Zero-Sequence Current Protection
1. Fundamental Principle
Zero-sequence current protection is based on Kirchhoff's current law: in a normal three-phase balanced system, the vector sum of the three-phase currents is zero (i.e., IU + IV + IW = 0).
When a ground fault occurs, the vector sum of the three-phase currents is not zero (i.e., a "zero-sequence current" I0 is generated), and a current will be induced on the secondary side of the CT.
(2) Three-phase CT synthesis method: The zero-sequence current component is obtained by connecting the secondary currents of three independent phase CTs in a specific way (such as connecting with the current).
2. Main application scenarios
(1) Large current grounding system (such as a neutral point directly grounded system): When a single-phase ground fault occurs, the fault current is very large. Zero-sequence protection, as a sensitive main or backup protection, will quickly trip and clear the fault.
3. Protection Objects and Purposes
(1) Protection Objects: Power equipment such as generators, transformers, and transmission lines.
(2) Purpose: To prevent equipment damage (such as arc burning of the iron core), system overvoltage, disruption of system stability, and phase-to-phase short-circuit faults caused by grounding faults.
4. Characteristics
(1) It focuses on grounding faults on the system side.
(2) The operating current value is usually large (from several amperes to several hundred amperes), which is related to the system scale and grounding method.
(3) It needs to be coordinated with the system's grounding method and involves complex setting calculations.
Residual Current Protection
1. Basic Principle
Residual current protection is also based on Kirchhoff's current law, but the focus is different: the current flowing into a node must be equal to the current flowing out of that node.
When leakage or electric shock occurs, some current flows back to the ground, resulting in "inflow ≠ outflow." This difference is the residual current (commonly known as "leakage current"). The CT detects this difference and drives the tripping mechanism.
2. Main Application Scenarios
(1) Low-voltage power distribution system terminals: distribution boxes in residences, office buildings, and shops.
(2) Power supply terminals of handheld power tools and mobile devices.
(3) High-risk environments such as damp places (e.g., bathrooms, kitchens) and temporary construction power supply.
3. Characteristics
(1) It focuses on leakage/electric shock on the load side. (2) The operating current is very small. High-sensitivity models have currents of 6mA, 10mA, and 30mA, used for direct personal protection; 100mA and 300mA are used for fire protection. (3) Both phase and neutral lines must be detected simultaneously.
conclusion:
(1) Zero-sequence current protection is the "internal doctor" of the power system, diagnosing and treating "serious diseases" (ground faults) within the system (power grid and equipment).
(2) Residual current protection is the user's "bodyguard," constantly preventing "accidental damage" (leakage and electric shock) from the outside (electrical equipment).
LVZW-35 current transformer
LVZW-35 current transformer is a sensor used to measure large current in 35kV system. It is mainly used in substations, power systems and electrical equipment. The transformer adopts magnetic core type, which is characterized by high linearity, strong anti-interference ability, small size and simple structure. It is a current transformer with very high cost performance.
1.Rated voltage：40.5kV
2.Primary current：50-1200A
3.Secondary current：5/1
4.Measurement level：0.2/0.2S/0.5/0.5S
5.Protection level：5P/10P
6.Installation method: vertical installation;
7.Applicable range: used with 35kV circuit breakers and transformers.
8.Product advantages：Safe and reliable, high measurement accuracy, wide measurement range, small size, light weight, good dynamic performance, low power consumption, convenient equipment standardization, easy to realize automatic monitoring and control.
Shaanxi West Power Tongzhong Electrical Co., Ltd. is a leading manufacturer with over 20 years of experience, specializing in high quality 7 to 40.5kV vacuum circuit breakers, switchgears, and a wide range of electrical products. Our advanced manufacturing process ensures reliable, durable solutions, especially our VTZ series vacuum circuit breakers, which are maintenance-free for up to 20 years. With a team of expert technicians, we excel in R&D, manufacturing, and after-sales service for both high and low voltage equipment, delivering excellence at every stage.
Shaanxi West Power Tongzhong Electrical Co., Ltd.Our address
No. 1 East Gaoxin Avenue in the High-Tech Development Zone of Baoji City, Shaanxi Province.
86-18091765882
