CA1104913A - Device for monitoring dissolved gases in electrical insulating liquids such as transformer oils - Google Patents
Device for monitoring dissolved gases in electrical insulating liquids such as transformer oilsInfo
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- CA1104913A CA1104913A CA286,799A CA286799A CA1104913A CA 1104913 A CA1104913 A CA 1104913A CA 286799 A CA286799 A CA 286799A CA 1104913 A CA1104913 A CA 1104913A
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Abstract
DEVICE FOR MONITORING DISSOLVED GASES IN ELECTRICAL
INSULATING LIQUIDS SUCH AS TRANSFORMER OILS
ABSTRACT
A device to monitor dissolved gases in electrical in-sulating liquids such as transformer oils. The monitoring device includes a sampling means to obtain a liquid sample from the electrical device whose liquid is being monitored, a gas extraction means to extract the dissolved gases from the liquid sample, an injection means to inject the ex-tracted gases into a gas chromatograph, and a gas chroma-tograph to analyze the dissolved gases to determine the concentration of various dissolved gases.
INSULATING LIQUIDS SUCH AS TRANSFORMER OILS
ABSTRACT
A device to monitor dissolved gases in electrical in-sulating liquids such as transformer oils. The monitoring device includes a sampling means to obtain a liquid sample from the electrical device whose liquid is being monitored, a gas extraction means to extract the dissolved gases from the liquid sample, an injection means to inject the ex-tracted gases into a gas chromatograph, and a gas chroma-tograph to analyze the dissolved gases to determine the concentration of various dissolved gases.
Description
~1~49~3 5D5443 BACKGROUNn OF THE INVENTION
.
This invention relates to a device for monitoring dissolved gases in ~rans-Eormers or other electrical appara-tus and, more particularly, to a free-standing instrument which is capable of sampling the electrical l.iquid in an electrical apparatus and measuring the gases which are dissolved in such liquid.
For the past sevçral years information has been accumu-lated that dissolved gas concentrations in electrical in-sulating liquid provide a good indicato~ of the functional condition of the electrical apparatus. Certain gases such as CO and CO2 increase in concentration with thermal aging and degradation of the cellulosic insulatin in the electri- `.
cal apparatus structure. Other gases notably H2 and the various hydrocarbon are ormed and built up in the electri- . . ; .
cal insulating liquids due to hot spots which are caused by circulating ~urrents and dielectric breakdown, such as corona and arcing. Concentrations of 2 and N in general, provide information on the quality of the gas pressurizing system employed with many Iarge electrical devices such as trans-formers.
There is increasing evidence that the relative con-centration of these gases provide information on the type of malfunction as well as the severity. .Additionally, information on their time rate of change provides guidance ~or making maintenance and repair decisions.
In~ormation which has been acquired to date is based .
on determination of dissolved gas concentration from oil ~ Isamples which are withdra~m at the test or the installa ; 30 tion sites and transported to a laboratory for gas ~:
:, O
. .
, ~ .
5D544~
e~tracti~n and analysis. lVhile this procedure has been used with much success, it has a number of shortcomings. The first recognized shortcoming errors which are due to vari-able and generally uncon~rollable oil sa~pling ~echniques, plus gas loss and air contamination of oil samples during transportation and handling. A second recognized shortcoming is generally inadequa~e sampling rates which are due to the cost and the severly limited number of such analysis that can be perormed in existing laboratories. These short-comings tend to discourage certain desirable monitoring pro- ~`
cedures on new electrical apparatus which, in general, call for high-sampling rates during ~actory heat runs and during early life use. Such test programs could provide early de-tection of design or construction deficiency. Also, such test programs could provide incipient fault detection in trans-Eormers or other liquid ~illed electrical apparatus.
From the above it ;s apparent that there is a need for a suitable instrument for monitoring dissolved gas contents in the electrical insulating liquid of electrical apparatus.
The instrument should be capable of automatically sampling , oil from the operating equipme~t at a selectable sampling rate and determining the dissolved gas concentration -for those gases which are oE interest. It should also provide data storage capacity for lung time periods.
It is, therefore, one object o-f this invention to pro-vide a gas sampling device which will sample the oil in an electrical appara~us, extract the gases from such oil sample and then determine the amount of dissolved gases within such oil sample.
A further object of this invention is to provide a gas .
.
sampling and monitoring device for oil-filled electrical devices and to provide storage capacity for maintaining the records of dissolved gas concentra~ion.
SU~RY OF THE INVENTION
This invention in one form comprises a samplin~ means for extracting a volume of electrical insulating li.quid from an electrical apparatus, a sample valve arranged or collect-ing a known fraction of extracted gases from such liquid sample and injecting the gases into a gas chromatograph for analysis, a gas chromatograph using neon as a carrier gas and a thermoconductivity cell detector with suitable separat-ing columns for gases of interest, a signal conditioning and control logic circuitry for proper sequencing of operations, as required, and a strip chart recorder used to display and store dissolved gas concentration data derived rom the analysis together with a record o the analysis of a standard gas mixture.
The invention which is sought to be protected will be particularly pointed out and distinctly claimed in the claims appended here~o. However, it is believed that this invention and the manner in which its various objects and advantages are obtained as well as other objects and advantages thereo will be better understood by reference to the following detailed description of a preferred embodiment particularly when considered in the light of the accom~anying drawings.
BRIEF DESGRIPTION OF THE_DRAWINGS
FIGURE 1 is a unctional diagram of the preferred embodi-; ment of the device for monitoring dissolved gases according to one form of this invention;
FIGURE 2 .is a sche~atic block diagram of one form of .~ ' .
` ~ ' :
,',. ' .' .' , control logic according to the preferred embodiment of this invention;
FIGURE 3 is a schematic diagram of the preferred gas analyzer si~nal conditioning circui~
FIGURE 3a is a schematic diagram of a preferrea form of zero correcting circuit;
FIGURE 4 is a schematic diagram of the preferred to~al gas signal conditioning circuit;
FIGURE 5 is a timing diagram which shows the actua~ion of the various components of the gas monitoring dev:ice of this invention in relation to time;
FIGURE 6 is a schematic diagram of the gas chromato-graph used in the preferred embodiment of this invention~
FIl,U~E 7 is t~e detector signal pattern obtalned by the gas chromatograph o~ FIGURE 6;
FIGURE 8 is a schematic diagram of the gas extraction arrangement according to the preferred embodiment of this invention; .
FIGURE 9 is a schematic diagram showing a preferred oil sampling arrangement according to this inventicn.
~ESCRIPTION 3F PREFERRED EMBODIMENT
The dissolved gas oil-monitoring device o:E this in-vention is an instrument which will measure the concentra-; tion of dissolved gases ;n electrical insu~.ting liquid such Z5 as, or example, transformer oil. As noted, such data, are of interes~ because the concentrations of certain dissolved gases increase as a result of dielectrical degrada~ion or :~ :
failure. Such information, thus, provides a means whereby 'internal arcing, corona, or ho~ spots~ which are caused by circulatin~ currents, may be diagnosed early befo-re major .- 4 -~' .
.
l~9L9~3 5~5443 fault occurs. This ~yp~ of instrument represents a key ele-me1l~ in an incipient fault detection system which might be applied particularly to large power transformers on line where major faul~s would be intolerable, yet internal inspec-tion is difficult OT impossible due to operational constrain~.
The dissolved gas oil monitor of this invention is pro-grammed to periodically extract an oil sample from an electri-cal apparatus such as, for example, a transformer and by chromatographic analysis determine the dissolved gas concentra-tion of nine gases of interest plus the ~otal dissolved gas concentration. A typical sampling rate may be, or example, once per week. The data are preferably displayed and stored in a bar chart form on a paper chart recorder. The preferred embodiment o~ the invention provides an instrument which is designed for field use, out of doors to provicle data over a one-year period o~f unattended operation.
A functional block diagram of the dissolved gas monitor of this invention is shown in FIGURE 1. There is shown a trans~ormer or other electrical apparatus 10 -from which the oil sample is to be obtained. An oil sampling device 12 is provided which will obtain an oil sample -from the transfoTmer , or other electrical apparatus 10. Next, a device 14 for extracting the gases from the oil sample and determining the volume o extracted gases is provided. The gases are compressed in 14 and then a known fraction is injected by ;~
valve 16 into the chromatographic analysis device 18. A
signal conditioning circuit 20 is provided which conditions the various signals for sending to the data recording device 22. A control logic circuit 24 is provided which con~rols ; 30 the operation of the various devices in a manner which will , : .
.. ~ .
, be explained further in this description.
