INTRODUCTION

TO SOFTSTARTER

General about motors

Squirrel cage motors

Voltage

NEMA Design

Voltage

Power factor

Efficiency

Speed

Torque

Different starting methods

Direct-on-line start (D.O.L)

Star-delta start

Frequency converter

Softstarter

Common problem when starting and stopping motors

Different applications

Centrifugal fan

Direct-on-line start (D.O.L)

Star-delta start

Softstarter

Selection of a suitable Softstarter

Centrifugal pump

Direct-on-line start (D.O.L)

Star-delta start

Softstarter

Selection of a suitable Softstarter

Compressor

Direct-on-line start (D.O.L)

Star-delta start

Softstarter

Selection of a suitable Softstarter

Conveyor belt

Direct-on-line start (D.O.L)

Star-delta start

Softstarter

Selection of a suitable Softstarter

How to select a softstarter

Description of the softstarters

Common settings

Start ramp

Stop ramp

Initial voltage

Current limit

Step down voltage

Adjustable rated motor current

Ambient temperature

High altitudes

Start of several motors

Parallel start of motors

Sequential start of motors

Different ways of connecting the softstarter

In-Line connection

Inside Delta connection

Location of the main contactor

Basic settings for different Applications

Frequently Asked Questions (FAQ)

General About Motors

Modern electrical motors are available in many different forms, such as single phase motors, three-phase motors, brake motors, synchronous motors, asynchronous motors, special customized motors, two speed motors, three speed motors, and so on, all with their own performance and characteristics.

For each type of motor there are many different mounting arrangements, for example foot mounting, flange mounting or combined foot and flange mounting. The cooling method can also differ very much, from the simplest motor with free self-circulation of air to a more complex motor with totally enclosed air-water cooling with an interchangeable cassette type of cooler.

Note that we will focus on asynchronous motors only.

Squirrel cage motors

The focus has been placed on the squirrel cage motor, the most common type of motor on the market. It is relatively cheap and the maintenance cost is normally low.

Voltage

q Always refer to motor’s nameplate for termination.

q For example, use delta connection for 50Hz/380~400 supply volt.

NEMA Design

Three-phase AC motors are classified by NEMA as NEMA A, B, C and D. NEMA specifies certain operating characteristics for motors when started by applying rated voltage and frequency (across the line starting). A NEMA B motor, for example, typically requires 600% starting current and 150% starting torque.

Power factor

q Ratio between the active power (kW) and the reactive power (kVA)

q Designated as the cos j.

q Normal power factor value is between 0.7 and 0.9,

q Small motors have lower value and large ones have higher value

Efficiency

q Expressed as a percentage.

q Indication of how much input electrical energy is converted to output mechanical energy.

Speed

Speed depends:

I. Number of poles of the stator winding

II. Main frequency.

To calculate the speed of a motor the following formula can be used:

n = 2 x f x 60

n = synchronous speed

f = net frequency

p = number of pole

Example: 4-pole motor running at 50 Hz

n = 2 x 50 x 60 = 1500 rpm

This speed is the synchronous speed and a squirrel-cage or a slip-ring motor can never reach it. At unloaded condition the speed will be very close to synchronous speed and will then drop when the motor is loaded.

The difference between the synchronous and asynchronous speed also named rated speed is ”the slip” and it is possible to calculate this by using the following formula:

s = n1 - n

s = slip (a normal value is between 1 and 3 %)

n1 = synchronous speed

n = asynchronous speed (rated speed)

Torque

q Torque is a twisting or turning force that tends to cause an object to rotate.

q Starting torque for a motor differs significantly depending on the size of the motor.

q A small motor, e.g. ≤ 30 kW, normally has a value of between 2.5 and 3 times the rated torque

q A medium size motor, say up to 250 kW, a typical value is between 2 to 2.5 times the rated torque.

q Really big motors have a tendency to have a very low starting torque, sometimes even lower than the rated torque. It is not possible to start such a motor fully loaded not even at D.O.L start.

The rated torque of a motor can be calculated using the following formula:

Mr = 9550 x Pr

Mr = Rated torque (Nm)

Pr = Rated motor power (kW)

nr = Rated motor speed (rpm)

Different starting methods

Direct-on-line start (D.O.L)

q The most common starting method available on the market.

q The disadvantage is it gives the highest possible starting current.

q The starting current normal value is between 6 to 7 times the rated motor current but values of up to 9 or 10 times the rated current exist.

q The starting torque is also very high, and is higher than necessary for most applications.

q The torque is the same as the force, and an unnecessary high force gives unnecessary high stresses on couplings and the driven application.

