OT: Y-Delta Start Time

I am in the process of upgrading a control that includes a 15HP high pressure pump controlled with a Y-Delta contactor setup.

Unfortunately the Y Start time was controlled by an external timer (with the range set to 0.1 to 12.0 seconds) and it was set to minimum - 0 seconds - when I checked inside the old panel.

I did a Google search for Y-Delta startup times and only got schematics and some very vague references to the time setting. One page said up to 2-3 seconds max, another said up to 15 max.

Does anyone know what would be a good startup time for a 15HP pump? I am going to control the time in the new PLC, changeable through the HMI I am also programming.

I would look into ditching the multiple contactor arrangements and put in a softstarter with the motor wired delta to the starter output. You might need a kickstart setting in the starter if the pump is a hard to start load.

Normally, the start dwell timing is not something you adjust. You set it and leave it alone. There are probably exceptions, but I would not leave it to be freely tinkered with once you dial in the time you want, lock it down. I can't even guess what the right time would be for your case. I have seen them set as short as 5 seconds and as long as 3 minutes (the latter being a 500 lb flywheel). You might try to get ahold of the OEM of the machinery for advice on start time.

I have had a handful of y-delta motor starters give me problems. It sucks when a little plastic tab on an auxiliary contact snaps and blows up a 250 HP compressor motor. It doesn't suck to throw three massive contactors in a dumpster and put in a shiny new softstarter.

Just my opinion...there rmay a valid reason to keep the y-delta started but 15hp? should be cheap and easy to make it simpler.

Hi Secpcb ,
Unfortunately there is no hard and fast setting - it depends on several factors such as mechanical load , number of poles and if the motor is unloaded till the change to delta run . If you set the time long initially to a value of , say , 10 sec. , then start the motor and measure the time till the motor stops accelerating , this will give a reasonable setting . Be ready to stop the motor if it starts slowing down and set the time to slightly less than that time . If this is a washdown application , you will need to check if the pump might start with and /or without backpressure , since this will affect the acceleration time .
Paul

The number is... Whatever time it takes for the motor and load to get to at least 80% speed. That number is different for every single load. If you have a tach and a timer you could get it gnats-*** accurate, otherwise, it's best guess and adjust as you see fit.

I agree though, ditch the whole thing and switch to a solid state soft starter. 1975 is calling and wants its Y-Delta starter back...

Thanks for the help guys. I will just have to test it under pressure & find a good time. Also, the time change is in MY HMI screen that only I will be able to get to, the operators and leaders won't have my passcode.

Changing to a soft-start would be great, but the budget for this upgrade is precisely: $0,000.00 UD dollars. The SLC5/04, Panelview900 & everything else is on-hand parts and use what I need from the old control panel. Actually the only thing I will have to purchase is a HSCE card for the conveyor motor encoder, which goes over-budget by about $130, and It's already been complained about.

So understand that there are two time frames involved, the time to change from Y to Delta, and an open transition time in which all contactors are open. If you have a special Y-Delta timer in there, it has the non-adjustable open transition time built-in. If it's a standard On-Delay timer, the transition time is incorporated into the mechanics of the timer and aux contact arrangements. If you replace that with PLC timing, you may end up destroying your motor if not done exactly right. Closing the contactors too quickly can result in extremely nasty voltage spikes because there is a phase angle shift that takes place between Y and Delta, closing them too slowly can result in a loss of rotation and a current spike that is actually up to twice as high as an Across-The-Line spike, and I have seen a shaft of a 500HP compressor motor shear off from that. It's a tricky business fraught with pitfalls, hence my preference for getting rid of them and never using them again.

The way the original contactors were controlled was by a simple on-delay timer. As soon as the timer open the NC contact the NO was closed without delay, then as soon as the MCS contactor's AUX-NC closed the MCD contactor was powered, so the only delay would have been the time the MCS contactor took to release - there is no time delay built into the contactors - just NC AUX contacts and the (instant) mechanical interlock.

I did figure that was wrong and there should be a slight delay between release of the MCS and engaging the MCD and am going to program that delay in, I have searched all the old control panels in storage here and none have a soft-start or VFD large enough for a 15HP pump, so I am stuck using this arrangement.