As will be described, the oil sam~le is collected by allo~ing the oil ~o fill a 200cc syringe by the oil head pressure of the electrical apparatus. Tf desired, the first oil sample may be dumped by siphon action to clear ~he line to ~he electrical apparatus. Then a second sample may be taken for the desired gas analysis. The oil is degassed, that is, the gas is extracted, by allowing the oil to enter an evacuated chamber. The gas thus extracted is increased in pressure by decreasing the oil and gas volume to a smaller, fixed value. A fixed portion of the extracted gas is injected into a gas chromatograph by~a,~gas sampling valve. The chromato~raph uses a system o columns to separate the ~ases of interest and these,gases are de$ected by a thermal conductivity detector. The output signal of the detector is processed ancl integrated to provide the con-centration of each gas. This information is displayed on a chart recorder in bar graph form. The control logic is responsible for automatically providing all of these func- ~' tions.
All operations of the dissolved gas trans~ormer oil monitor are implemented by a group of solenoid valves which are controlled in a fixed time sequence to accomplish all of the desired functions. Solid-state relays control the solenoid valves and are in turn controlled by a master solid-state clock oscillator with appropriate solid-state logic as will be further descrihed. The timing diagram for all of the controlled operation is shown in FIGURE 5. If desired, ' the various automatically controlled functions may be manual-Iy overridden or con~rQlled by means of manual switches.
, The preferred for~ of control logic is set forth in ~
FIGURE 2 to which re,Eerence will now be made. The control logic 24 performs all the operations necessary ~o make the oil monitor ~unction automa~ically and unattended. The control logic 24 comprises a series of solenoid valves 26 which are controlled by the solenoid valve logic circuit 28.
The solenoid valve logic 28 al50 initia1:es the operation of the analog control logic 30 which proceeds independently then from the solenoid logic 28. A clock 34 is provided which is in the form of a 128 Hz free-running multi~ibrator with several frequency dividers. Clock 34 is designed to produce the clock signals used to operate the logic circuits.
The solenoid valve logic 28 is the central control,sys-tem for the entire unit. The heart o~ this logic 28 is a clock-driven l-in-48 decoder. Each output is sequentially activated with the period of l.33 minutes so that the whole cycle takes approximately 65 minutes to complete. As each output o the decoder is activated it sets and resets vari- ' ous flip-flops that con~rol the turn-on and turn-off of the , ,~, 20 various solenoid valves, as can be seen from the timing diagram in FIGURE 5. As will be understood,'the time period in FIGURE 5 prior to zero is the warm-up period for the -~
equipment, which may be varied~ as necessary. The last out-; put of the decoder initiates a reset pulse that,actuates the '', 25 reset circuit 36 to return the logic to its reset condition.
The solenoid valve logic 28 also starts the operation of the -' analog control logic 30 which in turn controls the analog circuits 32.
The primary function of the analog control logic 30 is to establish the necessary timing sequence that assures ~hat " -, , , the analog circuits 32 are turned on during the time period when a peak is expected from the chromatograph 18. This logic is also involved with keeping track of the order o peaks to make sure that the carrcc~ amplifier gain is established for ~he chromatographic peak being measured.
In the preferred embodiment each chromatographic peak has two time intervals of interest. These are, first, the time from the end of the last peak to the beginning of the next peak and, second, the length of time it takes the next peak to elute from the chroma~ograph. Each o these two-time in~ervals are established by dividing a clock signal o$ a two-second period by an integer of choice between 2 and 255.
There~ore, each of the intervals may be set for periods o~
rom 4 to 510 seconds. Each of these intervals must time out sequentially and each one is initiated by the ending of the last one. During alternate intervals the analog circuits 32 are activated so a peak can be integrated and at the end -of the time period a circuit is activated that provides the read out of the integrated peak on the recorder.
The logic circuitry 24 may be reset in one of three ways.
The first is the automatic reset that takes place when the power supplies are turned on. The second is the automatic reset that takes place at the end of the normal measurement cycle. A third reset may be provided manua].ly by pressing a manual reset switch tnot shown). Of course, when manually resetting care must be taken not to reset during a measure-i ment cycle which would cause the sample oil to bé pumped into unwanted locations within the oil moni~oring device.
There are two analog signal conditioning circuits in 20, indicated as 20a and 20b, whlch ~re necessary for the ~ e~ ~ ~ 5D54~3 operation of the gas dissolved oil monitoring device. One circuit 20a conditions the signals from the thermal con-ductivi~y detector of chromatograph 18 in order to display them in bar graph form. The second circuit 20b operates on the ou~put from a pressure -transducer associated with the gas extraction device 14 to convert and display an indica-tion of the total dissolved gas. The control signals associat-ed with pressure measurements foT a total gas ~olume measure-ment are generated directly by the solenoid valve logic 28 rather than the analog logic 30.
FI~URE 3 provides a block diagram of the gas analyzer signal conditioning circuit 20a. The chromatograph cell 38 is in the form of a thermal conducti~ity detector and its output and residual offse-t voltage is connected to a series power supply where the offset voltage is balanced. The out-put is then connected to a solid-state, double-pole, double-throw switch 40 which is used to invert the signal polarity so that the amplifier 42 always sees a negative-going de-tector signal. The point where the switch reverses polarity is governed by the analog control logic 30. The signal is sent to am~lifier 42, which is a variable gain chopper stabiliz~ operational amplifier. The gain is controlled by gain logic 44 consisting oE a reed relay an~ a pai-r of resistors Eor each analyzed peak. The resistors, one fixed ~S and one adjustable, control ~he gain, and the reed relay switches the resistor pair into or out o-f the circuit. The i reed relay is controlled by the gain logic 44 which keeps track of the peak being measured and switches in the correct gain. The reed relay may be also controlled by a manual switch for purposes o~ calibration.
_ 9~ _ :
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The output of amplifier 42 passes to the amplifier 46.
Amplifier 46 is a unity gain amplifier that corrects or long-turn drifts in the thermal conductivity detector 38 and ' associated circuitry. Amplifier 46 is normally in its track condition except ~hen a peak is being read. In the track condition, the amplifier is connected as a differential amplifier with both inputs connected. It tracks signal changes on its input and the changing input is impressed across a capacitor. The output remains zero in the track condition~
~hen in the read condition amplifier 46 switches to a unity-gain inverting amplifier,and the voltage across the capacitor represents the true zero or base line for the peak being measured. At the end of the peak measurement the circuitry returns to the track condition. This circuit will eliminate long-term base-line drift effects. The switch points for amplifier 46 are controlled by the analog control logic 30.
A preferred form of schematic diagram for the unity gain ampliier 46 is shown in FIGURE 3a. As shown in FIGURE
3a, an FET 610 and a capacitor 612 are connected to one in-; 2~ put 614 of operational ampli-fier 616. The output 618 of the amplifier 42 is also connected through FET 610 to input 614 , and through resistor 620 to input 62Z o~ the operational amplifier 616. As will be apparent from PIGURE 3a, when the gate 624 of FET 610 is positive7 FET 610 is turned on and Z5 the operational amplifier 616 operates as a normal dif-ferent,ial amplifier, with both inputs 614, and 622 tied together through resistors 620, 628 and FET 610. While the input voltage 618 can vary, in this condition with FET 61~
conducting, the output voltage 626 of amplifier 616 remains at zero. The magnitude of the voltage on capacitor 612 will : ;:
depend on resistors 628 and 630 and the input voltage 618.
~en gate 624 of ~ET 610 is negative, FET 610 is turned off.
Amplifier 616 then tracks the input voltage 61~ with its gain set by resistors 620 and 632. During this period, the voltage on capacitor 612 applied to iJlpUt 614 of amplifier 616 pro-vides the desired zero ref2rence voltage.
The unity gain am~lifier 46 to correc:t long term drifts of ~he thermal conductivity detector 38 is !described in Canad~an application Serial No. ~ , filed ~ 1 in the name of M.D. Ketchum, one of the inventors herein, or "Re~erence Voltage S-tabilization Curcuit" and assigned to the same assignee as this invention.
Re~erring again to FIGUR~ 3, the signal ~rom ampli~ier ~6 is then integrated by the integrator circuit 48 to measure the area under the peak which represents the concentration of the constituént gas being measured. The integrator is pre-ferably semidigital and integrates in analog form but accumulates the integral in digital orm. This has two major advantages. ~irst, the integrator gain can be much larger ` than what would be usual for a regular analog integrator.
The larger gain means a smaller integrating resistor and capacitor can be used. Second, the analog signal is held as a digital eight bit number so that it may be stored for later display. The output of the integrator 48 passes through ; calibration CiTCUits 50 and is then displayed in the chart recorder or display 22.
The calibration circuits 50 are used to calibrate the gain for each gas peak being measured. The calibrat~on circuits S0 bypass the circuits 46 and 48, as shown, to :
,.
' place the output of amplifieT 42 directly on the recorder 22. It also generates a known signal to the input of switch 4n to simulate the output of detector 38. Using this signal the gain for each peak can be calibrated wi.th gain logic 44.