Star-delta start

q The starting current is about 30 % of the starting current during direct on line start

q The starting torque is reduced to about 25 % of the torque available at a D.O.L start.

q This starting method only works when the application is light loaded during the start.

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

q Applications with a load torque higher than 50 % of the motor rated torque will not be able to start using the start-delta starter.

Frequency converter

q By controlling the frequency, the rated motor torque is available at a low speed

q The starting current is low, between 0.5 and 1.0 times the rated motor current, maximum 1.5 x In.

q Another available feature is softstop, which is very useful, for example when stopping pumps where the problem is water hammering in the pipe systems at direct stop.

q The softstop function is also useful when stopping conveyor belts from transporting fragile material that can be damaged when the belts stop too quickly. It is very common to install a filter together with the drive in order to reduce the levels of emission and harmonics generated.

Softstarter

q It has thyristors in the main circuit, and the motor voltage is regulated with a printed circuit board.

q The softstarter makes use of the fact that when the motor voltage is low during start, the starting current and starting torque is also low. During the first part of the start the voltage to the motor is so low that it is only able to adjust the play between the gear wheels or stretching driving belts or chains etc. In other words, eliminating unnecessary jerks during the start. Gradually, the voltage and the torque increase so that the machinery starts to accelerate.

q One of the benefits with this starting method is the possibility to adjust the torque to the exact need, whether the application is loaded or not.

q The softstop function can also be used when stopping conveyor belts to prevent material from damage when the belts stop too quickly.

Different applications

All motors are used for starting and running different applications. The different applications will also result in different load conditions for the motor.

There are two factors to consider:

1. Braking load torque, a direct braking force on the motor shaft. To be able to accelerate, the motor has to be stronger than the load. The accelerating torque is the difference between the available motor torque and the load toque.

Accelerating torque = Available motor torque – load torque

2. Involved moment of inertia or flywheel mass will also affect the start. The bigger inertia the longer starting time for the same motor.

CENTRIFUGAL FAN

For some applications the motor is started with reduced load torque, i.e. unloaded start. Big centrifugal fans are often started with a closed damper and this will make the start easier (shorter) but since the moment of inertia is still present the starting time might be quite long anyway.

Direct-on-line start

q Centrifugal fans are very often driven by one or more drive belts.

q During a D.O.L start these belts have a tendency to slip because the starting torque from the motor is too high during the start sequence and the belts are not able to transfer these forces.

Star-delta starter (Y-D)

q Lower starting torque but depending on the fact that the load torque increases with the square of the speed,

q The motor torque will not be high enough in the star position to accelerate the fan to the rated speed.

q When switching over to delta position it will be both a high transmission and current peak, often equal to values when making a D.O.L startor even higher, with a slipping belt as a result.

Softstarter

q The key to solve these problems is to reduce the starting torque from the motor during start.

q By using an softstarter the voltage is decreased to a low value at the beginning of the start, low enough to avoid slip but high enough to start up the fan.

q The softstarter provides the ability to adjust to fit any starting condition, both unloaded and fully loaded starts.

Selection of a suitable softstarter for centrifugal fan

Normal start

For fans with small or medium large flywheels, select a softstarter according to the rated motor power. The above is valid if the time for D.O.L start is less than 5 seconds.

Heavy duty start

For fans with large flywheels, select a softstarter designed for heavy duty start according to the rated motor power. It is also possible to select a softstarter for normal start, select a unit with one size bigger power rating than the motor and use an overload relay class 30.

The above is valid if the time for D.O.L start is more than 5 seconds.

CENTRIFUGAL PUMP

There are a lot of different types of pumps; like piston pumps, centrifugal pumps, screw pumps etc. But the most common version is the centrifugal pump and we have selected this one to describe.

Direct-on-line start

q Wear and tear depending on pressure waves in the pipe system created when the motor starts and stops too quickly.

q During a D.O.L start the motor gives much too high starting torque with the result that the motor accelerates and reaches nominal speed too quickly. The reason is that the braking load torque is low for a pump during start.

Star-delta starter (Y-D)

q It is possible to reduce the starting torque but the motor torque in the star position is too weak to be able to complete the start and reach the rated speed.

q When the motor reaches approx. 80-85 % of the rated speed and the switch over to the delta position will give both high transmission and current peaks with pressure waves as a result.

q When stopping a pump, it is also normal to have problems. When making a direct stop by disconnecting the main supply the motor stops too quickly. Depending on high mass flow in the pipe system the water will continue with the same speed for a short period and then come back again, backwards in the pipe system. This creates high pressure shocks on valves and gives high mechanical stresses on the pipe system.

