CN86105996A

CN86105996A - High voltage digital megchma meter with self-selected measuring range

Info

Publication number: CN86105996A
Application number: CN86105996.4A
Authority: CN
Inventors: 张贻新; 王长富; 翟文敏
Original assignee: University of Science and Technology of China USTC
Current assignee: University of Science and Technology of China USTC
Priority date: 1986-09-03
Filing date: 1986-09-03
Publication date: 1988-03-16
Also published as: CN1005652B; JPS63139258A

Abstract

The invention belongs to the insulating of electric measurement of high pressure device for detecting performance, adopt pressure ratio meter principle, utilize two branch road sampling pressure ratio circuits, select for use the extensive integration module of double integration A/D conversion to constitute the V/R transducer, show tested resistance with numeral.But this device supplied by AC/DC electricity, the DC voltage source range is very wide, and high pressure can reach 15,000V, the accurately insulation resistance of detecting electric equipment and absorptance, it is 20M Ω-200 that degree of accuracy can reach 0.1% (± 1 word) measurement range, 000M Ω changes a little, can survey 1,000, more than the 000M Ω.This apparatus structure is simple, and debugging is convenient, and cost is lower, wide adaptability.

Description

The invention belongs to the pick-up unit of high-voltage electrical apparatus, insulating material

Detect the insulating property and the insulation absorptance of electrical equipment, cable and various materials at present, the tramegger that is adopted, megohmmeter or megger nearly all are to use the logolmeter principle, adopt magnetoelectricity series pointer-type reading.The U.S. wishes 3121 types and the 3122 type 5000V/100000M Ω trameggers that the upright company (KYORITSU) of 5000v/100000M Ω tramegger and Japan association that C Compaq (HIPORONICS) produces produces and all belongs to permanent-magnet moving coil instrument, and the latter has been introduced by Chinese Ningxia Electronic Instruments Plant and gone into operation.The readings of pointer type meters accuracy varies with each individual, and measuring error is bigger, uses very inconvenient, especially quite difficult to the absorptance measurement.By relevant rules: connect moment at high pressure, the instantaneous value R60 that measured respectively 60 seconds is an insulation resistance, and the ratio of the instantaneous value R15 of R60 and 15 seconds, promptly R60/R15 is defined as absorptance.With existing pointer instrument measurement insulation resistance and absorptance, at least need three people's close fit, harmoniously just can measure, if carelessness is arranged slightly, just may cause instrument to damage, and because factors influence such as timing, reading and scale be non-linear, the measuring error that causes is very big, can not reflect the true insulating property of measurand.

Inquiring into digital megger abroad in recent years, but generally all be to adopt the single sampling slip that is in series by measured object and reference resistance.On reference resistance, obtain sampling voltage, after the A/D conversion, again by Computing obtain a result (as JP59-5969), perhaps in single branch road, take out two voltages, utilize the method for double integrator (diclinic rate) A/D conversion to measure, two kinds of different dual slope integrating modes are arranged, can make digital ohmmeter or digital conductivity meter (as US 4,217,543).But owing to adopt single branch road sampling, integral voltage is directly obtained from measured object, be subjected to the restriction of A/D transducer or integrator incoming level, digital ohmmeter with the said method manufacturing, the voltage that is added on the measured object can only reach the three ten-day period of hot season to tens volt, can't measure the insulation resistance under the high pressure, and the highest measurement scope is only limited in the 20M Ω; For digital conductivity meter, by the same token, can't measure the insulation conductance under the high pressure conditions, and measurement result is not directly perceived, need do computing reciprocal.

At above-mentioned situation, task of the present invention is to improve the existing in prior technology deficiency, shows with numeral and accurately measures measured object insulation resistance and absorptance, and be suitable for high pressure and measure on a large scale, and a kind of new high resistant proving installation is provided.

