I need help with a current transformer diagram

[cadpoint]

081204-2001 EST

iwire:

I glanced thru your references. I believe this instrument works as I have suggested. Basically as three independent single phase meters and with the ability to sum the independent power measurements to obtain a total power reading.

...
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Now the coils come with a correction factor, as manufactured, I believe based on One or a muliplier AKA also called a "correction factor". I've got real proof here. Sorry not a photo hound, and nothing to display, as I speak. But the coil has a it's own ID as to how well it will work, or read current, as to reading anything the coil will be based on its own effieiency. Is there some correction factors that the meter summarizes ?

Frankly I'm not agreement with your statement but in respects to what you might have implied so be it!

 

[gar]

081204-2131 EST

cadpoint:

I would expect that you will have a correction factor associated with each individual current transformer for high accuracy applications. I did not look at the details of the gage in question, but it has to have scaling factors for each input and that is how the correction factor would be included. They may even have a specific parameter where you would enter the correction factor separate from the ratio.

Just by the size and shape of the box and the functions performed we know that some means is provided to electronically perform the equivalent of the instantaneous multiplication of current and voltage. One possibility is the use of a Hall device for each channel (phase or line if that term is more meaningful). A Hall device provides a small output voltage proportional to the current thru the device times the magnetic field applied. The voltage can supply the current and the measured current can supply the magnetic field.

.

 

[gar]

081205-0909 EST

If you look at the single phase circuit in
http://www.sea.siemens.com/pmt/docs/installs/9200IG.pdf
you will see the unsed channel current input shorted, and the voltage input connected to neutral.

This supports my point that there are three independent single phase channels with summation of the channel outputs for total power and energy.

There should be no need to connect the voltage input for a channel to anything if the current input for that channel is shorted except to make the voltage reading 0 on the unused channel.

In iwire's troubleshooting situation just shorting the current inputs should be sufficient. This probably really isn't needed because the data from each individual channel can be displayed, their term is phase measurement. In the manual under phase measurement they show it set for current measurement and one phase has a negative current. This probably means reverse power flow for that phase.

iwire if you select phase measurement and power display what do each of the phases read? Are the readings inconsistent with what you expect?

Also note that within this instrument you can program to invert individually any of the voltage of current inputs without any rewiring.

.

 

[weressl]

Mismatched devices?

Mismatched devices?

Here are the CTs being used.

H681x-V Install

Your problem may be that these are current TRANSDUCERS not current TRANSFORMERS. These won't be suitable to be used with the Siemens 9200 Series power meter.

Page 13

Current Input Specifications
Connector Type Ring or split-ring, or bare wire.
Wire 14 to 12 AWG (2.1 mm2 to 3.3 mm2)
Inputs I1, I2, I3
Rated Inputs 10 A RMS (+ 20% maximum, 300 V RMS to ground)
Compliance Installation category III (Distribution). Pollution degree 2
Overload 120 A RMS for 1 second, non-recurring
Dielectric Withstand 3000 V RMS, for 1 minute
Starting Current 0.005 A RMS
Burden 0.05 VA (typical) @ 5 A RMS
Current Transformers
Compliance UL3111-1; and IEC 61010-1, Pollution Degree 2, Overvoltage Category III
Primary CT Rating Equal to current rating of the power feed protection device.
Secondary CT Burden Capacity > 3VA​

H6810, H6811, H6812
1 VAC and 0.333 VAC Current Transducers
Output at Rated Current 0.333 or 1 VAC

 

[gar]

081205-1233 EST

weressl:

You have certainly identified a major problem.

Siemens requires 10 A for full scale and I calculate their input resistance for current at 0.002 ohms from their spec of 0.05 VA at 5 A. I doubt that the current transducer has anything like a 10 A short circuit output.

At 10 A input to the Siemens current input terminals the voltage across the terminals will 20 MV.

If the current transducer had an output short circuit current of 100 MA, and that may be a high value, then maximum input to Siemens would be 0.002 * 0.1 = 0.000,2 V and that is 1/100 of full scale.

.

 

[hillbilly1]

Here is some info about the meter itself if anyone is interested. :smile:

Siemens 9200 Installation & Basic Setup Instructions

9200 Power Meter Installation & Operation Guide

I've seen these same type of meters by Telemanque...Telemaniqe.... the heck with it, Square D (probably made by the same company, just with Siemens or Square D labels) If the meter is not set up correctly, you will get false readings also. These type require you to set the CT ratio in the meter along with voltage (PT), system type (Wye, Delta, ect.) The Ct polarity can also be flipped in the programming without having to physically do it.

