Download Mohamed Ashour

COMPARISON BETWEEN INDUCTION AND DIGITAL
ENERGY METER IN THE PRESENCE OF DISTORTION
Mohamed Ashour
Kamelia Youssef
Abstract
Power quality problems are often caused by the consumer's own installation and nonlinear loads. It is
therefore essential that a consumer considers this possibility before making a complaint.
Harmonic distortion is one of power quality problems, which typically arise from consumer's electrical
equipment. Many of the new equipments installed today create harmonics and are sensitive to harmonic
content, that means, most currents these days are distorted.
Alexandria Electricity Distribution Company (AEDC) has to identify the source of harmonic and work with the
relevant consumers to limit the harmonics to acceptable levels. Also AEDC plans to replace induction
meters by electronic meters. Although the induction meter have good long term stability and they are
reliable in simple measurement, but harmonics cause remarkable measurement errors to the induction
meters.
This paper presents the observations and remarks about real time measurement results carried out for
different nonlinear loads through induction meters, digital meters and portable energy analyzers.
1-Background
Harmonic currents and voltages are generated by non-linear loads connected on the electric distribution
system. All power electronic converters used in various types of electronic systems can increase harmonic
distortions by injecting harmonic currents directly into the grid.
Harmonics may cause cables to overheat. Motor may also overheat or become noisy. Capacitors overheat
with, in the most severe cases, the risk of explosion as the dielectric breaks down. Electronic displays and
lighting may flicker, circuit breakers can trip, computers fail and meters give false reading.
In 1994 Alexandria Electricity Distribution Company (AEDC) started a research program on harmonic
distortion levels at utility and user buses. All supply side buses, in Alexandria now have measurable
harmonic content in voltage and current. On end-consumer buses, the harmonic monitoring and
measurement are still going on.
This change in the end-consumer load profile is a disadvantage for energy distributors which bill energy
based only on active power. With the application of non-linear loads to power lines the active energy no
longer represents the total energy delivered. As a response to improve billing, the measurement of reactive
energy is gaining interest.
2-Three-phase watthour meter :

A digital electronic watthour meter.
Its type is described as a 3-element meter for four wire three-phase wye service. It has a specified
accuracy at unity power factor, rated voltage and frequency of ±0.5% error for currents between 0.1 and
20A

Induction watthour meter
It is a 3-stator induction watthour meter, which is probably the most familiar energy measurement device
with accuracy ± 2%.
Comparison between induction and electronic energy meters:

Accuracy :
While induction meters are normally available with class 2 accuracy , electronic meters of class 1 accuracy
are very common.

Installation :
The induction meter is very sensitive to the position in which it is installed . If it is not mounted vertically , it
will run slow , resulting in revenue loss. Electronic meters are not sensitive to their mounting position.

Tamper :
The induction meters can be tampered very easily even without disturbing the wiring , either by using
external magnet or by inserting a thin film into the meter to touch the rotating disc. Electronic meters cannot
be tampered by using any of these methods . Moreover they indicate the presence of tamper by indicator .

Low current performance :
Most of the induction meters tend to run slow after a few years and stop recording at low loads typically
below 40% of their basic current . Electronic meters record consistently and accurately even at 5% of their
basic current . Also they are guaranteed to start recording energy at 0.4% of their basic current.

Low voltage performance
Most of the mechanical meters became inaccurate at voltages below 75% of rated voltage whereas
electronic meters record accurately even at 50% of rated voltage.
The basic principle of operation of induction energy meter is very simple . The essential components of an
induction energy meter are two magnets and the rotating disc. The speed of rotation is proportional to the
rate of real power consumption and the rotating disc also serves as a mechanical integrator of kilowatt over
time , i,e, the familiar kilowatt hour unit .
The important remarks for induction energy meter in presence of harmonics [1] are :

The 2nd and 4th harmonic currents contribute surplus average forces (or torques) to the meter
which increase with increasing lagging power – factor (positive sign)