Basic design of the present invention is to adopt two branch road pressure ratio meter principles.Constitute two branch road sampling pressure ratio circuits by two connection in series-parallel resistor networks and take a sample, obtain two sampling voltages respectively and carry out high resistance measurement through double integrator division V/R conversion, its measuring process is:

A. high direct voltage is put on two branch road sampling pressure ratio circuits, obtains benchmark sampling voltage Vp and tested sampling voltage Vx respectively, deliver to double integrator divider input end,

B. under clock signal control, in the time of determining benchmark sampling voltage (Vp) is carried out the forward integration, the clock number that passes through in this time is N1,

C. tested sampling voltage (Vx) is made reverse integral, the clock number that passes through in the time at this reverse integral is N2,

D. by the pressure ratio circuit, because of Rx＞＞Rs, said tested sampling voltage Vx and measured object resistance Rx are inversely proportional to, i.e. Rx ∞ 1/Vx.By double integrator as can be known, reverse integral gained clock counts N2 and tested voltage Vx is inversely proportional to, i.e. Vx ∞ 1/N2, therefore reverse integral gained clock is counted N2 and is directly proportional with measured object resistance Rx, being write as relational expression is Rx ∞ N2/N1Vp, finishes the V/R conversion, reaches the purpose of test measured object.

Above said pressure ratio meter principle, relative the remaining unchanged of middle node potential of promptly said two sampling slip R1+R2 and Rx+Rs eliminated power-supply fluctuation and ripple and disturbed, and improved stability.

For realizing the test of above-mentioned high-voltage insulating resistance, adopt following technical measures, make high voltage digital megchma meter with self-selected measuring range.This megohmmeter is by DC high-voltage power supply, input circuit, and control circuit, the V/R transducer, clock generator, output system constitutes.Wherein DC high-voltage power supply can provide 500V, 1000V, 2500V, 5000V, 10000V, different high pressure such as 15000V according to different requirement of measurand.Input circuit is made up of two branch road sampling pressure ratio circuits and active low-pass filter, from the pressure ratio sample circuit, obtain benchmark sampling voltage Vp and tested sampling voltage Vx, after wave filter is eliminated low-frequency ripple, more tested sampling voltage is added in the control circuit respectively.This control circuit comprises that automatic range selects circuit, logic with shift circuit and open control circuit.By selective circuit of measuring range according to tested sampling voltage size, provide the respective attenuation amount, be added in the logic with shift circuit by the relevant logical signal (" 0 " or " 1 ") of comparer output, the radix point that goes to control display according to the logic function of this circuit is shifted, and reaches range and automaticallyes switch.The tested voltage signal of while after the selective circuit of measuring range decay, one the road delivers to the reverse integral input end (Vr end) of V/R transducer, one the road delivers to and opens control circuit, this circuit is the non-steady-state oscillation circuit of being opened by tested voltage, three kinds of signals of main generation: (1) cycle is 15 seconds sampling holding signals, be 1 second its sample time, and the retention time is 14 seconds, and the sampling that this signal is added to the V/R transducer keeps end (R/ H); (2) enabling signal of timing circuit guarantees that measurement and timing are synchronous, realizes that each cycle of measuring accurately is 15 seconds; (3) acoustic signal of hummer made hummer send the once sound of prompting record every 15 seconds.From the benchmark sampling voltage of low-pass filter output, deliver to V/R transducer forward integration input end (INHI end) and carry out the double integrator division arithmetic.This V/R transducer is to select for use the extensive integration module of double integration A/D conversion (5G7135 or similar device) to constitute the double integrator divider.Reasonable circuit parameter, under sampling holding signal and clock signal controlling, the digital quantity of this divider output has promptly been represented the insulation resistance value of measured object, delivers to digital indicator through code translator and bit driver, reads the insulation resistance value of measured object intuitively.

The present invention has been completely free of the shortcoming of existing magnetoelectricity series pointer instrument and the deficiency of external existing digit instrument.Select domestic and international universal large scale integrated circuit for use, the low index advanced person of cost, measuring accuracy can reach 0.1%(± 1 word), measurement range, is changed a little and can be surveyed 1 between 000M Ω at 20M Ω-200,000, more than the 000M Ω, keep and acoustic signal, only need a people can accurately measure the insulation resistance value and the absorptance (R60/R15) of measured object owing to possess sampling.This megohmmeter is equipped with the supplied by AC/DC electricity system, be applicable to indoor and outdoor different test occasion and environment, DC high-voltage power supply can satisfy the test request of different rules, taking mobile radix point to carry out range automaticallyes switch, need not tested scope given and put (estimation), because two branch road pressure ratio samplings and active power filtering are lower to the DC high-voltage power supply requirement, have improved job stability.This megohmmeter is an insulating material, the widely used measurement mechanism of departments such as electrical equipment and Measuring and testing.

