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IDAX 300
Insulation Diagnostic Analyzer
Dielectric Frequency Response
Also known as:
Frequency Domain Spectroscopy
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Typical power factor values for oil insulated
transformers and bushings
Typical power factor values @ 20° C
"New"
"Old"
Warning/alert limit
Power transformers,
oil insulated
0.2-0.4%
< 0.5%
> 0.5%
Bushings (OIP)
0.2-0.3%
< 1%
> 1%
IEEE 62-1995 states; “The power factors recorded for routine overall tests on
older apparatus provide information regarding the general condition of the
ground and inter-winding insulation of transformers and reactors. While the
power factors for most older transformers will also be <0.5% (20C), power
factors between 0.5% and 1.0% (20C) may be acceptable; however, power
factors >1.0% (20C) should be investigated.”
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Megger test sets for capacitance/tan delta testing
Application/Measurement
CB100
IDAX300
DELTA4000
Power frequency tan delta/power factor
Yes
Yes
Yes
Capacitance measurements
Yes
Yes
Yes
High voltage tan delta/power factor
No
Yes (VAX)
Yes
High power tan delta/power factor
No
No
Yes
Frequency range
No
0.1 mHz-10 kHz
1-500 Hz
Moisture assessment
No
Yes
No
Individual temperature correction
No
Yes
Yes
Temperature dependence analysis
No
Yes
No
Tip-up testing
No
Yes
Yes
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DFR/FDS measurement setup
Hi
V
A
Lo
Ground
Measure at several frequencies
Use Ohms law:
Z   
Z   
CHL
CL
CH
U  
I  
C, tand, PF
  and  
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Dielectric Frequency Response / Frequency
Domain Spectroscopy
 Changes in insulating materials (ageing) affect the
capacitance and loss factor (PF, tan)
 Measuring a frequency response, compared to traditional
power frequency dissipation factor and capacitance
measurements, provides a lot more information on:
•
•
•
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Insulation characteristics
Moisture/Ageing effects
Influence of temperature
Etc…
 DFR is the tool for investigation!
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DFR/FDS - 100 years of history
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1870’s; First systematic investigations of dielectric properties (Clausius and
Mosotti)
1885; The transformer is invented by Ottó Bláthy
1927; First Megger for DC insulation testing is patented and released
1990; ABB presents first results on dielectric response measurements on
insulating materials combined with model-based signal analysis of cellulose
insulation (NORD-IS 1990)
1993; Development of the first field instrument for Dielectric Frequency Response
measurements is started by Dr. Peter Werelius
1995; First IDA (Insulation Diagnostic Analyzer) instrument delivered
1995-2005; The interest in using DFR/FDS for investigating insulation properties
is rapidly growing and numerous papers on the method and technology are
presented at international conferences
2004; CIGRE report 254, ”Dielectric Response Methods for Diagnostics of Power
Transformers” is published
2006; Project REDIATOOL reported at CIGRE, recommending DFR as a
preferred method for moisture assessment of power transformers
2009; CIGRE report 414 “Dielectric response diagnoses for transformer windings”
finalized and published
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Methods for DFR measurements
DC (Polarization-Depolarization
Current measurements)
AC (Dielectric Frequency Response
measurements)
 Strenght
 Strenghts
 Shorter measurement time at very
low frequencies
 Weaknesses
 More sensitive to AC interference
(microamps...)
 More sensitive to DC interference
(nanoamps...)
 Limited frequency range (PDC
only)
 Data conversion necessary
(combined PDC/DFR only)
 Discharge before measurement
may be needed
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Less sensitive to AC interference
(milliamps...)
Less sensitive to DC interference
(microamps...)
Wide frequency range
No data conversion
No discharge necessarry
 Weakness

Longer measurement time for very
low frequencies
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Noise in substations
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Induced AC (50/60Hz)
Induced DC (Corona discharge)
Induced DC (HVDC stations)
DC offset from (varying) ground potential (mainly in HVDC
substations)
Other disturbancies (RF, power transients etc)
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Noise susceptibility
Max noise interference for different measurement technologies
Noise
source
LV DC/PDC (Omicron)
Amplitude
Amplitude
SNR
Amplitude
SNR
AC
~ 10 µA (?) not stated
(50/60Hz)
~ 1 mA
1:2
~ 15 mA
~ 1:20
”very
sensitive”
”not
sensitive”
DC
SNR
LV AC (IDAX300 4.0)
HV AC
(IDAX300+VAX020,
Delta4000)
”not
sensitive”
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Dielectric Frequency Response
- Dissipation Factor Changes with Frequency
Tan delta
/power factor
0.32 at 0.02 Hz
0.0031 at 60 Hz
Frequency
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- Moisture +
What affects the response?
- Moisture +
- Oil Conductivity +
- Temperature +
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Dielectric Frequency Response
- Single value @ 0.7% is not sufficient to make the right decision
- Dielectric Frequency Response tells the story!
Dry transformer with
bad oil (high
conductivity)
Same PF value at 60Hz
Wet transformer with good oil
(low conductivity)
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DFR Application Areas
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Power transformers
Bushings
Instrument transformers
Motors and generators
Insulating oil
Cables
Generic testing of any insulation system
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IDAX 300 – Insulation Diagnostic Analyzer
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VAX020/214/230 – High Voltage Amplifiers
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IDAX Test System
HW
0 – 200 V, 50 mA (IDAX300)
0 – 2kV, 50 mA (with VAX020)
0 – 10 kV, 40 mA (with VAX214)
0 – 30 kV, 40 mA (with VAX230)
Frequency:
0.0001 Hz – 10000 Hz
Capacitance range: 10 pF – 100 µF
Max interference:
1 mA or 1:2 SNR @ 50/60 Hz (IDAX300)
15 mA or 1:20 SNR (IDAX+VAX)
2-ch measurement: Multiplexing (IDAX300)
Simultaneous (IDAX300S)
 Test signal:
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SW
 IDAX SW for measurement control and analysis
 MODS SW for:
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Automatic moisture assessment of oil impregnated cellulose
Temperature dependence analysis by conversion of frequency data to temperature data
Individual temperature correction from measurement temperature to 20° reference
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IDAX300 with VAX020
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VAX020 – What?
 High voltage amplifier for IDAX300/350
 Increases IDAX 300/350 output voltage from 200 V to 2 kV
 Technical specification
• 2 kV output (peak)
• DC – 1 kHz @ 50 mA max current
• Capacitance range
o 4 µF @ 1 Hz
o 80 nF @ 50 Hz (67 nF @ 60 Hz)
o 4 nF @ 1 kHz
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VAX020 – Why?
Key benefits;
 DFR in substations with high DC or extreme low frequency
AC interference, e.g. HVDC substations
 2 kV DFR up to 1 kHz especially for low capacitance objects,
e.g. insulating oil, CTs and not mounted bushings
 2 kV capacitance and tan delta testing at power frequency
 Tip-up testing
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DFR summary and conclusions
 Dielectric response measurement is an excellent tool for insulation
diagnostics on power transformers, bushings, CT/VTs, generators,
motors etc
 Moisture assessment using DFR and transformer insulation modeling
is a generally accepted standard measurement method
 DFR together with insulation modelling can perform individual
temperature correction and temperature dependence analysis
 AC and DC interference is common in substation environment –
Choose a DR method with low noise susceptibility – An IDAX/VAX
system!
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The doctor is in...
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