diagnostic insulation testing l predictive maintenance issues l basis of insulation tests l spot...

Diagnostic Insulation Testing

Diagnostic Insulation Testing

Predictive Maintenance issues Basis of Insulation Tests Spot Tests & Polarisation Index Dielectric Discharge Test Power factor testing AVO Range

Maintenance RegimesMaintenance Regimes

Corrective maintenance Preventive (Periodic) Maintenance Predictive Maintenance

(Record & trend data to determine next action - variable maintenance periods)

Appropriate regime varies

Test Techniques - DC Testing

Test Techniques - DC Testing

Total Current has 3 componentsCapacitive Current - ChargingAbsorbtion Current -PolarisationLeakage Current

TIME DEPENDENT Temperature Dependent

Insulation Test CurrentsInsulation Test Currents

I/uA

T

1

10

100

0,1 1 10

Absorption

Total

Leakage

Charging

Insulation Equivalent CircuitInsulation Equivalent Circuit

Leakage Capacitance Absorption

Diagnosis from Insulation Tests

Diagnosis from Insulation Tests

Record & Trend

Spot Tests- Record conditions as well (Temp, RH)

Time resistance tests - Polarisation Index Test (PI)

Step Voltage Test (SV) Dielectric Discharge Tests (DD)

Insulation Test as a Go/NoGo Test

Insulation Test as a Go/NoGo Test

Spot Test carried out for given time (1 minute)

Commissioning National /Manufacturer’s Standards

Time Resistance TestsTime Resistance Tests

Independent of equipment size and temperature

Some information without past results Options;

Curves Time - Resistance Ratios

Time ResistanceTestTime ResistanceTest

R

Timet1 t2

Absorbtion current not seen

Absorbtion current visible


Polarisation Index(10 min/1 min ratio)

<1

1,0 - 2,0

2,0 - 4,0

>4,0

Insulation Condition

unsatisfactory

dubious

good

very good


Dielectric Absorption Ratio (60 s/30 s)

<1

1.0 - 1.4

1.4 - 1.6

>1.6


unsatisfactory

dubious

good

very good

Step Voltage TestStep Voltage Test

Test voltage is increased in 5 steps Lower insulation resistance values

at higher voltage indicate presence of cracks/holes

Step Voltage TestStep Voltage Test

Voltage

Resistance

1000 V

2000 V

5000 V

Dielectric Discharge TestDielectric Discharge Test

Test is run until currents stabilise

Measurements made on dischargeDD = Current after 1 min Voltage x Capacitance


-

+

-

+

-

+-

+

+

-

+ ++ +

--- --

+

+

-

-

+

+

--

+- +-

+++

-

--

+


DD Value

>4

2.0 - 4.0

<2.0


unsatisfactory

dubious

good

Tan Delta TestingTan Delta Testing

Polarisation and capacitive current dominate

Aging (moisture/dirt) sensitive Low voltages can be used

Perfect Insulation

V (applied)

ITOTAL

IR

= 0

I (capacitive)

Facts about Insulation

In a “REAL insulation system” there is also a loss current flowing in-phase with the voltage

// IR

= ITOTALIC

REAL Insulation

IC

V (applied)

ITOTAL

IR

I (capacitive)

Facts about Insulation

In practice NO insulation is perfect Resistive loss current is always

present Total current leads the voltage by a

phase angle and lags capacitive current by angle

REAL Insulation

IC

V (applied)

ITOTAL

IR

I (capacitive)

What is Tan Delta?

Tan Delta is the ratio of in-phase (resistive) current to the 90-degree (capacitive) current

Tan Delta equals Dissipation Factor

What is Power Factor?

Power factor is the ratio in-phase (resistive) current to the total

current.

Tan Delta Testing

IC

V(applied)

I(capacitive)

Tan = IR

IC

Power Factor = ITOTAL

IR

ITOTAL

IR

Tan Delta v. Power Factor

Both values are similar up to 20% power factor and tan delta; beyond 20% they diverge.