Softstarter

q By using an softstarter the voltage is reduced during the start sequence with the result that the motor torque is reduced. During the start sequence the softstarter increases the voltage so that the motor will be strong enough to accelerate the pump to the nominal speed without any torque or current peaks.

q During the stop sequence the softstarter reduces the voltage via a voltage ramp and the motor becomes weaker and weaker. Because of this the water speed slows down very smoothly without creating any pressure waves.

Selection of a suitable softstarter for centrifugal pump

Normal start

Starting a pump is a typical normal start condition.

Select a softstarter according to the rated

motor power.

Heavy duty start

Not applicable for this application.

COMPRESSOR

Smaller compressors are often of piston type and the load torque increases linearly with the speed. 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.

Direct-on-line start (D.O.L)

q Compressors started direct-on-line are exposed to high mechanical stresses on the compressor itself, but also on drive belts and couplings. The result is shortened endurance. In cases where the drive belts are used the belts very often slip during start.

q The high starting torque received during starting with this method is the source of the problems. The starting current is always high at D.O.L start. A normal value can be approx. 7 times rated motor current.

Star-delta starter (Y-D)

q Star-delta start gives a lower starting torque and starting current but the motor is too weak during the start up to be able to accelerate the motor up to nominal speed. When switching to the delta position both current and torque peaks will occur with high mechanical stresses as a result.

q Compressors are very often running at no load condition for longer periods when the pressure in the system is high. A motor running under these circumstances always has a poor power factor and low efficiency. Some times the value is so low that it must be compensated.

Softstarter

q By using an softstarter it is possible to limit the starting torque to a level suitable for all different applications. The result is less stress on couplings, bearings and no slipping belts during start. The maintenance cost will be reduced to a minimum.

q When using a softstarter the starting current received is approx. 3 to 4 times the rated motor current.

Selection of a suitable softstarter

Normal start

For compressors with D.O.L starting time less than 5 seconds, select a softstarter according to the rated motor power.

Heavy duty start

For compressors with D.O.L starting time more than 5 seconds, select a softstarter designed for heavy duty start according to the rated motor power. It is also possible to select a softstarter for normal start, select a unit with one size bigger power rating than the motor and use an overload relay class 30.

CONVEYOR BELT

It is a typical constant torque load with low to high braking torque depending on how heavy it is loaded.

Direct-on-line start (D.O.L)

q Conveyor belts often need a starting torque very near or just above the rated torque of the motor.

q A direct-on-line start with a normal squirrel cage motor gives approx. 1.5 to 2.5 times rated torque of the motor depending on motor size, type etc.

q When making a direct-on-line start there is a very high risk of slipping between the belt and the driving role depending on this high starting torque. Gearboxes and couplings are also exposed to high mechanical stresses. This result is considerable wear and tear and often high maintenance costs. Sometimes fluid couplings are used to reduce the transferred torque. This method is expensive and requires a lot of maintenance.

Star-delta start

q It is not possible to use this starting method when the load torque is close to the rated motor torque.

Softstarter

q By using an softstarter the starting torque can be reduced to a minimum value still able to start up the conveyor belt. The setting possibility of the softstarter makes it possible to adjust the torque to exactly the level that is necessary for the start. The result is the least possible stress on gearboxes and couplings and no slipping belts during start. This will reduce the maintenance cost to a minimum. When using a softstarter you will receive approx. 3 to 4 times rated motor current during start.

Selection of a suitable softstarter for conveyor belt

Normal start

A start of short and light loaded conveyor belt is a typical normal start. For conveyors with D.O.L starting time less than 5 seconds, select a softstarter according to the rated motor power.

Heavy duty start

Conveyor belts can in some cases be very long and if the belt is fully loaded during start the starting time can be very long. For such applications select a softstarter designed for heavy duty start. It is also possible to select a softstarter for normal start if the softstarter is chosen one size larger than the rated motor power and use an overload relay class 30.

How to select a softstarter for

different applications

Selecting Schneider’s Alistart 01 softstarter for 4KW,400V,3phase

Note that control voltage must be specified for some other brand of softstarter.

Description of the softstarters

Printed circuit board is used to control the firing of the thyristors based on the current and voltage references, and also for the calculation of different values, for example the power factor, active power, etc. It can also be used for storing historical data, the event log, indicating trends and much more.

Heat sink is used to get rid of the heat in the softstarter generated by the current during the start and the continuous run. The capacity of the heat sink very much reflects the starting capacity and the operational current of the softstarter.

