Serial Number:
-
.
ROGOWSKI CURRENT WAVEFORM TRANSDUCERS
INSTRUCTIONS FOR USE
CWT
POWERTEK
148 Beecham Road, Reading
Berkshire RG30 2RE United Kingdom
Tel: 0118 950 2468 Fax: 0118 958 8360
Email: info@powertekuk.com
March 2003
INTRODUCTION
POWERTEK’s Rogowski Current Waveform Transducers combine high bandwidth, safety, and the
minimum disruption to the circuit under test. These instructions should be followed whenever the unit
is used. They are intended to help you obtain the best and safest performance from the transducer.
SPECIFICATION
ACCURACY (5 to 100% full scale)
Within the limits of bandwidth and low frequency noise that are specified on the relevant CWT
specification sheet.
Calibration:
Normally ±0.2% (traceable to UKAS) with the
conductor central in the CWT loop. See the calibration
certificate for more details.
±1% typ. variation of accuracy with conductor position
in the loop (see ‘Obtaining The Best Measurement’)
±0.05% typ.
Positional accuracy:
(Standard coils)
Linearity:
POWER SUPPLY
The CWT can be powered by both battery and an external DC voltage. With the external DC supply
present the batteries are inoperative.
Battery type:
Battery life:
DC socket type:
DC voltage:
DC quiescent supply current:
4 (four) 1.5V AA alkali
70 hrs typ.
2.1 or 2.5mm jack socket – polarity indicated on front of
CWT
12 to 24V DC (±10%)
30mA (@12V DC) , 30mA (@ 24V DC)
When specified with rechargeable batteries the CWT operates directly from the batteries when there
is no DC supply present and is powered directly from the DC supply when present. With the DC
supply present the rechargeable batteries are permanently trickle charged.
Battery type:
Battery life:
Recharge time:
DC socket type:
DC voltage:
DC quiescent supply current:
4 (four) 1.2V NiMH rechargeable batteries
30 hrs typ. (based on a 1400mAH cell)
40 hrs typ.
2.1 or 2.5mm jack socket – polarity indicated on front of
CWT
12 to 24V DC (±10%)
70mA (@12V DC) , 70mA (@ 24V DC)
OUTPUT
Maximum output voltage:
Output cable:
Minimum output loading:
±6V (corresponding to ±Peak Current Rating of CWT)
0.5m BNC to BNC 50Ω cable
100kΩ
OPERATING TEMPERATURE RANGES
Rogowski coil and cable
Integrator electronics
March 2003
-20oC to 100oC
0 to 40oC
2
CWT – ROGOWSKI CURRENT TRANSDUCER
1. Rogowski coil (loop)
2. ‘Free end’ of the Rogowski
coil
3. Ferrule (the connecting
mechanism for closing the
Rogowski coil).
4. Cable connecting the
Rogowski coil to the
integrator electronics
5. Socket for external DC
supply
6. LED status indicator for
external DC supply
7. Enclosure for the integrator
electronics
8. Output BNC socket
9. 4 x AA batteries
10. LED indicator
- GREEN - CWT is ON
- RED – low battery
11. Push button ON / OFF
switch
March 2003
3
SAFETY AND PRE-USE CHECKS
Throughout this instruction sheet there are a number of warnings which must be observed to ensure
safe operation of this unit. These warnings are identified by the following symbol:
!
POWERTEK accepts no responsibility for any accidents or damage resulting from careless use, or
non- observance of these instructions.
THE ROGOWSKI COIL
!
The integrity of the insulation around the Rogowski coil itself should be VISUALLY
INSPECTED before use, and the unit should NOT BE USED if there are signs of damage.
!
When bending the flexible coil around a conductor, avoid tight bends and sharp edges that
could damage the coil.
!
!
The voltage rating (safe PEAK working voltage) is clearly labelled on the coil. The rating is
normally 10kV peak (red coil) but can also be 5kV peak (yellow coil) and 2kV peak (green
coil). The removable silicone sleeve supplied with the coil increases the voltage rating of
yellow and green coils to 10kV peak and provides mechanical protection.
The ratings are derived from the following standard test. All coils supplied by POWERTEK
including the ferrule connecting the coil to the cable are flash tested for 1 minute at
15kVrms using a 50Hz sinewave. Coils rated at 10kV peak (red coils) are tested without
the 10kV sleeve; coils rated below 10kV peak (yellow and green coils) are tested with the
10kV sleeve fitted.
!
