Search results for query: *

I've answered my own question. I came across a nameplate that instead of "STEP DOWN" or "STEP UP", it said "STEP UP / STEP DOWN". So I assume the transformer was rated for bidirectional flow. And this needs to be included in any transformer spec for BESS.

2) When we refer to a 50 MVA-rated transformer in IEEE World, we are discussing the transformer's output. Correct. Wouldn't the transformer be manufactured such that the output winding is rated for 50 MVA and the input winding is rated for 50 MVA + losses? My question is what if the input and...

C57.12.00 Section 5.4.1 states: The rated kVA of a transformer shall be the output that can be delivered for the time specified at rated secondary voltage and rated frequency without exceeding the specified temperature-rise limitations under prescribed conditions of test, and within the limits...

In the medium voltage world, we set our pickup above equipment ratings to allow the customer the flexibility of temporary overloads. We protect against short-circuit and not overload. For cable, this is allowed per NEC 240.101(A). For transformers, NEC Table 450.3(A). Is this discussed...

jghrist, sounds like the same as IEC 60287. I've read BS 7671 has a correction factor. Does anyone know it or is it a table? I know it only applies to LV cables.

cuky2000, the software I have (ETAP & SKM) cannot create such a model. I believe CYME does it, but it's a $30k software. I come across this maybe once a year and cannot justify the cost. I skimmed through those studies you mentioned (Trenwa sent them to me). I didn't find anything that useful in...

From my research, there is no ANSI standard to determine the ampacity of cables installed in a precast trench with solid, unventilated covers. I did find that IEC 60287-2-1 Section 4.2.6 has a method, but don't have the standard available. What do you use? I have ETAP to calculate the ampacity...

In order to calculate the cable ampacity for buried cables, the thermal resistivity needs to be determined. This is heavily dependent on the moisture content of the soil which varies. IEEE 442 Annex F has information on determining the "critical moisture content": "The critical moisture...

Yes, essentially you have to determine if an arc occurs downstream, does it have the capability of migrating to the line side of the main breaker. Your client says yes, it does. Or they simply want the entire MCC labeled the same in order to prevent confusion for those selecting the appropriate PPE.

Thanks. Those are the equations I extracted. I took it from your post back in January that they were taken from IEEE 738. Thanks for the sources.

I'm sorry, I can't seem to find a way to private message someone and the thread they posted on is closed. dauwerda, You posted a spreadsheet calculator on the below thread for the deratings of bundled conductors. I extracted the equations from the spreadsheet, but can't seem to find them in...

@7anoter4 I tried to PM you, but I don't see that option. Can you quote the relevant section in that standard? Our IHS subscription does not include it and it's $350 to purchase.

I cross posted this on the electrical forum, but thought some soil engineers could help. An underground cable ampacity study comes across my desk every month or so. The thermal resistivity of the soil (rho) has a fairly significant impact on the ampacity of the cable and it's always a question...

An underground cable ampacity study comes across my desk every month or so. The thermal resistivity of the soil (rho) has a fairly significant impact on the ampacity of the cable and it's always a question of what to use. With no soil test, I use a rho of 90 degC-cm/W unless it is in the desert...

Thanks for the replies. I think you’re right the the entire substation cannot trip for a ground fault. Maybe a possible solution is to make it high resistance grounded.

NEC 695.6(G) states "Ground-fault protection of equipment shall not be installed in any fire pump power circuit." Does this include upstream ground-fault protection all the way to the transformer? This would remove ground-fault protection from all other equipment fed from the substation. Or is...

yes

I was given a motor data sheet from the 90's that includes speed vs. current, power factor, average torque @ 100% and 90% V, load torque, and oscillating torque @ 100% and 90% V. What are the oscillating torque curves? I've never heard of that.

That is given by Zpt% in the Westinghouse equations.

My notes showing the sequence network interconnection for a fault on the primary.https://files.engineering.com/getfile.aspx?folder=40ec260a-bdcc-405d-b682-7cde23880aad&file=notes.jpg