Tan Delta 3 Terminal Test

Low voltage (L)

High voltage (H)

Ground Connection (G)

CLG

CHL

CHG

Tan Delta 3 Terminal Test

Configuration Measures

GST L-GND CHL + CHG

GST L-Guard CHG

UST CHL

GST H-Guard CLG

GST H-GND CHL + CLG

Why perform theTan Delta Test?

Normal insulation resistance testing limited to 5kV dc

Tan Delta is up to 12kV ac Most test specimens normally operate

with AC voltage Much closer resemblance to the normal

operating condition of the insulation

Tan Delta TestingTan Delta Testing

Comparison with name -plate values Very sensitive to small changes a.c. test at rated voltage Larger, heavier test equipment

Insulation Test DiagnosisInsulation Test Diagnosis

Test Type Main Failure Mode

“Spot” Insulation Test Go/no go

Polarisation Index Moisture/dirt

Step Voltage Cracks/holes

Dielectric Discharge Absorbedmoisture/dirt

Tan-delta Loss measurement

Tests Performed On

Transformers Circuit Breakers Rotating Machinery Insulating Liquids High Voltage Bushings Surge Arrestors High Voltage Coils

MEGGER BM11DMEGGER BM11D

Portable, IP54 , large PbAcid battery Readings to 500 GOhm Display is large, clear & Easy to Use Safety features

Automatic discharge, locking test leads, Hazard display

Integral Timer

MEGGER BM21MEGGER BM21

All BM11D features plus; Readings up to 5TOhm Selectable Test Voltage Selectable Test Time Checks Capacitance at test End Can show current as well as resistance Burn mode

MEGGER BM25MEGGER BM25

As BM21 features plus; Automated tests

Polarisation IndexStep VoltageDielectric Discharge

RS232 download results every 5 s Download software & lead

MEGGER S1-5005MEGGER S1-5005

As BM25 with 5 mA test current.

BM25 has 2 mA test current.


Heavy Duty - Mains & Battery Automated Tests Results Storage RS 232 communications Graphical Display


Memory for 75 sets of results Windows PC software

remote operationresults storage

External output for HV “ON” indicator Switchable digital filter for noise rejection IP54 weatherproofing

S1-5010 and S1-S1 software S1-5010 and S1-S1 software

S1-5010

S1-S1 softwareS1-S1 software

Duplicates the S1-5010 on your PC screen. Control the S1-5010 from your PC via an

RS232 link. Download tests to your PC

in real time.as a batch at the end of testing.

Annotate the tests results with details of the test.

Recreate graphs etc. in other software.

BIDDLE Delta 2000BIDDLE Delta 2000

500 V - 12 kV power factor tester Automatic bridge operation High noise immunity Menu driven display Measures voltage, current, power

(loss), power factor/tan-delta and capacitance


Results storage Printer for on-site results Downloading test data Accessories

Oil test cellBushing connectorsBar code wand

BIDDLE 2.5 & 12 kV semi-automatic units

BIDDLE 2.5 & 12 kV semi-automatic units

2.5 kV single unit construction 12 kV control unit and Measure capacitance, dissipation factor

and Watts

CB-100 Low Voltage BridgeCB-100 Low Voltage Bridge

28 V test voltage Safe Compact Low cost Often used on bushings & transformers

Testing with SafetyTesting with Safety

– How does the electrical risk appears ?

– - When an electrical line or conductor is unexpectedly still live - When current sources are not properly isolated- When power generators are connected to the network- When there are atmospheric phenomenons such as lightning- Through induced currents

Testing with SafetyTesting with Safety However, it has also been observed that

the most common causes of unexpected presence of voltage on electrical lines or installations were due to:- A mistake in operating a switch- A mistake in identifying the work to perform- A "faulty" switch (one of the links for example remaining partially engaged)


How does the electrical risk disappear ?