The total gas reading utilizes a differential p.ressure measurement of the gases evolved from the oil during the gas extraction. The total gas conditioning circuit ZOb is shown in block diagram in FIGURE 4. The measurement is the dif-ference between the extraction chamber vacuum and the final gas pressure measured be-fore compression~ The output of a solid-state pressure transducer 52 is.amplified by ampli-: fier 54. Amplifier 54 has three switch selected gains re-presenting a l per cent, Eive percent and ten per cent total gas full scale. The amplifier 56 is a drift corr~cting ampli~ier identical to amplifier 46 previously described and .
is used to correct the long-term drift in the pressure transducer 52 from run to run. The output of amplifier 56 must be stored for 30 to 40 minutes while the gas ana:Lysis is being run. This storing is provided by an A/D converter 58 which has its i.nternal analo~ signal available as an output. The conver~er 58 trac~sthe outpuk of ampli~ier 56 and during this period the output of the converter 58 is identical to its input. Where the final differential pressure . has been measured, the clock 34 signal operating the conver-ter 58 is ga*ed to prevent further tracking by converter ~ . .
58 and the last converted signal is held in a digital format but is available as an analog voltage at the output. At the ~ -' appropriate timeS this voltage is r0ad into the display 22 as the total gas measurement, as indicated in FIGURE S. . .~ :;
The gas chromatograph 18 employed in the preferred , embodiment of this invention inclucles a thermal conductivity detector 38 such as9 for example, a GOWMAG instrument, Model No. 10-952 Thermal Conductivity Detector. The gas chromato-graph is operated at a constant temperature of 80C in the preferred embodimen~ and employs neon as t:he carrier gas.
The thermal conductivity detector 38 provides a signal which is integrated for display. Neon is used because its thermal conduc~ivity is significantly different from all gases to be detected. This ensures good sensitivity for all compon- ;
ents. Of the gases which are analyzed, methane has a value of thermal conductivitr closest to that of neon and is~
therefore, detected with the least sensitivit~ which accounts for the somewhat lower resolution of methane wi~h the g~s chromatograph 18 o this invention.
The following are the relative values of thermal con~
ductivity of the gases which are of interest in accordance with the preferred embodiment of this invention.
Relative Thermal Conduc~ivitY at 80C
.~ , .
Neon 1.0 2n Carbon nioxide C02 0.38 Ethylene C2H~ 0.51 Ethane C2H6 0 53 Acetylene ~2H2 0 50 Hydrogen H2 3~75 Z5 Oxygen ~2 0.56 Nitrogen N2 0 54 Methane CH4 0.76 Carbon Monoxide C0 0.53 , ~ ~ 4 ~ ~ 3 SD5443 Since the signals produced by the detector 38 for a ixed amount of any of the gases is proportional to their thermal conductivity values, it is evident that a suitable correc-tion must be applied to provide an output signal for display in terms of volume concentration. This acljustment of sen-sitivity is accomplished by applying a diferent gain for each gas of interest by switching an appropriate gain network during a time when each gas is being detected in the thermal conductivity cell 38 as was explained~with reference to amplifier 42 in FIGURE 3 of the drawing.
The schematic diagram o~ the gas chromatograph 18 is shown in PIGURE 6. The chromatograph 18 contains three separating columns and one time-delay colu~n. It also employs a 4cc sample loop and a sample injection valve which, in the preerred embodiment, is Carl sample valve 2018-P, provided by Carl Instruments, Inc. FIGURE 6 of the drawing shows a schematic diagram of the gas chromatograph 18 and i~s associated circuitry in accordance with the pre-ferred embodiment o this invention. As can be seen, the thermal conductivity detector 38 is provided with three separating columns, columns 60, 62, and ~4, and one time-delay column, 66. Also shown is the gas sample valve 68 and the 4cc sample loop 69. As will be understood, all of these members are mounted in an oven as indicated by dotted line 70, in order to maintain a constant temperature o~ 80C.
A standard gas container 72 is shown which provides a standard gas of known composition to the gas chromatograph 18 in order to be certain that the chromatograph is function-, ing correctly. Also shown at 74, is the neon carTier gas which is used ~hroughout the gas chromatogra~h. As can be .
~ ~[~4 9 ~3 5D5443 seen, the standard gas from the holder 72 fills sample loop 69 when valve 76 is opened allowing the standard gas to flow to the sample valve 68. At this time sample ~alve 68 is in the sample position. When sample valve 68 is moved ~o ~he inject position, ~he standard gas sample is in~ec~ed into the flowing neon carrier gas stream and carried to de-tector 38. The standard gas sample is separaked and detect-ed in the ollowing manner. This sample gas mixture flows through columns 60, 62 and the first half of the thermal con-ductivity detector 38. These two columns ~0~ 62 wîll delay and separate C02 and the hydrocarbons C2H4, C2H and C ~2 from the sample while permitting the remaining gases to pass through with negligible separation. While the separated gases are being eluted from the ~irst two columns the remaining gas mixture enters column 64 where it is separated and then tra-~erses the delay column 66 be~ore entering the second hal of the thermal conductivity detector 38. This generates the de-tector signal pat~ern which is shown in FIGURE 7.
Because the thermal conductivity detector 38 contains four filaments connected in a full-bridge configuration, the gases detected in the first hal~ of the detector provide opposite polarity signals from those detected in the second hal~. In addition, hydrogen, because its thermal conductivity is higher than the carrier gas neon, provides a signal of ~ 25 same polarity as the C02 and the C2 hydrocarbons. Thus, -~ although hydrogen is the first of the second group detected, its signal polarity is the same as the firs~ group as can be readily seen from FIGURE 7.
In operation of the gas chromatograph, normal carrier gas flow is established from the gas container 74 by opening , .
Il3 valve 78 and valve 80. As can be seen~ this allows the carrier gas to flow through valve 78, the bypass part of sample valve 68, and through columns 60, 62 one-half of detector 38, columns 64 and 66 and the other hal~ of detect-or 38 and then out -through valve 80 to vent to the atmosphere.
A constant flow rate of the carrier gas is established by a flow regulator 82. After an ~analysis o~ the extracted gas has been completed, the columns 60, 62, 64 and 66 are back flushed by opening valves 84 and 86 and closing valves 78 and 80. As can be seen,~ this will allow the carrier gas to flow backward through detector cell 38 and columns 66, 64, 62 and 60, the sample valve 68 and through valve 86 to atmosphere.
This helps to prevent a buildup of the heavier hydrocarbon gases in the colurnn packing which, in time, af-fect the column separation of the gases of interest. Following the back flush, valves 84 and 86 are closed. This maintains a posi-tive pressure of carrier gas in the columns to prevent CQn-tamination during intervals between the analysis.
In the normal operating sequence of the gas chromato-graph, the 4cc sample loop 69 is first evacuated by opening valve 88. As will be understood, sample valve 68 is in th0 sample position during evacuation. A~ter evacuation, valve 88 is closed and valve 76 is opened to fill the sample loop 69 with standard gas at the pressure determined by the ~5 pressure regulator on the gas cylinder 72. Valve 76 is then closed and valve 9CI is briefly opened to vent the sample to one atmosphere through the length of small dia- -meter tube 91. Tube 91 prevents atmosphoric contamina~ion.
A~ter valve 90 closes, the sample of standard gas is in-jected into the chromatograph by actuating the sample valve .
~ ~ 49 13 sD5443 68 to connect the sample loop 69 in series with the neon carrier gas stream. ~nalysis of this standard sample provides data establishing the normal function of the chromatograph. After the standard sample injection, the S sample valve 68 is reset and valve 88 is again opened to evacuate the sample loop 69. Valve 8~ th~n remains opened during the oil-ejection gas-extraction gas-compression process which will be described with refer~nce to FICURE 8.
Valve 88 closes just before the extracted sample is inject-ed into the chromatograph 18 for analysis. The timing sequence or these operations is shown in FIGURE 5.
Referring now to FIGURE 8, which is a schematic diagram of the pre~erred gas extraction device 1~ and related equip-ment, the method o gases extractions will now ble described.
In the preferred embodlment shown, the gas extraction is accomplished in a horizontally disposed gas cylinder 92 which contains an aluminum piston 94. With the piston in its rest position, as shown in FIGURE 8, the right side of chamber 92 ; is normally evacuated through normally open valve 112. With valve 88 opened, the chamber volume is approximately 700 cubic centimeters. The cylinder 92 is evacuated through valve 96 and 98 to a pressure of approximately twenty micro-meters of mercury. The pressur0 rise within the cylinder 92 from the extracted gas is measured with a silicon pressure transducer 52 and is employed to determine total dissolved gas content o-f the oil sample as was earller described with reference to FI~URE 4.
~Ater evacuation, the cylinder 92 is isolated rom the vacuum pump ~y closing valve 96. The oil sample (approxi-mately 180cc) from sample container 100 is then admitted ~ 5D5443 slowly by opening valve 10~ partially filling cylinder 92.
The inle-t oil flow is controlled by a metering needle valve 104. A normal period for introducin~ the oil sample is 8 to lO minutes. At the end of the sample period, valve 102 is closed, as shown in FIGUR~ 5~ The maximum permissible ~ime for the introduction of the oiI sample is 13.3 minutes in accordance with the timing sequence of the preferred embodiment. This variable period is indicated by the dotted line in FIGURE 5.
