CN209250581U - A kind of PT secondary side neutral point multipoint earthing sensed current signal amplifying circuit - Google Patents
A kind of PT secondary side neutral point multipoint earthing sensed current signal amplifying circuit Download PDFInfo
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- CN209250581U CN209250581U CN201821604868.2U CN201821604868U CN209250581U CN 209250581 U CN209250581 U CN 209250581U CN 201821604868 U CN201821604868 U CN 201821604868U CN 209250581 U CN209250581 U CN 209250581U
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Abstract
The utility model discloses a kind of PT secondary side neutral point multipoint earthing sensed current signal amplifying circuits, belong to electric power network field.The amplifying circuit are as follows: two signal transmssion lines of Shielded Twisted Pair are connected as input with the non-inverting input terminal of the first order operational amplifier U1A and U1B；The inverting input terminal of U1A is connected by R2 with output end, and the inverting input terminal of U1B is connected by R3 with output end, is connected between U1A and the inverting input terminal of U1B by R1；The output end of U1A is connected by R6 with the non-inverting input terminal of U2A, and the output end of U1B is connected by R7 with the inverting input terminal of U2A, and the non-inverting input terminal of U2A is connected by R8 with output end, and the inverting input terminal of U2A is connected to the ground by R9；The output end of U1A is connected by R4 with the non-inverting input terminal of U2B, and the output end of U1B is connected by R5 with the non-inverting input terminal of U2B, and the inverting input terminal of U2B is connected with output end, and the output end of U2B is connected with the shielded layer of Shielded Twisted Pair.The utility model can effectively inhibit common mode interference, improve sampling signal-to-noise ratio.
Description
Technical field
The utility model relates to a kind of PT secondary side neutral point multipoint earthing sensed current signal amplifying circuits.
Background technique
Electric system countermeasure is grounded after all PT ground lines are all in parallel on one point, prevents in a substation
Potential difference leads to relay protection malfunction.If multipoint earthing occurs for the PT secondary side neutral conductor, at this time in case of ground fault, meeting
There is very big electric current to flow through earth mat, this short circuit current can form very important voltage between two grounding points, so as to
It can cause protection misoperation.
The generation of false protection in order to prevent needs to detect PT secondary side neutral point multipoint earth faults.Normally
In the case of, close to zero, after two points ground fault occurs, which can become larger the electric current on each PT secondary side ground line, pass through
The curent change is detected, discovery ground connection is abnormal, and issues alarm signal.However this current signal is very small, is easy to be passed by signal
Bring common-mode signal is interfered during defeated, influences signal measurement.
Utility model content
In view of this, the purpose of the utility model is to provide a kind of PT secondary side neutral point multipoint earthing sensed current signals
Amplifying circuit is able to solve the problem of current sampling signal is influenced measurement result by common mode interference.
The purpose of this utility model is achieved through the following technical solutions:
A kind of PT secondary side neutral point multipoint earthing sensed current signal amplifying circuit, the amplifying circuit are as follows: shielding multiple twin
Two signal transmssion lines of line are connected as input with the non-inverting input terminal of the first order operational amplifier U1A and U1B；
The inverting input terminal of U1A is connected by R2 with output end, and the inverting input terminal of U1B is connected by R3 with output end,
It is connected between U1A and the inverting input terminal of U1B by R1；The output end of U1A is connected by R6 with the non-inverting input terminal of U2A, U1B
Output end be connected with the inverting input terminal of U2A by R7, the non-inverting input terminal of U2A passes through R8 and is connected with output end, and U2A's is anti-
Phase input terminal is connected to the ground by R9；The output end of U1A is connected by R4 with the non-inverting input terminal of U2B, and the output end of U1B passes through
R5 is connected with the non-inverting input terminal of U2B, and the inverting input terminal of U2B is connected with output end, the output end of U2B and Shielded Twisted Pair
Shielded layer is connected；Output of the output end of U2A as differential amplifier circuit.
Further, the amplifying circuit further include pincerlike sensor, acquisition terminal, stand in oscillograph and shielded layer；
The output end of the amplifying circuit is connected with pincerlike sensor, what the pincer sensor was sampled by mutual inductance
Current signal is transferred to acquisition terminal by one section of Shielded Twisted Pair, and acquisition terminal passes through signal transmssion line again and is connected to record in station
Wave device, the shielded layer are in parallel with signal transmssion line.
Further, the signal transmssion line rated current is 4~20mA.
