Soft Start Contactor

[Shaneyj]

I'm using a weg ssw-07 soft start. The manual recommends either isolation contactor or circuit breaker with undervoltage release to "protect" motor in case thyristors short or some other condition that keeps motor running.
I dont think the primary language of the manuals author is English because there seems to be a few imcomplete or less than clear descriptions and phrases.
Anyway, in the context it's used, "protect" seems to mean the ability for the motor to be shut down.
Is there merit to using a contactor other than a method to control power input to the soft start. If the only reason is to be able to drop out power, can a shunt trip breaker be used in its place?
I'll be making an inquiry to the mfg, but your input is appreciated.
FWIW, 300 hp motor operating a pump drive pad operating 3 open loop hydraulic pumps.


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[ptonsparky]

I just worked on a 100 hp that used a shunt trip breaker for overcurrent via the SS control.
Seems logical that you could certainly get a shunt trip to work as you need.

 

[petersonra]

It seems a little hokey but I can't see any reason why you can't do what they're suggesting. I'm not real sure I would want to use an under voltage trip though. What's going to happen if you have a power failure?

 

[Shaneyj]

It seems a little hokey but I can't see any reason why you can't do what they're suggesting. I'm not real sure I would want to use an under voltage trip though. What's going to happen if you have a power failure?

A power failure would shut down anyways. I'm not sure what you're getting at.
As far as their suggestion, the contactor seems a clunky and expensive way to isolate power. I haven't yet priced a shunt trip coil for the breaker but I speculate its a fraction of the cost of a 400A contactor.
Thanks for the feedback.

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[Shaneyj]

I just worked on a 100 hp that used a shunt trip breaker for overcurrent via the SS control.
Seems logical that you could certainly get a shunt trip to work as you need.

My initial thought was to use the shunt trip as the emergency stop method, while using the SS discrete inputs as the normal start/stop operations.
When you say "via the SS control", do you mean you used SS discrete output to operate the shunt trip if overcurrent was detected?

 

[petersonra]

A power failure would shut down anyways. I'm not sure what you're getting at.

But someone would need to go reset the breaker.

 

[Shaneyj]

But someone would need to go reset the breaker.

Ahh... I see.
In my scenario using the shunt trip as an e-stop, that would be a requirement anyways.
This is a portable piece of equipment with a footprint of about 250 sq ft. - I am ok with resetting the breaker being part of the re-start process.

 

[ptonsparky]

My initial thought was to use the shunt trip as the emergency stop method, while using the SS discrete inputs as the normal start/stop operations.
When you say "via the SS control", do you mean you used SS discrete output to operate the shunt trip if overcurrent was detected?

Yes, it was a factory set up in an MCC. The SS logic detected when start up overcurrent was excessive and would trip the breaker.

 

[Jraef]

This is not about overcurrent. Soft starts use SCRs, which fail SHORTED, meaning when they fail, they CONDUCT. So if an SCR on Phase A shorts and another one on phase B, power will flow to the motor and there is no way to turn it off. However the risk of it happening on two phases at the same time is small. Most people ignore that risk.

On cheaper soft starters, they save money by only putting SCRs in 2 of the 3 phases, one phase (usually the center) is just a piece of bus bar. It works, but adds a serious risk in that instead of needing to have TWO shorted SCRs in different phases, any ONE shorted SCR is now going to make the motor burn up. This makes it IMPERATIVE that the system have this protection, which generally costs MORE than the money that was saved by using fewer SCRs, but people don’t pay attention to the details.

So in the soft starter there is a detection circuit for this that sees that there is no Run command, but current is still flowing. That then triggers a fault contact to change state. It can be done with a NO contact wired to a Shunt Trip on the breaker, if there is one. Many soft starters only have an SCCR above 5kA if protected by fuses, so having to have fuses AND a breaker gets large and expensive. If you only have fuses, you do it with a NC contact to a line isolation contactor.

