CAPÍTULO 5
EFECTOS DE LA MALA CALIDAD
DE SUMINISTRO ELECTRICO
2008
Dr. Luis Morán T.
1
General Comments
Electric power loads are designed to operate with sinusoidal
voltage (constant amplitude and frequency) within certain
tolerance defined and accepted by different standards.
Not all suppliers follow the same standards, specially with
electronic type of loads.
2008
Dr. Luis Morán T.
2
 Most of electrical and electronics loads are sensible
to voltage fluctuations (sags, swells, outage) and
voltage distortion.
 The basic problem is to know how much each load
can tolerate these fluctuations and distortions
without being damage and without affecting their
operation.
2008
Dr. Luis Morán T.
3
 The reliability of electronic loads is much more closely
tied to the quality of the power supply, as compared to
older or more traditional equipment that may have had
relay controls, or electrical contactor controls.
2008
Dr. Luis Morán T.
4
Voltage concern for electronic type of loads.
(The CBEMA Curve).
2008
Dr. Luis Morán T.
5
IEEE Transactions of Power Delivery, July 1990, pp. 1501-1513
“Power Quality – Two Different Perspective”
 None of these curves have been truly scientifically
generated in the sense that they were created from the
theory of power disturbances.
 The question of validity of these curves, their use in power
distribution assesment, and their appropriateness for
different types of loads are largely unknow and
uncorrelated to actual field evaluations.
2008
Dr. Luis Morán T.
6
The:
 Electric Power Research Institute (EPRI).
 The Canadian Electric Association (CEA).
 National Power Laboratory (NPL).
Combined and assembled their data on voltage sags, spikes and
interruptions.
2008
Dr. Luis Morán T.
7
Power Field Data.
Percent of Nominal Voltage
19 per year
> 700
Events per year
110 %
0 - 200 Events per year
106 %
ANSI C84.1 - 1989 Steady State Voltage Range
87 %
20 - 140Events per year
> 240
Events per year
70 %
0 - 16 Events per year
0 - 10/yr
0.01 s
0.02 s
1s
3s
Duration
2008
Dr. Luis Morán T.
8
In 1996, based on this study, the Information Technology
Industry Council (ITIC), formerly the Computer Business
Equipment Manufacturers Association (CBEMA), modified
the well-know CBEMA curve to the shape shown in next
slide.
2008
Dr. Luis Morán T.
9
Modified CBEMA curve; Actual ITIC/IEEE 1100
200
Overvoltage Conditions
0.5 Cycles
150
100
50
0
Rated
Voltage
Aceptable
Power
8.33 ms
Change in Bus Voltage (%)
250
-50
Undervoltage Conditions
-100
0.0001
0.001
0.01
0.1
1
10
100
1000
Time (s)
2008
Dr. Luis Morán T.
10
The following values have been picked from this new curve.
Voltage spike
500% V
0.01 cycle
200% V
1 us
120% V
0.53s
110% V
continous
Voltage sag
70% V
0.5 s
80% V
10 s
90% V
continous
Momentary interruption
0 V for 20 ms
2008
Dr. Luis Morán T.
11
Applicability:
The curve is applicable to 120 V nominal voltages
obtained from 120 V, 208 Y/120 V, and 120/240 V 60 Hz
systems. Other nominal voltages and frequencies are not
specifically considered and it is the responsibility of the
user to determine the applicability of these documents for
such conditions.
2008
Dr. Luis Morán T.
12
 For all conditions, the term “nominal voltage” implies
an ideal condition of 120 VRMS , 60 Hz.
 Seven types of events are described in this composite
envelope.
•
•
•
•
•
•
•
•
2008
Steady state tolerances.
Line voltage swell.
Low frequency decaying ringwave.
High frequency impulse and ringwave.
Voltage sags.
Drop out.
No damage region.
Prohibit region.
Dr. Luis Morán T.
13
Typical Voltage Tolerance Curve for Computers
2008
Dr. Luis Morán T.
14
Tolerance for Power Equipment.
 Most of the tolerance for power equipment, such as
motors, cables, transformers are specified by different
standard.
 Most of these standards dealt with classical voltage and
current limits.
 News analysis and studies have shown more concern about
the operation of power equipment with distorted voltages
and currents.
2008
Dr. Luis Morán T.
15
TRANSFORMERS
Harmonics applied to transformers may result in increased
audible noise  the effects on these components usually
are those arising from parasitic heating.
The effects of harmonics on transformers are the following:
i) Current harmonics cause an increase in copper losses
and stray flux losses.
ii) Voltage harmonics cause an increase in iron losses.
The overall effect is an increase in transformer heating, as
compared to purely sinusoidal operation.
2008
Dr. Luis Morán T.
16
IEEE C57.12.00-1987 proposes a limit on the harmonics in
transformer current.
 The upper limit of the current distortion factor is 5% at
rated current.
 Maximum rms overvoltages that the transformer should be
able to withstand in steady state 5% at rated load and 10%
at no load.
2008
Dr. Luis Morán T.
17
K – Factor Transformers.
To protect against transformer
harmonics, designers can specify:
overheating
caused
by
 derated equipment, that is oversized transformer that will run
at a fraction of this rated capacity,
 or K-factor transformer specially designed to accomodate
harmonics currents.
2008
Dr. Luis Morán T.
18
K-factor transformer have additional thermal capacity
of known limits:
 Designed features that minimize harmonic current losses.
 Neutral and terminal connection sized at 200 % of normal.
 Allow operation
derating.
2008
up
to
nameplate
Dr. Luis Morán T.
capacity
without
19

