Comparing two AC Currents and using the output to drive a alarm circuit.

@neo23-KisbGm • Oct 26, 2024

Oct 26, 2024

1.2K

I want to compare two AC currents . And if the difference between the two exceeds a certain limit it should give a output signal , to drive an alarm circuit. I can make the latter i.e the alarm circuit . But i do not know how to compare the AC Currents. Any ideas?

Note - The currents to be compared are as high as 120 Ampere.

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aarthivg

@aarthivg-HH344f • Feb 1, 2012

consider two currents i1 and i2. these currents can be given as input to a micro controller, difference in current can be found based on the coding. if the difference in current exceeds a certain value, it will drive the relay and energize the close coil of circuit breaker in order to give supply to the alarm circuit.
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Ramani Aswath

@ramani-VR4O43 • Feb 1, 2012

Try using two current transformers and compare the outputs.
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aarthivg

@aarthivg-HH344f • Feb 1, 2012

the secondary of current transformers is generally 1 amps or 5 amps, then we need a booster to boost the current rating.
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neo23

@neo23-KisbGm • Feb 1, 2012

can you name some devices which can compare ac currents? And yes i am using 2 ct s , plus i do not want to overburden them as they are already being used for metering and protection.
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neo23

@neo23-KisbGm • Feb 1, 2012

Please give ideas on comparing the ac currents , as this is the main part confusing me.
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aarthivg

@aarthivg-HH344f • Feb 1, 2012

i think, u can code such a way to compare two currents in microcontroller.
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Ramani Aswath

@ramani-VR4O43 • Feb 1, 2012

neo23
Please give ideas on comparing the ac currents , as this is the main part confusing me.
If you can have shunts on the neutral side of the loads, the two loads being compared can have a common ground. In which case the two shunt voltages can be compared. It should be possible to amplify the differential signal and use for control.
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neo23

@neo23-KisbGm • Feb 1, 2012

bioramani
If you can have shunts on the neutral side of the loads, the two loads being compared can have a common ground. In which case the two shunt voltages can be compared. It should be possible to amplify the differential signal and use for control.
Just like a differential relay works?
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neo23

@neo23-KisbGm • Feb 1, 2012

But i am afraid sir as i have my limits. The CT s are loaded on the first hand and i have to watch that too. Perhaps microcontroller method could be less power consuming.
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Ramani Aswath

@ramani-VR4O43 • Feb 1, 2012

neo23
But i am afraid sir as i have my limits. The CT s are loaded on the first hand and i have to watch that too. Perhaps microcontroller method could be less power consuming.
What is the load on the CTs? You may still be able to take out a small signal to asuitable op amp or comparator circuit. This should not add anything to the existing load on the CT.
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neo23

@neo23-KisbGm • Feb 1, 2012

Can the comparator work on AC or do i have to use an ADC in it?
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Ramani Aswath

@ramani-VR4O43 • Feb 1, 2012

neo23
Can the comparator work on AC or do i have to use an ADC in it?
If the two wave forms are in perfect phase it would work. It may be a better option to individually amplify the signal, rectify and compare.
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aarthivg

@aarthivg-HH344f • Feb 2, 2012

i do a similar project, when the ct current exceeds a certain value, this input is given to the micro controller to drive the relay.
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neo23

@neo23-KisbGm • Feb 2, 2012

aarthivg
i do a similar project, when the ct current exceeds a certain value, this input is given to the micro controller to drive the relay.
Are you experimenting on Ac Current or dc? and what are you using for comparing?
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aarthivg

@aarthivg-HH344f • Feb 2, 2012

ac only.
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neo23

@neo23-KisbGm • Feb 3, 2012

aarthivg
ac only.
But bro what exactly are you using for comparing? op amp ? Microcontroller? And are you using ADC to rectify the AC Currents?
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aarthivg

@aarthivg-HH344f • Feb 3, 2012

neo23
But bro what exactly are you using for comparing? op amp ? Microcontroller? And are you using ADC to rectify the AC Currents?
microcontroller and adc.
what "bro" stands for?
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Ramani Aswath

@ramani-VR4O43 • Feb 3, 2012

Brother
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Bionic

@bionic-y3kcfA • Feb 3, 2012

All you need to do is to connect the two different ac source to two different loads of the same magnitude, then calculate each separately and read off the excess ac current, then you can now compare them...
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aarthivg

@aarthivg-HH344f • Feb 3, 2012

Bionic
All you need to do is to connect the two different ac source to two different loads of the same magnitude, then calculate each separately and read off the excess ac current, then you can now compare them...
but this needs manual calculations?
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neo23

@neo23-KisbGm • Feb 4, 2012

bioramani
If the two wave forms are in perfect phase it would work. It may be a better option to individually amplify the signal, rectify and compare.
Bioramani sir , how about i use a null meter to see the difference in currents. I have seen null meter being used for to show the difference in two voltages. But i am not sure whether that would work out for 2 Currents.
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aarthivg

@aarthivg-HH344f • Feb 4, 2012

A null detector is a device built for maximum sensitivity to small voltages or currents. It is used in voltmeter circuits to indicate the absence of voltage between two points, thus indicating a condition of balance between an adjustable voltage source and the voltage being measured.
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Ramani Aswath

@ramani-VR4O43 • Feb 4, 2012

neo23
Bioramani sir , how about i use a null meter to see the difference in currents. I have seen null meter being used for to show the difference in two voltages. But i am not sure whether that would work out for 2 Currents.
If one terminal can be common you can do that without additional circuitry. Unless some sensitive info is involved and you cannot reveal data, we can advise better if we know the application, voltages involed, AC single /multiple phases and such details.
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Bionic

@bionic-y3kcfA • Feb 4, 2012

aarthivg
but this needs manual calculations?
yeaq that's what am saying you connect the two loads of same magnitude across the two ac read off the corresponding ac then do the calcutions that follow....
Or maybe you try using a potentiometer or you design a kechoff's circuit for it hope this helps?
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Ramani Aswath

@ramani-VR4O43 • Feb 7, 2012

An update. This component may help:
#-Link-Snipped-#

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