Zero sequence current transformer is a device that detects the current value called zero sequence current in a three-phase AC power supply.

       The sum of the current vectors flowing through the phases of a three-phase AC power supply is usually symmetric and therefore zero, but if the ground current flows, the balance will be disrupted and the sum will have a non-zero value. If a ground problem occurs, the zero-sequence current transformer kicks in, instantly disconnecting the fault location from the surrounding circuit. Therefore, it is pre-built into the leakage circuit breaker to play a role in constantly discovering accidents.

Application of zero sequence current transformer

       When the electrical path in the electrical equipment is connected to the ground electrical, a large current flows into the location as a ground fault current, creating the risk of a serious accident. To prevent this, a zero-sequence current transformer is used, which has the function of immediately disconnecting the ground fault from the surrounding area when the ground fault current is detected. Although they are also used in low-voltage general-purpose instruments, the role of zero-sequence current transformers becomes more important because they are more likely to occur because the higher the voltage.

Principle of zero sequence current transformer

       In a three-phase AC power supply, if the currents flowing in each phase are equal and symmetrical, their vector sum is zero. The average of the sum of the vectors is called the "zero sequence current", and in the case of the symmetrical shape shown above, the zero sequence current is zero. If any of the three phases flows through the ground fault current, the three-phase balance will be disrupted and the zero sequence current will not be zero. This enables immediate detection of ground faults. The "zero sequence current transformer" is a device that detects the zero phase current in these three phase AC power supplies. Like a typical current transformer, it is constructed by winding coils around a circular iron core, with a conductor passing through the center of the ring. However, a normal current transformer has only one conductor passing through it, while a zero-sequence current transformer has three conductors of three phases. If for some reason the balance of the three-phase current is disrupted, the secondary current will flow through the coil instantaneously, which will be detected as a ground fault. They are usually built into leakage circuit breakers along with relays and circuit breakers and play an important role in preventing leakage from causing accidents, fires and other disasters.