In the preferred embodiment, cylinder 92 is provided with a Teflon~lcoated stirring magnet 106 which is actuated by an external motor-driven bar magnet 108 to provide thorough liquid agitatian during the gas extraction sequence. At the comp:Letion of the gas extraction period a hold circuit is used to store a signal proportional to the pressure rise which has occurred. As earlier indicated this is subsequently displayed'on"display 22 as the total gas indication.
Valve 112 is then actuated to vent the rîght side of piston 92 to one atmosphere and force piston 94 over to the let-hand side of the cylinder, to a fixed final volume de-termined by piston stop 116. This reduces the cylinder volume to a smaller volume and compresses the extracted gas in-to a relatively small volume, approximately 15C. Shortly ater the compresslon stroke valve 8~ closes to isolate part of the extracted gas within the sample loop 69~ The sample valve 68 is then activated to inject the sample into the chromato-graph 18 as previously described.
After injection o the gas sample, valve 9'6 is opened ,and valve 98 is actuated to vent ~he left-hand side of the cylinder 92 to one atmosphere. Then valve 114 is opened to allow ~he oil to drain from the cylinder 920 After the oil drain is complete valve 112 is again opened to evacuate the righ~-hand side of the cylinder 92 so`that atmospheric pres-sure pushes piston 94 ~o its far right or rest position.
Sometime later, on svstem reset, valve 114 is closed and valve 98 is opened to evacuate the left-hand side of cylider 92.
FIGURE 9 shows a schematic diagram of the preferred oil sampling system which is utilized in the dissolved gas oil monitoring system of this invention. The oil sampling arrangement shown is designed to carry out the following functions:
1. Purge the oil sampling line to thè electrical apparatus, such as a transformer 10.
.
This invention relates to a device for monitoring dissolved gases in ~rans-Eormers or other electrical appara-tus and, more particularly, to a free-standing instrument which is capable of sampling the electrical l.iquid in an electrical apparatus and measuring the gases which are dissolved in such liquid.
For the past sevçral years information has been accumu-lated that dissolved gas concentrations in electrical in-sulating liquid provide a good indicato~ of the functional condition of the electrical apparatus. Certain gases such as CO and CO2 increase in concentration with thermal aging and degradation of the cellulosic insulatin in the electri- `.
cal apparatus structure. Other gases notably H2 and the various hydrocarbon are ormed and built up in the electri- . . ; .
cal insulating liquids due to hot spots which are caused by circulating ~urrents and dielectric breakdown, such as corona and arcing. Concentrations of 2 and N in general, provide information on the quality of the gas pressurizing system employed with many Iarge electrical devices such as trans-formers.
There is increasing evidence that the relative con-centration of these gases provide information on the type of malfunction as well as the severity. .Additionally, information on their time rate of change provides guidance ~or making maintenance and repair decisions.
In~ormation which has been acquired to date is based .
on determination of dissolved gas concentration from oil ~ Isamples which are withdra~m at the test or the installa ; 30 tion sites and transported to a laboratory for gas ~:
:, O
. .
, ~ .
5D544~
e~tracti~n and analysis. lVhile this procedure has been used with much success, it has a number of shortcomings. The first recognized shortcoming errors which are due to vari-able and generally uncon~rollable oil sa~pling ~echniques, plus gas loss and air contamination of oil samples during transportation and handling. A second recognized shortcoming is generally inadequa~e sampling rates which are due to the cost and the severly limited number of such analysis that can be perormed in existing laboratories. These short-comings tend to discourage certain desirable monitoring pro- ~`
cedures on new electrical apparatus which, in general, call for high-sampling rates during ~actory heat runs and during early life use. Such test programs could provide early de-tection of design or construction deficiency. Also, such test programs could provide incipient fault detection in trans-Eormers or other liquid ~illed electrical apparatus.
From the above it ;s apparent that there is a need for a suitable instrument for monitoring dissolved gas contents in the electrical insulating liquid of electrical apparatus.
The instrument should be capable of automatically sampling , oil from the operating equipme~t at a selectable sampling rate and determining the dissolved gas concentration -for those gases which are oE interest. It should also provide data storage capacity for lung time periods.
It is, therefore, one object o-f this invention to pro-vide a gas sampling device which will sample the oil in an electrical appara~us, extract the gases from such oil sample and then determine the amount of dissolved gases within such oil sample.
A further object of this invention is to provide a gas .
.
sampling and monitoring device for oil-filled electrical devices and to provide storage capacity for maintaining the records of dissolved gas concentra~ion.
SU~RY OF THE INVENTION
This invention in one form comprises a samplin~ means for extracting a volume of electrical insulating li.quid from an electrical apparatus, a sample valve arranged or collect-ing a known fraction of extracted gases from such liquid sample and injecting the gases into a gas chromatograph for analysis, a gas chromatograph using neon as a carrier gas and a thermoconductivity cell detector with suitable separat-ing columns for gases of interest, a signal conditioning and control logic circuitry for proper sequencing of operations, as required, and a strip chart recorder used to display and store dissolved gas concentration data derived rom the analysis together with a record o the analysis of a standard gas mixture.
The invention which is sought to be protected will be particularly pointed out and distinctly claimed in the claims appended here~o. However, it is believed that this invention and the manner in which its various objects and advantages are obtained as well as other objects and advantages thereo will be better understood by reference to the following detailed description of a preferred embodiment particularly when considered in the light of the accom~anying drawings.
BRIEF DESGRIPTION OF THE_DRAWINGS
FIGURE 1 is a unctional diagram of the preferred embodi-; ment of the device for monitoring dissolved gases according to one form of this invention;
FIGURE 2 .is a sche~atic block diagram of one form of .~ ' .
` ~ ' :
,',. ' .' .' , control logic according to the preferred embodiment of this invention;
FIGURE 3 is a schematic diagram of the preferred gas analyzer si~nal conditioning circui~
FIGURE 3a is a schematic diagram of a preferrea form of zero correcting circuit;
FIGURE 4 is a schematic diagram of the preferred to~al gas signal conditioning circuit;
FIGURE 5 is a timing diagram which shows the actua~ion of the various components of the gas monitoring dev:ice of this invention in relation to time;
FIGURE 6 is a schematic diagram of the gas chromato-graph used in the preferred embodiment of this invention~
FIl,U~E 7 is t~e detector signal pattern obtalned by the gas chromatograph o~ FIGURE 6;
FIGURE 8 is a schematic diagram of the gas extraction arrangement according to the preferred embodiment of this invention; .
FIGURE 9 is a schematic diagram showing a preferred oil sampling arrangement according to this inventicn.
~ESCRIPTION 3F PREFERRED EMBODIMENT
The dissolved gas oil-monitoring device o:E this in-vention is an instrument which will measure the concentra-; tion of dissolved gases ;n electrical insu~.ting liquid such Z5 as, or example, transformer oil. As noted, such data, are of interes~ because the concentrations of certain dissolved gases increase as a result of dielectrical degrada~ion or :~ :
failure. Such information, thus, provides a means whereby 'internal arcing, corona, or ho~ spots~ which are caused by circulatin~ currents, may be diagnosed early befo-re major .- 4 -~' .
.
l~9L9~3 5~5443 fault occurs. This ~yp~ of instrument represents a key ele-me1l~ in an incipient fault detection system which might be applied particularly to large power transformers on line where major faul~s would be intolerable, yet internal inspec-tion is difficult OT impossible due to operational constrain~.
The dissolved gas oil monitor of this invention is pro-grammed to periodically extract an oil sample from an electri-cal apparatus such as, for example, a transformer and by chromatographic analysis determine the dissolved gas concentra-tion of nine gases of interest plus the ~otal dissolved gas concentration. A typical sampling rate may be, or example, once per week. The data are preferably displayed and stored in a bar chart form on a paper chart recorder. The preferred embodiment o~ the invention provides an instrument which is designed for field use, out of doors to provicle data over a one-year period o~f unattended operation.
A functional block diagram of the dissolved gas monitor of this invention is shown in FIGURE 1. There is shown a trans~ormer or other electrical apparatus 10 -from which the oil sample is to be obtained. An oil sampling device 12 is provided which will obtain an oil sample -from the transfoTmer , or other electrical apparatus 10. Next, a device 14 for extracting the gases from the oil sample and determining the volume o extracted gases is provided. The gases are compressed in 14 and then a known fraction is injected by ;~
valve 16 into the chromatographic analysis device 18. A
signal conditioning circuit 20 is provided which conditions the various signals for sending to the data recording device 22. A control logic circuit 24 is provided which con~rols ; 30 the operation of the various devices in a manner which will , : .
.. ~ .
, be explained further in this description.