For additional safety it is recommended that the ferrule is not situated in direct contact with
conductors at voltages higher than 8kV peak. See also “Obtaining the Best Measurement”.
!
The voltage ratings are appropriate for intermittent use of the CWT as a test instrument
and not for continuous use in a permanent installation.
For permanent installation the coil should be situated such that corona, which would
eventually damage the coil insulation, cannot occur. For information regarding permanent
installation of POWERTEK’s Rogowski coils on high voltage equipment please consult
POWERTEK.
!
Voltage ratings are only valid if the ‘free-end’ of the coil is fully inserted into the socket, and
remains fully inserted during use.
The ‘free–end’ will be fully inserted when the user feels the free-end of the coil engage with
the internal click-in mechanism inside the ferrule.
Visual indication that the coil mechanism is fully inserted is provided by the black cable
marker situated near the end of the coil, as shown opposite
March 2003
4
10kV peak
10kV peak
!
✔
✖
If the coil is to be left in-situ for any period of time or is used in an environment where the
coil is subject to vibration the locking nut should be engaged as shown in the diagram
below.
To lock
the jaws
The locking mechanism must not be actuated at temperatures below 0oC
Care must be taken not to over-tighten the locking nut.
THE INTEGRATOR
!
The CWT must only be used with oscilloscopes or monitoring equipment which have
their BNC INPUTS PROPERLY GROUNDED.
March 2003
5
SWITCHING ON
!
!
Before installing the CWT and taking a measurement refer to SAFETY AND PRE-USE
CHECKS to ensure safe operation of your CWT
Do not fit a Rogowski coil to a live circuit; always de-energise the circuit first.
1. Connect the BNC plug on the output cable of the transducer to your oscilloscope or current
monitoring equipment. The CWT must only be used with oscilloscopes or monitoring equipment
which have their BNC INPUTS PROPERLY GROUNDED.
2. Having carried out the VISUAL INSPECTION of the Rogowski coil, un-clip the coil and wrap it
around the de-energised conductor under test.
3. Insert the free-end of the coil fully inside the ferrule and lock the jaws if necessary.
4. Re-energise the conductor.
5. The CWT is switched ON by pressing and releasing the ON push button, and is turned OFF by
depressing the button fully; the LED indicates that the CWT is ON when the LED is GREEN.
6. – EITHER - Standard alkali battery supplied CWT units - B
Four 1.5V AA alkali batteries provide about 70 hours operation. Battery voltage is continuously
monitored; healthy batteries are indicated by the GREEN LED. If the LED is RED the batteries are
delivering less than 2V and must be replaced by removing the sliding battery door in the back
cover of the integrator enclosure.
The units can also be powered by an external DC supply. The DC voltage can be between 12 and
24V (±10%). When the DC supply is present a RED indicating LED adjacent to the socket is
illuminated. With the DC supply present the batteries are inoperative.
- OR - Re-chargeable battery CWT units - R
When fully charged four 1.2V AA NiMH rechargeable cells provide about 30hrs operation. Battery
voltage is continuously monitored; healthy batteries are indicated by the GREEN LED. If the LED
is RED the batteries are delivering less than 2V and must be recharged.
The units can also be powered by an external DC supply. The DC voltage can be between 12 and
24V (±10%). When the DC supply is present a RED indicating LED adjacent to the socket is
illuminated. When the DC supply is present the batteries are inoperative and the external DC
voltage powers the integrator. In addition when the DC supply is present (regardless of whether
the integrator is on or off) the rechargeable batteries are trickle charged.
7. After switch-on the CWT requires a settling down time to attain its quiescent state before
providing correct current measurement. The time, which depends on warm-up and low frequency
bandwidth, can be as long as 2 minutes.
March 2003
6
OBTAINING THE BEST MEASUREMENT
The Rogowski coil should be positioned so that the conductor under test is encircled by the coil but is
not adjacent to the cable attachment (see picture below). The arrows across the coil show the
direction a positive current should pass through the coil loop in order to obtain a positive output
voltage. The CWT has been calibrated with the conductor near the centre, and this is the ideal
position.
I
current into
page
KEEP CO NDUCT ORS
AW AY FROM
SHADED AREA
The sensitivity of the CWT to currents that do not pass through the coil is very small, provided that
such currents are no greater than the CWT’s rating or such currents are relatively distant from the
coil. In the vicinity of a multi-turn inductor the ‘H’ field is far stronger than from a single conductor
carrying the same current, and such positions should be avoided.
