Alejandro Nava
Electrical engineer
631 followers · 51 following
Hello! I'm Alejandro Nava and I like science, specially physics and a few topics in math. In 2021 I got a
degree in electrical engineering. I ask/answer that kind of stuff but I also like to read life… Read more
Credentials & Highlights More
Electrical Engineer at Full Data Comunicaciones 2024–present
Bachelor’s degree in Electrical Engineering, Universidad Rafael Urdaneta Graduated 2021
Lives in Venezuela
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Knows Spanish
Joined September 2014
ES Active in Spanish 42 answers
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Summary of Alejandro Nava's answers
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Power Systems Engineering
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Alejandro Nava
Read books and took classes about power systems & circuits · Updated Dec 31
What is the power formula for the 3-phase system?
Short answer (summary): 1. Powers for single-phase AC systems operating in sinusoidal steady-state In
general: 2. Powers for three-phase balanced AC systems operating in sinusoidal steady-state 2.1. In
general: 2.2. In a wye-connected load: 2.3. In a delta-connected load: Long answer: Keep reading.Read
Most…
more
Alejandro Nava
Bachelor’s degree in Electrical Engineering, Universidad Rafael Urdaneta (Graduated 2021) · 14h
How should a power inverter be configured?
A (power) inverter has the purpose of transforming the energy stored in a battery bank, in the form of
DC voltage, into AC voltage to feed AC loads like appliances, lighting, motors, IT and networking
equipment, etc. Here’s how they should be configured: 1. DC input (battery side): These parameters…
Read more
Alejandro Nava
Electrical engineer · Mon
What is the ideal pixel density for a monitor or TV, and how do you calculate it?
Pixel density can be expressed in various ways, but the most common one is linear pixel density in
pixels per inch of diagonal. It indicates how many pixels there are in the diagonal line of the screen. In
other words, how tightly packed together the pixels are in the screen. Given resolution and siz… Read more
What's the difference between screens/displays (DLED, QLED, OLED) and panels (VA, IPS)? Why
are screen types specified in TVs and smartphones, while panel types in gaming monitors?
No answer yet · Last followed Sun
Alejandro Nava
Read books and took classes about power systems & circuits · Updated 14h
Can I connect the output Mcb breaker of the inverter to the output of the main circuit breaker of
the home directly in parallel (in order to connect to the loads)? The inverter support bypass
mode?
I think I know what you mean. I've worked with hybrid (all-in-one) PV inverters and inverter-chargers,
from brands like Victron, Growatt, MPP Solar, Powest. They have an AC input connection to the grid, an
AC output connection to the loads, a DC input connection to the battery bank (battery energy sto… Read more
Is the GIGABYTE Z790 AORUS Elite AX motherboard compatible with Intel Core i7-12700K
CPU? Some say yes, but the CPU chipset is Z690.
1 answer · Last followed Feb 20
Alejandro Nava
Bachelor’s degree in Electrical Engineering, Universidad Rafael Urdaneta (Graduated 2021) · Updated Feb 19
How can electrical harmonics affect the UPS operation and do they response of inverter
unsynchronize alarm?
UPSes, specially cheap ones that are line-interactive instead of online (double conversion), may not
recognize an AC input that is a modified sinusoidal waveform (such as from certain inverters) or that
has a high total harmonic distortion (such as from portable generators), or that has a too high o…Read more
Alejandro Nava
Bachelor’s degree in Electrical Engineering, Universidad Rafael Urdaneta (Graduated 2021) · Jan 18
How do I convert three phase (without neutral) to single phase?
Simply use any two phase wires of the three-phase system. If the nominal line-to-line voltage of the
system doesn't match the rated voltage of the single-phase loads, you'll need a transformer. If you need
one phase wire to be grounded, then from the previous transformer you can ground either wire;…Read more
Alejandro Nava
Bachelor’s degree in Electrical Engineering, Universidad Rafael Urdaneta (Graduated 2021) · Jan 16
Can old stranded electrical cable be used to make ground rods, similar to how bare solid wire is
used for grounding rods?
