Does the distance of the power distribution room affect the reading on the mechanical ammeter at the pump site?
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The ammeter was checked in the power distribution room, and its reading was within the normal range. However, the mechanical ammeter at the site showed a lower value. I would like to ask the experts: 1. Can the distance between the power distribution room and the location of the pumps affect the current reading at the site? (400-meter distance) ； 2. Will a small diameter of the cable affect the current readings during long-distance transmission? (I majored in engineering; please forgive me for asking such a basic question.)
Current transformers have a certain load-carrying capacity. If the circuit is long and has high resistance, this may cause the reading on the ammeter to decrease. If installation is necessary, the wires in the current circuit can be made thicker – for a distance of 400 meters, copper wires with a diameter of at least 4 mm2 should be used – in order to reduce the circuit resistance. This will result in more accurate readings.
The cables have already been wired, so replacing them with thicker wires is not a suitable approach. Are there any devices available to compensate for the loss in resistance?
First, use a stopwatch to measure the secondary current at the site, and check whether it matches the current reading on the meter there, in order to determine the accuracy of the meter. Secondly, if there is nothing wrong with the ammeter, the reason is as follows: the pump on site is located far away from the power distribution room, resulting in long cables; moreover, the model selected might be too small, which increases the resistance of the wiring and exceeds the load capacity of the current transformer, causing the reading on the ammeter at the site to be low. For projects up to 800 meters in length, I’ve used 4mm2 copper wire with no problems; you can give it a try.
400 meters should have an impact; we’ve seen this situation here. The reason is that the signal lines have resistance, and as the length of the signal lines increases, the impact becomes greater.
It has an impact; the solution is to determine the cross-sectional area of the wires appropriately based on the distance and the installation location of the current transformer, as well as the parameters of the transformer, in order to reduce the impedance value and improve the accuracy of the current measurement.
The ammeter in the distribution room shows a value significantly higher than that of the ammeter on site
If the cable has already been installed, try using a transformer with a higher load capacity; this will help overcome the losses caused by the long length of the cable and its high impedance.
But our wiring is already complete, so it’s not very practical to replace the wires
Is it connected in a single circuit? If it is in a single circuit, there is a problem with the ammeter on site; if not, it is normal for the ammeter on the distribution panel to show high readings.
To measure current in the distribution room, a clamp meter should be used; its accuracy is generally 1 level higher than that of on-site meters. 1. The on-site meters either have insufficient accuracy or poor quality. 2. The zero point of the on-site gauge is incorrect. Solutions: 1. Replace the on-site gauge; 2. Adjust the zero point of the on-site gauge
There is a huge difference between the clamp meters used in distribution rooms and the mechanical ammeters used on site; the difference is more than ten times
When high precision is not required, the simplest way to modify the on-site ammeter is to recalibrate the dial markings.
Actually, this is something that should be taken into consideration when selecting a design. For the current meters on site, I usually use 2 wires with a cross-sectional area of 1.5 square millimeters, along with the signal wires. As for the 400 meters you mentioned… . The display is small; you should refer to what was said on floor 9. A current transformer is essentially a small transformer, and it also has capacity specifications. Also, we now generally use /1A current transformers. DCS communication can also be used
Other comrades have already discussed a lot; I’ll add my two cents as well. A small CT capacity and excessive resistance in the secondary cable can cause inaccuracies in the current meter on site. If a CT with a secondary current of 1A is used, this problem is generally resolved.
There is definitely an impact, caused by various factors such as cable quality, distance, and transformers. It is recommended to first check whether there are any problems with the cable, and then consider other factors.