The 3rd and 5th harmonic currents contribute negligible forces (or torques) to the meter (negative
sign)

The induction energy meter will register real power due to the 2nd and 4th harmonics but not the 3rd
and 5th harmonics.
3 - Reactive and active power
The reactive power is defined in the IEEE 100-1996 (Standard Dictionary) under the energy manager as :

Q = Reactive Power =

h 1
Vh Ih sin (φh)
The average active power is define as :

P = Average active power =

Vh Ih cos (φh)
h 1
Where Vh and Ih are respectively the voltage and current rms values of the h
th
harmonics of the line
frequency, and φh is the phase difference between the voltage and current h th harmonics.
However, the energy contained in the harmonics causes measurement errors.
In the presence of harmonics, P and Q depend mainly on the direction of φh as follows :
Q is increased when 0o < φh < 180o
Q is decreased when 180o < φh < 360 o
P is increased when 90o > φh > 270 o
P is decreased when 90o < φh < 270 o
4- Monitoring and Measurement :
AEDC has just installed new electronic meters inside the existing induction meters for selected endcustomer which generate extensive harmonics.
The portable energy analyzer instrument is used for recording voltage, current, power, power factor, energy
and total & individual voltage and current distortion.
Several audit series of measurement and monitoring for electrical parameters for several customers, and
24-hour period -at least- per each (at low voltage bus), were carried out. The most new loads are electronic
based non-linear loads which represent the sources of harmonic distortions.
Electrical measurement for 23 case study have different activities such as : exchanger, textile, food, paper,
metal, --- are carried out. The mechanical and digital meters are installed together in each case study.
Accuracy of mechanical meters are adjusted at ± 0.5%.
Table (1) summarizes the consumption for each meter, error% and THDV% & THDI%.
Figs (1) & (2) give the results of electrical parameters measurement for case study (1), without and with
capacitor bank in service, respectively.
The observation of table (1) is :
-
Maximum difference (error%) is + 4.833% : - 4.737%
-
Case studies 18, 20 have no error%
-
Max THDV% is 1.7% : 7%
-
Max THDI% is 4.93% : 60%
-
Not any relation between error% and THD%
5 - Phase Difference (φh)
The phase difference between the voltage and current h th harmonics is studied and monitored for some
case studies.
Figs (3) & (4) represent time variation of cos φh and sin φh per phase R for case study No. (1) where h
equals 3, 5, 7. The cos φh and sin φh are alternating on positive and negative signs over measurement
duration, that means the harmonic power components eliminate each other. The result is + 0.487% error.
Table (2) summarizes the results of φh for some case studies.
The observation of table (2) is :
-
cos φ3 alternates on (+) & (-) sign
-
When cos φ5 and cos φ7 are positive, the error is high.
-
When cos φ3 , cos φ5 , cos φ7 alternate on (+) &(-) sign, the error is neglected.
Table (2) Phase difference Φh for some case studies
Case
Max.
Max.
study
THDV%
THDI%
4
5.18
12
15
Cos Φ3
Cos Φ5
Cos Φ7
Error %
37.65
(+) &(-)
+
+
+ 4.833
2.5
5.7
(+) &(-)
+
+
+ 2.239
3.6
25.35
(+) &(-)
(+) &(-)
(+) &(-)
- 0.089
Basically , the power factor improvement can be used when it is not necessary to take measures to avoid
resonance problems or to reduce or eleminate the harmonic distortions. This is the case when the resonant
frequency given by the supply network inductance and the capacitance of the capacitor is relatively high
and harmonic content of the system is very low. Also the shunt capacitor is not a source of harmonics but it
causes magnification of harmonic currents.
The shunt capacitor effects on phase difference (Φh) between the voltage and current hth harmonics.
Fig (5) shows time variation of cos Φh per phase R for case study No.(1) when capacitor is off by comparing
Fig (5) with Fig (3) , the cos Φh variation is changed from positive sign to alternate on positive and negative
sign.
Conclusion
With more and more non-linear loads at end-user, more signal harmonics are generated on the electricity
grid, at different voltage levels .
This change in the end-consumer profile is a disadvantage for energy distribution which bill energy based
only on active power . With application of disturbing loads to power lines the active energy no longer
represent the total energy delivered . As a response to improve billing, the measurement of reactive energy
is gaining interest.
Comparison between consumption of induction and digital meters in the presence of distortion is carried out.
The remarks are :