Yes, you can use stranded uninsulated wire as a grounding electrode, but not by driving it through the
soil like a ground instead, but instead by burying it. Make a loop or a grid.p That's called a ground ring or
ground mesh.… Read more
Alejandro Nava
Bachelor’s degree in Electrical Engineering, Universidad Rafael Urdaneta (Graduated 2021) · Jan 13
Can a wire with broken insulation cause a short circuit?
Well this proves Quora bot is still learning very basic logic.
Personal notes 3 · Follow
Posted by Alejandro Nava · Jan 10
Grounding and bonding for a multi-store mall [Unfinished answer draft]
Figure 1. Image source: own. Figure 2. Image source: own.… Read more
Alejandro Nava
Bachelor’s degree in Electrical Engineering, Universidad Rafael Urdaneta (Graduated 2021) · Updated Jan 31
What are the criteria for choosing an electrical circuit breaker?
For basic residential circuit breakers, at least the following: * Number of poles: Whether the circuit is
single-phase two-wire line-to-neutral, single-phase two-wire line-to-line or single-phase three-wire, or,
three-phase. * Mounting: DIN rail (European) or, for other countries, bolt-on, plug-in, or fee… Read more
Alejandro Nava
Bachelor’s degree in Electrical Engineering, Universidad Rafael Urdaneta (Graduated 2021) · Jan 6
Can you explain the differences between a TT, TNS, and TNCS earthing system?
Yes, I can, Quora bot. I already did it here, including the other arrangements: Alejandro Nava's answer to
What are the types of grounding (earthing) arrangements? What are IT, TT, TN-C, TN-S and TN-C-S
grounding arrangements?… Read more
Alejandro Nava
Bachelor’s degree in Electrical Engineering, Universidad Rafael Urdaneta (Graduated 2021) · Jan 5
Can you explain the difference between TT and TN earthing?
Yes, I can, Quora bot. I already did it here, including the other arrangements: Alejandro Nava's answer to
What are the types of grounding (earthing) arrangements? What are IT, TT, TN-C, TN-S and TN-C-S
grounding arrangements?
Alejandro Nava
Bachelor’s degree in Electrical Engineering, Universidad Rafael Urdaneta (Graduated 2021) · Jan 4
What happens to power if the current in an alternating current (AC) circuit is zero?
Depends on what you actually mean. When the instantaneous current is zero, the Instantaneous power
is also zero. However, the active/real power won't be zero, because the average of the instantaneous
power is not zero, even though the average current is zero. When the RMS (or peak) current is zero,
Read
th…more
Alejandro Nava
Bachelor’s degree in Electrical Engineering, Universidad Rafael Urdaneta (Graduated 2021) · Dec 31
What factors affect power factor in AC circuits?
For single-phase AC circuits (sinusoidal or not): * Power factor is the ratio of active power to apparent
power. So it depends on how much active power the device consumes or delivers relative to its
apparent power: \text{pf} = \dfrac{P}{S} \tag 1 For example, if a load consumes 1000VA and 800W, Read
then…
more
Alejandro Nava
Bachelor’s degree in Electrical Engineering, Universidad Rafael Urdaneta (Graduated 2021) · Updated Jan 4
Why do high voltage cables move and bend during a short circuit, even breaking insulation and
support?
Any conductor (wire) that carries current, AC or DC, creates a magnetic field, and hence a magnetic
force. The stronger the current, the stronger the force. Since current flows in closed circuits, at least two
wires are required. And usually the two wires are close together. So they exert forces on e… Read more
Personal notes 3 · Follow
Posted by Alejandro Nava · Updated Dec 31
Summary on harmonics in power systems [Unfinished answer draft]
* Balanced periodic non-sinusoidal instantaneous line voltages with half-wave symmetry can never
contain triplen harmonics (neither in a three-wire nor a four-wire three-phase network), they can contain
only the non-triplen odd harmonics. This is also true for phase voltages in a delta-connected devic…
Read more
Alejandro Nava
Bachelor’s degree in Electrical Engineering, Universidad Rafael Urdaneta (Graduated 2021) · Updated Sun
What is the neutral current magnitude of a four-wire three-phase network operating in
sinusoidal steady-state conditions with the line currents being balanced in phase shift but
unbalanced in magnitude?
Short answer: The magnitude of the neutral current in a three-phase four-wire network operating in
sinusoidal steady-state conditions, with the line currents having balanced phase shifts (120° between
one another) but unbalanced magnitudes, is the square root of the sum of the squares of the line
currents, minus the sum of all the possible products of any two line currents. See equation (6) below.
