O/C Relay Settings For Arc Flash 1

[nightfox1925]

We have a 4160-480V power transformers feeding 600V switchgears. These transformers are fed from a 4160 switchgear (switchgear #1).

Our Arc Flash levels are very high on the switchgear #2 480V bus. The 480V switchgear #4, the arc flash levels are high on both 'line' and 'bus'.

We have one GE F35 on each 480 switchgear incomer section and one GE MIFII on each 4160 outgoing feeders feeding the 4160-480V transformers.

We are planning to set the group 2 settings to instantaneous and name it as "maintenance settings".

For the 480V Switchgears that have high Arc Flash levels, we are going to run the arc flash with the F35 settings enabled to Group 2 and set O/C to instantaneous.

For the 480V switchgears with high Arc Flash Levels on BOTH 'line' and 'bus', will it help to set both the 4160V feeder and 480V incomer O/C to instantaneous?

If both are acceptable option, can we set the instantaneous P/U delay to 0.01 sec?

For the MIFIIs feeding the 4160-480V transformers, we are setting the P.U. delay to 0.2sec to overrride transformer inrush.

Hoping for your inputs based on experience...thanks

 

[dpc]

If these are "maintenance" settings, I would not put any time delay on the instantaneous trip.

"The more the universe seems comprehensible, the more it also seems pointless." -- Steven Weinberg

 

[alehman]

If it's a maintenance setting, is transformer inrush a concern?

Alan
----
"It’s always fun to do the impossible." - Walt Disney

 

[jghrist]

For the 480V switchgears with high Arc Flash Levels on BOTH 'line' and 'bus', will it help to set both the 4160V feeder and 480V incomer O/C to instantaneous?

If the 4160V relay PU is set low enough to see any fault on the 480V switchgear, then setting both to instantaneous will not reduce tripping time. I agree with dpc; you shouldn't put any time delay on the instantaneous trip. Transformer inrush won't be a problem as long as you don't close a breaker to energize the transformer while in maintenance mode.

 

[StaticShock]

If you have access to software that can analyze power systems (like SKM PowerTools, or similar), you can model the circuit, then make the trip device changes and immediately see the effect on arc flash levels and coordination. This is a relatively large investment for the software, especially during a recession, however, it is money well spent since bodily injury/death can be prevented based on the calculations.

 

[Maak]

Use either dedicated arc-flash protection relay or a numerical relay with arc-flash option. With trip initiation time of only a few milliseconds you increase safety and significantly mitigate damage to equipment and thus limit costs due to process interruption.

Choose fast circuit-breakers. Their operation time must be taken into account when you calculate the arcing time.

 

[nightfox1925]

Thank you for all the inputs. We have set the GE F35s to have group 2 settings set at the lowest IOC setting.

The arc flash results in SKM was significantly reduced to Level 2.

 

[jghrist]

I would add a well-labelled switch on the panel to assert an input on the GE F35s to change to Group 2 settings during maintenance.

 

[Pikoplatt]

Can remote faults at loads fed by the 480V Bus, cause tripping of the Instantaneous protection while in maintenance mode. How did you select the instantaneous pickup settings for the maintenance mode?

 

[nightfox1925]

The instantaneous settings for the incoming circuit breakers were based on the pickup that will result to category 3 level assuming minimum fault at the bus of the 480VAC switchgear.

 

[Zogzog]

Many people have opted to retrofit thier breakers with a arc flash reduction switch, like utulity relays Quick Trip system for example. Same concept as what you are doing but you have a pad lockable switch so you have control of who changes the settings and a light telling people QT is enabled, easier system to make sure you have the right settings for the right condition.

 

[croudk]

If you have a large motor or a group of motors downstream, you could nuisance trip the relay if the motor or group of motors start up while the relay is in the maintenance setting. For this reason, the relay's instantaneous maintenance setting should be set higher than the expected motor inrush current. If the pickup setting can't be reduced due to the arc flash incident energy consideration, you may consider putting in a small time delay to try and ride through the inrush or you will have to just be aware that a nuisance trip is possible.

 

[jghrist]

If the pickup setting can't be reduced due to the arc flash incident energy consideration, you may consider putting in a small time delay to try and ride through the inrush or you will have to just be aware that a nuisance trip is possible.

The time delay will increase arc incident energy. A lower pickup setting will not affect the incident energy so long as the original setting was lower than the available fault current. The fault current does not depend on the pickup setting. If you have an available fault current of 10 kA and set the pickup at 5 kA, the fault current will still be 10 kA.

 

[Pikoplatt]

Has anyone experienced failure of the Quick-Trip relays after commissioning? If yes, did it result in a false trip of the breaker, or did it fail to trip the breaker? I am considering installing these, and would like to get feedback from users of this product.

 

[Zogzog]

I have not heard of any failures of QT. We have upgraded hundreds (Maybe a thousand) breakers with this system and no failures reported to us.

QT is simply a additional trip setting that is enabled or disabled. If it did fail, the other settings in the trip unit would still apply. So the breaker would trip per the other settings, INST, ST< GF, LT, UB, etc...

Now if the entire system is not properly installed and tested in the first place the breaker may not trip at all.

 

[Pikoplatt]

Zogog, thanks for the feedback. Do you work with the Manufacturer or its representative? How did you upgrade so many breakers? Have you been able to track their performance for years after installation, or is your comment based on the number of retrofits you have commissioned?

 

[dpc]

Some of our customers have installed the Quick Trip option on these trip units. We have not heard of any problems.

"Theory is when you know all and nothing works. Practice is when all works and nobody knows why. In this case we have put together theory and practice: nothing works... and nobody knows why! (Albert Einstein)

 

[Zogzog]

Yes, I work direct with the manufacturer, we are actually the "factory authorized installer" for these,that dosent really mean much but we are. We are a dedicated breaker shop and do these on a regular basis. All our work has a waranty and I have never had a claim on these, or have never heard of a failure from anyone.

http://www.cbsnuclear.com

 

[Pikoplatt]

Zogzog, thanks for the clarification and information.