Hekang's inverter HID300A series applied to the air cooling island of a power plant

I. Project Background

The direct air cooling system (air cooling island) of power stations has the main characteristics of environmental protection, energy saving and water saving. Air cooling technology, especially direct cooling technology, has been widely used in the construction of domestic and foreign thermal power plants. A power company in Ordos built a 60 MW unit as a rear-mounted unit of a back pressure unit, using Dongfang Steam Turbine Co., Ltd. Low-pressure medium-temperature direct air-condensation steam turbine. There are 1 generating units in this project. Each cooling unit is equipped with 12 fans, and each fan is equipped with 1 frequency converter. Inverter rated power: 160kW fan pump.

After many inspections and tests by customers, we chose Hikvision HID300A series inverters. Since the air-cooled fans are designed based on the maximum throughput of the device and the highest monthly average temperature, the required air volume varies greatly between different seasons and different processing volumes. After adopting Hiconcom HID300A series frequency conversion control, the motor speed can be changed according to different climatic conditions. The air volume of the air cooler can change with the processing volume, the nature of the crude oil, and the temperature, thereby reducing energy waste. When the required air volume is relatively low, the inverter can run the motor at a low speed to meet the normal operating conditions of the unit, reduce noise and mechanical wear, extend equipment life and reduce maintenance costs.

Second, air-cooled fan frequency conversion cabinet selection requirements

The on-site air cooling fan system has the following requirements for the selection of frequency converter cabinets:

1. The air-cooled inverter and inverter power switch adopts the cabinet mode (single cabinet single circuit). The cabinet body adopts the fixed installation structure and the lower outlet mode. The main power supply of the inverter cabinet is connected to the busbars of the line cabinet and the protection level is not lower than IP42.

2. The main control loop in each cabinet shall include at least: feed line fuse switch or molded case circuit breaker, DC reactor, input filter, frequency converter, output reactor, etc.; other control loops configure transformer and all according to the control requirements. The electrical equipment that provides the necessary functions, including the frequency converter and all the equipment required to install it in the control cabinet. The frequency converter shall be equipped with a communication interface (the communication protocol is Modbus RS485). In order to consider the heat dissipation of the inverter system, the output reactor used must be installed outside the inverter or be of an integral type, so that the harmonic components on the bus voltage of the power plant at all levels can meet the requirements of the relevant standards.

3. The inverter will complete the operation of the entire fan drive system. The frequency range is within 0 % to 110 % of the rotation speed. Consider the power loss caused by cables, filters, and inverters placed in the inverter cabinet.

4. The inverter must be able to start the rotating fan motor (bidirectional restart).

5. The inverter is installed in the inverter cabinet. A button interface (control board) must be installed on the front door of the inverter casing in order to realize the operation of the fan and the adjustment of the AC drive device regulator through the inverter.

6. The design of the control cabinet must consider cooling and heat dissipation requirements caused by power loss. Air flow must not be blocked by built-in devices. Install the fan on the top of the cabinet. The air inlet in the converter area must meet the design environment requirements.

Third, system control principle

3.1 Direct air cooling system work

The direct air cooling system means that the steam exhaust of a steam turbine is directly condensed with air, and heat is exchanged between air and steam. The required cooling air is usually supplied by mechanical ventilation. The air-cooled condenser used in the direct air-cooling system is composed of several bundles of galvanized oval-shaped steel pipe jacketed rectangular fins. Turbine exhaust steam is sent to the outdoor air-cooled condenser through a thick exhaust pipe. During the process of heat exchange, the cold air flowing through the outside of the radiator fin tube is used to convert the condenser from a steam turbine under vacuum. The saturated steam discharged from the heat medium condenses, and finally the condensed water is sent back to the boiler after being processed.

According to the direction of the flow of condensate and steam, the direct air-cooling system can be divided into three types of work modes: the forward flow type, the reverse flow type, and the cis-reverse type. The co-current type means that the turbine exhaust gas enters the air-cooled condenser from top to bottom along the gas distribution pipe, and the condensed water flows in the same direction as the steam flow direction. In the opposite direction, it is counter-current. In the direct air-cooling system, both the heat transfer performance and the condensate freezing need to be placed, and the air-cooled condensers basically adopt the combination of forward and backward flow.

3.2 Air Cooler Fan Frequency Control System

The direct air-cooling system of this project adopts a forward flow method and a counter-current method. Among them, 8 sets of variable frequency fans are started in the forward flow mode, and 4 sets of variable frequency fans are started in the countercurrent mode. When the system is working, the counter-current fan is first started. As the steam flow increases, the back pressure increases, and the counter-current fan speed increases. When the requirements are not met, the downstream unit that is far from the air inlet is activated, and so on, to ensure that each tube bundle is filled with steam, and the air accumulates at the top of the counterflow tube bundle to avoid freezing tubes.

The air-cooling control system presets the setting value of the turbine back pressure, and compares the actual measured value with the set value after processing to issue an instruction to change the rotation speed of the fan and artificially determine whether to open or close the steam isolation valve on the distribution pipeline. The cooling air flow is coordinated with the operating conditions to keep the turbine exhaust pressure constant. If the actual measured value of back pressure is higher than the set value, the fan speed will be increased or more fans will be started. If the actual measured value of the back pressure is lower than the set value, then the fan speed will be reduced or the fan will be stopped. 12 sets of variable frequency fans perform centralized DCS control according to the system's steam pressure and temperature.

