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https://www.askthetrades.co.uk/cgi-bin/yabb/YaBB.pl DIY Forum >> Electrical Questions >> single phasing preventer https://www.askthetrades.co.uk/cgi-bin/yabb/YaBB.pl?num=1326516929 Message started by sinser11 on Jan 14^th, 2012, 4:55am

Title: single phasing preventer
Post by sinser11 on Jan 14^th, 2012, 4:55am

i have a project title is single phasing preventer

abstract:
three-phase motors and other appliances are widely used in all sectors of industry. These appliances are prone to damage to single phasing. Apart from damage the costly apparatus, it may also cause a production loss. The objective of this project is to design a single phase preventer to be used in lab. This circuit is meant for the 3 phase 1KW induction motor.

actually i found a circuit, anyone can tell me this circuit can i use for the project? what should i change in this circuit?

Title: Re: single phasing preventer
Post by Lectrician on Jan 14^th, 2012, 10:30am

That would certainly work, although a cheaper and easier way would be to simply have three replays connected one to each phase, placing the relay contacts in series, and in turn switching a triple pole contactor on for the load.

Title: Re: single phasing preventer
Post by The_Trician on Jan 15^th, 2012, 9:53pm

I don't get how the electronics are supposed to help on this one.

A relay set-up is the easiest and cheapest way.

TT

Title: Re: single phasing preventer
Post by Lectrician on Jan 16^th, 2012, 6:30am

The_Trician wrote on Jan 15^th, 2012, 9:53pm:

I don't get how the electronics are supposed to help on this one.

A relay set-up is the easiest and cheapest way.

TT

I believe the electronics will also be able to detect not onlt the loss of a phase, but also if two phases where from the same phase, or all phases from the same phase. The three transformers would produce a certain voltage if all on seperate phases, but would produce less if all on the same.

Title: Re: single phasing preventer
Post by wozzer on Dec 4^th, 2012, 1:01pm

Probably easier to use a phase imbalance detection relay e.g.
http://www.hobut.co.uk/protection-relays/phase-balance-protection-relay

Your circuit will work, with reservations, there may be sufficient regeneration in an inductive load which may render the detection of a phase loss doubtful using voltage alone - It would be better to monitor the phase currents instead (as commercial units mostly do).
In your circuit, putting the outputs from the three Transformers in series like that should give a resultant of zero with 3 balanced phases. i.e. 3 phases @ 120 degrees apart. If a phase is lost, then there should be (if regeneration does not take place) a resultant voltage at the AC terminals of the bridge rectifier. The 220Uf cap will smooth the DC and give a very small delay. The diode is purely back-emf protection. For a longer delay in operation increase the capacitor to say 1000Uf

Taking into account the cost of the transformers, a relay would probably be a viable option. But, if it is for a lab project, and you have to build it yourself, then go ahead and try it!