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Ⅰ. Overview

The customer adopts OCC (Old Corrugated Containers) as raw material to produce low-basis-weight and high-strength corrugated base paper through a high-speed paper machine (as shown in the picture above). This retrofitting is applied to the first stage coarse screening pulp feeding pump and first stage slag separator pulp feeding pump. The original asynchronous motor is replaced with a permanent magnet synchronous motor to drive the pulp feeding pump.

Ⅱ. Solution

1. Principle:

The first stage coarse screening pulp feeding pump is a device is that continuously screens pulp under pressure in a fully closed environment. During operation，pressurized unscreened pulp enter the outer periphery bottom of the screen cylinder through the pulp feeding pipe along the tangent line . Then, the clean pulp is lifted to the screening area. With the different pressure between the inside and outside of the screen cylinder, the qualified pulp flows through the sieve holes into the screen cylinder and is discharged from the bottom pulp pipe.

The first stage coarse screening pulp feeding pump is a device is that continuously screens pulp under pressure in a fully closed environment. During operation，pressurized unscreened pulp enter the outer periphery bottom of the screen cylinder through the pulp feeding pipe along the tangent line . Then, the clean pulp is lifted to the screening area. With the different pressure between the inside and outside of the screen cylinder, the qualified pulp flows through the sieve holes into the screen cylinder and is discharged from the bottom pulp pipe.

2. Inverter specifications

The rated current of synchronous motor at the first-stage cleaner pulp feeding pump is 810A. The motor speed is 1000rpm, rated power: 500kW.
According the model of the motor, Yolico select a frequency inverter with rated current 880A and rated power 500kW.
The rated current of synchronous motor at the first-stage coarse screening pulp feeding pump is 325A. The motor speed is 1000rpm. The rated power is 200kW. Base on different motor model, Yolico selects a frequency inverter with rated current 369A and rated power 200kW.

3. Commissioning

Under the condition of unload on the motor shaft, the equipment proceeds a self-learing action following the motor parameters. Dr30: 2 times phase resistance, Dr31, Dr64: 2 times phase inductance.

The “Analog Input Channel 1” is connected to remote singal 4-20mA. Choose “set 0” option and set the parameter to 4-20mA for the AN1 channel interface.

4. On-site operation situation

The customer has purchased domestic leading production equipment: 4400 and 5600 high-speed paper machines, equipped with a DCS full intelligent control system, realizing full-process intelligent management. The staff in the control room can monitor the actual current of the frequency inverter and the pressure at the feeding pump. When the level of stock chest is too low, the system will put more pressure at each feeding pump to increase the motor speed (adjusted through 4-20mA signal). When the level of stock chest reaches standard line, it will reduce the pressure at each feeding pump to slow the motor speed (adjusted through 4-20mA signal).

Ⅲ. Features of the Solution

Both of the two feeding pumps on site are equipped with asynchronous motors, which are inductive loads. Asynchronous motors need to draw inductive reactive power from the power grid and the motors reduce the grid power factor. To improve the power factor of an asynchronous motor, the only way is to increase the load rate as much as possible. However, the rotor current of synchronous motor can be used as the excitation current. By changing the rotor excitation current, the power factor of the motor can be adjusted. This is the greatest advantage of synchronous motor, as it can make the power factor COSφ = 1 under any conditions, or make it lagging or leading. For example, the normal grid voltage is 380V. After changing to a synchronous motor, when the feeding pump of the first-stage cleaner is under the maximum load, the input current of the frequency inverter is 650A. Compare to 730A while apply an asynchronous motor. According to the formula P = √3U*I, the power consumption is 40KW lower after changing to a synchronous motor. Which means, the power consumption of the equipment reduces 40kwh (40 degrees of electricity) a hour. The electricity meter installed by the customer on the frequency inverter has also proved that. If the equipment runs 16 hours a day and 300 days a year, around 192000 degrees will be saved. Based on 0.1136 RMB per degree of large electricity standard, it will save an amount around 21811.2 RMB in total. The customer has been satisfied with this retrofitting and willing to gradually replace all asynchronous motors with synchronous motors to drive feeding pumps of high-speed papermaking equipment.