Specialty Products and Services

Wound Rotor Motor Starters

Wound Rotor Motor Starters

Wound rotor motors are typically used in application requiring high starting torques, a limited number of operating speeds, or a stepped acceleration to achieve a soft start. Typically, existing applications utilize an electro-mechanical starter on the stator, and introduce multiple stages of resistance in the rotor via a contactor arrangement to achieve a soft ramp.

With the RediStart MX2/MX3, wound rotor control is greatly simplified. The RediStart consists of two main major sections:

  1. A solid-state stator control
  2. Secondary resistors into the rotor circuit from a separate 3-phase resistor bank.

This design achieves the high torque required by the application , with low inrush, while providing a smooth stepless start... greatly reducing the maintenance cost of the typical electromechanical control.

Power Factor Correction Products

Power factor correction capacitors are typically wired in parallel with the motor load at various points in the distribution system. In situations where a variety of inductive motors or loads are being switched on and off independently, it is desirable to apply the capacitance to the individual load. For that reason, it is important that power factor correction be specifically matched to the inductive load with which it is associated.

In an ideal system, a motor is corrected when its inductive reactance equals the capacitive reactance at the line frequency … over or under correction of the load will result in poor performance, and possible damage to the capacitors and motors. Over correction occurs when the resonance frequency is less than the line frequency.

Each inductive load — especially electric motors — requires a properly sized power factor correction capacitor. While a helpful starting point may be found in standard look-up tables, or other theoretical predictors of optimum capacitance, the better practice is to specifically match the capacitance to the measured characteristics of the particular motor design.

Available Models

Benshaw APFusion automatic power factor correction packages are designed to suit customer system requirements for power factor correction. These sytems are controlled by a Benshaw AP Fusion 12 step programmable controller with LED display, in a NEMA 1 enclosure, with disconnect and required capacitor steps.

IPFusion is a patented, integrated power factor correction product family that contains presized, preselected components within a modular housing structure. Benshaw’s IPFusion units have been pre engineered and preassembled for simple plug and play power factor correction. IPFusion power factor correction units are also designed to mate easily to your load—both electrically and physically. They occupy a minimum amount of space for ease of mounting near the load. Each unit includes the housing, terminal blocks, capacitor, precharge control, and a contactor. Integrated fuse protection is optional.

DC Injection Braking

Benshaw DC Injection Braking is available with the standard reduced voltage soft starters, or as a stand alone braking unit.

Available Models

Solid State Starter with DC Injection Braking
Benshaw MX2/MX3 starters with DC Injection Braking consist of a three phase solid state starter with an integrated SCR power block, power fuse, and control logic for the DC Injection circuit. The Brake stop mode allows a static DC field to be injected into the stator of the motor, which makes the rotor stop in a fashion similar to the way the three phase rotating magnetic field brings the motor up to operating speed. Examples: saws, E-stop applications, machine tools, and high inertia loads. Available in Standard Duty or Heavy Duty.

Synchronous Controllers

Brush and Brushless type exciters

Synchronous motors function as an induction motor during start-up. Once the motor approaches full synchronous speed, the RediStart DC exciter induces a constant polarity to the rotor, causing the motor to lock into sync. Because the rotor's field is constant, and separately excited, there is no slip required to produce torque, as with an induction motor, allowing the motor to run at synchronous speed.

Benshaw synchronous packages can be incorporated into solid state starters, full voltage starters, or supplied as a separate stand alone package.

The SEP (Synchronous Exciter Package) can be supplied for brush type and brushless exciters.

Available Models

Solid State Starter with SEP
The Benshaw synchronous solid state starter package consists of a RediStart series solid state starter connected to the stator to provide a smooth stepless acceleration, and the SEP section that is connected to the rotor, in conjunction with the discharge resistor to provide automatic synchronization. This can be supplied for brush type, and brushless exciters.

Full Voltage Starter with SEP
The Benshaw synchronous full voltage starter package consists of a contactor starter system that is connected to the stator, and the SEP section that is connected to rotor, in conjunction with the discharge resistor to provide automatic synchronization. This can be supplied for brush type, and brushless exciters.

Stand Alone SEP
The Benshaw stand alone Synchronous Excitation Package can be connected to the rotor section in conjunction with a discharge resistor, and incorporated into an existing starting system to provide automatic synchronization of the three phase AC synchronous motor.

- Download Synchronous Brochure

Ball Mill Positioning

When it comes time to service the mill an access hatch must be positioned to allow technicians to enter the mill and for the ball charge to be changed. That is when difficulty can begin. Positioning the access hatch is accomplished by a process known as spotting or inching. Without a dedicated inching system it can be difficult to precisely position the mill, since the technician has no way to accurately and effectively apply torque to the motor directly from the power system.

Traditional positioning technology involves applying a switched DC current to the stator windings in a specific pattern to simulate the sinusoidal AC wave form applied during normal operation while keeping the field excited. In addition to the issue of precisely moving the bulky mill, the cogging or abrupt starting and stopping of the motor can cause mechanical and electrical damage to the equipment. This, along with full voltage starting, stresses the overall electromechanical system and can cause excessive downtime interfering with maximized production.

Working with a long time customer and local Benshaw partner in the motor controls industry, Benshaw has successfully applied a 480VAC 700HP AC Variable Frequency Drive for positioning a MV synchronous motor driven ball mill. The Benshaw variable frequency drive powers the 4160Volt - 3500HP synchronous ball mill motor during positioning to smoothly rotate the ball mill and bring it to the proper position for maintenance. The customer’s previous system utilized multiple DC contactors and a motorized cam switch to position the mill. The speed of motor rotation was fixed at a slow 0.18 hertz by the cam switch operation. At this slow speed, mill maintenance took an entire day to complete with the resultant loss of production time.

Configured to replace the cam switch, the DC contactors and DC motor-generator set arrangement, the low-voltage Benshaw AC variable frequency drive has the capability to provide full torque at zero speed to start and rotate the mill during the positioning process. The use of a drive also provides speed adjustability to a maximum speed of six (6) hertz. This is thirty (30) times the previous inching speed, allowing the maintenance setup and process time to be significantly reduced. Further, the drive replaces the obsolete and unsupported cam switch, and eliminates the DC contactors and the associated contact tip maintenance.

Implementing the AC variable frequency drive technology from Benshaw will provide reliable motor control, along with financial savings and improved asset protection. The reliability of Benshaw’s drive technology leads to increased production and greater uptime by reducing maintenance downtime. 

- Download Ball Mill Positioning Brochure