Power Resistors

Often required as a replacement mill bank, the Penbro version of the mill bank is well suited with its rugged construction. Our mill-banks are manufactured locally which helps to significantly reduce the time of a breakdown.

• Dynamic braking and acceleration of small locomotives — for example those used at mines in Zambia, such as the 15T GOODMAN and other locos which require the MG8 and MG12 0.9 ohm mill bank.
• Dynamic braking of dragline excavators often used at coal mines, that require the MG5 mill bank.
• Neutral grounding applications.

Our High Power Braking Resistors (HPBR) are offered in two categories — the HPBR34 and the HPBR50 for higher power motors. These dynamic braking resistors are a low cost solution for high power and short duty cycle braking of electric motors driven by a variable speed drive (VSD).

The HPBR range incorporates special stainless steel grid resistors enclosed in a neat galvanized IP20 or IP22 enclosure.

A widely utilised approach to managing fault currents is the installation of neutral earthing resistors (NERs). NERs — sometimes called Neutral Grounding Resistors — are used in AC distribution networks to limit the fault current that flows through the neutral point of a transformer to a safe value.

Electrical equipment with non-linear characteristics creates harmonic currents that can lead to distortions of the network power. The increased usage of arc furnaces and static converters has forced electric companies to control and limit harmonic distortion rates in their distribution networks.

Harmonic Filtering Networks are passive circuits that lower distortions caused by harmonics and balance the power factor. The LC circuit filters all spurious frequencies, while Harmonic Filter Resistors (Damping Resistors) dissipate harmonic currents as heat energy.

VSD brake resistors are mainly used to quickly stop or slow down electrical motors by absorbing excess power and dissipating it as heat. They ensure much faster motor braking, lower wear on friction components and keep motor voltages within safe operating levels — extending overall motor lifespan.

VSD Brake Resistors are installed wherever a motor/drive controls machinery — including industrial factory applications and construction equipment such as cranes. Our brake resistors are offered in standard galvanized enclosures for fast production and an affordable price.

The locomotive brake resistor is used for regenerative braking of the locomotive, in both diesel and electric applications.

We are proud to be part of South Africa's largest ever locomotive project — supplying brake resistors for Transnet's new Bombardier and China South Rail (CRRC) locomotives, and for PRASA's new EMU passenger trains.

We offer green silicone-based coated wire wound resistors with power ratings from 20 W to 500 W per resistor. The heat-resistant VOC-compliant silicone coating protects the winding against moisture, outdoor weathering, UV light, salt spray and chemical erosion. Resistance values and power ratings are available to customer specification.

We also offer customer-specific assemblies such as locomotive headlight resistors, where two or more resistors are mounted onto a single pair of metal brackets.

A compact, robust enclosure housing a single or two wire-wound resistors. Due to the heat dissipated by resistors it is often required that the resistor be enclosed and mounted external to an equipment panel. It is also a suitable solution for dynamic braking of small electric motors driven by a variable frequency drive, or for training purposes at educational institutions.

Connected to the rotor circuit to limit starting current and provide the required starting torque. The resistance is progressively reduced through several switching stages using contactors. Once the motor reaches its normal operating speed, the resistors are completely short-circuited.

Connected to the rotor circuit of a slip-ring motor to control its operating slip, speed and torque. The resistor remains connected and dissipates power during normal operation.

The edge wound resistor is manufactured to handle higher power capacity and is used for high power dynamic braking on locomotives, older model PRASA coaches and their braking systems.

Penbro Kelnick offers and refurbishes oval edge-wound resistors, continuous ribbon resistors and stamped grid resistors. We also manufacture a range of replacement parts for resistors used in locomotives, and can assemble arrays of these robust resistors for large dummy load banks up to approximately 500 kW.

These resistors are non-inductive by having half the winding in one direction and the other half in the opposite direction, ensuring that the net inductance is nil.

The non-inductive resistor finds application in the high-frequency communication industry, usually connected to antennas and transmission towers.

Our DC and AC load banks range in size from 1 kW for a table-top unit to 75 kW for a floor standing unit. These load banks are ideally used as dummy loads for testing apparatus and for discharging battery banks. Load banks up to 500 kW are mounted on a factory-built trailer for mobility.

Current steps are obtained by switching circuit breakers in steps of 1 A to 100 A. Load banks are force air-cooled and supplied with digital meters to display voltage and current. Custom builds are available to any specification.

Our cab heater incorporates a single and/or dual heating arrangement, enabling train cabs and coaches to be used immediately rather than waiting for the train's water temperature to reach a suitable level. This is important to the train operator who must provide the driver with suitable working conditions.

Custom resistors sized and rated to customer specification are available for nearly all applications, from low to high voltage.