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Knobhead
I’ve asked Lenny to set up a new sticky thread for motors and their control. I hope others will help with diagrams and theories for the benefit of others.
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result are public - you can change your vote over time, which might genuinely be the case from time to time.
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Discuss Motors in the Electricians' Talk | All Countries area at ElectriciansForums.net
OP
Knobhead
It’s going to take some time to put together. I want to start with basic motors and control but then going in to some more complex motors and starters.
I’ll apologise for the control drawings, they will be line drawings, not little blocks showing wire A in to terminal B. your going to have to use some thought to transpose them to your application.
The motors and starters I want to cover are:
AC:
Squirrel cage
Wound rotor
Dual speed
Dahlander (dual speed)
Schrage (the motor in my avatar) (variable speed)
DC:
Series
Shunt
Compound
Starters:
DOL
Star Delta (open transition)
Star Delta (closed transition)
Auto transformer (open transition)
Auto transformer (closed transition Korndorfer)
It’s not going to be a definitive guide, but based purely on experience so at times you may have to bear with me.
Other members of the board will give better information on modern soft start and VFD’s than I can.
I’ll apologise for the control drawings, they will be line drawings, not little blocks showing wire A in to terminal B. your going to have to use some thought to transpose them to your application.
The motors and starters I want to cover are:
AC:
Squirrel cage
Wound rotor
Dual speed
Dahlander (dual speed)
Schrage (the motor in my avatar) (variable speed)
DC:
Series
Shunt
Compound
Starters:
DOL
Star Delta (open transition)
Star Delta (closed transition)
Auto transformer (open transition)
Auto transformer (closed transition Korndorfer)
It’s not going to be a definitive guide, but based purely on experience so at times you may have to bear with me.
Other members of the board will give better information on modern soft start and VFD’s than I can.
Last edited by a moderator:
OP
Silly Sausage
Courtesy of The silva.foxx, there's a very good link in here...
http://www.electriciansforums.net/e...stop-start-contactor-overload.html#post381564
http://www.electriciansforums.net/e...stop-start-contactor-overload.html#post381564
OP
gerard
Hi,
See attached file on various motors - DC, AC, Universal, etc. and their characteristics. It's not perfect (the spelling!) but it will help if trying to choose a motor. Hope this helps.
Regards,View attachment 8737
See attached file on various motors - DC, AC, Universal, etc. and their characteristics. It's not perfect (the spelling!) but it will help if trying to choose a motor. Hope this helps.
Regards,View attachment 8737
OP
Knobhead
Motor windings
For R, Y, B read Brn, Blk, Gry I’ve not gone decimal yet, plus it’s quicker to type.
The most basic motors will have just three terminals in the TB. How it’s connected internally isn’t an option. The plate rating will state one voltage so other than rotation there’s not a lot to worry about. These are for direct on line starting only.
View attachment 8907View attachment 8908
Regarding rotation the convention is connect R, Y, B to A, B, C the rotation will be clockwise looking at the shaft. (Works 99% of the time).
Most motors will have six terminals A1 B1 C1 top row C2 A2 B2 bottom row. 1 being the start of the winding, 2 the end.
View attachment 8906
Some will be dual voltage others suitable for star/delta starting.
Dual voltage will have two options, typical will be 230V delta 400V star. Some you may come across are:
400/230
415/240
433/250
690/400
750/433
(I’ve only ever come across the higher voltage ones a couple of time in 35 years).
Motors suitable for star/delta starting will usually just give one voltage for delta. If the supply is up to it they will start direct on line.
View attachment 8904View attachment 8905
For R, Y, B read Brn, Blk, Gry I’ve not gone decimal yet, plus it’s quicker to type.
The most basic motors will have just three terminals in the TB. How it’s connected internally isn’t an option. The plate rating will state one voltage so other than rotation there’s not a lot to worry about. These are for direct on line starting only.
View attachment 8907View attachment 8908
Regarding rotation the convention is connect R, Y, B to A, B, C the rotation will be clockwise looking at the shaft. (Works 99% of the time).
Most motors will have six terminals A1 B1 C1 top row C2 A2 B2 bottom row. 1 being the start of the winding, 2 the end.
View attachment 8906
Some will be dual voltage others suitable for star/delta starting.
Dual voltage will have two options, typical will be 230V delta 400V star. Some you may come across are:
400/230
415/240
433/250
690/400
750/433
(I’ve only ever come across the higher voltage ones a couple of time in 35 years).
Motors suitable for star/delta starting will usually just give one voltage for delta. If the supply is up to it they will start direct on line.
View attachment 8904View attachment 8905
OP
Knobhead
OK I know this is in electrical thories but I wanted to put it in “motors”
Squirrel Cage Motors.
On starting the rotor is stationary so it draws what is called locked rotor” current. This can be 5 to 8 times the FLC. The current is regulated primarily by the resistance of the winding with a small inductive element. As speed increases the inductance increases while the resistive element remains the same.
Running light the motor turns at near it’s synchronous speed causing high inductance in the stator windings and therefore low current. The motor cannot achieve full synchronous speed, as a small amount of “slip” is needed to induce current in to the rotor’s squirrel cage. As load on the shaft is increased slip increases inducing more current in to the squirrel cage, which in turn reduces the inductance of the rotor allowing more current to flow through the windings.
Synchronous speeds for an induction motor is governed by the number of poles in the rotor. This is give by Hz X 60 / No. of poles. So at 50Hz the synchronous speed for a 2 pole motor it will be 3000RPM.
Squirrel Cage Motors.
On starting the rotor is stationary so it draws what is called locked rotor” current. This can be 5 to 8 times the FLC. The current is regulated primarily by the resistance of the winding with a small inductive element. As speed increases the inductance increases while the resistive element remains the same.
Running light the motor turns at near it’s synchronous speed causing high inductance in the stator windings and therefore low current. The motor cannot achieve full synchronous speed, as a small amount of “slip” is needed to induce current in to the rotor’s squirrel cage. As load on the shaft is increased slip increases inducing more current in to the squirrel cage, which in turn reduces the inductance of the rotor allowing more current to flow through the windings.
Synchronous speeds for an induction motor is governed by the number of poles in the rotor. This is give by Hz X 60 / No. of poles. So at 50Hz the synchronous speed for a 2 pole motor it will be 3000RPM.
OP
Knobhead
Re: Autotransformer starters
View attachment 9101
There are two types of autotransformer starters and to add to the confusion they are wired the same. The sequence and the transformer construction are different.
The standard starter is open transition where at the change over from start to run there is a brief moment when no power is supplied to the motor. This can cause mechanical stress to the motor and load.
The Korndorfer starter is closed transition, so no loss of power at change over. Because of this the transformer has to be a bit more “beefy”. But because there is no break in the supply to the motor there is no mechanical stress.
