Condition Monitering on Motors and Generators

1

CONDITION MONITORING TESTS ON

HYDRO/TURBO GENERATORS AND

LARGE AC MOTORS

K.Mallikarjunappa

Central Power Research Institute Bangalore

2

CONDITION MONITORING TESTS ON

HYDRO/TURBO GENERATORS AND

LARGE AC MOTORS

* GENERATORS

- unit rating up to 500 MW

− − − − rated output voltage up to 30 kV

* MOTORS

− − − − unit rating up to 40 MW

− − − − rated terminal voltage up to 15 kV

3

* Reliability and life

* Stator winding

* Stator core

* Rotor winding

* Reliability and life

* Stator winding

* Stator core

* Rotor winding

4

INSULATION

• Operational reliability depends to a large extent on the

condition of the insulation system

• Insulation is the weakest link

• Any unexpected failure (forced outage) in generating

stations & process industries disrupt the system & cause

heavy financial losses

• Majority of failures have been attributed to the insulation

failures

5

LIFE LIMITING FEATURES

• Stator insulation

• Stator winding slot & end winding portions

• Tightness of stator bars in slots

• Stator core tightness & insulation

• Stator end winding bracing

• High levels of mechanical vibrations

• Frequent starts & stops

• Rotor winding wedging system & end winding portions

• Rotor end ring ( cracking, deformation )

• Rotor winding insulation

6

STATOR INSULATION

- composite type

(i) Mica

(ii) Glass fabric or cellulose paper

(iii) Resin [Synthetic, Non-synthetic]

7

STRESSES ACTING

• Stator winding is subjected to a combination

* Thermal …. High operating temp. during normal & abnormal

conditions

* Electrical…. Over Voltages during transient conditions

* Mechanical…. High levels of mechanical Vibrations

* Environmental…. Moisture, oil, dust, contaminants

8

Thermal stress - Delamination, tape separation, embrittlement,

strand separation, girth cracking.

Electrical stress - Cumulative electrochemical effects of

Partial discharges.

Mechanical stress - Loosening of wedges & end winding blocks,

abrasion of the insulation

- Erosion of stress grading paint & corona shielding paint

Coil

Core

Stress grading

coating

Corona shielding

coating

9

Environmental stress - Render stress grading coating ineffective.

- Electrical tracking.

• Slot discharges

• End winding discharges |

|

* Lead to rapid failure.

10

CONDITION ASSESSMENT PROGRAMME

# Consists of the following steps

• Collection of the historical data

• Visual inspection & examination

• Condition monitoring tests

11

HISORICAL DATA

# Can indicate problems which are generic/developed due to ageing

• Age of the machine

• Running hours

• Number of starts & stops

• Load levels

• Overloading

• Major electrical disturbances and faults

• Vibration & Temperature abnormality

• Record of repair and replacement of components etc.

12

VISUAL INSPECTION & EXAMINATION

• Visible symptoms of deterioration

• Mechanical damage to stator bars & end winding, migration of edges

• Deformation of the end winding sections

• Deterioration due to thermal effects .. Embrittlement, change in colour

• Corona damage & electrical tracking.. White/brown powdering

• Loose end winding blocks, ties, lashing

• Deposit of oil, dirt. moisture ingress, salt etc.

• Powdering due to abrasion

• Loose core laminations

• Core damage due to surface discharge

• Change in colour of core surface due to hot spots

• Abrasion of the slip ring and the like.

13

CONDITION MONITORING (DIAGNOSTIC) TESTS

# Conducted to

* Assess state, condition & extent of deterioration

*Assess trend in ageing

• Data logged enable to initiate appropriate remedial

measures to prevent forced outages

> Service life could be extended

14

HYDRO & TURBO GENERATORSDiagnostic tests…. Stator winding

Inter turn faults Surge comparison test7

Loose or bad conductor jointsWinding resistance measurement6

Discontinuities & cracksDC leakage current5

Loose wedges & Loose stator barsWedge mapping4

Incipient faults, slot & end

winding discharges

Partial discharge test3

Dielectric lossesTan delta & capacitance test2

Index of dryness,cleanlinessPolarisation index test1

Detection capabilityTestsSl. No

15

Stator core

Imperfections & hot spots in

the core

* ELCID Test

16

Rotor winding

* Dominating stresses

> Thermal & mechanical

Intern turn & earth faultsRecurring surge test

Inter turn shorts in polesWinding impedance

Loose or bad jointsConductor resistance

Index of dryness, cleanliness.IR/PI

Detection capabilityTests

17

IR Measurement :

- Reflects surface condition of the insulation

- Indicates surface contamination & moisture content

- PI is used as an index of dryness.

