuse element or automatic cutshyout for the control circuit 1No

Power Circuit of Star Delta Starter

The main circuit breaker serves as the main power supply switch that supplieselectricity to the power circuit

The main contactor connects the reference source voltage R Y B to the primaryterminal of the motor U1 V1 W1

In operation the Main Contactor (KM3) and the Star Contactor (KM1) are closedinitially and then after a period of time the star contactor is opened and then thedelta 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 preferablymechanically interlocked as well

Power circuit of StarshyDelta starter

In effect there are four states

11212015 StarshyDelta Motor Starter | EEP

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The starcontactorserves toinitially shortthe secondaryterminal of themotor U2 V2W2 for thestart sequenceduring theinitial run ofthe motor fromstandstill Thisprovides onethird of DOLcurrent to themotor thusreducing thehigh inrushcurrentinherent withlarge capacitymotors atstartup

Controlling theinterchangingstar connectionand deltaconnection ofan

is achieved by means of a star delta or wye delta control circuitThe control circuit consists of push button switches auxiliary contacts and a timer

Control Circuit of StarshyDelta Starter (Open Transition)Scheme ndash Control Circuit of StarshyDelta Starter (Open Transition)

AC induction motor

11212015 StarshyDelta Motor Starter | EEP

httpelectricalshyengineeringshyportalcomstarshydeltashymotorshystarter 513

The ON pushbutton startsthe circuit byinitiallyenergizing StarContactor Coil(KM1) of starcircuit andTimer Coil (KT)circuit WhenStar ContactorCoil (KM1)energized StarMain andAuxiliarycontactorchange itsposition fromNO to NC

When StarAuxiliaryContactor (1)(which isplaced on MainContactor coil

circuit ) become NO to NC itrsquos complete The Circuit of Main contactor Coil (KM3) soMain Contactor Coil energized and Main Contactorrsquos Main and Auxiliary ContactorChange its Position from NO to NC This sequence happens in a friction of time

After pushing the ON push button switch the auxiliary contact of the main contactorcoil (2) which is connected in parallel across the ON push button will become NO toNC thereby providing a latch to hold the main contactor coil activated whicheventually maintains the control circuit active even after releasing the ON push buttonswitch

When Star Main Contactor (KM1) close its connect Motor connects on STAR and itrsquosconnected in STAR until Time Delay Auxiliary contact KT (3) become NC to NO

Once the time delay is reached its specified Time the timerrsquos auxiliary contacts (KT)(3) in Star Coil circuit will change its position from NC to NO and at the Same Time

11212015 StarshyDelta Motor Starter | EEP

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Auxiliary contactor (KT) in Delta Coil Circuit(4) change its Position from NO To NC soDelta coil energized and Delta Main Contactor becomes NO To NC Now Motorterminal connection change from star to delta connection

A normally close auxiliary contact from both star and delta contactors (5amp6)are alsoplaced opposite of both star and delta contactor coils these interlock contacts servesas safety switches to prevent simultaneous activation of both star and delta contactorcoils so that one cannot be activated without the other deactivated first Thus thedelta contactor coil cannot be active when the star contactor coil is active andsimilarly the star contactor coil cannot also be active while the delta contactor coil isactive

The control circuit above also provides two interrupting contacts to shutdown themotor The OFF push button switch break the control circuit and the motor whennecessary The thermal overload contact is a protective device which automaticallyopens the STOP Control circuit in case when motor overload current is detected bythe thermal overload relay this is to prevent burning of the motor in case of excessiveload beyond the rated capacity of the motor is detected by the thermal overload relay

At some point during starting it is necessary to change from a star connected windingto a delta connected winding Power and control circuits can be arranged to this inone of two ways ndash open transition or closed transition

What is Open or Closed Transition Starting

1 Open Transition Starters

Discuss mention above is called open transition switching because there is an openstate between the star state and the delta state

In open transition the power is disconnected from the motor while the winding arereconfigured via external switching

When a motor is driven by the supply either at full speed or at part speed there is arotating magnetic field in the stator This field is rotating at line frequency The fluxfrom the stator field induces a current in the rotor and this in turn results in a rotormagnetic field

When the motor is disconnected from the supply (open transition) there is a spinningrotor within the stator and the rotor has a magnetic field Due to the low impedance ofthe rotor circuit the time constant is quite long and the action of the spinning rotor

11212015 StarshyDelta Motor Starter | EEP

httpelectricalshyengineeringshyportalcomstarshydeltashymotorshystarter 713

field within the stator is that of a generator which generates voltage at a frequencydetermined by the speed of the rotor

When the motor is reconnected to the supply it is reclosing onto anunsynchronized generator and this result in a very high current andtorque transient The magnitude of the transient is dependent on thephase relationship between the generated voltage and the line voltageat the point of closure can be much higher than DOL current and torqueand can result in electrical and mechanical damage

