Thanks for the reply... it's not just a disconnect - it's a fused disconnect right below the meter. So it is the Service and that cable going into the panel would be a feeder and the inside panel is a sub-panel. Yes one connection between the neutral and the ground - that is the main bonding...
A 200 Amp overhead service feeds an outdoor 200A fused disconnect on the outside of the house. Circa about 1960.
3 - #3/0 wires in metal conduit go from that disconnect, through the crawlspace 50', to a 200 Amp panel board in the middle of the house.
The conduit is bonded with a short piece of...
Oops.... The Client had guestimated 200V of voltage drop to where this hot switchover is located in the Plant. There is no metering at that point to confirm it.
Thus why we are trying to model it. But I input the data wrong on the original above. He told me the transformer tap is set to 4R...
We are trying to do a hot switchover of this 15kV bus that is fed from two different sources. I've tried to model it with EasyPower software.
According to the software there is a 400V difference between the one system and the other. Is there a problem doing this?
We have a 150 kVA dry type transformer that is a part of a bigger packaged unit. That question came up.
The transformer case will be bonded, there will be equipment grounding conductors run between the panel feeding it and the transformer.
Looking at the NEC 250.4 ... it doesn't appear this is...
Good info. These are new Basler digital relays that are replacing older digital relays, GE MDP type, that are discontinued.
The new relays kept the same settings and the same curves you would think. Basler was to replace in kind.
Basler provided the Client settings in a printout form of...
Basler provided printouts of their relay settings for new relays that replaced old ones in some old switchgear.
They specified E2 - IAC Extremely Inverse. EasyPower does not have that pick. It has: E2 - Extremely Inverse and C1 - IEC Extremely Inverse.
Note they specified IAC ... which isn't...
oops dealing with Basler on another model. I edited it to Schweitzer. Maintenance mode is a good idea - if it comes with that.
That's a good idea... specify the transformers with higher impedance to limit the fault current.
This project was a part of a purchase of a large portion of an...
Thanks for the good answers. Sounds like the consensus is that he's not answering the question. Might be worth more investigation and contact Schweitzer to confirm.
Seems the brand new switchgear should have the quality of CTs installed for the application. The high arc flash occurs on the...
On a recent project an old 15 kV fused switchgear was replaced by new switchgear that uses HV vacuum circuit breakers and SEL-351S relays on the feeders that land on step-down transformers. Looking at the curves for the new feeder relays vs old E-rated fusing … the instantaneous setting for the...
Wow... lotta power, did not realize that thanks. We were asked to give the short circuit value from our power software on the 138kV side of a plant regulating transformer - which they want to replace. Does a transformer itself have a maximum short circuit withstand value?
There are multiple...
The Utility says the available short circuit energy is 6964 MVA at 138kV at their substation. The 3-phase fault value from the Utility is 29.38kA.
6,964,000,000 / (138,000 * 1.732) = 29,136 Amps ...close to the value given. I'm not used to dealing with transmission voltage levels, but doesn't...
Circuit theory 101 I think...the dc coil has no resistance, therefore it's seen as a short-circuit and that Amber light is ON in normal operation. But when full voltage is applied in an alarm situation, the voltage will be the same on both sides of the Amber light - therefore no current and the...
Have been asked to make modifications to the existing 125VDC hard-wired control system at an industrial plant. Below is a portion of that control. It looks like the Amber light drops the voltage to less than the threshold voltage of the control relay that's in series with it. Should an alarm...
Thanks for the detailed reply. There is 20A load current measured at the main breaker. They had a thermal camera on it and they watched the temperature rise to 150 degrees. And that's when the circuit breakers tripped. The schematics don't show surge arresters.
A new rectifier system is installed on an existing unit substation as the simplified sketch shows below. The 45A thermal magnetic circuit breakers that feed the small rectifiers trip shortly after the system is powered up. They heat up to 150 degrees F per infrared testing. We measured the THD...
Looking at a proposed electrical design....they've got an SPD connected right at the new switchboard through a branch circuit breaker.
I'm thinking perhaps this just for disconnection means.... but they used a #6 wire on a 100A trip. #6 is too small for a 100A circuit breaker normally. But if...
https://www.hagerstowncc.edu/sites/default/files/2022-04/Square%20D%20Class%207230%20Manual.pdf
This is the transformer that is specified: Square D 7230. But it specifically says there is no fusing in the quote - and it looks like in the literature they are optional.
