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Application of SLANVERT SB70G Inverter in Traction of Electric Locomotive in Steel Coking

The electric locomotive for coke transport is mainly to transport the red hot coke from the furnace of the coke plant to the wet quenching yard 300m away to cool it with water, and transport the cooled coke back to the finished product pile-up near the tap-off point, and then the same work cycle will be repeated. The electric locomotive starts in full load of coke, which is heavy. It requires that the inverter should have large startup torque with short and smooth startup time, and that the load of two motors should be basically balanced.

The torque of SB70G Series Inverter can reach 200% at the frequency of 1Hz, which realizes high-accuracy control of motor in large-torque startup. The operation panel has the function of programmability, operation, parameter reproduction, hot plugging, which greatly facilitates the operator in changing the parameters (set the parameters of only one inverter; for others, the parameters can be reproduced, reducing the amount of work during commissioning). Speed setting can be switched over by terminal. In instantaneous power failure, uninterrupted operation can be achieved through the bus voltage control. SB70G Inverter has powerful modular design and programmable unit design and a variety of optional accessories, allowing the user to make the second development according to the production technological requirement to reduce external cumbersome control components. It can also make automatic adjustment of carrier frequency according to the characteristics of the load and ambient temperature. It adopts a variety of harmonic suppression techniques with the total harmonic content lower than the national standard.

As the traction system is jointly driven by two 75kW electric motors, there are two schemes for consideration. One is to drive two electric motors with one inverter at the same time. If the parameters of the two motors are different, the load will be unbalanced. The other is to use two use two inverters to drive the two motors respectively with main and auxiliary synchronization control method, and set the main inverter to be speed control, and set the auxiliary inverter to be torque control to achieve load balancing. Considering that when the electric locomotive travels to the track joint, its head will shake violently, and the current will jump to 315A, this requires augmentation of the inverter to guarantee that the inverter work normally without trip.

We select two SLANVERT SB70G160KW Inverters for transformation. Dynamic braking is adopted for braking, and braking unit together with braking resistor is adopted to absorb the kinetic energy in sudden braking of electric locomotive.

With the above parameters setting, after the startup and operation of the coke transporting electric locomotive, the observation shows that during operation of the two inverters, the operation current of the motor is 167A (within the rated current range of the motor), and the load rate is basically consistent.

Frequency Conversion Transformation for Fan of Coke Plant

I  Current Situation:
The coke oven air blast cooling system of a coke plant has two fans of 400kW, one for service and one as standby, installed in front of the two primary coolers, that is a blast fan extracts coal gas from two primary coolers at the same time. To technologically ensure the maintenance of positive pressure of 120Pa in the primary cooler, speed of the blast fan needs regulation. The previous system adopted hydraulic coupler for speed regulation. In addition, it is required that both the positive pressures in the two primary coolers should be 120Pa. In the previous system, a manual operated valve is provided at the outlet of the cooler for manual adjustment. In the adjustment process, not only the valve opening should be adjusted, the oil pressure of the hydraulic coupler should also be adjusted to regulate the speed of the fan. As the valve and speed need to be adjusted and there is certain degree of coupling between the two, the case is often that the two cannot be attended at the same time, and it is difficult to meet the technological requirements. In addition, the hydraulic coupler is poor in speed regulation stability and inconvenient in speed regulation and low in efficiency. To meet the technological requirements and energy saving, transformation is needed.

II  Transformation Scheme
In consideration of energy-saving, the hydraulic coupler speed regulation will be changed to frequency-conversion speed regulation. To control the pressure of the two primary coolers, the combination of pressure closed loop control and electric valve control is adopted. The method is to install two pressure transmitters on Primary Coolers 1# and 2#. The pressure values of the pressure transmitters represent the pressure in the primary coolers. The measurement of Primary Cooler 1# transmitter is used to control the output frequency of the inverter, to stabilize the pressure at 120Pa. But the outlet air ducts of Primary Coolers 1# and 2# are connected in parallel. Due to certain factors, the pressure value of Primary Coolers 1# and 2# may not be the same. At this time, the regulator sends out signal to the electric regulating valve of Primary Cooler 2# so that the pressure values of Primary Coolers 1# and 2# are equal. The pressure value required to maintain the technological requirement is 120Pa. The regulation process will be repeated for several times, which are automatically carried out without human intervention. The coking blast cooling system control schematic diagram is shown in Fig. 6.

Fig. 6 Coking Blast Cooling System Control Schematic Diagram

III  Schematic Circuit Diagram and Control Principle of Transformation Scheme
1. SLANVERT SB61P400KW Inverter is adopted. Taking into account that the motors are one for service and the other as standby, to save investment, two fan motors share an inverter. When the motor needs reverse turning, the external wiring of the motor can be changed. As shown in Fig. 7 of Inverter Control Schematic Diagram, PT means the pressure transmitter; the figure shows a four-line pressure transmitter connection, with two lines not drawn. R means given regulation, which may also be set by the operation panel. KM1 and KM2 control the operation of one motor respectively.

Fig. 7 Inverter Control Schematic Diagram

As the hydraulic coupler is low in efficiency, it may be removed with out reserve. In the vacancy left, a reduction gearbox can be installed and its speed reducing ratio should be decided based on the technological conditions, that is, when the output frequency of the inverter is 50 (60) Hz, the air output of the fan is maximum. To reduce the quantity of work in installation of reduction gearbox, a careful selection of reduction gearbox should be made.

2. Installation of pressure transmitter:
The pressure transmitter is installed on the primary cooler. To simplify the control, the signal from the pressure transmitter of Primary Cooler 1# is sent to the inverter to control the pressure of Primary Cooler 1#; and the signal from the pressure transmitter of Primary Cooler 2# is sent to the regulator of the electric regulating valve to control the valve opening, in order to balance the pressure values of the two primary coolers. It is shown in Fig. 6.

IV  Energy Saving
In the transformation process, the hydraulic coupler is replaced by reduction gearbox of 1.25:1. In production and operation, the output frequency of the inverter changes around 34Hz, and the energy saving effect is calculated as follows:
The air volume of the 400kW fan falls from 100% to 70%; (begin a new line up) as the flow rate is proportional to the first power of the speed, the speed can be reduced by 70%, and the load power is reduced to 34.3% in theory. If the efficiency-conversion speed regulation efficiency is calculated by 0.95, considering the efficiency of the motor will decrease in low power and pipeline system efficiency will decrease, the total input power of the power grid is about:

400×(34.3%/0.95/0.85/0.95)=400×44.71%=178.84kW

If hydraulic coupler is adopted, its efficiency is calculated as 0.665, and the total input power of the power grid is: 

400×(34.3%/0.665/0.85/0.95)=400×63.87%=255.12kW,

The difference between the two is the electric energy saved, that is:

255.12-178.84=76.28kW

Taking the whole year to be 300 days, the annual electric energy saved is: 

76.28×300×24=549216kWh.

Based on the actual measurement, the energy saved by this system is 21.9%, which achieves good economic benefit.