Grounding resistors wire model RMT RFC

USE

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.

DESCRIPTION

OFEL RMT resistors are robustly built earth connection resistors produced with materials that guarantee high dependability; the stainless steel protective casing, the support in thermo electric material, the ceramic insulators confer the RMT product with robustness, a high degree of insulation and make them non-inflammable.
Additionally, the FeCrAl alloy used for the winding guarantees limited resistance variations, maintaining current veritably constant during use.
RMT resistors are now a consolidated OFEL product, thanks to the experience acquired over the years, and have achieved a standard configuration that is developed in height in order to contain space required inside electric panels and cabinets.
The groups may start from a base of three or four elements and be developed in height up to 20 elements (max. 5 levels). Each level is insulated with ceramic insulators that have a guarantee for the required insulation class.

ELECTRICAL CHARACTERISTICS


· Tolerance on resistance value ±5%
· Low temperature coefficient ohm values 12 ppm
· High Ohm values 70 ppm
· Maximum utilisation temperature 55+350 [°C]
· Insulation current depends on requirements
· Minimum resistance value 1W x n° elements [W]
· Maximum resistance value 27kW x n° elements [W]
· Level of protection (IEC 529) IP 00
· Temperature reached on wire at end of transit less than 450 [°K]

MATERIALS USED

· Ceramics Cordierite C511
· Cementinorganic
· Resistive alloyFeCrAl/NiCr/Cuni
· SupportsAISI 304
· Insulators in porcelain

APPLICABLE STANDARDS


· IEC 529
· IEEE 32
· CEI EN 60694

DATA NECESSARY TO REQUEST AN OFFER


· The RMT resistor (n) RFC has dimensions established by our technical office, taking into consideration
· The maximum breakdown current Ig[A]
· The maximum duration of breakdown currentt[Sec]
· Level of potential respect for earth connection E[Kv]

OPTIONAL


· 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.

STANDARD CHARACTERISTICS


 
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