Further, the signal transmssion line is V1 and V2, shielded layer VCM；Resistance R10 and R11 are connected between V1 and V2,
R10 and R11 neutral earthing；
Current signal becomes voltage signal by R10 and R11, then accesses the non-inverting input terminal of U1A and U1B, guarantees to put
Big circuit has high input impedance to input signal；R1, R2, R3 form negative feedback network, obtain:
HaveI.e. Differential Input after the first order U1A and U1B by amplifyingTimes；
Difference output VO1-VO2 is converted Single-end output by the differential amplifier circuit that U2A and R6, R7, R8 and R9 are constituted, and enables
R6=R7=R, R8=R9=R':
Output VO is only exaggerated difference mode signal V1-V2, then there is very high rejection ability, i.e. common mode inhibition for common-mode signal
It is very higher than CMRR (Common Mode Rejection Ratio)；By adjusting R1, R2, R3, R6, R7, R8 and R9 resistance value just
It is able to achieve different amplification factors.
Further, if the shielded layer VCM of the signal transmssion line is grounded, with the increase of frequency, common-mode rejection ratio CMRR
Be gradually reduced, two of twisted pair between signal transmssion line and shielded layer there are parasitic capacitance, when existing between V1, V2 and VCM
When common mode pressure difference, due to the difference of parasitic capacitance size, different pressure drops is generated on signal transmssion line, is formed a difference and is missed
Difference signal causes CMRR to decline；
If the shielded layer VCM of the signal transmssion line is earth-free, the common-mode voltage of V1 and V2 are calculated, is madeCommon mode pressure difference is just not present in this way between V1, V2 and VCM, the decline of high frequency CMRR will not be caused, from
And improve signal-to-noise ratio, i.e.,
Further, the first order operational amplifier U1A and U1B model OPA1652AIDR.
The beneficial effects of the utility model are: the utility model proposes extraction common-mode signal and with signal transmission shielding it is double
The shielded layer of twisted wire is connected, and can effectively inhibit common mode interference, improves sampling signal-to-noise ratio.
Other advantages, target and feature of the utility model will be explained in the following description to a certain extent
It states, and to a certain extent, based on will be apparent to those skilled in the art to investigating hereafter, or
Person can be instructed from the practice of the utility model.The target of the utility model and other advantages can be said by following
Bright book and claims are achieved and obtained.
Detailed description of the invention
It is practical to this below in conjunction with attached drawing in order to keep the purpose of this utility model, technical solution and advantage clearer
It is novel to be described in further detail, in which:
Fig. 1 is Tthe utility model system structural schematic diagram；
Fig. 2 is the circuit diagram of the utility model embodiment.
Specific embodiment
Hereinafter reference will be made to the drawings, and the preferred embodiment of the utility model is described in detail.It should be appreciated that preferably real
Example is applied only for illustrating the utility model, rather than in order to limit the protection scope of the utility model.
As shown in Figure 1, Shielded Twisted Pair two signal transmssion lines as input, with first order operational amplifier U1A and
The non-inverting input terminal of U1B is connected.The inverting input terminal of U1A is connected by R2 with output end, the inverting input terminal of U1B pass through R3 and
Output end is connected, and is connected between U1A and the inverting input terminal of U1B by R1.The output end of U1A is same mutually defeated by R6 and U2A's
Enter end to be connected, the output end of U1B is connected by R7 with the inverting input terminal of U2A, and the non-inverting input terminal of U2A passes through R8 and output end
It is connected, the inverting input terminal of U2A is connected to the ground by R9.The output end of U1A is connected by R4 with the non-inverting input terminal of U2B, U1B
Output end be connected with the non-inverting input terminal of U2B by R5, the inverting input terminal of U2B is connected with output end, the output end of U2B and
The shielded layer of Shielded Twisted Pair is connected.Output of the output end of U2A as differential amplifier circuit.
The current signal that pincerlike sensor is sampled by mutual inductance is transferred to acquisition terminal by one section of Shielded Twisted Pair,
Due to there is a distance between pincerlike sensor and acquisition terminal, signal can bring common mode interference in transmission process, because
The design of this amplifier needs filtering common mode as far as possible to interfere.
The utility model realizes that PT secondary side neutral point multipoint earthing detects electric current using operational amplifier and resistance capacitance
Common mode interference is effectively reduced in signal amplification circuit, improves signal-to-noise ratio.
As shown in Fig. 2, V1 and V2 are signal transmssion lines, VCM is shielded layer.Current signal becomes voltage by R10 and R11
Then signal accesses the non-inverting input terminal of U1A and U1B, guarantee that amplifying circuit has high input impedance to input signal.R1,
R2, R3 form negative feedback network, can be obtained:
So:Differential Input after the first order U1A and U1B by amplifying
?Times.
Difference output VO1-VO2 is converted Single-end output by the differential amplifier circuit that U2A and R6, R7, R8 and R9 are constituted, and enables
R6=R7=R, R8=R9=R':
From above formula it can be seen that output VO is only exaggerated difference mode signal V1-V2, then there is very high inhibition for common-mode signal
Ability, i.e. common-mode rejection ratio CMRR are very high.By adjusting R1, R2, R3, R6, R7, R8 and R9 resistance value can realize it is different
Amplification factor.
