Neutral grounding resistors (NGR) are designed for grounding the neutral of 6–35 kV networks in order to limit overvoltages during single-phase earth faults (SEF), eliminate ferroresonance phenomena, and ensure selective operation of relay protection.
They provide uninterrupted power supply to consumers, as well as the safety of personnel and electrical equipment during a single-phase earth fault.
Neutral grounding resistors are certified by PJSC «Rosseti» and recommended for use at the facilities of subsidiaries and branches of PJSC «Federal Grid Company - Rosseti».
Neutral grounding resistors can be manufactured within the standard product line, as well as calculated and designed individually according to customer requirements specified in the technical specification or questionnaire.
| Technical parameters | NGR with short-time duty | NGR with continuous duty |
|---|---|---|
| Rated voltage | from 6 to 35 kV | from 6 to 35 kV |
| Rated current | from 7 to 1000 A | from 0.38 to 78 A |
| Rated resistance | from 5 to 500 Ω | from 300 to 9000 Ω |
| Load duration | 10 sec. | 24 hours |
| Climatic design | U, UHL, HL, T | U, UHL, HL, T |
| Placement category | 1, 2, 3 | 1, 2, 3 |
| Housing material | stainless steel / galvanized sheet steel / sheet steel with painting | stainless steel / galvanized sheet steel / sheet steel with painting |
| Degree of protection | from IP00 to IP54 | from IP00 to IP54 |
| Service life | at least 30 years | at least 30 years |
| Warranty period | 5 years | 5 years |
The resistive neutral grounding system is the best choice in terms of fast fault localization and, therefore, for preventing cable overheating.
Alternative protection systems, such as isolated neutral or solidly grounded neutral, have significant disadvantages, including dangerous transient overvoltages and difficulties in fault localization in isolated systems, or destructive short-circuit currents with possible arcing in solidly grounded systems.
By installing neutral grounding resistors with appropriate characteristics between the transformer neutral and ground, the earth fault current can be limited for a short time to ensure rapid fault localization and prevent equipment damage.
