Installation Precautions and Troubleshooting of Control Transformer

In the machinery industry, almost every machine tool equipment needs to use a control transformer. It is often used as a local lighting power supply, signal lamp or indicator power supply, and as a control circuit power supply in electrical equipment. However, when in use, you may encounter the problem of the control transformer being burned out. What is the cause? In fact, the reasons that cause the control transformer to burn out are nothing more than the following:

1. The control transformer is overloaded and the transformer is used, resulting in excessive temperature rise, which has exceeded the temperature resistance level of the insulating material, thus burning the transformer.
2. The inter-turn insulation of the original secondary coil is damaged or aging, and inter-turn short-circuit occurs, and local overheating causes burnout.
3. The welding part of the lead wire is welded, and the contact resistance is large, which causes the local current density to be too large, and even the wire can be blown.
4. If the core has threaded bolts, the bolts are insulated from the core at least on one side. Otherwise, if a magnetic short circuit is caused, the bolt will be burnt red.

Normally, the reasons that lead to the burning of the control transformer are basically the above four types. After understanding these 4 factors, you can prevent the control transformer from burning out when you use it with a little attention.

Countermeasures to control transformer burnout:

1. In view of the control transformer being burned out due to overload, it is required to replace with a larger capacity control transformer. The rated power of the applied control transformer must be greater than that of the driven electrical appliance.
2. The reason of the circuit failure causes the low-voltage control circuit to be short-circuited so that the secondary coil current of the control transformer was too large, which exceeded the rated current of the transformer and burned the machine tool control transformer. In this regard, a current limit fuse can be added in front of the transformer to protect it.
3. It is usually necessary to check the insulation of the line. When the insulation of the control transformer is found to be damaged or aging, the transformer should be replaced in time to avoid leakage and short circuit.
4. Check whether the special part of the mechanical vehicle is jammed to avoid over-current.

The installation precautions of transformer installation are generally divided into the following five points:

1. Short circuit between phases in the transformer, short circuit between turns or short circuit between winding and iron core; oil level drops or oil leakage;
2. The protection of power transformers generally includes main body gas protection, pressure release protection, and temperature protection;
3. Poor contact of tap switch or poor wire welding
   It can protect various faults in the transformer tank, and cannot fully reflect the fault of the transformer. It needs to cooperate with the differential protection to complete the protection task of the transformer;
4. Features of pressure release protection
   When the pressure inside the transformer exceeds the pressure release device due to a fault, the pressure release device should also act to release the internal pressure to prevent the transformer from exploding;
5. Features of temperature protection
   The temperature of the transformer will rise when the transformer is overloaded, the air cooler is faulty, or when there is a fault inside the transformer. When the temperature rise of the transformer exceeds the allowable range, the temperature protection device will alarm or trip to protect the transformer.
   The above precautions are just in case and must be understood clearly. At the same time, the preventive measures we must take are to prevent the damage caused by the disconnection of the neutral and ground wires of the transformer and the increase of ground resistance.

Reasons for the disconnection of transformer grounding wire and neutral wire and the increase of grounding resistance

• Due to the irregular burial of the grounding body, the sloppy installation process, the loose connection of the grounding body and the grounding wire, and the excessive dryness of the earth, it may cause the increase of grounding resistance;
• Due to insufficient understanding of the function and importance of the grounding wire during the design and installation of the transformer, the cross section of the neutral wire is selected too small, when the three-phase load is unbalanced, the neutral wire current is too large and it will be burnt.

Increased phenomenon and harm

• The grounding resistance of the grounding wire of the transformer is increased, and the insulation of the phase wire is also damaged. For example, phase B is grounded. At this time, a current will flow in the grounding wire of the transformer. The voltage of phase B is added to the ground and grounding resistance. The greater the ground resistance, the greater the voltage divider on the ground resistance. At this time, if someone accidentally touches the transformer grounding wire or neutral wire and the transformer shell, the human body will be connected in parallel with the grounding resistance. If the grounding resistance is large enough, the voltage applied to the human body will be very high, causing electric shock. If the human body accidentally touches the A phase or C phase, the voltage applied to the human body will be the line voltage 380V, which will pose a greater threat to personal safety.
• The grounding wire is broken, and the grounding wire near the transformer is broken, just like the grounding resistance has risen to infinity, at this time the ground potential is the ground phase potential, and all phenomena are the same as when the ground resistance increases, but the harm is greater.
• When the neutral line of the three-phase four-wire power supply transformer is disconnected, due to the unbalance of the three-phase load, the load grounding point will shift, and the grounding point potential is not zero, which causes the voltage of some phases to rise and burn the electricity. equipment. When the grounding wire is disconnected or the grounding resistance increases, the grounding wire of the lightning arrester of the transformer is disconnected or the grounding resistance increases. When lightning strikes over-voltage, the arrester cannot discharge to the ground normally, causing damage to the arrester or transformer.