a development of a measurement system using a rogowski coil to observe sprit lightning current flows...
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A Development of a Measurement System Using a Rogowski Coil to Observe Sprit Lightning Current Flows Inside and Outside a Wind Turbine GeneratorTRANSCRIPT
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2012 International Conference on Lightning Protection (ICLP), Vienna, Austria
A Development of a Measurement System Using a
Rogowski Coil to Observe Sprit Lightning Current
Flows Inside and Outside a Wind Turbine Generator
System
Tomoki Kawabata
Department of development
technology
Shoden Co., Ltd.
Chiba, Japan
Yuta Naito
Department of development
technology
Shoden Co., Ltd.
Chiba, Japan
Syunichi Yanagawa
Department of development
technology
Shoden Co., Ltd.
Chiba, Japan
Daisuke Natsuno Department of Alternative energy
Toyo Sekkei Co., Ltd.
Tokyo, Japan
Kazuo Yamamoto Department of electrical system engineering
Chubu University
Aichi, Japan
Keyword: Wind turbine generation system, Rogowski coil,
frequency characteristics, current distribution measurement
I. INTRODUCTION
In recent years, based on the magnification of usages of
renewable energy and smart usage of energy, the demands of
large-scale decentralized generating plants such as wind
turbine generator systems and photovoltaic power systems is
increasing. However, Large-scale wind and photovoltaic
power generation facilities are usually installed in locations
where few tall structures exist such as suburbs, resultantly, the
damages caused by lightning stroke convergence to those
facilities are serious problems [1-4]. In particular, in wind
turbine generator systems, the occurrence probability of the
damages caused by direct lightning strokes becomes higher
than that in other power-generation systems because (1) It has
rapidly high-structured in recent years, and (2) It has been
installed in the place where extremely few tall structures exist
such as hilly terrains and areas along sea shores. Many blade
damages caused by lightning strokes and troubles of controls
and communication facilities are reported [1-3]. The decline of
the capacity factor depending on the operation stopping time
and the increase of the repair cost became viewed with
suspicion.
At many wind turbine sites in Japan, in order to research
the lightning-stroke properties to the wind turbine, the large
caliber Rogowski coils are installed in the legs of the towers.
The measurement systems make it possible to record current
waveforms with wide range frequency [1-3]. Moreover, In
recent years, Solving the attachment mechanism of a lightning
stroke to a wind turbine blade has started using a high-speed
video camera. Thus, researches to clarify the relationship
between troubles in a wind turbine generator system and
lightning characteristics has been carried out.
Not only blades but also control and communication
facilities inside or in the vicinity of a wind turbine may be
damaged when a wind turbine generator system has a
lightning stroke. Most of causes of such troubles are over
voltages caused by grounding potential rise, the induced
voltage from lightning current flowing through path close to
the equipments or backflow current to neighborhood facilities.
In order to solve those mechanisms, it is necessary to clarify
the transient grounding characteristics of wind turbine
generator systems [5-6] and split lightning current flows inside
and outside wind turbine generator systems.
In this paper, in order to measure the split lightning current flows inside and outside wind turbine generator systems, the measurement system using a Rogowski coil which has wide frequency band and is low cost is reported.
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II. OUTLINE OF THE DEVELOPED SYSTEM AND INSTRUMENTAL EQUIPMENTS FOR TESTS
A. Outlines of the Development System
The developed measuring system consists of a Rogowski
coil part, a integration circuit with a low-frequency amplifier
and a low-pass filter, and a recording device. The
specifications are shown in TABLE . A Rogowski coil can be
made with lower cost than other current sensors like a current
transformer. Moreover, since this measuring system is
dividable, it can be easily installed to a small and unique shape
measuring place. The frequency response characteristic on the
specification of the measuring system designed using a circuit-
analysis software is wide range as 1Hz - 500 kHz .
B. Instrumental Epuipments for Tests
The instrumental equipments used for the tests are shown
in TABLE . TDS3054C made by Tektronix was used for an
oscilloscope. Its band width is DC - 500 MHz The passive
probe P6139A made by Tektronix was used for voltage
measuring. Its band width and input capacitance are DC - 500
MHz and 8pF respectively. Moreover, in order to compare
current measurement results, the current transformer (CT) of
Model 2877 made by PEARSON, which has a band width of
300 Hz - 200 MHz, was used.
III. THE PROPERTIES OF THE MEASURERING SYSTEM
A. Response Charactistics of the Rogowski Coil and the Synthetic Instrumental System
The response characteristics of only the Rogowski coil,
and the synthetic instrumental system which consists of the
Rogowski coil, the integration circuit with the low-frequency
amplifier and the low-pass filter, and a recording device were
measured. Test circuits are shown in Figure 1 and 2.