Describe embodiments of the invention in detail below in conjunction with accompanying drawing.Fig. 1 is a high-voltage digital megohmmeter general diagram, and 1 is DC high-voltage power supply among the figure, E wherein, and G, L are the external cabling terminal, " E " ground terminal, " G " shield terminal, " L " line terminal, measured object (Rx) is connected on E, between L.2 is two branch road sampling pressure ratio circuits, and 3,4 is active low-pass filter, 5 are automatic range selection circuit, 6 is the logic with shift circuit, and 7 for opening control circuit, and 8 is the V/R transducer, 9 is clock generator, 10 is bit driver, and 11 is code translator, and 12 is timing circuit, 13 is hummer, and 14 is digital indicator.

Fig. 2 is two branch road sampling pressure ratio circuits [2], by benchmark sampling slip [R1+R2] and tested sampling slip [Rx+Rs] resistor network that constitutes in parallel.Wherein constitute the benchmark sampling slip by fixed resistance R1 and R2 series connection, on node P and shielding end G(R2) between output reference sampling voltage Vp, constitute tested sampling slip by measured object (representing) and fixed resistance Rs series connection, on node (being line terminal L) and shielding end G(Rs with Rx) between export tested sampling voltage Vx.Then, two branch roads are connected between E-G, this pressure ratio circuit under high-pressure situations, must satisfy usually R1＞＞R2, Rx＞＞Rs.

Fig. 3 is active low-pass filter [3,4], is RC second-order low-pass filter network, mainly eliminates power network fluctuation and ripple and disturbs, and reduces the power supply cost, improves instrumentation stability.Because of two branch road samplings, have two groups of filtering circuits, wherein operational amplifier A 1 or A2 can select 5G7650(or ICL7650 for use).

Fig. 4 selects circuit [5] for automatic range, and wherein follower A3-A5 adopts 5G7650(or ICL7650), logic switch G0-G1 adopts CD4066(or C544), comparer A6-A7 adopts 5G14574(or MC14574).Adopt " 1403 " high precision energy gap power supply reference voltage of device as a comparison.Tested sampling voltage [Vx] by wave filter [3] output is added to selective circuit of measuring range [5] input end [Y point].If this tested sampling voltage [Vx] is lower than reference voltage, then comparer A6-A7 does not work, its output terminal DP1, and DP0 is logical zero, and switch G0-G1 disconnects, and measured signal is decay not.As with DP1, the DP0 logical signal is delivered in the logic with shift circuit [6], by the logic function of this circuit, determines DPR(the right of display [14]) radix point lights, and expression measured object range ability is very big.When the reference level of tested voltage [Vx] above comparer A7, then A7 is output as " 1 ", and G0 connects, and selects R9, the R10 parameter can make circuit provide the 20dB damping capacity, again behind logic with shift circuit [6], determine the DPM(intermediate point) to be lighted, the expression range reduces, and the rest may be inferred.

Fig. 5 is logic with shift circuit [6], mainly selects for use 5G4,081 four and door and 5G4,069 six not gates to make, and satisfies following logical relation:

DPL＝DP1·DP0

DPR＝ DP1· DP0

This circuit truth table is:

DP1 DP0	DPL DPM DPR
		0 0 0 1 1 0 1 1	0 0 1 0 1 0 0 1 0 1 0 0

Fig. 6 is V/R transducer [8], know by two branch road sampling pressure ratio circuits, tested sampling voltage [Vx] is inversely proportional to measured object resistance [Rx], for ease of direct-reading, tested sampling voltage [Vx] need be carried out division arithmetic, this function is finished by the V/R transducer, but, in electronic technology field, make the high-precision analog divider, cost is very expensive, for reducing cost of products, the present invention selects extensive integration module 5G7135(of the double integration A/D conversion of using as voltage table or 5G14433 for use, ICL7106,7126 etc.) constitute the double integrator divider, dexterously this integration module is done usually the signal input part (INHI) and the reference voltage terminal (Vr) of voltage table use and exchanged the use location, the signal input part (INHI) that is about to this module transforms benchmark sampling voltage [Vp] forward integration input end into, and the reference voltage terminal of this module (Vr) transforms tested sampling voltage [Vx] reverse integral input end into.Under clock signal control, the digital quantity of the last output of this V/R transducer directly reflects the insulation resistance value of measured object, finishes the division function of V/R conversion.

