Neutral grounding resistor for transformer

Brief Introduction to product

With neutral grounding resistance is installed, when nonmetal grounding, the current flowing through grounding point and neutral would be much less than that when metal grounding. Meanwhile sound phase voltage rise is lowered a lot and zero-sequence voltage is half of that when single-phase metal grounding. Therefore, adopting neutral grounding via resistance could decrease transient overvoltage when single-phase grounding, and eliminate arc flash hazards like transient overvoltage and some resonant overvoltage, and moreover it could adopt simple relays to quickly locate the fault line and clear it up.

Mingrui has outstanding technical researching team and superior equipments, specially concentrate on research & development, production, sales and service of neutral grounding series products of power distribution system. The transformer neutral grounding resistance we developed and produced is applicable to 6~35KV power distribution grid of cable lines in cities, large industrial enterprises, factories, airports, seaports, subway and etc. as well as 0.66KV system in mine digging and 0.4kv/6kv/10kv system in power plants.

Applicable Standards

The design of the product complys with the following standards:

IEC726    Dry-Type Power Transformer

IEC60-1    Experimental Technique of High Voltage

IEC60529:2001 Enclosure Protection Degree (IP code)

IEEE32-1972  Technique Terms and Experiment of Neutral Grounding Device

IEC60081    Insulation Co-ordination of Transmission and Distribution Device of High Voltage

The Characteristeic of the Product

3.1 Adopted high quality imported stainless steel or domestic stainless steel electric heating metal material,

the product operates safely and reliably with the advantages of high conductivity, high temperature coefficient, corrosion resistance, thermostability, good oxidation resistance, high tensile strength, resistance value stability and etc.

3.2 The device also could be applied in medium power distribution system. When transformer is angle-connected, independent grounding transformer could be installed with which the neutral point and resistance are connected.

3.3Resistance value could be designed from 1ohm to 2000ohm and current from 1A to 2000A

3. 4 The cabinet could be installed indoor or outdoor. As the cabinet body is corrosion-resistant and of high protection grade, made from stainless steel plate or painted cold rolled steel plate.

3.5 The counting function could be added to the device, which records times of resistance grounding.

3.6 Isolated switch could be added which convenient examination and repair and so does temp. or humidity controller.

3.7 Intelligent monitor is at customers' option, which could monitor un-balanced current of neutral point when resistance cabinet is in normal operation, temp. of resistance panel, and temperature of inside cabinet, measure transient current and records grounding times when single-phase grounding happens, reserve communication interface which could send monitored and recorded to master-control room so as to let operating people get the information in the first time.

Model Meaning

Typical Technology Parameters

Various resistors could be designed as per customers' requirement, value ranging from 1Ωto 2000Ω. Current allowed to flow through is  from 1A~2000A and the flowing time is 10s,15s,30s,60s and 2h.

Schematic Diagram for Wire Connection

6.1 The transformer adopts star connection with neutral leading-out wire ,connected as in figure 5.

6.2 If the neutral is triangle-connected, neutral grounding resistor is grounded by grounding transformers. Connection is as in figure 6

Service Condition

8.1 Generally applicable to outdoors,used in the system of 50 Hz and 60 Hz.

8.2 The altitude shall not exceed 3500m.

8.3 Ambient temperature : -20℃~+70℃,Relative humidity:≤95%

8.4 Wind pressure is not higher than 700Mpa (equal to wind velocity 34m/s) 

8.5 Earthquake intensity : ＜8 degree

8.6 Thickness of coated ice: ＜10mm

8.7 Grade of air pollution: not higher class Ⅳ

8.8 The air at the installation site shall be free from inflammable/ explosive/ corrosive gas,and conductive dust.

8.9 As resistor is heating device. The temperature will rise high when using it. Therefore, some space should be left around the the place where the resistor is installed, avoiding being influenced by external heating source. Please pay close attention to this.

Notice for Ordering

Please let us know the parameters below.

9.1 Rated Voltage of System: (kv)

9.2 Current Value Allowed to Flow Through in Short Time:(A)

9.3 Nominal Resistance Value:(Ω)

9.4 Whether current transformer needed or not (CT)?

  Ratio and capacity and composite error of it is required.                 

9.5 Wire-in and wire-out modes are for choice:

a. top-in and bottom-out,    b. bottom-in and bottom-out,  

c.side-in and side-out,      d. side-in and bottom-out.

9.6  Allowable Time of Current Flowing Through in Short Time:(S)

9.7 Material of resistor cubicle,protection grade of cubicle(IP), the color code and installation location.  

9.8 Optional Devices: Recorder of Grounding, Controlling Device of Temp. and Humidity.