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Inside delta connection on soft start


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#1 FLOW_EE

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Posted 15 August 2006 - 05:09 PM

Hello,

I have used the inside delta wiring with a certain electronic soft start for a motor (50hp) that is directly coupled to a hydraulic pump recently. This choice was prompted by obvious space saving and cost saving. I am starting to wonder now that the inside delta wiring may have been a wrong choice for the application. The hydraulic system that the motor is driving does not require very high starting torque, I was told, yet the soft start keeps faulting on startup, especially when the hydraulic fluid is cold. Our hydraulic guys told me that the system has variable starting load, sometimes higher than other, but on cold startup it is likely to have more starting load than normal.

Is the inside delta connection with a soft start only for very light or virtually no starting load? I would appreciate any advice.


Thank you.
FLOW_EE

#2 marke

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Posted 15 August 2006 - 06:53 PM

Hello FLOW_EE

Welcome to the forum.

Inside delta connection (six wire connection) of a soft starter is a valid connection provided that the soft starter is designed for this connection. Some soft starters are designed for in line connection only and can not be connected inside delta.
The motor is able to produce full torque inside delta or inline connected. The issue is not the connection, rather the capabilities of the soft starter.
The advantage of inside delta connection is that you can reduce the size of the soft starter to two thirds of the inline size. (Many quote divide by root three but this is incorrect. Root three works for a continuous sinewave, but during start, the wave form is quite different between inside delta and inline connections.)
The disadvantage of inside delta connection is the requirement for six cables to the motor rather than three and the obvious requirement for a contactor which is considered optional with inline connection.

Can you give more detail on the type of soft starter and the type of trip that you are experiencing.
I have used many soft starters connected inside delta on very high torque applications without problems.

Best regards,

#3 FLOW_EE

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Posted 15 August 2006 - 07:42 PM

Hi, marke,

I am not sure if it is cool to use the actual manufacturer name here, so I will describe the starter as follows :

It is designed to be wired for inside delta or inline connections. It only has a few adjustments available, as it is one of the less costly offerings by this manufacturer. The adjustments available are : start ramp, stop ramp, initial voltage (%) or current limiting (multiple of FLA), and the operating mode (inline or inside delta). I was using 4 second start ramp, 0 second stop ramp, 4 times the FLA current limit (this is max. setting), and inside delta mode. The unit is sized, according to the manufacturer's recommendation for 50 hp motor @ 480VAC with inside delta connection, i.e. I tried other start ramp setting with different current limit setting as well without much success.

The type of problem I am seeing are, either "internal fault" which is triggered during the ramp up before switching to the external bypass contactor, though the motor seems to spin up, or the motor itself doesn't seem to spin up right and end up with "internal fault" on the soft start. This happens often when the hydraulic system is cold. By trying to restart the motor again and again, I am able to start the motor successfully. Once it starts up, there is no further problem.

Thank you very much for any further thoughts on this would be appreciated.
FLOW_EE


QUOTE(marke @ Aug 15 2006, 11:53 AM) View Post

Hello FLOW_EE

Welcome to the forum.

Inside delta connection (six wire connection) of a soft starter is a valid connection provided that the soft starter is designed for this connection. Some soft starters are designed for in line connection only and can not be connected inside delta.
The motor is able to produce full torque inside delta or inline connected. The issue is not the connection, rather the capabilities of the soft starter.
The advantage of inside delta connection is that you can reduce the size of the soft starter to two thirds of the inline size. (Many quote divide by root three but this is incorrect. Root three works for a continuous sinewave, but during start, the wave form is quite different between inside delta and inline connections.)
The disadvantage of inside delta connection is the requirement for six cables to the motor rather than three and the obvious requirement for a contactor which is considered optional with inline connection.

Can you give more detail on the type of soft starter and the type of trip that you are experiencing.
I have used many soft starters connected inside delta on very high torque applications without problems.

Best regards,



#4 marke

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Posted 15 August 2006 - 08:41 PM

Hello FLOW_EE

Without knowing the actual device and information on it, it is difficult to surmise why it would be comming out on an internal fault, however the fact that it seems to do this when the fluid is cold and once it has started OK, it settles down, suggests to me that there is just no sufficient torque available at 400% current to start from cold. The answer is to increase the start current to say 450%. If you are not able to increase the start current higher, then you need to discuss this with the supplier and see if they can offer a higher start torque solution.
Some suppliers/manufacturers of this type of equipment seem to have lost sight of the fact that with some machines, you need to have a high start torque, and with some motors, it take a high start current to develop a high start torque. I commonly see "severe duty" soft starters rated at 400% current. With many high efficiency motors, this will only result in moderate start torque and is definitely insufficient for many loads.
If you are trying to start with too low a start torque, the motor will accelerate to part speed and then run either at that speed or with very low acceleration, or it may even begin to slow down before it trips out due to excess start time. Low torque is usually pretty obvious if you listen to the motor.

Best regards,

#5 FLOW_EE

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Posted 15 August 2006 - 08:47 PM

Thank you very much for the information, marke.

FLOW_EE


QUOTE(marke @ Aug 15 2006, 01:41 PM) View Post

Hello FLOW_EE

Without knowing the actual device and information on it, it is difficult to surmise why it would be comming out on an internal fault, however the fact that it seems to do this when the fluid is cold and once it has started OK, it settles down, suggests to me that there is just no sufficient torque available at 400% current to start from cold. The answer is to increase the start current to say 450%. If you are not able to increase the start current higher, then you need to discuss this with the supplier and see if they can offer a higher start torque solution.
Some suppliers/manufacturers of this type of equipment seem to have lost sight of the fact that with some machines, you need to have a high start torque, and with some motors, it take a high start current to develop a high start torque. I commonly see "severe duty" soft starters rated at 400% current. With many high efficiency motors, this will only result in moderate start torque and is definitely insufficient for many loads.
If you are trying to start with too low a start torque, the motor will accelerate to part speed and then run either at that speed or with very low acceleration, or it may even begin to slow down before it trips out due to excess start time. Low torque is usually pretty obvious if you listen to the motor.

Best regards,






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