single phasing preventer

Thread Starter


Joined Feb 22, 2012
hi all , i am doing final project now , and m title is single phasing preventer , below is about my project.

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.This circuitis meant for the 3 phase 1kW induction motor.

i have found a circuit , this circuit i can use for my project? here is the link

i try to connect it in multisim but i cant complete it , anyone can help me connect the circuit in multisim and sent it to me?
or anyone have another circuit which is suitable for my title
This is prolly considered "transformerless power supplies" and thus not allowed on this forum.

Either way i'd do it with three small transformers in star configuration with the center tap of the star connected to neutral, then feed the low voltage (5-12v) from each transformer to a triple input AND gate which when satisfied will close a NO contact in the control circuit, thus allowing the motor contactor to pull.

An example:
When tripped:
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Thread Starter


Joined Feb 22, 2012
thank you for the circuit.
can i have the link discuss about this circuit , because i need to know the working principle about this circuit and is this call single phasing preventer?
My circuit will disconnect if either of the three phases drops out, i have never built this and i do not recommend using DIY circuits in industrial applications.

It works by using a triple input AND gate which as the name suggest need all tree inputs active(high) to give a active signal out. This signal can control a relay which you put inline with the power supply that produces the power that controls the motor contactor coil, beeing either 12v, 24v or 120-230v mains. If a phase drops out, the AND gate will detect this and shut off its output, and thus release the main motor contactor, preventing the motor from single phasing and burning out.

If this is for use in your own home, then you may build such circuit yourself, provided that you have the knowlege and training in electrical safety.

But if it is for a industrial application thats designed to run 24/7-365 for decades such as a conveyor belt or pump in a factory, then i'd advice you to buy a professionally made motor protector from a electrical supplies store and have a licensed electrician install it.
You dont need them, some sim proggies come with a 3phase signal source, for those that don't, just use three single phase ones and phase shift them 120degrees from each other.