company news

The annual processing capacity of the mineral processing plant of a group Co., Ltd. is 1.1 million tons. The primary grinding machine consists of two 1000kW self grinding motors and one 400KW ball mill motor. The model of self grinding motor is yr-173/51-16, voltage is 6kV and power is 1000kW. According to the process, there is no speed regulation requirement in the operation of the mill. It is only necessary to reduce the starting current, the impact of starting torque and the voltage drop during the start-up.

The original method is the speed regulating starting mode of rotor loop series resistance. During the starting process, the resistance is cut off in five stages, and it is a speed regulation with stages, which has a great impact on the machinery. The pig iron resistance used for this starting also consumes a lot of electricity. The volume of the starting device is also large. Before the transformation, we use 15 square rooms to place the starting equipment. And the secondary control circuit of the starting device has many devices and many fault prone points. The control line is complex, the maintenance is large and difficult. The phenomenon that the mill can not start occurs frequently, which has brought great influence to normal production.

In order to solve the problem thoroughly, we compared the sex price of starting equipment at home and abroad. Although the performance of high voltage soft starter and high voltage converter abroad is good, it is expensive and the cost of input cannot be accepted. The domestic high voltage inverter in the use of high-power motor maintenance technology is not enough, and the price is not expensive. What we need is the equipment with good quality and low price, low technology complexity, convenient operation and debugging, and can meet the basic requirements of the equipment.

1. High pressure hydraulic resistance soft starter

1.1 working principle

The high pressure hydraulic resistance soft starter is made of 99% anhydrous sodium carbonate (Na2CO3) and water to form a certain concentration of water solution as the liquid resistance. The distance between two parallel plates in the conductive liquid is gradually reduced to zero by the negative resistance effect of the electrohydraulic and the distance between the two parallel plates in the conductive liquid through the mechanical transmission device, so that the resistance value in the series into the runner is gradually reduced from the maximum to zero, The speed of the motor is gradually smooth to the rated speed, so as to realize the soft start of the motor.

1.2 technical characteristics

(1) The starting current is small, which is no more than 1.3-3.5 times of the rated current of the motor, which reduces the starting heat of the motor, effectively prolongs the service life of the motor, and reduces the requirements of transformer capacity and one-time investment when the motor is started under heavy load;

(2) Smooth start, reduce impact on mechanical equipment, can extend the service life of mechanical equipment and motor by about 20%.

(3) The starting torque is large, and it can be started with heavy load;

(4) The structure is simple and maintenance is convenient.

2. Site implementation:

2.1 equipment selection: according to the technical indexes of self grinding motor, we have selected ydq5-1ppc liquid resistance starting cabinet, with the outer dimension of cabinet body of 1000 × nine hundred × 2000, one piece cabinet type.

2.2 installation:

(1) The liquid resistance starting cabinet is installed above the cable trench, equipped with channel steel base, and the cabinet body is installed on the vertical horizontal surface;

(2) Vv3 × 2.5＋1 × 1.5 the cable is led into three-phase four wire power supply for separate distribution;

(3) The motor rotor line is connected to the copper bar connected with the liquid resistance at the lower end of the short-circuit contactor (the rotor line is not fixed first, and then fixed after the resistance is measured);

(4) Kvv7 as per schematic × 1.5 control cable press three pairs of contacts in cabinet to motor cabinet, and use kvv10 × 1.5 control cable shall press four pairs of contacts in cabinet to the operation room.

2.3 liquid resistance preparation: liquid distribution according to resistance of motor rotor circuit.

(1) The supplier requires distilled water (about 700 kg) for liquid distribution. Due to the limited conditions, we use the boiled water in boiler room after cooling to prepare.

(2) Determination of liquid resistance R0: r0=0.577 (u2e/i2e) *kf* (ki/km)

Where: u2e: open circuit voltage of motor rotor circuit (V)

I2E: rated current of motor rotor circuit (a)

KF: motor power margin multiple = ne/n1 ne: motor rated power N1: required power for load

Ki: temperature coefficient, generally about 1.2

Km: starting torque multiple, generally about 1.1

According to the formula of the above formula, we determine the value of R0:

R0=0.577*（680/924）*（1000/700）*（1.2/1.1）=0.66

Compared with the electric powder preparation table in the instruction manual, the power powder quantity is about 6.5kg. First, 2/3 water is injected, and then electrolytic water is added gradually. The three-phase resistance liquid should be stirred evenly during preparation.

2.4 measurement of liquid resistance:

If the motor rotor line is not connected, the movable electrode plate of liquid resistance is moved to the starting position, and the power is supplied to each phase of the dynamic and static plates through the autotransformer. The current gradually increases from zero to about 5A. Record the reading of ammeter and measure the voltage drop between the two poles. Then the liquid resistance R (Ω) = V (V) /a (a)

If the resistance is too large, the concentration of resistance liquid should be increased, otherwise, it will be reduced.

2.5 power on test run

(1) First turn the switch on the starting cabinet panel to the test position, and then turn it to the working position if it is normal;

(2) The model test run shall be conducted according to the instruction;

(3) After the simulation test is normal, start the test run, observe the starting current. If it is too large, it means that the resistance is small, and water should be added at this time. If the starting current starts to be too small and the short-circuit contactor is closed, the impact is too large, indicating that the resistance is too large, powder shall be added.

During field commissioning, the concentration of resistance liquid is difficult to determine. Due to many factors, such as liquid temperature, ambient temperature, motor load, etc., the power powder and water quantity shall be added one by one, and it shall be repeatedly adjusted until the starting current is normal within the rated current range of 1.3-3.5 times of motor. Our final starting current is about 250 a, starting time is 20 seconds, resistance liquid resistance is 0.72 ohm.

3. Concluding remarks

3.1 liquid resistance starter is a good choice for equipment with speed regulation requirements only when starting. It has smooth start, small starting current, large starting torque, simple structure, convenient maintenance, small floor area and less investment.

3.2 if the high voltage motor is to solve both soft start and soft stop, and speed regulation and energy saving during operation, then high voltage inverter must be selected, which requires a large investment in the user's funds.

3.3 since the liquid resistance starter cabinet of the mill is put into operation and operation, there are few faults. We check the liquid level once a month and add water timely according to the mark. Water resistance shall be measured once a year to see if it is consistent with the original data. It is important to note that the liquid level probe should be removed frequently and polished with the yarn skin. The false alarm caused by probe fouling has occurred. During the operation of the mill, there are often cylinder screws that need to be tightened. In the evening, no operator, the operator repeatedly opens and stops the mill to locate, and the start and stop is too frequent to raise the liquid temperature. The number of fault alarms occurs more. Then the resistance cabinet will be powered off and cooled before operation.

3.4 the core device of liquid resistance cabinet is S7-200 (cpu224). Once there is any problem with this component, our maintenance technology cannot keep up with, and the manufacturer is far away from us and cannot be handled in time. We bought an empty PLC, after consultation with the manufacturer, we copy the program into it as a backup. In case of failure, we can resume production in a short time.