COORDINACION DE AISLAMIENTO

Facilitador: Jose Manuel Luque Nava

Incidencia de RayosObjetivo Principal

Determinar el nmero de rayos que terminan en la L. T., la S. E. o con cualquiera estructura.

Cmo se obtienen ?

Modelo Geomtrico de la ltima etapa(salto final).Ecuaciones de regresin.

Cmo se miden ?: Densidad de rayos a tierra Ng Rayos/Km2 ao.

Contadores de rayos (CIGRE); rango de observacin 15-20 Km los ms recientes 300-400 KmSistema buscador de direccin de banda ancha (sistema DF).Sistema de tiempo de llegada (sistema TOA).

Con el nmero de das tormenta (nivel ceruneo).

Con qu se mide ?:

En forma indirecta:

Descargas Atmosfricas

Descargas Atmosfricas

Descargas Atmosfricas

1.5 2 Km

Vientos hasta 20 Km/hTemp eratura hasta de 20 C

Descargas Atmosfricas

Tipos de Descargas Atmosfricas

Tipos de Descargas Atmosfricas (cont...)Del 84% al 96% de las descargas atmosfricas a estructuras

con alturas menores a 100 m son de tipo negativos descendentes. El resto de las descargas son negativas ascendentes o positivos.

The Coincident Lightning Events Detector (CLED) uses a flash counter to classify substation circuit breaker operations as either lightning-caused or not lightning-caused.

Ejemplos de un detector de fallas:

Con el contador CIGRE(10 kHz) se hicieron las primeras mediciones de la densidad para comparar con el nmero de das tormenta/km2.La forma general de la ecuacin de regresin es:

ag dN kT

Donde:Td es el da tormentas al ao (Nivel ceruneo)

FUENTE k aInglaterra (Stringfellow)

Suecia (Muller-Hillebrands)E.U.A (J. G. Anderson)

Young et. al.

0,00260,0046

0,120,177

2211

Otras ecuaciones de regresin propuestas:1,30,036g dN kT Kolokovov y Pavlova (ex

URSS)

1,250,04g dN kT

Eriksson (Sudfrica)

Aceptada por IEEE como por CIGREPromedio de NgDesviacin estndar = 32 % mediaAprox. 2 hr de tormenta por da

MAPAS DE DENSIDAD DE RAYOS A TIERRAAlgunos datos de inters:

El indice de incidencia ms alto en el mundo es de Java, 223 das tormenta por ao.El valor del nmero de das tormenta es un valor promedio, el cul es el utilizado en la conversin de densidad de rayos a tierra. La desviacin estndar es en promedio 19 % de la media.Para valores bajos de Td la desviacin estndar aumenta: ejem. 55 % para Td = 4. Para valores altos de Td, la desviacin estndar es 14 % para Td = 70

Los mapas tambin dan un estimado del nmero de horas de tormenta.La relacin sugerida por CIGRE entre el nmero de das tormenta y el nmero de horas tormenta es la siguiente:

0,05g hN kT Donde: Th es el nmero de horas tormenta-ao

MAPAS DE DENSIDAD DE RAYOS A TIERRA

Densidad de rayos a tierra de 1981 - 1991

Los mapas actuales indican que para 30 das de tormenta-ao la densidad de rayos vara de 1 a 2, empleando las ecuaciones de CIGRE e IEEE resulta 2,8 y si utilizan las ecuaciones de Young y Anderson resultan densidades entre 3-5,3.

MAPAS DE DENSIDAD DE RAYOS A TIERRA

La actividad atmosfrica se clasifica de la siguiente manera: 5 - 15 Nivel Bajo. 15 30 Nivel Medio 30 90 Nivel Alto Mayor de 90 Nivel Muy Alto

Dt

Angulo de Blindaje

Efecto de las sobretensiones

Descargas en la Torre de transmisin

Siluetas de Torres de Transmisin

Importancia del Sistema de tierra en una lnea de transmisin

Importancia del Sistema de tierra en una lnea de transmisin (cont. )

Determinacin de la resistencia considerando electrodos

Determinacin de la resistencia considerando electrodos (cont. )

Medidor de resistividad del terreno

Tipos de Resistividad del terreno

Ecuaciones para los tipos de electrodos

Ecuaciones para los tipos de electrodos (cont. )

Ejemplo.

Suponga que se tienen un terreno con resistividad de 500 m y que se instala una lnea que usa contrantenas como red de tierras, con conductores de acero de dimetro de a una profundidad de 50 cm.1. Calcular la longitud total de la contrantena para una

resistencia al pie de torre de 15 .2. Calcular la longitud total de la contrantena para una

resistencia al pie de la torre de 10 .

Determinacin de la resistencia considerando Contrtenas (cont. )

Determinacin de la resistencia considerando Contrtenas (cont. )

Determinacin de la resistencia considerando Contrtenas

Determinacin de la resistencia considerando Contrtenas (cont. .)