Heat Sink

Fans are used to increase the cooling capacity of the heat sink. Some smaller softstarters don’t have fans at all.

Housing can be made of plastic material, metal or a combination of these, and its function is to protect the inside components from mechanical and electrical damage. For total outside protection from dust and dirt a separate enclosure is often required since the degree of protection (IP class) of the unit itself is too low.

Thyristors are semi-conducting components connected in an anti-parallel fasion and placed in two or three phases of the main circuit. They regulate (by increasing or decreasing) the level of voltage during start and the stop ramp, as described in the picture below. During a continuous run the thyristors are conducting fully.

Start: The thyristors let part of the voltage through at the beginning and then increase it, according to the set ramp time for the start.

Stop: The thyristors are fully conducting and when soft stopping, they decrease the voltage according to the set ramp time for stop.

SOFTSTARTER COMMON SETTINGS

Excess Start Time

Relay Output

Phase Sequence

Motor Trip Class

Current Ramp

Current Limit

Aucom CSXi softstart parameter setting

Aucom CSX parameter setting

Start ramp is the time from were the softstarter start its ramp (initial voltage) until full voltage is reached. The ramp time should not be too long, as this will only result in unnecessary heating of the motor and a risk of the overload relay to trip. If the motor is unloaded the start time for the motor will probably become shorter than the set ramp time, and if the motor is heavily loaded, the start time will probably become longer.

Stop ramp is used when a soft stopping of the motor is required, for example a pump or a conveyor belt. The stop ramp is the time from full voltage until stop voltage (initial voltage) is reached. If the ramp time is set

Initial voltage. Sometimes named pedestrian voltage or torque, this is the point from where the softstarter starts or stops its ramps. The torque of the motor will drop with the square of the voltage and if the voltage is set too low, for example 20 %, the starting torque will become 0.22 = 0.04 = 4 % only, and the motor will not start from the very beginning. Therefore it is very important to find a level that is just high enough to make the motor take off directly to avoid unnecessary heating.

Current limit can be used in applications where a limited starting current is required, or at a heavy-duty start when it is difficult to achieve a perfect start with the setting of the initial voltage and the start ramp only. When the current limit is reached, the softstarter will temporarily stop increasing the voltage until the current drops below the set limit, and then continues ramping up to full voltage.

Note that this feature is not available on all softstarters.

Step down voltage gives a special type of stop ramp. It is possible to adjust the voltage to drop to a level where the speed of the motor starts to reduce immediately at the stop command. For low loaded motors the speed will not reduce until a very low voltage is reached, but using the step down voltage function can eliminate this phenomenon and is especially useful for stopping pumps.

Adjustable rated motor current makes it possible to set the motor rated current on the softstarter for the used motor. This setting may affect other values as well, such as the trip level of the electronic overload relay, the level of the current limit function and so on.

Derating when used above Ambient temperature

Above ambient temperature recommended by manufacture, the following formula can generally be used to calculate the operational current:

Ie derated = Ie - (Δ T x Ie x 0.008)

Ie derated = maximum operational current after derating

Ie = rated current of the softstarter

Δ T = temperature difference

0.008 = derating factor

Derating when used at high altitudes

% of Ie = 100 - x - z

150

x = actual altitude for the softstarter

z = manufacture’s recommended altitude

Start of several motors

Parallel start of motors

There are two important parameters to check:

1. The softstarter must be able to cope with the rated current for all motors together.

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

Note! If a by-pass contactor is used for the softstarter, only point 2 above has

to be taken into consideration.

Example:

Start of two motors with Ie = 100 A and

relative starting current 4 x Ie.

Starting time is 10 seconds.

Total starting current is 100 x 4 x 2 = 800 A

over 10 seconds.

Ie=200A

Ie=100A

Sequential start of motors

Example:

Start of three motors with Ie=100 A and relative starting current 4 x Ie.

Starting time for the motors is:

Motor 1 = 5 seconds

Motor 2 = 10 seconds

Motor 3 = 8 seconds

The starting current for the motors is 100 x 4 = 400 A and the total starting time is 5 + 10 + 8 = 23 seconds.

Note! It is not possible to add the starting time for each motor if the rated current is different from one motor to another. A separate calculation has to be made for those applications.

Different ways of connecting the

Softstarter

In-line connection

q The most common way to connect the softstarter. The selected devices for Inline connection must be chosen to cope with the rated motor current.

Example: 100 A motor requires a 100 A softstarter, 100 A main contactor etc.

