PARTIAL DISCHARGE DETECTION SYSTEMS

BIDDLE

Series 27000

• Key component of allBiddle partial dischargedetection systems

• Includes multipleinterference controlfeatures

• Five built-in typesof data readout

• RS-232C interface forcontrol and data export

Partial Discharge (Corona) DetectorINTRODUCTIONASTM defines a partial discharge as atype of localized discharge that resultsfrom transient gaseous ionization inan insulation system when the voltagestress exceeds a critical value. Theionization is localized over only a por-tion of the distance between theelectrodes of the system. The result-ant partial discharge signals appear asvery small magnitude, fast-rise pulseswith irregular waveshapes superim-posed on the high voltage at theterminals of the test sample. Partialdischarges cause deterioration of in-sulation materials and are a primarycause of insulation failure at moderateand high voltages.

The accepted unit for measurement ofpartial discharge magnitude is thepicocoulomb. The picocoulomb, a unitof charge, is columbs x 10-12. Charge ispreferred to voltage as a unit of mea-sure because it is proportional to thedestructive energy released at thedischarge site. Pulse voltage is unde-sirable because it is dependent onpartial discharge pulse waveshapewhich is irregular at best.

Partial discharge pulse waveshape isdependent on the location of the dis-charge site and changes as the pulsepropagates through the circuit. Thecharge, proportional to the number ofions formed at the discharge site, isrepresented by the area under the

partial discharge pulse waveshape.This area remains constant, indepen-dent of discharge site location. Theenergy released is proportional to theproduct of the number of ions formedand the critical voltage at the dis-charge site. It is therefore apparentthat the response from a properly de-signed partial discharge detectionsystem must be proportional to thearea under the partial discharge pulse.

The Biddle Partial Discharge Detec-tion System integrates the area underany partial discharge signals detectedand displays an output pulse-signal onthe oscilloscope which is proportionalin height to the integrated area. Theratio of proportionality, in pico-coulombs per unit of deflection, isestablished by using the built-in cali-bration equipment.

DESCRIPTIONThe Biddle Series 27000 Partial Dis-charge (Corona) Detector is composedof four functional units: the amplifier,display, calibrator and evaluation unit.

AmplifierThe amplifier provides low-noise gainand bandwidth limiting of the partialdischarge signals. The gain is continu-ously variable over four decade rangesand is determined by front-panel con-trols. The input of the amplifier isgalvanically isolated from the sourceof the signal to minimize grounding

problems and to provide protectionagainst common mode transients thatoften occur during routine testing. Dif-ferent partial discharge tests mayrequire amplifiers with different band-width limiting. In these cases, thedetector can be equipped with twoamplifiers.

DisplayThe display circuitry includes partialdischarge pulse rectification andbrightening circuits, a display timebase and an electrostatic CRT display.Pulse rectification is used to enhancethe clarity of the display and to makethe pulse polarity appear independentof the phase of the test voltage.

The display time base provides a CRTbaseline upon which the partial dis-charge pulses may be superimposed.This baseline is phase-locked to eitherthe test voltage or detector line voltage,providing a phase reference which isessential for ac partial discharge patternrecognition. The detector circuitry willdynamically choose between these tworeference signals to see whichprovides the more suitable phase refer-ence. Front-panel indicators show whichphase reference signal is being used.

Three different baselines are available:elliptical, linear and sinusoidal. Eachof the baselines is synthesized fromphase-locked-loop circuitry so thattest-voltage harmonics are completelysuppressed and do not appear on the

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PARTIAL DISCHARGE DETECTION SYSTEMS

Since partial discharge is often maskedby noise, internal digital filters may beused to minimize false trips, and to varythe sensitivity of the overlimit detector.

• Window-gating function: The win-dow-gating function allows the user todefine a window period during whichpartial discharge is measured. Any in-terference signals occurring outside ofthis window will be ignored by the sig-nal measurement and display circuitry.This feature may be used to blank spuri-ous signals that would normallyinterfere with the precision partial dis-charge measurement or to isolatesignals of interest.

