Prezentare izolatie Metrel

7/27/2019 Prezentare izolatie Metrel

1/15

High Voltage Insulation Diagnostics

Presented by: Bostjan Flis

[email protected]

WELCOME!


2/15

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


3/15

Application areas of HV insulation testing

Insulation resistance testing is part ofpredictive 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


4/15

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


5/15

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 (tg)

- Partial discharges

- U I characteristics


6/15

Insulation testing with DC test voltage - insulation characteristics

Riso Cpi

Rpi

Cis

Riss

Riss

Itot

+

Guar

U

ICisoIRCpiIRiso

IRiss U Test voltage

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

uA

0

10

20

30

40

t [s]0 200 400 600 800

IRiso

Itot

IRiss

IRCpi

ICiso


7/15

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 Discharge of

Ciss

Ito t

[s]10 20 30 40 50 6000

Badinsulation

Goodinsulation

Discharging of Cpi


8/15

Limit values for insulation testing

with DC voltage

Insulation resistance

Limit value

General applications > 1M per 1kV der Nennspannung des Prflings

Rotary machines according toIEEE 43-2000

a./ 1 M + 1 M/1kVb./ 5 M for motors under 600Vc./ 100 M for motors above 600V

Switching- and control devices according to IEC 60439-1 > 1k for 1V of the UN of the test object

Splitting transformers and safety low voltage transformers accordingto IEC 61558 a./ Basis insulation > 2Mb./ Additional insulation > 5M

c./ Reinforced insulation > 7M

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)

Dielektric absorption ratio (DAR)

DAR value

Evaluation

< 1 BAD

1 DAR 1.25 SUFFICIENT

> 1.4 VERY GOOD

kVM ni UR

Thumb rule(motors and generators):


9/15

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

VNNN

G

VNNN

G

VNNN

G

Power transformer

HV vs LV

HV vs G

LV vs GDevice A Device B

Device N

Power supply

PE - ground

Port A Port A Port A

Port BPort B

PE PE

Port C1

Port C2Port C2

Port C1Port C

Multiple devices


10/15

Test data evaluation i.e. statistics keeping

Statistics

- 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 75C)

rK

RR1

//i10/75i10

0304,028,2

10r

K


11/15

General requirements for HV insulation testers

Test functions:

- Insulation resistance

- Step voltage test

- Capacitance

- PI, DD, DAR

- Current in A and mA range

- Voltage AC/DC

Accessories:

- Shielded test leads

- High quality test terminals (HV, antistatic, high surface resistance)

- PC Software for downloading of test results and creating test reports

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)


12/15

Metrel HV insulation testers

Integrated features:

Test voltage up to 10kV DC

Resistance measuring range up to 10T

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 PlusHandbook Modern insulation testing on CD


13/15

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 products segments

(Hardware, Firmware, PC Software)

Customised solutions (Instruments, Software, Accessories)


14/15

WHY NOT

METREL?


15/15

THANK YOU!

You have already made a good decision

Documents

Prezentare izolatie Metrel