Underwriters Laboratiry (UL) recognized the potential safety hazards
associated with using standards tranformers with non linear loads
and developed a rating system to indicate the capability of a
transformer to handle harmonic loads.

The ratings are described in UL 1561 and know as K-factors.

K-factors is a weighting of the harmonic load currents according to
their effect on transformer heating, as derived from ANSI/IEEE C
57.110.

The K-factor indicates the multiple of the 60 Hz winding eddy current
losses the tranformer can safety dissipate.
2008
Dr. Luis Morán T.
20
Typical Tranformer Derating Factor
(for nonlinear loads)
2008
Dr. Luis Morán T.
21
The higher the K-factor, the greater the harmonic
heating effects:
K-Factor =
(I
2
h
) h
2
h
Ih is the load current at harmonic h, in (º/1) bases
such that the total RMS current equals to 1 p.u.
2008
Dr. Luis Morán T.
22
 Some K-factors use up to 15th harmonic, others 25th
harmonic, and still others include up to the 50th
harmonic.
 Based on the underlying assumptions of C57-110, it
seems reasonable to limit the K-factor calculation to
harmonic currents less than the 25th component.
2008
Dr. Luis Morán T.
23
K-Factor Calculation for a Typical Nonlinear Load
Ih (nonlinear load
current)
(Ih)2
ih = (Ih)/(S(Ih)2)1/2
(ih)2
(ih)2h2
1
100,00%
1,000
0,792
0,626
0,626
3
65,7
0,432
0,52
0,27
2,434
5
37,7
0,142
0,298
0,089
2,226
7
12,7
0,016
0,101
0,01
0,495
9
4,4
0,002
0,035
0,001
0,098
11
5,3
0,003
0,042
0,002
0,213
13
2,5
0,001
0,02
0,000
0,06
15
1,9
0,000
0,015
0,000
0,051
17
1,8
0,000
0,014
0,000
0,059
19
1,1
0,000
0,009
0,000
0,027
21
0,6
0,000
0,005
0,000
0,01
23
0,8
0,000
0,006
0,000
0,021
25
0,4
0,000
0,003
0,000
0,006
Total
-
1,596
-
1,00
6,33
h (harmonic
number)
2008
Dr. Luis Morán T.
24
 In establishing standards transformers K-factor ratings,
UL chose ratings of 1, 4, 9, 13, 30, 40 and 50.
 Office areas with non linear loads and large computers
rooms normally have observed K-factors between 4 to
9.
 Areas with high concentrations of single-phase
computers and terminals have observed K-factors of 13
to 17.
2008
Dr. Luis Morán T.
25
Overcurrent
protection Limits.
2008
Dr. Luis Morán T.
26
220 kV
52A-D01
50/51
150:5
34.68W
100A
KCGG-140
TRF-1
11/14.63/18.37 MVA
220/6 kV
Z=11%
A9
51
2000:5
IRI1-I5E5HD
A1
50/51
1000:5
Siemens
7SK88
A8
50:5
2008
Dr. Luis Morán T.
51G
IRI1-E5HD
27
Motors.

