What are the consequences of reverse polarity of current transformer?

1. Measurement
1. Increased measurement error
When the polarity of the current transformer is reversed, the current direction output by the secondary winding is opposite to the actual primary current direction. For example, when measuring current, if the polarity is reversed, the current direction displayed by the ammeter is opposite to the actual current direction, resulting in a sign difference between the measured value and the true value. This will make the measurement result completely wrong, unable to accurately reflect the actual current situation in the circuit, affect the accuracy of electric energy metering, and bring great inconvenience to the operation and management of the power system.
2. Power measurement error
When measuring power, the wrong polarity of the current transformer will cause deviations in the power measurement results. Power is the product of current and voltage, and the wrong current direction will cause the positive and negative signs of power to be wrong. For example, in a three-phase circuit, if the polarity of the current transformer of a phase is reversed, the power measurement result of that phase will be greatly different from the actual value, which will affect the power balance calculation of the entire system and bring wrong reference information to the dispatch and operation of the power grid.
2. Protection
1. Misoperation or refusal of protection device
Reverse polarity of current transformer will cause the current sampling signal of protection device to be wrong. For example, in differential protection, differential relay judges fault according to the current difference flowing into and out of the protected equipment. If the polarity of current transformer is reversed, the current flowing into differential relay will be in the wrong direction, resulting in misoperation of differential protection, and the normal operating equipment will be mistakenly cut off, causing unnecessary power outage. Or in some cases, the wrong direction of fault current may make the protection device unable to correctly judge the fault, resulting in protection refusal, and the failure to cut off the fault in time, expanding the scope of the accident, endangering the safe and stable operation of the power system.
2. Change of protection range
Reverse polarity may also change the protection range of protection device. For example, in distance protection, the wrong polarity of current transformer will cause the measured impedance direction to be wrong, resulting in the change of protection range of protection device. This may cause the protection device to operate when it should not operate, or not operate when it should operate, increasing the risk of power system failure and reducing the reliability of protection device.
3. Equipment safety
1. Increased risk of equipment damage
Reverse polarity may cause abnormal current distribution in the system. For example, in some complex power systems, due to the wrong current direction, some equipment may be subjected to excessive current or voltage stress. Long-term operation in this abnormal state will gradually reduce the insulation performance of the equipment, accelerate equipment aging, and eventually cause equipment damage, shorten the service life of the equipment, and increase the cost of equipment maintenance and replacement.
2. Reduced system stability
The wrong polarity of the current transformer has a negative impact on the stability of the entire power system. When the protection device malfunctions or refuses to operate due to the wrong polarity, it may trigger a chain reaction, causing other equipment in the system to also have abnormal operating conditions. For example, in a regional power grid, if the polarity of the current transformer in a substation is reversed, causing the protection device to malfunction, it may cause voltage fluctuations, frequency changes, and other problems in the regional power grid, thereby affecting the stable operation of the entire power grid, and may even cause large-scale power outages.
IV. Personal safety
1. Increased risk of electric shock
Since the reverse polarity of the current transformer may cause the wrong current direction in the system, when the staff is inspecting, maintaining or operating the equipment, they may mistakenly believe that the equipment has been powered off or the current direction is inconsistent with the actual situation, resulting in electric shock accidents when touching the equipment. For example, when performing equipment grounding operations, if the polarity of the current transformer is reversed, the grounding current may go in the wrong direction, causing electric shock to workers when they touch the grounding device, endangering their personal safety.