Standard starter, open transition:
contactors 1 and 3 close. Giving a reduced voltage to the motor
time delay
contactors 1 and 3 open
small time delay (no power to motor)
contactor 2 closes. Giving full power to the motor
Korndorfer starter, closed transition:
contactor 3 closes
small time delay
contactor 3 closes. Giving a reduced voltage to the motor
time delay
contactor 3 opens. The transformer is now acting as a choke
small time delay
contactor 2 closes. The transformer is now shorted between it’s incoming and % tappings. But as it's the same potential bewteen the two points there is no current flow
small time delay
contactor 1 opens.
As can you see the sequence for the Korndorfer puts stress on the transformer where it has to withstand acting as a choke. So for small motors it’s uneconomical.
View attachment 9101
There are two types of autotransformer starters and to add to the confusion they are wired the same. The sequence and the transformer construction are different.
The standard starter is open transition where at the change over from start to run there is a brief moment when no power is supplied to the motor. This can cause mechanical stress to the motor and load.
The Korndorfer starter is closed transition, so no loss of power at change over. Because of this the transformer has to be a bit more “beefy”. But because there is no break in the supply to the motor there is no mechanical stress.
Standard starter, open transition:
contactors 1 and 3 close. Giving a reduced voltage to the motor
time delay
contactors 1 and 3 open
small time delay (no power to motor)
contactor 2 closes. Giving full power to the motor
Korndorfer starter, closed transition:
contactor 3 closes
small time delay
contactor 3 closes. Giving a reduced voltage to the motor
time delay
contactor 3 opens. The transformer is now acting as a choke
small time delay
contactor 2 closes. The transformer is now shorted between it’s incoming and % tappings. But as it's the same potential bewteen the two points there is no current flow
small time delay
contactor 1 opens.
As can you see the sequence for the Korndorfer puts stress on the transformer where it has to withstand acting as a choke. So for small motors it’s uneconomical.
Last edited by a moderator:
OP
Knobhead
Re: Dahlander Motors
I hadn’t intended to cover these so soon but the thread about a roller shutter door prodded me to go ahead. I’ve only ever got involved with 2 of these motors, and in all honesty I hope I never see one again!
The motor for the roller shutter door would be drawing 2.
The Dahlander motor is a two speed motor that offers a 1 : 2 speed switching. It is a specially wound pole switching motor requiring a special dual speed starter.
The Dahlander motor is wound as a star motor or a delta motor with centre taps on each leg of the winding. The motor is connected in star or delta for one speed and in "double star" for the other speed.The starter requires three contactors (five for reversing), a speed 1 main contactor and a speed 2 main contactor and a star contactor that can differ in it’s connection depending on the motor layout. Two over load protection relays are required, one in series with each of the main contactors.
Dahlander motors can be wound for constant power, variable torque or constant torque applications.A constant power Dahlander motor is would as a delta motor, and a constant torque motor is wound as a star.I’ve done the drawings showing reversing starters as this is what I used to work on.
View attachment 9135
View attachment 9134
This is a simplified version of the above.
View attachment 9142
View attachment 9133
I hadn’t intended to cover these so soon but the thread about a roller shutter door prodded me to go ahead. I’ve only ever got involved with 2 of these motors, and in all honesty I hope I never see one again!
The motor for the roller shutter door would be drawing 2.
The Dahlander motor is a two speed motor that offers a 1 : 2 speed switching. It is a specially wound pole switching motor requiring a special dual speed starter.
The Dahlander motor is wound as a star motor or a delta motor with centre taps on each leg of the winding. The motor is connected in star or delta for one speed and in "double star" for the other speed.The starter requires three contactors (five for reversing), a speed 1 main contactor and a speed 2 main contactor and a star contactor that can differ in it’s connection depending on the motor layout. Two over load protection relays are required, one in series with each of the main contactors.
Dahlander motors can be wound for constant power, variable torque or constant torque applications.A constant power Dahlander motor is would as a delta motor, and a constant torque motor is wound as a star.I’ve done the drawings showing reversing starters as this is what I used to work on.
View attachment 9135
View attachment 9134
This is a simplified version of the above.
View attachment 9142
View attachment 9133
Last edited by a moderator:
OP
Knobhead
Correction to post#7
Korndorfer starter, closed transition:
contactor 3 closes
small time delay
contactor 1 closes. Giving a reduced voltage to the motor
time delay
contactor 3 opens. The transformer is now acting as a choke
small time delay
contactor 2 closes. The transformer is now shorted between it’s incoming and % tappings. But as it's the same potential bewteen the two points there is no current flow
small time delay
contactor 1 opens.
Korndorfer starter, closed transition:
contactor 3 closes
small time delay
contactor 1 closes. Giving a reduced voltage to the motor
time delay
contactor 3 opens. The transformer is now acting as a choke
small time delay
contactor 2 closes. The transformer is now shorted between it’s incoming and % tappings. But as it's the same potential bewteen the two points there is no current flow
small time delay
contactor 1 opens.
OP
Knobhead
Star delta overloads
View attachment 9231
The motor needs overload protection via an overload unit, with a S/D starter the O/L’s can be placed in the circuit in two different positions. With a DOL starter the setting is simple, just set at the FLC of the motor.
Method “B” is the preferred method as it provides the correct O/L protection during starting. The disadvantage is the setting of the O/L unit. In a S/D starter only a proportion of the current flows through the O/L unit, therefore the relay has to be set at 0.58 (1/√3) of the FLC. Not quite so simple.
At times there are advantages to method “A”. I’ve used it for starting very heavy inertia loads where there would be a risk of tripping during start up. Some early starters even shorted the O/L’s out all together.
View attachment 9231
The motor needs overload protection via an overload unit, with a S/D starter the O/L’s can be placed in the circuit in two different positions. With a DOL starter the setting is simple, just set at the FLC of the motor.
Method “B” is the preferred method as it provides the correct O/L protection during starting. The disadvantage is the setting of the O/L unit. In a S/D starter only a proportion of the current flows through the O/L unit, therefore the relay has to be set at 0.58 (1/√3) of the FLC. Not quite so simple.
At times there are advantages to method “A”. I’ve used it for starting very heavy inertia loads where there would be a risk of tripping during start up. Some early starters even shorted the O/L’s out all together.
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OP
alli
Thanks for this thread, really interesting.
Do you ever sleep? 03:31 AM
Do you ever sleep? 03:31 AM
OP
Knobhead
Insomnia
View attachment 9236
View attachment 9236
OP
alli
Sorry to hear that, I guess that's why your drawings are superb.
OP
silva.foxx
To supplement Tony's SD info Line and Delta contactors are sized at 58% flc and the Star contactor at 33% flc of the motor load.