Motors can be significantly impacted by the harmonic voltage
distortion.

Harmonic voltage distortion at the motor terminals is translated
into harmonic fluxes within the motor.

Harmonic fluxes do not contribute significantly to motor torque,
but rotate at a frequency different than the rotor synchronous
frequency  inducing high-frequency currents in the rotor.
2008
Dr. Luis Morán T.
28
The effect on motors is similar to that of negative sequence
currents at fundamental frequency:
 The additional fluxes do little more than induce
additional losses.
 Decreased efficiency, along with heating, vibration,
and high pitched noises.
2008
Dr. Luis Morán T.
29
 There is usually no need to derate motors if the
voltage distortion remains below 5% THD, and 3%
for any individual harmonic.
 Excessive heating problems begin when the voltage
distortion reaches 8 to 10% and higher.
 Such distortion should be corrected for long motor life.
2008
Dr. Luis Morán T.
30
Principal operation characteristics
connected to a PWM inverter.





of
a
motor
(TEFC)
The highest internal surface temperature can generally occur on the
surface of the rotor (including the end rings).
Rotor temperatures are generally increased when an induction motor
is fed from a PWM inverter instead of a sinusoidal voltage source.
The difference between the rotor and stator temperature varies with
inverter set up, operating point, and motor design.
Low flux and low carrier frequency are two conditions that increase
rotor temperature.
While the highest temperature (for a constant torque load) may occur
at the lowest speeds, the differential between the rotor and stator
tends to be maximum at the highest speed.
2008
Dr. Luis Morán T.
31
Temp. Rise at normal Flux Level 2-kHz PWM Carrier
Frecuency
Stator Winding (PWM)
Rotor (PWM)
Stator Winding (sine)
Rotor (sine)
Temperature Rise (ºC)
140
130
120
110
100
90
80
70
60
0
10
20
30
40
50
60
70
80
90
Frecuency in Hz
Temperature rise variation with speed (stator frequency)
2008
Dr. Luis Morán T.
32
Temperature Rise (ºC)
Temp. Rise at normal Flux Level 2-kHz
PWM Carrier Frecuency
Stator Rise @ 75% Load
Rotor Rise @ 75% Load
Stator Rise @ 100% Load
Rotor Rise @ 100% Load
140
120
100
80
60
40
0
10
20
30
40
50
60
70
80
90
Frecuency in Hz
Temperature-rise variation with speed and load.
2008
Dr. Luis Morán T.
33
Rotor / Stator Temperature Ratio
Rotor Rise Divided by Stator
Rise in %
100% Load
75% Load
170
160
150
140
130
120
110
100
0
10
20
30
40
50
60
70
80
90
Frecuency in Hz
Rotor rise relative to stator rise.
2008
Dr. Luis Morán T.
34
Motor Life Calculation:
Motor life computation is based on the experimental aging
curves derived by E. Brancato [1] and listed in the IEEE
Std. 117. The life of Class F insulation material can be
expressed by the following equation:
L = 6.0exp[0.0815(155 – T)] years
T = Ta + DT
The hot spot temperature of the stator insulation, Ta is the ambient temperature
in ºC, DT is the temperature rise ºC, determined from the heat transfer model.
[1] E. Brancato, “Estimation of Lifetime Expectancies of Motors,” in
IEEE Trans. Electrical Insulation Magazine, vol. 8, Nº 3, May/June
1992, pp. 5-15.
2008
Dr. Luis Morán T.
35
100 HP Motor: Percent Loss of Life vs. Percent
Harmonic Voltage.

