Softstarter handbook

A motor with two poles often has a lower starting torque than mo- tors with four or more poles. At 50 motor is loaded. At unloaded condition the 10 12 16 20 Diagram showing syncronous speed vs. The three stator windings connection is used. When changing the main voltage it is im- If the rating plate on a squirrel cage mo- portant to remember that for the same tor indicates voltages for both the star and power rating the rated motor current will delta connection, it is possible to use the change depending on the voltage level.

In the diagram below overloaded motor will use more current. Usually between The ratio between the active power P kW times the rated current, but it can be and the apperent power S kVA is known more than 10 times the rated current.

A normal value is be- diagram for the motor, which can be seen tween 0. As the motor accelerates the cur- the lower value is for small or low loaded rent will drop and when reaching the rated motors and the higher for large ones.

A small motor, e. A typical value is This special motor is started by changing between 2 to 3 times the rated torque. Re- the rotor resistance. When speeding up, ally big motors have a tendency to have a the resistance is gradually disconnected very low starting torque, sometimes even until the rated speed is reached and the lower than the rated torque.

It is not pos- motor is working at the equivalent rate of sible to start such a motor fully loaded, not a standard squirrel-cage motor. The advantage of a slip-ring motor is that The rated torque of a motor can be calcu- the starting current will be lower and it is lated using the following formula: possible to adjust the starting torque up x Pr to the maximum torque. The differ- ent applications will result in different load conditions for the motor. There are mainly two factors to consider; braking load torque and moment of inertia.

Braking load torque thereby reducing the accelerating torque This is a direct braking force on the mo- which will give a longer starting time. The accelerating torque is the difference The load curve can have different char- between the available motor torque and acteristic depending on the application. Many starting methods Some of the common load types can be will reduce the torque of the motor and seen below. Many applications are usually started unloaded, and the load is applied first when the motor has reached the rated speed.

An application with Examples of applications are fans, crush- a small moment of inertia is usually called ers, mills and long conveyor belts. Normal start Small moment of inertia, short starting time, normally OL class 10 is used. Examples of applications are pumps, compressors, bow thrusters and short conveyor belts. A bigger moment of inertia will require a longer starting time for the same motor and the same breaking load torque.

The table below gives an indication of normal starting times for different load conditions using 3 different starting methods. Approximate starting times Direct on line Star delta starter Softstarter ramp time 10 sec Motor without load 0.

An overview of common problems when starting and stop- ping a motor with these starting methods is available on page This solution. The starting equipment consists will cause unnecessary high stress on of only a main contactor and a thermal or driving belts, couplings and the driven ap- electronic overload relay.

The disadvan- plication. Naturally, there are cases where tage with this method is that it gives the this starting method works perfectly ine highest possible starting current. A normal and there is no need to use any other value is between 6 to 8 times the rated starting method.

There is also a stop the motor is to make a direct stop. The exact values are dependent on the design of the motor. In general, modern motors have a higher inrush current than older ones because of the lower resis- tance in the windings. This starting method can only be the impedance when delta connected. As used with a motor that is delta connected the voltage level is the same, the result- during continuous run.

After a preset time, the connection will change to As the main voltage is the same the mo- delta which will give the full current and tor feels a star connection as a voltage also the full torque.

This lower voltage will also each motor winding is same as the net- result in a torque reduction. The torque work voltage. However, this is only a theo- then the sum of impedance for the parallel retical value. This works well in an unloaded or rial connected. The resulting impedance very light loaded start, but it will not be possible to start heavier applications. To reach the rat- to stop when using a star-delta starter is ed speed, a switch over to delta position to make a direct stop.

Also, since the motor can able Frequency Drive or simply Drives. The be considered running at its rated speed, drive consists primarily of two parts, one the rated motor torque is available already which converts AC 50 or 60 Hz to DC and from start and the current will be around the a second part which converts the DC back nominal current.

Usually, the drive trips if the to AC, but now with a variable frequency of current reaches 1. By controlling the frequency, the When using a drive to control the motor it is drive can control the speed of the motor. This is espe- During start, the drive increases the fre- cially useful when stopping pumps in order quency from 0 Hz up to the network fre- to avoid water hammering but it can also be quency 50 or 60 Hz. By gradually increas- useful for conveyor belts.