For example: a 220kw 3ph AC induction motor pulling say, 360 amps and star-delta started. Line and Delta contactors to be sized min. 210 amps and Star contactor at 120 amps. So you'd use 2off 250 and 1off 140A contactors (assuming AC-3 inductive requirement) as opposed to 3off 400A contactors. This saves on both expense and panel space.
On much smaller motors this is less of an issue and you'd typically find the three contactors similarly, if not indentically, sized.
For example: a 220kw 3ph AC induction motor pulling say, 360 amps and star-delta started. Line and Delta contactors to be sized min. 210 amps and Star contactor at 120 amps. So you'd use 2off 250 and 1off 140A contactors (assuming AC-3 inductive requirement) as opposed to 3off 400A contactors. This saves on both expense and panel space.
On much smaller motors this is less of an issue and you'd typically find the three contactors similarly, if not indentically, sized.
OP
Knobhead
Slip Ring or Wound Rotor Motors
View attachment 9616
View attachment 9617
I’ve had a love / hate relationship with these motors for years. Maintenance of the brush-gear is a pain to any maintenance department. Overlook or ignore it and it comes back and bites you. Excessive carbon dust can cause flashover on start up. On initial start up the voltage on the rings is at it’s maximum (some motors I’ve worked on could have up to 3KV between them). Carbon dust will find it’s way in to any little crevice, let it build up enough and you can expect an explosion. The first picture shows a basic set up, the left side shows a “standard” brush box, the right a constant force box. The second picture shows a practical set up. The constant force box uses a spring similar to the ones used for cable earthing but in this case they are trying to un-coil.
View attachment 9618
View attachment 9619
The slip ring or wound rotor motor is an induction machine where the rotor comprises a set of coils that are terminated in sliprings to which external impedances can be connected. The stator is the same as is used with a standard squirrel cage motor.
View attachment 9620
By changing the impedance connected to the rotor circuit, the speed/current and speed/torque curves can be altered.
The slip ring motor is used primarily to start a high inertia load or a load that requires a very high starting torque across the full speed range. By correctly selecting the resistors used in the secondary resistance or slip ring starter, the motor is able to produce maximum torque at a relatively low current from zero speed to full speed. A secondary use of the slip ring motor, is to provide a means of speed control. Because the torque curve of the motor is effectively modified by the resistance connected to the rotor circuit, the speed of the motor can be altered. Increasing the value of resistance on the rotor circuit will move the speed of maximum torque down. If the resistance connected to the rotor is increased beyond the point where the maximum torque occurs at zero speed, the torque will be further reduced.
When used with a load that has a torque curve that increases with speed, the motor will operate at the speed where the torque developed by the motor is equal to the load torque. Reducing the lad will cause the motor to speed up, and increasing the load will cause the motor to slow down until the load and motor torque are equal. Operated in this manner, the slip losses are dissipated in the secondary resistors and can be very significant. The speed regulation is also very poor.
Motor Characteristics.
The Slip Ring motor has two distinctly separate parts, the stator and the rotor. The stator circuit is rated as with a standard squirrel cage motor and the rotor is rated in frame voltage and short circuit current. The frame voltage is the open circuit voltage when the rotor is not rotating and gives a measure of the turns ratio between the rotor and the stator. The short circuit current is the current flowing when the motor is operating at full speed with the slip rings (rotor) shorted and full load is applied to the motor shaft.
Secondary Resistance Starters.
The secondary resistance starter comprises a contactor to switch the stator and a series of resistors that are applied to the rotor circuit and gradually reduced in value as the motor accelerates to full speed. The rotor would normally be shorted out once the motor is at full speed. The resistor values are selected to provide the torque profile required and are sized to dissipate the slip power during start. The secondary resistors can be metallic resistors such as wound resistors, plate resistors or cast resistors.
View attachment 9621
Or they can be liquid resistors made up of saline solution or caustic soda or similar, provided there is sufficient thermal mass to absorb the total slip loss during start.
View attachment 9622
View attachment 9623
I worked on the same type of liquid starter shown in the photograph. They were obsolete and costing a fortune to have final contacts made for them. £2500 for a set of contacts was a bit OTT, so I came up with this idea, standard Telemecanique 315A contactors working at 1.7X their normal rated voltage. The final contact in the original design were slow making so at 1250A they didn’t last long, with my set up the contacts were high speed and so didn’t get eroded. The final load current dropped from 400A+ to 150A @11KV.
View attachment 9624
To select the values of the resistors, you need to know the frame voltage and the short circuit current. The maximum torque occurs approximately at the point where the rotor reactance equals the termination resistance. The final stage of the resistance should always be designed for a maximum torque close to full speed to prevent a very large step in current when shorting the final stage of resistance. If a single stage was used and the maximum torque occurred at 50% speed, then motor may accelerate to 60% speed, depending on the load. If the rotor was shorted at this speed, the motor would draw a very high current (typically around 1400% FLC) and produce very little torque, and would most probably stall!
High Inertia Loads
Slip ring motors are commonly used on high inertia loads because of their superior start efficiencies and their ability to withstand the inertia of the loads
When a load is started, the full speed kinetic energy of that load is dissipated in the rotor circuit. With a standard cage type induction motor, there only some motors that can be used on high inertia loads. Most will suffer rotor damage due to the power dissipated by the rotor. With the slip ring motor, the secondary resistors can be selected to provide the optimum torque curves and they can be sized to withstand the load energy without failure.
Starting a high inertia load with a standard cage motor would require between 400% and 550% start current for up to 60 seconds. Starting the same machine with a wound rotor motor (slip ring motor) would require around 200% current for around 20 seconds. A much more efficient solution.
Shorting the rings out on a slip ring motor with a high inertia load is not an option as the load energy must be dissipated in the rotor winding during start. This will cause insulation failure in the rotor circuit.
Now this is my idea of a resonable sized motor
View attachment 9625
View attachment 9616
View attachment 9617
I’ve had a love / hate relationship with these motors for years. Maintenance of the brush-gear is a pain to any maintenance department. Overlook or ignore it and it comes back and bites you. Excessive carbon dust can cause flashover on start up. On initial start up the voltage on the rings is at it’s maximum (some motors I’ve worked on could have up to 3KV between them). Carbon dust will find it’s way in to any little crevice, let it build up enough and you can expect an explosion. The first picture shows a basic set up, the left side shows a “standard” brush box, the right a constant force box. The second picture shows a practical set up. The constant force box uses a spring similar to the ones used for cable earthing but in this case they are trying to un-coil.
View attachment 9618
View attachment 9619
The slip ring or wound rotor motor is an induction machine where the rotor comprises a set of coils that are terminated in sliprings to which external impedances can be connected. The stator is the same as is used with a standard squirrel cage motor.
View attachment 9620
By changing the impedance connected to the rotor circuit, the speed/current and speed/torque curves can be altered.