PI = 2

R

Y

BNeutral

Line Test voltage

_-

Measuring connection of stator winding

18

DC Leakage current measurement

• DC voltage is increased in steps.

• At each step, voltage is maintained constant for a predetermined time interval

(100 sec.) and current is recorded

• Max. test voltage as per guidelines

• Plot current verses test voltage

19

(3)

(2)

(2α)

(1)M

icro

am

ps.

DC voltage (kV)

(1) - Solid homogeneous insulation in good dry condition

(2) - Faulty insulation due to dirt & oil, ageing, mechanical damage or tape separation

(2a) - Faulty insulation - step ladder curve due to internal voids & ionisation

(3) - Insulation in wet condition

Typical curves obtained when testing insulation of large

rotating machinery.

Vdc = 1.6 x (AC test voltage level)

1.5 Vph

20

Tan delta Test: Represents dielectric losses

Concept Of Tan delta

Insulation between two electrodes

Treated as Capacitor

HV

INSULATION

LV

Electrodes

21

Perfect Capacitor

In a Perfect Capacitor current leads the voltage

by 900

900

Phasor Diagram

V

I

Cp

22

I

V

δφ

Ic

Ir

I

Practically Phase angle is < 900

δ Loss angle

φ Phase angle

Due to dielectric losses

23

Lossy Dielectric

Ic I Ir I

Ic

Cos φ = Ir / I = Sin δ

Cp

Rp δ

φ

Ir

Phasor diagram

Tan δ = Ir/Ic

24

Measurement of Tan delta :

• High Voltage Schering Bridge

H.V.

Rx Cx Cn

R 4 C4 R 3

L.V

Z1

Z3

Z2

Z4

Rp +(1/jωCp)

CRO

25

Tan δδδδmeasurement procedure :

* Single phase testing transformer of suitable KVA rating

* Equipment under test needs to be disconnected from the system

* Tan δ kit to be grounded to the system grounding and test voltage is

raised in steps upto the rated phase voltage

Stator

Generator

Motor

HVR

Y

B

26

Tan δδδδ - Voltage characteristic.

Test voltage is raised in steps up to a maximum of rated

service voltage.

Tan δ is measured at each voltage level.

Plot Tan δ v/s Voltage.

Solid loss

Wet & contaminated

Tan δ

Voltage

Sound

Deteriorated

Gaseous loss

0

27

Test parameters:

- Tan delta & capacitance at 0.2 VL

- Tan delta tip-up tan delta Vph - tan delta (0.2VL)

2

- Capacitance tip-upCap. Vph - Cap. (0.2VL)

Cap. (0.2VL)

* Changes in the above quantities with machine age

* Statistical variation of these quantities of similar machines.

28

Rated line

voltage VL

(kV)

Mica with

synthetic

bond

Mica with

non-

synthetic

bond

tanδ at 0.2

VL

∆ tanδ Maximum

∆ tanδ per

0.2 VL

tanδ at 0.2

VL

∆ tanδ Maximum

∆ tanδ per

0.2 VL

6.6 0.04

0.02

0.03

0.03

0.003

0.0025

0.0025

0.003

0.006

0.005

0.005

0.006

0.05

0.04

0.03

0.05

0.006

0.003

0.0025

0.006

0.016

0.006

0.005

0.012

11.0 0.04

0.02

0.03

0.03

0.04

0.003

0.0025

0.0025

0.003

0.0025

0.006

0.005

0.005

0.006

0.005

0.05

0.05

0.03

0.05

0.006

0.003

0.0025

0.006

0.016

0.006

0.005

0.012

Limiting values of tan delta for new coils/new windings

a) BEAMA REM 500, 1969 (b) Balcombe and Statt (CEGB), 1973 (c) CENELEC, 1974

(d) ESI Standard 44-5, 1987 (e) VDE - 0530

a) BEAMA REM 500, 1969 (b) Balcombe and Statt (CEGB), 1973 (c) CENELEC, 1974

(d) ESI Standard 44-5, 1987 (e) VDE - 0530

29

Partial discharge Test

Partial discharges

Material loss

Gaseous loss

tan d

elta

Voltage

# PD occur due to the presence of

* voids, conducting particles, de-lamination

* PD are deleterious to the insulation

* Cause chemical & mechanical destruction of the surrounding

insulation

# PD occur due to the presence of

* voids, conducting particles, de-lamination

* PD are deleterious to the insulation


insulation

30

- Discharge process in which the gap between two

electrodes is only partially bridged.

