Armnicas en Sistemas ElctricosEstandar IEEE-519

Jess Baez Septiembre 2000

Referencia: Guide for Applying Harmonic Limits on Power Systems

http://www.electrotek.com

P519A/D5May 4, 1996

Distorsin de voltaje y distorsin de corriente

Carga NoLineal

+

Vs(t)

-

i (t)+

VL(t)

-

Voltaje de la Fuente Voltaje de la Carga(distorsionado)

Corriente de la carga

ProveedorTHDv mx

UsuarioTHDI mx

Distorsin de Voltaje

Distorsiones < 5% son recomendables Distorsiones de voltaje por arriba del 5% provocan efectos negativos en motores, transformadores, relevadores, medidores, etc.

Distorsiones arriba del 10% son INACEPTABLES

El Estandar IEEE-519 recomienda que las compaas suministradorasmantengan los niveles de distorsin de voltaje de acuerdo a la tablade la siguiente pgina y que losclientes mantengan la inyeccin de corriente debajo de valoresque dependen de la rigidez del sistema. Los lmites establecidos para la corriente son fijados de tal manera que si todos los usuarios los respetan, la compaa suministradora puede mantenerla distorsin por debajo de los lmites marcados por el estndar

IEEE-519

3.1 Basic Responsibilities

Harmonics are created by nonlinear loads and devices on the power system. There are a wide variety ofdevices that generate harmonics and they can be connected to the power system at any voltage level. Theone line diagram in Figure 3.1 provides a conceptual system illustrating the interconnection of differentharmonic-producing devices on the power system. The procedures outlined in IEEE 519-1992 aredesigned to limit harmonic currents from individual customers and equipment so that harmonic voltagelevels on the overall power system will be acceptable. The approach involves a divided responsibilitybetween the customer and the utility.

1. The customer. For individual customers, the revised standard limits the level of harmoniccurrent injection at the point of common coupling between the customer and the utility.Recommended limits are provided for individual harmonic components and for the Total DemandDistortion (TDD). These limits are expressed as a percentage of the customer's demand currentlevel, rather than as a percentage of the fundamental, in order to provide a common basis forevaluation over time.

2. The utility. The utility system is the transmission and/or distribution system that serves multiplecustomers. The utility is responsible for the voltage distortion at the point of common coupling.For most systems (below 69 kV), the Total Harmonic Distortion (THD) should be less than 5%.This means that the utility must make sure that system resonance conditions do not result inunacceptable voltage distortion levels, even if all customers are within the recommendedguidelines for harmonic current generation.

Bus Voltage at PCC (Vn)Individual Harmonic

Voltage Distortion (%)Total Voltage

Distortion - THDVn (%)

V kVn 69 3.0 5.0

69 161kV V kVn< 1.5 2.5

V kVn > 161 1.0 1.5

THD

V

VV

hh

nn

= =

22 100%

where:

Vh = magnitude of individual harmonic components (rms volts)h = harmonic orderVn = nominal system rms voltage (rms volts)

Lmites en distorsin de voltaje

T a b l e 3 . 3 . 2H a r m o n i c c u r r e n t d i s t o r t i o n l i m i t s ( Ih ) i n

% o f I L

V kVn 69

I Isc L/ h < 11 11 17

=

LIhI100(%)

hTDD

=

=

=L

maxhh

2hI

2I100(%)TDD

h

[ ]LL

CC

kVMVA

kAIcc3

)( =

Niveles de distorsin permitidos por el estndar IEEE-519

Distorsin en Corriente (Responsabilidad del usuario)

IL representa el valor de corriente correspondiente al valor promediode la demanda mxima que se ha presentado en los ltimos doce meses

Estndar IEEE-519 (Eleccin del punto de acoplamiento comn)

Utility System

Customer Under Study

Other UtilityCustomers

PCC

IL

Utility System

Customer Under Study

Other UtilityCustomers

PCC

IL

THD B ins (%)

Frequency

0

5

10

15

20

25

30

35

40

45

50

0.7 0.8 0.9 1 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9

0.00%

10 .00%

20 .00%

30 .00%

40 .00%

50 .00%

60 .00%

70 .00%

80 .00%

90 .00%

100.00%Site 1092 THD HistogramJune 19 - June 26 , 1992

Count = 305Min imum = 0 .739Max imum = 1 .949

Range = 1.211Mean = 1.406

Median = 1.489Standard Deviation = 0.318

Standard Error = 0.0182Variance = 0.101

Skewness = -0 .521Kurtosis = -0.777

IEEE 519-1992 states that the steady state harmonic limits can be exceeded by 50% for short periods oftime (up to one hour per day). One hour per day is approximately 4% of the time. Therefore, this limitationis consistent with using the design limits as the 95% probability of not being exceeded. The higher limit (1.5x the design limits) can be compared with the measured harmonic level that is not exceeded 99% of thetime (the 99% probability point).