The slip ring motor is used primarily to start a high inertia load or a load that requires a very high starting torque across the full speed range. By correctly selecting the resistors used in the secondary resistance or slip ring starter, the motor is able to produce maximum torque at a relatively low current from zero speed to full speed. A secondary use of the slip ring motor, is to provide a means of speed control. Because the torque curve of the motor is effectively modified by the resistance connected to the rotor circuit, the speed of the motor can be altered. Increasing the value of resistance on the rotor circuit will move the speed of maximum torque down. If the resistance connected to the rotor is increased beyond the point where the maximum torque occurs at zero speed, the torque will be further reduced.
When used with a load that has a torque curve that increases with speed, the motor will operate at the speed where the torque developed by the motor is equal to the load torque. Reducing the lad will cause the motor to speed up, and increasing the load will cause the motor to slow down until the load and motor torque are equal. Operated in this manner, the slip losses are dissipated in the secondary resistors and can be very significant. The speed regulation is also very poor.
Motor Characteristics.
The Slip Ring motor has two distinctly separate parts, the stator and the rotor. The stator circuit is rated as with a standard squirrel cage motor and the rotor is rated in frame voltage and short circuit current. The frame voltage is the open circuit voltage when the rotor is not rotating and gives a measure of the turns ratio between the rotor and the stator. The short circuit current is the current flowing when the motor is operating at full speed with the slip rings (rotor) shorted and full load is applied to the motor shaft.
Secondary Resistance Starters.
The secondary resistance starter comprises a contactor to switch the stator and a series of resistors that are applied to the rotor circuit and gradually reduced in value as the motor accelerates to full speed. The rotor would normally be shorted out once the motor is at full speed. The resistor values are selected to provide the torque profile required and are sized to dissipate the slip power during start. The secondary resistors can be metallic resistors such as wound resistors, plate resistors or cast resistors.
View attachment 9621
Or they can be liquid resistors made up of saline solution or caustic soda or similar, provided there is sufficient thermal mass to absorb the total slip loss during start.
View attachment 9622
View attachment 9623
I worked on the same type of liquid starter shown in the photograph. They were obsolete and costing a fortune to have final contacts made for them. £2500 for a set of contacts was a bit OTT, so I came up with this idea, standard Telemecanique 315A contactors working at 1.7X their normal rated voltage. The final contact in the original design were slow making so at 1250A they didn’t last long, with my set up the contacts were high speed and so didn’t get eroded. The final load current dropped from 400A+ to 150A @11KV.
View attachment 9624
To select the values of the resistors, you need to know the frame voltage and the short circuit current. The maximum torque occurs approximately at the point where the rotor reactance equals the termination resistance. The final stage of the resistance should always be designed for a maximum torque close to full speed to prevent a very large step in current when shorting the final stage of resistance. If a single stage was used and the maximum torque occurred at 50% speed, then motor may accelerate to 60% speed, depending on the load. If the rotor was shorted at this speed, the motor would draw a very high current (typically around 1400% FLC) and produce very little torque, and would most probably stall!
High Inertia Loads
Slip ring motors are commonly used on high inertia loads because of their superior start efficiencies and their ability to withstand the inertia of the loads
When a load is started, the full speed kinetic energy of that load is dissipated in the rotor circuit. With a standard cage type induction motor, there only some motors that can be used on high inertia loads. Most will suffer rotor damage due to the power dissipated by the rotor. With the slip ring motor, the secondary resistors can be selected to provide the optimum torque curves and they can be sized to withstand the load energy without failure.
Starting a high inertia load with a standard cage motor would require between 400% and 550% start current for up to 60 seconds. Starting the same machine with a wound rotor motor (slip ring motor) would require around 200% current for around 20 seconds. A much more efficient solution.
Shorting the rings out on a slip ring motor with a high inertia load is not an option as the load energy must be dissipated in the rotor winding during start. This will cause insulation failure in the rotor circuit.
Now this is my idea of a resonable sized motor
View attachment 9625
Last edited by a moderator:
OP
SirKit Breaker
Tony's posts always make good reading, he really knows his stuff. Any apprentices out there in the industrial field could do a lot worse than read through a lot of his posts. i know a few of mine have.
Cheers.......Howard
Cheers.......Howard
OP
Knobhead
Motor bearings
Before I start on this I want to know who would be interested in motor bearings.
Glennispark is willing to help on this subject, between us I think we’ve well over 60 years of experience to hand, hopefully others will add to the pool.
Please say Yay or Ney as it does take time to do drawings to make things clear.
Before I start on this I want to know who would be interested in motor bearings.
Glennispark is willing to help on this subject, between us I think we’ve well over 60 years of experience to hand, hopefully others will add to the pool.
Please say Yay or Ney as it does take time to do drawings to make things clear.
OP
alli
Re: Motor bearings
I would really appreciate a post on bearings, if you can afford the time.
I would really appreciate a post on bearings, if you can afford the time.
- Reaction score
- 1,597
Re: Motor bearings
id like to learn more about the effects of VSD's on bearings, and common solutions ect. I think Marvo has mentioned that hes encountered this problem before.
I along with others appreciate the time taken to write these threads.
id like to learn more about the effects of VSD's on bearings, and common solutions ect. I think Marvo has mentioned that hes encountered this problem before.
I along with others appreciate the time taken to write these threads.
OP
Knobhead
Give me a week or so and I’m sure with a bit of help it will get done.
Circulating rotor currents isn’t something I hadn’t considered for the post, but it’s an important thing to take in to consideration. They’ve caused me enough problems in the past so I should have thought of it!
Circulating rotor currents isn’t something I hadn’t considered for the post, but it’s an important thing to take in to consideration. They’ve caused me enough problems in the past so I should have thought of it!
- Reaction score
- 771
I have done quite a bit with bearings from many stand points including motor design & predictive maintenance for a global manufacturer of motors & drives.
OP
Knobhead
Bearing problems.
Right I started to write a piece about changing bearings, but then thought, hang on there’s got to be a reason to change them in the first place. Sounds logical to me anyway.
Lubrication:
Oil, used for small motors with phosphor/bronze sleeve or journal bearing for very large motors. Some large motors will have white metal as the running material. The only thing to say really is to follow the makers instructions as to the oil grade to be used. I’ve come across some weird specifications in the past. Two motors spring to mind each 2500HP, the recommended oil was B44 transformer oil? (Don’t ask me why, but they had been running happily 24/7 for 20 years). Even bigger motors may have oil lubricated bearing with water-cooled jackets around the bearings. One thing to watch for with large sleeve bearings is the oil thrower/pick up rings wearing through. Your quite happily keeping the oil level correct but it’s going nowhere and doing nothing!