It technically could be done with an under voltage trip, but every time there is a power loss, someone will have to reset the breaker, not just if there is a shorted SCR. I don’t recommend that.

 

[ptonsparky]

It is not about overcurrent. It is about the SS and if you can set it’s parameters to operate the breaker on a shorted SCR. Somewhere in TFM for the SS, it may indicate if that is an option.

 

[Shaneyj]

It is not about overcurrent. It is about the SS and if you can set it’s parameters to operate the breaker on a shorted SCR. Somewhere in TFM for the SS, it may indicate if that is an option.

TFM = the manual?
I need to read the manual to see if that is an output option on a shorted SCR.
As jraef stated, if just one of the thyristors shorts, the motor will be single phasing, causing rotation to stop. I can see a case where the operator is clueless to that condition - especially in the raucous environment in which this will be used (oilfield-wellpad).

 

[Shaneyj]

This is not about overcurrent. Soft starts use SCRs, which fail SHORTED, meaning when they fail, they CONDUCT. So if an SCR on Phase A shorts and another one on phase B, power will flow to the motor and there is no way to turn it off. However the risk of it happening on two phases at the same time is small. Most people ignore that risk.

On cheaper soft starters, they save money by only putting SCRs in 2 of the 3 phases, one phase (usually the center) is just a piece of bus bar. It works, but adds a serious risk in that instead of needing to have TWO shorted SCRs in different phases, any ONE shorted SCR is now going to make the motor burn up. This makes it IMPERATIVE that the system have this protection, which generally costs MORE than the money that was saved by using fewer SCRs, but people don’t pay attention to the details.

So in the soft starter there is a detection circuit for this that sees that there is no Run command, but current is still flowing. That then triggers a fault contact to change state. It can be done with a NO contact wired to a Shunt Trip on the breaker, if there is one. Many soft starters only have an SCCR above 5kA if protected by fuses, so having to have fuses AND a breaker gets large and expensive. If you only have fuses, you do it with a NC contact to a line isolation contactor.

It technically could be done with an under voltage trip, but every time there is a power loss, someone will have to reset the breaker, not just if there is a shorted SCR. I don’t recommend that.

That just about verbatim to the manual's description of the need for an e-stop circuit.
As far as scheme, I'm using an MCCB and high speed fuses.
I've removed the contactor I initially had in place and am replacing with a shunt trip coil for the MCCB which will be responsible for the emergency stop condition- echoed in my response to ptonsparky's post, I'll check manual for the fault contact you referenced and that will parallel the e-stop circuit.
Thanks for your input!

 

[GoldDigger]

TFM = the manual?
I need to read the manual to see if that is an output option on a shorted SCR.
As jraef stated, if just one of the thyristors shorts, the motor will be single phasing, causing rotation to stop. I can see a case where the operator is clueless to that condition - especially in the raucous environment in which this will be used (oilfield-wellpad).

Specifically = The Fine Manual or the obscene version, both readings for RTFM

 

[RumRunner]

I'm using a weg ssw-07 soft start. The manual recommends either isolation contactor or circuit breaker with undervoltage release to "protect" motor in case thyristors short or some other condition that keeps motor running.
I dont think the primary language of the manuals author is English because there seems to be a few imcomplete or less than clear descriptions and phrases.
Anyway, in the context it's used, "protect" seems to mean the ability for the motor to be shut down.
Is there merit to using a contactor other than a method to control power input to the soft start. If the only reason is to be able to drop out power, can a shunt trip breaker be used in its place?
I'll be making an inquiry to the mfg, but your input is appreciated.
FWIW, 300 hp motor operating a pump drive pad operating 3 open loop hydraulic pumps.
Sent from my SM-G965U using Tapatalk

The primary purpose of the SHUNT BREAKER is to interrupt power in case of emergency caused by smoke or fire. Although it will also function as a regular circuit breaker. The addition of remotely controlled shunt (to open) the circuit became de-facto standard for modern elevators.
Designers included this feature in their designs lately. . . which in your case –pump control application.
That statement in bold text in your post is the operative phrase.
The designer RECOMMENDS either isolating contactor or SHUNT TRIP BREAKER along with soft starter.
At the onset of soft starter (AKA electronic motor starter) in the 70s, industrial managers welcomed the idea. Not only for money saving but smooth starts without the jarring effect brought on -- and mostly reduced sudden surge of power demand during start.

