Motor Starting Current graph analysis
Motor Starting Current graph analysis
(OP)
Hi all,
I saw the subject on contactors come up again.
http://rapidshare.de/files/1496465/hb.pdf.html
Please download the above.
Page 3 of attachment (hb.pdf) shows wye delta starting of a 40HP/200V motor using 208V/60Hz/3Phase power supply.
Scale is 250A / div. (A) and 50ms/div (horizontal) Page 3 shows no problem during start.
Now please look at page 2
In this case, heavy arcing occurred. On delta connection the graph on page 2 shows how the current was interrupted during 2 cycles. I am not sure to attribute this to bouncing of the contactor or to a voltage drop in the power supply affecting the contactor magnetic coils capacity to hold.
Page 1 shows line to line voltage (V is 300V peak) and current under heavy arcing condition.
My thinking is that the surge of current(transient current) results in a large voltage drop in the voltage supply line. This drop in voltage results in contactor coil magnetic field weakening and causes delta contacts to break at high current causing the large arc. When delta is disconnected, supply voltage recovers and contactor closes once again.
Can you provide me with advice on my reasoning?
My main question is the time scale. Can all of the above happen within such a short time span of 2 cycles?
Thank you!!
I saw the subject on contactors come up again.
http://rapidshare.de/files/1496465/hb.pdf.html
Please download the above.
Page 3 of attachment (hb.pdf) shows wye delta starting of a 40HP/200V motor using 208V/60Hz/3Phase power supply.
Scale is 250A / div. (A) and 50ms/div (horizontal) Page 3 shows no problem during start.
Now please look at page 2
In this case, heavy arcing occurred. On delta connection the graph on page 2 shows how the current was interrupted during 2 cycles. I am not sure to attribute this to bouncing of the contactor or to a voltage drop in the power supply affecting the contactor magnetic coils capacity to hold.
Page 1 shows line to line voltage (V is 300V peak) and current under heavy arcing condition.
My thinking is that the surge of current(transient current) results in a large voltage drop in the voltage supply line. This drop in voltage results in contactor coil magnetic field weakening and causes delta contacts to break at high current causing the large arc. When delta is disconnected, supply voltage recovers and contactor closes once again.
Can you provide me with advice on my reasoning?
My main question is the time scale. Can all of the above happen within such a short time span of 2 cycles?
Thank you!!





RE: Motor Starting Current graph analysis
Reminds me of something I saw once.. probably not related to what you saw but here it is...
We instrumented switchgear for a 13.8kv motor prior to starting. When we reviewed the traces afterwards we saw several very steep-sloped blips of current over about a 2 cycle period before we saw the normal pattern we expected. We thought we were looking at some weird contact bounce. But it didn't make sense that the actual current could change that quickly in an inductive motor circuit, even if the contacts did bounce. Further investigation showed that the instrumentation was picking up false readings due to switching of relay coils within the breaker prior to closure.
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RE: Motor Starting Current graph analysis
Is this still the same problem you posted back in September thread237-104589 ? You also have posted several other issues with 40HP Y-D elevator motor starters. I found them when searching for some of the many threads to direct you to in this forum that have dealt with this issue. You seem to have a recurring problem with this. If this is a different application with similar problems, you may have a bigger issue to contend with, i.e. supply problems or transformer sizing issues. That would be especially suspicious if it is happening on the same phase each time. If it is the same elevator and you upgraded to 50HP but the problem didn't go away, I would suggest that you check into a solid state starter and be done with it.
"Venditori de oleum-vipera non vigere excordis populi"
RE: Motor Starting Current graph analysis
"Venditori de oleum-vipera non vigere excordis populi"
RE: Motor Starting Current graph analysis
RE: Motor Starting Current graph analysis
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