I hope this message finds you well. I am currently working on an engineering project involving the design of a high AC load current monitoring device for a distribution transformer. The transformer has a capacity of 37.5 kVA and a rated current of 163 Amperes, and the device's goal is to monitor the real-time load current accurately and safely.
I came across a [link to the resource/method/device] and was wondering if this approach is feasible for my application. I am planning to used a ct current sensor with a ratio of 200/5Amps. Has anyone here tried a similar method, or would you recommend a different approach or specific equipment for such a setup?
I would greatly appreciate your insights, suggestions, or any relevant experiences. Thank you for your time and support!
That link is for a current transformer type sensor. There are also Hall effect sensors for contactless high amperage current measurement.
Disclaimer: I have no direct experience here but if you are working on the secondary side of this, you don't have any concerns about arcing etc at 230 volts.
the ESP32-4-Channel-Mains-Current-Sensor module contains the circuits to offset the AC current to suit the ADC input which is positive DC - a lot simpler than using a UNO and building external circuits
remember the SCT-013 reads the instantaneous current - you have to sample over several cycles to calculate the RMS value
Secondary open circuit condition should NEVER be allowed as the voltage there can go to many thousands of volts.
Hense the use of shorting straps and terminations always supplied.
Certainly a current transformer (sensor type) should always have a burden resistor across the output to protect against high voltages which could otherwise occur if there was an open circuit.
Does this mean the method can be used for the project, assuming the burden resistor is correctly matched to the 200/5A current transformer sensor I am using?
Yes, my team and I will be connecting the sensor to the secondary side of the distribution transformer, and will be using blynk for the development of the app that will view the recorded and real-time reading of the device.
if you get a clamp without a burden resistor and connect a suitable resistor to match the 200amp load it should work
have you got a current clamp meter? I find one useful for checking results
Which current transformer type are you using (part number) ? If 200/5A means a secondary output of 5A it sounds rather high and would require quite a low value burden resistor.
If, however, the current transformer you use is a voltage output type then it will already have a built-in burden resistor and it will specify its output in terms of millivolts per amp or similar. You simply have to ensure that at 200A it delivers less than 3.3 or 5 volts depending on your Arduino board.
Looks like I have to go through an age verification procedure to see that video.
Anyway, he has said that he's working on the secondary side of the thing and probably well away from it.
I would also guess that this is an electrical engineering student project where the safety issues have already been addressed. After all, hobby electronics such as Arduino is unlikely to be used as production components in a electrical power distribution infrastructure.
reminds me of an accident where I was working some ago
an engineer was replacing a 400amp fuse to an induction motor
the power had not been switched off and the fuse exploded
The CT sensor we plan to use is a general product widely available in the online market. Based on my understanding and research, the sensor has a maximum primary current rating of 200A and outputs 5A on the secondary side. Additionally, this is an ampere-output type CT sensor, not the voltage-output type, meaning it does not have a built-in burden resistor.
Regarding the installation of the device, my team has coordinated with the local power provider, who will handle the installation process.
As was previously pointed out to you, you cannot use real-time recording and reading from the device. You must average over several cycles or you will get zero current some times and maximum current at other times.
OK. A few cycles to obtain the peak to peak voltage for the RMS calculation but at 50Hz these would be 20ms so although not instantaneous, it could be "near real time".
Sorry but you are wrong.
Go back and start again.
Current transformers, as I said earlier, must be either shorted on the secondary or have meters firmly connected to stop voltage rise to thousands of volts.
How would I go about it? The 200/5 is a pretty common CT. I have used up to 1000/5 CTs but here nor there. Companies like Omega Engineering and Simpson Electric Co. make digital panel meters with a 0 to 5 Amp AC input range. These meters also have available scaling so you can scale the meter for your shunt and desired readout. These meters also can provide an analog DC output proportional to the AC input. That is where I would be looking for a start. Next if you want to data log the current I would be thinking about using a data logger. The analog Vout of my panel meter to my data logger. You make no mention of budget constraints? No mention of desired accuracy?
Next and another solution is the use of a Current Transducer rather than a CT. The cost is higher but you have close to a turn key solution. I have used and like Current Transducers from CR Magnetics.
I am also assuming you are measuring a nice clean sine wave or all bets are off.
I also strongly suggest you read about, as mentioned, the open circuit Vout of a CT. This is lengthy but I suggest you read it.
To calculate the high voltage output of a current transformer when its secondary circuit is open, you need to consider the transformer ratio (turns ratio) and the primary current, as the open circuit causes the core to saturate, leading to a significantly elevated secondary voltage; however, this calculation is often complex and requires specific details about the CT design, including its core material and saturation characteristics, making it more practical to consult the manufacturer's data for accurate estimations.
Key points to remember:
Danger of open circuit:
Never intentionally open the secondary circuit of a current transformer as it can produce very high voltages, potentially causing damage to the CT or electrical shock hazards.
Basic formula:
While not always accurate due to saturation effects, a basic calculation can be done using the transformer equation: V_secondary = (N_secondary / N_primary) * V_primary.
Saturation effect:
When the secondary is open, the core of the CT can become highly saturated, leading to a much higher induced voltage than the calculated value based on the turns ratio alone.
Factors affecting the open circuit voltage:
Current transformer ratio (CT ratio): The ratio between the primary current and the secondary current.
Primary current magnitude: Higher primary currents will result in a higher open circuit voltage.
Core material properties: The type of core material used in the CT affects its saturation point and thus the potential open circuit voltage.
Secondary winding resistance: Although small, the resistance of the secondary winding can slightly limit the open circuit voltage.
Important considerations:
Consult manufacturer data:
For accurate estimations of the open circuit voltage, always refer to the manufacturer's specifications for the specific current transformer model.
Safety precautions:
When working with current transformers, always ensure the secondary circuit is properly connected to a load to avoid potential high voltage situations.
