1. High Voltage Insulation Diagnostics
WELCOME!
Presented by: Bostjan Flis

2. Content overview Application areas of HV insulation testing
What influences insulation resistance
Symptoms of bad insulation
Testing methods
Insulation testing with DC test voltage - insulation characteristics
Insulation testing with DC test voltage - test parameters
Limit values
Connection schemes
Test data evaluation i.e. statistics keeping
General requirements for HV insulation testers
Metrel HV insulation testers
Metrel's solution providing, services and development

3. Application areas of HV insulation testing
Insulation resistance testing is part of predictive maintenance of:
Rotary machines (generators, motors)
Transformers (industry, utilities, power distribution)
Cables
Measuring transducers
Distribution boards
Benefits:
Lower TCO (total cost of ownership)
increased electrical safety
prevention against fire hazard

4. What influences insulation resistance
Thermal exposure
Overload
Moisture
Electrical shocks
Mechanical shocks (vibrations, bad transportation)
Dirt (oil, dust, conductive materials)
General ageing of insulation
Symptoms of bad insulation
Insulation breakdowns in a form of electrical short-circuits
Fire
Long-term downgrading values of insulation resistance
Insulation resistance values under by standards determined values

5. Insulation testing methods
AC insulation testing (50/60Hz, 1 minute)
Insulation surge breakdown testing
Insulation testing with switching voltage
Insulation testing with DC voltage
Dielectric losses (tgδ)
Partial discharges
- U – I characteristics

6. Insulation testing with DC test voltage - insulation characteristics
Riss1 and Riss2
Insulation surface resistance
Riso
Insulation resistance
Ciso
Capacitance of an insulation system
Rpi
Polarisation resistance
Cpi
Polarisations capacitance
Itot
Total insulation current
IRiss
Insulation surface leakage current
IRiso
Resisitve part of the insulation current
IRCpi
Polarisation current
ICiso
Capacitive part of the insulation current

7. Insulation parameters
Polarisation Index (PI)
PI = R tot (10 Min) / R tot (1Min)
Dielectric absoption ratio (DAR)
DAR = R tot (1 Min) / R tot (30 Sek)
Dielectric discharge (DD)
DD = I DIS (1 min) / (U * C ISO )
I DIS ….a discharge current measured 1 minute after disconnecting the insulation system from the test voltage
C ISO …. capacitance of the insulation system
U …test voltage

8. Limit values for insulation testing with DC voltage
Insulation resistance
Limit value
General applications
> 1MΩ per 1kV der Nennspannung des Prüflings
Rotary machines according to
IEEE
a./ 1 MΩ + 1 MΩ/1kV
b./ 5 MΩ for motors under 600V
c./ 100 MΩ for motors above 600V
Switching- and control devices according to IEC
> 1kΩ for 1V of the UN of the test object
Splitting transformers and safety low voltage transformers according to IEC 61558
a./ Basis insulation > 2MΩ
b./ Additional insulation > 5MΩ
c./ Reinforced insulation > 7MΩ
Polarisation index (PI)
PI Wert
Evaluation
1 to 1.5
BAD (valid for older types of insulation materials)
2 to 4
SUFFICIENT (valid for older types of insulation materials)
> 4
VERY GOOD (also for the modern type of insulation materials)
Thumb rule
(motors and generators):
Dielektric absorption ratio (DAR)
DAR value
Evaluation
< 1
BAD
1 ≤ DAR ≤ 1.25
SUFFICIENT
> 1.4
VERY GOOD

9. Connection schemes Precondition!
Measuring object has to be disconnected from power supply network (voltage – free)
Surface of the insulation system has to be dry and clean
Power transformer
HV vs LV
HV vs G
Multiple devices
LV vs G

10. Test data evaluation i.e. statistics keeping
- Always assure the same measuring conditions
(connection, temperature, test voltage, diagnostics parameters)
Regular test intervals (6 months or one year)
Results keeping for the entire life period of the equipment
Observation of downgrading trends
Temperature coefficient
(all values are to be calculated on 75ºC)

11. General requirements for HV insulation testers
Test functions:
Insulation resistance
Step voltage test
Capacitance
PI, DD, DAR
Current in µA and mA range
Voltage AC/DC
Other features:
Guard terminal to eliminate surface insulation currents
Automatic discharging of the test object after measurement
Built-in timer
On-Line graph R = f(t)
EM immunity for usage in HV environments
EM Filters for improved accuracy
Good charging system (accus or mains or both)
Accessories:
Shielded test leads
High quality test terminals (HV, antistatic, high surface resistance)
PC Software for downloading of test results and creating test reports

12. Metrel HV insulation testers
Integrated features:
Test voltage up to 10kV DC
Resistance measuring range up to 10TΩ
Automated calculation of PI, DAR and DD for profound insulation diagnostics
On-Line R=f(t) display
Test voltage setting in 25V steps
Shielded 12kV test leads to reduce influence of external EM fields
CAT IV/600V over-voltage category for utilities and industrial applications
New TeraLink PRO Windows PC Software for TeraOhm 5kV Plus
Handbook “Modern insulation testing” on CD

13. Metrel's solution providing, services and development
Product training in Metrel training centre
On-Line technical support
Application training and publications
Repair & Calibration training
Calibration equipment
Repair & Calibration services
Advanced technical solutions for all product‘s segments
(Hardware, Firmware, PC Software)
Customised solutions (Instruments, Software, Accessories)

14. WHY NOT
METREL?

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THANK YOU!
You have already made a good decision