Turbine motor pressure drop

A turbine device has the unique characteristic that it will allow circulation independent of what torque or horsepower the motor is producing. In the example where the turbine motor has a 10-lb/gal mud circulating at 400 gal/ min, the pressure drop through the motor is about 1,324 psi. This pressure drop is approximately constant through the entire speed range of the motor. 

When sufficient weight has been placed on the turbine motor and bit, the motor will cease to rotate and the motor is described as being stalled. At this condition, the turbine motor produces its maximum possible torque. Even when the motor is stalled, the drilling mud is still circulating and the pressure drop is approximately 1,324 psi. 

The pressure drop Ap (psi) through a given turbine motor design is usually obtained empirically. Once this value is known for a circulation flowrate and mud weight, the pressure drop for other circulation flowrates and mud weights can be estimated. 

Using the basic performance data given in Table 4-110 for the 6-f--in. outside diameter turbine motor with 212 stages, determine the stall torque, maximum horsepower and pressure drop for this motor if only one motor section with 106 stages were to be used for a deviation control operation. Assume the same circulation flow rate of 400 gal/min, but a mud weight of 14 Ib/gal is to be used. 

The last column in Tables 4-110 and 4-111 show the thrust load associated with each circulation floWrate (i.e.,-pressure drop). This thrust load is the result of the pressure drop across the turbine motor rotor and stator blades. -The magnitude. of this pressure drop, depends. on the individual internal design details of the turbine motor (i.e., blade angle, number of stages, axial height of blades and The radial width of the blades) and the operating conditions. The additional pressure. drop results in thrust, T (lb), whicit is... 

Planning for a positive displacement motor run and actually drilling with such a motor is easier than with a turbine motor. This is mainly due to the fact that when a positive displacement motor is being operated, the operator can know the operating torque and rotation speed via surface data. The standpipe pressure will yield the pressure drop through the motor, thus the torque. The circulation flowrate will yield the rotational speed. 

Frequently, a major unit shuts down when a compressor trips off. The cause may be low lube- or seal-oil pressure. The pumps providing the lube- and seal-oil pressure are typically spared (backed up). A steam turbine-driven pump is normally backed up by a motor-driven spare. The motor-driven pump should come on when the lube-oil pressure drops below a preset point. 

The symptoms of surge are pulsating pressure, rapid flow reversals, a drop in motor current and a jump in turbine speed. Continuous, rapid flow reversals can cause severe damage to the compressor. In axial compressors the blades may touch, resulting in instant destruction. However, centrifugal compressors are more mgged, and only seal damage results [15]. 

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