AHJs got into action requiring industries to have physical disconnects when maintenance is being performed on equipment.
Electronic motor starters or soft starters don’t break the power to the equipment. . . rather, they only switch to NULL ( or lowered state) when command to stop is given.

These are done by the wonders solid state.
This was where AHJs and OSHA were leery about.

Maintenance mechanics, untrained electricians and operators may think that power is off because there is no motion.. . . when in fact there is power to the equipment , but not enough to drive it.
Given this scenario—safety authorities scramble to come up with safety regulation to safeguard workers.
The City of Los Angeles-- being one of the early adopters of VFD and Soft Starters in the industry—included in their municipal ordinance to include PHYSICAL DISCONNECT, CONTACTORS and SHUNT TRIP CIRCUIT BREAKERS.
Contactors are the cheapest approach (outside of primitive drum switches) to comply with the mandate—but, unlike shunt trip breakers, they don’t monitor the condition downstream.
You made a good choice in deciding to use the SHUNT TRIP BREAKER vs CONTACTOR.
As a moral responsibility. . . you’ve got to have one or the other if you want to save your career if the unexpected happens. . . being the engineer.
In the case of elevator control-- the shunt circuit breaker receives a signal from a smoke detector to interrupt power to--quell the possibility of expensive electronics getting damage when fire sprinklers get activated. False alarms are an ever-present curse.
The designers have all these figured out and not simply giving you the choice of different options--as others are trying to make you believe.

...........

BTW:

Keep us updated if you’re able to contact the manufacturers’ rep . . if it’s not asking too much.

 

[petersonra]

The primary purpose of the SHUNT BREAKER is to interrupt power in case of emergency caused by smoke or fire. Although it will also function as a regular circuit breaker. The addition of remotely controlled shunt (to open) the circuit became de-facto standard for modern elevators.
Designers included this feature in their designs lately. . . which in your case –pump control application.
That statement in bold text in your post is the operative phrase.
The designer RECOMMENDS either isolating contactor or SHUNT TRIP BREAKER along with soft starter.
At the onset of soft starter (AKA electronic motor starter) in the 70s, industrial managers welcomed the idea. Not only for money saving but smooth starts without the jarring effect brought on -- and mostly reduced sudden surge of power demand during start.

AHJs got into action requiring industries to have physical disconnects when maintenance is being performed on equipment.
Electronic motor starters or soft starters don’t break the power to the equipment. . . rather, they only switch to NULL ( or lowered state) when command to stop is given.

These are done by the wonders solid state.
This was where AHJs and OSHA were leery about.

Maintenance mechanics, untrained electricians and operators may think that power is off because there is no motion.. . . when in fact there is power to the equipment , but not enough to drive it.
Given this scenario—safety authorities scramble to come up with safety regulation to safeguard workers.
The City of Los Angeles-- being one of the early adopters of VFD and Soft Starters in the industry—included in their municipal ordinance to include PHYSICAL DISCONNECT, CONTACTORS and SHUNT TRIP CIRCUIT BREAKERS.
Contactors are the cheapest approach (outside of primitive drum switches) to comply with the mandate—but, unlike shunt trip breakers, they don’t monitor the condition downstream.
You made a good choice in deciding to use the SHUNT TRIP BREAKER vs CONTACTOR.
As a moral responsibility. . . you’ve got to have one or the other if you want to save your career if the unexpected happens. . . being the engineer.
In the case of elevator control-- the shunt circuit breaker receives a signal from a smoke detector to interrupt power to--quell the possibility of expensive electronics getting damage when fire sprinklers get activated. False alarms are an ever-present curse.
The designers have all these figured out and not simply giving you the choice of different options--as others are trying to make you believe.