In spite of THDI% & THDV% are exceed the standard limit , not any relation between errors % and
THD%

There is relation between phase difference Φh and errors%

There is signification for presence of power factor improvement

The energy meter will register surplus power due to the harmonics have positive signs.
This project is still in going on to prepare empirical formela between errors % and Φh.
References :
[1] Huen Y.K. “Harmonic Forces of An Induction Energy Meter”
http://web.singnet.com.sg/huens/
[2] A. Domijan , E. Embriz – Santader , G. Lamer , C. Stiles
“Watthour Meter Accuracy Under Controlled Unbalanced Harmonic Voltage and Current
Conditions”
IEEE Transactions on Power Delivery , Vol. 11 No. 1,January 1996
[3] Ashok. S “Power and Energy Measurements”
I STE Winter School on Power Quality Problems and Remedial Measures.
[4] Wilsun Xu, Yilu Liu “ A Method for Determining Customer and Utility Harmonic contributions at
the Point of Common Coupling” IEEE Transactions of Power delivery , Vol. 15 , No. 2, April 2000.
[5] Etienne Moulin “Measuring Reactive Power in Energy Meters” Metering International – Issue12002.
[6] Rajendra Prasad “Electrical Measurements and Measuring Instruments” KHANNA PUBLISHERS
DELHI-6 1984
Table ( 1) Consumption registration errors and range of harmonic distortions.
Duration of
Consumption (KWH)
consumption
Activity
KWH
Error*
difference
%
Day
month
Induction meter
Electronic meter
EX 1
4
‫ـــ‬
11180
11125.6
54.4
T1
10
5
5261200
5182977.2
T2
22
6
2454600
T3
22
6
T4
22
T5
THDI %
TH
Min
Max.
Min
+0.487
10
60
2
78222.8
+1.486
17.3
59.5
2.1
2474915.2
-20315.2
-0.828
2.4
10.9
1
354750
337606.7
17143.3
+4.833
12.17
37.65
2.22
6
2228100
2205174.1
22925.9
+1.029
6.35
31.11
1.93
-
2
1566936
1557400.4
-9535.6
-0.607
4.1
12.4
1.7
T6
-
2
1845360
1805530.7
-39829.8
-2.158
3.9
12.6
1.9
T7
10
7
490800
493383
-2583
-0.53
0
25
1.3
F8
11
10
776480
782257.7
-5777.7
-0.744
5.3
18.8
0.8
F9
‫ـ‬
2
700920
701252.2
-332.2
-4.736
2.35
8.15
1.2
F 10
‫ـ‬
2
253800
261008.9
-7208.9
-2.840
1.9
26.8
0.7
F 11
‫ـ‬
2
15152
14812.7
339.3
+2.239
3.8
5.7
1.4
F 12
‫ـ‬
2
389040
386314.6
2725.4
+0.700
4.91
14.15
1.95
F 13
19
3
266580
260613.6
5966.4
+2.238
0
6.6
1.2
F 14
‫ـ‬
2
90540
90027.6
-809736
-0.089
4.43
25.35
1.91
F 15
1
2
616050
610506.7
5543.3
+0.899
0.87
4.93
1.11
F 16
1
2
644100
636948.5
7151.5
+1.110
2.41
15.55
1.53
F 17
24
3
85740
85740.6
-0.6
-0.001
10.4
53.9
2.2
P 18
15
6
4230600
4167481.8
63118.2
+1.492
2.75
9.31
1.44
-
-
3.5
16.2
0.8
* Error based on consumption of induction meter
P 19
22
2
3567.8