HV Void

Conductor

Insulation


medium & hence premature failure.

Concept of Partial dischargesConcept of Partial discharges

31

32

Effects of PD

PD can give rise to• Ozone

• Nascent oxygen

- strong oxidising agents

• Nitric acid in presence of moisture

• Oxalic acid in polymeric insulation

• Mechanical erosion due to ion bombardment

• Intense heat in the discharge channel

• Power loss

* PD cause chemical & mechanical destruction of

adjacent materials.

33

1

2

3

Dielectric

HV

1 - Internal partial discharge (Cavity discharge)

2 - Internal partial discharge ( between metallic & dielectric surfaces)

3 - Surface discharge (outside the insulation)

Representation of a partially defective dielectric

34

Cx

Cc

Cb

Ec

Detection

impedance

Test

object

Discharge

detector

Basic Partial Discharge Detection Circuit

Z1

Cb - Blocking capacitor

PARTIAL DISCHARGE TEST

IEC-60270


IEC-60270HVHV

GG

35

ANALYSIS OF PD DATA

* PD are highly stochastic in nature

36

Calibration

• Effected by injecting pulses of known charge contents.

• Calibrating pulse -- PD pulse

- Magnitude & time characteristics must be comparable.

• Rise time -- 50 - 100 nano sec.

• PD magnitude, q = eq. Cq

0

V

Calibrating pulse

37


* Found to be effective

* Capable of revealing incipient faults

* By analysing the PD data it is possible to identify type

of fault in the machine

38

Partial discharge test continued….

• Hydro & Turbo generators

* Internal discharges ….. Occur in voids / cavities

* Surface discharges…… Highly deleterious

> Slot discharges ….. Between coil surface & iron core

• > End winding discharges ….. Junctions of corona shielding

• & Stress control coatings

39

PD AnalysisContinued…..

• Need to be analysed statistically

• PD Quantities

* Magnitude (q)

* Number density (n)

* Polarity

* Phase angle of occurrence (ø)

* Quadratic rate

# Distribution profiles

* Magnitude - Number density distribution (q-n)

* Magnitude - Phase angle distribution (q- ø)

* Number density - Phase angle distribution (n-ø) and

* 3D patterns of ( q-n- ø )

# Finger prints and temporal changes can be used to characterize

defects

40

Comparison of PD patterns

Int. Void Void facing the Void facing the

HV electrode grounded electrode

41

Comparison of PD Patterns

Int. Void Void facing the Void facing the

HV electrode grounded electrode

42

On-line Condition monitoring of Turbo & Hydro

Generators Using P.D Testing

On-line Condition monitoring of Turbo & Hydro

Generators Using P.D Testing

• Deterioration mechanisms result in P.Ds caused by• Deterioration mechanisms result in P.Ds caused by

* Voids in the Insulation

* Electrical tracking on the end windings

* Sparking between the stator core and loose stator coils

* Voids in the Insulation

* Electrical tracking on the end windings

* Sparking between the stator core and loose stator coils

• Insulation deterioration can be detected by monitoring P.Ds • Insulation deterioration can be detected by monitoring P.Ds

43

How to detect PD in Generators ?How to detect PD in Generators ?

• Three Types of PD sensors• Three Types of PD sensors

* Capacitive couplers

* HFCT

* Stator slot couplers

* Capacitive couplers

* HFCT

* Stator slot couplers

• Sensors are permanently installed in the stator

winding during planned outage or during

manufacturing stage.

• Sensors are permanently installed in the stator

winding during planned outage or during

manufacturing stage.

44

1. Capacitive couplers (80 pF - 1000 pF) 1. Capacitive couplers (80 pF - 1000 pF)

• Coupled to the stator winding at

* Generator bus bars.

* Stator winding connecting rings at the

overhang portions

* Can be retrofitted to old generators.

• Coupled to the stator winding at

* Generator bus bars.

* Stator winding connecting rings at the

overhang portions

* Can be retrofitted to old generators.

