CARGAS NO LINEALES
Joaquin Osorio Bedoya
--
JOAQUIN OSORIO B.
Ingeniero Electricista
Jose Luis Falcon Chavez
En el libro esmeralda IEEE-1100 te indica lo siguiente:
2.2.44 linear load: A load that draws a sinusoidal current wave when supplied by a sinusoidal voltage
Source
2.2.51 nonlinear load: A load that draws a nonsinusoidal current wave when supplied by a sinusoidal
voltage source. (IEEE Std 519)
2.2.52 nonlinear load current: Load current that is associated with a nonlinear load. See also: nonlinear
load.
En la NOM-001-SEDE-2005 (Norma Mexicana) te indica:
Carga no lineal: Aquella donde la forma de onda de la corriente eléctrica en estado estable no siga la
forma de onda de la tensión eléctrica aplicada.
NOTA: Ejemplos de cargas que pueden ser no lineales: equipo electrónico, alumbrado de descarga
eléctrica/electrónica, sistemas de velocidad variable, hornos de arco eléctrico y similares.
Y el neutro se debe dimensionar al 173% mínimo debido a un análisis que viene en el IEEE Std 1100, del cual te pongo un resumen
IEEE
Std 1100-2005 CHAPTER 4
90 Copyright © 2006 IEEE. All rights reserved.
The following example, for the purpose of analysis, shows that the practical worst-case neutral current is
approximately 1.73 times the phase current. (See EPRI PQTN Brief No. 33 [B13].) Following is the formula
for rms current, Irms of the function i(t). For a particular period of time T, the area of the function squared
[i2(t)] is divided by the time period T, and then the square root taken.
As shown in Figure 4-27, phase currents consisting of pulses of short duration could create a situation in
which the frequency of the neutral current was three times the fundamental. Though this may not be the
theoretical maximum of distortion, it certainly is very significantly distorted. The rms values of phase and
neutral currents are shown below the pulses. Notice that the a2t/T cancels out, and the ratio between the
phase current and the neutral current is 1.73.
If the example is changed to be triangular shaped pulses, the area of each pulse is 1/2 of the previous
example, but the ratio remains 1.73.
This true-rms current can dangerously overload the neutral conductor path itself, buses, or the end
terminations/connections, unless they are suitably rated for the increased ampacity. Since the neutral
conductor can be subject to approximately 1.73 times the rms current of the phase conductor, which can
cause overheating of wiring systems and in equipment where this was not taken into consideration, a 200%
rated neutral path, buses, and termination/connection system is the recommended practice for circuits where
the load is primarily made up of switch-mode power supplies, such as those found in computer, office of
information technology equipment (ITE). This subject is discussed in more detail in Chapter 8.
This is a particular problem in that neutral conductors are not subject to the normal overcurrent protection
(provided for the phase conductors) in ac distribution systems (see NFPA 75 and IEEE Power Systems
Harmonics Working Group Report [B28]).
The most common effect observed to date, however, appears to be the burning open of the neutral path at a
point of connection or splice (e.g., at the transformer or panel board neutral bus-lug-wire point), with the
result that the line-neutral connected nonlinear (and any other) loads are left connected to a floating neutral.
This condition easily results in current unbalance conditions with the result that victim loads are forced to
carry excess line current as dictated by the demands of the loads connected across the other two phases and
neutral. They also experience excessive voltage being applied to their input power terminals during these
kinds of events. Therefore, damage to the involved loads is almost certain and can be very costly if they are
associated with electronic equipment and systems.
It should be noted from a practical standpoint, most wiring systems are not predominantly loaded to capacity
with balanced single-phase nonlinear loads, so the likelihood of a serious problem is minimal. The
consideration for neutral conductor component overheating is most applicable to those circuits in
commercial buildings where the predominant loads are switch-mode power supplies.
Espero te sirva…saludos desde México
ING. JOSE LUIS FALCON
DIPSA CONSTRUCTORA
AREA ELECTRICA
55-3400-4806
JOACO
Agradezco las respuestas de todos los compañeros y de mi parte queda
resuelta la inquietud.
Atentamente,
JOAQUIN OSORIO B.
Ingeniero Electricista
Pereira - Colombia
>
> ING. JOSE LUIS FALCON
>
> DIPSA CONSTRUCTORA
>
> AREA ELECTRICA
>
> 55-3400-4806
>
> De: listaele...@googlegroups.com
> [mailto:listaele...@googlegroups.com] En nombre de Joaquin Osorio
> Bedoya
> Enviado el: sábado, 02 de julio de 2011 12:52 p.m.
> Para: lista Eléctrica SM
> Asunto: [LESM] CARGAS NO LINEALES
>
> Buenas tardes.
>
> En el reglamento tecnico colombiano RETIE, establece en el numeral f del
> articulo 15.2 lo siguiente:
>
> "En sistemas trifásicos de instalaciones de uso final con cargas no
> lineales, el conductor de neutro
>
> debe ser dimensionado con por lo menos el 173% de la capacidad de corriente
> de las cargas no
>
> lineales de diseño de las fases, para evitar sobrecargarlo."
>
> Mi pregunta es: A que cargas se refieren como cargas no lineales? Los
> computadores podrian considerarse como tal?
>
> Muchas gracias.
>
> --
> JOAQUIN OSORIO B.
> Ingeniero Electricista
>
> Pereira - Colombia
>
> 43 KVerDescargar
Andres Felipe Jaramillo
Andres Felipe Jaramillo
Ing. Henry Vargas
Yo tengo el documento tecnico que justifica el 1,73 veces el dimensionamiento del neutro en función del calibre de la fase.
Efectivamente es una cuestión de armónicos mas que de cargas no lineales.
Lo publicaré mañana en la Lista, ya que no tengo mi laptop cerca.
Saludos,
Ing. Henry Vargas
Director General
Electric Force Solutions, C.A.
RIF: J-29996292-9
Correo Electronico: cont...@electricforcesolutions.com.ve
Directo: +58 414 6584384 / +58 426 5162282
PIN BlackBerry: 218D1F20
Skype: electricforceve
Twitter: @electricforceve
Caracas, Venezuela
"Soluciones de Ingeniería para Sistemas de Energía de Cargas Críticas"
www.electricforcesolutions.com.ve
Joaquin Osorio Bedoya
--
JOAQUIN OSORIO B.
Ingeniero Electricista
Pérez Jiménez, Raúl
Andres Felipe Jaramillo
Joaquin Osorio Bedoya
Ingeniero Electricista