Similarly if there is a surface with a high voltage very close to the coil, and the voltage is subject to
high rates of change (e.g. several 100 V/µs) or high frequency oscillations in the MHz range, then
measurement error can arise due to capacitive coupling to the coil.
As a check on any unwanted response to adjacent fields, it is wise to display the output of the CWT
when close to (but not encircling) the conductor whose current is to be measured. This will reveal the
magnitude of any unwanted response to currents close to but outside the coil.
EMC
EMISSIONS
POWERTEK’s Rogowski current waveform transducers are certified to: BS EN 50081-2:1994
IMMUNITY
POWERTEK’s Rogowski current waveform transducers are certified to: BS EN 50082-2:1995
OUTPUT CABLES
A 0.5m BNC-BNC output cable is supplied with the unit but a longer cable can be used. The cable
should be a 50 ohm singly screened co-axial cable. Although at present this has not been included in
the immunity tests and may decrease RF noise immunity, POWERTEK does not consider the use of
extension cables to be problematic from the noise viewpoint. POWERTEK has conducted tests using
a 25m extension and no discernible attenuation of measured current signal has occurred although, as
is to be expected, there is an increased measurement delay of 5ns/m.
March 2003
7
WARRANTY
The coil is guaranteed to be free from defects due to materials and workmanship for 12 months and
the integrator for 24 months from the date of despatch from Powertek Ltd. In the event of a defect or
incorrect operation of the unit where the transducer has not been misused the CWT should be
returned to POWERTEK with all freight charges to be paid by the customer. Correction shall be in the
form of repair or replacement.
RETURNING CWTs FOR RECALIBRATION OR REPAIR
If it is necessary to return the CWT to POWERTEK for repair whether or not under warranty please
contact POWERTEK in advance for shipping instructions (see last below for contact details). To
facilitate customs clearance it is important to follow the correct procedure otherwise import tax will be
charged. POWERTEK will not accept units sent for recalibration or repair if the relevant procedure is
not followed.
For technical updates and the latest product releases please contact
www.powertekuk.com
POWERTEK
148 Beecham Road, Reading
Berkshire RG30 2RE United Kingdom
Tel: 0118 950 2468 Fax: 0118 958 8360
Email: info@powertekuk.com
March 2003
8
CWT SPECIFICATION
The CWT from Power Electronic
Measurements Ltd. is a state of
the art wide-bandwidth ac
current probe.
The CWT is ideal for power
electronics development work
because it combines an easy to
use thin, flexible, clip-around coil
with an ability to accurately
replicate fast switching current
waveforms be they sinusoidal,
quasi-sinusoidal or pulsed.
A 2700A current pulse with a 6700A/ms falling edge
measured by a CWT15 with a 500mm coil and a very
high bandwith coaxial shunt - 10ms/div.
Applications
Features
Ü
Ü
Ü
Ü
Ü
Ü
Ü
Ü
Ü
Ü
Ü
Monitoring current waveforms for
semiconductor switches
Development and servicing of power electronic
equipment
Monitoring high frequency sinusoidal currents
Measuring fault currents or circuit breaker interruption
currents
Measuring pulses of current
Measuring ac currents superimposed on large dc
currents
Measuring harmonic current components
Measuring signal or earth leakage currents in 3-phase
supply systems
Ü
Ü
Ü
Ü
Ü
Measurement range from 300mA to 300,000A
Typical bandwidths from 0.1Hz to 16MHz
The DC offset is no greater than 2mV over the operating
temperature range.
Thin and flexible, ‘clip-around’ coil in lengths from
300mm to 1000mm – other lengths available as custom
designs
ð Easy to insert probe in confined spaces
ð Robust lockable ‘clip-in’ mechanism
ð Non-intrusive – loading the circuit under test by only
a few pH
Coil peak voltage isolation capability up to 10kV
Instantaneous ±6V peak to peak output to plug directly
into scope, data acquisition equipment, DVM or power
recorders
CE Marked
Accuracy of ±1% of reading
POWER ELECTRONIC MEASUREMENTS Ltd.,
Nottingham, U.K.
Tel: +44 (0) 115 946 9657 Fax: +44 (0) 115 946 8515
Email: info@pemuk.com Website: www.pemuk.com
PERFORMANCE CHARACTERISTICS
Type
Sensitivity
(mV/A)
Peak
current
(kA)
Peak
di/dt
(kA/mS)
Noise
max*1
(mV pk-pk)
Droop
typ.
