The electric energy meter with capacitor and resistor in series has the resistor burnt out after several years of use. Please help analyze it.

一沙一世

The electric energy meter with capacitor and resistor in series has the resistor burnt out after several years of use. Please help analyze it. [Copy link]

 

邀请：@maychang   @huo_hu   @freebsder   @吾妻思萌   参与回复

The RC step-down electric energy meter with capacitor and cement resistor in series has had the cement resistor burn out (cement collapsed) and the digital tube does not display after several years of use. Please help analyze the cause. Is it possible that the capacitor inside the electric energy meter and the inductor in the external electrical equipment form a parallel resonance, causing overcurrent in the cement resistor and causing high temperature to burn out the cement resistor? There is a motor for pumping water in the external equipment of this electric energy meter.

maychang

[Is it possible that the capacitor inside the energy meter and the inductor in the external electrical equipment formed a parallel resonance, causing overcurrent in the cement resistor, causing high temperature and burning of the cement resistor?]

Impossible. There are indeed many inductive-resistive devices connected to the AC power grid, but these inductors cannot reach the conditions for parallel resonance with your capacitors because the Q value is too low.

tagetage

How many resistors were found to be broken? One? Or many?

一沙一世

tagetage posted on 2023-4-5 08:46 How many resistors were found to be broken? 1? ? Or many? ?

Batch Problems

qwqwqw2088

From the production principle of cement resistor,

Its interior is nickel-chromium resistance wire or constantan resistance wire, wound on an alkaline-free heat-resistant ceramic sheet.

Long-term operation at high current and high voltage will damage the

The author's working environment is that there is a motor for pumping water in the equipment connected to the electric energy meter. After using it for a few years,,,,

Also normal

The key to the problem is that in recent years,

tagetage

An electric energy meter with resistance-capacitance step-down function, in which a capacitor and a cement resistor are connected in series. Can the resistance and capacitance parts of the circuit be posted?

After using it for a few years, -----What are the outdoor working conditions like? Is it humid? ? ? .

This is how the cement resistor breaks down. Have you opened the cement resistor to take a look? ???

Is it just the cement resistor that is broken. Or is it the capacitor that is broken as well? ? ?

一沙一世

maychang posted on 2023-4-5 08:03 [Is it possible that the capacitor inside the energy meter and the inductor in the external electrical equipment formed a parallel resonance, causing overcurrent in the cement resistor and causing high temperature...

Will the inductance of the pumping motor resonate with the capacitance of the meter? Another question is that the meter is installed in a greenhouse, where the humidity is very high in the morning and the temperature is very high at noon in summer. What effect will this environment have on the cement resistance?

一沙一世

tagetage posted on 2023-4-5 08:46 How many resistors were found to be broken? 1? ? Or many? ?

Will the inductance of the pumping motor resonate with the capacitance of the meter? Another question is that the meter is installed in a greenhouse, where the humidity is very high in the morning and the temperature is very high at noon in summer. What effect will this environment have on the cement resistance?

tagetage

Will the inductance in the pumping motor resonate with the capacitance in the meter? -----No, it won't.

Another question is, this energy meter is installed in a greenhouse, especially in the morning, the humidity is very high, and the temperature is very high at noon in summer, what effect will this environment have on the cement resistor? -----This is why I asked you whether the environment is humid or not. Cement resistors are mainly afraid of humidity and high temperature. You have both of these conditions. When the cement resistor is working, it is like a small heating furnace, which will dry the internal moisture. When it is not working, it will slowly absorb moisture. Of course, the process is very slow. After several years of slow corrosion, the internal moisture absorbed is more. The cement resistor will heat up when working, and the internal moisture cannot evaporate quickly, forming pressure, which will "explode" the resistor.

tagetage

The humidity in the plastic greenhouse is very high, sometimes even over 90%. Electronic equipment in the plastic greenhouse needs to be moisture-proof and even waterproof, such as sealed casing, three-proof paint, glue filling and other moisture-proof treatments, otherwise the electronic equipment will be damaged by moisture after a period of time.

maychang

Yishayishi published on 2023-4-5 10:02 Will the inductance in this pumping motor resonate with the capacitor in the meter? Another question is that this energy meter is installed in a greenhouse, especially...

