The Application of the Drilling Motor

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IADC Members Abstract Proper application of the DC Drilling Motor Proper application of the DC Drilling Motor to drill rig equipment, including mud pumps, rotary table, top drive and drawworks, is essential in obtaining maximum performance and long life from the motor. Emphasis is placed on taking advantage of the motor's placed on taking advantage of the motor's torque and speed characteristics with a variable DC voltage source such as the SCR. Comparison of the advantages and disadvantages of the shunt and series type DC motor are analyzed. Recommendations are given on proper methods of motor cooling, storage, maintenance, troubleshooting and returning the drilling motor to service. Introduction The DC drilling motor, originally used on Diesel-electric locomotives, has established itself as a standard in the drilling industry for equipment requiring variable speed and controlled torque. Because of the production volume involved in using the motor production volume involved in using the motor in both industries, its cost is less than one-half that of industrial motors of similar ratings. It is also much smaller and lighter than comparable ratings and has proven itself in many years of severe duty in proven itself in many years of severe duty in locomotive and drilling applications. Over the years, several manufacturers have provided the motor in horsepower sizes of provided the motor in horsepower sizes of 600, 800 and 1000 with a typical top speed of 1000–1200 RPM. Because of the demand for more power in top drives, higher horsepower and torques are forthcoming for the drilling industry for this and other applications with an advanced motor. Better insulation, improved mechanical design and spiral grooving of the commutator provide better cooling to allow for this increase in rating in a similar size. A typical drilling motor is shown in Figure 1 in a cutaway view. Because of the reduction in rig count over the past several years, drilling rig equipment has been stored, modified, scrapped or replaced by the contractor. In addition, new personnel have appeared on the drilling scene as attrition of experienced ones has occurred. With these changes, a review and reorientation of the application, maintenance, troubleshooting and repair of the DC drilling motor is appropriate. DRILLING MOTOR TYPES The drilling contractor has several choices to select from when making a decision for a DC drive motor. The most popular ones are the Shunt Type DC Motor and the Series Type DC Motor. Each has its advantages and disadvantages as outlined below. The Shunt Type DC Motor When the DC motor was first introduced to the drilling industry offshore, the desire to have positive control of motor speed and a minimum of problems with the application led the driller to the shunt-type of motor design. Sometimes referred to as a separately excited motor because the field is supplied power separately from the armature, the shunt motor provides variable speed by adjusting its armature voltage. The schematic of this motor is shown in Figure 2. P. 353