In Figure 1, the integrated value of the voltage appearing
on the output terminals of the Rogowski coil and the current
measured using the CT are compared. In Figure 2, the current
measured using the synthetic instrumental system and that
measured using the CT are compared.
The above mentioned results are shown in Figure 3 - 6.
Figure 3 (a) is an example of an induced voltage appearing
between the output-terminals of the Rogowski coil. The deep
continuous line shown in Figure 3 (b) shows the integrated
values of the induced voltage. The induced voltage and the
integrated value are oscillating with the resonance frequency
of the Rogowski coil. When the current flowing through the
Rogowski coil has frequency components near the resonance
frequency (In the case of the Rogowski coil used in this
experiments, the resonance frequency is about 700 kHz - 800
kHz), such oscillation appears. In the low-pass filter shown in
Figure 2. On the other hand, the low frequency components of
TABLE I. SPECIFICATIONS OF THE MEASURING SYSTEM USING A ROGOWSKI COIL.
Items Specifications
Sensor Rogowski coil
Coil (Inside diameter) 70 (Division type)
Frequency response 1 Hz500 kHz
Measuring range of
current
30 kA
(All of not less than 30 kA current displays it as 30 kA.)
Power supply voltage 5.0V
Consumption current 300mA (MAX 500mA)
Temperature -20 C +50 C
Power Battery drive or Commercial power
TABLE II. MEASURING DEVICES FOR TESTS.
Equipment Manufacturer Type
Transmitter Agilent 33250A
Power amplifier NF CORPORATION HSA4101
Oscilloscope Tektronix TDS3054C
Voltage probe Tektronix P6139A
Current sensor PEARSON Model 2877
Model 101
the current flowing through the Rogowski coil makes only
small induced voltage on the coil. The small induced voltage
is amplified linearly. The pale continuous line in Figure 3(b)
shows the measured result using the synthetic instrumentation
system. The pale continuous line laps over the broken line
which is the measured result using the CT. From those results,
the precision of the developed measuring system can be
confirmed.
In Figure 4-6, currents with different waveforms flow
through the Rogowski coil. It became clear that the smaller
current components around the resonance frequency of the
Rogowski coil is, the smaller oscillation of the output voltage
and its integration with the resonance frequency become.
Moreover, From the comparisons between the measured
results using the synthetic instrumentation system and the CT,
the precision of the developed measuring system can be
confirmed for several current waveforms.
B. Various Fequency Response Caracteristics
The test circuit is shown in Figure 7. A sinusoidal wave
generated from an oscillator is inputted into a power amplifier,
and the amplified sinusoidal current flow through the
Rogowski coil. In the low-frequency measurements, the
number of turns to the Rogowski coil are increased to amplify
the induced voltage on the Rogowski coil. The input -output
characteristics is shown in Figure 8. It has checked that
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Impulse
generator
Current transformer
Rogowski coil
Oscilloscope
Figure 1. Test Circuit for the Time Response Characteristic of a Rogowski Coil
Impulse
generator
Current transformer
Rogowski coil
Oscilloscope
Integration
circuit
Recording
equipment
Figure 2. Test Circuit for the Time Response Characteristic of the Synthetic Instrumentation System
(a) Rogowski Coil Output Voltage
(b) Comparisons
Figure 3. Time Response Characteristic 1
(a) Rogowski Coil Output Voltage
(b) Comparisons
Figure 4. Time Response Characteristic 2
(a) Rogowski Coil Output Voltage
(b) Comparisons
Figure 5. Time Response Characteristic 3
-150
-100
-50
0
50
100
150
200
0 5 10 15 20 25 30 35
volt
ag
e [V
]
time [s]
0
50
100
150
200
250
0 5 10 15 20 25 30 35
curr
en
t [A
]
time [s]
Rogowski current
CT current
equipment current
-60
-10
40
90
140
0 5 10 15 20 25 30 35
volt
ag
e [V
]
time [s]
0
30
60
90
120
150
180
0 5 10 15 20 25 30 35 cu
rren
t [A
]
time [s]
Rogowski current
CT current
equipment current
-10
0
10
20
30
40
0 5 10 15 20 25 30 35
volt
ag
e[V
]
time[s]
0
50
100
150
200
0 5 10 15 20 25 30 35
curr
en
t [A
]
time [s]
Rogowski current
CT current
equipment current
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(a) Rogowski Coil Output Voltage
(b) Comparisons
Figure 6. Time Response Characteristic 4
FunctionGenerator Power Amplifier
oscilloscope
R
CT
Rogowski coil
Figure 7. Test Circuit to Measure the Frequency Response of a Rogowski Coil
the Rogowski coil can be used to measure until 500 kHz
which is the maximum frequency on the specification as
shown in Table 1. The low frequency bound which can be
measured using the system in Figure 7 is 1 kHz. However, the
Rogowski coil developed in this paper is for the measurements
of the split current flows inside and outside a wind turbine
generator system. On the tower foot of a wind turbine
generator system, the large caliber Rogowski coil which can
be used for the lightning current measurements with wide
frequency domain of 0.1Hz to 1 MHz is installed. On low
frequency domain under 1 kHz, we can guess that there is no
large differences of the ratio of the split lightning currents and
the total lightning current measured by the large caliber
Rogowski coil at the bottom of the tower. It means that the
split lightning currents under 1 kHz can be estimated from the
currents at 1 kHz.
