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MICAMAXXTMplus Partial Discharge Basics

Partial discharge Basics of Monitoring


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Table of contents1.0 Partial discharge introduction ..................................................................................................... 31.1 Partial Discharge Detection from the Inventor of PRPDA...................................................... 3

1.2 PD Tech Power Engineering AG the partner for condition monitoring............................... 3

1.4 Partial Discharge and Insulation Failure............................................................................... 42.0 Partial discharge basics .............................................................................................................. 53.0 What is partial discharge? ........................................................................................................... 63.1 Examples: slot section/generators and motors .................................................................... 6

3.2 How do we know there is a problem ................................................................................... 8

3.3 Why monitoring is necessary ............................................................................................... 84.0 Typical Discharge Patterns of Rotating Machines........................................................................ 94.1

Discharges in Endwindings .................................................................................................. 9

4.2

Endwindings Problems....................................................................................................... 10

4.3 Endwinding Continued...................................................................................................... 10

4.4 Delamination of Main Insulation........................................................................................ 11

4.5 Delamination & PD Traces ................................................................................................. 11

4.6 On-line partial discharge monitoring................................................................................. 125.0 The MICAMAXXTMplus machine monitoring through the web ..................................................... 135.1 The MICAMAXXTMplus monitoring structure......................................................................... 15

5.2 Datahandling Database................................................................................................. 166.0 Sensor and Coupler Installation................................................................................................. 17


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1.0 Partial discharge introduction1.1 Partial Discharge Detection from the Inventor of PRPDAAfter 14 years experience with phase resolved partial discharge detection (PRPDA), we introduce a full

line of new detectors and monitoring systems for field applications with an unmatched

price/performance ratio, partial discharge testing today is an indispensable tool for preventive

maintenance and increase of equipment availability by reducing unplanned outages

1.2 PD Tech Power Engineering AG the partner for condition monitoringPD tech provides instruments, installation and engineering services, as well as development and design

integration know-how for most monitoring applications in the industrial and energy sectors. Significant

investments into personnel and tools over the last two years have moved us to the forefront of internetintegration.

Our partial discharge monitoring solutions now include:

Gas insulated switchgear UHF monitoring and ultrasonic inspection

Medium voltage switchgear monitoring and ultrasonic inspection

Transformers

Rotating machines (generators and motors) including full off-line inspection and tool kit supply.

Furthermore we design and provide mobile test equipment and specialised tools for insulation quality

assurance and inspection.

The MICAMAXXTM product family now includes partial discharge insulation condition monitoring for

motors and generators ranging from a cost efficient trending and alarming system to a full expandable

internet solution with analytic capabilities. The units are available as multi-purpose portable detectorsfor periodic on-line and off-line inspections.


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1.4 Partial Discharge and Insulation FailureAll high voltage machines will exhibit partial discharge, even from new. As a result, over 30% of

unplanned outages and subsequent production loss can be attributed to insulation failure.

The MICAMAXXTM product range is PD Techs state-of-the-art solution for monitoring partial discharge,

ensuring greater availability of plant.

All high voltage machines will experience partial discharges even from new!

Discharge levels increase over time until eventually failure occurs.

Can you afford the consequences?

Partial Discharge Testing - The only access to the stator insulation performance on-line

no interruption of service for testing

solutions for permanent monitoring - perodic testingexpert support and tests

pd test is non-destructive

tests possible: on-line and off-line

determines insulation condition

identifies detrimental trends

an indispensable tool for maintenance planning underpins maintenance contracts

Partial discharges comes from different factors

TEAM stresses of the insulation

Thermal, temperature

Electrical, electric field

Ambient (environment)

Mechanical, vibrations

lead to:electrical discharges (PD) which in consequence are an indicator for such stresses

these indicators are not the cause but the consequence of stresses (TEAM).

severe defects are always localised, a global aging does practically not exist

diagnosis and monitoring analyse causes & effects of defects or aging.

often defects occur in specific locations, there is no overall average ageing, e.g. using a hammer for

placing only one bar might harm that specific bar.

