Zero-sequence current, voltage
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This post was last edited by zhaohh3211 on 2011-9-5 20:03. How are zero-sequence voltage and current generated, and how should they be understood? What is zero-sequence protection?
http://bbs.hcbbs.com/viewthread.php?tid=438006
Well, thank you so much. Although it was all conceptual explanations, I still learned a lot!
Zero-sequence current is generally generated due to three-phase imbalance or single-phase grounding. In a three-phase four-wire circuit, the phasor sum of the three phase currents is zero, that is, Ia + Ib + IC = 0. If a current transformer is connected to the three-phase four-wire system, the induced current is zero at this time. When an electric shock or leakage fault occurs in the circuit, a leakage current flows through the circuit. At this time, the vector sum of the three-phase currents passing through the transformer is not zero; its vector sum is given by: Ia + Ib + Ic = I (leakage current). As a result, an induced voltage is generated in the secondary coil of the transformer. This voltage is applied to the electronic amplification circuit in the detection section, and it is compared with the preset operating current value of the protection device. If this value is greater than the operating current, the sensitive relay will activate, thereby causing the actuating element to operate and shut down the circuit. The transformer connected here is called a zero-sequence current transformer; since the phasors of the three-phase currents do not sum to zero, the current generated is known as zero-sequence current. When a ground fault occurs in a system with a directly grounded neutral point (also known as a high-ground-current system), a large zero-sequence current is generated. Also, in a system with a neutral point that is not directly grounded, zero-sequence voltage is generated when a single-phase ground fault occurs.
I see; zero-sequence current exists only when there is zero-sequence voltage