Product Usage
In the 6-35kV AC power grid, the neutral point of the power grid may adopt grounding methods such as ungrounded, arc suppression coil grounding, high resistance grounding, medium resistance grounding, and low resistance grounding. In cable powered systems, the grounding capacitance is relatively large. When the current exceeds the specified value, there is a possibility of arc grounding overvoltage. The purpose of using neutral point resistance grounding method is to inject resistive current into the fault point, making the grounding fault current exhibit resistance capacitance properties, reducing the phase difference angle with voltage, reducing the reignition rate of the fault point current after zero crossing and arc extinguishing, and limiting the overvoltage to 2.6 times the phase voltage. Simultaneously improving the sensitivity of relay protection to act on tripping, thereby effectively protecting the normal operation of the system.
ZW-ZTJ type metal resistors are suitable for medium and small resistance grounding methods. It is installed on the neutral point of transformers or generators in 0.4kV and 6-35kV AC power grids, such as power plant systems, substation power supply systems, and industrial and mining enterprise distribution systems, to achieve the operation mode of using resistance grounding for the neutral point.
Product features
1. Manufacturing according to standards and meeting system requirements
The ZW-ZTJ type metal resistor is strictly designed and manufactured in accordance with the DL/T780-20 (neqANSI/IEEE32-1990) standard for neutral point grounding resistors in distribution systems, and meets the requirements for system use.
2. Made of nickel chromium alloy resistance material, resistant to high temperature
The resistance material of ZW-ZTJ type non-metallic resistors is made of nickel chromium alloy. The melting temperature of nickel chromium alloy is 1500 ℃, and the working temperature can reach over 1000 ℃. Therefore, this type of resistor can withstand high temperatures and is particularly suitable for systems with high ground capacitive currents.
3. High resistivity, low temperature coefficient, stable resistance value
The resistivity of nickel chromium alloy material is higher than other stainless steel materials, with a resistivity of up to 1.08 µ Ω · m, a small temperature coefficient, stable resistance value, which is conducive to ensuring the sensitivity of relay protection.
4. High tensile strength and strong toughness
The mechanical strength of nickel chromium alloy material remains basically unchanged at high temperatures, and it still maintains good toughness and is not easy to fracture under conditions of rapid temperature changes. It is suitable for working conditions with instantaneous high current impact at the neutral point.
5-unit modularization, flexible and convenient to use
When designing the ZW-ZTJ type metal resistor, full consideration is given to the usage situation. The resistor unit is modular and can be combined in series or parallel to meet the needs of different currents, voltages, and resistance values.
At the same time, the resistor can be used in parallel with resistors or reactors. Generally, in the early stage of power grid construction, the scale is relatively small, so the resistance value of the neutral point resistor is relatively large and the grounding current is relatively small; As the system gradually expands and requires a small grounding resistance, the grounding current increases. At this point, as long as the original resistor is combined with an adapter resistor, it is convenient to achieve expansion and capacity increase. Reactors can also be connected in parallel to form an impedance grounding method.
6. Heat dissipation structure design to ensure safe operation of equipment
Metal resistors have a small thermal capacity and increase in temperature during operation. Therefore, when designing, heat dissipation needs should be fully considered. The cabinet structure has a cooling airflow path, which has a good heat dissipation effect, ensuring the rapid cooling of resistance components and the safe operation of resistors in various working conditions.
7. Complete monitoring functions, providing analog output for microcomputer protection
The ZW-ZTJ type metal resistor is equipped with a current transformer and an action counter, which can monitor the unbalanced current at the neutral point during normal operation. The action counter can effectively record the number of times the resistor is connected to the grid (i.e. the number of times it is grounded in a single phase). And can provide analog output to the protection and monitoring system according to the requirements of relay protection.
8 can be used in conjunction with grounding transformers
When the transformer winding is delta connected and requires independent installation of a Z-shaped winding grounding transformer, ZW-ZTJ type metal resistors can be used in conjunction with grounding transformers.
9. Suitable for different working environments
The ZW-ZTJ type metal resistor housing can be made of stainless steel or cold-rolled steel plate spray coating according to user requirements, to meet different indoor and outdoor environments. Moreover, nickel chromium alloy materials have strong oxidation resistance and can maintain good oxidation resistance even at high temperatures, making them suitable for a wide range of working environments.