How- requires more space. The drive is also much ever, in many applications a drive is used heavier than a softstarter making it a less de- only for starting and stopping the motor, sirable solution on, for instance ships where even though there is no need for continu- weight is important.

Finally, since the drive ous speed regulation. This will create an un- changes the frequency and actually creates necessarily expensive solution if comparing the sinus wave, a drive will cause harmon- with, for instance a softstarter.

Additional ilters as well as shielded cables are used to reduce these problems but the harmonics will typically not be totally eliminated. Instead it current and thereby avoid voltage drops in ramps up the voltage applied to the motor the network.

It will also reduce the start- from the initial voltage to the full voltage. Gradually, the voltage and mering and pressure surges in pumping the torque increase so that the machinery systems and avoiding damage to fragile starts to accelerate. One of the beneits material on conveyor belts. Softstarter The line contactor is not required and sometimes the overload is built-in.

These are the thyristors that can regulate the voltage to the motor and the printed circuit board assembly PCBA that is used to control the thyristors. In addition to this, there are the heat sink and fans to dissipate the heat, current transformers to measure the current and sometimes display and keypad and then the housing itself.

It is more and more common to offer integrated by-pass contacts in the main circuit minimizing the power loss in normal operation. Depending on the model of the softstarter, it can be equipped with a built-in elec- tronic overload relay EOL eliminating the need for an external relay, PTC input, fieldbus communication possibilities etc. These thyristors are semiconductor components which normally are isolating but by sending a iring signal, they can start to conduct, allowing the voltage and the current to pass through.

Zero crosses When performing a soft start, a iring signal is sent to the thyristors so that only Firing angle the last part of each half period of the volt- age sinus curve passes through. Then during the start, the iring signal is send earlier and earlier allowing a bigger and Start: The thyristors let part of the voltage through bigger part of the voltage to pass through at the beginning and then increase it, according to the set ramp time for the start.

When performing a soft stop, the opposite U happens. Then no more voltage is applied to the motor and the motor stops. Finally, by using a stop ramp, water ham- mering is avoided in pump systems, which will further reduce the stress on the equip- ment. However, a linear change of the voltage does not necessarily give When performing a stop with a normal a linear change of the torque or of the voltage ramp, the voltage starts to de- speed.

This is where torque control comes crease as soon as the stop command is in. With a torque ramp, it is not the volt- given. However, as the voltage decreases age that is ramped up or down linearly, the current will instead increase. This is it is the torque. This is done by using a because the motor will try to remain in its regulation loop where the torque is calcu- current state. Since the torque depends lated by measuring both the voltage and on both the voltage and the current, it the current.

This torque is then compared will remain more or less unchanged. Then to the required torque and the voltage is after some time when the voltage has adjusted so that the torque is changed in dropped enough, there will be a sudden the required way. This stop will still Torque control is especially useful for stop- be far better than a direct stop but in many ping pumps where a sudden decrease of pump systems this is not good enough, so the speed may lead to water hammering another solution must be found.

This will force the motor to slow down immedi- ately and perform a controlled decelera- tion all the way until it comes to a com- plete stop, see igure to the right. Being able to have a good control of the torque of the motor is crucial to being able to prevent water hammering. However, this is not enough.

What is also needed is a torque curve that has been designed in such a way that the water hammering is avoided. In fact, a linear decrease of the Torque control will ensure a more direct effect and a torque is not a very good way to stop a more linear decrease of the speed during stop.

This is why ABB for a long time has worked closely together with pump manu- facturers in order to gain knowledge about how to best stop pumps. After more than a thousand different tests and simulations with different combinations of pumps and motors ABB has developed the optimal stopping curve — the perfect way to stop the pump.

Symbol for torque control. This chapter covers some of the most common ones — fans, pumps, compressors, conveyor belts, crushers and mills. The different applications will result in different load conditions for the motor as described on pages Some fans can be started with reduced load torque, with a closed damper.

This is called an un- loaded start and will make the start easier shorter but cause of the high moment of inertia, the starting time might still be quite long.

Direct on line start Star-delta starter Y-D The high moment of inertia of fans will lead The star-delta starter gives lower starting to a longer starting time.

With the high torque. However, depending on the fact starting current of a direct on line start, that the load torque increases with the this might lead to severe voltage drops in square of the speed, the motor torque will the network, disturbing other equipment.