45

2. HF CTs :- Can be incorporated at2. HF CTs :- Can be incorporated at

• Neutral end

• Frequency range 0.3 - 100 MHz

• can be retrofitted to old generator

• Neutral end

• Frequency range 0.3 - 100 MHz

• can be retrofitted to old generator

46

3. SSC :-3. SSC :-

•SSC is a broad band antenna (UHF Band)

•SSCs are installed under the wedges in the stator

• Coaxial cables are routed to a point outside the

generator.

•SSC is a broad band antenna (UHF Band)

•SSCs are installed under the wedges in the stator

• Coaxial cables are routed to a point outside the

generator.

47

Interpretation of PD quantities

* Still a challenging task

* Often subjective

* Depends on experience and

expertise

* Subject of intense research

48

WEDGE TIGHTNESS TEST

> Important test specified for RLA studies on Generators

# Stator wedges may be slackened due to

* Shrinkage of slot packing materials

* High mechanical stresses

* Vibration

^ Loose wedges cause

* Loosening of stator bars

* Excessive vibrations

* Erosion of corona shielding & stress grading coatings

* Abrasion of insulation

$ EVENTUALLY LEAD TO FAILURE OF STATOR WINDING.

49

ELECTRONIC WEDGE TIGHTNESS

EVALUATION

# Electronic method

* Sophisticated

* Provides map of wedge tightness

* Data can be stored for accurate trending of WT data

* Hand tapping method with a hammer

> Crude method

> Highly subjective

> No data can be generated

> Trend analysis is not possible.

50

WTD Methodology

* Each wedge is tapped automatically by a magnetic hammer

> Tapping force is constant

* Accelerometer picks up the signals

* Signals are processed & stored

* Software provides a map of relative tightness of the wedges.

51

STATOR CORESTATOR CORE

Made up of thousands of thin steel Laminations

(typically 0.5 mm)

Laminations are coated with a thin layer of electrical insulation

to prevent eddy currents.

Laminations are frequently shorted together at the back by

support bars

Made up of thousands of thin steel Laminations

(typically 0.5 mm)

Laminations are coated with a thin layer of electrical insulation

to prevent eddy currents.

Laminations are frequently shorted together at the back by

support bars

52

DEGRADING FACTORSDEGRADING FACTORS

* Mechanical damage to the stator bore surface or top slot walls

* Vibrations in the core may cause abrasion of inter laminar

insulation & short circuits

* Shorts between adjacent laminations cause eddy currents to be

induced by the rotating magnetic flux.

* These currents can produce dangerous local overheating/hotspots

in the damaged areas

* In extreme cases sufficient heat is generated to locally melt small

parts of the core

* Hot spots may lead to premature failure of stator winding

insulation

* Mechanical damage to the stator bore surface or top slot walls

* Vibrations in the core may cause abrasion of inter laminar

insulation & short circuits

* Shorts between adjacent laminations cause eddy currents to be

induced by the rotating magnetic flux.

* These currents can produce dangerous local overheating/hotspots

in the damaged areas

* In extreme cases sufficient heat is generated to locally melt small

parts of the core

* Hot spots may lead to premature failure of stator winding

insulation

53

DEGRADING FACTORS

54

Vibrations

Erosion of corona

shielding coating

Erosion of stress

control coatingAbrasion, fretting of

core laminations

End winding

DischargesSlot Discharges Short circuiting of

adjacent laminations

* Pittings on statorbar insulation

* Fusion of core

laminations

(short circuiting)

* Damage to core

end portion

* fusion of core

lamination

CPRI

55

CPRI

Eddy currents induced

circulate (Hot spots)

Local burn out of

the core

Extensive damage

to the core

56

Conventional Test on Core

* Core loop test- to detect hotspots in the core

Core

Cable loop

CPRI

High current

source Water

RheostatCT

Schematic diagram of Core Loop Test

Voltmeter

TESTING OF STATOR CORETESTING OF STATOR CORE

57

* A no. of turns of heavy cable is wrapped toroidally

around the core & frame.

* Very high AC current (hundreds of amps.)

sufficient to produce flux density almost equal to

operating level.

* Core gets heated up.

* Temp. is measured at several points on the core surface.

* Infra red scanning to detect hotspots.