As will be described, the oil sam~le is collected by allo~ing the oil ~o fill a 200cc syringe by the oil head pressure of the electrical apparatus. Tf desired, the first oil sample may be dumped by siphon action to clear ~he line to ~he electrical apparatus. Then a second sample may be taken for the desired gas analysis. The oil is degassed, that is, the gas is extracted, by allowing the oil to enter an evacuated chamber. The gas thus extracted is increased in pressure by decreasing the oil and gas volume to a smaller, fixed value. A fixed portion of the extracted gas is injected into a gas chromatograph by~a,~gas sampling valve. The chromato~raph uses a system o columns to separate the ~ases of interest and these,gases are de$ected by a thermal conductivity detector. The output signal of the detector is processed ancl integrated to provide the con-centration of each gas. This information is displayed on a chart recorder in bar graph form. The control logic is responsible for automatically providing all of these func- ~' tions.
All operations of the dissolved gas trans~ormer oil monitor are implemented by a group of solenoid valves which are controlled in a fixed time sequence to accomplish all of the desired functions. Solid-state relays control the solenoid valves and are in turn controlled by a master solid-state clock oscillator with appropriate solid-state logic as will be further descrihed. The timing diagram for all of the controlled operation is shown in FIGURE 5. If desired, ' the various automatically controlled functions may be manual-Iy overridden or con~rQlled by means of manual switches.
, The preferred for~ of control logic is set forth in ~
FIGURE 2 to which re,Eerence will now be made. The control logic 24 performs all the operations necessary ~o make the oil monitor ~unction automa~ically and unattended. The control logic 24 comprises a series of solenoid valves 26 which are controlled by the solenoid valve logic circuit 28.
The solenoid valve logic 28 al50 initia1:es the operation of the analog control logic 30 which proceeds independently then from the solenoid logic 28. A clock 34 is provided which is in the form of a 128 Hz free-running multi~ibrator with several frequency dividers. Clock 34 is designed to produce the clock signals used to operate the logic circuits.
The solenoid valve logic 28 is the central control,sys-tem for the entire unit. The heart o~ this logic 28 is a clock-driven l-in-48 decoder. Each output is sequentially activated with the period of l.33 minutes so that the whole cycle takes approximately 65 minutes to complete. As each output o the decoder is activated it sets and resets vari- ' ous flip-flops that con~rol the turn-on and turn-off of the , ,~, 20 various solenoid valves, as can be seen from the timing diagram in FIGURE 5. As will be understood,'the time period in FIGURE 5 prior to zero is the warm-up period for the -~
equipment, which may be varied~ as necessary. The last out-; put of the decoder initiates a reset pulse that,actuates the '', 25 reset circuit 36 to return the logic to its reset condition.
The solenoid valve logic 28 also starts the operation of the -' analog control logic 30 which in turn controls the analog circuits 32.
The primary function of the analog control logic 30 is to establish the necessary timing sequence that assures ~hat " -, , , the analog circuits 32 are turned on during the time period when a peak is expected from the chromatograph 18. This logic is also involved with keeping track of the order o peaks to make sure that the carrcc~ amplifier gain is established for ~he chromatographic peak being measured.
In the preferred embodiment each chromatographic peak has two time intervals of interest. These are, first, the time from the end of the last peak to the beginning of the next peak and, second, the length of time it takes the next peak to elute from the chroma~ograph. Each o these two-time in~ervals are established by dividing a clock signal o$ a two-second period by an integer of choice between 2 and 255.
There~ore, each of the intervals may be set for periods o~
rom 4 to 510 seconds. Each of these intervals must time out sequentially and each one is initiated by the ending of the last one. During alternate intervals the analog circuits 32 are activated so a peak can be integrated and at the end -of the time period a circuit is activated that provides the read out of the integrated peak on the recorder.
The logic circuitry 24 may be reset in one of three ways.
The first is the automatic reset that takes place when the power supplies are turned on. The second is the automatic reset that takes place at the end of the normal measurement cycle. A third reset may be provided manua].ly by pressing a manual reset switch tnot shown). Of course, when manually resetting care must be taken not to reset during a measure-i ment cycle which would cause the sample oil to bé pumped into unwanted locations within the oil moni~oring device.
There are two analog signal conditioning circuits in 20, indicated as 20a and 20b, whlch ~re necessary for the ~ e~ ~ ~ 5D54~3 operation of the gas dissolved oil monitoring device. One circuit 20a conditions the signals from the thermal con-ductivi~y detector of chromatograph 18 in order to display them in bar graph form. The second circuit 20b operates on the ou~put from a pressure -transducer associated with the gas extraction device 14 to convert and display an indica-tion of the total dissolved gas. The control signals associat-ed with pressure measurements foT a total gas ~olume measure-ment are generated directly by the solenoid valve logic 28 rather than the analog logic 30.
FI~URE 3 provides a block diagram of the gas analyzer signal conditioning circuit 20a. The chromatograph cell 38 is in the form of a thermal conducti~ity detector and its output and residual offse-t voltage is connected to a series power supply where the offset voltage is balanced. The out-put is then connected to a solid-state, double-pole, double-throw switch 40 which is used to invert the signal polarity so that the amplifier 42 always sees a negative-going de-tector signal. The point where the switch reverses polarity is governed by the analog control logic 30. The signal is sent to am~lifier 42, which is a variable gain chopper stabiliz~ operational amplifier. The gain is controlled by gain logic 44 consisting oE a reed relay an~ a pai-r of resistors Eor each analyzed peak. The resistors, one fixed ~S and one adjustable, control ~he gain, and the reed relay switches the resistor pair into or out o-f the circuit. The i reed relay is controlled by the gain logic 44 which keeps track of the peak being measured and switches in the correct gain. The reed relay may be also controlled by a manual switch for purposes o~ calibration.
_ 9~ _ :
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The output of amplifier 42 passes to the amplifier 46.
Amplifier 46 is a unity gain amplifier that corrects or long-turn drifts in the thermal conductivity detector 38 and ' associated circuitry. Amplifier 46 is normally in its track condition except ~hen a peak is being read. In the track condition, the amplifier is connected as a differential amplifier with both inputs connected. It tracks signal changes on its input and the changing input is impressed across a capacitor. The output remains zero in the track condition~
~hen in the read condition amplifier 46 switches to a unity-gain inverting amplifier,and the voltage across the capacitor represents the true zero or base line for the peak being measured. At the end of the peak measurement the circuitry returns to the track condition. This circuit will eliminate long-term base-line drift effects. The switch points for amplifier 46 are controlled by the analog control logic 30.
A preferred form of schematic diagram for the unity gain ampliier 46 is shown in FIGURE 3a. As shown in FIGURE
3a, an FET 610 and a capacitor 612 are connected to one in-; 2~ put 614 of operational ampli-fier 616. The output 618 of the amplifier 42 is also connected through FET 610 to input 614 , and through resistor 620 to input 62Z o~ the operational amplifier 616. As will be apparent from PIGURE 3a, when the gate 624 of FET 610 is positive7 FET 610 is turned on and Z5 the operational amplifier 616 operates as a normal dif-ferent,ial amplifier, with both inputs 614, and 622 tied together through resistors 620, 628 and FET 610. While the input voltage 618 can vary, in this condition with FET 61~
conducting, the output voltage 626 of amplifier 616 remains at zero. The magnitude of the voltage on capacitor 612 will : ;:
depend on resistors 628 and 630 and the input voltage 618.
~en gate 624 of ~ET 610 is negative, FET 610 is turned off.
Amplifier 616 then tracks the input voltage 61~ with its gain set by resistors 620 and 632. During this period, the voltage on capacitor 612 applied to iJlpUt 614 of amplifier 616 pro-vides the desired zero ref2rence voltage.
The unity gain am~lifier 46 to correc:t long term drifts of ~he thermal conductivity detector 38 is !described in Canad~an application Serial No. ~ , filed ~ 1 in the name of M.D. Ketchum, one of the inventors herein, or "Re~erence Voltage S-tabilization Curcuit" and assigned to the same assignee as this invention.
Re~erring again to FIGUR~ 3, the signal ~rom ampli~ier ~6 is then integrated by the integrator circuit 48 to measure the area under the peak which represents the concentration of the constituént gas being measured. The integrator is pre-ferably semidigital and integrates in analog form but accumulates the integral in digital orm. This has two major advantages. ~irst, the integrator gain can be much larger ` than what would be usual for a regular analog integrator.
The larger gain means a smaller integrating resistor and capacitor can be used. Second, the analog signal is held as a digital eight bit number so that it may be stored for later display. The output of the integrator 48 passes through ; calibration CiTCUits 50 and is then displayed in the chart recorder or display 22.
The calibration circuits 50 are used to calibrate the gain for each gas peak being measured. The calibrat~on circuits S0 bypass the circuits 46 and 48, as shown, to :
,.
' place the output of amplifieT 42 directly on the recorder 22. It also generates a known signal to the input of switch 4n to simulate the output of detector 38. Using this signal the gain for each peak can be calibrated wi.th gain logic 44.
