DFA100 Dielectric Fault Analyzer User Guide
Doble TransiNor AS Sorgenfriveien 9 N-7037 TRONDHEIM Norway
Notice This User Guide (the “User Guide”) is solely the property of the Doble Engineering Company (Doble®) and, along with the subject matter to which it applies, is provided for the exclusive use of Doble Users (the “User”) under contractual agreement for Doble® test equipment and services. In no event does the Doble Engineering Company assume liability for any technical or editorial errors of commission or omission; nor is Doble liable for direct, indirect, incidental, or consequential damages arising out of reliance, inaccurate third party information or the inability of the User to use this User Guide properly. Copyright laws protect this User Guide; all rights are reserved. No part of this User Guide shall be reproduced, stored in a retrieval system, or transmitted by any means, electronic, mechanical, photocopying, recording, or otherwise without written permission from the Doble Engineering Company. Doble and the Doble logo are registered in the U.S. Patent and Trademark Office and are trademarks of the Doble Engineering Company. Doble® is providing the information contained herein for reference purposes only. Doble® makes no warranty or representation that the User Guide will meet the User's requirements. This User Guide is intended to provide a basic understanding and general application of the principles set forth herein. Comments contained herein relating to safety represent minimum guidelines, and should never be compromised; however, it is foreseeable that the minimum safety guidelines may be supplemented in order to conform to User's company safety and compliance regulations. User is responsible for applying the information contained herein in strict accordance with industry as well as User's company compliance and safety regulations. The techniques and procedures described herein are based on years of experience with some tried and proven methods. However, the basic recommendations contained herein cannot cover all test situations and there may be instances when Doble® should be consulted directly. Doble® is not responsible for the MISUSE OR RELIANCE ON THIS PUBLICATION; ANY OPINIONS CONTAINED HEREIN OR AS A RESULT OF MODIFICATION BY ANYONE OTHER THAN DOBLE® OR AN AUTHORIZED DOBLE REPRESENTATIVE. Copyright © 2007 Doble Engineering Company All Rights Reserved
Warranty Equipment Limited Warranty Doble Engineering Company (DOBLE) warrants the products that it manufactures to be free from defects in material and workmanship for a period of one year from the date shipped from the factory. During the one year warranty period, DOBLE will repair or replace, at its option, any defective products or components thereof at no additional charge, provided that the product or component is returned, shipping prepaid, to DOBLE. The Purchaser is responsible for insuring any product or component so returned and assumes the risk of loss during shipment. All replaced products and components become the property of DOBLE. THIS LIMITED WARRANTY DOES NOT EXTEND TO ANY PRODUCTS WHICH HAVE BEEN DAMAGED AS A RESULT OF ACCIDENT, MISUSE, ABUSE, OR AS A RESULT OF MODIFICATION BY ANYONE OTHER THAN DOBLE OR AN AUTHORIZED DOBLE REPRESENTATIVE. EXCEPT AS EXPRESSLY SET FORTH ABOVE, NO OTHER WARRANTIES, EXPRESSED OR IMPLIED, ARE MADE WITH RESPECT TO THE PRODUCT INCLUDING, BUT NOT LIMITED TO, ANY IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. DOBLE EXPRESSLY DISCLAIMS ALL WARRANTIES NOT STATED HEREIN. IN THE EVENT THE PRODUCT IS NOT FREE FROM DEFECTS AS WARRANTED ABOVE, THE PURCHASER’S SOLE REMEDY SHALL BE REPAIR OR REPLACEMENT AS PROVIDED ABOVE. UNDER NO CIRCUMSTANCES WILL DOBLE BE LIABLE TO THE PURCHASER OR ANY USER FOR ANY DAMAGES, INCLUDING WITHOUT LIMITATION, PERSONAL INJURY OR PROPERTY DAMAGE CAUSED BY THE PRODUCT, ANY INCIDENTAL OR CONSEQUENTIAL DAMAGES, EXPENSES, LOST PROFITS, LOST SAVINGS, OR OTHER DAMAGES ARISING OUT OF THE USE OF OR INABILITY TO USE THIS PRODUCT.
Software Limited Warranty Doble warrants that: (i) for a period of one hundred twenty (120) days from the date of shipment from Doble, the media on which the Software is furnished will be free of defects in materials and workmanship under normal use; and (ii) for a period of one year from the date of shipment from Doble, the Software will perform in substantial conformance to its published specifications. This limited warranty extends only to Customer as the original licensee. Customer’s exclusive remedy and Doble’s entire liability under this limited warranty will be, at Doble’s option, to repair or replace the Software, or to refund a pro rata portion of the purchase price. Doble makes no warranty or representation that its software products will meet Customer’s requirements, that the operation of the software products will be uninterrupted or error free, or that all defects in the software products will be corrected. This warranty does not apply if the software (a) has been altered, except by Doble, (b) has not been installed, operated, repaired, or maintained in accordance with instructions supplied by Doble, (c) has been subjected to abnormal physical or electrical stress, misuse, negligence, or accident, or (d) is used in ultra hazardous activities.
Disclaimer THE FOREGOING WARRANTIES AND REMEDIES ARE EXCLUSIVE AND ARE IN LIEU OF ALL OTHER WARRANTIES, TERMS, OR CONDITIONS, EXPRESS OR IMPLIED, WHETHER ALLEGED TO ARISE BY LAW, BY REASON OF CUSTOM O R USAGE IN THE TRADE, OR BY COURSE OF DEALING, INCLUDING WARRANTIES, TERMS, OR CONDITIONS OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE, SATISFACTORY QUALITY, CORRESPONDENCE WITH DESCRIPTION, AND NO INFRINGEMENT, ALL OF WHICH ARE EXPRESSLY DISCLAIMED. IN NO EVENT WILL DOBLE BE LIABLE FOR ANY LOST REVENUE, PROFIT, OR DATA, OR FOR SPECIAL, INDIRECT, CONSEQUENTIAL, INCIDENTAL, OR PUNITIVE DAMAGES HOWEVER CAUSED AND REGARDLESS OF THE THEORY OF LIABILITY ARISING OUT OF THE USE OF OR INABILITY TO USE THE SOFTWARE EVEN IF DOBLE HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES. In no event shall Doble’s liability to Customer, whether in contract, tort (including negligence), or otherwise, exceed the price paid by Customer. The foregoing limitations shall apply even if the above-stated warranty fails of its essential purpose. SOME STATES DO NOT ALLOW LIMITATION OR EXCLUSION OF LIABILITY OR CONSEQUENTIAL OR INCIDENTAL DAMAGES.
Limitations of Remedies DOBLE’s entire liability and Purchaser’s exclusive remedy shall be: 1. 2.