Determinacin del facto de acoplamiento capacitivo con un solo hilo de guardaComo es sabido las lneas de transmisin con un cable de guarda presentan un blindaje ms deficiente que cuando se usan dos cables de guarda en trminos generales, sin embargo las ondas que inciden sobre este cable induce una tensin en todas las fases de los conductores que conducen la potencia. El valor del factor de acoplamiento cambia para cada conductor de fase dependiendo de su posicin.

Determinacin del facto de acoplamiento capacitivo con un solo hilo de guarda

(cont. )

Determinacin del facto de acoplamiento capacitivo con un solo hilo de guarda

(cont. )El factor de acoplamiento se obtiene con la siguiente expresin:log

2log

baC hr

Donde: C = es el factor de acoplamiento capacitiva.a = distancia del conductor a hilo de guarda.b = distancia del conductor a la imagen del hilo de guarda.h = altura del hilo de guarda hasta tierra.r = radio del hilo de guarda.

Determinacin del facto de acoplamiento capacitivo con dos

hilos de guardaLa mayora de las lneas de transmisin por razones de proteccin efectiva contra descargas atmosfricas, usan dos cables de guarda, en este caso se supone que la onda de corriente del rayo se induce en partes iguales en cada conductor de guarda y el factor de acoplamiento se calcula para cualquiera de los conductores de fase, como una resultante de las ondas en los cables de guarda.

Determinacin del facto de acoplamiento capacitivo con dos hilos de guarda (cont.

)

STANDARD ATMOSPHERIC CONDITIONS

All specifications of strength are based on the following atmospheric conditions:1. Ambient temperature: 202. Air pressure: 101.3 kPa or 760mm Hg3. Absolute humidity: 11 grams of water/m3 of air4. For wet tests: 1 to 1.5 mm of waterlminuteIf actual atmospheric conditions differ from these values, the strength in terms ofvoltage is corrected to these standard valuesTYPES OF INSULATION

Insulation may be classified as internal or external and also as self-restoring and nonself-restoring. Per ANSI C92.l (IEEE 13 13.1) [1,2].

External Insulation: External insulation is the distances in open air or across the surfaces of solid insulationin contact with open air that are subjected to dielectric stress and to the effects of the atmosphere. Examples of external insulation are the porcelain shell of a bushing, bus support insulators, and disconnecting switches.Internal Insulation: Internal insulation is the internal solid, liquid, or gaseous parts of the insulation of equipment that are protected by the equipment enclosures from the effects of the atmosphere. Examples are transformer insulation and the internal insulation of bushings. Equipment may be a combination of internal and external insulation.Examples are a bushing and a circuit breaker.Self-Restoring (SR) Insulation: Insulation that completely recovers insulating properties after a disruptive discharge (flashover) caused by the application of a voltage is called self-restoring insulation.This type of insulation is generally external insulation.Non-Self-Restoring (NSR) Insulation: This is the opposite of self-restoring insulators, insulation that loses insulating properties or does not recover completely after a disruptive discharge caused by the application of a voltage. This type of insulation is generally internal insulation.

DEFINITIONS OF APPARATUS STRENGTH, THE BIL AND THE BSL

The BIL or basic lightning impulse insulation level is the electrical strength of insulation expressed in terms of the crest value of the "standard lightning impulse."That is, the BIL is tied to a specific waveshape in addition being tied to standard atmospheric conditions. The BIL may be either a statistical BIL or a conventional BIL. The statistical BIL is applicable only to self-restoring insulations, whereas the conventional BIL is applicable to non-self-restoring insulations. BILs are universally for dry conditions.

The statistical BIL is the crest value of standard lightning impulse for which the insulation exhibits a 90% probability of withstand, a 10% probability of failure.The conventional BIL is the crest value of a standard lightning impulse for which the insulation does not exhibit disruptive discharge when subjected to a specific number of applications of this impulse.

BIL-Basic Lightning Impulse Insulation Level

In IEC Publication 71 [3], the BIL is known as the lightning impulse withstand voltage. That is, it is defined the same but known by a different name. However, in IEC, it is not divided into conventional and statistical definitions.

DEFINITIONS OF APPARATUS STRENGTH, THE BIL AND THE BSL (CONT..)

DEFINITIONS OF APPARATUS STRENGTH, THE BIL AND THE BSL (CONT..)BSL-Basic Switching Impulse Insulation Level

The BSL is the electrical strength of insulation expressed in terms of the crest value of a standard switching impulse. The BSL may be either a statistical BSL or a conventional BSL. As with the BIL, the statistical BSL is applicable only to selfrestoring insulations while the conventional BSL is applicable to non-self-restoring insulations BSLs are universally for wet conditions.The statistical BSL is the crest value of a standard switching impulse for which the insulation exhibits a 90% probability of withstand, a 10% probability of failure.The conventional BSL is the crest value of a standard switching impulse for which the insulation does not exhibit disruptive discharge when subjected to a specific number of applications of this impulse.In IEC Publication 71 [3], the BSL is called the switching impulse withstand voltage and the definition is the same. However, as with the lightning impulse withstand voltage, it is not segregated into conventional and statistical.