Defects Identified by Partial Discharge Measurements

Loose Wedges and Bar Vibration, Slot Discharges

Broken Conductors

Contamination (Salt, Cement, Oil) of Damage of End-WindingDischarges between Phases as a Result of

Vibration or Design Problems especially new machinesnAgeing/Delamination of Main

Insulationincluded:

brush sparking, collector problems

pd in busbars

Partial Discharge is a local brakdown phenomenon which short circuits a part of an insulation and leads

to ageing and accompanies ageing! Partial discharge takes place in defects of the insulation.

formation ionised species

formation of corrosives ions, acids, nitrogen oxides, ozone

light, sound and electromagnetic waves are emitted

we use these effects for identification and localisation of partial discharges (=insulation defects):

antennae, chemical sensors, ultrasonic devices, cameras..


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2.0 Partial discharge basicsPartial discharges occur wherever the electrical field is higher than the breakdown field of an insulatingmedium:

Air: ca. 27 kV/cm (1bar)SF6: ca. 360 kV/cm (4bar)Polymers: 4000kV/cmThere are two necessary conditions for a partial discharge to occur in a cavity:

(1) presence of a starting electron to initiate an avalanche

(2) the electrical field must be higher than the ionisation inception field of the insulating medium

the availability of this initial electron influences significantly the partial discharge inception of each individualdischarge pulse

Partial discharges occur wherever the electrical field is higher than the breakdown field of an insulating

medium:We speak about partial discharges because the discharges are created within the insulation.

To explain how partial discharge is

created, we take a Sample of one

period of the applied sine wave

voltage (50Hz). During the increasing

position, the electrons and ions from

the gas losed ions are separated

and went to the surface of the hole

(electrons to one side/ ions to the

other side) in the insulation of the

material. At one point there is an

higher charge on the surface as the

insulation gas can keep a

breakdown within this hole will

happen. That is not a full discharge,

it is a partial discharge within the

insulation material.

To visualize this effect, an aquisiton

of these discharges will made over a

certain time. We recommanded to

chose an ACQ time of 30 sec.

During aquistion all discharges are

sorted out to their time position

(position within a period of the sinewave) and to the amplitude position

streagth of the discharge) if there

exists several discharges within these

windows there are added, that

finally a 3D matrix is created. This 3D

matrix is visualised typically in a 2Dpattern with color shows intensity ofthe number of discharges.


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3.0 What is partial discharge?Partial discharge (PD) is an incomplete electrical discharge that occurs between insulation or insulation

and a conductor. Overtime the insulation system of the machine will deteriorate, a process accelerated

by thermal, electrical, ambient and mechanical stresses. By assessing the partial discharge levels of the

machine winding, the deterioration can be effectively monitored.

3.1 Examples: slot section/generators and motors

Picture 1 Picture 2

This two pictures shows a physical experience of an acelerated evolution of electrical discharges in the

epoxy resine trought one insulation paper how is using in the manufacturing of the generator bars. In

the top of the picture we have an high voltage electrode and in the bottom the ground electrode, the

second picture shows the evolution of the electrical treeing. Picture 2 is near of a brekown beetween

high voltage and ground electrode because the electrical trees has reached the ground electrode.

This is an accelerated experience of a generator breakdown, this process lasted one hour.

Wedges/

Wedge

thigness

testing

Insulation/

windingcopper


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Statistics shows that the most troubles in the generators are by the stator windings [Allianz 99]

Electrical treeing creep beetween the Mica tape bandage to reach the ground potential.


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3.2 How do we know there is a problemThe occurrence of sparks, arcs and electrical discharges is a sure indication that insulation problems

exist.