Fig. 7 is for opening control circuit [7], by the astable oscillator that tested sampled signal is opened, has only when measured object and high direct voltage all connect, measured signal just appears, by selective circuit of measuring range [5] output one enabling signal, through comparer A8, make logic switch G2 closure, this oscillatory circuit is just started working.This circuit can be by 5G7556(or ICM7556) dual time base circuit constitutes, exportable three kinds of control signals, the holding signal of promptly taking a sample, be 1 second its sample time, the retention time is the R/ H end that 14 seconds oscillator signal is delivered to V/R transducer [8]; Start timing circuit [12] simultaneously and pick up counting, provide time showing; This circuit also produces a sound signal simultaneously, uses for hummer [13], makes it send one time the sound every 15 seconds, as the signal of reminding record.Used timing circuit [12] can select for use LCL102 to constitute.The result of last test is read by display [14].

Enforcement of the present invention links up the same numeral by input and output point in each accompanying drawing, promptly constitutes high-voltage digital megohmmeter of the present invention.This device is 21 ℃ of environment temperatures, under humidity 70% condition, through metrological service's testing result such as following table:

Nominal value (M Ω)	Measured value (M Ω) 15S 30S 45S 60S
		20000 50000 100000	19630 19800 19750 19760 48210 48300 48310 48310 96880 98390 97680 97440

Claims

1, a kind of by DC high-voltage power supply [1], clock generator [9], the high voltage digital megchma meter with self-selected measuring range that output system constitutes, wherein DC high-voltage power supply can provide 500V, 1000V, 2500V, 5000V, 10000V, different high pressure such as 15000V; Output system comprises: bit driver [10], code translator [11], timing circuit [12], digital indicator [14], hummer [13], it is characterized in that this megohmmeter is provided with input circuit, control circuit and V/R transducer [8], said input circuit is made up of two branch road sampling pressure ratio circuits [2] and active low-pass filter [3,4], said control circuit comprises that automatic range selects circuit [5], logic with shift circuit [6] and open control circuit [7] formation.

2, megohmmeter according to claim 1 is characterized in that said V/R transducer [8] is to constitute with the extensive integration module of double integration A/D conversion.

3, as megohmmeter as described in the claim 2, it is characterized in that said double integrator integration module is that signal input part (INHI) and the reference voltage terminal (Vr) of doing the voltage table use are usually exchanged the use location, the signal input part (INHI) that is about to this module transforms benchmark sampling voltage [Vp] forward integration input end into, and the reference voltage terminal of this module (Vr) transforms tested sampling voltage [Vx] reverse integral input end into.

4, megohmmeter according to claim 1 is characterized in that said pair of branch road sampling pressure ratio circuit [2] is by benchmark sampling slip [R1+R2] and tested sampling slip [Rx+Rs] resistor network that constitutes in parallel.

5,, it is characterized in that constituting the benchmark sampling slip, hold on the G(R2 with shielding at node P by fixed resistance R1 and R2 series connection as megohmmeter as described in claim 3 or 4) between output reference sampling voltage Vp; Constitute tested sampling slip by measured object (representing) and fixed resistance Rs series connection, on node (being line scan pickup coil side L) and shielding end G(Rs with Rx) between export tested sampling voltage Vx.

6, as megohmmeter as described in the claim 1,4, it is characterized in that two branch road sampling pressure ratio circuits, must satisfy Rx＞＞Rs, R1＞＞R2.

7, as megohmmeter as described in the claim 5, it is characterized in that two branch road sampling pressure ratio circuits, must satisfy Rx＞＞Rs, R1＞＞R2.