How does sequential electric motor starting works.
How does sequential electric motor starting works.
Sequential electric motor starting involves starting of two or more electric motors one after the other in an orderly pattern.
The sequential motor starting is most applicable in situations like production of goods which involves various stages.
They are some stages which need to run first before others and when stages supposed to run first stop working, others which follows should also stop.
For example in production of gravel, let start at the stage of crushing rocks into gravel used in construction using the crushing machine and after crushing, the produced gravel need to be moved to a certain place for storage using a conveyor belt.
In the example the electric motor used to turn the crushing machine uses a stardelta starter and the other causing the belt to move uses direct online starter (DOL).
Since after crushing of rocks, we need the gravel to be moved away from the crushing machine by the conveyor belt to prevent accumulation of gravel on and in the crushing machine, that is where the sequential motor starting came into action.
In sequential starting we want the conveyor belt electric motor to run first before the crushing machine motor run and also if the conveyor belt electric motor stops working the crushing machine should also stop working.
The diagrams below shows the power and control circuits of sequential motor starting we previous talked about and the explanation on how it work follows.
Power Circuit.
Control Circuit.
- TP Breaker - Tripple pole breaker
- SP Breaker - Single pole breaker
- K - Contactor
- btn - Button
- NC - Normal close
- N - Neutral
- O/L - Overload relay
- NO - Normal open
- T - Timer
- F-R - Rervese contactor
Key
Explanation
In this article we are not covering how various parts of the circuits works, we have already covered them in the articles; how a direct online and stardelta starter works, we are only looking on how the sequential motor starting works.
On the control circuits we have two neumatic timers, one labeled T2 is for switching the Stardelta motor from star to delta and the other labeled T1 is for putting the crushing machine electric motor in ON position after the DOL motor run first for four seconds.
To start running the electric motors the start button is pressed, this enable current to flow through the DOL motor contactor coil causing the power contacts of DOL motor contactor to close resulting in power reaching the DOL motor and start running.
The T1 timer is connected in a way such that it start working when the DOL motor start running, as the DOL motor start running the T1 timer is put in ON position.
As soon as the timer T1 is put in ON position, it start counting up to four seconds and close the contact connecting the stardelta motor control circuit labeled "T1-NO" and and the stardelta motor start to work.
We have already covered how a stardelta starter work you can check out.
In the previous control circuit diagram we use the timer to put the stardelta motor in on position, they is another control circuit we can use.
In this circuit each control circuit has its on start and stop buttons but there is an interlock as shown in the following circuit diagram.
- DOL-NO - Interlock (normal open)
Key
The control circuit of a stardelta starter is connected through the normal open contact labeled "DOL-NO" of a DOL contactor such that when the DOL is OFF this contact is open and the Stardelta motor can't work.
And also when DOL is ON this contact "DOL-NO" closes, such that when the start button of stardelta starter is pressed current can pass through enabling the stardelta motor to work.
Using this control circuit stardelta motor will not automatically run after the DOL run after four seconds as in the previous control circuit diagram, they is a need of an operator who then switches ON the stardelta motor after switching ON the DOL motor.