Three phase supply need help.......

[malik_zohaib]

Thanx Prototyp.
I have attached the relay circuit. My supply voltage is red, yellow, and blue. I always want phase red at pint A, phase yellow at point B, and phase blue at point C.

If any phase change its position then by switching relay i should be at the restricted points (as mentioned above). But this circuit is not working properly; Can you tell me that is wrong in this circuit??????????

 

[FvM]

As Prototyp_V1.0 explained, you only need to change two phases, so I don't see an understandable motivation for using three relays. The standard design for automatic phase reversal is to have two 3-pole contactors for the motor, one is energized with correct mains phase and the other with reversed phase. Phase sequence monitoring relays to control it are industry standard products.

When using double throw relays for phase switching as in your circuit, you have to care, that the "break" arc is extinguished reliably before "make", otherwise the relay will be distroyed quickly. Using separate contactors allows to keep an intentional deadtime during switchover.

 

[malik_zohaib]

Thnx FvM, i know i can change any two phases by using just single dt relay. But i want i them at the desired point.

 

[DXNewcastle]

Basically i want to correct the sequence; if fault occurs. Only two of them need to swap. But the problem is which ones??

So why are you using such a complex circuit with three relays?

Then it doesn't matter wich two phases you chose to swap. It will have the same effect.

. . . you only need to change two phases, so I don't see an understandable motivation for using three relays.

Exactly!

If you think it makes any difference, can you explain why you always want Point A to be connected to Red phase? And explain how switching all 3 phases will be of any significance which isn't achieved by simply switching between two states: 1. the 3 phases rotating in one sequence, or 2. the 3 phases rotating in the opposite sequence?

The tricky part is in identifying whether or not to switch, which requires a circuit with some sensitivity to time (others have advised either a phase shift or a schmitt triggers. Both will work correctly), but you do not need to switch all 3 phases.

 

[malik_zohaib]

yah i know by changing any two phases it will do the job.

But this is the task assign to me; phases should be at their respective point... .
I am tired man....:sad:but not mad......8-O
Trust me i give up.........

 

[FvM]

The connection matrix between ABC and RYB has 6 possible states, all can be achieved with your relays circuit. So although, I don't see it's purpose for driving a motor, it's basically working.

 

[Prototyp_V1.0]

Only way I can see this being achieved is by having wires between the source phases and the respective load phase, and a relay inseries to each of those wires. The wire length will need to be exactly as long as the supply cable.
Then if one phase is shifted, then there will be voltage over one relay, and then the relays can activate some logic circuit that shifts the phases until you have a match.

 

[FvM]

But this circuit is not working properly

I don't know what's exactly meant with this statement. As mentioned repeatedly, from the motor's perspective there are only two states forward and reverse (power off and phase failure in addition, of course). But if you have an absolute phase A (or time) reference, then the said six connection cases exist. In so far, the shown circuit is supposed to work.

 

[DXNewcastle]

. . . . . . if you have an absolute phase A (or time) reference, then the said six connection cases exist. In so far, the shown circuit is supposed to work.

I agree, the circuit CAN achieve all 6 permutations.

However, the circuit as posted has 8 possible states. Two are redundant.
When Rly B is energised, you have the same output state as when Rly A, B & C are energised.
When Rly A & C are energised, you havet he same output state as when Rly A & B are energised.
I wouldn't call that "not working properly".

Unfortunately the questions about why there is anything absolute about the phases remains unanswered.

The choice of method for controlling the relays also has to be considered, and for that we have to know what external reference is available against which the absolute phases can be measured. Will this reference come from a radio time-clock, or from yet another three-phase supply (to which we might have to synchronise a local supply)?

 

[malik_zohaib]

Hi thnx guys.
DXNewcastle can you give some direction how to eliminate these two redundant stages? Can you show me the circuit???? or i have to drop one relay???

Surly another supply for reference.

 

[FvM]

DXNewcastle can you give some direction how to eliminate these two redundant stages

They can't be "eliminated", they are just there, because two raised 3 equals eight. It get's more and more mysterious what you are trying to achieve.

As been said, one (DPDT) relay would be sufficient to reverse the motor. To be able to connect all phases at will, you need more than two relays, because 2 raised 2 equals four, which is less then six.

 

[DXNewcastle]

Yes, FvM, the redundancy is in 2 of the possible 'states' of the 3 relays, not in components in the circuit.
Nothing has to be eliminated, but the relay controller must be designed so that the 6 useful 'states' are possible outputs (and 2 'states' will never be used).

Surly another supply for reference.

Malik, if the task is in synchronising a generating set with a remote mains supply, then I wish you had told us that is the task before now, because there are other issues to consider in building synchronising equipment.
The relays must be capable of carrying full-load line-line fault currents.
There must be a visual indication of phase error ideally with a resolution down to 1%.
There must be a visual indication of phase sequence (ie the direction. Only 2 possible directions apply, as discussed to death in this thread).
It is prefered to have displays of frequency on both supplies.
There must be a means of adjusting the speed (frequency) of the local supply. (This can be done manually or automatically, and it might make the relay switching unnecessary)
There must be fail-safe interlock to ensure that phases cannot be connected without proving a neutral connection, and, all of the phases will be dis-connected if ever any one phase becomes dis-connected.
It is preferred to have another interlock that prevents phases being connected while the frequency is out of tolerance or either supply is over voltage thresholds.
There must always be a means of manual isolation of the local equipment which is capable of full-load line-line fault currents.
And the over-current protection for the entire system must be designed to protect every component of the system, including seizure of the turbine, stuck relay/contactor, and every permutation of short circuit; without this protection the risk of fire will always be high.

I hope this helps.

But if its NOT a project to synchronise 2 supplies then please explain what actual work you are attempting to do with the 3 relays.

 

[malik_zohaib]

Thnx a lot DXNewcastle.
That is all i got.

Thnx everyone.