Tolerancias en niveles de distorsin

Case A

0.0%

2.0%

4.0%

6.0%

8.0%

10.0%

0 20 40 60 80 100

Time (minutes)

Tota

l D

em

and D

isto

rtio

n

(%)

Tmaximum = 50 minutes

Ttotal = 50 minutes

Case B

0.0%

2.0%

4.0%

6.0%

8.0%

10.0%

0 20 40 60 80 100

Time (minutes)

Tota

l D

em

and D

isto

rtio

n

(%)

Tmaximum=10 minutes

Ttotal = 50 minutes

4.2.2 Magnitude/Duration Limits for Short Duration HarmonicLevels

The probability distributions do not distinguish between many short bursts of harmonics and one longerburst of harmonics that may exceed a specified threshold. Figure 4.2.2 provides an exaggeratedcomparison of two time trends of harmonic levels illustrating the difference. Both of the cases have thesame total duration where the harmonics exceed a threshold (e.g. 8%) but they may have significantlydifferent impacts on motor or transformer heating.

Tolerancias en niveles de distorsin

There a re tw o indices that can be ca lcu la ted to character ize the t ime va ry ing nature of the ha rmon ics andtake into account both of these cases:

1. The tota l durat ion of harmonic bursts (Ttotal) is the summ a tion of all the t im e in terva ls in w h ich themeasured leve l exceeds a par t icu la r leve l dur ing a spec ified measurement pe r iod.

2. The max imum dura t ion of a single burst (Tm a x i m u m) is the longest t im e in terva l in w hich themeasured d istort ion leve l cont inuously exceeded a par t icu la r leve l dur ing the spec ifiedmeasurement pe r iod.

Both Ttotal and Tm a x i m u m a r e functions of the threshold se lec ted . Spec ific lim its can be deve loped for rangesof these indices and then the lim its can be p lot ted on a magnitude durat ion plot (see example in Sec t ion 5)for compar ison w ith the m e a surement resu lts. Tab le 4 .2.1 provides example magn itude/durat ion lim its thatcan be used to inc lude the t ime va ry ing nature of ha rmon ics in the eva luat ion [6]. They use the steady statelim its from I E E E 519-1992 as a basis (r e fer red to as des ign lim its in the table ). N ote that harmonic burstsw ith durat ions less than 5 seconds are ignored. W hile these short durat ion bursts of harmonics cou ld bevery important , it is difficu lt to apply steady state lim its to control them. W hile r e fe r e n c e [6] uses 5 secondsas the defining per iod for these short bursts, it may be des irab le to use 3 seconds s ince that is the samplingper iod used in IEC 1000-4-7.

T a b l e 4 . 2 . 1 .S h o r t d u r a t i o n h a r m o n i c d i s t o r t i o n l i m i t s

b a s e d o n a 2 4 h o u r m e a s u r e m e n t p e r i o d .

A c c e ptable harmonic d istort ionle v e l (indiv idual or TD D )

M a x imum durat ion o f a s ing leharmonic burst

(Tm a x i m u m)

Tota l duration of all harmon icbursts(T to ta l)

3.0 x (design lim its) 1 sec < Tm a x i m u m < 5 sec 15 sec < Ttotal < 60 sec

2.0 x (design lim its) 5 sec < Tmaxim u m < 10 min 60 sec < Ttotal < 40 min

1.5 x (design lim its) 10 min < Tm a x i m u m < 30 min 40 min < Ttotal < 120 min

1.0 x (design lim its) 30 min < Tm a x i m u m 120 min < Ttotal

Tolerancias en niveles de distorsin

Choose PCC

Calculate Short CircuitCapacity (ISC)

Stage 1:Is Detailed Evaluation

Necessary?

Estimate Weighted DisturbingPower (SDW) or % Nonlinear

Load

Is Power FactorCorrection Existing or

Planned?

No

Calculate Short Circuit Ratio(SCR=ISC/IL)

Yes

Characterize Harmonic Levels(Measurements, Analysis)

Stage 2:Does facility

meet harmoniclimits?

Calculate Average MaximumDemand Load Current (IL)

Yes

No

Design Power FactorCorrection and/or HarmonicControl Equipment (includeresonance and interaction

concerns)

Verification Measurementsand Calculations

(if necessary)

Yes

No

UTILITY CUSTOMER

Procedimiento para la evaluacin de lmites de armnicas