You may notice on this drawing the shaft has no shoulder on the shaft to locate it. When a large motor is first run the bolts are left out of the coupling, this allows the motor shaft to find it’s magnetic centre. Once the centre is found the coupling is assembled with spacers to hold the shaft in position.
View attachment 10700
Grease, here we go for the first argument. Some motor manufactures will claim maintenance free bearings. Yeh right, so why the hell am I mauling my nuts off changing this motor?
Grease is oil held in a suspension medium. There are 1000’s of grades each with it’s own bit of magic. (The one thing I do know is the moment I go near it I get covered in the bloody stuff)!
If grease nipples are fitted to a motor then a shot of grease every 3 to 6 months won’t go amiss, but use your judgment as to how much. Big bearings 2 or 3 shots, small, ½ a shot. Over greasing is as big a killer as no grease at all. The grease needs room to move about in the bearing, too little and it gets pushed out of the bearing, too much and it clogs in the races, over heats and fries it’s self. 2/3[SUP]rds [/SUP]full is the usual recommended amount, but again go by the manufacturers recommendations.
(This may amuse you, going back years we had an old guy going around the plant doing nothing other than lubrication. He had a schedule to follow but was a bit over enthusiastic. One shot every 3 months became 2 a week. I got called to a motor that was tripping on overload, opened the terminal box and it was full of grease. The entire motor was full. Motors, fans, pumps, conveyors nothing escaped Juffy! So much for preventative maintenance, he must have cost us tens of thousands)!
I’ve done two drawings the first shows a standard set up with ball and roller bearings. The second is a foundry motor, where each bearing is in a separate cassette. Not the easiest to strip down.
View attachment 10701
View attachment 10702
Right I started to write a piece about changing bearings, but then thought, hang on there’s got to be a reason to change them in the first place. Sounds logical to me anyway.
Lubrication:
Oil, used for small motors with phosphor/bronze sleeve or journal bearing for very large motors. Some large motors will have white metal as the running material. The only thing to say really is to follow the makers instructions as to the oil grade to be used. I’ve come across some weird specifications in the past. Two motors spring to mind each 2500HP, the recommended oil was B44 transformer oil? (Don’t ask me why, but they had been running happily 24/7 for 20 years). Even bigger motors may have oil lubricated bearing with water-cooled jackets around the bearings. One thing to watch for with large sleeve bearings is the oil thrower/pick up rings wearing through. Your quite happily keeping the oil level correct but it’s going nowhere and doing nothing!
You may notice on this drawing the shaft has no shoulder on the shaft to locate it. When a large motor is first run the bolts are left out of the coupling, this allows the motor shaft to find it’s magnetic centre. Once the centre is found the coupling is assembled with spacers to hold the shaft in position.
View attachment 10700
Grease, here we go for the first argument. Some motor manufactures will claim maintenance free bearings. Yeh right, so why the hell am I mauling my nuts off changing this motor?
Grease is oil held in a suspension medium. There are 1000’s of grades each with it’s own bit of magic. (The one thing I do know is the moment I go near it I get covered in the bloody stuff)!
If grease nipples are fitted to a motor then a shot of grease every 3 to 6 months won’t go amiss, but use your judgment as to how much. Big bearings 2 or 3 shots, small, ½ a shot. Over greasing is as big a killer as no grease at all. The grease needs room to move about in the bearing, too little and it gets pushed out of the bearing, too much and it clogs in the races, over heats and fries it’s self. 2/3[SUP]rds [/SUP]full is the usual recommended amount, but again go by the manufacturers recommendations.
(This may amuse you, going back years we had an old guy going around the plant doing nothing other than lubrication. He had a schedule to follow but was a bit over enthusiastic. One shot every 3 months became 2 a week. I got called to a motor that was tripping on overload, opened the terminal box and it was full of grease. The entire motor was full. Motors, fans, pumps, conveyors nothing escaped Juffy! So much for preventative maintenance, he must have cost us tens of thousands)!
I’ve done two drawings the first shows a standard set up with ball and roller bearings. The second is a foundry motor, where each bearing is in a separate cassette. Not the easiest to strip down.
View attachment 10701
View attachment 10702
OP
vaughant
Some great info there Tony,top man.
You have a very good way of explaining things,clearly cos you've done the job not just read about it in a text book!
You have a very good way of explaining things,clearly cos you've done the job not just read about it in a text book!
OP
Knobhead
Star Delta closed transition
A closed transition star delta avoids the jolt and current peak at the point of change over. The resistors have to be quite substantial, ones I worked one they would fill a small wardrobe. OK they were 800HP. At one point the star contactor shorts the phases but the resistors keep this under control.
Start
Main and star contactors 1 and 4 close.
Time delay (running up to speed)
Transition contactor 3 closes
Small time delay
Star contactor 4 opens
Small time delay
Delta contactor 2 closes
Small time delay
Transition contactor 3 opens
Running
There’s a fair few timers involved. T5 in this diagram is a watchdog to ensure the motor is running in delta within time. R3/4/5 were for our process controller. I’ve had to split the diagram to get it on the forum.
1 Main contactor
2 Delta contactor
3 Transition contactor
4 Star contactor
5 Overload
6 Resistor over temp
7 Lockout reset P/B
T1 Close transition timer
T2 Open star timer
T3 Close delta timer
T4 Open transition timer
T5 Sequence failure timer (lockout)
R1 O/L, interlocks & stops OK (PC)
R2 Control relay
R3 Drive ready (PC)
R4 Drive starting (PC)
R5 Drive running (PC)
View attachment 11469
View attachment 11468
View attachment 11467
View attachment 11466
A closed transition star delta avoids the jolt and current peak at the point of change over. The resistors have to be quite substantial, ones I worked one they would fill a small wardrobe. OK they were 800HP. At one point the star contactor shorts the phases but the resistors keep this under control.
Start
Main and star contactors 1 and 4 close.
Time delay (running up to speed)
Transition contactor 3 closes
Small time delay
Star contactor 4 opens
Small time delay
Delta contactor 2 closes
Small time delay
Transition contactor 3 opens
Running
There’s a fair few timers involved. T5 in this diagram is a watchdog to ensure the motor is running in delta within time. R3/4/5 were for our process controller. I’ve had to split the diagram to get it on the forum.
1 Main contactor
2 Delta contactor
3 Transition contactor
4 Star contactor
5 Overload
6 Resistor over temp
7 Lockout reset P/B
T1 Close transition timer
T2 Open star timer
T3 Close delta timer
T4 Open transition timer
T5 Sequence failure timer (lockout)
R1 O/L, interlocks & stops OK (PC)
R2 Control relay
R3 Drive ready (PC)
R4 Drive starting (PC)
R5 Drive running (PC)
View attachment 11469
View attachment 11468
View attachment 11467
View attachment 11466
Last edited by a moderator:
OP
Knobhead
Open Transition star delta
An open transition star delta has the disadvantage of the jolt and current peak at the point of change over.