[Will the inductance in this pumping motor resonate with the capacitance in the electric meter? ]

Won't.

Note that when talking about resonance in "Circuit" or "Electrical Engineering", there are only three components: inductance, capacitance and resistance. In addition to your electric meter and water pumping motor, your power grid is connected in parallel with many electrical devices, such as incandescent lamps, fluorescent lamps, etc. These electrical devices are connected in parallel with your water pumping motor. It is precisely because of the parallel connection of these devices that the capacitor in your electric meter and the water pumping motor cannot resonate.

maychang

Yishayishi published on 2023-4-5 10:02 Will the inductance in this pumping motor resonate with the capacitor in the meter? Another question is that this energy meter is installed in a greenhouse, especially...

[Another question is, this energy meter is installed in a greenhouse, where the humidity is very high, especially in the morning, and the temperature is very high at noon in summer. What effect will this environment have on the cement resistor? ]

As long as people can stay there and the fruits and vegetables grown in the greenhouse are not steamed, your cement resistor will not be damaged.

maychang

Yishayishi published on 2023-4-5 10:02 Will the inductance in this pumping motor resonate with the capacitor in the meter? Another question is that this energy meter is installed in a greenhouse, especially...

[Another question is, this energy meter is installed in a greenhouse, where the humidity is very high, especially in the morning, and the temperature is very high at noon in summer. What effect will this environment have on the cement resistor? ]

I guess your capacitor was damaged first (short circuit), and then the cement resistor was damaged. Sometimes the damage of the capacitor cannot be seen from the surface. You can know it by removing the capacitor and measuring it.

maychang

Yishayishi published on 2023-4-5 10:02 Will the inductance in this pumping motor resonate with the capacitor in the meter? Another question is that this energy meter is installed in a greenhouse, especially...

This kind of capacitor and resistor series circuit often has a high-value resistor in parallel at both ends of the capacitor. If this high-value resistor is damaged (short-circuited), your cement resistor will also be damaged.

一沙一世

qwqwqw2088 posted on 2023-4-5 09:42 From the principle of cement resistor production, its internal is nickel-chromium resistor wire or constantan resistor wire, wound on alkaline-free heat-resistant ceramic sheet for long-term work in large...

It is said that the cement resistors started to burn out after one year. The cement resistors were so hot that the nearby shells were deformed.

一沙一世

tagetage posted on 2023-4-5 09:58 Capacitor and cement resistor in series, resistance-capacitance step-down electric energy meter,-----Can the resistor and capacitor circuit be posted? It has been used for several years...

The greenhouse where vegetables are grown must be very humid in the morning. If you have been to the countryside, you will see many water droplets on the grass leaves on the roadside in the morning, and you will understand how humid it is. Capacitors can also crack.

tagetage

Yishayishi published on 2023-4-5 14:45 The greenhouse where vegetables are grown must be very humid in the morning. If you have been to the countryside, you will see many water droplets on the grass leaves on the roadside in the morning, and you will understand...

I know the environment of the vegetable greenhouse very well. When you use resistors and capacitors to reduce voltage, are the capacitors very close to the resistors? When the resistors are working, they generate heat, and the CBB capacitors are also heated? ? ?

一沙一世

tagetage posted on 2023-4-5 15:21 I am very clear about the environment of the vegetable greenhouse. When you use resistors and capacitors to reduce voltage, are the capacitors very close to the resistors? When the resistors are working, they generate heat, which also heats up the CBB capacitors...

Not very close, probably a few centimeters away.

damiaa

There is an article on Doc88.com titled "Analysis and Countermeasures for Causes of Continuous Burning of Electric Energy Metering Equipment" http://www.doc88.com/p-59116940045622.html. I don't know if it is similar to the situation you mentioned.

chunyang

Although cement resistors have good temperature resistance, they are limited. The correct way to deal with this is to test products from the same batch or with the same design and components, and check the temperature rise of the resistors by comparing them with the device manual.

If this happens, it is certain that there is a problem with component selection or thermal design.