Design of the earthing resistors

GINO earthing resistors consist of resistor packs with cast iron resistor elements with or without surface protection or stainless steel grid elements. Alternatively, earthing resistors with all other resistor designs can also be offered and manufactured.

Characteristics of earthing resistances

In addition to the conductor voltage to earth, the parameters are

• the cold resistance, which determines the initial current,
• the current flow time,
• the temperature increase during the switch-on time
• and the resulting hot resistance, which also determines the current at the end of the switch-on time.

The capacity of the resistor is expressed by the current-time integral [i2t] = kA2s.

The insulation of the resistors is rated for the system voltage. System voltages are 12, 24, 36 and 52 kV. Depending on the climatic conditions, the risk of soiling and the geodetic height at the installation site, increased air and creepage distances may need to be provided.

Types of protection

Resistors for indoor installation in electrical operating rooms are manufactured with protection class IP00 or IP20. Important: For outdoor installation, protection class IP23 is required as a minimum. Higher degrees of protection are problematic in view of the limited ventilation due to the thermal load on components, insulators and housings.

The maximum temperature must be agreed between the manufacturer and user in accordance with IEEEStd32-1972. Depending on the resistor material used, high temperatures do not pose a problem for the resistor itself.

Special protective measures are only required:

• Housing,
• insulators,
• current transformers
• switches/vacuum contactors
• and cable terminations

Special measures must be taken to protect these components against excessive heating.