To be honest I don’t like these starters, but I’ve been lucky in that the places I’ve worked in that motors up to 300HP would be started DOL
Start
Main and star contactors 1 and 3 close.
Time delay (running up to speed)
Star contactor 3 opens
Small time delay
Delta contactor 2 closes
Running
I’ve shown two timers but single proprietary units are available.
1 Main contactor
2 Delta contactor
3 Star contactor
4 Overload
T1 Open star timer
T2 Close delta timer
View attachment 11484
View attachment 11487
View attachment 11482
An open transition star delta has the disadvantage of the jolt and current peak at the point of change over.
To be honest I don’t like these starters, but I’ve been lucky in that the places I’ve worked in that motors up to 300HP would be started DOL
Start
Main and star contactors 1 and 3 close.
Time delay (running up to speed)
Star contactor 3 opens
Small time delay
Delta contactor 2 closes
Running
I’ve shown two timers but single proprietary units are available.
1 Main contactor
2 Delta contactor
3 Star contactor
4 Overload
T1 Open star timer
T2 Close delta timer
View attachment 11484
View attachment 11487
View attachment 11482
Last edited by a moderator:
OP
Knobhead
Motor testing
One thing before testing a motor is check the mechanical loading. I’ve had many an argument with fitters who insist the gearbox or what ever is free.
A classic being “Jock” (fitter) insisting the Radicon gearbox was free. I was doing pull ups on a set of 18” stillsons trying to turn the motor shaft. Jock insisted it was an electrical problem, fortunately the manager showed up before we came to blows.
In a production environment you will discover everything is an electrical fault. The conveyor motor won’t run, it’s got nothing to do with the tonnes of spillage burying it.
Bearings:
If the motor is still running use a long screwdriver as a stethoscope to listen to the bearings. Place the blade of the driver on the bearing housing or the motor end bell and put your ear against the end of the handle. A rumbling noise tells you all is not well. You can try a few shots of grease, if that doesn’t quieten it down then it’s time to get the spanners out. With the motor stopped place a bar under the shaft and see if there is any “lift” in the bearing. With roller or ball bearings you shouldn’t be able to detect any. Sleeve bearings you may get a slight amount, I’m sorry but this is one where there’s no definite answer, experience is needed with them.
Electrical tests:
I was taught to use twice the terminal voltage for IR tests but some don’t agree with this. As for minimum values I use the M&Q test method. Where leakage current should not exceed 1/10,000[SUP]th[/SUP] of the FLC. This then takes in to account that a large motor has a lot more windings than a small one and therefore a higher leakage current. With a motor that’s been in service you can’t expect to be getting infinity readings.
A motor with an internally connected star point there’s only limited tests you can do. But there again they are cheap enough to be more or less disposable.
IR test:
Due to the internal star connection you can only test the windings to earth.
CR tests:
A to B, B to C, C to A. Compare each of the three readings, they should be within a few % of each other.
View attachment 11929
A motor with six terminals whether it’s connected star of delta can be tested the same way.
IR tests:
With the links still connected test to earth. With the links in one test covers all the windings.
Remove the links and test A1 to B1, B1 to C1, C1 to A1. This checks the insulation between the individual windings.
CR tests:
A1 to A2, B1 to B2, C1 to C2. Compare each of the three readings, they should be within a few % of each other.
If the motor tests OK then it’s time to look at the starter, isolator and supply cables.
One thing before testing a motor is check the mechanical loading. I’ve had many an argument with fitters who insist the gearbox or what ever is free.
A classic being “Jock” (fitter) insisting the Radicon gearbox was free. I was doing pull ups on a set of 18” stillsons trying to turn the motor shaft. Jock insisted it was an electrical problem, fortunately the manager showed up before we came to blows.
In a production environment you will discover everything is an electrical fault. The conveyor motor won’t run, it’s got nothing to do with the tonnes of spillage burying it.
Bearings:
If the motor is still running use a long screwdriver as a stethoscope to listen to the bearings. Place the blade of the driver on the bearing housing or the motor end bell and put your ear against the end of the handle. A rumbling noise tells you all is not well. You can try a few shots of grease, if that doesn’t quieten it down then it’s time to get the spanners out. With the motor stopped place a bar under the shaft and see if there is any “lift” in the bearing. With roller or ball bearings you shouldn’t be able to detect any. Sleeve bearings you may get a slight amount, I’m sorry but this is one where there’s no definite answer, experience is needed with them.
Electrical tests:
I was taught to use twice the terminal voltage for IR tests but some don’t agree with this. As for minimum values I use the M&Q test method. Where leakage current should not exceed 1/10,000[SUP]th[/SUP] of the FLC. This then takes in to account that a large motor has a lot more windings than a small one and therefore a higher leakage current. With a motor that’s been in service you can’t expect to be getting infinity readings.
A motor with an internally connected star point there’s only limited tests you can do. But there again they are cheap enough to be more or less disposable.
IR test:
Due to the internal star connection you can only test the windings to earth.
CR tests:
A to B, B to C, C to A. Compare each of the three readings, they should be within a few % of each other.
View attachment 11929
A motor with six terminals whether it’s connected star of delta can be tested the same way.
IR tests:
With the links still connected test to earth. With the links in one test covers all the windings.
Remove the links and test A1 to B1, B1 to C1, C1 to A1. This checks the insulation between the individual windings.
CR tests:
A1 to A2, B1 to B2, C1 to C2. Compare each of the three readings, they should be within a few % of each other.
If the motor tests OK then it’s time to look at the starter, isolator and supply cables.
Last edited by a moderator:
OP
Knobhead
Single Phase Motors
I’ve not done a lot of work with single phase motors, so this will be fairly basic.
The stator will have two windings. Start and run set at 90° to each other, start will have a capacitor in series with it to cause a phase shift.
Capacitor start.
During starting both windings are used, nearing full speed the start winding is disconnected leaving just the run winding in circuit.
Capacitor start / Capacitor run.
During starting both windings are used, but with this type there are two capacitors in a series / parallel network. Nearing full speed the one of the capacitors is disconnected. Leaving just one in series with the start winding.
Disconnection is done by either a centrifugal switch or a timer. Both methods gave disadvantages. The centrifugal switch is prone to jamming either open or closed and dirty contacts. The timer being remote from the motor doesn’t know if the motor is up to speed or not.
View attachment 12674
View attachment 12673
I’ve not done a lot of work with single phase motors, so this will be fairly basic.
The stator will have two windings. Start and run set at 90° to each other, start will have a capacitor in series with it to cause a phase shift.
Capacitor start.
During starting both windings are used, nearing full speed the start winding is disconnected leaving just the run winding in circuit.
Capacitor start / Capacitor run.
