motor circuit analysis of 31 and iv

8/9/2019 Motor Circuit Analysis of 31 and IV

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Motor Circuit Analysis Principles & Case Studies

Treadstone Rubber Pvt. Ltd.


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MCA Capabilities

Test directly from the MCC

Check connections, cable & motor

Detect broken bars, inter-turn shorts, winding contamination,insulation problems & air-gap eccentricity

Check AC/DC motors, generators, servos & transformers


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Motor basics - stator construction


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Motor basics - stator failure modes

Turn to TurnCoil to CoilOpen CircuitPhase to PhaseCoil to Ground


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W hat is Motor Circuit Analysis?

Measurement & analysis of the following parameters:R esistance

Inductance

Impedance

Phase Angle

Current/Frequency R esponse (I/F)

Capacitance


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W hat are Phase Angle & Current/Frequency R esponse?

P hase AngleThe relative angle between the two vectors of the appliedtest voltage & drawn current

C urrent/Frequency ResponseV oltage is applied to the winding at different frequencies &

the change in the current drawn is assessed


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Evaluation of W indings

W inding ShortsPhase Angle and Current/Frequency Response

Loose C onnectionsResistance

W inding C ontamination/OverheatingInductance, Impedance & Capacitance

Rotor C ondition and SeverityInductance and Impedance W aveforms


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Setting the R ules

P hase Angle and I/F readingsBoth Fi and I/F > +/- 2 Shorted TurnsFi > +/- 1, I/F Balanced Shorted Coils in the same phaseFi Balanced, I/F > +/- 2 Shorted Phase to Phase

Rules stand regardless of motor size

Resistance ~ +/- 5%


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Setting the R ules (Cont.)

Impedance, Inductance & C apacitanceIf impedance and inductance are parallel, winding is clean.

If impedance and inductance are not parallel, windingcontamination or overheating has occurred.

If capacitance changes over time, winding contamination&/or partial discharges are indicated.


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Setting the R ules (Cont.)

Inductance and Impedance Rotor TestsMeasurements of inductance at different rotor positions willindicate the condition of the rotor bars.

Rotor tests should be symmetrical and not necessarilyperfect sine-waves


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Insulation Diagram of Motor

G round

P hase A

Phase B

P hase C

Circuit capacitancechanges due to charge

effects of molecules in aninsulation medium.Dipoles are createdas electric field crosses themolecules. As they align,capacitance increases.


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- -

The Dipole

+N eg Potential Pos Potential


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Dipolar Motion in Operation

G RN D

W ire

W ire

V oltage

Capacitance

High

Low

MegOhms

High

Low

High

High

Ground Insulation


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Dipolar Motion in Surge Test

C onductor 1 C onductor 2

Voltage

Time

Impulse

Overcomes Dipolar Spin.

R equires Higher V oltagein order to cross air gap.

Potentially Destructive!!!


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Dipolar Motion in MCA - 1

wire

wire

wire

wire

wire

wire

G ood P haseP hase Angle: 77 degreesC urrent/Frequency: -44%


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Dipolar Motion in MCA - 2

wire

wire

wire

wire

wire

wire

Bad P haseP hase Angle: 73 degreesC urrent/Frequency: -40%

C apacitiveDefect


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Insulation Test Method Overview

Electrical Insulation is a dielectric.

Electric fields cause atoms to polarize with a change to capacitanceas they polarize.

DC insulation tests measure change to capacitance as charge

crosses in one direction.

Surge test uses a high voltage impulse in order to detect defects bycausing an arc. V oltages too high to detect small changes incapacitive reactance due to defects in insulation.

MCA fully excites the insulation at low voltage. Small changes willeffect circuit capacitance, which will not be masked by highvoltage.

MCA method also allows early detection of faults and, as a result,can trend winding faults over time.


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Case Study 1 650 K W motor with interturnshort in stator

Data courtesy R ajashree Cement, Malkhed

Motor is not grounded but trips on start-up !


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Case Study 2 900 K W motor with windingcontamination & loose overhang

Data courtesy R eliance Industries, Hazira

Motor had significant contamination,also the overhang lacing was completely broken !


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Case Study 3 6000 K W synchronous motor with interturn short in rotor

6000 K W , 200 R PM SynchronousMotor 36 rotor coils and 244 stator coils.

Failed on start-up but unable todetermine cause over two dayswith surge testing and other winding test technologies.

Motor circuit analysis applied,which identified faults within therotor.

Four rotor coils found to be directly shorted, causing a fault in themotor secondary circuit.

Repaired and returned to service.

Data courtesy BJ M Corporation, USA


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Case Study 4 300 K W motor with repetitivebearing failures

300 K W , 3000 RPM motor withcontinuous bearing faults

MCA rotor test shows combinationof casting voids (resulting in severe rotor heating), and eccentric rotor

Fault detected on inspection -combined casting void andeccentric end-shield bearing fit.



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Case Study 5 N oisy 150 K V A transformer



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Software Evaluation: EMCAT

EMCAT software for MCA automatic data interpretation from direct data access fromALL-TEST IV PR O Data collector or manual data entry of combined technologies.


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EMCAT: Automated analysis of AC motors


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EMCAT: Automated analysis of AC rotors


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EMCAT: Trending charts


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TFE Software estimation of residual life!


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All-Test: W hich one suits your needs?

All-Test 31ImpedancePhase AngleCurrent/Frequency Response

Insulation ResistanceAutomated Rotor Test

All-Test IV P roImpedancePhase AngleCurrent/Frequency R esponse

Insulation R esistanceManual Rotor TestR esistanceInductanceCapacitanceData logging

R outes


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For more details, contact:

TREADSTONE RUBBER PVT. LTD.TREADSTONE RUBBER PVT. LTD.COMMERCE HOUSE COMMERCE HOUSE

ROOM#307 ROOM#307 SHARDA BABU STREET,SHARDA BABU STREET,

RANCHI RANCHI- -834001834001JHARKHAND JHARKHAND Tel: 91Tel: 91- -651651- -32906913290691Fax: 91Fax: 91- -651651- -2305307 2305307

E E- -mail: [email protected] mail: [email protected]

motor circuit analysis of 31 and iv

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