Centrifugal fans are very often driven by When switching over to delta position it one or more drive belts. During a DOL will be both a high transmission and cur- start these belts have a tendency to slip.

It is possible to and the belts are not able to transfer these reduce the slip by stretching the belts forces. This typical problem gives high very hard. But this gives high mechanical maintenance costs but also production stresses on bearings both in the motor losses when you need to stop production and the fan with high maintenance costs to change belts and bearings.

By using an start. Select a softstarter one size larger ABB softstarter the voltage is reduced to than the motor kW size. Then gradually the voltage is increased in Since the big lywheel of a fan will cause order to start up the fan. The softstarter a long slow down period before the fan provides the ability to adjust the settings stops, a stop ramp should never be used to it any starting condition, both unloaded for this kind of application.

Using a softstarter Recommended basic settings: will also greatly reduce the high inrush cur- Start ramp: 10 sec. The most common version is the centrifugal pump and this is the one focused on here. Direct on line start Starting up a pump is normally not a the pump creating water hammering and big problem electrically.

The problem pressure surges. During a single stop this is the wear and tear caused by pres- is merely an inconvenience but when per- sure waves in the pipe system created forming several starts and stops per hour when the motor starts but especially day in and day out, the whole pump sys- when it stops too quickly.

Due to the tem will soon be worn out. This will creat a small lywheel mass and the high big need for service and maintenance and breaking torque of a pump, a direct even worse unplanned shutdowns.

There will By using a star-delta starter it is possible still be a magnetic ield in the motor and to reduce the starting torque. However, when the delta contactor closes the dif- the motor does not have enough torque ference in potential between the network in the star position to be able to complete and the motor might be twice that of the the start and reach the rated speed. The network voltage, reacting up to V in an quadratic load torque will become too V network.

To continue to These V will create a huge current spike, accelerate to full speed, a switch over to possibly even higher than the magnetiza- the delta connection is needed. There will also be a huge torque peak that after several When switching to the delta connection, starts might even damage the connections the star contactor is opened and the delta between the motor axis and the load.

However, to prevent a short circuit there needs to be a time In addition, the only possible method of delay of 50 ms between opening the star stopping the pump is to perform a direct contactor and closing the delta contactor.

Unfortunately, due to the high break- surges as for a DOL start. A pump usually has a very small pump- wheel with a low moment of inertia. This Also during the stop sequence the soft- makes the pump a normal start so the starter is the solution. A softstarter using softstarter can be selected according to a normal voltage ramp will for sure reduce the kW rating.

If more than 10 starts per the problems with water hammering but in hour are performed it is however recom- many pump systems this is still not good mended to upsize the softstarter one size. The solution is to use a softstarter with torque control in order to reduce the Recommended basic settings: torque and stop the motor in the most op- Start ramp: 10 sec.

Screw compressors are often used when there is a bigger need for air flow and this type has a load torque increasing with the square of the speed. Drive belts are often used between motor and compressor but direct connections via some type of toothed couplings are also common. Most compressors are started unloaded. Direct on line start DOL Star-delta starter Y-D Compressors started direct on line are ex- Star-delta start gives a lower starting posed to high mechanical stresses on the torque and starting current but the mo- compressor itself, but also on drive belts tor is too weak during the start up to be and couplings.

The result is shortened en- able to accelerate the motor up to nominal durance. In cases where the drive belts speed. When switching to the delta po- are used the belts very often slip during sition both current and torque peaks will the start. The source of these problems is occur with high mechanical stresses as a the high starting torque occurring with the result. DOL method. The result cording to the motor kW size.

If the com- is less stress on couplings, bearings and pressor is a heavy duty start, the softstart- no slipping belts during start. The mainte- er should be upsized one size. The same nance cost will be reduced to a minimum. Start ramp: 5 sec. Stop ramp: 0 sec. The length can vary from only a few meters up to several kilometres and the belt can be horizontal or inclining. Typically, the conveyor belt has a constant load torque with low to high braking torque depending on the load.

Direct on line start DOL pending on this high starting torque. Gear- Conveyor belts often need a starting boxes and couplings are also exposed to torque very near or just above the rated high mechanical stresses. This result is torque of the motor. A direct on line start considerable wear and tear and often high with a normal squirrel cage motor gives maintenance costs. This method type etc.

