Neutral Grounding Resistors limit fault current to ensure safety of workers and equipment in electrical systems. In such a way, the fault currents that may occur may be in high enough current values to damage the generator, motor, cable or other critical elements of the facility. The neutral ground resistors used limit the current by increasing the resistance value. On LV and MV distribution networks, neutral points of power transformers and generators are grounded through a resistor.

Why use Neutral Grounding Resistors?

  • Limit the ground fault current to prevent any damage to the transformer and the generator and ensure operation continuity and safety
  • Provide sensing the fault current with the relays by means of current transformer mounted inside the neutral grounding resistor  limiting the fault duration.
  • Limit oscillating and non-oscillating transient voltage caused by the interruption of the failure current and so protect the insulation level of system equipment
  • Improve personnel safety by ensuring that the step voltage on the site is maintained at safety levels prevent overheating and mechanical stress on the equipment subject to failure current.

Phase-ground short-circuit current of the transformer and the generator is calculated to determine the limit current of the neutral grounding resistor. The resistor is designed to limit the failure current to 10% of this short-circuit current. This value shall be optimal to allow detection of the selected limited fault current value by the relays. Therefore, primary value of the current transformers used on the neutral grounding resistor can be different from the limited fault current value.

Fault duration is generally 5 – 10 seconds. This can be up to 30 seconds at plants which do not have any tolerance to sudden power interruptions. At hospitals, data centers, textile plants, cement plants and other facilities that manufacture with injection, fault duration can be continuous unless the fault current do not damage the system to ensure continuity of system and determine the fault point without any power interruption. For more information check our "High Resistance Neutral Grounding Systems".

The following basic parameters and a single-line scheme of the system, if possible, are required for preparing an offer for a neutral grounding resistor.

  • Phase to phase and phase to neutral voltage of the transformer or generator to which the resistor is connected
  • Fault current level
  • Fault duration

Technical Specifications of Neutral Grounding Resistors

  • Suitable up to 110/√3 kV
  • Applicable for fault currents up to 5000 A
  • Stainless steel resistance material suitable for extreme ambient conditions, resistant to oxidation and corrosion (AISI304, AISI310, AISI316, AISI430, CrAl, CrNi)
  • Special mechanical and electrical design to withstand high temperature and extreme current values
  • Internal current transformer detecting failure current (IEC-61869-2)
  • Design and tests in accordance with ANSI-IEEE 32 standard and special specifications

Resistor Element

  • Spring-wound, edge-wound or grid resistor elements with a cross-section suitable for the nominal current
  • Fully-modular, bended and stainless steel bolt connections in order to ensure electrical continuity at high temperature High conductivity for high current with bended and cascaded terminal connectors suitable for serial and/or parallel connections with high cross-section, low contact resistance
  • High internal insulation and high mechanical resistance against to shocks and sagging thanks to the use of large surface satiated bushings and M16 shear connectors
  • Special designed to dissipate the thermal and mechanical effects of over current to the surface grid resistors

Enclosure

  • Standard IP23 Protection Level suitable for outdoor usage and perfect cooling
  • IP 67 terminal box
  • Standard hot-dipped galvanized steel
  • Fully-modular, rigid, strong enclosure design with resistor blocks mounted to the frame for safety lifting from the upper or lower side
  • Easy access to and maintenance for resistor blocks on site thanks to blocks independently mounted to the frame, no overlapping
  • Lockable door with hinges
  • Corrosion-resistant handling rings and connectors
  • Stainless Steel product and warning labels

Neutral Grounding Resistors Options

  • Requested protection level from IP00 to IP55
  • Stainless Steel ,aluminum enclosure
  • Painting enclosure in desired color code
  • Entry from top or bottom with bushings
  • Additional equipment including separators, voltage transformer, grounding transformer, surge arrester, relay, panel heater etc.
  • Modular elevation legs suitable for extreme environmental conditions
  • Special design for high altitude
  • Special design suitable for explosive environments ATEX
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General Catalog PDF 1 MB Download
Neutral Grounding Resistors Catalog PDF 1 MB Download

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