Voltage drop caused by motor starting
Voltage drop caused by motor starting
(OP)
Hello,
Is there any standard or practical recommendation to limit the magnitude and duration of a voltage drop caused by a motor starting?
We have done some analysis and the voltage drop is 12%, however, our customer says it is not significative if not forbiden by a standard.
So we have explained some effects on motors, the limits given by IEEE Emerald book and so on, however, we are looking for something more "specific"
I thank you in advance
Is there any standard or practical recommendation to limit the magnitude and duration of a voltage drop caused by a motor starting?
We have done some analysis and the voltage drop is 12%, however, our customer says it is not significative if not forbiden by a standard.
So we have explained some effects on motors, the limits given by IEEE Emerald book and so on, however, we are looking for something more "specific"
I thank you in advance






RE: Voltage drop caused by motor starting
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If we learn from our mistakes I'm getting a great education!
RE: Voltage drop caused by motor starting
As for running motors on the same bus, again it is the actual voltage that is the main concern, not the % drop.
If you are concerned with voltage dip and flicker imposed on other utility customers or others, then there are different concerns.
You also have to consider how often the motor will be started.
For a typical industrial facility, I would not be too concerned about a temporary dip of 12% for infrequent starting of a large motor.
RE: Voltage drop caused by motor starting
I thank your answers.
My concern is related to the effect on the motors and other equipments.
11% is on the busbar but, at motor terminals it is higher, besides the starting time is around 15 s, because it is a full voltage starting (100% of nominal voltage).
During these 15 s, all the other motors and loads connected on the MCC's will experience a voltage drop (sag) that may affect them.
This is our concern!
Related to the starting frequency, at least once per day!
Best regards
RE: Voltage drop caused by motor starting
RE: Voltage drop caused by motor starting
Some plants may have loads that are particularly sensitive to voltage droop. Perhaps contactors/relays may drop out or electronics may respond unexpectedly. Depends what those other loads are and whether sensitive loads have voltage regulating supply tranformer.
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(2B)+(2B)' ?
RE: Voltage drop caused by motor starting
For instance IEC 60034-1:
"A machine shall be capable of performing its primary function, as specified in Table 3,
continuously within zone A, but need not comply fully with its performance at rated voltage
and frequency (see rating point in Figures 11 and 12), and may exhibit some deviations".
Table 3 primary function for a.c. motor=rated torque[Nm]
Zone A [granted performances] frequency minimum=0.96 voltage minimum 0.95 from rated
Zone B [temporary admitted]] frequency minimum=0.95 voltage minimum 0.90 from rated
As a designer I should not dare to take more than 10% temporary deviation from rated motor voltage at any running motor terminals
[when any other motor will start].
If Utility will supply %5 less ,sometime, you'll get 15% temporarily.
But I saw 15% drop [at a running motor terminals from the beginning temporarily]-and all was o.k.
RE: Voltage drop caused by motor starting
I believe you may have an ally in your power utility (assuming you have one and are not generating on-site). Here in the US, Utility regulations, generally in the form of local Public Utility Commissions, call for THEM to deliver power +-5% to their customers. So if you are causing a sag that shows up as 5.1% at the NEXT DOOR NEIGHBOR's facility, the utility may / will force you, in the form of penalties, to limit your starting power draw. I would call them and elicit their help, I'm sure they can come up with a convincing argument, like a gun to his head...
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