Tech W Shop 1998 5kv

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Diagnostic Insulation Testing

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

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Maintenance Regimes

• Corrective maintenance
• Preventive (Periodic) Maintenance
• Predictive Maintenance(Record trend data to
  determine next action - variable maintenance
  periods)
• Appropriate regime varies

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Maintenance Regimes

• Value of Assets ?
• Critical role of Assets ?
• Costs of failure ?
• Costs of Maintenance regime ?
• Manpower
• Skills
• Tools - Testing / Monitoring / I.T.

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Why test insulation?

• System performance
• System safety
• System reliability
• Economic asset management
• Over 60 failures caused by Insulation problems
  (CEGB ERA Technology)

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Insulation Failure

• Oil
• Contamination
• Mechanical damage
• Pin holes
• Vibration
• Temperature cycling
• Moisture humidity
• Cracks

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Test Techniques - DC Testing

• Total Current has 3 components
• Capacitive Current - Charging
• Absorbtion Current -Polarisation
• Leakage Current
• TIME DEPENDENT
• Temperature Dependent

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Insulation Test Currents
100
I/uA
Charging
Total
10
Leakage
Absorption
1
0,1
1
10
T
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Insulation Equivalent Circuit
Leakage
Capacitance
Absorption
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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)

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Insulation Test as a Go/NoGo Test

• Spot Test carried out for given time (1 minute)
• Commissioning
• National /Manufacturers Standards

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Time Resistance Tests

• Independent of equipment size and temperature
• Some information without past results
• Options
• Curves
• Time - Resistance Ratios

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Time ResistanceTest
R
Absorbtion current visible
Absorbtion current not seen
t1
t2
Time
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Time Resistance Tests
Polarisation Index (10 min/1 min ratio) lt1 1,0 -
2,0 2,0 - 4,0 gt4,0
Insulation Condition unsatisfactory dubious good
very good
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Time Resistance Tests
Dielectric Absorption Ratio (60 s/30 s) lt1 1.0 -
1.4 1.4 - 1.6 gt1.6
Insulation Condition unsatisfactory dubious good
very good
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Step Voltage Test

• Test voltage is increased in 5 steps
• Lower insulation resistance values at higher
  voltage indicate presence of cracks/holes

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Step Voltage Test
5000 V
Resistance
2000 V
1000 V
Voltage
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Dielectric Discharge Test

• Test is run until currents stabilise
• Measurements made on dischargeDD Current
  after 1 min Voltage x Capacitance

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Dielectric Discharge Test

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Dielectric Discharge Test
DD Value gt4 2.0 - 4.0 lt2.0
Insulation Condition unsatisfactory dubious good
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Tan Delta Testing

• Polarisation and capacitive current dominate
• Aging (moisture/dirt) sensitive
• Low voltages can be used

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Perfect Insulation
I (capacitive)
ITOTAL
IR 0
V (applied)
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Facts about Insulation

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

//

IR
ITOTAL
IC
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REAL Insulation
I (capacitive)
IC
ITOTAL
IR
V (applied)
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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 ?

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REAL Insulation
I (capacitive)
IC
ITOTAL
d
?
IR
V (applied)
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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

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What is Power Factor?

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

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Tan Delta Testing
I(capacitive)
IR
Tan d
IC
IC
ITOTAL
IR
Power Factor
d
ITOTAL
?
IR
V(applied)
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Tan Delta v. Power Factor

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

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Tan Delta 3 Terminal Test
Low voltage (L)
High voltage (H)
CHL
CLG
CHG
Ground Connection (G)
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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
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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

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Tan Delta Testing

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

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Insulation Test Diagnosis
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Tests Performed On

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

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Diagnostic Testing - Where Used

• P.I. Testing Trending
• Generators / Aerospace
• Petrochemical/Process Industry
• Transmission/Distribution
• Pass/Fail
• All electrical Equipment gt 3 kV
• Commissioning Routine Maintenance
• TREND to TRENDING !