3567.8
Ex: Exchange
T: Textile
F: Food
P: Paper
M: Metal
P 20
14
9
307820
304810
3010
+0.977
0
47.54
2.52
M 21
8
5
337458.9
340462.8
-3003.9
-0.89
4.1
20.2
1.5
M 22
8
5
206840
205733.2
1106.8
-0.535
0
5.8
1.48
Slide 1
COMPARISON BETWEEN
INDUCTION AND DIGITAL
ENERGY METER IN THE
PRESENCE OF DISTORTION
Mohamed Ashour
Kamelia Youssef
Alexandria Electricity Distribution Company
Alexandria – Egypt
Email : [email protected]
Slide 2
Abstract
Power
quality
consumer's
problems
own
are
installation
often
caused
by
and
nonlinear
the
loads.
Harmonic distortion is one of power quality problems,
which
typically
arise
from
consumer's
electrical
equipment. Many of the new equipments installed today
create harmonics and are sensitive to harmonic content,
that means, most currents these days are distorted.
Slide 3
Alexandria Electricity Distribution Company (AEDC) has
to identify the source of harmonic and work with the
relevant consumers to limit the harmonics to acceptable
levels. Also AEDC plans to replace induction meters by
electronic meters. Although the induction meter have
good long term stability and they are reliable in simple
measurement, but harmonics cause remarkable
measurement errors to the induction meters.
Slide 4
1-Background
In 1994 Alexandria Electricity Distribution Company (AEDC)
started a research program on harmonic distortion levels at
utility and user buses. All supply side buses, in Alexandria
now have measurable harmonic content in voltage and
current. On end-consumer buses, the harmonic monitoring
and measurement are still going on.
This
change
in
the
end-consumer
load
profile
is
a
disadvantage for energy distributors which bill energy based
Slide 5
only on active power. With the application of non-linear loads
to power lines the active energy no longer represents the
total energy delivered. As a response to improve billing, the
measurement of reactive energy is gaining interest.
Slide 6
•
The important remarks for induction energy meter in
presence of harmonics [1] are :
•
The 2nd and 4th harmonic currents contribute surplus
average forces (or torques) to the meter which increase
with increasing lagging power – factor (positive sign)
•
The 3rd and 5th harmonic currents contribute negligible
forces (or torques) to the meter (negative sign)
•
The induction energy meter will register real power due
to the 2nd and 4th harmonics but not the 3rd and 5th
harmonics.
Slide 7
3 - Reactive and active power
The reactive power is defined in the IEEE 100-1996
(Standard Dictionary) under the energy manager as :

