Inspection of factory current transformers and resolution of abnormalities

 

Current transformers need to be inspected regularly when in use so that faults can be discovered and handled in a timely manner. Generally, the fault of the transformer is diagnosed through some abnormal phenomena, such as overheating of the equipment, smoke inside the equipment, odor inside the equipment, etc. At the same time, these abnormalities are checked and handled one by one to ensure the normal operation of the equipment.

 

 

1. What items should be checked during the regular inspection of current transformers ? How to correctly judge whether there is a fault and how to deal with it. What are the common faults of current transformers?

 

 

 

Transformer

 

Common faults of current transformers are:

 

1. The secondary side of the current transformer is open

 

2. The temperature of the current transformer is too high during operation

 

3. There is smoke or odor inside the current transformer during operation

 

4. The screws of the current transformer are loose. There is a short circuit between turns or layers.

 

5. The current transformer is charging and discharging internally. The sound is abnormal or sparks are formed between the wires and the case.

 

6. The oil-filled current transformer leaks seriously or the oil level is too low.

 

1. Usually faults are identified and handled based on actual abnormal conditions. If you use a temperature test wax piece to check the temperature, judge the open circuit based on the sound emitted by the device and the indication value of the needle.

 

 

 

Generally, it should be judged and solved based on the abnormal situation that occurs. For example, use a temperature test wax piece to check the heating status. Use the sound and meter indication value to determine whether there is a lead. Once a fault is seen, repair or replace it immediately. The normal inspection items are as follows:

 

 

1. Check whether there is any over-temperature problem or abnormal odor

 

2. Check the condition of the insulation layer on time

 

3. Check whether the three-phase indication value of the ammeter is within the allowable standard and whether it is operating under load.

 

4. Is the porcelain part clean and complete? Is there any damage or discharge?

 

5. Is the oil level of the oil-type current transformer within the normal range? Is there any oil leakage?

 

 

 

2. Why is it not allowed to open the secondary side of the current transformer? What are the risks after opening the circuit?

 

 

1. Generally, the magnitude of the primary current of a current transformer is irrelevant to the magnitude of the current of the secondary load.

 

 

 

When the current transformer is operating normally, because the secondary impedance is not large (close to the short-circuit fault condition), most of the magnetic lines of force caused by the primary current are compensated by the secondary current, the total magnetic flux density is not large, and the secondary potential is not high. But when the secondary circuit is open, the secondary current is equal to zero, and the primary current completely becomes the excitation current, which will generate a very high potential in the secondary coil (the peak value can reach several thousand volts or even higher), which will not only damage the secondary insulation, but also threaten personal safety. In addition, the excessive expansion of the core magnetic flux density may also cause the core to overheat and be destroyed.

 

 

3. Damage caused by long-term overload of current transformer

 

Once the current transformer is overloaded for a long time, the core magnetic flux density will reach saturation, which will increase the deviation of the current transformer and make the meter reading incorrect, making it difficult to grasp the actual load or operating conditions. In addition, due to the increase in magnetic flux density, the core and secondary coil will overheat and the insulation layer will be damaged.

 

4. Symptoms and solutions of open circuit on the secondary side of current transformer:

 

 

 

When the secondary side of the current transformer is open, it is often accompanied by the following conditions:

 

1. The ammeter and power factor meter show zero, the meter does not rotate, and a buzzing sound is heard.

 

2. If the current transformer itself makes a squeaking discharge sound or other abnormal noise, the terminal block is likely to be burnt.

 

 

 

When the current transformer is open-circuited, the potential difference caused is related to the size of the primary current. Therefore, when solving the open-circuit fault of the current transformer, the load must be reduced or made zero, and then the insulation tool must be used to solve it, and the corresponding protective equipment must be used when solving it.

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