diagnostic insulation testing l predictive maintenance issues l basis of insulation tests l spot...
Post on 22-Dec-2015
223 views
TRANSCRIPT
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
Time Resistance TestsTime Resistance Tests
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
Time Resistance TestsTime Resistance Tests
Dielectric Absorption Ratio (60 s/30 s)
<1
1.0 - 1.4
1.4 - 1.6
>1.6
Insulation Condition
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
Dielectric Discharge TestDielectric Discharge Test
-
+
-
+
-
+-
+
+
-
+ ++ +
--- --
+
+
-
-
+
+
--
+- +-
+++
-
--
+
Dielectric Discharge TestDielectric Discharge Test
DD Value
>4
2.0 - 4.0
<2.0
Insulation Condition
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.
MEGGER S1-5010MEGGER S1-5010
Heavy Duty - Mains & Battery Automated Tests Results Storage RS 232 communications Graphical Display
MEGGER S1-5010MEGGER S1-5010
MEGGER S1-5010MEGGER S1-5010
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
BIDDLE Delta 2000BIDDLE Delta 2000
Results storage Printer for on-site results Downloading test data Accessories
Oil test cellBushing connectorsBar code wand
BIDDLE Delta 2000BIDDLE Delta 2000
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)
Testing with SafetyTesting with Safety
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.
Testing with SafetyTesting with Safety
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.
Testing with SafetyTesting with Safety
4. SHOWN, WARN OTHERS AND LIMIT THE WORK AREAeven during the most simple temporary maintenance operation
Testing with SafetyTesting with Safety
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
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 OTSAF/2
MEGGER Foster OTSAF/2
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