(a) Gain
(b) Phase
Figure 8. Frequency Response of the Rogowski Coil
(a) Impedance
(b) Phase Figure 9. Impedance Characteristic of the Rogowski Coil
-100
-50
0
50
100
150
1.0E+02 1.0E+03 1.0E+04 1.0E+05 1.0E+06 1.0E+07
ph
ase
[]
frequency[Hz]
0
50
100
150
200
1.0E+03 1.0E+04 1.0E+05 1.0E+06 1.0E+07 P
hase
[rad
] Frequency[Hz]
1
10
100
1000
10000
1.0E+02 1.0E+03 1.0E+04 1.0E+05 1.0E+06 1.0E+07
imp
ed
an
ce [
]
frequency[Hz]
-20
0
20
40
60
80
100
120
0 5 10 15 20 25 30 35
volt
ag
e [
V]
time [s]
-100
100
300
500
700
900
0 5 10 15 20 25 30 35
curr
ent
[A]
time [s]
Rogowski current
CT current
equipment current
-60
-40
-20
0
20
1.0E+03 1.0E+04 1.0E+05 1.0E+06 1.0E+07
Gain
[dB
]
Frequency[Hz]
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The properties of the Rogowski coil in the high frequency
region can be also confirmed from its impedance characteristic.
Figure 9 is the measured results between the output-terminals
of the Rogowski coil by use of an impedance analyzer. From
this result, the Rogowski coil has many resonance points over
500 kHz region. It means the high frequency bound of the
Rogowski coil is about 500 kHz.
IV. THE PROPERTIES OF THE MEASURERMENT SYSTEM
In this paper, the measuring system using a Rogowski coil
which has wide frequency band and is low cost is reported to
measure the split lightning current flows inside and outside
wind turbine generator systems. the measuring system can be
used until the high frequency bound of about 500 kHz. From
now on, the split lightning current flows are going to be
measured at several wind turbine sites using the measuring
system.
REFERENCES
[1] NEDO, Wind Turbine Failures and Troubles Investigating Committee Annual Report, (2006) (in Japanese).
[2] NEDO, Wind Turbine Failures and Troubles Investigating Committee Annual Report, (2007) (in Japanese).
[3] NEDO, Wind Turbine Failures and Troubles Investigating Committee Annual Report, (2008) (in Japanese).
[4] NEDO Analyses and Evaluations of Lighting Damages and Its Protection Methods on Photovoltaic Generation systems, (2009-10) (in Japanese).
[5] K. Yamamoto, S. Yanagawa, K. Yamabuki, S. Sekioka, S. Yokoyama, Analytical Surveys of Transient and Frequency Dependent Grounding Characteristics of a Wind Turbine Generator System on the Basis of
Field Tests, IEEE Transactions on Power Delivery, Vol. 25, Issue 4, pp 3034-3043 (2010-10).
[6] K. Yamamoto, S. Yanagawa, S. Sekioka and S. Yokoyama, Transient Grounding Characteristics of an Actual Wind Turbine Generator System at a Low Resistivity Site, IEEJ Transactions on Electrical and Electronic Engineering, Vol. 5, No. 1, pp 21-26 (2010-1).