Dear fellows,
Currently, we are working on a harmonics study involving medium and low voltage network.
As in that network there have been some prrevious problems and some equipments were reported to be damaged, we are trying to
create a very detailed model based on the available information...
Dear Colleagues,
Does anybody knows if the rated shortcircuit value of the LV fuses is related to:
Symmetrical, peak or what current?
We are trying to understand it because the manufacturer manual says shortcircuit based on IEC 60947-2 (and we have only fuses gG, not fused circuit...
Hello fellows,
I have one question related to the way impedances for 3W xfmrs are given in a text protocol.
We have the following:
HV-MV = 4.23%
HV-LV = 2.51%
MV-LV = 6.55%
However, the same test protocol has some other values refered to the HV rated power:
HV-MV = 6.77%
HV-LV = 6.70%
MV-LV...
Dear friends,
We are involved in another grounding grid analysis for an industrial system.
Now, we are trying to calculate the current division factor, which for a transmission network it seems very easy to determine following some equations.
However, for an industrial network in medium...
Hello,
Is there any standard or practical recommendation to limit the magnitude and duration of a voltage drop caused by a motor starting?
We have done some analysis and the voltage drop is 12%, however, our customer says it is not significative if not forbiden by a standard.
So we have...
Dear friends,
Does anybody kbow what the standard to verify fuses interrupting capabilities is?
I mean, we alredy look at IEEE red book, violet book and nobody talk about low voltage fuses.
For medium voltage there are some other standards but, we are not fully sure if the procedure...
Hello friends,
I would like to get your oppinions about the procedure to perform earth resistance measurements oriented to determine resistivity.
1) IEEE std 81 says that at least two traverses may be done and it does not set any limit on the distance between electrodes.
2) Some equipment...
Dear colleagues,
This may be a very fool question, however, I would like to receive some feedeback related to the standarized way to express in a single line diagram the following:
Size of conductors
Number of conductors
Typically, we receive many one line diagramas showing data in a non...
Dear guys,
I come to you asking for some advice in order to get some technical references that may help us explain/understand the following:
When we have a grounding grid, we evaluate it from the standpoint of step and touch voltages considering the single phase to ground at the PCC because...
Hello,
I am looking for some technical references about xfmr sizing, under the following possibilities:
a) This motors would allow an overload of 250% during some seconds, let's say 15.
b) There is another option that one motor to be fed is to have a startinh torque of 2.5 p.u. during 60...
Hello guys,
In a project we are participating, there is a transformer wye-wye grounded on both sides, the HV side is grounded through a surge arrester, while the secondary (LV) side is through a resistor.
My question is:
Has anybody dealt with something similar (H0 terminal earthed through a...
Hello everybody,
We have found some PT's installed in 230 kV that apparently have no problem, however, their fuses have been blown.
I looked at their name plate data and they are no capacitive.
Based on your experiences, any clues about the possible reasson of this fault?
Best Regards
Hello everybody,
We are currently working in a project where some old fashion circuit breakers are still in use, they are H-3 from Federal Pacific and they are equipped with its "control unit" kind SD-3 or SD-6.
We used to have a manual of these control units, however, it has disappeared, my...
Hello everybody,
If a transformer neutral is grounded through a resistor to limit the magnitude of the single line to grund current, on the "healthy phases", there will be some overvoltages lasting the time overcurrent protection clears the fault.
Well, my question is related to these...
Hello,
IEC std 60909 for short-circuit calculations determine a thermal current Ith for 1 or 3 seconds.
I would like to get your feedback about:
If a busbar of a swicthgear was design under IEC Std, to determine if it is appropiate, is it enough to compare the calculated Ith (thermal current)...
Hello friends,
At one industrial facility, there are some capacitors which include their tunning reactor (at 4th component) to compensate PF, they are located at medium voltage.
However, very oftenly the fuses of the "capacitor+ reactor circuit" are burn out, I mean, they are not blown, after...
Hello everybody,
When you have a large industrial plant extended over a large area there are typically several electrical rooms, each one has its own grounding grid, all of the buildings have a ground ring and the main substation has another grounding grid and all of these elements are joined...
Hello,
In some medium voltage circuits feeding motors, there are some capacitors installed.
These capacitors are receiving some harmonics in excess, so we think that some reactors should be installed "in series" with them, to tune the circuit and avoid the resonances.
We already analized and...
Hello,
We are working in modelling for a power system analysis the drive performance for harmonics and things like those.
We have found that according to manufacturer manual, the drive has a topology which includes:
An income reactor in AC
A DC link (another reactor)
The question is:
Does...
Hello,
When we are using a circuit breaker to protect a capacitor, we typically consider a special circuit breaker able to interrupt the capacitive currents.
If we are using a vacuum contactor (or SF6 contactor), is it also important or any specific characteristic should be considered?
or only...
