What protection functions does a current transformer have?

1. Overcurrent protection
The current transformer converts the large current on the primary side into a small current on the secondary side for use by the overcurrent protection device. When an overcurrent fault occurs in a line or device (such as a short circuit, overload, etc.), the protection device detects that the secondary current has increased abnormally. According to the preset protection setting and delay, the circuit breaker trips and cuts off the fault circuit to protect the safety of the equipment and line.
2. Quick-break protection
Quick-break protection (instantaneous current quick-break protection) is a fast-acting protection method. The current signal provided by the current transformer is detected by the protection device. When the current exceeds the action value of the quick-break protection, the protection device immediately acts to quickly cut off the fault circuit to prevent the fault from expanding. This protection method is usually used for near-end fault protection of the line.
3. Differential protection
Differential protection is a way to achieve protection by using the difference in current between the normal operation and fault state of the current transformer. For example, in the transformer differential protection, the secondary currents of the current transformers on both sides of the transformer are compared to determine whether there is a fault. If the difference between the currents on both sides exceeds the set value, it means that there is a fault inside the transformer or in the lead, and the protection device trips.
4. Distance protection
Distance protection uses the current and voltage signals provided by the current transformer and the voltage transformer to calculate the electrical distance between the fault point and the protection installation. When the fault distance is detected to be within the protection range, the protection device is activated to cut off the fault line. The accurate current signal provided by the current transformer is one of the key factors for the distance protection to operate correctly.
5. Grounding protection
In a neutral point grounding system, the current transformer can be used for grounding protection. When a single-phase grounding fault occurs, the grounding current will flow into the earth through the grounding device. The current transformer detects the change in the grounding current. The protection device determines the fault type according to the magnitude and phase of the grounding current, and trips to cut off the fault circuit.
6. Busbar protection
Busbar protection is one of the important protection methods in the power system. The current transformer is installed at the outlet of each connecting element (such as line, transformer, generator, etc.) on the busbar to provide current signals to the busbar protection device. When a busbar fault occurs, the protection device determines the fault location based on the current signal provided by each current transformer, and trips all connected components on the faulty busbar to prevent the fault from expanding.
7. Overload protection
Overload protection is used to prevent electrical equipment from being damaged due to long-term overload operation. The current transformer converts the current signal on the primary side into a small current on the secondary side for use by the overload protection device. When the current exceeds the rated current of the equipment and lasts for a certain period of time, the protection device will operate, send out an alarm signal or cut off the power supply to protect the equipment.
8. Failure protection
Failure protection is a backup protection method. When the main protection is activated, the circuit breaker fails to operate correctly for some reason. The failure protection determines whether the circuit breaker has failed by detecting the current signal provided by the current transformer. If the circuit breaker failure is detected, the failure protection will operate to expand the power outage range, cut off the faulty equipment, and prevent the fault from further expanding.