(%/ ms)
LF (3dB)
bandwidth
typ. (Hz) fL
Phase lead
at 50Hz
typ. (deg)
HF (3dB) bandwidth
typ. (MHz) fH *2
Coil Length
Coil Length
150
105
80
50
25
3.5
2.0 @ 6kHz
2.0 @ 4kHz
2.0 @ 3kHz
1.9 @ 2kHz
1.9 @ 1kHz
1.0 @ 300Hz
6
10
16
16
10
16
4
6.5
10
10
5
10
1.0
1.0
0.8
0.6
0.4
0.2
0.1
0.05
0.03
1.7
1.7
1.3
0.9
0.6
0.3
0.2
0.1
0.06
10
16
16
16
16
16
16
16
16
5
10
10
10
10
10
10
10
10
300mm
700mm
High Sensitivity Ranges of CWT ... measuring currents from 300mA
CWT015
CWT03
CWT06
CWT1
CWT1N
CWT3
200.0
100.0
50.0
20.0
20.0
10.0
0.03
0.06
0.12
0.3
0.3
0.6
0.2
0.4
0.8
2.0
2.0
4.0
6.5
4.5
3.0
2.5
2.0
8.0
130
90
70
40
20
3.0
Standard Ranges of CWT ... measuring currents from 15A
CWT3N
CWT6
CWT15
CWT30
CWT60
CWT150
CWT300
CWT600
CWT1500
10.0
5.0
2.0
1.0
0.5
0.2
0.1
0.05
0.02
0.6
1.2
3.0
6.0
12.0
30.0
60.0
120.0
300.0
4.0
8.0
20.0
40.0
40.0
40.0
40.0
40.0
40.0
14.0
14.0
7.0
5.0
3.5
3.0
3.0
3.0
3.0
0.9
0.9
0.7
0.5
0.35
0.2
0.1
0.06
0.035
*1
. Distributed around the fL (-3dB) bandwidth.
. For 2.5m cable length. Contact PEM for values of fH for other coil and cable lengths
*2
TYPICAL ACCURACY
Traceable calibration to ±0.2% with conductor central in the loop TYPICAL LINEARITY
Variation with conductor position in the coil loop typically ±1%
ABSOLUTE MAXIMUM
VALUES OF di / dt (kA/ms)
(value must not be exceeded)
CWT 03, 06
CWT 015, 1N, 3N
PEAK 40.0
PEAK 20.0
PEAK 40.0
all other CWT’s
RMS 1.2 @ 70°C
RMS 1.0 @ 70°C
RMS 1.5 @ 70°C
±0.05% (Full Scale)
(Further information available on request)
COIL AND CABLE
 COIL CIRCUMFERENCE
300, 500, 700 or 1000mm
‚ COIL CROSS SECTION (max)
8.5mm - (14 mm with sleeve)
PEAK COIL VOLTAGE ISOLATION
10kV
TEMPERATURE RANGE
-20°C to 100°C
ƒ CABLE LENGTH (from box to coil)
2.5m or 4m
Safe peak working voltage to earth. The coils are flash tested at 15kVrms for 60 seconds. The coil is supplied with a removable
silicone sleeve which provides additional mechanical protection. Information about continuous use of the coils at high voltage can
be obtained from PEM.
For de-rating due to temperature cycling please consult PEM
INTEGRATOR
„ POWER SUPPLY
B Battery 4 x AA (1.5V standard alkali batteries)
-plus2.1/2.5mm socket for 12 to 24V (±10%) DC input
R Rechargeable battery 4 x AA (rechargeable NiMH batteries)
-plus2.1/2.5mm socket for 12 to 24V (±10%) DC input
Typical life 70hrs
Battery inoperative with DC supply present
Recharge time 40hrs, Typical life 30hrs
Battery is charged whenever DC supply present
INTEGRATOR BOX DIMENSIONS
H = 183mm, W = 93mm, D = 32mm
† OUTPUT SOCKET
BNC
MIN. OUTPUT LOADING
100kW
TEMPERATURE RANGE
0°C to 40°C
(output impedance 50W - unit supplied with
0.5m BNC - BNC coaxial cable)
(for rated accuracy)
ORDERING
e.g. order code
Type + Power supply
Cable Length
Coil Circumference
CWT30 B
4
700
If you have any queries regarding the CWT or require specifications outside our standard ranges please do not hesitate to contact us.
Nov 2010