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...
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...
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...
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...
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...
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.
I have a Yg-D-Yg three winding transformer used on a wind farm collector station. It is a buried delta and I'm trying to find the winding current in the delta for a primary or secondary ground fault. I used symmetrical components to find current for a primary ground fault (see attached from the...
I am looking at calculating line capacitance / line charging in VAR or VAR/mile for a HV line. Not charging current. I find plenty of sources on what it is, but not how to calculate it. I have the transmission line parameters such as R, X, and Y.
If a panel has molded case circuit breakers for both the main and feeders, they are technically not coordinated for a short-circuit fault (looking at a TCC). However, feeders always trip first. This happens at my house panel. Never once has my main tripped for a short-circuit even though it does...
I have an electromechanical relay (Westinghouse CO-11) feeding a transformer. The instantaneous element is set above a symmetrical through fault, but below an asymmetrical through fault. Will the instantaneous operate for a secondary fault?
I'm using IEEE Std. C62.22-2009 to determine if particular surge arresters adequately protect a transformer. Section 5.2 gives a guide. Part 1.3 says "switching impulse energy capability > that produced by the system (see 5.2.1.3)."
Section 5.2.1.3 gives no guidance on how to determine "that...
We are in a remote area and have installed miles of distribution line and have voltage drop issues. We have installed voltage regulators and capacitor banks to mitigate the situation. What is the best approach to setting the tap change delay at the voltage regulators?
First thoughts are set the...
I have a surge arrester at the 69 kV transformer bushing which adequately protects it (per IEEE C62.22-2009 Section 5.2). The transformer is connected to GIS 30 feet away by overhead line. I'm trying to determine if the GIS is protected by the same arrester. Can this be done without EMTP? I'm...
