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38 www.coalage.com May 2017 plow mining continued a lot more precise than a voltage source inverter (VSI) with VFDs, delivering a very clean, near sinusoidal current and voltage waveform with total harmonic distortion (THD) below 5%. The CSI VFDs used at Bog- danka have regenerative power capabilities, thus they can absorb power flow back from the motor into the power supply. All four VFDs together with a special liquid cooling station are positioned in the energy train on the tailgate side of the plow system. The cooling station is working on all four VFDs, using a closed circuit for the coolant. The application of VFDs brings a sig- nificant improvement for the plow and AFC operation. It implements among oth- ers the following advantages: • Application of standard asynchronous motors; • Distance between motors and power- ing VFDs up to a few miles; • Variable speed for AFC and plow in a wide range (0 to 120% of nominal speed); • Precise torque control of the asyn- chronous motors; • Full use of installed power on both plow's motors through load sharing; • Improvement of overload protection for motors and chains; • Braking possibilities and thus return- ing back power to the network; • Unlimited startups of the motors; • No significant voltage drop during startups; and • The usage of "weaker" networks is possible. The parameterization and control of the VFDs is realized from the control sys- tem located on the surface. Another important technical inno- vation is the very first application of a new CST gearbox. This unit is designed for operation at any rotational speed, at the perpetuation of all previous features of CST drives in worldwide operation. Thus the ap- plication of CST drives delivers a very sensi- tive overload protection for the chains. During November 2014, the third GH1600 plow system commenced oper- ation at the Nadrybie plant. The length of the Bogdanka III longwall was 1,000 ft. This system was very similar to the previous one i.e., to the Bogdanka II plow system. The fourth plow system of type GH 1600 started the operation in May 2015. This sys- tem was for the first time implemented at the Bogdanka plant i.e., at the main shafts, where past mining activities took place. The Bogdanka IV system cuts coal in difficult geological conditions. Bogdanka is one of the most advanced mines worldwide. The performance mag- nitude and mining efficiency are their most important decision criteria for the selection of mining equipment. The Bog- danka miners are well-skilled and moti- vated, possessing a very high level of tech- nical knowledge. The Cat plow systems running at Bog- danka have in the last five years achieved a total performance of about 30 million raw tons, although in many periods only two or three plow systems were opera- tional simultaneously. All presented plow systems delivered in the past interesting performance. Table 1 presents the daily achievements from eight GH1600 plow panels operating at Prosper Haniel, Pinnacle and Bogdanka. The Potential for Future Development Contemporary plow systems possess strong potentials for a high performance. A GH 1600 plow system equipped with 2,146 hp is able to reach an average performance of more than 11,000 t/d, even in seams with very hard coal. The diagram in figure 10 presents a theoretical calculation of a per- formance potential of a GH 1600 plow sys- tem as a function of the coal hardness (ac- cording to the DMT scale) and of the total daily running time. This calculation was car- ried out based upon a 990-ft-long face with working height between 59 in. and 71 in. The performance achieved by the plow systems presented in previous chap- Figure 10—Performance potentials of a GH 1600 plow system. Table 1—ROM Performance of the GH 1600 plow systems at Prosper Haniel, Pinnacle and Bogdanka mines.