The total gas reading utilizes a differential p.ressure measurement of the gases evolved from the oil during the gas extraction. The total gas conditioning circuit ZOb is shown in block diagram in FIGURE 4. The measurement is the dif-ference between the extraction chamber vacuum and the final gas pressure measured be-fore compression~ The output of a solid-state pressure transducer 52 is.amplified by ampli-: fier 54. Amplifier 54 has three switch selected gains re-presenting a l per cent, Eive percent and ten per cent total gas full scale. The amplifier 56 is a drift corr~cting ampli~ier identical to amplifier 46 previously described and .
is used to correct the long-term drift in the pressure transducer 52 from run to run. The output of amplifier 56 must be stored for 30 to 40 minutes while the gas ana:Lysis is being run. This storing is provided by an A/D converter 58 which has its i.nternal analo~ signal available as an output. The conver~er 58 trac~sthe outpuk of ampli~ier 56 and during this period the output of the converter 58 is identical to its input. Where the final differential pressure . has been measured, the clock 34 signal operating the conver-ter 58 is ga*ed to prevent further tracking by converter ~ . .
58 and the last converted signal is held in a digital format but is available as an analog voltage at the output. At the ~ -' appropriate timeS this voltage is r0ad into the display 22 as the total gas measurement, as indicated in FIGURE S. . .~ :;
The gas chromatograph 18 employed in the preferred , embodiment of this invention inclucles a thermal conductivity detector 38 such as9 for example, a GOWMAG instrument, Model No. 10-952 Thermal Conductivity Detector. The gas chromato-graph is operated at a constant temperature of 80C in the preferred embodimen~ and employs neon as t:he carrier gas.
The thermal conductivity detector 38 provides a signal which is integrated for display. Neon is used because its thermal conduc~ivity is significantly different from all gases to be detected. This ensures good sensitivity for all compon- ;
ents. Of the gases which are analyzed, methane has a value of thermal conductivitr closest to that of neon and is~
therefore, detected with the least sensitivit~ which accounts for the somewhat lower resolution of methane wi~h the g~s chromatograph 18 o this invention.
The following are the relative values of thermal con~
ductivity of the gases which are of interest in accordance with the preferred embodiment of this invention.
Relative Thermal Conduc~ivitY at 80C
.~ , .
Neon 1.0 2n Carbon nioxide C02 0.38 Ethylene C2H~ 0.51 Ethane C2H6 0 53 Acetylene ~2H2 0 50 Hydrogen H2 3~75 Z5 Oxygen ~2 0.56 Nitrogen N2 0 54 Methane CH4 0.76 Carbon Monoxide C0 0.53 , ~ ~ 4 ~ ~ 3 SD5443 Since the signals produced by the detector 38 for a ixed amount of any of the gases is proportional to their thermal conductivity values, it is evident that a suitable correc-tion must be applied to provide an output signal for display in terms of volume concentration. This acljustment of sen-sitivity is accomplished by applying a diferent gain for each gas of interest by switching an appropriate gain network during a time when each gas is being detected in the thermal conductivity cell 38 as was explained~with reference to amplifier 42 in FIGURE 3 of the drawing.
The schematic diagram o~ the gas chromatograph 18 is shown in PIGURE 6. The chromatograph 18 contains three separating columns and one time-delay colu~n. It also employs a 4cc sample loop and a sample injection valve which, in the preerred embodiment, is Carl sample valve 2018-P, provided by Carl Instruments, Inc. FIGURE 6 of the drawing shows a schematic diagram of the gas chromatograph 18 and i~s associated circuitry in accordance with the pre-ferred embodiment o this invention. As can be seen, the thermal conductivity detector 38 is provided with three separating columns, columns 60, 62, and ~4, and one time-delay column, 66. Also shown is the gas sample valve 68 and the 4cc sample loop 69. As will be understood, all of these members are mounted in an oven as indicated by dotted line 70, in order to maintain a constant temperature o~ 80C.
A standard gas container 72 is shown which provides a standard gas of known composition to the gas chromatograph 18 in order to be certain that the chromatograph is function-, ing correctly. Also shown at 74, is the neon carTier gas which is used ~hroughout the gas chromatogra~h. As can be .
~ ~[~4 9 ~3 5D5443 seen, the standard gas from the holder 72 fills sample loop 69 when valve 76 is opened allowing the standard gas to flow to the sample valve 68. At this time sample ~alve 68 is in the sample position. When sample valve 68 is moved ~o ~he inject position, ~he standard gas sample is in~ec~ed into the flowing neon carrier gas stream and carried to de-tector 38. The standard gas sample is separaked and detect-ed in the ollowing manner. This sample gas mixture flows through columns 60, 62 and the first half of the thermal con-ductivity detector 38. These two columns ~0~ 62 wîll delay and separate C02 and the hydrocarbons C2H4, C2H and C ~2 from the sample while permitting the remaining gases to pass through with negligible separation. While the separated gases are being eluted from the ~irst two columns the remaining gas mixture enters column 64 where it is separated and then tra-~erses the delay column 66 be~ore entering the second hal of the thermal conductivity detector 38. This generates the de-tector signal pat~ern which is shown in FIGURE 7.
Because the thermal conductivity detector 38 contains four filaments connected in a full-bridge configuration, the gases detected in the first hal~ of the detector provide opposite polarity signals from those detected in the second hal~. In addition, hydrogen, because its thermal conductivity is higher than the carrier gas neon, provides a signal of ~ 25 same polarity as the C02 and the C2 hydrocarbons. Thus, -~ although hydrogen is the first of the second group detected, its signal polarity is the same as the firs~ group as can be readily seen from FIGURE 7.
In operation of the gas chromatograph, normal carrier gas flow is established from the gas container 74 by opening , .
Il3 valve 78 and valve 80. As can be seen~ this allows the carrier gas to flow through valve 78, the bypass part of sample valve 68, and through columns 60, 62 one-half of detector 38, columns 64 and 66 and the other hal~ of detect-or 38 and then out -through valve 80 to vent to the atmosphere.
A constant flow rate of the carrier gas is established by a flow regulator 82. After an ~analysis o~ the extracted gas has been completed, the columns 60, 62, 64 and 66 are back flushed by opening valves 84 and 86 and closing valves 78 and 80. As can be seen,~ this will allow the carrier gas to flow backward through detector cell 38 and columns 66, 64, 62 and 60, the sample valve 68 and through valve 86 to atmosphere.
This helps to prevent a buildup of the heavier hydrocarbon gases in the colurnn packing which, in time, af-fect the column separation of the gases of interest. Following the back flush, valves 84 and 86 are closed. This maintains a posi-tive pressure of carrier gas in the columns to prevent CQn-tamination during intervals between the analysis.
In the normal operating sequence of the gas chromato-graph, the 4cc sample loop 69 is first evacuated by opening valve 88. As will be understood, sample valve 68 is in th0 sample position during evacuation. A~ter evacuation, valve 88 is closed and valve 76 is opened to fill the sample loop 69 with standard gas at the pressure determined by the ~5 pressure regulator on the gas cylinder 72. Valve 76 is then closed and valve 9CI is briefly opened to vent the sample to one atmosphere through the length of small dia- -meter tube 91. Tube 91 prevents atmosphoric contamina~ion.
A~ter valve 90 closes, the sample of standard gas is in-jected into the chromatograph by actuating the sample valve .
~ ~ 49 13 sD5443 68 to connect the sample loop 69 in series with the neon carrier gas stream. ~nalysis of this standard sample provides data establishing the normal function of the chromatograph. After the standard sample injection, the S sample valve 68 is reset and valve 88 is again opened to evacuate the sample loop 69. Valve 8~ th~n remains opened during the oil-ejection gas-extraction gas-compression process which will be described with refer~nce to FICURE 8.
Valve 88 closes just before the extracted sample is inject-ed into the chromatograph 18 for analysis. The timing sequence or these operations is shown in FIGURE 5.
Referring now to FIGURE 8, which is a schematic diagram of the pre~erred gas extraction device 1~ and related equip-ment, the method o gases extractions will now ble described.
In the preferred embodlment shown, the gas extraction is accomplished in a horizontally disposed gas cylinder 92 which contains an aluminum piston 94. With the piston in its rest position, as shown in FIGURE 8, the right side of chamber 92 ; is normally evacuated through normally open valve 112. With valve 88 opened, the chamber volume is approximately 700 cubic centimeters. The cylinder 92 is evacuated through valve 96 and 98 to a pressure of approximately twenty micro-meters of mercury. The pressur0 rise within the cylinder 92 from the extracted gas is measured with a silicon pressure transducer 52 and is employed to determine total dissolved gas content o-f the oil sample as was earller described with reference to FI~URE 4.
~Ater evacuation, the cylinder 92 is isolated rom the vacuum pump ~y closing valve 96. The oil sample (approxi-mately 180cc) from sample container 100 is then admitted ~ 5D5443 slowly by opening valve 10~ partially filling cylinder 92.