Q  Reactive power  
h 1
Vh Ih sin (φh)
The average active power is define as :

P = Average active power = 
h 1
Vh Ih cos (φh)
Slide 8
Where Vh and Ih are respectively the voltage and current
rms values of the h
th
harmonics of the line frequency,
and φh is the phase difference between the voltage and
current h th harmonics.
However, the energy contained in the harmonics causes
measurement errors.
In the presence of harmonics, P and Q depend mainly on
Slide 9
the direction of φh as follows :
Q is increased when 0o < φh < 180o
Q is decreased when 180o < φh < 360 o
P is increased when 90o > φh > 270 o
P is decreased when 90o < φh < 270 o
Slide 10
4-Monitoring and Measurement
AEDC has just installed new electronic meters inside the
existing induction meters for selected end- customer
which generate extensive harmonics.
The portable energy analyzer instrument is used for
recording voltage, current, power, power factor, energy
and total & individual voltage and current distortion.
Slide 11
Several audit series of measurement and monitoring for
electrical parameters for several customers, and 24-hour
period -at least- per each (at low voltage bus), were carried
out. The most new loads are electronic based non-linear
loads which represent the sources of harmonic distortions.
Slide 12
Electrical measurement for 23 case study have different
activities such as : exchanger, textile, food, paper, metal, -- are carried out. The mechanical and digital meters are
installed together in each case study. Accuracy of
mechanical meters are adjusted at ± 0.5%.
Table (1) summarizes the consumption for each meter,
error% and THDV% & THDI%.
Figs (1) & (2) give the results of electrical parameters
Slide 13
Table ( 1) Consumption registration errors and range of harmonic distortions.
Case
study
Activity
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
EX 1
T1
T2
T3
T4
T5
T6
T7
F8
F9
F 10
F 11
F 12
F 13
F 14
F 15
F 16
F 17
P 18
P 19
P 20
M 21
M 22
Duration of
consumption
Day
4
10
22
22
22
10
11
‫ـ‬
‫ـ‬
‫ـ‬
‫ـ‬
19
‫ـ‬
1
1
24
15
22
14
8
8
month
‫ـــ‬
5
6
6
6
2
2
7
10
2
2
2
2
3
2
2
2
3
6
2
9
5
5
Consumption (KWH)
Induction meter
11180
5261200
2454600
354750
2228100
1566936
1845360
490800
776480
700920
253800
15152
389040
266580
90540
616050
644100
85740
4230600
3567.8
307820
337458.9
206840
Electronic meter
11125.6
5182977.2
2474915.2
337606.7
2205174.1
1557400.4
1805530.7
493383
782257.7
701252.2
261008.9
14812.7
386314.6
260613.6
90027.6
610506.7
636948.5
85740.6
4167481.8
3567.8
304810
340462.8
205733.2
* Error based on consumption of induction meter
Ex: Exchange
T: Textile
F: Food
P: Paper
KWH
difference
Error*
%
54.4
78222.8
-20315.2
17143.3
22925.9
-9535.6
-39829.8
-2583
-5777.7
-332.2
-7208.9
339.3
2725.4
5966.4
-809736
5543.3
7151.5
-0.6
63118.2
3010
-3003.9
1106.8
+0.487
+1.486
-0.828
+4.833
+1.029
-0.607
-2.158
-0.53
-0.744
-4.736
-2.840
+2.239
+0.700
+2.238
-0.089
+0.899
+1.110
-0.001
+1.492
+0.977
-0.89
-0.535
M: Metal
THDI %
Min
10
17.3
2.4
12.17
6.35
4.1
3.9
0
5.3
2.35
1.9
3.8
4.91
0
4.43
0.87
2.41
10.4
2.75
3.5
0
4.1
0
Max.
60
59.5
10.9
37.65
31.11
12.4
12.6
25
18.8
8.15
26.8
5.7
14.15
6.6
25.35
4.93
15.55
53.9
9.31
16.2
47.54
20.2
5.8
THDV %
Min
2
2.1
1
2.22
1.93
1.7
1.9
1.3
0.8
1.2
0.7
1.4
1.95
1.2
1.91
1.11
1.53
2.2
1.44
0.8
2.52
1.5
1.48
Max.
7
6.5
2.7
5.18
5.15
3.4
5.1
5.002
2
3.34
2.7
2.5
3.86
2.8
3.6
2.94
4.29
6.4
5.94
1.7
4.78
5.5
4.36
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KW
KW
Slide 14
TIME
phase= .
Avg.Value for
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phase= .
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P
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Fig ( ) Electrical parameters
with capacitor bank
for case study ( )
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Fig ( ) Electrical parameters
without capacitor bank
for case study ( )
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THDV
IEEE LIMIT
%
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TIME
IEEE LIMIT
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IEEE
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KVAR
KVAR
TIME
Slide 15
easurement for case study (1), without and with capacitor
bank in service, respectively.
The observation of table (1) is :
Maximum difference (error%) is + 4.833% : - 4.737%
