Memoirs of a GDC intern

Doing a course that encompasses both Electronics and Mechanical aspects of engineering gets you the key to open up anything. I am not limited. Hence when the Electrical technician called us in for dismantling of electrical connections, we were happy, I and my friend Justus to quickly come on board.

So before we started the job, the technician in charge of electrical systems had to explain to us about the electrical systems before we touched anything. The Drilling rig is powered by 4 large diesel engine sets of type CAT 3512B that output 600V,50Hz AC that is changed to 0-750DC through the SCR cabinets in the adjacent room to drive the drawworks, rotary table and mud pumps…all YZC-800A motors of the series excitation type. The DC motors driving the mud pumps and rotary tables are independently driven in a 1 to 2 model with AC-SCR-DC drive. Each of the motors has a max current of 1600A and max speed of 1500rpm. There is one extra auxiliary CAT 3406 generator that has a battery starting system that produces AC voltage used to support minor rig operations and also power up the two LS-12 Sullair compressors that provide pneumatic power, stored in a tank and maintained 0.8-1.2 bar for starting the four massive generators.

Behind the generator rooms, there are large powerful transformers used to take the 600V generated AC voltage down to 220V for basic lighting, 480V MCC and distribution (MCC is motor Control Center). MCCs control the motors and hence the auxiliary components associated with the drilling process. The drilling equipment like mud pumps, drawworks and the rotary table actually consume most of the power and only a small quantity goes to lighting, powering the maintenance, mess, toilets, geology and operations cabins. Each rig at Geothermal Development Company has three triplex type mud pumps, the F1600 type and the maximum power to their motors is limited by the SCR so that the pump can receive more power than what it is supposed to receive.

Rig 1 and Rig 4 have top drive systems though both are spoilt and not functioning. A top drive is just an alternative method of rotating the drill string by putting a motor in the derrick below the travelling block and the hook. This is the only motor that I have ever seen running vertically.

The two LS12 compressors are configured to work together such that one is a master and the other is a slave. In case the master compressor needs more aid to fill up the 2.5 cubic meter tank, it can switch on the slave and can again put it off. The compressor is put on and off manually.

CAT 3512B

The 12 in the model type should be enough to tell you that the engine is a V12 diesel engine equipped with the latest technologies that CAT has showered over its latest models like MEUI (Mechanically Activated Electronically Controlled Unit Injectors). It has an advanced ECM and sensors to control its functioning. Normally, the ECM has a flash file that contains operating maps which define characteristics of the engine like Horse Power and the Torque curves.

The ECM detects the timing and amount of fuel delivered to the cylinders based on the actual conditions and/or the desired conditions at any given time. It also compares the desired engine speed and the actual speed given by the engine speed sensor. Desired engine speed is determined by the throttle signal and other inputs and if the desired engine speed is higher than the actual one, the ECM injects more fuel to increase actual engine speed.

Thus the ECM controls fuel injection by varying the signals being sent to the injectors. We know that the injector only pumps fuel when its solenoid is energized by a high voltage signal, so by controlling the timing and duration of the high voltage signal, engine timing and RPM can be controlled. The limits of the fuel injection are on the flash file in the ECM. ECM normally determines the timing by calculating the TDC of each cylinder and decides when each of these cylinders should fire. The ECM configurations can be done by connecting an adaptor cable to the ECM and computer running CAT SIS or a lighter CAT ET. I remember using CAT SIS 2012B and playing around with a few flash files in the “Test ECM mode”.

Otherwise, for any of us who has been in the automotive industry, apart from the pneumatic starting, the engine is just the same-with alternator, fuel filters (these are larger), fuel priming pump, engine oil pump, turbocharger, inlet air manifold, fuel transfer pump, exhaust manifold, air control valve, Clean Gas Induction (CGI) actuator, oil cooler, oil filters etc….just like any large Diesel engine.