In being normally applied, the shielded layer VCM of signal transmssion line can be grounded, with the increase of frequency, common-mode rejection ratio
CMRR can be gradually reduced, the reason is that two of twisted pair between signal transmssion line and shielded layer there are parasitic capacitance, as V1, V2 and
There are when common mode pressure difference between VCM, due to the difference of parasitic capacitance size, different pressure drops is generated on the transmission line, forms one
A differential error signal, causes CMRR to decline.
Shown in Fig. 2, shielded layer is not directly grounded, but calculates the common-mode voltage of V1 and V2, so thatCommon mode pressure difference is just not present in this way between V1, V2 and VCM, the decline of high frequency CMRR will not be caused, from
And improve signal-to-noise ratio.
The case study on implementation of the utility model makees amplifier and several resistance capacitances using two panels OPA1652AIDR, in reality
Circuit application in, technical staff can need to select suitable amplifier and electricity according to the bandwidth and amplification factor of amplifying circuit
Resistance.
Finally, it is stated that above embodiments are merely intended for describing the technical solutions of the present application, but not for limiting the present application, although ginseng
The utility model is described in detail according to preferred embodiment, those skilled in the art should understand that, it can be to this
The technical solution of utility model is modified or replaced equivalently, should all without departing from the objective and range of the technical program
Cover in the scope of the claims of the utility model.
Claims (3)
1. a kind of PT secondary side neutral point multipoint earthing sensed current signal amplifying circuit, it is characterised in that: the amplifying circuit are as follows:
Two signal transmssion lines of Shielded Twisted Pair are as input, with first order operational amplifier U1A and first order operational amplifier U1B
Non-inverting input terminal be connected；
The inverting input terminal of first order operational amplifier U1A is connected by resistance R2 with output end, first order operational amplifier U1B
Inverting input terminal be connected with output end by resistance R3, first order operational amplifier U1A and first order operational amplifier U1B's
It is connected between inverting input terminal by resistance R1；The output end of first order operational amplifier U1A is transported by resistance R6 and the second level
The non-inverting input terminal for calculating amplifier U2A is connected, and the output end of first order operational amplifier U1B passes through resistance R7 and second level operation
The inverting input terminal of amplifier U2A is connected, and the non-inverting input terminal of second level operational amplifier U2A passes through resistance R8 and output end phase
Even, the inverting input terminal of second level operational amplifier U2A is connected to the ground by resistance R9；First order operational amplifier U1A's is defeated
Outlet is connected by resistance R4 with the non-inverting input terminal of second level operational amplifier U2B, the output of first order operational amplifier U1B
End is connected by resistance R5 with the non-inverting input terminal of second level operational amplifier U2B, and the reverse phase of second level operational amplifier U2B is defeated
Enter end to be connected with output end, the output end of second level operational amplifier U2B is connected with the shielded layer of Shielded Twisted Pair；Second level fortune
Calculate output of the output end of amplifier U2A as differential amplifier circuit.
2. a kind of PT secondary side neutral point multipoint earthing sensed current signal amplifying circuit according to claim 1, special
Sign is: the amplifying circuit further include pincerlike sensor, acquisition terminal, stand in oscillograph and shielded layer；
The output end of the amplifying circuit is connected with pincerlike sensor, the electric current that the pincer sensor is sampled by mutual inductance
Signal is transferred to acquisition terminal by one section of Shielded Twisted Pair, and acquisition terminal passes through signal transmssion line again and is connected to recording in station
Device, the shielded layer are in parallel with signal transmssion line.
3. a kind of PT secondary side neutral point multipoint earthing sensed current signal amplifying circuit according to claim 2, special
Sign is: the signal transmssion line rated current is 4~20mA.
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| Application Number | Priority Date | Filing Date | Title |
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| CN201821604868.2U CN209250581U (en) | 2018-09-29 | 2018-09-29 | A kind of PT secondary side neutral point multipoint earthing sensed current signal amplifying circuit |
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| CN201821604868.2U CN209250581U (en) | 2018-09-29 | 2018-09-29 | A kind of PT secondary side neutral point multipoint earthing sensed current signal amplifying circuit |
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Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN109067375A (en) * | 2018-09-29 | 2018-12-21 | 贵州电网有限责任公司 | A kind of PT secondary side neutral point multipoint earthing sensed current signal amplifying circuit |
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Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN109067375A (en) * | 2018-09-29 | 2018-12-21 | 贵州电网有限责任公司 | A kind of PT secondary side neutral point multipoint earthing sensed current signal amplifying circuit |
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