Types of resistors

Neutral point grounding resistor Forcing resistors

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SIMPAX - medium and low voltage forcing resistors for power networks

The series of ZKFW forcing resistors manufactured by SIMPAX is used in compensated MV networks. The use of this type of forcing resistor improves the operation of earth-fault protection devices.

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Resonant earthed (neutral) system – a network where the neutral point is connected to earth by inductive reactance (Petersen coil) chosen in such a way that a one-phase short-circuit with earth results in compensation of volumetric component of current to an extent enabling self-damping..

SIMPAX manufactures medium and low voltage forcing resistors:

  • [primary] medium voltage forcing resistors - the transformer neutral point is grounded by the arc-suppression coil so-called Petersen coil. Parallel to the Petersen coil, a forcing resistor equipped with the medium voltage vacuum circuit breaker and an optional with the current transformer is connected to the ground. During ground fault of one of the MV phases, it is activated for a few seconds in order to force the flow of the active component of the earth current. In this case the use of a resistor results in better detection of short-circuits.
  • [secondary] low voltage forcing resistors - it is also earthed by an arc-suppression coil (mentioned so-called Petersen coil) but has a low voltage secondary winding to which the resistor is connected. The resistor is activated by the contactor and forces the active component of the earth current.

Forcing resistors parameters

Network rated voltage Unetwork:  6,3kV – 24kV
Rated operating voltage: Uoper = Unetwork / √3
Rated short-circuit current Iz: 20A – 300A (possibility to create resistor adjusted for different current values – tapping connections):
Rated resistance of the resistor R [Ω -5%]  R = Upracy / 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 In accordance with IEC for Unetwork
Thermal strength: According to client requirements.  Standard: 10s. in two cycles 5s each.
Protection class:  IP00 - IP23

Design of forcing resistors

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 Forcing resistors consist of the following components:

  1. Metal housing made of:
  • Version A: powder-coated galvanized tinplates
  • Version B: powder-coated welded frame. The frame is 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)

2. Medium voltage bushing

3. Connection unit one-phase vacuum circuit breaker adapted to the resistor parameters.

  • Control box / control unit – includes a control switch which regulates the connection unit

4. Current transformer

5. Resistance elements (resistor) connected in series. The whole unit is installed on a frame made form material acting as an electrical insulator

  • Support insulators – the frame with resistance elements is mounted on them. They also ensure necessary air

6. Low voltage bushing – made of porcelain, M12.

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The resistor may optionally include:

  • possibility to activate different short-circuit currents (manual jumper)
  • other additional equipment according to demand 

SIMPAX sp. z o.o.

Grabonóg 76
63-820 Piaski
(k. Gostynia)

+48 65 571 20 60

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