Hi all

Attached is the circuit diagram, please can anyone have a look at the re-start timer & re-start timer relay. How does both work in circuit. I am thinking that on energisation, the timer coils starts delay time. But I reckon that if the timers operate, the re-start relay will come on and shutdown the circuit. What keeps the re-start timer from operating on expiration of the time. Will it be a pulse signal the soft starter?

Be grateful cos, I'll love to be able to appreciate the circuit rather than assume it works (we've been connecting this in several jobs).

Hope to hear from someone. Cheers!

It appears to be a fairly standard restart delay time logic using off-the-shelf components. There are timers out there that do this in one device but for whatever reason the engineer wanted to separate the functions. Not a problem really, it may just be an issue of familiarity for operators.

When power is first applied, the RT timer coil is energized. That N.O.T.C. (Normally Open, Timed to Close) contact of RT prevents the RTR1 relay coil from being energized until RT finishes its time sequence. Once the startup delay time is done, RTR1 energizes and enables the rest of the control circuit. By the way, you seemed to imply that RTR1 would shut down the system when the timer operated, but if you look, the relay contacts (at least those I can see) are Normally Open, so they would just PREVENT operation until the relay gets energized.

The purpose of this circuit is to prevent an immediate restart of a system after a power failure. What the user will do is to go around to each controller that has this circuit and set the time value of RT to different levels, creating a staggered restart when power is resumed so as to not cause another shutdown from the inrush of everything automatically re-starting. This timer circuit serves no other function in this panel. So in some panels, the delay may be seconds, but others it may be minutes. Once the timer has finished and energized relay RTR1, it seals itself in and stays that way until the power fails (or a disconnect switch is opened).

The "Reset" button is probably mis-labeled, depending on how you look at the logic. This is not a "failure" of any sort, it is a Lock-Out, so I would have used the label "Restart Delay Override" instead of "Reset", but Reset is a commonly available standard label, so maybe that's why they selected it. What it does s to provide a means by which a local operator, who for example has just done service work and had the power disconnected, to not have to wait for that delay timer to expire every time he wants to test the system. So he presses that "Reset" (override) button which energizes the RTR1 relay in spite of the RT timer still being open because of the power having been disconnected. However, he will have to hold that button in until RT finishes timing out. I would have put in a seal-in contact around the PB as well. That function is only going to be used by someone standing in front of the panel, who presumably knows that there was not a system-wide power failure.
Some soft starters also have this functionality built-in. The only thing is, if a facility has operating personnel who are accustomed to always looking for "RT" as the timer to adjust the restart delay, they may object to having to program that function into a soft starter.

Thanks, I have gained considerably from reading thru your response and I do appreciate it. Everything now looks really clear to me.

Thanks

Hi jraef

Please take a look at 2 additional pages attached. if RTR1 energises, this will cause ESR & MOR to operate. ESR has NO contact to PLC, will this not give wrong PLC alarm, as though Emergency stop is operated?

Well, it all depends upon how the logic in the PLC is designed. You are correct, those relays will be energized. I would expect that for the ESR, that is typically how you would do an Emergency Stop circuit to make it (somewhat) fail-safe. As to the MOR, as I said, it depends upon how they have the logic in the PLC configured. If they have it set up so that it looks for the logic to be high UNLESS the Kilxon temperature switch opens, then that would be correct, and most Kilxon switches operate in that manner.

But by having the RRTR1 N.O. contact enabling each of those circuits, they avoid getting an alarm condition at every power up until after the re-start delay.

Thanks, made my day. The Signals to PLC are connected for failsafe conditions so its high for healthy.

Do appreciate.