CPRICore loop test …. continuedCore loop test …. continued

58

ELCID TESTELCID TEST

* Induce only about 4 % of the flux in the core by passing an AC

current (5 - 15 Amps) through a excitation winding looped

toroidally around the stator frame.

• Small pick coil senses the fault current induced at the defective

core section

> Excitation current

* Single turn voltage of the generator,Vp

Vp= V ph/ ( ktp) where V ph=Phase voltage

k = pitch factor,0.92

tp = Number stator bars per

phase

# For ELCID test, single turn voltage=4%Vp

* Induce only about 4 % of the flux in the core by passing an AC

current (5 - 15 Amps) through a excitation winding looped

toroidally around the stator frame.

• Small pick coil senses the fault current induced at the defective

core section

> Excitation current

* Single turn voltage of the generator,Vp

Vp= V ph/ ( ktp) where V ph=Phase voltage

k = pitch factor,0.92

tp = Number stator bars per

phase

# For ELCID test, single turn voltage=4%Vp

59

Schematic diagram of ELCID test ing

60

ELCID Test on 27Mw Hydro generator

61

A view of ELCID test set up

62

A view of ELCID testing in progress

63

TYPICAL ELCID DATATYPICAL ELCID DATA

64

DEFECTIVE COREDEFECTIVE CORE

65

Rotor winding

66

Rotor Winding (Turbo generator)

67

ROTOR WINDINGROTOR WINDING


* Thermal

* Mechanical


* Thermal

* Mechanical

TESTSTESTS

* IR/PI Deterioration, dampness, Contamination (cleanliness)

* Field Impedance Interturn faults

* Conductor Resistance Bad conductor joints

* IR/PI Deterioration, dampness, Contamination (cleanliness)

* Field Impedance Interturn faults

* Conductor Resistance Bad conductor joints

68

SURGE TESTSURGE TEST

* Rotor winding -- RLC circuit

* LV Surge ( ≈≈≈≈ 250 V) is applied

* Resultant waveform is recorded

* Both the waveforms are super imposed

* Waveform coincide each other and appear as a single

waveform if there is no interturn fault

* Rotor winding -- RLC circuit

* LV Surge ( ≈≈≈≈ 250 V) is applied

* Resultant waveform is recorded

* Both the waveforms are super imposed

* Waveform coincide each other and appear as a single

waveform if there is no interturn fault

69

CASE STUDIES

• 1) 11 kV, 144 MVA Hydro generator

Stator winding:

• IR = 700 MΩΩΩΩ

• tan δδδδ = 0.87%

• ∆∆∆∆T = 0.29%

• ∆∆∆∆ C = 0.36%

• IDE = 1.01 µµµµJ/pF/cycle

• Vi = 5.3 kV

• Qc = 3600 pC

• Assessment:

* Low dielectric losses * Low void content

* Insulation condition of stator winding healthy

70

Rotor winding

• Pole impedance

• Varied from 4.82 Ω to 10.67 Ω

• Visual inspection revealed migration of turn insulation of

02Nos. of poles

71

Migration of turn insulation

at the top of the poles


72


at the bottom of pole


73

13.8kV 100Mw Hydro Generators

* Operating in a Hydro power station

• Age varying from 19 years to 26 years

• Conducted Tan delta & PD tests

74

PD Patterns

75

13.8kV 100Mw Hydro Generators

3.448,9430.260.141.25G8

3.2511,5020.280.141.89G7

3.968600.270.171.14G6

3.269,3850.740.291.48G5

3.2111,7550.930.371.4G4

3.3111,6290.760.311.30G3

3.2273630.410.181.40G2

3.9653001.780.682.81G1

Vi (kV)PD mag.(pC)∆C (%)∆T (%)Tan ∂ (%)Generator


* Stator windings are in healthy condition



76

11kV, 115Mw Hydro GeneratorsSalal Power Station

4.440000,08440.03150.8764.216

3.9615000.0640.0350.9252.695

4.440000.0530.0210.883.744

4.020000.0250.0581.0494.843

4.025000.190.181.022.542

3.2111000.220.230.414.151

DIV (kV)PD Level

(pC)

∆C (%)∆T (%)Tan delta

(%)

PIGenerator





77

2) 11kV, 7.2Mw Turbo generator

• 18 years old class-F machine installed in a Polyfibres industry

• PI = 2.9

• tan δδδδ = 1.85%

• ∆∆∆∆T = 0.22%

• ∆∆∆∆ C = 0.40%


• Vi = 4.8 kV

• Qc ~ 40,000 pC. Discharges of very high magnitude in R & Y phase

sections

* Slot / end winding discharges were suspected.