The replacement of any disks not meeting DOBLE’S DOBLE’S “limited warranty” which are returned to DOBLE. If DOBLE is unable to deliver replacement disks which are free from defects in materials and workmanship, workmanship, Purchaser may terminate this agreement. By returning the software product and all copies thereof in any form and affirming compliance with this requirement in writing, DOBLE will refund the purchase price.
IN NO EVENT WILL DOBLE BE LIABLE TO PURCHASER FOR ANY DAMAGES, INCLUDING ANY LOST PROFITS, LOST SAVINGS OR OTHER INCIDENTAL OR CONSEQUENTIAL DAMAGES ARISING OUT OF THE USE OR INABILITY TO USE SUCH SOFTWARE PRODUCT, EVEN IF DOBLE OR AN AUTHORIZED DEALER HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES, OR FOR ANY CLAIM BY ANY OTHER PARTY. Some states do not allow the limitation or exclusion of liability for incidental or consequential damages, so the above limitation or exclusion may not apply. For equipment maintenance, contact: Doble TransiNor AS Sorgenfriveien 9 N-7037 TRONDHEIM Norway Telephone Fax Email
: +47 73 82 53 50 : +47 73 82 53 79 :
[email protected] [email protected]
www.doble.com www.doble.com
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Index 1
2
SAFETY FIRST..................................................................................................................................................4 1.1
GENERAL RULES ..........................................................................................................................................4
1.2
GROUNDING .................................................................................................................................................4
1.3
PERSONNEL SAFETY ....................................................................................................................................4
INTRODUCTION .................................................... ............................................................................................................... ..........................................................................................5 ...............................5 2.1
3
AE TESTING .................................................................................................................................................5
INSTRUMENT ......................................................... .................................................................................................................... ..........................................................................................5 ...............................5 3.1
POWERING UP AND TESTING THE DFA100 FOR THE FIRST TIME .................................................................5
3.2
USER INTERFACE..........................................................................................................................................5
3.2.1 3.2.2 3.2.3 3.2.4 3.2.5 3.2.6 3.2.7
Connector Plate (Top)............................................................................................................................5 Battery Access Panel (Bottom)............................................................. (Bottom). .............................................................................................................. ..................................................6 6 Keypad....................................................................................................................................................6 Buttons.................................................................................................. Buttons...................................... .............................................................................................................. ..................................................7 7 Toolbar...................................................................................................................................................7 Menus ........................................................... ...................................................................................................................... ..........................................................................................8 ...............................8 Memory Management..................................................................................... Management......................... ....................................................................................................8 ........................................8
4
SPECIFICATIONS SPECIFICATIO NS .................................................. ............................................................................................................. ..........................................................................................9 ...............................9
5
INSTRUMENT SETTINGS ........................................................ ................................................................................................................... ....................................................................10 .........10 5.1
5.1.1 5.1.2 5.1.3
6
Settings ......................................................... .................................................................................................................... ........................................................................................10 .............................10 Nameplate.......................................................................................................................... Nameplate............................................................... ..............................................................................12 ...................12 Volume..................................................................................................................................................12
SETUP ........................................................................................................................................................10
OPERATION....................................................................................................................................................13 6.1
SURVEY TESTING .......................................................................................................................................13
6.1.1 6.2
Continuous Mode .................................................................................................................................13 SYNCHRONIZED MEASUREMENT ................................................................................................................13
6.2.1 Phase Mode..........................................................................................................................................13 6.2.2 Pulse Mode...........................................................................................................................................13 6.3 SF6-F ILLED DEAD-TANK CIRCUIT BREAKERS ...........................................................................................14 6.3.1 Test Plan...............................................................................................................................................14 6.4 GIS .......................................................... ............................................................ ......................................14 6.4.1 Test Plan...............................................................................................................................................15 6.5 MOUNTING THE SENSOR FOR ACCURATE MEASUREMENTS .......................................................................15 6.6 MANAGING DATA ......................................................................................................................................16 6.6.1 Saving...................................................................................................................................................16 6.6.2 Recalling....................................................... Recalling.................................................................................................................. ........................................................................................16 .............................16 6.6.3 Deleting ........................................................ ................................................................................................................... ........................................................................................16 .............................16 6.6.4 Creating Apparatus Files ........................................................... ..................................................................................................................... ..........................................................16 16 6.6.5 Accessing Internal Storage and the Storage Card ...............................................................................16 ...................................................................... .........16 6.6.6 Transferring Files to and from the DFA100.........................................................................................16
7
8
TYPICAL TEST PROCEDURE.....................................................................................................................18 7.1
EASY STEP-BY-STEP...................................................................................................................................18
7.2
SURVEY TESTING .......................................................................................................................................18
7.3
OBTAINING A MEASUREMENT....................................................................................................................18
7.4
SAVING AND VIEWING RESULTS ................................................................................................................18
ANALYSIS........................................................................................................................................................19 8.1
FAILURE MODES DETECTED
8.1.1 8.1.2
BY
ACOUSTIC EMISSIONS ..............................................................................19
Analysis of Measurements and Failure Modes.....................................................................................19 Modes..................................................................................... 19 Magnetostriction ..................................................................................................................................21 ............................................................................................ ......................................21
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1 SAFETY FIRST Safety cannot be overemphasized when working on or around high voltage electrical apparatus. Companies that generate, transmit, distribute, or utilize high voltage electricity should, and do, have precise rules for safe practices and procedures for personnel whose working responsibilities involve testing and maintaining the various types of high voltage apparatus, and their associated lines, cables and conductors, as well as the associated accessories. accessories.
1.1 Rules under test may fail, precautions (such as barriers or entrance restrictions to the General Because the apparatus test area) must be taken to avoid harm in the event of a violent failure. All of your company rules for safe practice in testing must be strictly conformed to, including all practices for tagging and isolating apparatus during testing and maintenance work. State, local, and federal regulations, regulation s, e.g., OSHA, HSE, may also apply.
Note Company rules and government regulations take precedence over Doble recommendations. Personal protective equipment suitable for electrical testing is recommended.
1.2 Grounding The apparatus under test must be solidly and commonly grounded or earthed.
Note Proper grounding techniques are important for safety.
1.3 Personnel Safety Safety A pretest meeting is recommended. Other crews may be working on non-test related tasks in close proximity to equipment being tested. The pretest meeting should include all personnel who will be working in proximity to the area where testing will be performed. In this meeting, the tests to be performed; the apparatus and the voltage test levels involved; potential hazards involved with the work; and the individual assignments should all be reviewed with the crew members. Test personnel must remain aware of the work activity taking place around them and alert to the possibility that non-test personnel may enter the test area. A consistent and uniform set of signals, both visual and verbal, should be agreed upon, and should be followed by all crew members during testing.