It is also likely that one or more of the following defects will be exhibited:

Bar vibrations (loose wedges)

End winding contamination

Slot discharge

Broken conductors

3.3 Why monitoring is necessaryInsulation Condition Monitoring provides an early warning of critical problems in the stator insulation of

electrical machines, so that corrective measures can be undertaken before costly damage occurs.Failures such as earth faults, phase-to-phase faults or shorted turns will eventually develop as a result of

the known defects. In this situation a new machine winding is likely and lead time for replacement coils

can be lengthy.

Failure due to discharge activity! It can be avoided!

If the problem is identified early enough, the situation can

be contained, by implementing a temporary repair to

enhance machine life, whilst necessary spares are

manufactured. In this situation, a MICAMAXXTM is a partial

discharge trending system comprising of an on-line

monitoring unit and PD transducers, which are fitted to the

machine as a permanent installation, to enable

continuous on-line monitoring of the insulation system

How does it work?

Partial discharge produces high frequency current pulses,

which are picked up by the PD transducers (fitted one

per phase) and which are connected via co-axial cable

to the MICAMAXXTMsystem.

Partial Discharge Footprints The Partial Discharge Pattern Pulse Distribution Function

Thermal Ageing Loose Copper Pollution

Once the initial analysis has been performed, the continuous on-line monitoring unit MICAMAXXTMplus

can be configured.


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4.0 Typical Discharge Patterns of Rotating Machines

typically a triangle form

4.1 Discharges in Endwindings

typically clonds

Pump Storage Plant

Load Variation, differential

thermomechanical mouvement

Insulation separated from conducteurs

Partial discharge


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4.4 Delamination of Main Insulation

4.5 Delamination & PD Traces


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4.6 On-line partial discharge monitoringElimination of electromagnetic noise

- elimination of pulse noise by coincidence technique

- frequency domain techniques- application of spectrum analysis since 1988

- reduction of pulses attenuation by adaptive frequency band (MICAMAXX)

-

pattern without noise with noise (excitation of generator)

Why choose MICAMAXX?

Traditionally off-line monitoring techniques such as Di-Electric Loss Analysis (DLA) and Tan Delta Testing

have been used. Yet these methods as well as being considered yesterdays technologyare

expensive, and require a lengthy machine outage. MICAMAXXTMplus sets new standards for the

monitoring of electrical machines and is based on field-proven sensor technology. It can be an

indispensable element in planning, life span extension and preventative maintenance programs,

serving to reduce unscheduled and expensive failures and outages.

Installation

A system that has been designed specifically to allow a fast and as far as possible, a non-intrusive

installation. An outage, typically during a regular service standstill is all that is required.

Benefits

MICAMAXXTMplus is a system which is simple to install and provides a cost effective solution for on-line

PD monitoring, without compromising technical integrity.

The MICAMAXXTMplus monitoring system

calculates parameters directely from

the pattern. The left graph shows the

calculated parameters from laboratoryof insulation breakdown tests on

generator bars.

As shown the partial discharge level be

stable over a certain time and after

starts to increase exponentially until

breakdown. The experience of long

term trending on real generators has

shown the same results.

With the monitoring system

MICAMAXXTMplus we try to found the

critical level, and gives an

Warning/Alarm.

Sharp bend:

Critical level

Alarm

Warning


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Do you need instant expert advice, do you need expandability?

5.0 The MICAMAXXTMplus machine monitoring through the webThe MicamaxxTMplus is a real-time, 4 channel partial discharge pattern recording systems for permanent

installation with remote diagnostic capabilities and embedded alarm algorithms which reduce user

interaction to the bare necessities. The system trends the deviation from an assessed condition. The unit

permanently informs the user about potential ageing problems.

Remote access allows experts to access the system to perform full analyses from their office. Internet

server, LAN and modem features allow our experts to provide support to customers world-wide.

Pattern and analogue view of partial discharges.


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Three Phase Pattern Results

GUI: Trending Parameter Calculations (IEC60270 et al.), apparent charge, current quadratic rate.