The inle-t oil flow is controlled by a metering needle valve 104. A normal period for introducin~ the oil sample is 8 to lO minutes. At the end of the sample period, valve 102 is closed, as shown in FIGUR~ 5~ The maximum permissible ~ime for the introduction of the oiI sample is 13.3 minutes in accordance with the timing sequence of the preferred embodiment. This variable period is indicated by the dotted line in FIGURE 5.
In the preferred embodiment, cylinder 92 is provided with a Teflon~lcoated stirring magnet 106 which is actuated by an external motor-driven bar magnet 108 to provide thorough liquid agitatian during the gas extraction sequence. At the comp:Letion of the gas extraction period a hold circuit is used to store a signal proportional to the pressure rise which has occurred. As earlier indicated this is subsequently displayed'on"display 22 as the total gas indication.
Valve 112 is then actuated to vent the rîght side of piston 92 to one atmosphere and force piston 94 over to the let-hand side of the cylinder, to a fixed final volume de-termined by piston stop 116. This reduces the cylinder volume to a smaller volume and compresses the extracted gas in-to a relatively small volume, approximately 15C. Shortly ater the compresslon stroke valve 8~ closes to isolate part of the extracted gas within the sample loop 69~ The sample valve 68 is then activated to inject the sample into the chromato-graph 18 as previously described.
After injection o the gas sample, valve 9'6 is opened ,and valve 98 is actuated to vent ~he left-hand side of the cylinder 92 to one atmosphere. Then valve 114 is opened to allow ~he oil to drain from the cylinder 920 After the oil drain is complete valve 112 is again opened to evacuate the righ~-hand side of the cylinder 92 so`that atmospheric pres-sure pushes piston 94 ~o its far right or rest position.
Sometime later, on svstem reset, valve 114 is closed and valve 98 is opened to evacuate the left-hand side of cylider 92.
FIGURE 9 shows a schematic diagram of the preferred oil sampling system which is utilized in the dissolved gas oil monitoring system of this invention. The oil sampling arrangement shown is designed to carry out the following functions:
1. Purge the oil sampling line to thè electrical apparatus, such as a transformer 10.
2. Withdra~ a fixed volume of oil samples from 1, or up to 4 electrical apparatus 10 for analysis.
3. Analyze an oil sample obtained manually, if -desired.
4. Discharge purged oil and sample oil to a waste oil-holding tank external of the equipment.
This system is designed to operate rom the head avail-able at the electrical apparatus and requires at least a 7 foot minimum oil head and atmospheric pressure. Por an installation to monitor a single transformer 10, a solenold valve 118 and a filter 120 must be installed at the transformer 10. Additionally, a small diameter metal tubing run 110 is connected between the filter 120 and the oil sample inlet manifold 121 of ~he dissolved gas, oil monitor-'ing device of this in~ention. Additionally, it is desirable that the length o line or run 110 be limited to approximately .
.
.~
.. . . . ~
~ 9:~3 sD5443 40 feet of 1/4 inch diame-ter copper tubing to provide a volume of less than 200cc of oil so that line 110 can be purged before each oil sample is wi~hdrawnO
Of course, it will be apparent that from 1 to 4 electri-cal apparatus can be connected to the inlet manifold 121 to provide analysis of the gas samples from each of the electri-cal apparatus, sequentially.
A second requirement which must be satis~ied for the preferred embodiment of the invention is that the sample arrangement be such that a minimum oiI flow rate of SOcc per minute is available ~rom ~he oil head of the transformer.
This will ensure transfer of a complete oil sample within the 4 minute time slot available for sampling, see FIGURE 5.
Since at lower temperatures large increases in oil viscosity can occur, which can great].y reduce the flow rate, where co~d temperatures are expected it will be necessary to provide auxiliary heat to the oil sampling line to maintaln its temperature at an adequately hlgh level.
The remote sampling valve 118 is in series with valve 122. Both of valves 118 and 122 are opened for either line , purge or sampling. From FIGURE 5 it can be seen that valve 118 is opened throughout the analysis cycle whi.le valve 122 is opened only for line purge or for sampling.
~or both line purge and oil sampling an oil sample container 100, in the form of a sampling syringe 124 with piston 126 is provided. During either sampling or purging oil flows into ~he 200cc sampling syringe 124 and continues until the syringe piston 126 bottoms on the adjustable stop 128. This limits either the line purge or the sample volume to a nominal 200cc. In the case of line purge, after val.ve .
: .
~t~ ~ ~ 3 122 closes, valve 130 opens to drain the syrin~e 124 by siphon action. Valve 130 then closes and valve 122 reopens for approximately 5 minutes to collect ~he oil sample, as sho~n in FIGURE 5. If a line purge is not desired, valve 130 can be deactivated to prevent the purge.
At the proper time in the sequence> as can be seen in FIGURE 5, valve 102 opens and atmospheric pressure acting on the syringe piston 126 forces the oil sample into ~he gas extraction chamber 92~ which is evacuated. Flow rate at this part of the cycle is controlled by the $hrottling valve 104.
This should be adjusted to provide slow oil injection which provides better extraction efficiency. However, flow must be fast enough to insure injection of the complete sample within the 13.3 minutes time slot which is available in the preferred embodiment. An 8-minute sample injection time has been found to represent a good operating point.
While one end of the stroke of syringe piston 126 is limited by the adjustable stop 128, the other end is con-trolled by a microswitch ~not shown) which i5 actuated to close valve 102 before the piston 126 reaches the end o the upward stroke in syringe 124. This insures that oil in the line between the syringe 124 and the gas extraction chamber 92 always has atmospheric pressure applied and cannot outgas until it enters the gas extractlon chamber 92.
As has been previously noted, a~ the -end of the gas extraction, the oil sample is discharged when valve 114 is opened.
; As can be seen from PIGUR~ 9, provisions for sampling o-f more than one tTansformer sequentially is made by means of the manifold 121 with the plurality of inlet ports as noted.
T~o outlet ports are also provided. In the preferred embodi-ment shown in FIGURE 9 the upper inlet port is fitted with a three-way valve 132 which will permit manual introduction of an oil sample for analysis and necessary preliminary line purging. The top outlet port is controlled by the shut-off valve 134 which permits initial purging of the sample lines on the manifold 121. After such initial purging the valve 134 is kept closed.
As will be understood each transformer to be sampled - 10 must be equipped with a filter such as 120 and a solenoid valve such as 118 and a sampling line. The various trans-formers to be sampled sequentlally will be controlled by the actuation of the ~arious valves 118 which are connected in parallel with valve 122.
Prom the above description, it is believed that there has been set forth a dissolved gas oil monitoring device which performs all of the desired features of the invention. While many of the circuits have been disclosed in blpck diagram form, it is believed clear that various solid-state devices 2a for actuation thereof are well know. Obviously~ various orms of micro processors could be used, utilizing known techniques, if desired. Also, the various sampling valves and gas ch~o-matograph has been set forth in what is, at presentJ the pre-ferred embodiment of this invention. However, it is believed that it will be well understood, by those skilled in the art, that various changes may be made in the various features of this invention without departing from the inventive concept as is set forth in the appended claims.
~ .
~ .
.. . . - ~ ~ . . .:
, ~ : . ... . .
:. .. . :
This system is designed to operate rom the head avail-able at the electrical apparatus and requires at least a 7 foot minimum oil head and atmospheric pressure. Por an installation to monitor a single transformer 10, a solenold valve 118 and a filter 120 must be installed at the transformer 10. Additionally, a small diameter metal tubing run 110 is connected between the filter 120 and the oil sample inlet manifold 121 of ~he dissolved gas, oil monitor-'ing device of this in~ention. Additionally, it is desirable that the length o line or run 110 be limited to approximately .
.
.~
.. . . . ~
~ 9:~3 sD5443 40 feet of 1/4 inch diame-ter copper tubing to provide a volume of less than 200cc of oil so that line 110 can be purged before each oil sample is wi~hdrawnO
Of course, it will be apparent that from 1 to 4 electri-cal apparatus can be connected to the inlet manifold 121 to provide analysis of the gas samples from each of the electri-cal apparatus, sequentially.
A second requirement which must be satis~ied for the preferred embodiment of the invention is that the sample arrangement be such that a minimum oiI flow rate of SOcc per minute is available ~rom ~he oil head of the transformer.
This will ensure transfer of a complete oil sample within the 4 minute time slot available for sampling, see FIGURE 5.
Since at lower temperatures large increases in oil viscosity can occur, which can great].y reduce the flow rate, where co~d temperatures are expected it will be necessary to provide auxiliary heat to the oil sampling line to maintaln its temperature at an adequately hlgh level.
The remote sampling valve 118 is in series with valve 122. Both of valves 118 and 122 are opened for either line , purge or sampling. From FIGURE 5 it can be seen that valve 118 is opened throughout the analysis cycle whi.le valve 122 is opened only for line purge or for sampling.
~or both line purge and oil sampling an oil sample container 100, in the form of a sampling syringe 124 with piston 126 is provided. During either sampling or purging oil flows into ~he 200cc sampling syringe 124 and continues until the syringe piston 126 bottoms on the adjustable stop 128. This limits either the line purge or the sample volume to a nominal 200cc. In the case of line purge, after val.ve .