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2 INTRODUCTION The DFA100, Dielectric Fault Analyzer, is designed to detect faults in grounded SF 6 gas-insulated systems, such as SF6-filled dead-tank circuit breakers or Gas Insulated Substations. The DFA100 can also be applied to grounded oil-filled instrument transformers. The DFA100 can be directly applied to any grounded component associated with the apparatus under test. In addition, the DFA100 can also be used for testing live cable terminations by using an insulating waveguide. During acoustic emission measurement, the DFA100 processes the results and determines the fault characteristics. characteristic s. The DFA100 has the ability to differentiate between PD, particles, and mechanical defects.
2.1 AE Testing Acoustic emission (AE) diagnosis is a test that detects acoustic signals produced by partial discharge and loose components. AE is effective in detecting faults in SF 6 gas-insulated insulation systems. AE can identify and locate partial discharge (PD), particles and mechanical defects within the equipment. AE testing can be performed either with the equipment in-service or in-conjunction with an external source: a series resonance or an AC hipot. Main benefits with DFA100:
-
Identification and location of partial discharge, particles, and mechanical defects
-
Condition-based monitoring of GIS, SF6-filled dead-tank breakers, and instrument transformers, transformers, during commissioning and while in service
-
Immunity to external noise
AE measurements are relative and indicate only the presence of energy. The sensor transforms the energy, which is reported in mV, unlike calibrated PD measurements, which are reported in pC. PD, particles and mechanical defects produce acoustic acoustic emissions in the 10 kHz to 500 kHz range.
Figure 2-1: DFA100
3 INSTRUMENT 3.1 Powering Up and and Testing the DFA100 DFA100 for the First Time To power up: 1.
Press the Power Power button, located located just below the display, and and hold it until the display lights up, then release it. The The Windows CE CE sign-on screen and its desktop icons appear.
2.
Within a few seconds seconds the DFA100 DFA100 software launches launches automatically, automatically, showing the the main Continuous Continuous mode display. display. At this point, the unit is running but is in idle.
3.
Press Start/Stop Start/Stop to activate activate the instrument and perform perform Continuous Continuous mode measurement.
3.2 User interface 3.2.1
Connector Plate (Top)
The connector plate contains connections for the sensor, external synchronization, synchronization, and the 12 VDC adapter (see Figure 3-1, page 5).
Sensor The Sensor connector is the AE input to the DFA100. The AE sensor plugs directly into the connector using an SMB cable connector. Apply pressure to connect the sensor cable; the SMB connector will lock in when properly connected.
External Synchronization The EXT SYNC connector can be used to hardwire the synchronizing feature. Using this connector with the AC synchronization cable bypasses the Bluetooth wireless module. It may be necessary to hardwire the synchronizing feature if severe RF interference or other obstructions are present.
Figure 3-1: Connector plate (top)
Figure 3-2: Battery Access Panel (Bottom)
12-Volt Power The 12 VDC power adapter plugs into this connector to charge the batteries inside the unit when they get low or to keep the unit powered for long periods without using the batteries.
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The adapter cannot charge the batteries quickly when operating the DFA100, as it has enough power to either charge the batteries when system power is off or run the unit when the power is on. (Charging the batteries takes about three times as long when operating the unit.)
3.2.2
Battery Access Panel (Bottom)
The removable panel at the bottom of the DFA100 provides access to the batteries, a removable CompactFlash card, and the USB port. To remove the panel, note the grips on either side of the DFA100 case. Place a thumb on one grip and middle finger on the other and press in on the grips, pulling down at the same time to remove the panel. Once the panel is removed, you will note a layout similar to Figure 3-2 above.
Battery Pack To replace the battery pack (such as when the existing battery is low), push down on the tab and slide the pack out of the unit. Push the new pack into the unit until the tab clicks as it latches the pack in place. To check the battery level, select Windows menu > Settings > Control Panel > Power or click the battery icon in the toolbar (visible only when the instrument is not plugged into a wall outlet). Battery power should be Good. If it reads Low or Very Low, charge the battery or use the device with the AC adapter.
CompactFlash Port The CompactFlash (CF) port accepts all CF cards, including high-speed ULTRA cards in all sizes up to 4 GB. Doble recommends the ULTRA card, which provides a substantial increase in data transfer speed for both acquisition and transfer of large files to a hard disk.
USB Port The USB download port is a data transfer connection to a desktop for offloading data or to transfer data and layout files to the DFA100. It functions the same as the USB port on a PDA. A USB cable is included with the DFA100.
3.2.3
Keypad The keypad can be divided into two functional areas: the top section, with Backlight and Power control and LED indicators, and the bottom section, with sixteen dual-function buttons. The keypad incorporates a Num Lock feature similar to that on a full-size keyboard. Most of the keys have two functions, which differ based on whether Num Lock is on or off. The Num Lock LED indicates this status. Unlike with a keyboard, the software here handles the Num Lock feature automatically. Num Lock on is the default state when you power the system up. It is also the state the software enters automatically when you open a dialog box that requires numeric keypad input. Num Lock will be off at all other times while DFA100 is running. This allows you to access the command functions coloured in blue on the keypad.
Power Button The Power button is the main power control for the DFA100. To turn power on, press Power until the display lights. This should take less than 2 seconds. To turn power off, press and hold Power for 4 or 5 seconds, until the unit shuts down.
Backlight Button The Backlight button toggles the backlight on and off. The LCD display in the DFA100 is transflective, which means means it can be seen with or without a backlight. In low or normal light, the backlight should be on, which uses the “transmissive” characteristic (backlight runs through the display). In strong light, it is best to turn the backlight off and use the display’s “reflective” characteristic, in which it absorbs or reflects light to provide contrast. Figure 3-3: Keypad
LED Indicators Next to the Power button and above the Num Lock LED are a green Ch 1 hit indicator LED and a synchronization indicator LED that illuminate on power-up and during AE acquisition. On power-up, they blink as part of a test to verify proper operation. During AE acquisition, they illuminate to show AE hit activity.
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3.2.4
Buttons
Button
Num Lock On
Num Lock Off
0 (Recall)
Used in edit fields; applies the number or character “0”, depending on the field format.
Actives an Open dialog box to recall data stored in memory.
1 (Save)
Used in edit fields; applies the number or character “1”, depending on the field format.
Actives a Save dialog box to save collected data.
2 (Delete)
Used in edit fields; applies the number or character “2”, depending on the field format.
Deletes any active data that has been collected in either Phase or Pulse mode.
3 (Setup)
Used in edit fields; applies the number or character “3”, depending on the field format.
Activates the Settings menu.