Open transition starting is the easiest to implement in terms or cost and circuitry and ifthe timing of the changeover is good this method can work well In practice though itis difficult to set the necessary timing to operate correctly anddisconnectionreconnection of the supply can cause significant voltagecurrenttransients

In open transition there are four states

1 OFF State All Contactors are open2 Star State The Main [KM3] and the Star [KM1] contactors are closed and the

delta [KM2] contactor is open The motor is connected in star and will produceone third of DOL torque at one third of DOL current

3 Open State This type of operation is called open transition switching becausethere is an open state between the star state and the delta state The Maincontractor is closed and the Delta and Star contactors are open There isvoltage on one end of the motor windings but the other end is open so nocurrent 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 contactoris open The motor is connected to full line voltage and full power and torque areavailable

2 Closed Transition StarDelta Starter

There is a technique to reduce the magnitude of the switching transients This requiresthe use of a fourth contactor and a set of three resistors The resistors must be sizedsuch that considerable current is able to flow in the motor windings while they are incircuit

The auxiliary contactor and resistors are connected across the delta contactor In

11212015 StarshyDelta Motor Starter | EEP

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operation just before the star contactor opens the auxiliary contactor closes resultingin current flow via the resistors into the star connection Once the star contactoropens current is able to flow round through the motor windings to the supply via theresistors These resistors are then shorted by the delta contactor

If the resistance of the resistors is too high they will not swamp the voltage generatedby the motor and will serve no purpose

In closed transition the power is maintained to the motor at all time

This is achieved by introducing resistors to take up the current flow during the windingchangeover A fourth contractor is required to place the resistor in circuit beforeopening the star contactor and then removing the resistors once the delta contactor isclosed

These resistors need to be sized to carry the motor current In addition to requiringmore switching devices the control circuit is more complicated due to the need tocarry out resistor switching

In close transition there are four states

1 OFF State All Contactors are open2 Star State The Main [KM3] and the Star [KM1] contactors are closed and the

delta [KM2] contactor is open The motor is connected in star and will produceone third of DOL torque at one third of DOL current

3 Star Transition State The motor is connected in star and the resistors areconnected across the delta contactor via the aux [KM4] contactor

4 Closed Transition State The Main [KM3] contactor is closed and the Delta[KM2] and Star [KM1] contactors are open Current flows through the motorwindings and the transition resistors via KM4

5 Delta State The Main and the Delta contactors are closed The transitionresistors are shorted out The Star contactor is open The motor is connected tofull line voltage and full power and torque are available

Effect of Transient in Starter (Open Transient starter)

It is Important the pause between star contactor switch off and Delta contactor switchis on correct This is because Star contactor must be reliably disconnected beforeDelta contactor is activated It is also important that the switch over pause is not too

11212015 StarshyDelta Motor Starter | EEP

httpelectricalshyengineeringshyportalcomstarshydeltashymotorshystarter 913

long

For 415v Star Connection voltage is effectively reduced to 58 or 240v Theequivalent of 33 that is obtained with Direct Online (DOL) starting

If Star connection has sufficient torque to run up to 75 or 80 of full load speedthen the motor can be connected in Delta mode

When connected to Delta configuration the phase voltage increases by a ratio of V3 or173 The phase currents increase by the same ratio The line current increasesthree times its value in star connection

During transition period of switchover the motor must be free running with littledeceleration While this is happening ldquoCoastingrdquo it may generate a voltage of its ownand on connection to the supply this voltage can randomly add to or subtract from theapplied line voltage This is known as transient current Only lasting a few millisecondsit causes voltage surges and spikes Known as a changeover transient

Size of each part of StarshyDelta starter

1 Size of Over Load Relay

For a starshydelta starter there is a possibility to place the overload protection in twopositions in the line or in the windings

Overload Relay in Line

In the line is the same as just putting the overload before the motor as with a DOLstarter

The rating of Overload (In Line) = FLC of Motor

Disadvantage If the overload is set to FLC then it is not protecting the motor while itis in delta (setting is x1732 too high)

Overload Relay in Winding

In the windings means that the overload is placed after the point where the wiring tothe contactors are split into main and delta The overload then always measures thecurrent inside the windings

The setting of Overload Relay (In Winding) =058 X FLC (line current)

11212015 StarshyDelta Motor Starter | EEP

httpelectricalshyengineeringshyportalcomstarshydeltashymotorshystarter 1013

Disadvantage We must use separate short circuit and overload protections

2 Size of Main and Delta Contractor

There are two contactors that are close during run often referred to as the maincontractor and the delta contactor These are AC3 rated at 58 of the current ratingof the motor