When making a direct on line is expensive and requires a lot of mainte- start there is a very high risk of slipping nance. A star delta starter can only be used successfully with a very lightly loaded conveyor belt. For a normal start, select belt. The setting feature of the softstarter the softstarter according to the motor kW makes it possible to adjust the torque to rating.

For a heavy duty start, select one exactly the level that is necessary for the size bigger. The result is the least possible stress on gearboxes and couplings and no slip- If more than 10 starts per hour are done, ping belts during the start. This will re- select one size bigger softstarter. Recommended basic settings: When using a softstarter you will receive Start ramp: 10 sec. Softstarters may also have under- or overload protection to detect if the load is too low or too high, and then kick-start to be able to start jammed belts.

These applications can have a very big flywheel and can be a very heavy duty start. In most cases, both these applications are started unloaded, and when full speed is reached, the load is applied. Direct on line start DOL Star-delta starter Y-D When starting direct on line there will be Applications such as these are often start- high mechanical stresses leading to a ed unloaded, and it will then be possible shortened life length for all parts of the to start with a star delta starter.

Loaded drive chain. In addition, the inrush current starts on the other hand will require a high will be high and as a result of this in com- torque of the motor, so such starts are not bination with the long starting times, there possible with a star delta starter. Even though these applications normally are started unloaded, there may be oc- casional loaded starts, for instance if an emergency stop has been performed on a crusher.

The material is then still in the crusher and it must be started with the load already applied. Under such circum- stances, a star-delta starter may not be a feasible option. The the softstarter is selected one size larger result is less stress on the machinery than the motor kW size.

For extremely big and greatly reduced inrush current. For lywheels, the use of Prosoft selection pro- an unloaded start the inrush current can gram is recommended. Recommended basic settings: Start ramp: 10 sec. The starting capacity of a softstarter is very much depending on the thyristor capacity and the heat sink. The table below can be used as a guide to select a softstarter if you need a quick answer and you want to be sure that the size is large enough to suit the application.

This selection will however not give the most optimized solution. For more information see page Quick guide for selection Normal start Heavy duty start Heavy duty Selection Selection Select the softstarter according to the Select one size larger softstarter compared rated motor power. For units with built-in overload, select trip For units with built-in overload, select trip class For most types of softstarter the temperature may not exceed 40 oC without derating the operational current for the unit.

For a A motor, a used for For a A motor, a larger PST needs to be used. For most manufacturers the catalogue values are valid up to m above sea level before derating is necessary.

In some cases a larger softstarter is required to be able to cope with the motor current when used at high altitudes. The maximum permitted starting current When starting DOL this starting current is for a softstarter depends on the starting typically times the nominal current and time. The ratio between the current and when using a softstarter it is reduced to time is displayed in the starting capacity times the nominal current. Depending on the application, the start The voltage or current to the motor is not can be short or long.

Since the current is affected by selecting a bigger softstarter. It is very impor- ger softstarter is that the softstarter is di- mensioned to cope with a higher current tant to select a softstarter with thyristors for a longer time and thus being able to and heat sink dimensioned for the motor start bigger motors or heavier applica- and the start performed.

The softstarter tions. These In some applications where the overload overload protections have different trip- protection is by-passed other protection ping classes, describing how fast they are active during a start to achieve a longer tripping for a speciic current.

A class 10 available starting time, it is particularly im- relay is used for normal starts in general portant to check the softstarter starting capacity since this will be the limitation. This will work fine in the majority of cases but by using the softstarter se- lection tool ProSoft, a more optimized selection will be achieved. Especially in extremely heavy duty applications with several minutes starting time, the use of ProSoft is recommended.

When using ProSoft, the selection is done in 3 steps, which can be seen as 3 different tabs in the program: 1. Input tab — Type in the general data and information about the motor and about the load. Try to use as accu- rate data as possible to get the most accurate results. Calculation tab — Here it is possible to see how long the start will be de- pending on how high the current is.

This tab will indicate which settings should be used and it might affect the selection. The selection tab — Select which of the suggested softstarters to use. Here it is also possible to generate a report containing all information about the selection. Not all softstarters can be connected inside delta however. In-line connection Inside Delta connection This is the most common and also the The Inside Delta connection makes it pos- easiest way to connect the softstarter.