4 (Nameplate)
Used in edit fields; applies the number or character “4”, depending on the field format.
Activates the Nameplate dialog box.
5 (Start/ Stop)
Used in edit fields; applies the number or character “5”, depending on the field format.
The Start/Stop control has two functions:
•Performs general Start/Stop functions of sensor input while the instrument is in Continuous mode.
•Performs Start/Stop functions during an active acquisition in either Phase or Pulse mode. 6 (Pause/ Resume)
Used in edit fields; applies the number or character “6”, depending on the field format.
Performs Pause/Resume functions during an active acquisition in either Phase or Pulse mode.
7 (Cont)
Used in edit fields; applies the number or character “7”, depending on the field format.
Activates the Continuous mode display.
8 (Sync)
Used in edit fields; applies the number or character “8”, depending on the field format.
Activates the Phase mode display.
9 (Pulse)
Used in edit fields; applies the number or character “9”, depending on the field format.
Activates the Pulse mode display.
+/(Up Arrow)
Used to add a minus sign while working with an edit field.
Used to increase the input gain setting. Active when the instrument is in Continuous, Phase, or Pulse mode.
Tab (Down Arrow)
Used to move between edit fields and shift between controls in a dialog box.
Used to decrease the input gain setting. Active when the instrument is in Continuous, Phase, or Pulse mode.
Enter
Used to activate controls or menu items in the same way as left-clicking a mouse. Used while traversing the main menu to select a highlighted menu item. Also used to “press” buttons in dialog boxes.
. (Volume)
Used in edit fields; applies the period or decimal point character “.”.
Bksp (Left Arrow)
Used to manipulate certain controls in dialog boxes: • Backspace in an Edit control (deletes the previous character). • Select the previous item in a dropdown menu. • Switch to the previous page on a page control.
Right Arrow
Used to manipulate certain controls in dialog boxes: • Move cursor to the right in an Edit control. •• •
3.2.5
Activates the volume control option.
Select the next item in aon dropdown menu. Switch to the next page a page control. Select the next item in a group of option buttons.
Toolbar
Figure 3-4 shows the DFA100 toolbar. Table 3-1 page 8 describes icon functionality. functionality.
Figure 3-4: DFA100 toolbar icons.
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Table 3-1: Description of DFA100 toolbar icons.
Icon
Name
Description
Windows
Click to display the Windows menu.
Screen
Click to display the name of the active window. Click to toggle between the active window and the desktop.
Battery
Click to display the Power Properties window and view the battery status, power schemes, and device status.
Click to show or hide the keyboard. To display the keyboard, select Keyboard. To hide the keyboard, select Hide Keyboard Input Panel. When the icon has a red slash through it, the keyboard is hidden.
3.2.6
Time/Date
Click to display the Date/Time Properties window window and set the current date, time, and time zone.
Window
Displays the open windows.
Menus
File File menu items are:
Save Data Opens the Save Data dialog box to allow you to save collected data.
Recall Data Opens an Open dialog box to recall data stored in memory.
Delete Data Deletes any active data that has been collected in either Phase (Synchronization) (Synchronization) or Pulse mode.
Exit Terminates the DFA100 program. DFA100 will prompt you to confirm this command.
Setup See page 10, for details on setup menus.
About The About menu contains version, system, and copyright information. Click System Info for details on the operating system and CPU.
3.2.7
Memory Management
DFA100 has two accessible memory devices:
-
Internal memory, referred to as Internal Storage by the CE operating system
-
The CompactFlash CompactFlash card slot, slot, referred referred to as Storage Card by the operating operating system.
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Figure 3-5: Menu in DFA100
4 SPECIFICATIONS Characteristic
Specification
Physical Size (WxHxD)
89 mm x 241 mm x 36 mm / 3.5” x 9.5” x 1.4”
Weight (with batteries)
1.1 kg / 2.5 lb
Environmental Oper ating Tempe rature
–5°C –5° C to +45°C / +23°F to +115°F
Stora ge Tempe rature
–20°C to +60°C / –4° –4°F F to +140°F
Power Power Requirements
External DC adapter (12V @ 1.5A) or internal 7.2V NiMH battery pack, rechargeable in situ or using optional external charger
Battery Life
4–6 hours intermittent use
Display Display
3.52” colour LCD, QVGA portrait mode 240 pixels wide x 320 high, transflective with LED backlight
Display Touchpad
Built-in touchpad on screen for use with stylus and onscreen processing
Miscellaneous Storage Memory
128 MB flash for OS and data storage
External Interfaces
CompactFlash port and USB 2.0 port
AE Channel Description
Connector inputs. Low voltage (5 volt), phantom power is available on the AE input connector for powering an external low power preamplifier or integral preamplifier sensor.
AE Frequency Response
1.0 kHz to 1.0MHz ±1.5 dB
Software Selected Filters
The DFA100 comes with high-pass and low-pass software selectable analog filters and multiple digitally synthesized filters, providing exceptional filtering characteristics for maximum noise rejection and signal to noise.
Digitizing
Internal 18 bit, 20 MSPS ADC for each channel
Digital Signal Processing
Real Time FIR low-pass filtering, multiple AE feature extraction (each extracted feature is processed by a dedicated real-time, pipelined processor), and waveform recording and processing.
Extracted Hit Features
Typical AE features including Time of 1 Threshold Crossing (Time of Hit), Time to Peak, Peak Amplitude, Signal Strength, Duration, Rise Time, Counts, True Energy, RMS, ASL, Parametric Input and calculated features including Average Frequency, Peak Frequency and Ring Down frequency.
Parametric Input
Single parametric input via a SMB_F (socket) connector ±10 volt input range, sampled by a
st
100kSPS, 16 bit A/D converter. AST
•Internal Preamp
•Pulse-through, pulsing to crystal with programmable tone burst.
•External Preamp
•Trigger for external preamplifiers available on Phantom power.
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5 INSTRUMENT SETTINGS 5.1 Setup 5.1.1
Settings
The Setup menu (Figure 5-1) allows you to set parameters to process signals for best performance. The three Settings tabs allow you to enter default settings. Table 5-1: DFA100 Default settings Default Setting
SF6-Filled
Oil-Filled
Integral Pre-Amp
On
On
Sensor Type
R3a
R15a
Lower Roll-off Frequency
5 kHz
20 kHz
Upper Roll-off Frequency
100 kHz
300 kHz
Trigger Level
30 dB
30 dB
Trigger Ref Time Constant
10 ms
10 ms Figure 5-1: Setup Menu
Trigger Reference Gain
6 dB
6 dB
Phase Units
deg.
deg.