Additional Capabilities• Partial discharge signal level graph-ing: Some power cable testing spe-cifications require a graph of the par-tial discharge level as a function oftest voltage. This capability is pro-vided by using the picocoulombchannel analog output for one axisand the Biddle kilovoltmeter analogoutput for the second axis. The scaleof the plot may be calibrated to repre-sent any picocoulomb value.

• The Biddle Series 27000 Partial Dis-charge Detector with RS-232 portpermits creation of a computerized testreport. Microsoft Windows-basedsoftware that will generate a one-pagetest report is optionally available. Twotest report formats are available bymenu selection. One format is for rou-tine testing of power cable; the otherformat is for general-purpose use. Thetest report includes an X-Y graph ofpartial discharge level versus test volt-age. Menu-driven software permits theoperator to enter descriptive informa-tion, calibrate the system and initiatedata collection.

Upon completion of the test, the opera-tor can view the test data on the monitorto check for compliance with the testrequirements before printing or saving.

• Interference control: Window gating,overlimit trip functions and digital fil-tering all serve to minimize or eliminatethe effects of unwanted continuous andsporadic signals. Additional shieldingand filtering techniques are optionallyavailable to augment this capability andensure accurate measurement of par-tial discharge.

As an example, common interferencefrom single-phase SCR noise occursas a pulse on every half-cycle of thetest voltage. If the pulse is stationarywith respect to the phase of the testvoltage, its effects may be completelyeliminated by setting the windowphase angles so that the pulse isexcluded from any measurements. Of-ten, however, the SCR pulse is notstationary. In these cases, the interfer-ence is suppressed simply byselecting, via front-panel controls,the criterion of a specified number ofpulse repetitions per half-cycle. Suit-able settings for various types ofinterference conditions must be deter-mined on an individual basis.

• Multiple passbands: The BiddleSeries 27000 detector includes thecapability to operate with differentpassbands. Some test specifications/applications define the passbandneeded for the detector system. Some-times the interference to be expectedwith a certain application will dictatethe pass-band requirement. Biddleprovides superior noise rejection bydesigning specific passband amplifierswith integrated filtering circuits for op-timum noise suppression. Threestandard passband amplifiers areavailable: one for cable testing, one forgeneral purpose use and one for trans-former testing at test frequencies from180 to 400 Hertz. Any two of the threecan be installed in the Series 27000detector.

System RequirementsThe Biddle Series 27000 detector is thekeystone of any partial discharge de-tection system. A fully operationalsystem requires, in addition to the de-tector, a power separation filter, abushing tap coupler or a bridge cou-pling unit to couple the detector to atest circuit. A properly rated noise-freetest voltage source is also required fora complete system.

To graph any of the output channelsas a function of test voltage and to op-erate the apparent power loss readoutchannel, an optional Biddle kilovolt-meter with recording output is needed.

CRT display. The rotation of the ellip-tical time base may be altered fromthe factory-set conventions to suituser requirements.

Two phase-reference markers may bemanually activated by pressing apushbutton switch on the detector frontpanel. These markers appear as pulseson the display time base. One markerindicates the 0° phase position and theother indicates the 270° phase positionof the display time base. They may beused to assist the user in determiningthe phase angle of partial discharge sig-nals and to remind the user of theelliptical display conventions.

CalibratorThe calibrator provides a precisionsignal that is used to calibrate thedesired readout in units of pico-coulombs. The output of the calibratoris continuously variable from 0.1 to999 pC via a digital control. A digitaldisplay with automatic decimal pointindicates the actual output level. Cali-bration can be either direct or indirect(in accordance with IEC 270, ASTM D-1868, method 3 or ASTM D-1868,method 4, respectively).

Evaluation UnitThe evaluation unit is used to measure,process and display several variablespertaining to the partial discharge sig-nal. The variables measured are peakpartial discharge in picocoulombs,average partial discharge in microam-peres and apparent partial dischargepower loss in milliwatts. A front-panelliquid crystal display as well as rear-panel terminal block outputs are usedto convey the measurements to theuser. These outputs may be used todrive strip chart or X-Y graphic record-ers when this capability is required.The evaluation unit also provides thefollowing two important functions:

• Overlimit trip function: The overlimittrip function monitors the detector’speak partial discharge signal and indi-cates when that signal exceeds theoverlimit level via a front-panel con-trol. If the partial discharge exceedsthis level, then a trip will occur. A tripis indicated by a front-panel LED andrelay contacts which are accessible ona rear-panel terminal block.