Therefore it is possible to with the full rated motor current. The mo- downsize the devices in order to achieve a tor itself can either be star connected or more cost-effective solution. However, with the inside delta connection, 6 cables are required between the soft- starter and the motor, and if this distance is long, an in line connection might be a more cost eficient solution.

Example: A A motor requires a 58 A softstarter, a 58 A main contactor if placed in the delta circuit, etc. A motor used for an Inside Delta connec- tion must be able to delta-connect during a continuous run. In the USA and some other countries a special six-wire motor has to be ordered for this type of connec- Softstarter connected Softstarter connected tion. Both locations will stop the motor but in alternative A, the motor is still considered to be under tension.

This is often possible to do but some data has to be taken into consideration. Parallel start of motors If a softstarter is going to be used for start- ing several motors at the same time par- allel start , there are two important param- eters to check: 1.

The softstarter must be able to cope with the rated current for all motors together. The softstarter must be able to cope with the starting current for all mo- tors together until rated speed is achieved.

KM 1 Note! If a by-pass contactor is used for the softstarter, only point 2 above KM 1 Main contactor Q1 FR 1, 2 Overload relay has to be taken into consideration. FR 1 FR 2 Starting time is 10 seconds. Check the softstarter starting capacity graph to verify the selected size. Parallel start of motors using a softstarter Make sure that you are using separate overload relays, one for each motor.

This is needed to achieve a good start if the mo- tor sizes are different or if the applications are different. Q1 Softstarter Usually, separate protections need to be used for each of the motors. The terminals are usually the softstarter. See table below. A common voltage is V AC. Analog output Some softstarters are equipped with an Functional earth analog output signal that can be connected On softstarters with a functional earth, this to an analog meter or be used as an analog shall be connected to the mounting plate, input to a PLC.

The analog output can be using an as short cable as possible. This used to see the current to the motor on an will ensure the most reliable operation of analog current meter, eliminating the need the softstarter.

Control circuit For connection diagrams, see The control circuit is used to give a start www. Depend- ing on the softstarter, the control voltage may be taken from the softstarter itself or may be supplied externally. Most often the control voltage is 24 V DC.

Also depend- ing on the softstarter model, the signals re- quired may need to be maintained or it may be enough with a pulse. Run Closes as soon as a start signal is given and remains closed all the time when the softstarter is feeding voltage to the motor. Usually used to control a line contactor. Usually used to control an external by-pass contactor.

Event This relay will close or open when any fault or protection occurs. Can be used to signal an error or to open a line contactor.

Common output signals relays on softstarters. It is very important to make Today, many softstarters can be connect- sure that the software ile used, matches ed to a PLC using a ieldbus system such the softstarter version. For each version of as Proibus or Modbus. Depending on the the software ile there is also one corre- softstarter and the ieldbus protocol it may sponding manual to explain the informa- be possible to start and stop the soft- tion that can be sent. Both the software starter, to see status information and to iles and the manuals are available at change the settings of the softstarter from www.

Just select the plug that matches the protocol used. An overview of the con- nection is showed to the right. For more detailed information about connection, see the manual for the corresponding ieldbus protocol, avaliable at www. The table below explains which iles are required for the different Fieldbus protocol Type of ile Versions Proibus gsd-ile The latest version of the gsd-ile supports all softstarter versions.

However, in order to reduce the number of components used and to minimize the size of the softstarter, a solution where only 2 of the 3 phases are controlled is possible. In this solution, the third phase is just passing through the softstarter without con- trolling the voltage or the current. Not possible to connect Inside Delta Since one of the phases is not controlled by the softstarter, the current would pass through that phase without giving a start signal to the softstarter.

This would not start the motor but it would heat up the Softstarter motor and eventually damage the motor. SCR SCR Even if a line contactor would be used Motor to avoid this during stand by, the curent would basically not be reduced at all when starting, and reducing the current perhaps the most important beneit of using a soft- starter.

Notify me of new posts via email. About Motors. To ensure a long lifetime for the motor it is important to keep it with the correct degree of protection when under heavy-duty conditions in a servere environment. Note that in this handbook we will focus on asynchronous motors only.

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