# Test Points
1000
1000
Pulse Gating Time
150 µs
150 µs
Pulse Blocking Time
2 ms
2 ms
Frequency 1
60 Hz
60 Hz
Frequency 2
120 Hz
120 Hz
Periodic Gating Time
50 ms
50 ms
The following apply to all tabs:
Save Settings Click to save your settings. It is not necessary to save each tab individually—you can enter data on all tabs and then save. New settings overwrite previous ones. The settings file is layout.lay.
Cancel Click to exit the Settings window without saving any changes.
Settings Page 1 Figure 5-2 shows Page 1 of the Settings menu.
SF6 Defaults Click to activate default settings for SF 6-filled apparatus ( below).
Oil Filled Defaults
Figure 5-2: Settings page 1
Click to activate default settings for oil-filled apparatus ( below).
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Integral Pre-Amp Check the box to activate the integral pre-amp. This is the default setting, used for all passive sensors: R3a, R6a, and R15a.
Sensor Type Select the sensor type: type: R3a, R6a, or R15a (see DFA100 DFA100 Sensor Sensor Types). Table 5-2 DFA100 Sensor Types Sensor Type
Application
Resonance
Range
R3a
SF6-filled
30 kHz
5 kHz–100 kHz
R6a
General
60 kHz
5 kHz–100 kHz
R15a
Oil-filled (IT, XFMR)
150 kHz
5 kHz–500 kHz
Lower Roll-Off Freq You can eliminate low-frequency noise by increasing the lower roll-off frequency. Partial discharges give signals from approximately 20 kHz up to 80 kHz. If the surrounding noise is of higher frequency, selecting a higher frequency may be necessary. Lower roll-off frequency is set in the following steps:
R3a: 5 R3a: 5 kHz, 20 kHz, 40 kHz, 100 kHz
R6a: 5 R6a: 5 kHz, 20 kHz, 40 kHz, 100 kHz
R15a: 5 R15a: 5 kHz, 20 kHz, 100 kHz, 200 kHz
•
•
•
Upper Roll-Off Freq You can adjust the upper roll-off frequency to eliminate high-frequency noise. It is preferable to filter out most of the high-frequency noise without losing too much of the original signal. Upper roll-off frequency is set in the following steps:
•
•
•
R3a: 40 R3a: 40 kHz, 60 kHz, 80 kHz, 100 kHz R6a: 40 kHz, 60 kHz, 80 kHz, 100 kHz R6a: 40 R15a: 200 R15a: 200 kHz, 300 kHz, 400 kHz, 500 kHz
Settings Page 2 Figure 5-3 on page 11 below shows “Page 2” of the Settings menu.
Trigger Level (mV) Trigger reference level should be high enough to avoid unwanted triggering on noise at low signal levels and low enough to trigger on weak particle impact or corona discharge signals. Set trigger level (U) from 1 to 100 mV.
Trigger Ref Time Constant (ms) The time constant of this trigger level signal must be long enough not to lose weak pulses with slow rise times, and short enough to allow triggering on signals from new particle impacts after echoes from previous particle impacts are fully attenuated. Trigger reference time constant (T) is set in the following steps: 10 ms, 30 ms, 100 ms. Figure 5-3: Settings menu – Page 2
Trigger Reference Gain (dB) (dB) Fixed.
Phase Units Determines how the x -axis -axis is displayed in Phase mode. It can be displayed in either degrees or time (ms).
# Test Points Sets the number of test points to be collected during an active measurement in Phase or Pulse mode.
Settings Page 3 Figure 5-4 shows “Page 3” of the Settings menu.
Pulse Gating Time (µs) The registration of a particle impact starts with a trigger signal. The peak value of the signal is then measured during a given time period, the pulse gating time. Selecting this gating time may influence your results, depending on the signal type. Pulse gating time is from 50 µs to 30,000 µs.
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Figure 5-4: Settings menu – Page 3
Pulse Blocking Time (ms) Selecting this pulse blocking time may influence your results, depending on the signal type. Pulse blocking time is from 1 ms to 25 ms.
Frequency 1 (Hz), Frequency 2 (Hz) To be able detecting partial discharges due to corona, etc., the instrument is measuring two frequencies: the power cycle frequency (normally 50/60Hz) and two times the power cycle frequency (meaning 100/120Hz). The two frequencies are set separately in steps. The center frequencies 1 and 2 are set in the following steps: 16.6 Hz, 33.3 Hz, 50 Hz, 60 Hz, 100 Hz, 120 Hz, 150 Hz, and 180 Hz.
Periodic Gating Time Periodic gating time is from 50 ms to 1000 ms.
5.1.2
Nameplate
The five Nameplate tabs allow you to enter nameplate information and notes. Required nameplate fields are Location, Apparatus Type, Serial #, Time, and Date. The following apply to all tabs:
Clear All Settings Click to clear the data fields on that tab.
Save/Exit Click to save your settings and exit Setup. It is not necessary to save each tab individually—you can enter data on all tabs and then save once.
Figure 5-5: Nameplate Page 1
Figure 5-6: Nameplate Page 2
Figure 5-7: Nameplate Page 3
Figure 5-8: Nameplate Page 4
Nameplate Page 1 On Page 1 (Figure 5-5), enter the company, location, division, and operator names.
Nameplate Page 2 On Page 2 (See Figure 5-6), enter a special ID (if desired), apparatus type, serial number, and manufacturer. manufacturer.
Nameplate Page 3 On Page 3 (see Figure 5-7), enter the manufacturer type, year of manufacture, kV rating, number of phases, and apparatus status for switching devices.
Nameplate Page 4 On Page 4 (see Figure 5-8), enter the time and date of the test. Click Update Time/Date to automaticall automatically y enter the current date and time for the test.
Notes Enter any notes related to the test.
5.1.3
Volume
The Volume menu allows you to set the volume of the audible signal from the internal speaker. Use the up or down arrow on the keypad or click the arrows at the right of the data field to adjust the volume. Press the Volume keypad button to accept the new setting or cancel by pressing X on the keyboard to discard the change. You can also bring up the Set Volume dialog box by pressing the Volume button.
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6 OPERATION DFA100 provides three measuring modes: Continuous, Phase, and Pulse.
6.1 Survey Testing 6.1.1
Continuous Mode
Continuous mode is used for surveying the apparatus and locating the primary source of the AE signal. Continuous mode provides four scales of acoustic signal measurement: the RMS signal, peak signal, degree of modulation with fundamental, and degree of modulation with second harmonic. Figure 6-1 is an example of Continuous mode locating a PD source. Continuous mode measurements are defined as follows:
-
RMS. Effective energy of the AE signal during one power RMS. frequency cycle.
-
Periodic Peak. Peak. Peak signal during one power frequency cycle.