Inside Delta connection

q The Inside Delta connection makes it possible to place the softstarter in the delta circuit and in that way it can easily replace an existing Y/D-starter. When the softstarter is Inside Delta it will only be exposed to 58 % (1/√3) of the In-line current. Therefore it is possible to downsize the devices in order to achieve a more cost-effective solution.

Example: A 100 A motor requires a 58 A softstarter, a 58 A main contactor if placed in the delta circuit, etc.

q Note that only a few types of softstarters can actually be connected Inside Delta.

Location of the main contactor

q When using the softstarter Inside Delta there are two options for the main contactor: in the delta circuit or outside. Both locations will stop the motor but in alternative A, the motor is still considered to be under tension.

q In alternative B the main contactor must be chosen according to the rated current of the motor, while the contactor in alternative A can be chosen according to 58 % (1/√3) of the rated current.

Basic settings for different

Applications

Note ! All settings below are only proposals and may change from one application

to another and therefore need to be checked individually.

Frequently asked questions (FAQ)

Main contactor

Q Is there any requirement to put a main contactor in series before the softstarter?

A The softstarter does not require any main contactor but we recommend the use of one for emergency stop and/or trip of the overload relay. In some applications an MCCB can be used instead of the main contactor.

Advantages of by-pass

Q What are the advantages of using by-pass?

A Reduction of power loss. It is also possible to reduce the enclosure size and use a higher IP-class since air ventilation is not required.

Test without motor

Q Can I test a softstarter without using a motor?

A No, this is not possible since there will be no current going through the softstarter and some types will also indicate loss of load.

Different frequency

Q Can I use the same softstarter at both 50 and 60 Hz?

A It is possible with all type of ABB softstarters as long as the curve is sinusoidal.

Overload relay trips during start

Q Why does the overload relay trip during start?

A Possible reasons can be one of these or in a combination:

- too low current limit

- too long ramp time

- too low initial voltage

- wrong tripping class on the overload

- wrong setting on the overload

Voltage fluctuations

Q What voltage fluctuations are allowed for the softstarters?

A The minimum and maximum value where we can guarantee full function is -15 % to +10 % of the rated value. This is also stated in the IEC-standard.

Example: 400 V - 15 % to +10 % ≥ 340 V - 440 V range

Saturday 14 July 2012

Friday 13 July 2012

HMI အား iphone မွထိန္းခ်ဳပ္ေမာင္းႏွင္ျခင္း

Saturday 7 July 2012

Thursday 5 July 2012

Monday 2 July 2012

SOFT STARTER INTRODUCTION

INTRODUCTION

TO SOFTSTARTER

Contents

Centrifugal fan

How to select a softstarter

Different ways of connecting the softstarter

General About Motors

Speed

Different starting methods

Star-delta start

Different applications

Accelerating torque = Available motor torque – load torque

Normal start

Smaller compressors are often of piston type and the load torque increases linearly with the speed. 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.

Heavy duty start

Direct-on-line start (D.O.L)

Star-delta start

Softstarter

Selection of a suitable softstarter for conveyor belt

How to select a softstarter for

different applications

Description of the softstarters

SOFTSTARTER COMMON SETTINGS

Derating when used above Ambient temperature

Derating when used at high altitudes

Start of several motors

Sequential start of motors

Different ways of connecting the

Softstarter

Basic settings for different

Applications

Frequently asked questions (FAQ)

Advantages of by-pass

Saturday 14 July 2012

Friday 13 July 2012

HMI အား iphone မွထိန္းခ်ဳပ္ေမာင္းႏွင္ျခင္း

Saturday 7 July 2012

Thursday 5 July 2012

Monday 2 July 2012

SOFT STARTER INTRODUCTION

INTRODUCTION TO SOFTSTARTER

Contents

Centrifugal fan

How to select a softstarter

Different ways of connecting the softstarter

General About Motors

Speed

Different starting methods

Star-delta start

Different applications

Accelerating torque = Available motor torque – load torque

Normal start

Smaller compressors are often of piston type and the load torque increases linearly with the speed. 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.

Heavy duty start

Direct-on-line start (D.O.L)

Star-delta start

Softstarter

Selection of a suitable softstarter for conveyor belt

How to select a softstarter for

different applications

Description of the softstarters

SOFTSTARTER COMMON SETTINGS

Derating when used above Ambient temperature

Derating when used at high altitudes

Start of several motors

Sequential start of motors

Different ways of connecting the

Softstarter

Basic settings for different

Applications

Frequently asked questions (FAQ)

Advantages of by-pass

INTRODUCTION

TO SOFTSTARTER