Size of Main Contactor= IFL x 058

3 Size of Star Contractor

The third contactor is the star contactor and that only carries star current while themotor is connected in star The current in star is 1 radic3= (58) of the current in deltaso this contactor can be AC3 rated at one third (33) of the motor rating

Size of Star Contactor= IFL x 033

Motor Starting Characteristics of StarshyDelta Starter

Available starting current 33 Full Load CurrentPeak starting current 13 to 26 Full Load CurrentPeak starting torque 33 Full Load Torque

Advantages of StarshyDelta starter

The operation of the starshydelta method is simple and ruggedIt is relatively cheap compared to other reduced voltage methodsGood TorqueCurrent PerformanceIt draws 2 times starting current of the full load ampere of the motor connected

Disadvantages of StarshyDelta starter

1 Low Starting Torque (Torque = (Square of Voltage) is also reduce)2 Break In Supply ndash Possible Transients3 Six Terminal Motor Required (Delta Connected)4 It requires 2 set of cables from starter to motor

5 It provides only 33 starting torque and if the load connected to the subject

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11212015 StarshyDelta Motor Starter | EEP

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Auxiliary contactor (KT) in Delta Coil Circuit(4) change its Position from NO To NC soDelta coil energized and Delta Main Contactor becomes NO To NC Now Motorterminal connection change from star to delta connection

A normally close auxiliary contact from both star and delta contactors (5amp6)are alsoplaced opposite of both star and delta contactor coils these interlock contacts servesas safety switches to prevent simultaneous activation of both star and delta contactorcoils so that one cannot be activated without the other deactivated first Thus thedelta contactor coil cannot be active when the star contactor coil is active andsimilarly the star contactor coil cannot also be active while the delta contactor coil isactive

The control circuit above also provides two interrupting contacts to shutdown themotor The OFF push button switch break the control circuit and the motor whennecessary The thermal overload contact is a protective device which automaticallyopens the STOP Control circuit in case when motor overload current is detected bythe thermal overload relay this is to prevent burning of the motor in case of excessiveload beyond the rated capacity of the motor is detected by the thermal overload relay

At some point during starting it is necessary to change from a star connected windingto a delta connected winding Power and control circuits can be arranged to this inone of two ways ndash open transition or closed transition

What is Open or Closed Transition Starting

1 Open Transition Starters

Discuss mention above is called open transition switching because there is an openstate between the star state and the delta state

In open transition the power is disconnected from the motor while the winding arereconfigured via external switching

When a motor is driven by the supply either at full speed or at part speed there is arotating magnetic field in the stator This field is rotating at line frequency The fluxfrom the stator field induces a current in the rotor and this in turn results in a rotormagnetic field

When the motor is disconnected from the supply (open transition) there is a spinningrotor within the stator and the rotor has a magnetic field Due to the low impedance ofthe rotor circuit the time constant is quite long and the action of the spinning rotor

11212015 StarshyDelta Motor Starter | EEP

httpelectricalshyengineeringshyportalcomstarshydeltashymotorshystarter 713

field within the stator is that of a generator which generates voltage at a frequencydetermined by the speed of the rotor

When the motor is reconnected to the supply it is reclosing onto anunsynchronized generator and this result in a very high current andtorque transient The magnitude of the transient is dependent on thephase relationship between the generated voltage and the line voltageat the point of closure can be much higher than DOL current and torqueand can result in electrical and mechanical damage

Open transition starting is the easiest to implement in terms or cost and circuitry and ifthe timing of the changeover is good this method can work well In practice though itis difficult to set the necessary timing to operate correctly anddisconnectionreconnection of the supply can cause significant voltagecurrenttransients

In open transition there are four states

1 OFF State All Contactors are open2 Star State The Main [KM3] and the Star [KM1] contactors are closed and the

delta [KM2] contactor is open The motor is connected in star and will produceone third of DOL torque at one third of DOL current

3 Open State This type of operation is called open transition switching becausethere is an open state between the star state and the delta state The Maincontractor is closed and the Delta and Star contactors are open There isvoltage on one end of the motor windings but the other end is open so nocurrent 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 contactoris open The motor is connected to full line voltage and full power and torque areavailable

2 Closed Transition StarDelta Starter

There is a technique to reduce the magnitude of the switching transients This requiresthe use of a fourth contactor and a set of three resistors The resistors must be sizedsuch that considerable current is able to flow in the motor windings while they are incircuit

The auxiliary contactor and resistors are connected across the delta contactor In

11212015 StarshyDelta Motor Starter | EEP

httpelectricalshyengineeringshyportalcomstarshydeltashymotorshystarter 813

operation just before the star contactor opens the auxiliary contactor closes resultingin current flow via the resistors into the star connection Once the star contactoropens current is able to flow round through the motor windings to the supply via theresistors These resistors are then shorted by the delta contactor

If the resistance of the resistors is too high they will not swamp the voltage generatedby the motor and will serve no purpose