...........

Both VFDs and soft starters have power on the output to some degree when the device is "off". It just can't develop torque to turn the motor.

Having a contactor on a soft starter is a perfectly safe way to make sure it shuts off if a semiconductor fails. So is a shunt trip breaker.

Here is a typical suggestion from a Square D soft start manual on how this should be handled. Note that the contactor is in front of the starter and is separately controlled. The contactor is also turned off by the starter if it detects a fault. This way you can start and stop the motor using the control input on the starter (in this case represented by the motor run selector switch.

 

[Shaneyj]

The primary purpose of the SHUNT BREAKER is to interrupt power in case of emergency caused by smoke or fire. Although it will also function as a regular circuit breaker. The addition of remotely controlled shunt (to open) the circuit became de-facto standard for modern elevators.
Designers included this feature in their designs lately. . . which in your case –pump control application.
That statement in bold text in your post is the operative phrase.
The designer RECOMMENDS either isolating contactor or SHUNT TRIP BREAKER along with soft starter.
At the onset of soft starter (AKA electronic motor starter) in the 70s, industrial managers welcomed the idea. Not only for money saving but smooth starts without the jarring effect brought on -- and mostly reduced sudden surge of power demand during start.

AHJs got into action requiring industries to have physical disconnects when maintenance is being performed on equipment.
Electronic motor starters or soft starters don’t break the power to the equipment. . . rather, they only switch to NULL ( or lowered state) when command to stop is given.

These are done by the wonders solid state.
This was where AHJs and OSHA were leery about.

Maintenance mechanics, untrained electricians and operators may think that power is off because there is no motion.. . . when in fact there is power to the equipment , but not enough to drive it.
Given this scenario—safety authorities scramble to come up with safety regulation to safeguard workers.
The City of Los Angeles-- being one of the early adopters of VFD and Soft Starters in the industry—included in their municipal ordinance to include PHYSICAL DISCONNECT, CONTACTORS and SHUNT TRIP CIRCUIT BREAKERS.
Contactors are the cheapest approach (outside of primitive drum switches) to comply with the mandate—but, unlike shunt trip breakers, they don’t monitor the condition downstream.
You made a good choice in deciding to use the SHUNT TRIP BREAKER vs CONTACTOR.
As a moral responsibility. . . you’ve got to have one or the other if you want to save your career if the unexpected happens. . . being the engineer.
In the case of elevator control-- the shunt circuit breaker receives a signal from a smoke detector to interrupt power to--quell the possibility of expensive electronics getting damage when fire sprinklers get activated. False alarms are an ever-present curse.
The designers have all these figured out and not simply giving you the choice of different options--as others are trying to make you believe.

...........

BTW:

Keep us updated if you’re able to contact the manufacturers’ rep . . if it’s not asking too much.

Thanks for your feedback.
I spoke with Weg today and they have a relay function that will close its contacts on any fault condition (phase loss, overcurrent, undervoltage and more) - I am going to use that in parallel with my e-stop buttons.

 

[Shaneyj]

Both VFDs and soft starters have power on the output to some degree when the device is "off". It just can't develop torque to turn the motor.

Having a contactor on a soft starter is a perfectly safe way to make sure it shuts off if a semiconductor fails. So is a shunt trip breaker.

Here is a typical suggestion from a Square D soft start manual on how this should be handled. Note that the contactor is in front of the starter and is separately controlled. The contactor is also turned off by the starter if it detects a fault. This way you can start and stop the motor using the control input on the starter (in this case represented by the motor run selector switch.

View attachment 2558348

Good input... typically a contactor is what I would use just because I have plenty of experience with them. This is my first soft starter, hence the uncertainty.
In this case the contactor is (obviously) larger than a shunt trip coil and more expensive. Space claim is always a fight, and less cost is always desirable.