Application of High Voltage VFD (Variable-frequency Drive) on Wire Cable Conveyor

overview

The four major pieces of equipment in coal mines are mainly lifting and transportation equipment, coal mine main ventilation equipment, coal mine drainage equipment and coal mine pressure air equipment. Coal mine lifting and transportation equipment is the "money printing machine" of coal mines. Important equipment for coal mine production. Belt conveyor plays an important role in coal mine hoisting and transportation equipment. As a kind of belt conveyor, steel cable conveyor has always played an important role in coal mine production.

The steel cable traction belt conveyor (hereinafter referred to as the cable belt conveyor) in the No. 1 shaft of Sangshuping Coal Mine is responsible for the transportation of raw coal in the inclined shaft and the tasks of people going up and down the shaft. The current drive system of this belt conveyor adopts thyristor cascade speed regulation, the motor is JRQ158-6 high-voltage winding motor (power 550kW, voltage 6kV), the reducer is NGW172 planetary gear reducer, without soft start device. The tensioning method is heavy hammer tensioning.

This steel cable belt conveyor was installed in 1978 and handed over for use in November 1979. It has been in service for nearly 30 years. Over the past 30 years, despite several overhauls of on-site components, production can barely be maintained. Since 2007, the operating condition of the equipment has deteriorated sharply, and all major technical indicators have dropped severely. The main problems that exist are:

1. There are defects in the motor, and the main performance indicators have dropped significantly.

2. The operating conditions of the two planetary gear reducers are very poor, seriously affecting production.

3. The SECJ-06 full-digital inverter controller often fails, resulting in failure to work normally.

4. The high-voltage contactor that supplies power to the main motor is seriously aging and often breaks down.

5. The high-voltage switchgear is an oil circuit breaker with oil leakage and insufficient protection.

1. Transformation plan

In order to ensure the safe operation of the steel cable belt conveyor and ensure the safe production of Sangshuping Coal Mine, Xianyang Shun’an Coal Mine Design Institute conducted a serious analysis and demonstration on the electrical control system transformation of the mine’s steel cable belt conveyor according to the requirements of the Sangshuping Coal Mine. , under the premise of meeting the "Coal Mine Safety Regulations" and the actual requirements of the mine, in line with the principles of safety, efficiency and economic feasibility, a high-voltage frequency conversion speed regulation transformation plan is proposed:

Update the high and low voltage power distribution system at the user's site, adopt the PLC electric control system, adopt the high voltage VFD (Variable-frequency Drive) drive system, and replace the motor and reducer.

In this transformation plan, the high and low voltage power distribution system, PLC electric control system, motor and reducer have mature manufacturers and equipment; in the selection of high voltage VFD (Variable-frequency Drive), because in the dragging of domestic steel cable machines in China There is no successful case of using high-voltage VFD (Variable-frequency Drive) for reference, and the wire rope machine in Sangshuping Coal Mine has negative force during operation, and reverse rotation is required under special circumstances, which further improves the VFD (Variable-frequency Drive) Drive), the Design Institute and Hancheng Mining Bureau did a lot of work, and finally selected two sets of HFV1000 serious high-voltage VFD (Variable-frequency Drive) produced by Chengdu Sunwoele Co., Ltd. The VFD (Variable-frequency Drive) is a VFD (Variable-frequency Drive) with vector control, regenerative braking, and four-quadrant operation. During operation, they have the same operating parameters, start synchronously, and the power balance is completed by the participation of the electronic control system.

Wire rope traction belt conveyor is a long-distance, large-capacity, high-efficiency transportation equipment. In the Sang Mine, the steel cable belt conveyor is used not only for coal transportation, but also for the upper and lower personnel.

The schematic diagram of the transmission device of the steel cable belt conveyor in this mine is shown in Figure 1.

Figure 1 Schematic diagram of the transmission device of the steel cable belt conveyor

In order to improve the flexibility and reliability of the belt conveyor, the mine steel cable belt conveyor has two working modes:

(1) In normal working mode (i.e. two-motor dragging), without using a mechanical differential, each motor drives a driving wheel. There is no rigid connection between the two motors, but an elastic connection made of steel wire ropes and tapes. The two motors The speed control loops are independent.

(2) Standby working mode (that is, single-machine driving). When one of the speed regulating devices fails, the double-machine driving can be changed to single-machine driving to maintain normal production.

2. Synchronous start and power balance control scheme of the drag motor

In the normal working mode, that is, when the two machines are dragging, since the two driving motors of the steel cable belt conveyor are connected with different shafts, in order to realize the speed synchronization and power balance between the two driving motors of the belt conveyor, the control of the two motors They should not be independent of each other, but interrelated with each other. Therefore, the master-slave control method is adopted in the design, and the PID adjustment is carried out by collecting the motor current to judge, so as to achieve the speed synchronization and power balance between the two drive motors. System speed, current closed-loop control block diagram 2 is as follows.

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Figure 2 System block diagram

Four-quadrant high-voltage VFD (Variable-frequency Drive)

During the operation of the motor, the torque direction is the vertical axis, and the speed direction is the horizontal axis. When both the torque and speed directions are positive, it is positive traction, which is the first quadrant; when the torque is positive and the speed is negative, it is reverse braking, which is the second quadrant; both torque and speed directions are negative, which is the reverse quadrant. To traction, it is the third quadrant; if the torque is negative, the speed is positive, it is positive braking, it is the fourth quadrant. As shown in Figure 3. For VFD (Variable-frequency Drive), it can promote the rapid acceleration and braking of the motor, and can quickly reverse the acceleration and braking. Energy can quickly flow in both directions between the motor and the grid, and the four-quadrant VFD (Variable-frequency Drive) acts as a bridge.

Figure 3 Four-quadrant operation diagram

master-slave control

VFD (Variable-frequency Drive) needs this function in the case of multi-machine follow-up. The way to realize this function is to network the controller of high-voltage VFD (Variable-frequency Drive) through a high-speed communication network. In the parameter setting , set the VFD (Variable-frequency Drive) that needs to be followed as the slave, and set the VFD (Variable-frequency Drive) that needs to be controlled by the electronic control system as the master. The schematic diagram of the master-slave control network is shown in Figure 4. In master-slave control mode, synchronous start and stop and power balance can be controlled.

Figure 4 Master-slave control network

Synchronous start and stop

Simultaneous start