For a 6% of 5th voltage
harmonic component motor
loss of life is 18%.

For a 0.25% of interharmonic
(h=0.1), the motor loss of life
is 18%.
2008
Dr. Luis Morán T.
36
All motors : Percent Loss of Life vs Percent Voltage
Imbalance (sinusoidal voltages).
 The percentage of motor
loss of life is not equal for all
type of motors, since it
depends on the motor rated
power.
2008
Dr. Luis Morán T.
37
100 HP motor with 2% voltage unbalance :
Percent Loss of Life vs Percent Harmonic Voltage.
 The motor loss of life
increases if voltage harmonic
and unbalance are combined.
2008
Dr. Luis Morán T.
38
Temperature at the stator winding.
(Steady state temperature for normal operating conditions 122 ºC)
Case 1:
 5% voltage unbalance in
the supply voltage.
 Final
stator
winding
temperature 128 ºC.
2008
Dr. Luis Morán T.
39
Temperature at the stator winding.
(Steady state temperature for normal operating conditions 122 ºC)
Case 2:
 Voltage harmonic distortion
of 22% with 5th, 7th, 11th,
13th.
 Final stator winding temperature 126 ºC.
2008
Dr. Luis Morán T.
40
Temperature at the stator winding.
(Steady state temperature for normal operating conditions 122 ºC)
Case 3:

Voltage harmonic distortion
of 30% with 5th, 7th, 11th,
13th.

3% voltage unbalance.