-
Freq. 1 Content. Content. Degree of modulation with the power cycle.
-
Freq. 2 Content. Content. Degree of modulation with twice the power cycle.
Figure 6-1: Continuous Mode
See Table 8-2 page 19 for typical measurement characteristics characteristics associated with particular types of faults.
6.2 Synchronized Measurement 6.2.1
Phase Mode
Phase mode correlates the acoustic signal and the fundamental power signal and generates an amplitude vs. phase plot. You can use this information to determine the synchronizing nature of the acoustical discharges relative to the fundamental power signal. The patterns identify the nature of the source: PD, particles, and mechanical defects. The plot of Phase mode data can be viewed against degrees or time (ms). Figure 6-2 illustrates mechanical vibration of a contact assembly.
Synchronization with Power Cycle Synchronization The DFA100 physically monitors the power cycle via hardware. You can synchronize the AE measurement to either a 50 Hz or 60 Hz power system waveform, using either of two methods:
-
Wireless Synchronizat Synchronization ion.. Uses a Bluetooth transmitter with a range of roughly 30 m (100 ft). The receiver module plugs in to any power outlet.
-
Hardwire Synchronization. Synchronization. Uses a cable connection between the instrument and the Bluetooth transmitter.
Figure 6-2: Phase Mode
Note The synchronization module is necessary only if a measurement is required, not for survey testing.
6.2.2
Pulse Mode
Pulse mode is used primarily for monitoring particles. Particles are dynamic and produce both electrical discharges and mechanical impacts. This dynamic behavior is best represented in Pulse mode, in which DFA100 displays the results in an amplitude vs. elevation time plot. You can interpret this information to determine number, size, and severity of the active particles. If the signal is from a single particle, it produces a characteristic pattern, pattern, as in Figure 6-3, which illustrates the behaviour of a 5 mm aluminium particle.
Figure 6-3: Pulse Mode
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6.3 SF6-Filled Dead-Tank Circuit Breakers 6.3.1
Test Plan
The circuit breaker size, rating, and design will determine the test plan. 1.
Generally, no more than five five survey points are required required for each pole. The The number of survey points should be determined determined by the number of breaks per phase (contact assemblies), bushing connection assemblies, assemblies, and insertion resistor assemblies (if applicable).
2.
Apply clean clean silicone silicone grease grease at each survey point, to ensure an adequate adequate interface. interface.
3.
Compare each survey point point against a known baseline baseline in Continuous Continuous mode. This baseline baseline is provided provided in Figure Figure 6-4 below. below. Even in a 345 kV switchyard, where high external levels of corona exist, the circuit breaker internals should still produce the expected baseline.
4.
If you obtain any any acoustic emissions emissions while while surveying in Continuous mode, mode, determine the location of of the strongest strongest signal and take take a Phase and Pulse mode interval recording.
Figure 6-4: Expected Baseline: No Acoustic Emissions (AE) pres ent
Figure 6-5 below is an example of a test plan for an SF 6-filled dead-tank circuit breaker consisting of five survey points. This example assumes this breaker has two breaks per phase and is equipped with insertion resistors. Five survey points are identified, along with the circuit breaker’s associated components.
A Mechanism, Cabinet, Shield, Bushing Connection Assembly, Supports Structure B Contact Assembly, Shield, Cabinet, Particle Trap C Contact Assembly, Shield, Shield, Particle Trap D Resistor Assembly (optional), Particle Trap E Shield, Bushing Connection Assembly, Supports Structure
Figure 6-5: Survey Point Location
Note
The breaker type and design will dictate the test plan. If needed, consult Doble to obtain a recommended test plan.
6.4
GIS
Before performing a GIS measurement, you will need to evaluate a number of factors: 1.
Check whether whether the GIS enclosure enclosure is made made of aluminium aluminium or steel. steel. You can do this by placing a permanent permanent magnet magnet onto the enclosure. enclosure. If the enclosure is made of steel, be aware of the potential for magnetostriction (magnetic (magnetic noise in the steel due to re-magnetizati re-magnetization), on), which may occur if, for instance, the load current in the bay is significant (see “Magnetostriction” “Magnetostriction” on p. 53).
2.
Find out if the the voltage transformers transformers are are inductive or capacitive. capacitive. If the voltage voltage transformers transformers are inductive, inductive, they have have a built-in iron core that that may generate magnetic noise due to magnetostriction.
3.
Find out which which bays and compartment compartments s are energized energized and which which are not. Test Test compartments compartments that are are energized (high-voltage (high-voltage). ). There is no no reason to test compartments that are not energized.
4.
Make a plan of where and and how you should measure. measure. A drawing drawing of the GIS is an advantage in planning the measureme measurements. nts. Make a detailed plan of sensor positions for each layout of the GIS, so that each time you measure, you test the same places.
5.
Minimize surrounding surrounding noise. noise. All sorts of of mechanical work on the GIS or in its vicinity, people people other than the instrument instrument operator climbing climbing on the GIS, transformer fans, and so on, can make measurements difficult to perform.
6.
Measure the background noise noise in the area area of the GIS by leaving the sensor free in the air while while DFA100 rests on a solid solid object. Note Note the measured values in the Continuous mode. This procedure sets the level of background noise, which should be kept in mind through the measurements.. Measuring the noise on a de-energized part of the GIS (if possible) is also an advantage. measurements
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6.4.1
Test Plan
Selecting the correct places to put the sensor in the GIS is important. Knowledge of the GIS design and construction is a huge advantage. The basic rule is that all separate gas compartments must have at least one measuring point. It is also necessary to have one measurement between each two flanges. Choose the measuring points from the knowledge of where particles may exist. Usually they move toward the lowest point in the gas compartment. The most useful locations are:
-
Disconnectors. In disconnectors, the contacts may produce free metal Disconnectors. particles. Also the other moving parts may create particles.
-
Earthing connectors. connectors. These are similar to disconnectors disconnectors..
-
Circuit breakers. breakers. Moving parts may create particles.
-
Horizontally mounted spacers/insulators. spacers/insulators. Vertical disconnectors and enclosures have horizontally mounted insulators. Particles may rest on these insulators and produce partial discharges.
Figure 6-6 suggest where to put the sensor on a single-phase, encapsulated, doublebusbar, double-circuit-breaker system.
Locating the Fault 1.
Move the sensor sensor from from compartment compartment to compartment. compartment. Hold the the sensor sensor gently. gently. The slightest movement of the sensor creates disturbances and high (and wrong) periodic peak values.
2.
When you you locate something, it is necessary to identify identify the source of of the signal as closely as possible. Do this by monitoring the signal levels in Continuous mode and moving the sensor step by step along the enclosure until the highest signal is located.
