Arc Flash Mitigation
Arc Flash Mitigation
(OP)
We have a stepdown transformer connected to a downstream switchgear. This transformer is also fed from an upstream switchgear feeder. We are getting high arc flash energy values on both bus side and line side of the downstream switchgear. We have set a 'maintenance' setting on the main circuit breaker of the downstream switchgear to instantaneous and brought down the bus arc flash result to Level 2.
However, the line side of the breaker remains high. We tried to set the instantaneous of the uptream switchgear breaker to slightly override the transformer inrush but could not bring down the arc flash level on the line side of the secondary circuit breaker.
Does anyone have suggestion or other option to bring the line side A/F level?
However, the line side of the breaker remains high. We tried to set the instantaneous of the uptream switchgear breaker to slightly override the transformer inrush but could not bring down the arc flash level on the line side of the secondary circuit breaker.
Does anyone have suggestion or other option to bring the line side A/F level?






RE: Arc Flash Mitigation
Differential protection
or something with an arc flash detection sensor like this
http://
RE: Arc Flash Mitigation
RE: Arc Flash Mitigation
"The more the universe seems comprehensible, the more it also seems pointless." -- Steven Weinberg
RE: Arc Flash Mitigation
The transformer is a 4.16-0.6kV step down connected to a downstream 600V switchgear.
Is it possible to set the overcurrent pickup of the primary protection to be just above the transformer FLA for purpose of reducing the line side arc flash temporarily during maintenance?
I am proposing to use IOC 2 = 1.75*FLA primary for 'maintenance' purposes only. The present settings are based on 1.75*highest Ifault secondary.
RE: Arc Flash Mitigation
The transformer is a 4.16-0.6kV step down connected to a downstream 600V switchgear.
Is it possible to set the overcurrent pickup of the primary protection to be just above the transformer FLA for purpose of reducing the line side arc flash temporarily during maintenance?
I am proposing to use IOC 2 = 1.75*FLA primary for 'maintenance' purposes only. The present settings are based on 1.75*highest Ifault secondary.
P.S.: CAN I SET IT TO VALUE BELOW FLA TOO?
RE: Arc Flash Mitigation
RE: Arc Flash Mitigation
Right now, these settings are going to be used ONLY for commissioning the 600V switchgear. That means, the transformer will not be loaded at all.
If we could not reduce the A/F level at FLA setting, then we have no choice but to set it lower than FLA.
My logic that since the transformer will operating at NO-LOAD, only NO LOAD current will be flowing on the transformwer primary...hence we have the flexibility to set it lower as long as it is higher than the NO-LOAD current. Again this is for commissioning purposes ONLY.
Is my option acceptable?
RE: Arc Flash Mitigation
"The more the universe seems comprehensible, the more it also seems pointless." -- Steven Weinberg
RE: Arc Flash Mitigation
RE: Arc Flash Mitigation
What will you do for arc flash mitigation once the system has been placed in service? The settings for commissioning may be fine, but you'll need a (higher) IOC maintenance setting that will accommodate (some) loads eventually.
Depending on what sorts of procedures might be acceptable to the AHJ and/or owner, it might be permissible to have a low (below full load) maintenance trip setting. One sufficient to run critical loads, but make disconnecting non-critical loads a part of the maintenance procedure.
RE: Arc Flash Mitigation
Basically, for now, these settings will be strictly used for commissioning the 600V switchgears at this point of time only. We will ensure that everybody in construction will know that.
A separate study will be performed for the settings intended for maintenance wherein in this case the transformer will loaded somewhere below FLA.
RE: Arc Flash Mitigation
The real issue is whether or not the instantaneous element will be able to "see" through the transformer when an arcing fault occurs on the secondary of the transformer. Source-impedance, arc-impedance, and the turns ratio could result in very low primary currents (not to mention a L-G fault on the secondary of a D-Yg would result in a further reduction of primary line currents - which aren't addressed in 1584). So, relying on the 50 element to reduce incident energy levels isn't a good idea to begin with, and setting it artifically low will probably result in miscoordination with downstream devices.
Arc-detecting relays are nice, but if you're tripping the primary side breaker, that 3-5 cycle interrupting time can still result in significant energy levels.
RE: Arc Flash Mitigation
RE: Arc Flash Mitigation
Except the times they forget to switch back to normal.
"The more the universe seems comprehensible, the more it also seems pointless." -- Steven Weinberg
RE: Arc Flash Mitigation
RE: Arc Flash Mitigation
RE: Arc Flash Mitigation
If only a very short arcing time is allowed, the answer is arc eliminator.
Manufacturers with a lot of experience: ABB and Vamp.
RE: Arc Flash Mitigation
The customer suffored an incidend some months before that caused a complete plant shut down of several weeks. Before the incidend the customer was not convinced about Arc Flash protection, now he is a big believer.
regards
RE: Arc Flash Mitigation
RE: Arc Flash Mitigation