Each inverter in the inverter cabinet is controlled independently and has two remote and local control modes. When in the local working state, the fan can be started and stopped manually on the panel of the inverter cabinet, and the operation of the fan can be controlled and the parameters of the inverter can be set. When in the remote working state, the frequency converter is put into operation, and the optimal operating state of the fan can be automatically controlled through the air-cooling unit DCS control room. Air-cooling unit DCS control room output frequency control signal to control the fan speed, frequency control cabinet feedback current and frequency signal into the DCS control room. The frequency converter cabinet has a communication management unit, which can summarize all the data sent by the serial interface (RS485) through the bus, such as the switching status of each circuit and the state of the inverter.

Fan motor heaters and gearbox oil heaters are fed in the inverter cabinet and can be grouped and single-circuit automatically enabled in the DCS. When the oil pressure of the reducer does not meet the design requirements during the operation of the system, the pressure switch will give a switch signal to the control system to alarm. At this time, the control system must stop the operation of the frequency converter cabinet to fully protect the reducer from lubrication. Working under unfavorable conditions. Pictured:

3.3 Performance Advantages of Hicontech's HID300A Series

Hekang HID300A series inverter has automatic torque boost, automatic slip compensation, automatic output voltage stabilization, speed tracking start function, over-current suppression during acceleration, over-current over-frequency reduction at constant speed, over-voltage suppression during deceleration, and automatic energy-saving Run other functions. In particular, the AVR automatic voltage regulation function can output a constant voltage under the fluctuation of the power grid. The load can still operate normally under severe fluctuations.

(1) Unique speed tracking function

HID300A series does not need dedicated hardware detection circuit and special function code setting. In rated speed range, the inverter completes the identification of motor speed, steering and phase angle in 0.2s, and smoothly tracks and starts the free-rotating motor, and can be stable. Run to solve some high inertia loads. In the air-cooling system, abnormal shutdown sometimes occurs. Since the fan inertia is large, the fan is still running at a high speed. The speed tracking function possessed by the inverter can realize rapid coasting and greatly improve the stability of the system.

(2) Unique Instantaneous Power-Down Processing - Instantaneous Nonstop Function

Many large-scale power plant equipment, often start and stop, due to a large momentary start current, network cable pressure drop sharply increased, it is easy to instantly pull down the grid voltage, causing the inverter undervoltage shutdown. This function ensures that the inverter will not stop when there is a momentary power failure. In the event of a momentary power outage or a sudden drop in voltage, the inverter reduces the output speed and compensates the voltage through the load feedback energy to maintain the inverter running for a short period of time.

(3) Unique air duct design

The air-cooled island frequency conversion control is a group machine working method. The device centralized layout plus external environment temperature difference puts forward high requirements for the adaptability of the frequency converter. The HID300A series inverter in the cabinet adopts an independent air duct design. The internal circuit also adopts independent fan heat dissipation, which improves the heat dissipation effect of the product and makes up for the defects of shared cooling channels shared by some brands' internal circuits and module heat sinks, which greatly reduces dust and miscellaneous items. The object enters the inverter. Radiators and fans can be individually cleaned and maintained, improving product life.

(4) Using self-developed reactors

As the inverter will generate high-frequency harmonics and the grid-side harmonics of the incoming power supply during the rectification process, the frequency conversion cabinets are equipped with filters and line reactors to effectively suppress the influence of harmonics on the grid and the motor. The on-site electrical room is far away from the fan, and the motor cable is 200 meters. In addition to the motor load, the output current of the inverter also flows into the distributed capacitance of the cable. Therefore, if the power cable is too long, the inverter will increase the inverter. The current load may even cause the overcurrent fault of the inverter, so the output reactor must be configured on the inverter motor side. The HID300A series AC and DC reactors are all independently developed. They are tailor-made for various kinds of harmonic analysis generated by the inverter, which perfectly suppresses most of the harmonic components, and they are excellent in performance, exquisite workmanship, and reliability. Strong.

3.4 Function parameter setting and description:

IV. Energy Saving Analysis of Hikvision Inverter HID300A Series in Air Cooling Island Application

According to fluid mechanics, P (power) = Q (air flow) × H (pressure), the air flow rate Q is proportional to the primary speed of the motor speed n, that is, Q∝n; the wind pressure H is proportional to the quadratic power of the motor speed n, that is, P∝n2. The power P is proportional to the third power of the motor speed n, that is, P∝n3. After the inverter decelerates, the output power of the motor decreases.

The site technical parameters are as follows:

According to the electricity saving rate of about 15% ~ 25%, the calculation of electricity consumption throughout the year: 380V (voltage) × 280A (current) × 0.87 (power factor) × 24 (hours) × 1.732 × 330 (year working days) = 1269796 (kW·h); The electricity rate is calculated as 0.40 yuan per kW·h: 1269796×0.40=507918 yuan. Total power consumption of 12 stations: 507918×12=6095020 yuan.

Fifth, application effect

1. Due to the instability of the on-site power supply environment, the power supply is often interrupted instantaneously. After using the inverter's instantaneous stop function, the operation is stable, and it is highly recognized by customers.

2. Compared with the traditional way of adjusting the air flow, pressure, and temperature by adjusting the degree of opening of the windshield or controlling the valve, the HID300A series inverter is simple in operation, complete in function, high in stability and reliability, and not only reduces the on-site human operation. Abnormalities caused can also save energy for enterprises and increase economic efficiency.

Sixth, concluding remarks

The air-cooled blower motor adopts Hikvision inverter HID300A series control, which can change the motor speed according to the on-site operating conditions, reduce the equipment wear, and save energy. Built-in various protection functions ensure the normal operation of the equipment. Practice has proved that Hikvision inverter HID300A series has excellent speed control performance and good energy-saving value, and it is worth to be widely used in air-cooled systems.

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