In closed transition the power is maintained to the motor at all time

This is achieved by introducing resistors to take up the current flow during the windingchangeover A fourth contractor is required to place the resistor in circuit beforeopening the star contactor and then removing the resistors once the delta contactor isclosed

These resistors need to be sized to carry the motor current In addition to requiringmore switching devices the control circuit is more complicated due to the need tocarry out resistor switching

In close transition there are four states

1 OFF State All Contactors are open2 Star State The Main [KM3] and the Star [KM1] contactors are closed and the

delta [KM2] contactor is open The motor is connected in star and will produceone third of DOL torque at one third of DOL current

3 Star Transition State The motor is connected in star and the resistors areconnected across the delta contactor via the aux [KM4] contactor

4 Closed Transition State The Main [KM3] contactor is closed and the Delta[KM2] and Star [KM1] contactors are open Current flows through the motorwindings and the transition resistors via KM4

5 Delta State The Main and the Delta contactors are closed The transitionresistors are shorted out The Star contactor is open The motor is connected tofull line voltage and full power and torque are available

Effect of Transient in Starter (Open Transient starter)

It is Important the pause between star contactor switch off and Delta contactor switchis on correct This is because Star contactor must be reliably disconnected beforeDelta contactor is activated It is also important that the switch over pause is not too

11212015 StarshyDelta Motor Starter | EEP

httpelectricalshyengineeringshyportalcomstarshydeltashymotorshystarter 913

long

For 415v Star Connection voltage is effectively reduced to 58 or 240v Theequivalent of 33 that is obtained with Direct Online (DOL) starting

If Star connection has sufficient torque to run up to 75 or 80 of full load speedthen the motor can be connected in Delta mode

When connected to Delta configuration the phase voltage increases by a ratio of V3 or173 The phase currents increase by the same ratio The line current increasesthree times its value in star connection

During transition period of switchover the motor must be free running with littledeceleration While this is happening ldquoCoastingrdquo it may generate a voltage of its ownand on connection to the supply this voltage can randomly add to or subtract from theapplied line voltage This is known as transient current Only lasting a few millisecondsit causes voltage surges and spikes Known as a changeover transient

Size of each part of StarshyDelta starter

1 Size of Over Load Relay

For a starshydelta starter there is a possibility to place the overload protection in twopositions in the line or in the windings

Overload Relay in Line

In the line is the same as just putting the overload before the motor as with a DOLstarter

The rating of Overload (In Line) = FLC of Motor

Disadvantage If the overload is set to FLC then it is not protecting the motor while itis in delta (setting is x1732 too high)

Overload Relay in Winding

In the windings means that the overload is placed after the point where the wiring tothe contactors are split into main and delta The overload then always measures thecurrent inside the windings

The setting of Overload Relay (In Winding) =058 X FLC (line current)

11212015 StarshyDelta Motor Starter | EEP

httpelectricalshyengineeringshyportalcomstarshydeltashymotorshystarter 1013

Disadvantage We must use separate short circuit and overload protections

2 Size of Main and Delta Contractor

There are two contactors that are close during run often referred to as the maincontractor and the delta contactor These are AC3 rated at 58 of the current ratingof the motor

Size of Main Contactor= IFL x 058

3 Size of Star Contractor

The third contactor is the star contactor and that only carries star current while themotor is connected in star The current in star is 1 radic3= (58) of the current in deltaso this contactor can be AC3 rated at one third (33) of the motor rating

Size of Star Contactor= IFL x 033

Motor Starting Characteristics of StarshyDelta Starter

Available starting current 33 Full Load CurrentPeak starting current 13 to 26 Full Load CurrentPeak starting torque 33 Full Load Torque

Advantages of StarshyDelta starter

The operation of the starshydelta method is simple and ruggedIt is relatively cheap compared to other reduced voltage methodsGood TorqueCurrent PerformanceIt draws 2 times starting current of the full load ampere of the motor connected

Disadvantages of StarshyDelta starter

1 Low Starting Torque (Torque = (Square of Voltage) is also reduce)2 Break In Supply ndash Possible Transients3 Six Terminal Motor Required (Delta Connected)4 It requires 2 set of cables from starter to motor

5 It provides only 33 starting torque and if the load connected to the subject

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11212015 StarshyDelta Motor Starter | EEP

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field within the stator is that of a generator which generates voltage at a frequencydetermined by the speed of the rotor

When the motor is reconnected to the supply it is reclosing onto anunsynchronized generator and this result in a very high current andtorque transient The magnitude of the transient is dependent on thephase relationship between the generated voltage and the line voltageat the point of closure can be much higher than DOL current and torqueand can result in electrical and mechanical damage

Open transition starting is the easiest to implement in terms or cost and circuitry and ifthe timing of the changeover is good this method can work well In practice though itis difficult to set the necessary timing to operate correctly anddisconnectionreconnection of the supply can cause significant voltagecurrenttransients