PARTIAL DISCHARGE DETECTION SYSTEMS

Power Separation Filter

U ~

~

U ~Bushing

BushingTap

Coupler

U ~

BridgeCoupling

Unit

OR

OR

APPLICATIONSThe keystone of all partial dischargedetection systems is the partial dis-charge detector. This unit provides all ofthe instrumentation necessary for mak-ing partial discharge levelmeasurements when used with appro-priate auxiliary components. The Biddlepartial discharge detector combines cali-bration, amplification and oscilloscopedisplay sections in an attractive panelsuitable for rack mounting.

Electronic measurement circuitrycontained within the Series 27000detector permits quantifying andexpressing partial discharge in objec-tive terms. This decreases the need forreliance on subjective operator inter-pretations of test results, andallows for consistent, repeatable evalu-ation and comparison of test data.

FEATURES AND BENEFITSFive built-in types of data readout pro-vide a wide range of test data formats:• CRT display• Three simultaneous channels off

analog output suitable for graphicrecording of peak partial discharge

(picocoulombs), average partial dis-charge (microamperes) andapparent partial discharge energyor power loss (milliwatts)

• Digital display of any of the aboveselected data channels

• Programmable partial dischargeoverlimit trip indicator

• RS-232C interface permits dataarchiving and test report generation.

A standard computer interface unitprovides for archiving data and re-motely controlling detector sensitivityand calibration.

Three built-in types of interference con-trol permit testing under adverse localnoise conditions:• Fully adjustable partial discharge

inspection windows automaticallysynchronized to the test voltage

• A partial discharge level detectorwith programmable response forpartial discharge signal magnitudelevel, signal repetitions per half-cycle and consecutive half-cycles

• A partial discharge measurementcircuit that employs digital filteringfor minimizing the effects of noise

Automatic synchronization of scopedisplay, calibration signals and window-gating circuits allows full function test-ing at frequencies from 50 to 500 Hertz.

Switchable passband options increaseinterference control and expand therange of testing applications.

Selectable, multiformat scope displayaccommodates user preferences:• Available baseline formats: sinusoi-

dal, flat-line and elliptical. Baselinephase verification is provided by 0and 270° markers.

• Available partial discharge signalformats: unrectified pulses, or posi-tive or negative polarity only

Built-in calibration signal generatorsimplifies test data quantification.

Detector meets the requirements of IEC270, IEEE 454-73; ASTM D-1868; IEEEC57.113; ICEA T-24-380; AEIC CS5, CS6, CS7;NEMA WC5, WC7, 502, 540; UL 1072; ICEA S61-402, S 66-524, S 68-516; and MIL-T-27.

Schematic diagram showing basic partial discharge detection system configurations available with Series 27000 detector

PARTIAL DISCHARGE DETECTION SYSTEMS

7. Automatic scope display synchro-nization indicators

8. Calibrator controls and indicators

9. LCD partial discharge display

10. Partial discharge display channelselector

11. pC trip level adjustment

12. Trip indication lamp

13. Window gating controls

14. Markers on/off for window gat-ing

15. Pulse count per half cycle (fornoise control)

DETECTOR CONTROLS

1. Power switch on/off

2. CRT display adjustments

3. CRT display mode - sine wave oreliptical

4. Amplifier gain controls

5. Remote indication for externalcontrol

6. Marker indicates zero or negativepeak on CRT display waveform

SPECIFICATIONS

InputInput Voltage

120/240 V (+10%, –17.5%), 47 to 500Hz (selectable at the power inputreceptacle)

Power Burden: 100 VA max.