Long answer (proof): Keep reading.
In a three-phase four-wire network operating in sinusoidal steady-state conditions, if the line currents
are balanced in phase shift but not in magnitude, then their instantaenous value, as well as that of the
neutral current, is the following, taking the line current of phase A as angular reference with the cosine
function; we’ll assume a positive (abc) phase sequence, but the result will be valid also for negative
(acb) phase sequence:
ia (t) = Ia cos (ωt)
∘
ib (t) = Ib cos (ωt − 120 )
(1)
∘
ic (t) = Ic cos (ωt − 240 )
in (t) = In cos (ωt + θn )
The reference directions for the currents are shown in the following figure.
Figure 1. Circuit diagram of a four-wire (and four-terminal) three-phase network, with the currents labeled.
Image source: own.
Their corresponding phasors are:
~ ∘
I a = Ia ∠0
~ ∘
I b = Ib ∠ − 120
~ (2)
∘
I c = Ic ∠ − 240
~
I n = In ∠θn
The open-form phasor diagram of the currents is shown below.
Figure 2. Open-form phasor diagram. Image source: own.
In such a power system, from Kirchhoff’s current law applied in the phasor domain to the star point,
assuming no ground faults/leakage, we have:
~ ~ ~ ~
0 = +I a + I b + I c − I n
~ ~ ~ ~
⟹ I n = I a + I b + I c (3)
So, the neutral phasor current is just the sum of the three line/phase phasor currents. The closed-form
phasor diagram of the currents is shown below; it graphically represents the vector addition using the
polygon method applied to phasors.
Figure 3. Closed-form phasor diagram. Image source: own.
Expressing each line phasor current in rectangular form (i.e. decomposing each line current “vector” into
its real part/”x axis component” and imaginary part/”y axis component”), and then separating the
neutral phasor current into is real and imaginary parts, we have in (3):
~ ∘ ∘
I n = [Ia cos (0 ) + jIa sin (0 )]
∘ ∘
+ [Ib cos (−120 ) + jIb sin (−120 )]
∘ ∘
+ [Ic cos (−240 ) + jIc sin (−240 )]
1 √3
= [Ia ] + [− Ib − j Ib ]
2 2
1 √3
+ [− Ic + j Ic ]
2 2
1 1 √3 √3
= (Ia − Ib − Ic ) + j (− Ib + Ic ) (4)
2 2 2 2
Now, we can form a right triangle in the complex plane, with the sum of the real part of the line phasor
currents as one side (the real part of the neutral phasor current), and the sum of the imaginary part of
the line phasor currents as the other side (the imaginary part of the neutral phasor current); the
hypotenuse is the neutral current magnitude:
2 2
1 1 √3 √3
In = √(Ia − Ib − Ic ) + (− Ib + Ic ) (5)
2 2 2 2
Figure 4. Image source: own.
Then we combine like terms and simplify:
2 1 1
In = [(Ia − Ia Ib − Ia Ic )
2 2
1 1 1
2
+ (− Ia Ib + I + Ib Ic )
2 4 b 4
1 1 1 2
+ (− Ia Ic + Ib Ic + Ic )]
2 4 4
3 2 3 3 3 2
⎷+ [( I − Ib Ic ) + (− Ib Ic + Ic )]
4 b 4 4 4
2 2 2
⟹ In = √Ia + I + Ic − (Ia Ib + Ib Ic + Ic Ia ) (6)
b
Or if you want a more general form:
c c
2
In = ∑ I − ∑ Ik Ir (7)
k
k=a k=a
⎷
k≠r
(If we had used the RMS value instead of peak value, the formula would have had the same form.)
Notice if the magnitude of the line currents were also balanced (had same magnitude I ), then
2 2 2
, and Ia Ib + Ib Ic + Ic Ia = , so , as expected for
2 2 2 2
Ia + I + Ic = 3I 3I In = √3I − (3I ) = 0
b
perfectly balanced three-phase four-wire systems.