In open transition there are four states

1 OFF State All Contactors are open2 Star State The Main [KM3] and the Star [KM1] contactors are closed and the

delta [KM2] contactor is open The motor is connected in star and will produceone third of DOL torque at one third of DOL current

3 Open State This type of operation is called open transition switching becausethere is an open state between the star state and the delta state The Maincontractor is closed and the Delta and Star contactors are open There isvoltage on one end of the motor windings but the other end is open so nocurrent 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 contactoris open The motor is connected to full line voltage and full power and torque areavailable

2 Closed Transition StarDelta Starter

There is a technique to reduce the magnitude of the switching transients This requiresthe use of a fourth contactor and a set of three resistors The resistors must be sizedsuch that considerable current is able to flow in the motor windings while they are incircuit

The auxiliary contactor and resistors are connected across the delta contactor In

11212015 StarshyDelta Motor Starter | EEP

httpelectricalshyengineeringshyportalcomstarshydeltashymotorshystarter 813

operation just before the star contactor opens the auxiliary contactor closes resultingin current flow via the resistors into the star connection Once the star contactoropens current is able to flow round through the motor windings to the supply via theresistors These resistors are then shorted by the delta contactor

If the resistance of the resistors is too high they will not swamp the voltage generatedby the motor and will serve no purpose

In closed transition the power is maintained to the motor at all time

This is achieved by introducing resistors to take up the current flow during the windingchangeover A fourth contractor is required to place the resistor in circuit beforeopening the star contactor and then removing the resistors once the delta contactor isclosed

These resistors need to be sized to carry the motor current In addition to requiringmore switching devices the control circuit is more complicated due to the need tocarry out resistor switching

In close transition there are four states

1 OFF State All Contactors are open2 Star State The Main [KM3] and the Star [KM1] contactors are closed and the

delta [KM2] contactor is open The motor is connected in star and will produceone third of DOL torque at one third of DOL current

3 Star Transition State The motor is connected in star and the resistors areconnected across the delta contactor via the aux [KM4] contactor

4 Closed Transition State The Main [KM3] contactor is closed and the Delta[KM2] and Star [KM1] contactors are open Current flows through the motorwindings and the transition resistors via KM4

5 Delta State The Main and the Delta contactors are closed The transitionresistors are shorted out The Star contactor is open The motor is connected tofull line voltage and full power and torque are available

Effect of Transient in Starter (Open Transient starter)

It is Important the pause between star contactor switch off and Delta contactor switchis on correct This is because Star contactor must be reliably disconnected beforeDelta contactor is activated It is also important that the switch over pause is not too

11212015 StarshyDelta Motor Starter | EEP

httpelectricalshyengineeringshyportalcomstarshydeltashymotorshystarter 913

long

For 415v Star Connection voltage is effectively reduced to 58 or 240v Theequivalent of 33 that is obtained with Direct Online (DOL) starting

If Star connection has sufficient torque to run up to 75 or 80 of full load speedthen the motor can be connected in Delta mode

When connected to Delta configuration the phase voltage increases by a ratio of V3 or173 The phase currents increase by the same ratio The line current increasesthree times its value in star connection

During transition period of switchover the motor must be free running with littledeceleration While this is happening ldquoCoastingrdquo it may generate a voltage of its ownand on connection to the supply this voltage can randomly add to or subtract from theapplied line voltage This is known as transient current Only lasting a few millisecondsit causes voltage surges and spikes Known as a changeover transient

Size of each part of StarshyDelta starter

1 Size of Over Load Relay

For a starshydelta starter there is a possibility to place the overload protection in twopositions in the line or in the windings

Overload Relay in Line

In the line is the same as just putting the overload before the motor as with a DOLstarter

The rating of Overload (In Line) = FLC of Motor

Disadvantage If the overload is set to FLC then it is not protecting the motor while itis in delta (setting is x1732 too high)

Overload Relay in Winding

In the windings means that the overload is placed after the point where the wiring tothe contactors are split into main and delta The overload then always measures thecurrent inside the windings

The setting of Overload Relay (In Winding) =058 X FLC (line current)

11212015 StarshyDelta Motor Starter | EEP

httpelectricalshyengineeringshyportalcomstarshydeltashymotorshystarter 1013

Disadvantage We must use separate short circuit and overload protections

2 Size of Main and Delta Contractor

There are two contactors that are close during run often referred to as the maincontractor and the delta contactor These are AC3 rated at 58 of the current ratingof the motor

Size of Main Contactor= IFL x 058

3 Size of Star Contractor

The third contactor is the star contactor and that only carries star current while themotor is connected in star The current in star is 1 radic3= (58) of the current in deltaso this contactor can be AC3 rated at one third (33) of the motor rating

