motors generators monitoring eng

7/28/2019 Motors Generators Monitoring Eng

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Partial Discharge

Monitoring Systems forElectric Motors & GeneratorsCondition Assessment Solutions for Rotating Machines.

PD Based innovative tools for

the Condition Based Maintenance.

MD-04.05.012- rev. 00 - 08/10/2006


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TechImp Systems S.r.l. Via Toscana, 11/C - 40069 Zola Predosa BO, Italy Tel. +39.051.19986050 and fax +39 051.19986199e.mail: [email protected] URL: www.techimp.com

Product Card MD-04.05.012 rev. 00 09/10/2006

TechImp innovativetechnology

TechImp technology (patented) allowsdifferent PD phenomena to be classified on

the basis of their pulse shape and split indifferent clusters, so that further analysiscan be carried out on each dataset,separately. This enhances the likelihood ofPD source identification, even in theabsence of a skilled operator.

TechImp acquisition technology alsoprovides efficient noise rejection in mostcases without adding any suppressiondevice. As a matter of fact, noise signals

have been observed to be very differentfrom PD signals; therefore, TechImpclassification system can be successful inseparating the contributions of PD fromthose generated by disturbances.Specifically, each PD pulse waveform isacquired and the so-called equivalent time-length and bandwidth are evaluated andplotted on the TF map. Different types ofdischarges (e.g. PD and noise) shall groupinto different clusters in the TW map being

characterized by different pulse shapes.Therefore, on the basis of the TF map, it ispossible to achieve noise rejection andseparation of PD phenomena. An exampleof this separation for a badly impregnatedcoil is shown in the picture below, in whichPD due to different phenomena group intodifferent clusters.

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Phase (deg)

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T (ns)

619.72 5 2. 5 3 00 . 0 3 50 . 0 4 0 0. 0 4 50 . 0 5 0 0. 0 5 50 . 0

ClassificationMap

W(MHz)

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Phase (deg)

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Light blue cloud

Surface/delamination

Green cloud

Cavity

(delamination)

Red cloud

Cavity

(delamination)

White cloud

Microvoids

After the separation has been carried out,patterns associated with eachphenomenon can be extracted andprocessed separately. The system softwareis also endowed with an automatic fuzzy

logic based, defect identification tooldedicated to rotating machines.

Defect identification tool

Diagnostic database

Diagnostic data storage and retrieving is afundamental support for TechImpinstruments as well as service department.

A database containing thousands of datarelevant to partial discharge activitiesoccurring in electrical system has beendeveloped. The database approach isfundamental for both identification andrisk assessment purpose. As a matter offact, through data analysis and comparisonPD phenomena can be successfullyrecognized and followed over time so asto recognize the need for a maintenanceaction. Thanks to the diagnostic database,identification algorithms can becustomized for machines of each specifictechnology.


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The database shall be shared withcustomers and accessed via internet.

Diagnostic techniqueintegration

Since PD may be affected by other factorsof influence, such as temperature, humidity,

vibrations, the monitoring system can alsocollect these kind of data from dedicatedsensors.

All these data can be stored in the machinedatabase and correlated with PD readingsfor an optimal condition assessment of theconsidered machine.

In case a continuous PD monitoring iscarried out, the acquisitions of PD andother quantities can be mutually triggered,so that if the one of the parameter trendgenerates an alarm, the system immediatelystarts to acquire also the other (and vice-

versa).

System lay-out and installation

The system can be easily installed and it isessentially made up of the followingcomponents:

- Sensors (one for each phase, ingeneral permanently installed);

- Derivation box (permanentlyinstalled);

- PD monitoring system (to beconnected at the measuring stageforperiodicmonitoring sessions or to

be permanently installed forcontinuousmonitoring).

A schematic layout of the monitoringsystem is shown in the picture below,

where the connection points A1, B1, C1represent the machine terminals.Capacitive type sensors are normally usedfor rotating machines. These sensors, are1000 pF high voltage dry-type(mica/epoxy) capacitors. These capacitors

are permanently installed at the machine

terminals (generally in the bus duct). Thehigh frequency PD pulses originated inthe machines are derived by capacitivecouplers so that they can be measured.

G/M

3~

RA1

DerivationBox

LP

Filter

HP

Filter

HP

Filter

HP

FilterPD

measuringEquipment

SyncIn

Ph.A

In

RB1

RC1

Ph.B

In

Ph.C

In

Sync

PD

Capacitive Coupler

Sensor

PD

PD

System Layout

Downstream the capacitive sensor asuitable resistor is provided. Theresistance forms together with thecapacitance the measurement voltagedivider. A surge arrester is also providedin parallel to the impedance to protect the

whole system from over-voltages.Downstream the voltage dividers, aderivation box with a set of 3 high-passfilters and 3 low-pass filters is installed.

The 3 high-pass filters are aimed at PDmeasuring. The low-pass filters are used toderive power frequency reference signals(synchronisation with line-to-ground

voltages).

Cable Derivation Box

If the installation of capacitive couplers isfor any reason not possible, other sensorscan be used. Among those, High

Frequency Current Transformers (HFCT)


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can be effectively employed. The HFCThas to be connected around one (or more)grounding connection(s) of the machines.For synchronisation purposes, a PowerFrequency Current Transformer (PFCT) or

Rogowski coil may be used.

Even though this measurementconfiguration can provide useful diagnosticindications about the machine conditions, ithas lower sensitivity with respect to theprevious configuration.In case the machine is supplied by means ofinsulated cables, a feasible solution is theuse of HFCT installed around the earthingconnection of the sheath of the cables

relevant to each phase or around the powercables themselves.

Sheath

MV Conductor

MV Cable Termination

HFCT

PFCT

Example of HFCT Installation

Permanent Monitoring andPeriodic Assessment

For Permanent Monitoring, the PDacquisition unit is always connected to thederivation box (or directly to the sensors in

case HFCT are used) and to other sensors(temperature, humidity, vibrations, etc.), ifavailable.PD signal cables are connected to the PDMonitoring device, which, in turn, must belinked to an Ethernet network for remotesupervision and control.

Monitoring System

Interconnection with SCADA systems canbe realized in several ways.If an Ethernet network (and a static IPaddress) is available in the plant, themonitoring equipment can be directlyconnected to it. Otherwise, a dedicated

phone line can be also used with a PSTNmodem. When such communicationfacilities are both not available, a GSM orsatellite modem (depending on thecoverage of the area) can also be used.

For the Periodic Assessment, it isassumed that the PD measuringinstrument is connected to the PD sensorsfrom time to time (the same equipmentcan be used to check several machines).

The Derivation Box is provided with 4sockets (one for each phase for the PDsignal + the synchronisation signal) sothat when the periodic measurement mustbe carried out, the PD acquisition unitcanbe easily and quickly connected to it,

without need of putting the machine outof service.

For further information, please

contact:

TechImp S.p.A. Via Toscana, 11/C40069 Zola Predosa BO ITALY

Tel.: +39.051.19986050

Fax: +39.051.19986199Email: [email protected]

URL: www.techimp.com

motors generators monitoring eng

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