MechanicalDesigned for 19-in. (48.3-cm) relay rackmounting

Signal Connectors: BNC (MIL UG625)

Front-Panel Dimensions7 H x 19 W in.17.8 H x 48.3 W cm

Weight: 25 lb (11.3 kg)

EnvironmentalStorage Temperature Range

–40 to +149° F (–40 to +65° C)

Operating Temperature Range32 to 122° F (0 to 50° C)

Relative Humidity5 to 95% (noncondensing)

Maximum Altitude: 10,000 ft (3030 m)

CRT Display3 x 4 in. (8 x 10 cm) with Z-axis modula-tion

Cable Test Amplifier SpecificationsBandpass: 20 to 110 kHz at –3 dBGain: 92 dB at midbandPulse Resolution Time: 5 ±1 µsNegative Superposition: Less than15%

Transformer Test AmplifierSpecificationsBandpass: 75 to 290 kHz at –3 dBGain: 86 dB at midband

Analog Recording Outputs fromEvaluation Unit ChannelsPeak partial discharge, average par-tial discharge, apparent partialdischarge power loss: 0 to 5 Vdc

Serial Interface: RS-232C, 1200 baud,RTS/CTS handshake

CalibratorOutput Range: 0.1 to 999 pC in three

ranges, continuously variable

Output Impedance: 75 ΩAccuracy

±1.5% full scale on 100-pC range±4% full scale on 10- and 1000-pC

ranges

Modes Provided: Direct in accordancewith IEC 270, ASTM D-1868, method3; indirect, ASTM D-1868, method 4;average channel

Vertical Deflection Linear Range 0 to 2.7 in. (0 to 7 cm)

Display Synchronization Range47 to 500 Hz

Display Synchronization ModesPower lineTest voltage

Automatic Display Synch Switchover(from power line to test voltage)At approx 5% of rated voltage

Display Sweep ModesEllipseSine waveFlat line

Display Sweep Phase MarkersAt negative-going zero crossingAt negative voltage peak

Display Pulse Characteristics(available by internal jumper)Negative polarity onlyPositive polarity onlyBoth polarities (unrectified)

AmplifierAnalog Output: 1-volt output per cm of

deflection on CRT to maximum of 8 V

General-Purpose AmplifierSpecificationsBandpass: 40 to 200 kHz at –3 dBGain: 86 dB at midband

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

PARTIAL DISCHARGE DETECTION SYSTEMS

Pulse Rise TimeLess than 100 ns (10 to 90%)

Pulse Repetition Rate: Once per half-cycle of the test voltage

Repetition Synchronization Range47 to 500 Hz

Pulse PhasingContinuously adjustable

Evaluation UnitDigital Display

31/2 digits, 0.5 in. (13 mm) high, di-rect reading (of selected channel)

Available ChannelsPeak, average, power

Peak Partial Discharge ChannelSpan: 1 to 1000 pCRanges: 0 to 5/10/50/100/500/1000 pCAccuracy: ±3% of full scale

Rise TimeAnalog Mode (10 to 90%) : 80 µs to

2.2 ms, variableDigital Mode (0 to 100%): Less

than 1.0 sFall Time

Analog Mode (90 to 10%): 2 sDigital Mode (100 to 0%): Less

than 1.0 s

Average Partial Discharge ChannelSpan: 0.01 to 50 µA. in six rangesAccuracy: ±3% of full scaleAveraging Time Constant: 1.3 s

Apparent Partial Discharge Power LossSpan: 0.01 to 10,000 mWAccuracy: ±5% of full scale

Trip Level DetectorSpan: 0 to 100% of selected peakpartial discharge range

Trip Relay Contacts1.0 A (max. carrying current)0.25 A (resistive switching current)

Pulse Count per Half-Cycle SelectorPulses per Half-Cycle: 1, 2, 3 or 5Half-Cycle Logic Range: 1 to 8 half-

cycles of the test voltage (byinternal dip switches)

Display WindowsSynchronization Frequency Range:

47 to 500 HzStart Angle Range: 0 to 180°Duration Angle Range: 5 to 180°

ORDERING INFORMATION

Item Cat. No.Series 27000 Partial Discharge (Corona) Detector............... 6627000

Optional AccessoriesCable test amplifier ...................................................................... 25960General-purpose amplifier ....................................................... 25960-2Transformer test amplifier ....................................................... 25960-3Windows-based software package for test report generation,

including fiber-optic RS-232C interconnection cable,486-class, IBM-compatible computer, 3.5-in., high-densityfloppy drive, VGA color monitor and compatible dotmatrix printer ........................................................................... 33730

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