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We offer the Power+N range of Neutral Grounding Resistor (NGR) Panels up to 66 KV. Ngr’s are used to connect the neutral phase and the earth to limit the earth fault current to a safe value thereby protecting the transformer, generator system. The Typical operation conditions are A No Earth Fault: Continuous current (5 % to 10 % of full load current) may pass through the resistor due to system unbalance or Earth Fault Condition where restricted fault current passes through the resistor protecting the system till automatic protection takes place.
Purpose: Neutral Grounding Resistor is connected between the neutral & the earth so that it will limit the earth fault current to a safe value [Normally full load current of the generator, transformer, etc. thereby protecting the transformer, generator system].
Typical operation conditions:
1. No Earth Fault: Continuous current (5 % to 10 % of full load current) may pass through the resistor due to system unbalance.
2. Earth Fault Condition: Restricted fault current passes through the resistor protecting the system till automatic protection takes place. The earth pressure (Rated Voltage) is absorbed by the resistor protecting the winding etc.
Enclosure: For outdoors application enclosure designed to give degree of protection of IP 33 is normally used. Enclosure upto IP 65 protection are offered. Enclosure material can be Mild Steel, Aluminium or Stainless Steel. Painting / Galvanizing or Hot Dip Galvanizing or Powder Coating is offered as per requirement. Safety screen enclosure is provided if required. For continuous rating enclosure protection is not above IP 43.
Material of Resistor Element: A Neutral Grounding Resistor is a very simple yet technical equipment that is an absolute requirement depending on the design of the installation. Our NGR panels are fitted with resistor elements made from stainless steel or cast iron or CU-NI or NI-CR or any other resistance material as per requirement. From our experience, formed stainless steel elements are best and economical for NGRS.
Construction: NGR include resistor assembly, plus required insulators, internal connections and hardware.
Options/Accesories: Few of the following are usually incorporated. Current Transformers, Potentials Transformers, Grounding Transformers, Two bushing, Elevating Stands, Manual/ Electrical operated/ Motorized Isolator, Earth Leakage Relay, Lightning Arrestors, Auxiliary Control Wiring Terminal Box with Cable Glands, Termination Kit, Stand Off Insulator, Space Heater with Thermostat Control are also offered.
Cabling/ Termination: Suitable arrangement is provided for termination of cable, flats or bus duct as per requirement. Incase of XLPE cable terminal box with suitable clearance and undrilled removable gland plate is provided.
Rated Voltage: In an NGR this voltage means value of line to neutral voltage (ie System Voltage divided by 1.732)
Rated Current: This is the value of initial current that will flow through resistor when it is cold. Normally rated current value is same as full load current.
Duty rating or Time Rating:Also referred to as Duty rating, is length of time for which NGR must withstand rated voltage.
Short Time Rating: This is dependent on the design parameters of the protection system, normally it is 10 or 30 or 60 seconds. When a fault is immediately cleared and system made healthy then chances of fault repetition should be considered. 30 sec is the typical rating recomemded b y IS-304.
Continuous Rating: This is typically 10 % of full load current. For a healthy systems the NGR can be designed for a continuous rating of 5% to 10 % of full load current.
Temperature Rise Allowed: Normally Temp. Rise is restricted to 375 deg.c ie as per BS 587. It can be 760 deg.c. As per IEEE-32. We can offer NGR of any other temp. Rise as per the design requirements.