 

[weressl]

Fundamental, not just major problem.

Fundamental, not just major problem.

081205-1233 EST

weressl:

You have certainly identified a major problem.

Siemens requires 10 A for full scale and I calculate their input resistance for current at 0.002 ohms from their spec of 0.05 VA at 5 A. I doubt that the current transducer has anything like a 10 A short circuit output.

At 10 A input to the Siemens current input terminals the voltage across the terminals will 20 MV.

If the current transducer had an output short circuit current of 100 MA, and that may be a high value, then maximum input to Siemens would be 0.002 * 0.1 = 0.000,2 V and that is 1/100 of full scale.

.

I think it isn't just a 'major' problem, but fundamental

Page 19:
Configurable Settings
String Description Range (Values) Default
Ct2 CT2 (Secondary) 1 to (65.53 x 1000 LED) 5

Siemens is looking for a standard 5A secondary CT, but it has the range to accomodate 1A and up to 10A can be used as well.

The voltage value is practicly immaterial, as various CT's with different burden will produce different voltage output and the scaling does not take that into consdieration.

 

[weressl]

081204-1757 EST

steve66:

What does "The CT's measure the total current" mean? Are you saying that if I have 3 Amprobes in place of the current transformers that the sum of these three readings is "total current"? If not what does "total current" mean?

To measure average power of a load I need the average of the product of the instantaneous voltage across the load and its associated instantaneous current.

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You can't conenct CT's in series and get any emaningful reading out of them. You can connect them parallel, but the diferent phase angles will produce invalid totals.

 

[gar]

081205-1412 EST

weressl:

Relative to my post on the question of "total current" I was trying to find out from steve66 what he meant. Thus, if I put 3 Amprobe meters on the system, one on each hot conductor, use my eyes to read each of these meters, no interconnection of the meters, write down the values, and sum these three readings, then is this what he meant by "total current". I have no idea what "total current" means.

Yes, I am aware that in current transformer mode that putting the outputs in series produces no useful results. These are essentially current sources when loaded with a sufficiently low load resistance so that the core is not saturated.


The voltage at the input of the Siemens current inputs is always going to saturate at 20 MV and they also expect 10 MV at 5 A current as the nominal full scale. 20 MV will be saturation of the A/D converter. It also appears that resolution is either 1 part in 4096 or 2048 of the 20 MV value. There is always a fixed 0.002 ohm shunt resistor at each current input. The 10 MV input can be scaled to produce any desired display value within the adjustment range of the appropriate parameter. It appears they use a 16 bit word for storing this scale factor plus decimal point selection.

My point was that the current transducer probably has no chance of producing anything close to amperes into a 0.002 ohm load. And thus not much input voltage, and not much of a reading.

If these current transducers are actually what is connected to the Siemens instrument, then if there is known reasonable current thru one of the transducers, then a voltmeter measurement across the input terminals of Siemens should read near zero. If the transducer is disconnected from Siemens, then something between 0 and 1 V AC should appear across the transducer output. However, the transducer output leads should not be removed unless one is absolutely certain that this is a voltage output transducer vs a current transformer.

.

 

[weressl]

081205-1412 EST

weressl:

Relative to my post on the question of "total current" I was trying to find out from steve66 what he meant. Thus, if I put 3 Amprobe meters on the system, one on each hot conductor, use my eyes to read each of these meters, no interconnection of the meters, write down the values, and sum these three readings, then is this what he meant by "total current". I have no idea what "total current" means.

Yes, I am aware that in current transformer mode that putting the outputs in series produces no useful results. These are essentially current sources when loaded with a sufficiently low load resistance so that the core is not saturated.


The voltage at the input of the Siemens current inputs is always going to saturate at 20 MV and they also expect 10 MV at 5 A current as the nominal full scale. 20 MV will be saturation of the A/D converter. It also appears that resolution is either 1 part in 4096 or 2048 of the 20 MV value. There is always a fixed 0.002 ohm shunt resistor at each current input. The 10 MV input can be scaled to produce any desired display value within the adjustment range of the appropriate parameter. It appears they use a 16 bit word for storing this scale factor plus decimal point selection.

My point was that the current transducer probably has no chance of producing anything close to amperes into a 0.002 ohm load. And thus not much input voltage, and not much of a reading.

If these current transducers are actually what is connected to the Siemens instrument, then if there is known reasonable current thru one of the transducers, then a voltmeter measurement across the input terminals of Siemens should read near zero. If the transducer is disconnected from Siemens, then something between 0 and 1 V AC should appear across the transducer output. However, the transducer output leads should not be removed unless one is absolutely certain that this is a voltage output transducer vs a current transformer.

