lighting system along frequently used roadway 100 lamps, 277 volts to ground, distributed eveny along the 3 phases ,480 volt 1:1 lighting transformer, photocell swithces contactor on at night .Should contactor be on primary side of transformer or secondary side leaving transformer on and idle all the time?. I have mostly seen the contactor on the secondary side
which is correct design?
- Thread starter a.bisnath
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LarryFine
Master Electrician Electric Contractor Richmond VA
- Location
- Henrico County, VA
- Occupation
- Electrical Contractor
The transformer might be hard on the contacts, but a 1:1 transformer means (pracitcally) the same current.
Logically, as you mentioned, it's silly to leave the transformer idling, but that does help keep it dry.
Logically, as you mentioned, it's silly to leave the transformer idling, but that does help keep it dry.
jamesweinn
New member
clarification
clarification
In a lighting distribution design ,do you put the power switching contactor on the primary side of the transformer or do you put it on the secondary side leaving the lighting transformer on at all times what is the reccommeded practice?
clarification
In a lighting distribution design ,do you put the power switching contactor on the primary side of the transformer or do you put it on the secondary side leaving the lighting transformer on at all times what is the reccommeded practice?
broadgage
Senior Member
- Location
- London, England
Either would work.
Switching the primary would be more efficient since it would eliminate the iron losses in the transformer, which would otherwise be paid for when the lights or not lit.
The drawback is that the contactor will have to handle the inrush current of the transformer which may require the use of a larger or better qaulity contactor.
Before deciding to switch the primary, make very certain that the customer does not expect to use power from the transformer secondary for any other purpose, such as 24/7 lighting, security cameras, illuminated signs etc.
Switching the secondary side does have the advantage of keeping the transformer warm, and therefore dry, as posted above.
I doubt however that damp would be a problem if the unit is energised every night.
Switching the primary would be more efficient since it would eliminate the iron losses in the transformer, which would otherwise be paid for when the lights or not lit.
The drawback is that the contactor will have to handle the inrush current of the transformer which may require the use of a larger or better qaulity contactor.
Before deciding to switch the primary, make very certain that the customer does not expect to use power from the transformer secondary for any other purpose, such as 24/7 lighting, security cameras, illuminated signs etc.
Switching the secondary side does have the advantage of keeping the transformer warm, and therefore dry, as posted above.
I doubt however that damp would be a problem if the unit is energised every night.
RETRAINDAILY
Senior Member
- Location
- PHX, arizona
are you are using 277v photocell and contractor ? or 480v
Ken9876
Senior Member
- Location
- Jersey Shore
What is the reason for the 1:1 transformer?
broadgage
Senior Member
- Location
- London, England
I would suspect a 480 volt 3 phase 3 wire supply without neutral, therefore not able to supply 277 volt ballasts.
Use of a suitable transformer would allow the provision of a grounded neutral.
1:1 transformer/reply
1:1 transformer/reply
a 1:1 transformer or isolation transformer is one where the turns ratio of primary to secondary windings is unity ,it is used in lighting distribution designs where the graph of a earth current fault is very sharp,if sensed by the substation's main breaker's protective relays will trip and everything will go down,to avoid this the isolation transformer is used as the current pull reflected back to the windings will cause only those sub-circuit breakers to be affected for those of us in the field ,many times if a supply leg goes to ground ,like a motor leg ,the fault is so sudden that the line and load protection for the motor may not trip but the substation's main breaker may trip.As this lighting design use 277 volt to earth on their ballasts the isolation transformer is used,good discrimination design will also be required
a 110volt contactor and photocell is to be used with 480v to110v control transformer, delta to star with grounded neutral transformer is to be used
1:1 transformer/reply
a 1:1 transformer or isolation transformer is one where the turns ratio of primary to secondary windings is unity ,it is used in lighting distribution designs where the graph of a earth current fault is very sharp,if sensed by the substation's main breaker's protective relays will trip and everything will go down,to avoid this the isolation transformer is used as the current pull reflected back to the windings will cause only those sub-circuit breakers to be affected for those of us in the field ,many times if a supply leg goes to ground ,like a motor leg ,the fault is so sudden that the line and load protection for the motor may not trip but the substation's main breaker may trip.As this lighting design use 277 volt to earth on their ballasts the isolation transformer is used,good discrimination design will also be required
a 110volt contactor and photocell is to be used with 480v to110v control transformer, delta to star with grounded neutral transformer is to be used
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