Figure 6-6: Recommended Sensor Positions (Black Dots) in a Single-Phase Encapsulated GIS
6.5 Mounting the Sensor Sensor for Accurate Accurate Measurements Measurements Ensure that the sensor is in good contact with the enclosure, use grease to prevent air bubbles between the sensor surface and the enclosure. It is important that the applied grease not contain water. Figure 6-7 shows how to mount the sensor onto an enclosure using a strap rather than holding it in place, which may be advisable for aluminum enclosures or delicate measurements. Place the strap across the sensor housing and not across the cable. Make sure the cable applies sufficient pressure between the sensor and the GIS surface. Where the enclosure material is steel, the magnetic hold-down supplied with the instrument can be used.
Fixing Strap Lock
AE Sensor
Figure 6-7: Mounting the sensor on the GIS Enclosure Using a Strap
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6.6 Managing Data 6.6.1
Saving
To save a test result: 1.
Press Save or select File > Save Data.
2.
The Save Data dialog box appears. appears. If the required nameplate nameplate information information has not been entered, a dialog box appears, prompting to enter it.
3.
If you wish wish to save save to a different folder from the one shown, click click Change Folder (see (see ”Select Data Folder” on p. 29).
4.
Use the keyboard to enter a name for the file.
5.
Click Accept.
6.6.2
Recalling
To recall a test in the device’s memory: Figure 6-8: Save Data Dialog Box
1.
Press Recall or select File > Recall Data.
2.
The Open dialog box appears (Feil! Fant ikke referansekilden.). referansekilden.).
3.
Tap the name of the file to be opened.
4.
Click OK.
6.6.3
Deleting
To delete a file: 1.
Click Delete or select File > Delete Data.
2.
A dialog box appears, asking for confirmation to delete.
3.
Click Yes.
Figure 6-9: Open (Recall) Dialog Box
6.6.4
Creating Apparatus Files
It can be convenient to create a file on a PC for each apparatus to be tested, using the Nameplate tab of DFA100 Viewer Software (see ”Creating Apparatus Files in DFA100 Viewer” on p. 412). Then these files can be loaded into the DFA100 and be left there. This eliminates the need to enter nameplate data onsite using the stylus. When ready to perform a new test, merely update the time and date in DFA100 and save the test as a new file. To update time and date in DFA100 and save a test as a new file: 1.
Press Recall or select File > Recall Data.
2.
Open the desired file by double-clickin double-clicking g it or by selecting it and clicking OK. OK.
3.
Press Nameplate or select Setup > Nameplate.
4.
On Page Page 4 of the the Nameplate Nameplate dialog box, click Update Time/Date.
5.
Click Save/Exit.
6. 7.
Press Save or select File > Save Data. The Save Data dialog box appears.
8.
Click Accept.
6.6.5
Accessing Internal Storage and the Storage Card
When using your DFA100, you can access either the internal storage or storage card from the My Device file icon or folder. You can access these folders using the file browser capability built into the CE operating system or from the Files menu in the DFA100 software when reading or writing setup or test data files.
6.6.6
Transferring Files to and from the DFA100
Transferring Files between the DFA100 and a PC DFA100 is designed for ease in transferring files back and forth to a PC for offline analysis and data storage. The unit should be thought of as a temporary storage device that should be downloaded and cleared out regularly. DFA100 Viewer software supplied with the unit allows you to view data files on a PC for analysis and reporting. The main method of transferring files between the DFA100 and your PC is the USB port. A USB cable has been supplied with your unit. The USB port on the instrument is inside the bottom panel. The USB connection is hot-swap. Both the DFA100 and the PC should be on when transferring files. The PC must use Windows ME, 2000, or XP (Windows 98 or 98SE will not normally work), as only these operating systems have true built-in USB compatibility.
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When the USB cable is plugged into both systems, a removable disk will appear in the PC’s file structure, just as with a memory stick. Search for the removable disk to access either the internal storage or the storage card memory on the DFA100. The USB port and the CF card cannot be used at the same time. Because of the way transferred files are stored, they will not immediately appear if you open a My Device window on the DFA100, even though they are clearly visible in the removable drive on the PC. You will need to cycle the power (turn off, wait a few seconds then turn on again) on the DFA100, to allow the file system in Windows CE to update and display the files. Unexpected results can occur if you attempt to access files before cycling the power.
Note When deleting or renaming files in the DFA100 using the USB connection, take the same precaution as with transferring data files to the unit, as described above. The DFA100 will show the file even after the file has been deleted, or it will show the original name of a renamed file, even though the new name appears in the PC. To avoid this, power down the unit after the delete and renaming operations.
Transferring Files between the DFA100 and a CF Card When a CompactFlash card is plugged into the DFA100, internal storage is not accessible via USB. You can transfer data between internal storage and the CF card using the instrument’s file browser. From the main screen, double-click My Device to open the file browser. To move a file from the DFA100 to the CF card: 1.
On the DFA100 desktop, double-click My Device.
-
The Windows CE file browser opens.
2.
Double-click Internal Storage.
3.
Double-click AEData-DF AEData-DFA. A.
4.
Select a file you wish to transfer.
5.
To select several contiguous or noncontiguou noncontiguous s files:
6.
Open the keyboard.
7.
Click Shift Shift (to select contiguous files) or or Ctrl. (to select select noncontiguous noncontiguous files).
8.
Click the desired files.
9.
To select all files, select Edit > Select All.
10. 11.
Select Edit > Copy. Click the left blue blue arrow at the top of the screen screen twice to return return to the original file browser screen. screen.
12.
Double-click Storage Card.
13.
Click Edit > Paste.
- 14.
The copied files are pasted to the CF card.
Click the X at the upper upper right of of the screen screen to exit the file browser. browser.
-
The procedure procedure for moving moving a file from the CF card to the DFA100 DFA100 is similar, similar, except that you begin begin with the Storage Card in step step 2.
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7 TYPICAL TEST PROCEDURE 7.1 Easy Step-by-step Step-by-step 1.
Power on the DFA100.
2.
The instrument boots in Continuous mode and remains in idle.
3.
Plug the wireless synchronization synchronization module into into an outlet less less than 100 ft (30 m) away.
4.
Check the the DFA100 DFA100 for adequate battery charge (see (see ”Battery ”Battery Pack” Pack” on p. 15).
5.
Connect the the sensor and sensor sensor cable to the DFA100 (see (see ”Sensor ”Sensor Type” on p. 23). 23).
6. 7.
Press Cont to ensure ensure that the DFA100 DFA100 is in Continuous mode. Use the blue blue up and down arrows arrows on the keypad to set the RMS RMS display to its most most sensitive scale: 2 mV.