Case studies 18, 20 have no error%
Max THDV% is 1.7% : 7%
Max THDI% is 4.93% : 60%
Not any relation between error% and THD%
Slide 16
5 - Phase Difference (φh)
The phase difference between the voltage and current h th
harmonics is studied for some case studies.
Figs (3) & (4) represent time variation of cos φh and sin φh
per phase R for case study No. (1) where h equals 3, 5, 7.
The cos φh and sin φh are alternating on positive and
negative signs over measurement duration, that means
the harmonic power components eliminate each other.
The result is + 0.487% error.
Slide 17
able (2) summarizes the results of φh for some case
studies.
he observation of table (2) is :
cos φ3 alternates on (+) & (-) sign
When cos φ5 and cos φ7 are positive, the error is high.
When cos φ3 , cos φ5 , cos φ7 alternate on (+) &(-) sign,
the error is neglected.
Slide 18
Table (2) Phase difference Φh for some case studies
Case
Max.
study THDV%
Max.
Cos Φ3
Cos Φ5
Cos Φ7
Error %
37.65
(+) &(-)
+
+
+ 4.833
THDI%
4
5.18
12
2.5
5.7
(+) &(-)
+
+
+ 2.239
15
3.6
25.35
(+) &(-)
(+) &(-)
(+) &(-)
- 0.089
Slide 19
Basically , the power factor improvement can be used
when it is not necessary to take measures to avoid
resonance problems or to reduce or eleminate the
harmonic distortions. This is the case when the resonant
frequency given by the supply network inductance and the
capacitance of the capacitor is relatively high and
harmonic content of the system is very low. Also the shunt
capacitor is not a source of harmonics but it causes
magnification of harmonic currents.
Slide 20
The shunt capacitor effects on phase difference (Φh)
between the voltage and current hth harmonics.
Fig (5) shows time variation of cos Φh per phase R for
case study No.(1) when capacitor is off by comparing Fig
(5) with Fig (3) , the cos Φh variation is changed from
positive sign to alternate on positive and negative sign.
Slide 21
Cos
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Fig( ) Time variation of Cos
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per phase R for case study ( )
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Fig( ) Time variation of Sin
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per phase R for case study ( )
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Fig( ) Time variation of Cos
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per phase R for case study ( ) when capacitor off
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Slide 22
onclusion
Compar0ison between consumption of induction
and digital meters in the presence of distortion is
carried out. The remarks are :
•
In spite of THDI% & THDV% are exceed the standard
limit , not any relation between errors % and THD%
•
There is relation between phase difference Φh and
errors%
Slide 23
There is signification for presence of power factor
improvement The energy meter will register surplus power
due to the harmonics have positive signs.
This project is still in going on to prepare empirical formela
between errors % and Φh.
Biography
Speaker : Mohamed Ashour
Position : Chairman
Company : Alexandria Electricity Distribution Company
Country : EGYPT
Mohamed Ashour is chairman of AEDC. He obtained his B.SC. in Electrical of Engineering, in 1967.
He is member of the CIRED and CIGRE.
After graduation, he worked at Cairo Electricity Distribution Company as a network distribution engineer for
low voltage. He was involved in the planning, installation and maintenance of low voltage networks at one of
Cairo’s many districts. He was promoted in his job to add to his responsibilities the installation, maintenance
and testing of medium voltage distribution networks. In 2001, he was Head of Sectors for distribution
networks.
Company Background Information
Company : Alexandria Electricity Distribution Company
Country : EGYPT
Objective of the Company :

Distribution and sale of electrical energy to the consumers on the medium
and low voltages and to carry out all the work and transactions needed to
fulfill the objective of the company in Alexandria Governorate.

Carry out erection of electrical connections for the different uses on
medium and low voltage without conflicting with existing laws.

Carry out operation and maintenance for the electrical networks in the
company and for others.