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The MICAMAXXTMplus is a true system solution and investment in the future of your machines. A series of

expansion modules and communication options will be available shortly.

Main Module Incorporates:

Partial discharge (stator) monitoring system

All Internet/LAN, storage, trending and alarm functions

Serves as an Internet node (CAN-Bus and modem optional)

Prepared for expansion modules (under development)

Rotor monitor: synchronous and asynchronous rotors

Condition module (temperature, current power etc.),

analog an CAN-Bus inputs (others on request)

Vibration and mechanical condition module

Ozone Acquisition

Brush Monitor

The user will be supported by our experts through communication possibilities and web data base

functions.

5.2 Datahandling Database

Partial Discharge Features

4 Channel PD Acquisition, Coupler-, Line- and External Synchronisation possibility

Results: 8 x 8 x 16Bit Colour PD Pattern

Variable Frequency Range for Noise Suppression

0.3 to 5.5 MHz, 0.5 to 5.8 MHz, 1 to 6.4 MHz, 1.5 to 7 MHz, 2.3 to 7.9 MHz

2.9 to 8.5 MHz, 3.5 to 9.1 MHz, 4 to 9.7 MHz (optional lower frequencies on

request and necessity)

Input Impedance: 2 k, Input Sensitivity (2pC, depends on machine impedance andnoise spectrum)

Coupler compatibility: PD Tech Range: CC7 to CC30 (1nF cap.), CT85, CT17 (RF current

transformers), ALSTOM (PAMOS, GOLD), Rogowski Sensors, SIEMENS, IRIS, ADWEL, surge

capacitor installations)


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6.0 Sensor and Coupler InstallationCompact, sensitive and reliable couplers, which are perfectly adapted to the machine types and a

world-wide installation service, are a speciality of PD Tech Power Engineering AG.

In order to ensure compatibility and cost-efficiency, the MICAMAXXTM detection systems are

compatible with third party sensors, this allows the use of already existing coupling systems as well.

(e.g. ALSTOM (PAMOS, GOLD), Rogowski Sensors, SIEMENS, IRIS, ADWEL, surge capacitor installations)

A complete range of 1 nF coupling

capacitors with I-match technology is

available from PD Tech Power

Engineering AG. The unique I-match

technology avoids eddy currents

caused to ground loops, incorporates

provides a stable voltage divider and I-

match impedance matching which

allows to look deep into the machine

winding at a high sensitivity which was

virtually only possible with higher

capacitance values.

Capacitve Coupplers CC15;CC20;CC30 Surge Condensator

Retrofitting or installation of surge capacitors with high frequency current transformers is the solution for

sensitive pd measurements on generators and motors. Furthermore, if surge capacitors are already

fitted it is useless to fit additional coupling capacitors as the surge capacitors drain their signal energy.

When installing coupling capacitors, why not install surge capacitors to protect the machine against

surges at the same time. PD Tech Power Engineering AG provides services to optimise insulation

coordination.

Confined space in industrial motors and

generators often complicated the installation of

coupling capacitors. The ultra compact CC7

coupling capacitor design fits into most

termination boxes.

CC7 capacitors installed on a large motor


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Basic Insulation Technology Research Analytic Services Consulting

PD Tech Power Engineering is active in Swiss project in co-operation with the Swiss Federal Institute of

Technology and ISOLA Ltd. To explore and understand the basic failure mechanisms in rotating

machine insulation.

Microscopic analyses of mica-glass fibre-epoxy and asphalted insulation for generators

(Courtesy Swiss Federal Institute of Technology)

Further Consulting and Engineering Services

Insulation Coordination, Overvoltage Analyses, Transient Simulation

Testing and Commissioning Experts

Development Support

Fault Analysis

Maintenance and Repair ManagementTesting of Components

Rental of Test Equipment

Impulse and AC HV Testing on Site

Specifications subject to change without notice

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