Wire wound earthing resistors model RMT GRF


The purpose of an earth resistor of the star centre is to protect transformers and generators from short circuits between phases and between phases and the earth connection. In fact, when a resistor is inserted between the star and the earth connection the short circuit current is limited to a pre-set value that does not damage the equipment connected.
Additionally, the use of the resistor has the following advantages over other systems:
· It minimizes damage caused by mono phase failures at the earth connection
· It prevents the formation of temporary overloads;
· It limits the electro dynamic strain deriving from external breakdowns (in the network and down line);
· It decreases needless interruptions by protective devices.


OFEL RMT GRF resistors are robustly built earth connection resistors produced with materials that guarantee high dependability; the stainless steel protective casing, the stainless steel grid, the insulators in steatite and the insulating materials used confer robustness and a high degree of insulation to the RMT GRF product, also making it non-inflammable.
The RMT GRF resistors are used in all cases where there are high breakdown voltages and low electrical resistance values are required.
The groups are mounted on modular grid elements on two M12 braces and realise connections through reinforced stainless steel bridges with copper bars in the event of strong voltages.


Tolerance on resistance value ±10% Standard
Temperature coefficient 570 ppm
Maximum utilisation temperature 55+450 [°C]
Insulation current depends on requirements
Minimum resistance value depends on the number of elements
Maximum resistance valuedepends on the number of elements
Level of protection (IEC 529) IP 00 standard Maximum temperature reached on elements at end of transit 450 [°K] (unless requested otherwise)


· Active material:X10CrAl13
· Support BracesAISI 304
· Insulators steatite C221
· ScrewsInox A2


· IEC 529
· IEEE 32
· CEI EN 60694


The RMT GRF resistor has dimensions established by our technical office, taking into consideration:
Ohm valueR[Ohm]
The maximum breakdown current Ig[A]
The maximum duration of breakdown currentt[Sec]
Level of potential respect for earth connection E[Kv


· Ohm values off standard compatibly with production
· Off standard tolerances
· Special production with increased protection level up to IP IP54.
· Epoxy powder paint in RAL colours on request


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