As the economic level continues to increase, the variety of transformers continues to increase. Transformers are widely used in our lives, so people are paying more and more attention to the choice of transformers. Today, Xiaobian will introduce the grounding transformer to everyone, let everyone know what the classification of the grounding transformer is and what the role of the grounding transformer is.
Classification of grounding transformers:
1. Three-phase grounding change. The function of the grounding transformer is to use the neutral point for adding the arc suppression coil or resistor when the system is △-type wiring or the neutral point of the Y-type wiring cannot be taken out. This type of transformer adopts Z-type. Wiring (or zigzag wiring) is different from ordinary transformers in that each phase coil is divided into two groups and wound on the phase magnetic column in reverse. The advantage of the connection is that the zero-sequence flux can circulate along the magnetic column. The zero-sequence flux of the transformer circulates along the magnetic flux leakage path, so the zero-sequence impedance of the Z-type grounding transformer is small (about 10 Ω), while the ordinary transformer is much larger. According to the regulations, when using an ordinary transformer with an arc suppression coil, its capacity shall not exceed 20% of the transformer capacity. The Z-type transformer can be equipped with an arc-extinguishing coil with a capacity of 90% to 100%. The grounding can be replaced with an arc-extinguishing ring or a secondary load, which can replace the used variable, thereby saving costs.
2. Single-phase grounding change, single-phase grounding change is mainly used for neutral point grounding resistance cabinets with neutral point generators and Satons transformers to reduce the cost and volume of the resistance cabinet.
The role of the grounding transformer:
In the 6kV, 10kV, and 35kV power grids in China's power systems, the neutral point is not grounded. The distribution voltage side of the main transformer in the power grid is generally a delta connection, and there is no neutral point for the grounding resistance. When a single-phase ground fault occurs in a neutral point ungrounded system, the line voltage triangle remains symmetric, which has little effect on the user's continued operation, and when the capacitor current is relatively small (less than 10A), some transient ground faults can disappear by themselves. It is effective to improve power supply reliability and reduce power outages.
However, with the growing and growing power industry, this simple method is no longer meeting the current needs. Nowadays, the number of cable circuits in urban power grids is increasing, and the capacitor current is getting larger and larger (more than 10A). At this time, the grounding arc cannot be reliably extinguished. , the following consequences will occur.
1) Intermittent extinguishing and reignition of single-phase grounding arc, arcing grounding overvoltage, amplitude up to 4U (U is the normal phase voltage peak) or higher, long duration, insulation of electrical equipment Causes great harm, forming a breakdown in the weak insulation; causing significant losses.
2) The dissociation of air caused by continuous arcing destroys the insulation of the surrounding air and is prone to phase-to-phase short circuit.
3) The ferromagnetic resonance overvoltage is generated, which easily burns the voltage transformer and causes damage to the arrester and may even cause the arrester to explode. These consequences will seriously threaten the insulation of the grid equipment and endanger the safe operation of the grid.
In order to prevent the above accidents, provide enough zero-sequence current and zero-sequence voltage for the system to make the grounding protection work reliably. It is necessary to artificially establish a neutral point to connect the grounding resistance at the neutral point. A grounding transformer (referred to as grounding) is generated under such circumstances. Grounding is the artificial creation of a neutral grounding resistor, which has a small grounding resistance (generally less than 5 ohms). In addition, the grounding has electromagnetic characteristics, and the positive sequence negative sequence current is high impedance, and only a small excitation current flows through the winding. Since the two windings on each core column are wound in opposite directions, the equal zero-sequence current flowing through the two windings on the concentric column exhibits low impedance, and the voltage drop of the zero-sequence current on the winding is small. That is, when a ground fault occurs in the system, positive sequence, negative sequence and zero sequence current will flow in the winding, the winding exhibits high impedance to the positive sequence and the negative sequence current, and for the zero sequence current, due to the same phase The two windings are connected in reverse polarity, and the induced electromotive forces are equal in magnitude and opposite in direction, which cancel each other out, thus exhibiting low impedance. Since many grounding transformers only provide a neutral point grounding small resistance without carrying a load, many grounding changes are secondary. When the grounding becomes normal during the operation of the power grid, the grounding becomes equivalent to the no-load state. However, when the grid fails, the fault current is only passed for a short time. When the neutral point is single-phase ground fault through the small resistance grounding grid, the high-sensitivity zero-sequence protection judges and cuts the fault line for a short time. The grounding change only starts from the ground fault to the fault line zero-sequence protection action to cut off the fault line. Function, neutral point grounding resistance and grounding change will pass the zero sequence current.
The above is a brief introduction to the classification of the grounding transformer and the role of the grounding transformer. I believe that everyone has seen the classification of the grounding transformer and the role of the grounding transformer. It will enable everyone to better classify the grounding transformer, understand the role of the grounding transformer, and better familiarize with the grounding transformer.
Silicon TVS / TSS:
Diode TVS (Transient Voltage Suppressor), also known as Transient suppression diodes, is widely used a new type of high efficient circuit protection device, it has a fast response time (the nanosecond) and high surge absorbing ability.When it ends of stand moments of high energy shock, TVS can bring the two ends at high rate from high impedance to a low impedance between impedance values, to absorb a large current moment, put it at both ends of the voltage restraint on a predetermined value, thus protecting the back of the circuit components are not affected by the impact of the transient high pressure spikes.
Silicon TVS Transient Voltage Suppresso,Silicon TSS Transient Voltage Suppresso
YANGZHOU POSITIONING TECH CO., LTD. , https://www.cnchipmicro.com