Personal notes 3 · Follow
Posted by Alejandro Nava · Dec 23
What is the instantaneous active and reactive power of a single-phase non-sinusoidal AC circuit
in terms of active and reactive power, when the voltage and current have the same fundamental
frequency? [Unfinished answer draft]
In a two-terminal network/circuit/device/component/load operating in non-sinusoidal steady-state
conditions, the instantaneous voltage v(t) across the network and the instantaneous conventional
current i(t) through the network are given by: v(t) = V_0 + \sqrt{2} \displaystyle\sum_{n = 1}^{\infty}
ReadV_{…
more
Personal notes 3 · Follow
Posted by Alejandro Nava · Dec 23
What are the instantaneous active and reactive currents of a single-phase non-sinusoidal AC
circuit, when the voltage and current have the same fundamental frequency? [Unfinished
answer draft]
Let’s assume that the instantaneous voltage v(t) across a two-terminal network and the instantaneous
current i(t) through the network are both periodic in time with same fundamental period (or frequency):
v(t) = V_0 + \sqrt{2} \displaystyle\sum_{n = 1}^{\infty} V_{n, \text{rms}} \cos{(n \omega_0 t +… Read more
Summary of Alejandro Nava's answers · Follow
Posted by Alejandro Nava · Dec 23
All my answers on direct/constant/average and alternating/oscillating components
instantaneous power
* Direct/constant/average and alternating/oscillating components of the instantaneous power of a
single-phase network operating in AC steady-state conditions: Alejandro Nava's answer to What are the
direct/constant/average and the alternating/oscillating components of the instantaneous power?R…ead more
Summary of Alejandro Nava's answers · Follow
Posted by Alejandro Nava · Dec 23
All my answers on instantaneous active power and instantaneous reactive power
* Instantaneous active power and instantaneous reactive power of a single-phase network operating in
sinusoidal steady-state conditions: All my answers on instantaneous active power and instantaneous
reactive power of a single-phase network operating in sinusoidal steady-state conditions… Read more
Which PG number of cable gland can be used for 1/2", 3/4" and 1" knockouts?
No answer yet · Last followed Dec 13
Alejandro Nava
Bachelor’s degree in Electrical Engineering, Universidad Rafael Urdaneta (Graduated 2021) · Dec 11
What is meant by the term power factor in electricity?
The physical meaning of power factor of a device is how much average power is consuming the device,
relative to a DC circuit with same voltage and current. Average power is more commonly called active
power or real power, but it is literally the average of instantaneous power, i.e. the average rate o…Read more
How would it be dangerous if a circuit breaker opened a neutral wire, in addition to the hot wire?
5 answers · Last followed Dec 5
Alejandro Nava
Bachelor’s degree in Electrical Engineering, Universidad Rafael Urdaneta (Graduated 2021) · Nov 29
Can I expand my existing solar system by adding more panels or batteries later?
Yes if the inverter, wiring, breakers/fuses support it, as well as if the panels and batteries are of similar
characteristics than the actual ones.
Alejandro Nava
Designed PV arrays, BESS, inverters, power shelves · Updated Nov 27
How should the power of a PV array be sized to feed the load and recharge the battery bank in a
power system?
To choose the size (i.e. rated peak/maximum power) of a PV array that will both feed the load and
recharge the battery bank in a power system (be it a microgrid/hybrid PV system, an off-grid PV
system), simply sum your AC load, DC load, and charging power for the battery bank; then divide Read
by the…
more
Alejandro Nava
Designed PV arrays, BESS, inverters, power shelves · Nov 24
How should the number of rectifiers of an embedded power system (power shelf) be chosen
considering redundancy for a data center?
To choose the number of rectifiers of an embedded power system (EPS) / power shelf, simply divide the
total power required from the rectifiers by the rated power of each rectifier, then add the number of
desired redundant rectifiers. If this results in a number with decimals, round it up. But to comp… Read more
Alejandro Nava
Bachelor’s degree in Electrical Engineering, Universidad Rafael Urdaneta (Graduated 2021) · Nov 22
What is the difference between fuses and circuit breakers in terms of surge protection?
Surge of current or voltage? If of voltage: None. Neither circuits breakers nor fuses are designed for
voltage surges, only for overcurrents (overloads and short-circuits). If of current: Both breakers and
fused can be fast acting. Use a fast-blow fuse, or a class Z or B miniature circuit breaker (MCB… Read more
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