Size of Star Contactor= IFL x 033

Motor Starting Characteristics of StarshyDelta Starter

Available starting current 33 Full Load CurrentPeak starting current 13 to 26 Full Load CurrentPeak starting torque 33 Full Load Torque

Advantages of StarshyDelta starter

The operation of the starshydelta method is simple and ruggedIt is relatively cheap compared to other reduced voltage methodsGood TorqueCurrent PerformanceIt draws 2 times starting current of the full load ampere of the motor connected

Disadvantages of StarshyDelta starter

1 Low Starting Torque (Torque = (Square of Voltage) is also reduce)2 Break In Supply ndash Possible Transients3 Six Terminal Motor Required (Delta Connected)4 It requires 2 set of cables from starter to motor

5 It provides only 33 starting torque and if the load connected to the subject

SHARE

TOP

GetPDF

11212015 StarshyDelta Motor Starter | EEP

httpelectricalshyengineeringshyportalcomstarshydeltashymotorshystarter 813

operation just before the star contactor opens the auxiliary contactor closes resultingin current flow via the resistors into the star connection Once the star contactoropens current is able to flow round through the motor windings to the supply via theresistors These resistors are then shorted by the delta contactor

If the resistance of the resistors is too high they will not swamp the voltage generatedby the motor and will serve no purpose

In closed transition the power is maintained to the motor at all time

This is achieved by introducing resistors to take up the current flow during the windingchangeover A fourth contractor is required to place the resistor in circuit beforeopening the star contactor and then removing the resistors once the delta contactor isclosed

These resistors need to be sized to carry the motor current In addition to requiringmore switching devices the control circuit is more complicated due to the need tocarry out resistor switching

In close transition there are four states

1 OFF State All Contactors are open2 Star State The Main [KM3] and the Star [KM1] contactors are closed and the

delta [KM2] contactor is open The motor is connected in star and will produceone third of DOL torque at one third of DOL current

3 Star Transition State The motor is connected in star and the resistors areconnected across the delta contactor via the aux [KM4] contactor

4 Closed Transition State The Main [KM3] contactor is closed and the Delta[KM2] and Star [KM1] contactors are open Current flows through the motorwindings and the transition resistors via KM4

5 Delta State The Main and the Delta contactors are closed The transitionresistors are shorted out The Star contactor is open The motor is connected tofull line voltage and full power and torque are available

Effect of Transient in Starter (Open Transient starter)

It is Important the pause between star contactor switch off and Delta contactor switchis on correct This is because Star contactor must be reliably disconnected beforeDelta contactor is activated It is also important that the switch over pause is not too

11212015 StarshyDelta Motor Starter | EEP

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For 415v Star Connection voltage is effectively reduced to 58 or 240v Theequivalent of 33 that is obtained with Direct Online (DOL) starting

If Star connection has sufficient torque to run up to 75 or 80 of full load speedthen the motor can be connected in Delta mode

When connected to Delta configuration the phase voltage increases by a ratio of V3 or173 The phase currents increase by the same ratio The line current increasesthree times its value in star connection

During transition period of switchover the motor must be free running with littledeceleration While this is happening ldquoCoastingrdquo it may generate a voltage of its ownand on connection to the supply this voltage can randomly add to or subtract from theapplied line voltage This is known as transient current Only lasting a few millisecondsit causes voltage surges and spikes Known as a changeover transient

Size of each part of StarshyDelta starter

1 Size of Over Load Relay

For a starshydelta starter there is a possibility to place the overload protection in twopositions in the line or in the windings

Overload Relay in Line

In the line is the same as just putting the overload before the motor as with a DOLstarter

The rating of Overload (In Line) = FLC of Motor

Disadvantage If the overload is set to FLC then it is not protecting the motor while itis in delta (setting is x1732 too high)

Overload Relay in Winding

In the windings means that the overload is placed after the point where the wiring tothe contactors are split into main and delta The overload then always measures thecurrent inside the windings

The setting of Overload Relay (In Winding) =058 X FLC (line current)

11212015 StarshyDelta Motor Starter | EEP

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Disadvantage We must use separate short circuit and overload protections

2 Size of Main and Delta Contractor

There are two contactors that are close during run often referred to as the maincontractor and the delta contactor These are AC3 rated at 58 of the current ratingof the motor

Size of Main Contactor= IFL x 058

3 Size of Star Contractor

The third contactor is the star contactor and that only carries star current while themotor is connected in star The current in star is 1 radic3= (58) of the current in deltaso this contactor can be AC3 rated at one third (33) of the motor rating

Size of Star Contactor= IFL x 033

Motor Starting Characteristics of StarshyDelta Starter

Available starting current 33 Full Load CurrentPeak starting current 13 to 26 Full Load CurrentPeak starting torque 33 Full Load Torque

