Telema - Earthing, Load, Harmonic Filter and Motor Control Resistors

Telema Spa is a leading manufacturer of a wide range of electric power resistors, including neutral earthing resistors (grounding resistors), starting and braking resistors for motor control, load resistors, harmonic filter resistors and resistors for railway applications.

NEUTRAL EARTHING RESISTORS

The best way to protect transformers and generators against ground fault currents is to install a Telema neutral earthing resistor between the star point and the earth.

The Telema neutral earthing resistor provides many advantages over other protection systems such as reactances, isolated neutral or direct grounding. These advantages include moderate fault currents, the absence of temporary excess voltage, a reduction of untimely protection operations as well as a facility for locating failures.

We produce grounding resistors ranging from class 3.6kV to 72.5kV, with currents at several thousand amperes and chassis protection from IP23 to IP55. These resistors can incorporate load-less switches, load-break switches, vacuum contactors, CT, VT, etc.

RESISTORS FOR MOTOR CONTROL

Telema makes rugged, stainless steel resistors designed for trouble-free service:

Wound rotor motor control resistors - used on cranes, pumps, large blowers, mil drives, etc. Telema can provide torque and speed control performance to suit any application.

Reverse braking resistors (plugging) - when wound rotor motors brake by applying reverse currents. Plugging resistors provide the precise control of torque braking and speed characteristics.

Primary starting resistors - when it is necessary to limit the starting current of squirrel-cage induction motors.

Braking resistors for inverter drives - for when applications needing high braking energy require dynamic braking resistors. Telema provides a wide variety of inverter braking resistors, custom-tailored to the client's needs.

LOAD RESISTORS

Telema load resistors are custom-designed to optimise your testing capabilities. Made from low temperature-coefficient resistance materials, they provide an accurate and stable load to minimize unwanted variables in your testing.

The Telema charge resistors feature low inductance, high overload capabilities and long life. Ideally suited to either convection or forced-air cooling, our designs allow the utmost flexibility in tailoring your load bank:

• Mixed loads, including inductance and capacitance, provide any electrical characteristics you may require
• Complete control and instrumentation
• Indoor or outdoor enclosures, suitable for any environment
• Portable or mobile construction

HARMONIC FILTER RESISTORS

Complex waveforms, created by the increasing use of solid-state devices in power system converters, motor controls etc., feed harmonics into power systems, causing trouble with equipment connected elsewhere in the system.

Filters, consisting of tuned RC circuits, are used to remove harmonics from industrial plant power supplies and distribution networks. Since RC circuits can be difficult to tune, resistors are often used to increase bandwidth.

Telema harmonic filter resistors feature:

• Element design, which minimizes both skin effect and reactance
• Outdoor stainless steel enclosure as standard equipment
• Custom enclosure and finishes available
• Protection from IP23 (standard) to IP55
• In-house BIL testing available

RESISTORS FOR RAILWAYS APPLICATIONS

Telema has a range of power resistors that covers all railway applications, including:

• Dynamic braking resistors
• Snubber resistors
• Filter charging / discharging resistors
• Soft crow bar resistors
• di/dt resistors

Owing to our full range of elementary components, a full industrialized and very simple assembly and our property simulation and design software, we are able to meet the optimal characteristics typically requested of a traction resistor: minimum weight and bulk, high reliability, low operating temperature, high vibrations resistance and high maintainability.