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MEGGER 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

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MEGGER 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

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MEGGER BM25

• As BM21 features plus
• Automated tests
• Polarisation Index
• Step Voltage
• Dielectric Discharge
• RS232 download results every 5 s
• Download software lead

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MEGGER S1-5005
As BM25 with 5 mA test current. BM25 has 2 mA
test current.
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MEGGER S1-5010

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

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MEGGER S1-5010
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MEGGER S1-5010

• Memory for 75 sets of results
• Windows PC software
• remote operation
• results storage
• External output for HV ON indicator
• Switchable digital filter for noise rejection
• IP54 weatherproofing

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

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S1-5010 via software
Voltage ON lamp
S1-5010
Soft keys
Soft keys
Test Start/Stop button
Instrument On/Off switch
Soft keys
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S1-S1 Menu Bar - Window

• Remote Control
• Selects the remote control window if a Database
  Viewer window is active.
• Database Viewer
• Selects a database viewer window if the Remote
  Control window is active or switches between
  Database Viewer windows if more than one is
  active.

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Database Viewer - Details
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Database Viewer - Graph
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MEGGER EDA

• Electronic Dielectric Analyser
• Used on rotating machines
• Simple to use
• Automatic testing
• Normalised parameters
• Database of results

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MEGGER EDA
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MEGGER EDA

• Insulation of rotating machines
• hydraulic power generators
• turbo-generator
• 6/12 kV motors
• Technique used for 15 years

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EDA Software
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MEGGER EDA

• Automatic testing
• PC controlled
• Motor data input
• Test voltage input
• Calculation of results

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EDA Software
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MEGGER EDA

• Results at 2 test voltages
• Resistance
• Polarisation Index
• Time constant (RC)
• Dielectric Discharge
• Absorption Index
• Capacitance (ac dc)

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EDA Software
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MEGGER EDA

• Results
• Print out report
• Print out graphs
• Expert analysis
• Comparison with previous results

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BIDDLE 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

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BIDDLE Delta 2000

• Results storage
• Printer for on-site results
• Downloading test data
• Accessories
• Oil test cell
• Bushing connectors
• Bar code wand

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BIDDLE Delta 2000
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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

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CB-100 Low Voltage Bridge

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

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Testing 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

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Testing 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)

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Testing 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.

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Testing 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

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Testing with Safety

• 2. CHECK THE ABSENCE OF VOLTAGEat 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.

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Testing with Safety

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

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Testing with Safety

• Discharge Sticks
• Slowly discharge capacitive items (cables,
  capacitors.)
• Discharge to a safe level in 5 - 10 times RC
  (time constant)

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Discharge Sticks

• Voltage Length Resistance Max. cap.
• 35 kV 50 cm 10 kOhm 6 uF
• 50 kV 136 cm 100 kOhm 6 uF
• 75 kV 156 cm 150 kOhm 4 uF
• 100 kV 176 cm 200 kOhm 3 uF
• 150 kV 208 cm 300 kOhm 2 uF

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Oil Testing

• MEGGER Foster Oil Electric Strength Testers

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Why test switchgear oil?

• Prevent Transformer failure
• Principle problems are
• humidity
• oxygen
• temperature

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Oil Testing Methods

• Water content
• Acidity
• Colour
• Flash point
• Gas content
• Oil provides HV insulation
• Electric strength is the most important test

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Electric strength Test techniques

• Electrode gap
• Electrode shape
• Vessel size
• Voltage rise rates
• Stand and stir times

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Electric strength test results

• Temperature affects values
• Record results
• Low results show presence of moisture or
  particles
• Impurities from air, operator or equipment

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Breakdown Testing
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Electric Strength Test Results

• Average over six tests
• Scatter can be large
• Standard deviation calculated
• Report breakdown values, date, temperature

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New Specification EN60156

• Replaces IEC156 (1963)
• Optional stirring
• Current limited breakdown for silicone oils
• Gives guidance on scatter of results

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Withstand Testing

• Test voltage held at preset level for 1 minute
• Quick test of level of contamination
• Increase to breakdown to find headroom?

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Withstand Testing
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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

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MEGGER Foster OTSAF/2
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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

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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

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MEGGER KF2000

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

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MEGGER KF2000
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AVO INTERNATIONAL

• Bringing
• Reliability to
• Amps
• Volts
• Ohms

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