78

11kV, 7.2Mw Turbo generatorcontinued…..

• Decision was taken to visually inspect the stator winding and

• Conduct inductive probe test to locate the sites slot/end winding discharges

• Results of visual inspection & inductive probe test

• Presence of white powder at the end winding regions of several bars

• Visible sparking was observed at the end winding regions two bars bearing No.2

& 22 ( Line end of R & Y phases )

• Deposits of white powder were found both on exciter & turbine ends.

• Deposits of white powder are a symptoms of end winding discharges

• Inductive probe test indicated presence of slot discharges—900mV

• Recommended for re-wedging.

79

11kV, 7.2Mw Turbo generatorcontinued…..

• Company accepted the recommendation & initiated action

• Tests were conducted after re-wedging with side packing materials &

varnishing

• PI = 2.8

• tan δδδδ = 0.93%

• ∆∆∆∆T = 0.087%

• ∆∆∆∆ C = 0.26%


• Vi = No discharges up to 6.35 kV

• Generator is in healthy condition.

80

1). 11kV, 2700kW Synchronous motor

* Class - F, 10 years old

* Fertilizer Company

tan δδδδ = 2.51%

∆∆∆∆T = 2.64%

∆∆∆∆ C = 9.28%

IDE = 6.96 µµµµJ/pF/cycle

Vi = 3 kV

1). 11kV, 2700kW Synchronous motor

* Class - F, 10 years old

* Fertilizer Company


∆∆∆∆T = 2.64%

∆∆∆∆ C = 9.28%


Vi = 3 kV

* Indicate high level of deterioration

# Recommended for rewinding

# Failed after a year

* Indicate high level of deterioration


# Failed after a year

81

2). 6.6kV, 5.1MW Synchronous motor

* Class B, 12 years old

* Petrochemical Plant

∆∆∆∆T = 3.38%

∆∆∆∆ C = 11.6%

Vi = 2.10 kV

* DLA pattern indicated presence of end winding discharges

(unstable pattern)


# Failed after two months

2). 6.6kV, 5.1MW Synchronous motor

* Class B, 12 years old

* Petrochemical Plant

∆∆∆∆T = 3.38%

∆∆∆∆ C = 11.6%

Vi = 2.10 kV

* DLA pattern indicated presence of end winding discharges

(unstable pattern)


# Failed after two months

* High value* High value

82

3). 6.6kV, 1750KW, Induction motor

* Class - F, 1 year old

* Cement Industry

IR = 700 MΩΩΩΩ


∆∆∆∆T = 0.39%

∆∆∆∆ C = 1.29%


* Due to intense slot or end-winding discharges

# loop trace distorted & unstable

# wavy unstable pattern appeared beyond 2kV

* Failed after a week

3). 6.6kV, 1750KW, Induction motor

* Class - F, 1 year old

* Cement Industry

IR = 700 MΩΩΩΩ


∆∆∆∆T = 0.39%

∆∆∆∆ C = 1.29%


* Due to intense slot or end-winding discharges

# loop trace distorted & unstable

# wavy unstable pattern appeared beyond 2kV

* Failed after a week

83

CONCLUSIONS

• Condition monitoring tests are Non-destructive type

• * Defective components can be identified

• * Premature failures can be avoided

• * State & condition of the equipment can be

assessed

• * Impending problems or deteriorating factors can be

detected

• Systematic diagnosis programme and periodic monitoring

enable life extension

84

THANK YOU

85

11kV/220kV, 43.33MVA Generator Transformers (18 Nos.)

GT1

0.3141.89720HV/LV(B)

0.3411.836000LV/HV+G(B)

2250<2.00.3381.814580HV/LV+G(B)

0.3581.516400HV/LV(Y)

0.3531.579750LV/HV+G(Y)

30002.540.361.566200HV/LV+G(Y)

0.3621.763580HV/LV(R)

0.3572.072100LV/HV+G(R)

24003.180.3672.191680HV/LV+G(R)

PD Level (pC)Moisture level

(%)

Tan delta (%)PIIRInsulation

section

Condition Monitering on Motors and Generators

Documents

corona shielding

void void

phase angle

broad band

2mw turbo

corona shielding

visual inspection

rotating magnetic