– 1. By observing Simple Electrical Safety Rules directed by common Sense(even if Working Practices vary from a country to another, GOLDEN RULES always apply).2. By using Simple, Light and Reliable Electrical Safety Equipment.


1. SEPARATE THE WORK AREA FROM ALL POSSIBLE SOURCES OF POWER SUPPLYby opening circuit-breakers, switches… AND LOCK THE LINKS IN THE OPEN POSITION

Testing with SafetyTesting with Safety 2. CHECK THE ABSENCE OF VOLTAGE

at source and on site, on each conductor and apparatus involved.

3. APPLY APPROPRIATE SHORT-CIRCUIT AND EARTHING SYSTEMSin sufficient numbers on the conductors of your network where operation is taking place.


4. SHOWN, WARN OTHERS AND LIMIT THE WORK AREAeven during the most simple temporary maintenance operation


Discharge Sticks Slowly discharge capacitive items

(cables, capacitors….) Discharge to a safe level in 5 - 10

times RC (time constant)

Discharge SticksDischarge Sticks

Voltage Length Resistance Max. cap.

35 kV 50 cm 10 kOhm 6 uF50 kV 136 cm 100 kOhm 6 uF75 kV 156 cm 150 kOhm 4 uF100 kV 176 cm 200 kOhm 3 uF150 kV 208 cm 300 kOhm 2 uF

Oil TestingOil Testing

MEGGER Foster Oil Electric Strength Testers

Why test switchgear oil?

Why test switchgear oil?

Prevent Transformer failurePrinciple problems are: humidity oxygen temperature

Oil Testing MethodsOil Testing Methods

Water content Acidity Colour Flash point Gas content Oil provides HV insulationElectric strength is the most important

test

Breakdown TestingBreakdown Testing

0

20

40

60

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

Time

Test

Volta

ge

Electric Strength Test Results

Electric Strength Test Results

Average over six tests Scatter can be large

Standard deviation calculated

Report breakdown values, date, temperature

New Specification EN60156

New Specification EN60156

Replaces IEC156 (1963) Optional stirring Current limited breakdown for silicone

oils Gives guidance on scatter of results

Withstand TestingWithstand Testing

Test voltage held at preset level for 1 minute

Quick test of level of contamination

Increase to breakdown to find headroom?

Withstand TestingWithstand Testing

0

10

20

30

40

50

60

0 10 20 30 40 50 60 70 80 90

Time

Test

Vol

tage

MEGGER Foster OTSAF/2


Fully automatic, unattended operation Wide range of tests including five custom Results include standard deviation, time,

date Results printed or download via RS232 Stirring options for magnetic or propellor 60 kV, 80 kV and 100 kV versions

MEGGER Foster OTS60PB

MEGGER Foster OTS60PB

Portable oil test set for on site measurement Battery powered for two days continuous

use Fully automatic, unattended operation Pass/fail levels for go/no go testing Small and lightweight (19 kg = 42 lb) Complete with battery charger Variety of electrodes RS232 interface plus optional printer

MEGGER Foster OTS60SX

MEGGER Foster OTS60SX

Low cost, Semi automatic set 60 kV maximum output, 0,1 kV resolution Simple START, STOP & PAUSE control Weighs only 17,5 kg Optional vessels for all specifications Auto 60 second timer for withstand

testing Operates from 110/230 V power supply

MEGGER KF2000MEGGER KF2000

Karl Fischer moisture in oil test set Simple to use Quick results Low cost Battery powered, portable

MEGGER KF2000MEGGER KF2000

AVO INTERNATIONALAVO INTERNATIONAL

BringingReliability toAmps Volts Ohms

BringingReliability toAmps Volts Ohms

diagnostic insulation testing l predictive maintenance issues l basis of insulation tests l spot...

Documents

test insulation

good slide

cracks slide

temperature dependent

test leads

gonogo test

integral timer slide

presence of cracksholes