Solution for measuring voltage of three phase supply

[lats]

3 phase voltage formulas

ianp the circuit of peak detector which u suggested is giving wrong voltage (almost double) on 150hz ac sine wave input signal.please let me know how to correct it.

 

[IanP]

three phase voltages

Ianp, the peak detector circuit is amazing. It's working out damn perfectly, although i'm using OP07 instead of LM353 (it isn't available in my area).

What has happened since then?
I am not aware of any problems with that circuit if based on LF353 (or similar) ..
Bias current:
OP7 -->nA
LF353 -->pA
Maybe you should increase the value of the 0.47µF cap and decrease the value of 10MΩ resistor ..

Regards,
IanP

 

[lats]

tree phase voltage formulas

instead of feeding voltage directly from power line ,m feeding voltage to it through a UPS unit . a readymade voltmeter and a multimeter both are showing 203 volts AC ,but this circuit shows 436 volts.my ad and microcontroller section is perfect and voltage divider section too is perfect,but peak detector circuit is showing error at the output. i sholud be getting voltage at around 1.1volts DC at peak detector output but now its showing something around 2.08 volts dc. i think the UPS unit isnt providing full sinewave and that too not at 50 hz. how can i make this peak detector a generalized one.

sorry for disturbing u again. i tried changing the values of capacitor and resistor and even the opamp which u said,but still not done...

 

[IanP]

three phase voltage measurement

Try to test peak detector with dc voltage <--> peak voltage ..
Apply 0-5Vdc to input (pin3) and you should read the same dc voltage at the output (pin7) ..

Regards,
IanP

 

[lats]

3 phase ac voltage measurement

Actually Ianp what i've found is the circuit is working fine for sine wave but if the waveform changes the value disturbs.How can i make a generalized one? is there a circuit which could give me a DC RMS voltage propotional to AC input voltage instead of peak detector (which gives me ac peak level dc equal voltage output)?

Thanks.

 

[IanP]

three phase voltage formulas

There are special ICs which convert RMS to DC ..
One of them is the LTC1966 ( https://www.linear.com/pc/downloadDocument.do?navId=H0,C1,C1154,C1086,D4563 ) ..
Maybe you should go that way ..

Regards,
IanP

 

[lats]

measurement of phase to phase voltage

Thanks Ianp for replying till now. I was almost done with my project when i was asked for 3-phase 3 wire input. I think what i have designed is a 3-phase 4-wire system. i'm being asked how'll the system work in a 3-phase 3-wire situation cause for phase to phase measurement we have done the formula technique ({(Va+Vb)/2}*√3) and not the hardware way.

Can u please guide me what should i do to make the system both compatible for 3-phase 4-wire as well as 3-phase 3-wire.

Thanks a lot.

 

[IanP]

measurement three phase voltage

In the 3-wire configuration (delta) you can artificially create neutral by connecting three resistors in a star configutation - the centre point will be new N(eutral) which, for measurement purposes, can be used in similar way as the forth wire in 3-pahase system with Neutral ..

Regards,
IanP

 

[lats]

three phase voltage current formulas

thanks. that's a brillant idea. today i'll try out for the same. for my system, which is measuring from 0-1000 volts, I think three resistors each of 10Kohm will do. right?

i found this link can it help in some way to decide the values of the three resistors.
**broken link removed**

 

[IanP]

voltage drop formula in three phase

10kΩ may be to small as you need to watch out for the heat generated in them ..
In this case you might consider two sets of resistors: one, for voltages below 100V, and in this case 10kΩ/2W will be probably the right choice, and the second set for voltages >100V --> 100kΩ or something like that ..

Regards,
IanP

 

[lats]

phase voltage

actually the system can't be differentiated between 0-100 volts and 100-1000v cause it's bieng used to measure unknown voltages. if i use only 100kohm resistor won't that help.

 

[IanP]

20w three-phase

100kΩ should work well for the whole range, but, still, keep in mind the heat ..

W24: https://www.welwyn-tt.com/pdf/datasheet/W20.PDF
For 1000V you may need to connect two 50kΩ in series ..

Regards,
IanP

 

[randell_xtian]

3 phase ac voltage output picture

hi...

can you guyz help me with this, my current transformer has a ratio of 30/5A and i used a voltage divider to detect its output... the R1(4.9K) and R2(1K). the output of the divider is connected to the microcontroller so that i can read what would be the output of the CT.

question, thus may value of resistor is correct for reading a CT for that ratio? can you guyz give me some information regarding computation of CT being read.

attached is the block diagram of my designed...thanks guyz...

best regards,
chris

 

[lats]

measuring 3 phase system using 2 cts

you'll have to regulate it to DC then feed to ADC

 

[randell_xtian]

3 phase voltages equations

hi thanks for the reply...

how can i rectify the signal if its very small..the value that i read via voltmeter is in between mV to uV. any suggestion?

best regards,
chris