Advantages of StarshyDelta starter

The operation of the starshydelta method is simple and ruggedIt is relatively cheap compared to other reduced voltage methodsGood TorqueCurrent PerformanceIt draws 2 times starting current of the full load ampere of the motor connected

Disadvantages of StarshyDelta starter

1 Low Starting Torque (Torque = (Square of Voltage) is also reduce)2 Break In Supply ndash Possible Transients3 Six Terminal Motor Required (Delta Connected)4 It requires 2 set of cables from starter to motor

5 It provides only 33 starting torque and if the load connected to the subject

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11212015 StarshyDelta Motor Starter | EEP

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long

For 415v Star Connection voltage is effectively reduced to 58 or 240v Theequivalent of 33 that is obtained with Direct Online (DOL) starting

If Star connection has sufficient torque to run up to 75 or 80 of full load speedthen the motor can be connected in Delta mode

When connected to Delta configuration the phase voltage increases by a ratio of V3 or173 The phase currents increase by the same ratio The line current increasesthree times its value in star connection

During transition period of switchover the motor must be free running with littledeceleration While this is happening ldquoCoastingrdquo it may generate a voltage of its ownand on connection to the supply this voltage can randomly add to or subtract from theapplied line voltage This is known as transient current Only lasting a few millisecondsit causes voltage surges and spikes Known as a changeover transient

Size of each part of StarshyDelta starter

1 Size of Over Load Relay

For a starshydelta starter there is a possibility to place the overload protection in twopositions in the line or in the windings

Overload Relay in Line

In the line is the same as just putting the overload before the motor as with a DOLstarter

The rating of Overload (In Line) = FLC of Motor

Disadvantage If the overload is set to FLC then it is not protecting the motor while itis in delta (setting is x1732 too high)

Overload Relay in Winding

In the windings means that the overload is placed after the point where the wiring tothe contactors are split into main and delta The overload then always measures thecurrent inside the windings

The setting of Overload Relay (In Winding) =058 X FLC (line current)

11212015 StarshyDelta Motor Starter | EEP

httpelectricalshyengineeringshyportalcomstarshydeltashymotorshystarter 1013

Disadvantage We must use separate short circuit and overload protections

2 Size of Main and Delta Contractor

There are two contactors that are close during run often referred to as the maincontractor and the delta contactor These are AC3 rated at 58 of the current ratingof the motor

Size of Main Contactor= IFL x 058

3 Size of Star Contractor

The third contactor is the star contactor and that only carries star current while themotor is connected in star The current in star is 1 radic3= (58) of the current in deltaso this contactor can be AC3 rated at one third (33) of the motor rating

Size of Star Contactor= IFL x 033

Motor Starting Characteristics of StarshyDelta Starter

Available starting current 33 Full Load CurrentPeak starting current 13 to 26 Full Load CurrentPeak starting torque 33 Full Load Torque

Advantages of StarshyDelta starter

The operation of the starshydelta method is simple and ruggedIt is relatively cheap compared to other reduced voltage methodsGood TorqueCurrent PerformanceIt draws 2 times starting current of the full load ampere of the motor connected

Disadvantages of StarshyDelta starter

1 Low Starting Torque (Torque = (Square of Voltage) is also reduce)2 Break In Supply ndash Possible Transients3 Six Terminal Motor Required (Delta Connected)4 It requires 2 set of cables from starter to motor

5 It provides only 33 starting torque and if the load connected to the subject

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TOP

GetPDF

11212015 StarshyDelta Motor Starter | EEP

httpelectricalshyengineeringshyportalcomstarshydeltashymotorshystarter 1013

Disadvantage We must use separate short circuit and overload protections

2 Size of Main and Delta Contractor

There are two contactors that are close during run often referred to as the maincontractor and the delta contactor These are AC3 rated at 58 of the current ratingof the motor

Size of Main Contactor= IFL x 058

3 Size of Star Contractor

The third contactor is the star contactor and that only carries star current while themotor is connected in star The current in star is 1 radic3= (58) of the current in deltaso this contactor can be AC3 rated at one third (33) of the motor rating

Size of Star Contactor= IFL x 033

Motor Starting Characteristics of StarshyDelta Starter

Available starting current 33 Full Load CurrentPeak starting current 13 to 26 Full Load CurrentPeak starting torque 33 Full Load Torque

Advantages of StarshyDelta starter

The operation of the starshydelta method is simple and ruggedIt is relatively cheap compared to other reduced voltage methodsGood TorqueCurrent PerformanceIt draws 2 times starting current of the full load ampere of the motor connected

Disadvantages of StarshyDelta starter

1 Low Starting Torque (Torque = (Square of Voltage) is also reduce)2 Break In Supply ndash Possible Transients3 Six Terminal Motor Required (Delta Connected)4 It requires 2 set of cables from starter to motor

