need help rotophase
- Thread starter kc7uno
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- Lockport, IL
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- Retired Electrical Engineer
Re: need help rotophase
I?m not sure what a ?roto-phase? would be. But if it involves a large bank of capacitors, and if by ?compromised? you mean that some number of the capacitors have failed, then that could indeed cause a current imbalance. This would be especially true if the failed capacitors affect only one or two phases, and not all three. Can you be more specific with your question?
I?m not sure what a ?roto-phase? would be. But if it involves a large bank of capacitors, and if by ?compromised? you mean that some number of the capacitors have failed, then that could indeed cause a current imbalance. This would be especially true if the failed capacitors affect only one or two phases, and not all three. Can you be more specific with your question?
- Location
- Illinois
- Occupation
- retired electrician
Re: need help rotophase
A "rotophase" is a static phase converter, and problems with the capacitors will create create?current balance problems. Even using the wrong number of capacitors causes problems. The number of capacitors has to be matched to the load.
Don
A "rotophase" is a static phase converter, and problems with the capacitors will create create?current balance problems. Even using the wrong number of capacitors causes problems. The number of capacitors has to be matched to the load.
Don
Re: need help rotophase
Here is the scenario for the "Roto-Phase" Add-a-Phase, Phase converter. I recently troubleshot a client's call for help involving their roto phase which let the magic smoke out. The old one was not happy and a replacement was installed, however this replacement was a re-built phase converter which was in a clean condition, owned by the client, but had been sitting for 15 years without operating. In my experience capacitors do not like to sit that long without being energized. The phase convertor had been wrapped in plastic and protected. It was located in a farm shed but not totally protected from moisture, condensation etc.
To continue, the replacement unit was installed and I advised the customer he should be aware there could be a failure of the capacitor bank. A couple of days goes by and then I get a call. A motor fed by this phase convertor began tripping the overloads on its controller.
I checked the amperage draw of the motor and found the following Tested from the load side of the motor controller : 240v 3 phase, abotu 1 hp motor runnign hydraulinc fluid pump T1- 4.8 amps , T-2 12.6, T-3- 10.8 amps. The overloads kept tripping and had to be reset.
To rule out this motor , I went to another motor (different circuit) and tested it underload. The results were the same imbalance as the other motor. I did not think it was the motor.
I advised the client the only variable that had been changed in the whole conveyor system was the add-a-phase and recommended replacement of the add-a- phase most recently installed.
A couple of days went by and I called the customer as a follow up and he had advised me he had called another electrician and had them check it out. This electrician said he did not think it was the add-a-pause and thought it was the overloads of the motor. I did not agree with this as the rule out factor of testing the second motor with the same imbalance leads me to beilieve the add-a-phase is the guilty party.
This electrician attempted to increase the setting of the overloads with no success. I still think because of the currrent inmbalance the overloads are tripping.
I guess the question arises , how is the current unbalanced as it feeds the motor through the phase converter if the capacitor bank has failed.
If you would like to discusss this via telelphone please give me a call, Thank you for your replies. Dan
{Moderator's Note: Edited to remove personal contact information. If you wish to contact this person, please send a Private Message.}
[ June 27, 2005, 10:02 AM: Message edited by: charlie b ]
Here is the scenario for the "Roto-Phase" Add-a-Phase, Phase converter. I recently troubleshot a client's call for help involving their roto phase which let the magic smoke out. The old one was not happy and a replacement was installed, however this replacement was a re-built phase converter which was in a clean condition, owned by the client, but had been sitting for 15 years without operating. In my experience capacitors do not like to sit that long without being energized. The phase convertor had been wrapped in plastic and protected. It was located in a farm shed but not totally protected from moisture, condensation etc.
To continue, the replacement unit was installed and I advised the customer he should be aware there could be a failure of the capacitor bank. A couple of days goes by and then I get a call. A motor fed by this phase convertor began tripping the overloads on its controller.
I checked the amperage draw of the motor and found the following Tested from the load side of the motor controller : 240v 3 phase, abotu 1 hp motor runnign hydraulinc fluid pump T1- 4.8 amps , T-2 12.6, T-3- 10.8 amps. The overloads kept tripping and had to be reset.
To rule out this motor , I went to another motor (different circuit) and tested it underload. The results were the same imbalance as the other motor. I did not think it was the motor.
