Application of Altivar38 inverter in water treatment system

Frequency conversion Energy-saving technology principle: Generally, the design of electrical traction equipment takes into account the possibility of short-term overload operation. The power configuration of the motor is often greater than about 10% of the maximum load power, or even greater.

1 Problem Statement

The water treatment center in the steel rolling area is part of the second phase of technical transformation of Xinyu Iron and Steel Co., Ltd. It is mainly responsible for processing and supplying the turbid circulating water and clean circulating water required by the medium and thick plate plant and wire rod. The turbid circulating water system of the medium and thick plate plant is a 24-hour uninterrupted water supply. Since its operation, due to frequent roll changes and different production process requirements, the water consumption has been unstable, resulting in the water level of the cold water pool being high and low, unstable and unsafe operation, and frequent overflow, causing waste of resources and environmental pollution. For this reason, the water level of the pool must be adjusted by frequently operating the reflux valve and starting and stopping the pump. According to statistics, from June to August 2006, the reflux was adjusted at least 18 times a day on average, and the pump was started and stopped at least 3 times. Frequent power frequency starting of the pump shortens the service life of the motor. The current shock during power frequency starting, the pressure shock of the pipe network, and the water hammer effect during instantaneous stop cause high equipment failure rate, frequent maintenance, and increased maintenance costs. A large part of the power energy consumed by the power frequency operation of the motor is used for system reflux, doing useless work, and increasing power consumption. The original system is an open-loop system that only starts and stops the pump and cannot be adjusted automatically. It is difficult for operators to monitor and need to monitor all the time. If they are not careful, the water level adjustment will be affected. In addition, the water level fluctuates greatly, the level gauge is not properly selected, and the computer display cannot accurately reflect the on-site situation. Operators must often go to the site to check, which can neither provide timely and accurate adjustment data, resulting in delayed adjustment and increased workload.

2 Design and determination of system transformation plan

2.1 Selection

The current operation mode is that the No. 1 to No. 4 pumps in the de-oiling pump room supply water to the medium and thick plate turbid ring cold water pool. According to production needs, it is decided to add a frequency conversion device to implement frequency conversion transformation, using the "one to two" form, that is, one set of frequency conversion devices can interchangeably drive two water pump motors for the No. 3 and No. 4 pump motors in the de-oiling pump room. In this way, one is in frequency conversion operation and the other is on standby. The unit maintenance does not affect the operation of the frequency conversion system. The selected motor model is Y2-315M-4 (380 V 132 kW 240 A), and the frequency conversion device uses Schneider Telemecanique's Altivar38 energy-saving frequency converter with a power of 132 kW. It complies with IEC, UL and CSA standards, and has a wide speed regulation range, good acceleration and deceleration braking performance, adaptive adjustment and energy saving, as well as protection functions such as power supply overvoltage, motor phase loss, motor overheating, and frequency converter overheating.

There are many ways to set the variable frequency speed regulator (VVVF for short). Here, the PI setting of the inverter panel and the current feedback detected by the liquid level meter are used to form a closed-loop automatic control system with PID regulation by setting the internal parameters.

2.2 Control loop

The original control circuits of the two pump motors are retained as the power frequency bypass of the new control system, which is determined by the power frequency/variable frequency selection switch on the frequency conversion cabinet. There is an electrical interlock between the power frequency conversion of the two pump motors and between the frequency conversions to avoid misoperation. The electrical control circuit is shown in Figure 1.