During starting both windings are used, but with this type there are two capacitors in a series / parallel network. Nearing full speed the one of the capacitors is disconnected. Leaving just one in series with the start winding.
Disconnection is done by either a centrifugal switch or a timer. Both methods gave disadvantages. The centrifugal switch is prone to jamming either open or closed and dirty contacts. The timer being remote from the motor doesn’t know if the motor is up to speed or not.
View attachment 12674
View attachment 12673
OP
Knobhead
To add to the above, these drawings show the phase seperation of the windings. Also I made a bog up in the above drawings, I'd shown the centrifugal switch as open, where as it's closed on start up.
View attachment 12700
View attachment 12699
View attachment 12700
View attachment 12699
OP
Knobhead
Squirrel cage motors.
Should have done this first really, but I’m not the best organised person.
This shows an exploded view of a motor to give some idea of what goes where.
View attachment 12926
The motor can be star or delta connected.
If needs be to allow star delta starting. (See other posts)
View attachment 12927
The basic windings are brought out to the terminal box. Shown here as Delta to the left and Star to the right.
View attachment 12928
Delta terminal box
View attachment 12929
Star terminal box
The rotating field is created by the 6 coils for a 2 pole motor by the rotation phase rotation of the three phase supply
View attachment 12930
View attachment 12931
The motor gets it’s name from the construction of the rotor windings. Take away the rotor laminations you have a squirrel cage.
Transformer induction induces a fixed field on the rotor cage. The cage rotates in an attempt to catch up with the rotating stator field. A forlorn hope as there has to be a certain amount of slip to give the induced current to give rotation and torque.
Early motors had copper bars brazed to copper end rings. Later the copper was replaced by aluminium injection to form a solid casting.
The cage could be in several forms.
A standard cage that would give normal acceleration and torque
View attachment 12932
Double cage where due to the higher flux density on the inner bars at high slip would give twice the torque on start up. It had the down side of higher inrush current.
View attachment 12933
Modern cages are a highbred of both. With aluminium injection these are easier to make now.
View attachment 12934
There are a few companies now doing copper injection for the cage.
As for the motor being constant speed, I’m afraid that’s a myth. As load increases more slip is needed to produce the torque. The motor name plate gives speed at a % of loading.
Should have done this first really, but I’m not the best organised person.
This shows an exploded view of a motor to give some idea of what goes where.
View attachment 12926
The motor can be star or delta connected.
If needs be to allow star delta starting. (See other posts)
View attachment 12927
The basic windings are brought out to the terminal box. Shown here as Delta to the left and Star to the right.
View attachment 12928
Delta terminal box
View attachment 12929
Star terminal box
The rotating field is created by the 6 coils for a 2 pole motor by the rotation phase rotation of the three phase supply
View attachment 12930
View attachment 12931
The motor gets it’s name from the construction of the rotor windings. Take away the rotor laminations you have a squirrel cage.
Transformer induction induces a fixed field on the rotor cage. The cage rotates in an attempt to catch up with the rotating stator field. A forlorn hope as there has to be a certain amount of slip to give the induced current to give rotation and torque.
Early motors had copper bars brazed to copper end rings. Later the copper was replaced by aluminium injection to form a solid casting.
The cage could be in several forms.
A standard cage that would give normal acceleration and torque
View attachment 12932
Double cage where due to the higher flux density on the inner bars at high slip would give twice the torque on start up. It had the down side of higher inrush current.
View attachment 12933
Modern cages are a highbred of both. With aluminium injection these are easier to make now.
View attachment 12934
There are a few companies now doing copper injection for the cage.
As for the motor being constant speed, I’m afraid that’s a myth. As load increases more slip is needed to produce the torque. The motor name plate gives speed at a % of loading.
OP
nickblake
i always get confused with motors star and delta and how , have no problem fixing faults with them then again i am a tad odd , nice post tony
OP
Bobster
Was braught up in another thread but here's some bumf on artificial 3phase motor connections.
Now this is taken from my little motor bible and is the only way I've seen in person a 3ph motor run on single phase.
This is another way of connecting it up, now I've only ever read the theory about this. Never seen it in the real world. It's called a steinmetz connection.
I'll write a post with the theory explained when I can spend some time and edit it properly, rather than on my phone.
Now this is taken from my little motor bible and is the only way I've seen in person a 3ph motor run on single phase.
This is another way of connecting it up, now I've only ever read the theory about this. Never seen it in the real world. It's called a steinmetz connection.
I'll write a post with the theory explained when I can spend some time and edit it properly, rather than on my phone.
OP
lemau
Hi all,Topic for motor and starter is common topic for all electrical person..i would to share some post about electrical motor and motor starter. I hope it can help for more understanding about motor and starter 
OP
Knobhead
Simplified the drawing for you. Also made it so the start P/B doesn’t carry the full starting current and the main contactor can’t close with the switch in the run position.
View attachment 13926
View attachment 13926
OP
Knobhead
Primary resistance starter
Primary resistance starter
I’ve only ever seen two of these, they were used on lift motors.
As you can see from the drawing they are pretty simple. On start up contactor K2 closes allowing a reduced voltage to the stator windings, after a short time delay contactor K1 closes and K2 drops out.
They suffer from being limited to X number of starts per hour due to heat build up.
View attachment 14202
View attachment 14201
Primary resistance starter
I’ve only ever seen two of these, they were used on lift motors.
As you can see from the drawing they are pretty simple. On start up contactor K2 closes allowing a reduced voltage to the stator windings, after a short time delay contactor K1 closes and K2 drops out.
They suffer from being limited to X number of starts per hour due to heat build up.
View attachment 14202
View attachment 14201
OP
Bobster
Re: Primary resistance starter
Is this not just effectively a liquid starter?
Any advantage to this design?
Is this not just effectively a liquid starter?
Any advantage to this design?
OP
Knobhead
Liquid starters are normally used on slip ring motors where isolation of the phases isn’t as important. There’s no reason a liquid starter couldn’t be used as a primary resistance but it would need major re-engineering to make it safe. Instead of one earthed tank for the electrolyte, three separate insulated tanks would be needed. There was a company in the 70/80’s that made Statormatic starters, the same company made Vapormatic starters for slip-ring motors.
View attachment 14208
Slip ring rotor
View attachment 14207
Stator
View attachment 14208
Slip ring rotor
View attachment 14207
Stator
OP
Bobster
Delt with a lot of liquid starters at the cement plant I used to work, usually with 3.3kv drives, had a few long days when the brush gear flashed over with carbon dust, we did try to blow them oh weekly but production often superseded maintenance.
I was just thinking about the therory behind it, am I right in thinking a star delta starter would be a cheeper way of setting this up? I take it the resistor bank is used for the same reason the liquid starters are used? Never seen that set up before.