I advised the client the only variable that had been changed in the whole conveyor system was the add-a-phase and recommended replacement of the add-a- phase most recently installed.
A couple of days went by and I called the customer as a follow up and he had advised me he had called another electrician and had them check it out. This electrician said he did not think it was the add-a-pause and thought it was the overloads of the motor. I did not agree with this as the rule out factor of testing the second motor with the same imbalance leads me to beilieve the add-a-phase is the guilty party.
This electrician attempted to increase the setting of the overloads with no success. I still think because of the currrent inmbalance the overloads are tripping.
I guess the question arises , how is the current unbalanced as it feeds the motor through the phase converter if the capacitor bank has failed.
If you would like to discusss this via telelphone please give me a call, Thank you for your replies. Dan
{Moderator's Note: Edited to remove personal contact information. If you wish to contact this person, please send a Private Message.}
[ June 27, 2005, 10:02 AM: Message edited by: charlie b ]
Re: need help rotophase
I agree the phase converter is the most likely problem. The motor that is tripping may be more nearly loaded to its limit than the others or it may be damaged already.
My one static phase converter installation is a success so far (4 years seasonal use). it is on a centrifugal pump so restriction of the flow drops the load which is good because the amperages are very unbalanced even with a good capacitor.
The one you describe must run several motors. There is a beneficial rotary transformer effect of operating a large 3 phase motor on synthesizing the 3 phase. Sometimes an "idler" motor is started first and the largest motor should always be started first anyway. The client may have stopped running some large lightly loaded motor that has been helping things.
This converter uses the capacitors to shift the phase of the single phase source but I don't think it can shift it more than 90 degrees when it needs to be shifted 120 degrees to be balanced 3 phase. If the capacitance is not up to spec, it won't do a good job of the shift it is capable of producing.
I would examine the capacitor bank for bad connections and check each one for shorts and open circuit at least. Maybe they are a value which can be checked with a commonly available meter. Mine only goes to 200 mfd, so I can't check the larger start capacitors, but can do most of the common run capacitors.
The capacitor bank could also be connected improperly. series connections do not add capacitance, only voltage rating. parallel connections add capacitance, but do not change voltage rating.
good luck,
Jim
I agree the phase converter is the most likely problem. The motor that is tripping may be more nearly loaded to its limit than the others or it may be damaged already.
My one static phase converter installation is a success so far (4 years seasonal use). it is on a centrifugal pump so restriction of the flow drops the load which is good because the amperages are very unbalanced even with a good capacitor.
The one you describe must run several motors. There is a beneficial rotary transformer effect of operating a large 3 phase motor on synthesizing the 3 phase. Sometimes an "idler" motor is started first and the largest motor should always be started first anyway. The client may have stopped running some large lightly loaded motor that has been helping things.
This converter uses the capacitors to shift the phase of the single phase source but I don't think it can shift it more than 90 degrees when it needs to be shifted 120 degrees to be balanced 3 phase. If the capacitance is not up to spec, it won't do a good job of the shift it is capable of producing.
I would examine the capacitor bank for bad connections and check each one for shorts and open circuit at least. Maybe they are a value which can be checked with a commonly available meter. Mine only goes to 200 mfd, so I can't check the larger start capacitors, but can do most of the common run capacitors.
The capacitor bank could also be connected improperly. series connections do not add capacitance, only voltage rating. parallel connections add capacitance, but do not change voltage rating.
good luck,
Jim
Re: need help rotophase
Thank you for the replies, and to the Moderator my apologies for the gentle slap for the "personal information." I thought that was allowed, but now know not to do that
I still have not heard about the status fo what the other electrcian found. I am also looking for reference material as well, but have found ads for roto-phases but not technical information.
Thank you Jim for the comprehensive report.
Dan
[ June 28, 2005, 12:05 AM: Message edited by: kc7uno ]
Thank you for the replies, and to the Moderator my apologies for the gentle slap for the "personal information." I thought that was allowed, but now know not to do that
I still have not heard about the status fo what the other electrcian found. I am also looking for reference material as well, but have found ads for roto-phases but not technical information.
Thank you Jim for the comprehensive report.
Dan
[ June 28, 2005, 12:05 AM: Message edited by: kc7uno ]
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