Final stator winding temperature 132 ºC
2008
Dr. Luis Morán T.
41
Stator temperature rise and percentage motor loss of life.
Unbalance (%)
Harmonics (%)
2
5
10
15
5
10
15
20
25
Stator Temp (ºC)
122,7
127,
2
141,0
3
161,2
123,
37
123,4
7
123,
7
125,
9
126,
8
Motor life reduction (%)
4
32,9
80,14
97
9,15
9,89
11,8
26,9
31,6
 A larger unbalance in the supplied voltage increases the final
temperature in the stator winding and therefore reduces the motor
life.
 Voltage harmonic components slightly increase the stator winding
temperature.
2008
Dr. Luis Morán T.
42
Voltage fluctuation tolerance in static frequency changers.
Eurotherm Drives
Serie 690+.
ABB
ACS 600.
ABB ACS 500
SAMI GS.
Overcurrent
Protection
Yes
3.5xIn
3.75xIn
(Instantaneous),
2.65xIn (rms)
Overload protection
n.e.
No
1.5xIn (rms)
Dc overvoltage
Protection
Si
1.3xUn
1.35xUn
Dc undervoltage
protection
Si
0.65xUn
0.65xUn
Yes
125 ºC
70 ºC
< 17 V
n.e.
Protected against
short circuit.
Ground Fault
Protection
n.e.
Yes
Yes
Protection against
locked rotor
Yes
Yes
Yes
Overtemperature in
the motor
Yes
Yes
Yes
Open phase
Yes
13% ripple in dc
bus
n.e.
Protections
Maximum
Temperature
Auxiliary Voltage
2008
Dr. Luis Morán T.
43
Ejemplos industriales, Planta Inforsa.
• Análisis de señales de voltaje y corriente en barras de alta, media y baja tensión del
sistema de distribución de energía eléctrica de la Planta Inforsa de CMPC.
• Los puntos de medición en las distintas barras fueron los siguientes:
Scc = 1315 MVA Coci 3Ф
RPM¹³
Osciloscopio
Barra 220 kV
60 MVA
220/13.2 KV
Z= 10 %
TR 3
60 MVA
220/13.2 KV
Z= 10 %
TR 1
RPM²³
Barra A4 13.2 kV
TR 2
60 MVA
220/13.2 KV
Z= 10 %
RPM²
K24
K01
Barra A1 13.2 kV
K22
Leyenda para Instrumentos.
Osciloscopio
El superíndice ¹²³ : indica el período
en donde se efectuó la medición.
TR 4
20 MVA
13.2/6.6 KV
Z= 8.7 %
- período 1: entre 13-18 Julio.
- período 2: entre 18-20 Julio.
- período 3: entre 20-27 Julio.
Osciloscopio
Barra B2 6.6 kV
TR
1.5 MVA
6.6/0.460/0.266
KV
Z= 6.5 %
RPM¹
Osciloscopio
2008
Dr. Luis Morán T.
44
Ejemplos industriales, Planta Inforsa.
• Existen perturbaciones transitorias de alta frecuencia y de
menos de un ciclo de duración que exceden los límites
establecidos. (1.3 veces el valor máximo a 750 Hz).
• Registros en 220 kV.
2008
Fase
Amplitud
(valor peak)
Frecuencia
Duración
Fecha
registro
a
141.66 kV
798 Hz
20 ms
15 Julio
17:52:27,73
b
160.97 kV
794 Hz
20 ms
15 Julio
17:52:27,73
c
138.00 kV
791 Hz
20 ms
15 Julio
17:52:27,73
Dr. Luis Morán T.
45
Ejemplos industriales, Planta Inforsa.
• Registros baja tension Barra 480 V, máquina 1
Efecto NOTCH provocado por la conmutación.
Formas de onda de un ciclo del
voltaje y de la corriente (2.5
ms/div)
2008
Forma de onda del voltaje y de
la corriente en el instante del
cruce por cero de la tensión (50
ms/div), canto de bajada del
voltaje
Dr. Luis Morán T.
Forma de onda del voltaje y de la
corriente en el instante del cruce
por cero de la tensión (50
ms/div), canto de subida del
voltaje.
46
Ejemplos industriales, Planta Inforsa.
• Registros baja tension Barra 480 V, máquina 2
Efecto NOTCH provocado por la conmutación.
Formas de onda de un ciclo del
voltaje y de la corriente (2.5
ms/div)
2008
Forma de onda del voltaje y de
la corriente en el instante del
cruce por cero de la tensión (50
ms/div), canto de bajada del
voltaje
Dr. Luis Morán T.
Forma de onda del voltaje y de la
corriente en el instante del cruce
por cero de la tensión (50
ms/div), canto de subida del
voltaje.
47
Ejemplos industriales, Palas P&H
•Cargas en Operación: 2 palas P&H y 1 perforadora (Subestación Móvil de 10 MVA).
Desde Tesoro 23 kV
Circuito Mina
Barra 23 kV
S/E Móvil 2
10 MVA
23/7.2 kV
900 mts
940 mts
1800 mts
600 mts – 350 MCM
300 mts – 2/0 AWG
640 mts – 350 MCM
300 mts – 2/0 AWG
600 mts – 350 MCM
1200 mts – 2/0 AWG
Pala 1
Pala 2
7.2 kV
7.2 kV
6.9 kV
PV-02
600 V
2008
600 V
Dr. Luis Morán T.
48
Ejemplos industriales, Palas P&H
Perfil de Tensión en Puntos de medición
6,99 V
23,6 kV
(a)
(b)
581 V
7,04 kV
(c)
(d)
Registros de Voltaje en distintos puntos de medición (a) 23 kV Primario S/E (b) 7.2 kV Secundario S/E
(c) Terminales pala primario (d) Terminales pala secundario
2008
Dr. Luis Morán T.
49
Ejemplos industriales, Palas P&H
Ciclo de Trabajo de la Pala
Etapa
1
2
3
4
5
6
Ciclo de Trabajo de la Pala
Movimiento
Se carga el balde con mineral
Giro de la tornamesa hacia el camión
Frenado de la tornamesa y descarga del balde
Giro de la tornamesa hacia el lado del mineral
Frenado de la tornamesa y bajada del balde
Se baja el balde
Las fluctuaciones de voltaje
asociadas a las fuertes variaciones
de potencia activa y reactiva
asociados al ciclo de trabajo
de las palas.
Caídas de voltaje en terminales de las palas son atribuibles a la pérdida de
voltaje en las impedancias equivalentes de los transformadores
(S/E móvil y pala) y de la línea (23 kV).
2008
Dr. Luis Morán T.
50