I was just thinking about the therory behind it, am I right in thinking a star delta starter would be a cheeper way of setting this up? I take it the resistor bank is used for the same reason the liquid starters are used? Never seen that set up before.
OP
Knobhead
The primary resistance has the beauty that it’s flexible as to the % of torque at start up. Star/delta is 1/√3 only.
The beauty of a slip ring motor is it’s high starting torque, something you wouldn’t get with start/delta. A cement mill would just sit there and not move in star. On top of that even at √3 of the DOL starting current (say 6X FLC/√3 = 3.46X FLC) the 3.3 OCB would trip on instantaneous overload. The cement mills I’ve worked on ranged from 900 to 6000HP, I wouldn’t like to be around when the breaker opened. I was stood in front of a 3.3 ACB when that tripped due to a slip-ring flashover, I near had to go and change my underpants.
For heavy starting loads you can’t beat slip-ring motors.
Some I’ve worked on were variable speed using the Kramer system. They started using a liquid starter. Once at full speed the Kramer control would kick in and regulate the current in the rotor, the recovered energy being fed back in to the 11KV system via an inverter and step up transformer.
View attachment 14214
The beauty of a slip ring motor is it’s high starting torque, something you wouldn’t get with start/delta. A cement mill would just sit there and not move in star. On top of that even at √3 of the DOL starting current (say 6X FLC/√3 = 3.46X FLC) the 3.3 OCB would trip on instantaneous overload. The cement mills I’ve worked on ranged from 900 to 6000HP, I wouldn’t like to be around when the breaker opened. I was stood in front of a 3.3 ACB when that tripped due to a slip-ring flashover, I near had to go and change my underpants.
For heavy starting loads you can’t beat slip-ring motors.
Some I’ve worked on were variable speed using the Kramer system. They started using a liquid starter. Once at full speed the Kramer control would kick in and regulate the current in the rotor, the recovered energy being fed back in to the 11KV system via an inverter and step up transformer.
View attachment 14214
OP
Bobster
We had a system very similar to that tuning one of the kiln firing fans, it was an abb multidrive invertor 2Mva, that used a resistor bank to start and also managed to recover energy from the drive.
Never got my head around how that worked, it was only on site a couple of months before I left. Was delivered in a steel container as a plug and play system, it weighed 27tonnes.
Never got my head around how that worked, it was only on site a couple of months before I left. Was delivered in a steel container as a plug and play system, it weighed 27tonnes.
OP
Knobhead
The ones we had for the ID fans were about 20 years old. I had one of the thyristor packs fail, I was near it when it went. When we opened the panel we were expecting a charred mess but no the only thing was a blown fuse. That is what I’d heard. Changed the fuse and it’s thyristor pack and it ran perfectly afterwards.
The fuse went in spectacular style, the thyristor tested perfectly?
View attachment 14226View attachment 14227
The fuse went in spectacular style, the thyristor tested perfectly?
View attachment 14226View attachment 14227
OP
DurhamSparky
Hi tony, on one of our sites we are running the supply fans for cooling at 120% and 45% above the working Limit of the supply fuses and thyristor. Every 2-3 months we have to replace the lot. Occasionally the supply cable melts and that gets changed as well.... Oh and the cab door is fully open as to keep temp down
Madness but cheaper than upgrading the whole system.......
Madness but cheaper than upgrading the whole system.......
OP
Knobhead
I'll bet it's not that cheap either.
OP
DurhamSparky
Yes, costs us approx 200-300 for replacement parts, (fuses we change more regular weekly)
Upgrade the system for additional capacity and improved running efficiency = £5.4million
We are upgrading in the next 12 months as part of the phase 3 improvements which will see data storage at the site increased by 40% and power increase from grid upped to silly levels.
Nedl currently pulling new 300mm Hv supply cables in directly from the sub station 15 miles away. With a secondary supply coming in from another site. That's costing £15million alone.
So until then we have to live with repairs!!! Lol
Upgrade the system for additional capacity and improved running efficiency = £5.4million
We are upgrading in the next 12 months as part of the phase 3 improvements which will see data storage at the site increased by 40% and power increase from grid upped to silly levels.
Nedl currently pulling new 300mm Hv supply cables in directly from the sub station 15 miles away. With a secondary supply coming in from another site. That's costing £15million alone.
So until then we have to live with repairs!!! Lol
OP
Knobhead
Kramer speed control
This is a somewhat bizarre method of controlling the speed of a slip-ring motor. I’ve worked on them up to 2500HP, RoB2, has I think worked on bigger drives.
View attachment 14587
The motor starts as a normal motor using the liquid starter. Contactors 1 and 3 close and the motor runs up to speed using the liquid starter. Once at full speed the shorting contactor 2 closes.
The motor can then work like this or the speed can be controlled. For speed control contactor 4 closes and the inverter synchronises to the transformer. Contactor 2 and 3 then open, all the current from the slip-rings is then fed via the inverter and transformer to the incoming supply. Slowing the speed raises the ring voltage at the same time reducing the current. Reducing the current allows the slip of the motor to increase thus slowing it. This excess power feeds back in to the supply. I’ve watched one of the 2500HP (1865KW) feeding back up to 750KW in to the system.
The transformer has a six phase primary Star and Delta with a delta secondary DSd.
These are now superceded by MV VSD’s. these come with their own headaches such as 11KV water cooled inverters.
View attachment 14588View attachment 14589
This fuse was out of a Kramer drive. It near gave me heart failure when it blew, but the drive just carried on as if nothing had happened!
This is a somewhat bizarre method of controlling the speed of a slip-ring motor. I’ve worked on them up to 2500HP, RoB2, has I think worked on bigger drives.
View attachment 14587
The motor starts as a normal motor using the liquid starter. Contactors 1 and 3 close and the motor runs up to speed using the liquid starter. Once at full speed the shorting contactor 2 closes.
The motor can then work like this or the speed can be controlled. For speed control contactor 4 closes and the inverter synchronises to the transformer. Contactor 2 and 3 then open, all the current from the slip-rings is then fed via the inverter and transformer to the incoming supply. Slowing the speed raises the ring voltage at the same time reducing the current. Reducing the current allows the slip of the motor to increase thus slowing it. This excess power feeds back in to the supply. I’ve watched one of the 2500HP (1865KW) feeding back up to 750KW in to the system.
The transformer has a six phase primary Star and Delta with a delta secondary DSd.
These are now superceded by MV VSD’s. these come with their own headaches such as 11KV water cooled inverters.
View attachment 14588View attachment 14589
This fuse was out of a Kramer drive. It near gave me heart failure when it blew, but the drive just carried on as if nothing had happened!
Last edited by a moderator:
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What is it called IR testing?That seems a really annoying long time for most test! Maybe if it only applied above 500V it...
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Unreasonably high invoice bill from an electricianI would think that most employers now have to think about the lone working risks and address...
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