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ZGNGR Neutral Grounding Resistor for Distribution Systems

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With the recent development of distribution systems and further renovation of urban and rural distribution networks, numerous cables have replaced previous overhead transmission lines. To a certain extent, the decrease in the probability of single-phase earth faults reduces the high trip-out rate arising from low-resistance grounding systems. However, the high line selection accuracy of such low-resistance grounding systems are accepted by the majority of users. Consequently, they still have a wide range of applications in some urban distribution networks.

 

Product Description:
Such neutral grounding is realized through low resistance. In case of single-phase grounding in the connected system, higher zero sequence current flows through a zero sequence circuit formed by low resistance and transition resistance. When such current flows through a grounding line, the zero sequence overcurrent protection is immediately enabled to remove such circuit. The auxiliary GRM-01 resistance monitor can perform real-time monitoring of voltage, current and resistance temperature. For such unit integrated with measurement, display and communication functions, the system-on-a-chip (SOC) is used as a core arithmetic unit and Featuring a high arithmetic speed, good reliability and excellent interference immunity. With RS-485 photoelectric-isolated communication port, it supports open communication protocols and is convenient for communicating with an automatic back-end.
   
System Principle:
1. Grounding transformer
For 35 kV and 66 kV distribution networks, the Y-connection is applied for the transformer winding. The leading-out mode of neutral points is adopted. In case of low zero sequence impedance in a transformer, there is no need to use the grounding transformer. For 6 kV and 10 kV distribution networks, the Δ-connection is applied for the transformer winding, so the grounding transformer should be used to generate a neutral point and install a grounding resistor. To reduce zero sequence impedance, generally the Z-connection is applied for the grounding transformer. Appropriate secondary capacities may be provided to substitute a substation transformer.
2. Neutral grounding resistor
It may have a separate housing, or may be assembled in the same housing with the grounding transformer.
3. Single-phase isolating switch
For a system in which the grounding transformer is complete with secondary windings, used as substation transformers or resistors and directly connected to the neutral point of a winding in the main transformer. A single-phase isolating switch is installed between the system neutral point and resistor to ensure the normal operation of other components when the resistor is out of service.
4. Current and potential transformers and infrared temperature probe for neutral points
They are used to collect resistor current, voltage and temperature readings for measurement and zero sequence protection.
5. Primary Equipment Housing
For easy installation, maintenance and aesthetic appearance, a grounding transformer and a grounding resistor can be assembled in the same integrated housing. If the auxiliary dry-type grounding transformer is installed outdoors, an external enclosure is required.
6. GRM-01 resistance monitor
It performs real-time display of the system voltage, current and resistance temperature and communicates with the automatic back-end.
 
Technological Advantages:
We have stainless resistor elements imported from MS, an Italy-based company and are granted the exclusive rights to sell them in China's electric power industry. Such resistor has the following benefits:
1. The optimal resistor shearing mode and grid layout ensure a large radiation area and low temperature rise of the whole resistor. Under the rated voltage, the design temperature rise within 10s is less than 700 K and the actual value is lower than 600 K (lower than 760 K specified in relevant professional standards).
2. The excellent stainless steel and the special and effective structure ensures the high strength of the whole resistor. Each part of the resistor can be protected from swinging, vibration and temperature variations without any deformation.
3. Optimal temperature coefficient: it ensures flexible protections; it can also limit the fault current to a certain extent in case of protection failure.
4. Such resistor made of perfect stainless steel has outstanding resistance to oxidation and a melting point not less than 1,450 ℃, so that it also has extreme applications in tropical areas and very dirty circumstances.
5. Its desirable structure ensures small size and light weight and avoids any higher local temperature rise.
6. Its accurate design and assembly ensure the possible replacement or addition of a unit without removal of the whole structure.
7. The best insulating materials in the resistor ensure its high insulation level.
8. Highly accurate potential and current transformers, infrared temperature probe, real-time monitoring of voltage, current and temperature, automatic fault oscillograph, and convenient back-end communication

 

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