: .
~t~ ~ ~ 3 122 closes, valve 130 opens to drain the syrin~e 124 by siphon action. Valve 130 then closes and valve 122 reopens for approximately 5 minutes to collect ~he oil sample, as sho~n in FIGURE 5. If a line purge is not desired, valve 130 can be deactivated to prevent the purge.
At the proper time in the sequence> as can be seen in FIGURE 5, valve 102 opens and atmospheric pressure acting on the syringe piston 126 forces the oil sample into ~he gas extraction chamber 92~ which is evacuated. Flow rate at this part of the cycle is controlled by the $hrottling valve 104.
This should be adjusted to provide slow oil injection which provides better extraction efficiency. However, flow must be fast enough to insure injection of the complete sample within the 13.3 minutes time slot which is available in the preferred embodiment. An 8-minute sample injection time has been found to represent a good operating point.
While one end of the stroke of syringe piston 126 is limited by the adjustable stop 128, the other end is con-trolled by a microswitch ~not shown) which i5 actuated to close valve 102 before the piston 126 reaches the end o the upward stroke in syringe 124. This insures that oil in the line between the syringe 124 and the gas extraction chamber 92 always has atmospheric pressure applied and cannot outgas until it enters the gas extractlon chamber 92.
As has been previously noted, a~ the -end of the gas extraction, the oil sample is discharged when valve 114 is opened.
; As can be seen from PIGUR~ 9, provisions for sampling o-f more than one tTansformer sequentially is made by means of the manifold 121 with the plurality of inlet ports as noted.
T~o outlet ports are also provided. In the preferred embodi-ment shown in FIGURE 9 the upper inlet port is fitted with a three-way valve 132 which will permit manual introduction of an oil sample for analysis and necessary preliminary line purging. The top outlet port is controlled by the shut-off valve 134 which permits initial purging of the sample lines on the manifold 121. After such initial purging the valve 134 is kept closed.
As will be understood each transformer to be sampled - 10 must be equipped with a filter such as 120 and a solenoid valve such as 118 and a sampling line. The various trans-formers to be sampled sequentlally will be controlled by the actuation of the ~arious valves 118 which are connected in parallel with valve 122.
Prom the above description, it is believed that there has been set forth a dissolved gas oil monitoring device which performs all of the desired features of the invention. While many of the circuits have been disclosed in blpck diagram form, it is believed clear that various solid-state devices 2a for actuation thereof are well know. Obviously~ various orms of micro processors could be used, utilizing known techniques, if desired. Also, the various sampling valves and gas ch~o-matograph has been set forth in what is, at presentJ the pre-ferred embodiment of this invention. However, it is believed that it will be well understood, by those skilled in the art, that various changes may be made in the various features of this invention without departing from the inventive concept as is set forth in the appended claims.
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:. .. . :
Claims (10)
1. A monitoring device for monitoring dissolved gases in the electrical insulating liquid of an electrical apparatus comprising:
a) valve means connected to an electrical apparatus to allow release of a portion of the electrical insulating liquid in such apparatus, b) a sample means connected to said valve for receiving a predetermined amount of electrical insulating liquid from the electrical apparatus, c) a gas extraction chamber connected to said sample means, d) means to evacuate said gas extraction chamber, e) means for moving said predetermined amount of liquid from said sample means to said gas extraction chamber, 1) said gas extraction chamber evacuating said liquid to extract a portion of gases dissolved in said liquid, f) a gas chromatograph for receiving said extracted gases and analyzing the constituent parts thereof, g) sample valve means between said gas extraction chamber and said gas chromatograph for injecting a predetermined quantity of extracted gases into said gas chromatograph, and h) recording means for recording the results of said gas chromatograph analysis of said extracted gases.
a) valve means connected to an electrical apparatus to allow release of a portion of the electrical insulating liquid in such apparatus, b) a sample means connected to said valve for receiving a predetermined amount of electrical insulating liquid from the electrical apparatus, c) a gas extraction chamber connected to said sample means, d) means to evacuate said gas extraction chamber, e) means for moving said predetermined amount of liquid from said sample means to said gas extraction chamber, 1) said gas extraction chamber evacuating said liquid to extract a portion of gases dissolved in said liquid, f) a gas chromatograph for receiving said extracted gases and analyzing the constituent parts thereof, g) sample valve means between said gas extraction chamber and said gas chromatograph for injecting a predetermined quantity of extracted gases into said gas chromatograph, and h) recording means for recording the results of said gas chromatograph analysis of said extracted gases.
2. A monitoring device as set forth in claim 1 in which said gas extraction chamber includes means for compressing said extracted gases to a predetermined volume.
3. A monitoring device as set forth in claim 1 in which a transducer is connected to said gas extraction chamber, said transducer providing a measurement of the total volume of said extracted gases.
4. A monitoring device as set forth in claim 1 in which a sample loop is connected between said gas extraction chamber and said sample valve, said sample loop receives a predetermined volume of extracted gases for injection by said sample valve.
5. A monitoring device as set forth in claim 1 in which said gas chromatograph includes a thermal conductivity detector and delay and separating columns, said delay and separating columns separating the constituent gases of interest in said extracted gases and said thermal conductivity detector detecting said constituent gases of interest.
6. A monitoring device as set forth in claim 5 in which neon gas is used as a carrier gas in said gas chromatograph.
7. A monitoring device as set forth in claim 1 in which means are connected to said sample means to discharge said predetermined amount of electrical insulating liquid, purging said sample means.
8. A monitoring device as set forth in claim 1 in which a manifold means is connected to said sample means, said manifold means having a plurality of inlet ports to allow a plurality of electrical apparatus to be connected to said sample means, for sequentially analyzing dissolved gases in each of said plurality of electrical apparatus.
9. A monitoring device as set forth in claim 8 in which said manifold means is provided with a separate inlet port to receive a sample of electrical insulating liquid to provide analysis of dissolved gases in said sample.
10. A monitoring device as set forth in claim 1 in which a standard gas of known composition is provided and means are provided to inject a sample of said standard gas
10. A monitoring device as set forth in claim 1 in which a standard gas of known composition is provided and means are provided to inject a sample of said standard gas
Claim 10 continued:
into said gas chromatograph to establish the proper functioning of said gas chromatograph.
into said gas chromatograph to establish the proper functioning of said gas chromatograph.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA286,799A CA1104913A (en) | 1977-09-15 | 1977-09-15 | Device for monitoring dissolved gases in electrical insulating liquids such as transformer oils |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA286,799A CA1104913A (en) | 1977-09-15 | 1977-09-15 | Device for monitoring dissolved gases in electrical insulating liquids such as transformer oils |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1104913A true CA1104913A (en) | 1981-07-14 |
Family
ID=4109540
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA286,799A Expired CA1104913A (en) | 1977-09-15 | 1977-09-15 | Device for monitoring dissolved gases in electrical insulating liquids such as transformer oils |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1104913A (en) |
Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN112147100A (en) * | 2020-10-14 | 2020-12-29 | 海南电网有限责任公司电力科学研究院 | Portable device for detecting furfural in transformer oil |
| CN112639464A (en) * | 2018-09-05 | 2021-04-09 | 赖茵豪森机械制造公司 | Analysis of gases dissolved in the insulating medium of a high-voltage instrument |
| CN115097056A (en) * | 2022-07-25 | 2022-09-23 | 广东电网有限责任公司佛山供电局 | Full-automatic degassing device for online monitoring of transformer oil chromatography and control method thereof |
| CN118067967A (en) * | 2024-02-27 | 2024-05-24 | 一通科技发展(广东)有限公司 | Transformer oil liquid on-line monitoring system and method and electronic equipment |
-
1977
- 1977-09-15 CA CA286,799A patent/CA1104913A/en not_active Expired
Cited By (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN112639464A (en) * | 2018-09-05 | 2021-04-09 | 赖茵豪森机械制造公司 | Analysis of gases dissolved in the insulating medium of a high-voltage instrument |
| CN112147100A (en) * | 2020-10-14 | 2020-12-29 | 海南电网有限责任公司电力科学研究院 | Portable device for detecting furfural in transformer oil |
| CN112147100B (en) * | 2020-10-14 | 2023-11-14 | 海南电网有限责任公司电力科学研究院 | Portable device for detecting furfural in transformer oil |
| CN115097056A (en) * | 2022-07-25 | 2022-09-23 | 广东电网有限责任公司佛山供电局 | Full-automatic degassing device for online monitoring of transformer oil chromatography and control method thereof |
| CN115097056B (en) * | 2022-07-25 | 2023-01-13 | 广东电网有限责任公司佛山供电局 | Full-automatic degassing device for online monitoring of transformer oil chromatography and control method thereof |
| CN118067967A (en) * | 2024-02-27 | 2024-05-24 | 一通科技发展(广东)有限公司 | Transformer oil liquid on-line monitoring system and method and electronic equipment |
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