I have an equipment that measures the PF, it works fine on 100% , 50% load but start to work wrong on 20 % or less, and the manufacturer tells me that this is normal cause of the errors of the CT, with a accuracy class 0,5.. i´ll like to know if there´s some standard that talks about it, and what´s your opinion..... they says that measure the angle between the voltage and current... that´s why the error is so important.... please send me some link to the standard... and if you know the european standard..... i think i´m asking so much.
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how is the minimum current for measure in a CT
- Thread starter gaux
- Start date
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- #3
What type of error are you seeing, and how do you know it is wrong.
The current transformer requires excitation current. As the primary current decreases, this excitation current becomes a larger part of the total current, increasing the error.
Also, many of these probes have a small shunt resistor and sometimes a diode that is used to provide a voltage output to the measurement device. At very low currents these can be an issue.
If these are clamp-on style current probes, be sure to check the mating surfaces where the two jaws meet. Any gap will definitely cause an error. I like to clean these off with alcohol to make sure that there is good contact between the two halves of the CT.
The current transformer requires excitation current. As the primary current decreases, this excitation current becomes a larger part of the total current, increasing the error.
Also, many of these probes have a small shunt resistor and sometimes a diode that is used to provide a voltage output to the measurement device. At very low currents these can be an issue.
If these are clamp-on style current probes, be sure to check the mating surfaces where the two jaws meet. Any gap will definitely cause an error. I like to clean these off with alcohol to make sure that there is good contact between the two halves of the CT.
- Thread starter
- #5
Hi Gaux.
It will possible a long story.
Please give us more info
1. What is voltages
2. What is a your CT, class, connection erc.
3. What is a net company CT, class, etc.
4. Same for VT
5. What is your revenue meter, what is a net company revenue meter.
Difference 0.01 is .....not so big error.
What about kWh and kVarh difference.
Yep, we have some "boost" effect in the low current, <10% of load, but same error for net company.
Best Regards.
Slava
It will possible a long story.
Please give us more info
1. What is voltages
2. What is a your CT, class, connection erc.
3. What is a net company CT, class, etc.
4. Same for VT
5. What is your revenue meter, what is a net company revenue meter.
Difference 0.01 is .....not so big error.
What about kWh and kVarh difference.
Yep, we have some "boost" effect in the low current, <10% of load, but same error for net company.
Best Regards.
Slava
- Thread starter
- #8
- Thread starter
- #9
Hey Gaux.
Spanish isn't my srong side
.
But isn't same CT and VT.
Your side is 0.5S class, cogeneration side is 0.2S
Your side is 10-20/5A, company side is 50-100/5A.
0.01 for PF is nothing in this case.
Maybe your meas on the generator side?
Best Regards.
Slava
Spanish isn't my srong side
.But isn't same CT and VT.
Your side is 0.5S class, cogeneration side is 0.2S
Your side is 10-20/5A, company side is 50-100/5A.
0.01 for PF is nothing in this case.
Maybe your meas on the generator side?
Best Regards.
Slava
ameeraqeel
Electrical
Hi Gaux ,
You are right and your readings are correct for load more than 20% , I have the same with my equipments,If you use second CT with half ratio of installed one you will get correct results,this case is explained well by IEC conerning with p.f measuring equipment.
Ameer
You are right and your readings are correct for load more than 20% , I have the same with my equipments,If you use second CT with half ratio of installed one you will get correct results,this case is explained well by IEC conerning with p.f measuring equipment.
Ameer
- Thread starter
- #12
No, they use the 0,5s class current transformer, cause they mesasure with the same CT that the measuring device used by the net company....
I don´t know so much about currents, but i thought in a fast thinking that if we measure the same current and the same voltage, we´ll have to measure the same pf, but the manufacturer of the new device says that below 20% it´s no possible to measure with acuracy the pf cause of the error in the CT´s,
My other question is that voltage transformer have an error,does this error changes with voltage? I mean if I rise voltage or reduce, does the voltage transformer error change?
In other thinking, they use a CT 5A/5A, to take the signal from the ct (used by the net company) and send this signal with a 6mm^2 wire, with a distance of 30 metres, what do you think about this? could be a diference on the measuring? How much is admisible?
I don´t know so much about currents, but i thought in a fast thinking that if we measure the same current and the same voltage, we´ll have to measure the same pf, but the manufacturer of the new device says that below 20% it´s no possible to measure with acuracy the pf cause of the error in the CT´s,
My other question is that voltage transformer have an error,does this error changes with voltage? I mean if I rise voltage or reduce, does the voltage transformer error change?
In other thinking, they use a CT 5A/5A, to take the signal from the ct (used by the net company) and send this signal with a 6mm^2 wire, with a distance of 30 metres, what do you think about this? could be a diference on the measuring? How much is admisible?
- Thread starter
- #13
ameeraqeel
Electrical
Hi,
Which country you are from .
Ameer
Which country you are from .
Ameer
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- #15
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