8.
Make the appropriate appropriate entries in the the Settings Settings and Nameplate menus.
9.
Doble recommends the default settings.
10.
Press Start/Stop Start/Stop to activate activate Continuous Continuous measuremen measurementt mode. mode.
11.
Verify that the Sync LED illuminates.
12.
If the Sync LED does not illuminate, illuminate, reposition the wireless synchronization synchronization module module closer to the instrument.
Note The synchronization module is necessary only if a measurement is required, not for survey testing.
7.2 Survey Testing 1.
Create a test plan for the apparatus under under test (see the test plans plans for various various types of apparatus apparatus under under chapter 0 page 14 and chapter 6.4 page 14.
2.
Following all safety procedures, procedures, apply a small amount amount of clean clean silicone grease supplied supplied with the the instrument instrument to the appropriate sensor.
3.
Connect the sensor to the apparatus.
4.
Using the up and down arrows on the keypad, adjust adjust the gain setting setting as needed, needed, so that the reading reading is optimal without without clipping any any of the Continuous mode measurements measurements..
5.
On Page 2 of the Settings menu, menu, adjust the Trigger Trigger Level to optimize optimize the hit indicator. indicator. The optimal optimal trigger level level will cause the the indicator to spit intermittently; the CH1 LED should flicker slightly.
7.3 Obtaining a Measurement 1.
Verify that the Sync LED is illuminated.
2.
If the Sync LED LED is not illuminated, illuminated, reposition reposition the wireless wireless synchronization synchronization module closer closer to the DFA100 DFA100 or plug the hardwire hardwire sync cable into into the sync module and the EXT SYNC connector of the DFA100.
3.
Press Sync to place the DFA100 in Phase mode.
4.
Press Start/Stop to initiate Phase measureme measurement. nt.
5.
The instrument instrument will collect and and display the number number of test points points specified on Page 2 of Settings. Settings.
7.4 Saving and Viewing Results 1.
Select File > Save to save the results.
2.
When all tests are done, download the data to a PC.
3.
Open the data data in DFA100 DFA100 Viewer Viewer to analyze analyze the data and print reports reports (see Chapter 4, ”DFA100 Viewer Viewer Software”). Software”).
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8 ANALYSIS 8.1 Failure Modes Detected by Acoustic Acoustic Emissions The Acoustic Emission (AE) diagnostic technique has the ability to detect a variety of failure modes, while the unit is in-service. The AE diagnostic technique focuses on failure modes associated with partial discharge, particles, and mechanical defects, such as loose components. The AE diagnostic technique only considers failure modes that are static in nature; tests are not conducted while the circuit breaker is tripping or closing.Table 8-1 links failure modes associated with partial discharges, particles, and mechanical defects to various circuit breaker components. Table 8-1: Failure Modes Detected by Acoustic Emissions Partial Discharge (PD)
Particles
Mechanical Defects
Support Structure Tracking
Static particles on support structures, energized conductors, and grounded surfaces.
Contact Assemblies
Floating Electric Shields
Dynamic (moving or bouncing) particles produce both mechanical and electrical burst-type emissions.
Resistor Assemblies (optional)
Burning Contacts
Bushing Connection Assemblies
PD - Corona type discharges caused by protrusions, uneven surfaces, and inadequate clearances
Electric Shields
Particle Traps Leaking Valves Mechanism Cabinet
It is important to note that these failure modes are induced by two energy sources: the electric field (applied system voltage) and magnetic field (load current). When comparing the failure mode type versus energy sources, partial discharges and mechanical defects are paired with electric fields and magnetic fields, respectively.
8.1.1
Analysis of Measurements and Failure Modes
Noticeable acoustic emissions detected during the measurements warrant further investigation to determine the nature of the source. Properly analyzing the results will provide information such as:
Source type: partial discharge, particles, and/or mechanical defects
Source location
Relative strength of the failure mode
Risk: severity of the failure mode
•
•
•
•
Characteristics such as amplitude, amplitude scatter, periodic modulation (60Hz/120Hz), crest factor, and pulse shape are used in conducting the analysis. These characteristics characteristics will be matched to source type and then the failure mode will be determined by comparing the source type and general location of the source. All of this information in conjunction with the relative signal strength will be used to estimate risk. Table 8-2 illustrates the analysis fundamentals, based on knowledge of the features of the various sources generated within SF6-filled dead-tank circuit breaker, to recognize the different types of defects. Table 8-2: Analysis Features versus Failure Modes
Baseline The expectedinmeasurement by the DFA100 the absence reported of acoustic emissions. Most favorable measurements will produce similar results.
Continuous Mode “Survey”
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Phase Mode
Partial Discharge (PD) PD caused by protrusions and tracking produces results that are generally low in magnitude while favoring Frequency 1 modulation content.
Continuous Mode “Survey”
Phase Mode
Electrically Floating Shields Floating shields produce results generally higher in magnitude while favoring Frequency 2 modulation content. The Phase plot produces dual clouds.
Continuous Mode “Survey”
Phase Mode
Particles The main indication of particles is the fluctuating periodic peak signal. Furthermore, the signal level is typically several decades higher than that with partial discharges and corona. Particles are generally not phase synchronized and appear random. Particles also produce a unique Pulse mode pattern. The magnitude of mV and time are used to determine the severity and size of the particle contaminatio contamination. n.
Phase Mode
Continuous Mode “Survey”
Pulse Mode Mechanical Defect Loose components produce results generally higher in magnitude and having a dominant Frequency 2 modulation content. The Phase plot produces a mirror image.
Continuous Mode “Survey” Phase Mode
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8.1.2
Magnetostriction
The acoustic signals from inductive voltage transformers and steel enclosures normally show low signal levels (only a few mV). Similar signals are measured on most or all of the inductive voltage transformers of the same type. However, when performing acoustic measurements measurements on inductive voltage transformers (with iron core) and on apparatus with steel enclosures, acoustic signals may occur that are different from the background noise and modulated to 100/120 Hz. These can be similar to signals produced by partial discharges from electrically floating shields. Such noise is due to the magnetic phenomenon of magnetostriction in the steel. During one power frequency cycle, the steel (magnetic material) changes its state of magnetization. This creates acoustic noise that is picked up by the acoustic emission sensor. The magnetic noise is not related to the dielectric integrity of the insulation system and is therefore harmless.
Figure 5.1 Example of Magnetostrictive Noise in Continuous Mode, Measured Onsite (230 kV VT)
Figure 5.2 Example of Magnetostrictive Noise in Particle/Pulse Mode, Measured Onsite (230 kV VT)
Figure 5.3 Example of Magnetostrictive Noise in Phase Mode, Measured Onsite (230 kV VT)
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