Types of resistors

Neutral point grounding resistor

SIMPAX - neutral pointgrounding resistors of the transformer and generator neutral point

Neutral grounding resistors are high power resistors that are mainly used in the power industry. They are used in power networks as neutral grounding resistors of the transformer's own needs. They are used as support devices in the detection of earth faults in medium voltage main power supply station, to reduce earth-fault overvoltage and to create better conditions for earth-fault protection devices. Neutral grounding resistor is permanently connected to the transformer neutral point and during normal operation it takes over minor loads (up to 10% of Iz) resulting from phase asymmetry.

Frame Earth fault at any of the phases (L1, L2, L3) causes a difference of potentials at the neutral point, which results in the flow of short circuit earth current. Rated resistance of the neutral grounding resistor (R) limits that current to the value of IZ which is equal to the rated short-circuit current of the resistor.

The current flows through the neutral earthing resistor and the primary side of the current transformer, connected to the resistor in series. Current formed at the transformer secondary side flows to the resistor distribution box to which disconnecting automation is connected. The signal is used as information on short circuit.

The manufacturing of neutral grounding resistors in the SIMPAX company is carried out in accordance with the ISO 9001:2015 quality system. For the production of resistors, we use the latest technologies, proprietary construction solutions, modern resistance elements and materials tested in the railway industry. Our neutral grounding resistors meet the highest requirements in terms of quality, safety and durability. These reliable units are characterized by failure-free operation over a long period of time. [see our REFERENCES]

SIMPAX manufactures neutral grounding resistors for every application, power (from a few Watts to a MW) and load cycle.

Note:Based on many years of experience and advanced 3D modeling, we can individually custom design a non-standard neutral grounding resistor, requiring unusual resistance elements and power [see SPECIAL DESIGN RESISTORS], including replacements units for neutral grounding resistors.

Due to several types of solutions for grounding the transformer neutral point, there are the following resistors:

  • neutral grounding resistors - click
  • high and medium voltage forcing resistors - click
  • AACF cabinets - click

Parameters of neutral grounding resistor

Znamionowe napięcie sieci Usieci:   6,3kV – 30kV
Znamionowe napięcie pracy rezystora:   Upracy = Usieci / √3
Znamionowy prąd zwarcia rezystora Iz:   Zgodnie z wymaganiem
Znamionowa rezystancja rezystora R [Ω -5%]:   R = Upracy / Iz
Znamionowa częstotliwość:   50Hz
Znamionowe napięcie wytrzymywane o częstotliwości  sieciowej przez 1 min.:   Zgodnie z IEC dla Usieci
Znamionowe napięcie wytrzymywane udarowe piorunowe  1,2/50 μs:   Zgodnie z IEC dla Usieci
Wytrzymałość cieplna:   Zgodnie z wymaganiem odbiorcy.  Standardowo 10s.
Stopień ochrony:   IP00 - IP23

Design of neutral point grounding 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. (colour INOX)

The neutral grounding resistor housing contains the following components:

1. 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

5. The resistor may optionally include:

  • possibility to activate different short-circuit currents (manual jumper)
  • additional equipment such as: voltage transformer, disconnector or circuit breaker


SIMPAX sp. z o.o.

Grabonóg 76
63-820 Piaski
(k. Gostynia)

+48 65 571 20 60

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