SIMPAX – neutral grounding resistors for power networks, transformer stations, wind turbines
Grounding resistors, formerly and today, are used in power networks as neutral point grounding resistors of the transformer's own needs.
Neutral earthing resistors are connected permanently to the transformer neutral point on the one side and to the operational earthing from the other side, form the entire medium voltage distribution boxes equipped additionally with a medium voltage current transformer plugged in series.
During a earth-fault of one of the phases of the medium voltage network, at the transformer neutral point, a short-circuit of the earthed phase with a healthy phase arises. The energy of this short circuit is momentarily reduced on a resistor, the resistance of which limits the short-circuit current to the rated current of the resistor operation. The current transformer then gives a short circuit signal to the automation mounted on the power station.
Today SIMPAX [see HISTORY] is a supplier of neutral earthing resistors for renowned domestic and global energy industry companies.
Parameters of neutral grounding resistor
| Network rated voltage Unetwork: | 6,3kV – 30kV |
| Rated operating voltage: | Uoper = Unetwork / √3 |
| Rated short-circuit current Iz: | According to requirements |
| Rated resistance of the resistor R [Ω -5%]: | R = Upoer / Iz |
| Rated frequency: | 50Hz |
| Rated withstand voltage with power frequency for 1 min: | In accordance with IEC for Unetwork: |
| Rated lightning impulse withstand voltage 1.2/50 μs: | In accordance with IEC for Unetwork |
| Thermal strength: | According to client requirements. Standard: 10s. |
| Protection class: | IP00 - IP23 |
Design of neutral earthing resistors
Neutral earthing resistor consists of a metal housing made of:
- Version A: powder-coated galvanized tinplates
- Version B: powder-coated welded frame founded on moving wheels. Housing walls are made of powder-coated galvanized tinplates
For both versions, the galvanized tinplates may be replaced by stainless steel plates. In this case, they do not require painting. (color INOX)
1. There are the following elements in the housing of the neutral earthing resistor:
- HV side terminal – medium-voltage bushing
- Bushing for Euromold connector head
- Porcelain bushing
2. Current transformer with appropriate reduction ratio as per specification. The primary side is connected in series to the resistor's power circuit, and the secondary side is led out to the terminal box.
- Terminal box of the current transformer’s secondary circuit
3. Steel grid resistance elements – made of FeCr steel, mounted on an insulated frame equipped with support insulators
4. Low voltage bushing - porcelain. The resistor operational earthing is connected to it
The resistor may optionally include:
- possibility to activate different short-circuit currents (manual jumper)
- additional equipment such as: voltage transformer, disconnector or circuit breaker
