Littelfuse Startco Protection Relays Technical Note - Resistance Grounding RG-12 : IMPLEMENTING RESISTANCE GROUNDING ON UNGROUNDED SYSTEMS
Resistance grounding protects a system against transient overvoltages caused by arcing ground faults and it provides adequate fault current for selective ground-fault detection and coordination.
Delta-connected supplies and wye-connected supplies with inaccessible neutrals cannot have neutral grounding resistors (NGR’s) directly connected to them; however, resistance grounding can be achieved on an ungrounded system by establishing an artifi cial neutral with a zigzag transformer.
A zigzag transformer is a six-winding, three-phase transformer that is wye-connected with a pair of series-connected, phase-displaced windings symmetrically connected to each phase. It can be used to establish an artifi cial neutral for a three-phase system by connecting its neutral point to ground through a NGR. During normal operation the only current that fl ows in the zigzag transformer is an extremely small magnetizing current. When one phase is grounded, the NGR and the zigzag transformer provide a path for ground-fault current to fl ow. See Figure 1.
Note:Operation with one ground-fault on a resistance-grounded system is possible if the NGR is correctly sized and if it is allowable by Code for the installation.
Protection, coordination, and annunciation systems depend on the integrity of the NGR. Use a Littelfuse Startco SE-330 or SE-325 to continuously monitor the NGR. See Figure 2, and Figure 3.
A pulsing NGR system can be used to modulate the ground-fault current to assist in locating a ground fault.
For more information about ground-fault protection and resistance-grounding, refer to the Littelfuse Startco papers: Ground-Fault Protection and Ground-Conductor Monitoring for Mine Power Centres and Monitoring Neutral-Grounding Resistors. Littelfuse Startco can provide application assistance and a custom designed, CSA-certified, “turn-key” package.
|
|
|
|
Application note & Design Guide |
|
|
|
|
Please see the document for details |
|
|
|
|
|
|
|
|
|
|
|
English Chinese Chinese and English Japanese |
|
|
March 1, 2011 |
|
|
|
|
|
|
|
|
281 KB |
- +1 Like
- Add to Favorites
Recommend
All reproduced articles on this site are for the purpose of conveying more information and clearly indicate the source. If media or individuals who do not want to be reproduced can contact us, which will be deleted.
Integrated Circuits
Discrete Components
Connectors & Structural Components
Assembly UnitModules & Accessories
Power Supplies & Power Modules
Electronic Materials
Instrumentation & Test Kit
Electrical Tools & Materials
Mechatronics
Processing & Customization
