Phase sinc for 3 phase loads

Dave S

Member
Location
Grand island, NE
I have three 3 phase loads, two liquid pumps and one heatpump, that are all fed from a utility source backed up by an emergencygenerator via automatic transfer switch. The issue is the heat pump has ascroll compressor and is not in phase sinc to operate properly in bothconditions. The two liquid pumps have correct rotation through both utilitypower and generator cycles. If I were to sinc the phases for the heat pump will the rotationchange at the liquid pumps? Note they are controlled by a VFD without bypass.
dave

 

Smart $

Esteemed Member
Location
Ohio
If your liquid pump motors have proper rotation, I fail to see why the heat pump motor compressor has any problem. The rotation should be the same.

And if you are talking about synchronizing the voltage phase angle of a generator to a utility, you can't during a utility outage.

PS: Welcome to the forum... :thumbsup:
 

Dave S

Member
Location
Grand island, NE
I have three 3 phase loads, two liquid pumps and one heatpump, that are all fed from a utility source backed up by an emergencygenerator via automatic transfer switch. The issue is the heat pump has ascroll compressor and is not in phase sinc to operate properly in bothconditions. The two liquid pumps have correct rotation through both utilitypower and generator cycles. If I were to sinc the phases for the heat pump will the rotationchange at the liquid pumps? Note they are controlled by a VFD without bypass.
dave
They are all in proper rotation under utility power, however when the generator takes over the heat pump is not. My question is when I change the generator feed (swap 2 leads) can I expect the VFD to keep the liquid pumps in proper rotation?
 

don_resqcapt19

Moderator
Staff member
Location
Illinois
They are all in proper rotation under utility power, however when the generator takes over the heat pump is not. My question is when I change the generator feed (swap 2 leads) can I expect the VFD to keep the liquid pumps in proper rotation?
Yes, you can expect the motors on the VFDs will have the correct rotation after you swap the generator leads. After you swap the generator leads, that rotation will match that of the utility.
 

Smart $

Esteemed Member
Location
Ohio
Yes, you can expect the motors on the VFDs will have the correct rotation after you swap the generator leads. After you swap the generator leads, that rotation will match that of the utility.
I agree, but I'll state it another way.

The generator is connected with reversed phase rotation compared to utility as I see it. You need to swap one end of two line conductors on the generator side of the ATS.

If the VFD motor controllers maintain rotation as connected now, they should maintain the same rotation after altering the generator connections, but I suggest verifying it with the motors disconnected from the pumps first.
 

Dave S

Member
Location
Grand island, NE
Thank, I educated this old brain and now have a better understanding of the DC isolation between the line and load on the VFD and can understand how the output should remain unchanged phase wise. Today I will swap the generator output legs, restart the liquid pumps and see the results.
 

Besoeker

Senior Member
Location
UK
Thank, I educated this old brain and now have a better understanding of the DC isolation between the line and load on the VFD and can understand how the output should remain unchanged phase wise. Today I will swap the generator output legs, restart the liquid pumps and see the results.
Standard VFDs simply rectify, that is produce DC from the incoming AC using a plain (uncontrolled) rectifier. B6U is how we would designate it. It is not phase sensitive.
 

Jraef

Moderator
Staff member
Location
San Francisco Bay Area, CA, USA
Occupation
Electrical Engineer
Standard VFDs simply rectify, that is produce DC from the incoming AC using a plain (uncontrolled) rectifier. B6U is how we would designate it. It is not phase sensitive.
Correct. The incoming voltage is just a "raw material" for the rectifier from which it makes DC.

The output of the VFD is "manufactured" by the VFD transistors from that DC source and made to LOOK LIKE it is AC to the motor, based on what the microprocessor tells them to do. So if the VFD is programmed to put out A-B-C, that's what it does until told to do otherwise. There is no relationship to the input phase sequence, or even the number of phases for that matter.
 
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