Recloser Hot Line Tag Time Delay

[wbd]

How many people put in an intentional time delay for a HLT function on a recloser? I am looking at one with settings that have a 0.016 sec (1 cycle) time delay on the HLT. Since this is for personnel safety, why would any time delay be inserted?

Thanks in Advance.

 

[crshears]

Looks like you're talking about two different animals...

If reclosure is blocked for personnel safety, the device won't reclose at all.

Time delays on reclosure on the other hand are put there for various reasons, such as allowing for residual voltage collapse without actually measuring for it, allotting time for the voltage-presence plus time breaker to place the circuit back on potential first, etc., etc.

CR

"As iron sharpens iron, so one person sharpens another." [Proverbs 27:17, NIV]

 

[wbd]

Sorry, I was not clear. There is a time delay that can be inputted on the HLT function to delay the trip. There is no reclose.

 

[JG2828]

Not sure which controller that is, but the 0.016 seconds is probably the smallest number you can enter. It probably is not an intentional delay, but represents the minimum operating time of the relay. The 50 High Current Trip setting probably only goes down to .016 seconds also.
I'm not sure why you would want to add an additional intentional time delay. Maybe for lines that feed factories with large motors, to prevent false trips?

 

[wbd]

It is a Cooper F6 and you can make that time 0. This one happens to be set this way and I cannot think of a good reason why you would want any time delay.

 

[JG2828]

Good question. I checked to see if that happened to be the default setting, but it is not. The default setting is .05 seconds for those three settings.

 

[bacon4life]

Perhaps to allow for transformer inrush or unbalanced phases during switching?

 

[wbd]

Perhaps to allow for transformer inrush or unbalanced phases during switching?

No as the Hot Line Tag function is typically used to place the recloser in one shot mode with a lower trip pickup or different curve to provide for lineworker protection when working the line energized, i.e. gloving.

 

[dpc]

Well, customer transformers can get energized even while in HLT. And large motors can be started. I'm guessing it is to allow for some inrush current.

 

[jghrist]

The hot line tag adds a definite time relay element to the normal fast curve inverse time overcurrent element. It provides faster clearing for faults during maintenance. The time delay, as noted by others, could be there to allow transformer inrush, motor starting. I don't think the delay is needed for transformer inrush because you can't energize the line with the recloser when the hot line tag is on. I doubt that motor starting would exceed the pickup value for most distribution lines that serve multiple customers. I would set the time delay to zero to get an instantaneous trip for maximum worker safety.

 

[bacon4life]

Oh, sounds like your HLT is a bit different I assumed. I assumed HLT is enabled anytime personal are working on the circuit. This work could include closing fuses, switches, or reclosers downstream of the breaker/recloser with the HLT. The newest generation SEL451 feeder relays include transformer inrush blocking, but old instantaneous relays are susceptible to tripping on transformer inrush.

Even with a 1 to 3 cycle delay, turning on the HLT on a long overhead distribution feeder likely reduces the clearing time very dramatically. When evaluating maximum worker safety, I want to consider both the reduced arc flash danger and any offsetting increased risks. A power outage increases the danger of vehicular accidents due to the loss of power to traffic lights. Both workers patrolling the distribution circuit and the public thus have an increased risk if the recloser falsely trips on inrush.

 

[dpc]

Pretty common to have HLT on when working to restore power. This sometimes involves closing in local disconnects or pad-mounted switches and interrupters to energize customer transformers. Clearly, 0 time delay is faster than 1 cycle. But I wouldn't be overly concerned about a 1 cycle delay. Still pretty fast.