5 It provides only 33 starting torque and if the load connected to the subject

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11212015 StarshyDelta Motor Starter | EEP

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motor requires higher starting torque at the time of starting than very heavytransients and stresses are produced while changing from star to deltaconnections and because of these transients and stresses many electrical andmechanical breakshydown occurs

6 In this method of starting initially motor is connected in star and then afterchange over the motor is connected in delta The delta of motor is formed instarter and not on motor terminals

7 High transmission and current peaks When starting up pumps and fans forexample the load torque is low at the beginning of the start and increases withthe square of the speed When reaching approx 80shy85 of the motor ratedspeed the load torque is equal to the motor torque and the acceleration ceasesTo reach the rated speed a switch over to delta position is necessary and thiswill very often result in high transmission and current peaks In some cases thecurrent peak can reach a value that is even bigger than for a DOL start

8 Applications with a load torque higher than 50 of the motor rated torque willnot be able to start using the startshydelta starter

9 Low Starting Torque The starshydelta (wyeshydelta) starting method controlswhether the lead connections from the motor are configured in a star or deltaelectrical connection The initial connection should be in the star pattern thatresults in a reduction of the line voltage by a factor of 1radic3 (577) to the motorand the current is reduced to 13 of the current at full voltage but the startingtorque is also reduced 13 to 15 of the DOL starting torque

10 The transition from star to delta transition usually occurs once nominal speed isreached but is sometimes performed as low as 50 of nominal speed whichmake transient Sparks

Features of starshydelta starting

1 For lowshy to highshypower threeshyphase motors2 Reduced starting current3 Six connection cables4 Reduced starting torque5 Current peak on changeover from star to delta6 Mechanical load on changeover from star to delta

11212015 StarshyDelta Motor Starter | EEP

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Application of StarshyDelta Starter

The starshydelta method is usually only applied to low to medium voltage and lightstarting Torque motors

The received starting current is about 30 of the starting current during direct on linestart and the starting torque is reduced to about 25 of the torque available at aDOL start This starting method only works when the application is light loadedduring the start

If the motor is too heavily loaded there will not be enough torque to accelerate themotor up to speed before switching over to the delta position

Recommended EE articles

About Author

Jignesh Parmar

jiguparmar shy Jignesh Parmar has completed MTech (PowerSystem Control) BE(Electrical) He is member of Institution ofEngineers (MIE)India Membership NoMshy1473586He hasmore than 13 years experience in Transmission shyDistributionshyElectrical Energy theft detectionshyElectrical MaintenanceshyElectrical Projects (PlanningshyDesigningshyTechnical Reviewshycoordination shyExecution) He is Presently associate with one of

the leading business group as a Deputy Manager at AhmedabadIndia He haspublished numbers of Technical Articles in Electrical Mirror Electrical IndiaLighting India Industrial Electrix(Australian Power Publications) Magazines He isFreelancer Programmer of Advance Excel and design useful Excel base ElectricalPrograms as per IS NEC IECIEEE codes He is Technical Blogger and Familiar with

11212015 StarshyDelta Motor Starter | EEP

httpelectricalshyengineeringshyportalcomstarshydeltashymotorshystarter 1213

Share with engineers

Application of StarshyDelta Starter

The starshydelta method is usually only applied to low to medium voltage and lightstarting Torque motors

The received starting current is about 30 of the starting current during direct on linestart and the starting torque is reduced to about 25 of the torque available at aDOL start This starting method only works when the application is light loadedduring the start

If the motor is too heavily loaded there will not be enough torque to accelerate themotor up to speed before switching over to the delta position

Recommended EE articles

About Author

Jignesh Parmar

jiguparmar shy Jignesh Parmar has completed MTech (PowerSystem Control) BE(Electrical) He is member of Institution ofEngineers (MIE)India Membership NoMshy1473586He hasmore than 13 years experience in Transmission shyDistributionshyElectrical Energy theft detectionshyElectrical MaintenanceshyElectrical Projects (PlanningshyDesigningshyTechnical Reviewshycoordination shyExecution) He is Presently associate with one of

the leading business group as a Deputy Manager at AhmedabadIndia He haspublished numbers of Technical Articles in Electrical Mirror Electrical IndiaLighting India Industrial Electrix(Australian Power Publications) Magazines He isFreelancer Programmer of Advance Excel and design useful Excel base ElectricalPrograms as per IS NEC IECIEEE codes He is Technical Blogger and Familiar with

11212015 StarshyDelta Motor Starter | EEP

httpelectricalshyengineeringshyportalcomstarshydeltashymotorshystarter 1313

English Hindi Gujarati French languages He wants to Share his experience ampKnowledge and help technical enthusiasts to find suitable solutions and updatingthemselves on various Engineering Topics

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