DEFINITIONS OF APPARATUS STRENGTH, THE BIL AND THE BSL (CONT..)

DEFINITIONS OF APPARATUS STRENGTH, THE BIL AND THE BSL (CONT..)

Statistical vs. Conventional BIL/BSL

As noted, the statistical BIL or BSL is defined statistically or probabilistically. For every application of an impulse having the standard waveshape and whose crest is equal to the BIL or BSL, the probability of a flashover or failure is 10%. In general, the insulation trength characteristic may be represented by a cumulative Gaussian distribution as portrayed in Fig. 3. The mean of this distribution or characteristic is defined as the critical flashover voltage or CFO. Applying the CFO to the insulation results in a 50% probability of flashover, i.e., half the impulses flashover. Locating the BIL or BSL at the 10% point results in the definition that the BIL or BSL is 1.28 standard deviations, f, below the CFO. In equation form

Sigma in per unit of the CFO is properly called the coefficient of variation. However, in jargon, it is simply referred to as sigma. Thus a sigma of 5% is interpreted as a standard deviation of 5% of the CFO. The standard deviations for lightning and switching impulses differ. For lightning, the standard deviation or sigma is 2 to 3%, whereas for switching impulse, sigma ranges from about 5% for tower insulation to about 7% for station type insulations, more later.

The conventional BIL or BSL is more simply defined but has less meaning as regards insulation strength. One or more impulses having the standard waveshape and having a crest value equal to the BIL or BSL are applied to the insulations. If no flashovers occur, the insulation is stated to possess a BIL or BSL. Thus the insulation strength characteristic as portrayed in Fig. 4 must be assumed to rise from zero probability of flashover or failure at a voltage equal to the BIL or BSL to 100% probability of flashover at this same BIL or BSL.

Statistical vs. Conventional BIL/BSL (CONT)

Statistical vs. Conventional BIL/BSL (CONT)

Statistical vs. Conventional BIL/BSL (CONT)

There exists a standard number series for both BILs and BSLs that equipment standards are encouraged to use. In the USA, ANSI C92 and IEEE 1313.1 lists the values shown in Table 2, while IEC values are shown in Table 3.

These values are "suggested" values for use by other equipment standards. In other words, equipment standards may use these values or any others that they deem necessary. However, in general, these values are used. There are exceptions. For any specific type of equipment or type of insulation, there does exist a connection between the BIL and the BSL. For example, for transformers, the BSL is approximately 83% of the BIL. Thus given a standard value of the BIL, the BSL may not be a value given in the tables. In addition, in IEC, phase-phase tests are specified to verify the phase-phase BSL. The phase-phase BSL is standardized as from 1.5 to 1.7 times the phase-ground BSL. Thus, in this case, the BSL values are not the values listed.

Standard BILs and BSLs

Standard BILs and BSLs (CONT.)

Standard BILs and BSLs (CONT.)

Standard BILs and BSLs (CONT.)

Standard BILs and BSLs (CONT.)

CALCULO DE DISTANCIAS EN AIREA partir del concepto de tensin crtica de flameo, se establecen los valores de tensin de aguante o nivel bsico de aislamiento al impulso (NBI) que se establecen como valores tericos para una distribucin de Gauss normal.

Ejemplo. Para determinar el aislamiento en aire en una lnea de transmisin con tensin nominal de 765 kV, se hicieron pruebas de impulso por rayo y se aplico el siguiente criterio de prueba: 20 impulsos o tensiones de prueba para cada nivel de tensin. Ondas de rayo con polaridad negativa.

Tensin de Prueba (kV)

Nmero de pruebas

Nmero de flmeos o fallas

% de fallas

1750 20 1 1/20 = 5%1850 20 5 5/20 = 25%1900 20 10 10/20 = 50%2000 20 17 17/20 = 85%2150 20 20 20/20 = 100%

Total de fallas= 53

Coordinacion de aislamientoSlide 2Slide 3Slide 4Slide 5Slide 6Slide 7Slide 8Slide 9Slide 10Slide 11Slide 12Slide 13Slide 14Slide 15Slide 16Slide 17Slide 18Slide 19Slide 20Slide 21Slide 22Slide 23Slide 24Slide 25Slide 26Slide 27Slide 28Slide 29Slide 30Slide 31Slide 32Slide 33Slide 34Slide 35Slide 36Slide 37Slide 38Slide 39Slide 40Slide 41Slide 42Slide 43Slide 44Slide 45Slide 46Slide 47Slide 48Slide 49Slide 50Slide 51Slide 52Slide 53Slide 54Slide 55Slide 56Slide 57Slide 58Slide 59Slide 60Slide 61Slide 62Slide 63Slide 64Slide 65Slide 66Slide 67Slide 68Slide 69Slide 70Slide 71Slide 72Slide 73Slide 74Slide 75Slide 76Slide 77Slide 78Slide 79Slide 80Slide 81