.

I think you are missing the main point is that Siemens requires current TRANSFORMERS and not TRANSDUCERS.

I don't know where you get your information on the information that the Siemens input uses 20MV as the FS input measurement. They measure CURRENT. No conversion is necessary like 4-20mA into a 0-10VDC measurement.

 

[richxtlc]

I think that there is some confusion as to what total current is, it is not the sum of the currents in each phase, it is the current in an individual phase. When measuring power the watt meter multiplies the current times the voltage in each phase taking into account the phase angle between the current and voltage in that phase, then sums the total for each phase. The sqrt of 3 may be factored in depending on whether the voltage is p-p or p-n.

in answer to the question about connecting the cts in series, this is used for measuring zero-sequence current in a protective relay circuit.

 

[gar]

081205-1540 EST

weressl:

In the area of electronic instrumentation there are very few ways to directly measure current. Therefore it is reasonable to assume that a low resistance shunt is used to provide a means to measure current. This is no different than what is done with 50 MV shunts for DC current measurement. From the data in the Siemens specifications I worked backwards from current and their burden value to determine resistance for the shunt. In my post of 1233 today I included that information --- their spec of 0.05 VA at 5 A. This occurs at a voltage of 0.01 V and thus at a maximum input current of 10 A we get 0.02 V.

I am well aware that Siemens requires current transformers or a transducer that can provide the required amount of current. I see no reason for a transducer manufacturer to make a high current output device, and thus this device requires a convention current transformer. I have no argument with this.

Since the title of the thread was "current transformer" my earlier comments were based on that information. I never bothered to assume a non-transformer was being used and I did not pay attention to iwire's reference to the part number of the device. You solved the problem by knowing it was not a transformer or by looking at the reference. That was very important.

.

 

[gar]

081205-1602 EST

richxtlc:

What kind of wattmeter are you describing?

For a description of how an electrodynamometer movement works see
"Basic Electrical Measurements" by Melville B. Stout, 1950, Prentice-Hall, page 442 and that page on wattmeters also references p 418.

Quoting from Stout
" --- the torque depends upon e x i. If e and i vary in time, the torque also varies, and if the variations are rapid, the moving coil cannot follow them but takes up a position so that the control spring torque equals the average value of the torque produced by the electromagnetic action. ---- "

Thus, this type of meter measures the instantaneous product of the voltage and current, and averages that to indicate the average power. This device does not know anything about power factor. It just directly measures power. It will measure DC power. Somewhere between DC and 60 Hz it is not very useful because the needle will move around. The lowest useful AC frequency is a function of the mechanical time constant of the movement.

Why would you describe the current in one wire (phase) as "total current"? Why not just "current" or "line current"?

Unless there is a clear definition of terms and how devices work it is hard to communicate.

.

 

[weressl]

081205-1540 EST

weressl:

In the area of electronic instrumentation there are very few ways to directly measure current. Therefore it is reasonable to assume that a low resistance shunt is used to provide a means to measure current. This is no different than what is done with 50 MV shunts for DC current measurement. From the data in the Siemens specifications I worked backwards from current and their burden value to determine resistance for the shunt. In my post of 1233 today I included that information --- their spec of 0.05 VA at 5 A. This occurs at a voltage of 0.01 V and thus at a maximum input current of 10 A we get 0.02 V.

I am well aware that Siemens requires current transformers or a transducer that can provide the required amount of current. I see no reason for a transducer manufacturer to make a high current output device, and thus this device requires a convention current transformer. I have no argument with this.

Since the title of the thread was "current transformer" my earlier comments were based on that information. I never bothered to assume a non-transformer was being used and I did not pay attention to iwire's reference to the part number of the device. You solved the problem by knowing it was not a transformer or by looking at the reference. That was very important.

.

The burden data was given as "typical" for the 0.05VA it has nothing to do with the measurement method. In the same fashion as in 4-20mA loops the internal resistance is given for each device and your loop ?driver? is capable to support so many Ohms of total resistance before the accuracy and repeatability starts to go south, but the internal resistances vary, even between like devices based on the design of the circuit they need to drive. Transformers and transmitters and transducers are all different animals and can not be used interchangeably. The installation manual clearly indicates that the required input device is a current transducer that complies with specific IEC and UL standards and requirements. Those are not applicable to transducers.

I do NOT know what method is used to measure the current, hall-effect is the most common nowadays, but I do not believe that your conclusion offered above is correct.

