Simplest Single Phase Preventor Circuit for Three Phase Motor Potection

 For a 3-phase induction motor,Lit is necessary that all the three phases of supply are present while it is on load.
When any one of the fuses goes out, or a phase is missing, the motor will continue to run with two phases only, but it will start drawing a huge current for the same load.

This high current may ruin the motor, unless switched off immediately. A single phase preventor circuit avoids such a mishap. With this circuit the motor will not run, unless all the three phases are present. In a 3-phase supply, the voltages are 120 degrees apart from each other. Thus the addition of three phases gives zero voltage. lf any one of the phase goes, voltage present at the summing point equals half the line voltage. ‘ In this circuit, the three phases (R, Y, B) are connected to line neutral, which in turn is connected to the ground of the   circuit.

When all three phases are present, voltage at point D is zero. So potential at pin 3 of 1C 741 is also zero, but voltage at pin 2 is nearly 4V. Here 741 is used as a comparator and the voltage at pin 6 is zero. Hence the relay cannot operate. When a phase goes out, voltage at point D goes up to about halt the line voltage. This voltage is divided by 150k and 50k resistors. The voltage at pin 3 is about 8V when 50k potentiometer is properly adjusted. The voltage at pin 6 is about 12V. This base voltage can drive the relay into operating condition. So, the relay would operate when any of the phases goes out.  This relay, when used in the control circuit of the 3-phase motor, or with a circuit breaker, would switch the power oft on operation.

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How to make a simple motor

This is a simple moter circuit.These pictures show how to make a simple motor.first of all you should take two plates that I have mentioned bellow.and set it up on a wooden plate as picture 3 has shown.Then after take coils and wrap it around the plastic stick. When the stick rotates the coil should have a contact with the current supplier so after wrapping place the coil as picture shows.place a magnet middle of the stick as picture shows.

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Rolling Shutter Motor Control

An electrically operated rolling shutter usually has a standard control panel with a three-position switch: up, down and stop. If you would like to automate the opening and closing with a time controlled switch, a few additional wires will have to be connected. Typically, the controls are implemented as indicated in the schematic ‘Normal Situation’. If this is indeed the case, then you can see in ‘New Situation’ how the shutter can be automated with a timer. There is only one method to determine the actual schematic of your control circuit, and that is to open the control box and using an ohmmeter, pencil and paper to check out and draw the circuit. Make sure you turn the power off first though! Connect a 230-V relay (with both the contacts and the coil rated 230 VAC) to the timer.

 

The changeover switch between automatic and manual control needs to be rated 230 VAC as well and may not be a hazard for the user. The relay and switch are preferably fitted in a plastic mains adapter enclosure with built-in plug, which is plugged into the timer. It is a good idea to check first if this will actually fit. Because of the manual/automatic-switch, the operation is completely fail-safe and misunderstandings are out of the question. The switch prevents the issue of conflicting commands (with disastrous consequences) when, for example, the shutter is being automatically raised and manually lowered at the same time.

Source: http://streampowers.blogspot.com/2012/06/rolling-shutter-motor-control.html

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