Regardless, the meat of the issue is that Bob was using the wrong devices in conjunction with the meters and the inconsistent and wrong wiring may even further confused the issue. The base of the problem is to get the right 5A secondary current transformers and then to wire them as it is shown in the manual carefully observing CT polarity on both the primary AND secondary sides.

 

[iwire]

Regardless, the meat of the issue is that Bob was using the wrong devices in conjunction with the meters and the inconsistent and wrong wiring may even further confused the issue.

Keep in mind Bob did not choose any of the equipment. :smile:

That said I think you have hit the main problem. For that I owe you a debt of gratitude. I thank you.

Coworkers of mine did the original wiring between the CTs and the meters but they have been consistently being told they wired it wrong because it is not working as expected.

Since that time twice I have been sent to meet with the meter people and twice they had me randomly moving the CTs onto different phases which is both difficult and seemed quite unprofessional.

The base of the problem is to get the right 5A secondary current transformers and then to wire them as it is shown in the manual carefully observing CT polarity on both the primary AND secondary sides

That seems to be the right move.

From what you have seen is there no chance that the Siemens meter can be ordered with an option for these transducers?

I would really like not to eat crow in front of the customer.


I thank all that have been responding, you all have added to my knowledge of metering.

 

[weressl]

Keep in mind Bob did not choose any of the equipment. :smile:

That was very clear from your post. If I recall correctly you wrote that the Siemens engineer specified and created the drawings?

That said I think you have hit the main problem. For that I owe you a debt of gratitude. I thank you.

You are more than welcome. I should have stated: Bob is dealing with a system where the wrong input devices were specified and the situation further deteriorated by miswiring. This is where this forum shines!

Coworkers of mine did the original wiring between the CTs and the meters but they have been consistently being told they wired it wrong because it is not working as expected.

Since that time twice I have been sent to meet with the meter people and twice they had me randomly moving the CTs onto different phases which is both difficult and seemed quite unprofessional.

Yep. At one time I had a guy come to service some old Parajust drives. He kept swapping boards and the boards kept blowing after he left. They charged for each blown board, until I discovered it. (The guy would just come in, unsupervised, and deal directly with production people on our end who did not know any better.) These 'meter' people could be just like trained monkeys and only know how to set up the network and scaling and interface, but clueless when it comes to the measurement side. It could be that the whole thing WAS wired up properly, but some people may have 'heard' that polarity can be a problem and started swapping wires to see if that fixes the problem, only to screw it up even worse.

That seems to be the right move.

From what you have seen is there no chance that the Siemens meter can be ordered with an option for these transducers?

I would really like not to eat crow in front of the customer.

I thank all that have been responding, you all have added to my knowledge of metering.

Bob, from the manual you have posted, it is clear that the meter is designed for XXX/5A current transformers. Contact me directly via PM if you want me to review some documents, I would be more than glad to do it.

 

[richxtlc]

I was describing a digital wattmeter, shown in the attached diagram
View attachment 2591

 

[gar]

081205-1941 EST

richxtlc:

My guess is that in this circuit many simultaneous samples of the two inputs are obtained, maybe 256 to 1024 per cycle. Probably starting at the positive zero crossing of the voltage channel an accumulator is zeroed. For one full cycle, until the next positive zero crossing, each sample pair would be multiplied together, this product would be added to the accumulator, and at the end of the cycle with appropriate scaling the average power for that cycle is obtained. Further averaging might be done, or more cycles might be included in the first average. This might relate to the display update rate.

This is simply calculating the instantaneous power, v*i, and averaging it. The same as the electrodynamometer, except using a digital signal processor.

.

 

[Cold Fusion]

(cut)From what you have seen is there no chance that the Siemens meter can be ordered with an option for these transducers?

I would really like not to eat crow in front of the customer.


I thank all that have been responding, you all have added to my knowledge of metering.

I've seen similar instruments with rogowski coil (high impedance) inputs. Ask them how do you check the model number against the option list? Innocent enough question.

Besides, crow isn't so bad. I've found that eating it warm helps alot.:smile: However, I don't think I have ever found anybody that makes the magnitude and quanity of mistakes that I do. So maybe I just have more practice

cf

 

[iwire]

Bob is dealing with a system where the wrong input devices were specified and the situation further deteriorated by miswiring. This is where this forum shines!

I agree on all three points.

It could be that the whole thing WAS wired up properly, but some people may have 'heard' that polarity can be a problem and started swapping wires to see if that fixes the problem, only to screw it up even worse.

I think that may be 90% of the issue, on my first trip out to the site I did find a CT facing the wrong direction and one mislabeling issue.