Application of high voltage frequency conversion t

Application of high-voltage frequency conversion technology in the primary air fan of power station

abstract in the work of energy conservation and consumption reduction in power plants, high-voltage frequency conversion technology is the main application technology. For some high-voltage motors with high energy consumption, frequency conversion transformation is carried out, and the power saving effect is generally more than 30%~40%. This paper introduces the background, transformation scheme and energy-saving effect of the frequency conversion transformation of the primary air fan system in a power plant, analyzes the problems existing in the frequency conversion operation of the primary air fan and the solutions, and puts forward some suggestions

keyword energy saving and consumption reduction; Frequency conversion technology; Primary air fan; Cooling system

0 introduction

with the continuous deepening of the reform of the power industry, power enterprises have gradually changed from production-oriented to business-oriented, and developed from high energy consuming enterprises to energy-saving enterprises. In order to improve the efficiency of enterprises and reduce the cost of power generation will be the long-term goal of operating enterprises. Therefore, energy conservation and consumption reduction has become an important part of the production and management of power generation enterprises. How to achieve low consumption and high efficiency in thermal power plants is a long-term concern and continuous development of the industry. In the context of the global energy crisis, energy-saving technologies have also been rapidly developed and popularized. Using some relatively mature and stable new technologies to carry out technical transformation of equipment, one-time investment, and realize long-term energy conservation and consumption reduction, which is a matter of great benefit to enterprises and the country

Tianjin Datang International Panshan Power Generation Co., Ltd. 2 × 600MW thermal power unit is the first 600MW Subcritical thermal power unit built and put into operation in North China. It is the main unit of Beijing Tianjin Tangshan power plant. It was listed by the State Development Planning Commission as a pilot project to use the national foreign exchange reserves to purchase domestic power generation equipment to develop national industry in 1996. The project was started in October 1998, of which 3# unit was officially put into operation on December 18, 2001, and 4# unit was officially put into operation on June 5, 2002. The frequency conversion transformation of boiler primary fan and steam turbine condensate pump is a specific example of energy saving and consumption reduction

1 introduction to primary air fan system

each unit of the company is equipped with two double suction forward bending centrifugal primary air fans produced by Shenyang Blower Factory. The fan adopts the constant speed operation of the motor and the inlet electric moving blade to adjust the fan output. The capacity of one primary air fan is 50% BMCR (maximum continuous load of boiler). The specific parameters are as follows

the layout of the fan system is shown in Figure 1

fan type double suction centrifugal pump

fan model G × 36No. 17F

wind pressure 15542pa

air volume 160.5m3/s

motor model YKK

rated voltage 6kV

rated current 260a

power 2400kw

speed 1494r/min

insulation grade F

boiler primary fan is mainly used to provide the boiler pulverizing system with the air source of powder conveying

, which is one of the three fans of boiler and the main fan of thermal power plant

.High energy consuming equipment. For the positive pressure direct blowing pulverizing system, the primary air fan

mainly plays the role of carrying and drying pulverized coal during normal operation, and provides

air for the initial stage of pulverized coal ignition. Introduction to the frequency conversion transformation of primary fan of Panshan Power Generation Company boiler

2

it can be seen from fluid mechanics that

p=qh (1)

where: P is power

q is the flow

h is pressure

and Q ∝ n; h∝n2； P ∝ N3 (n is the speed). If the efficiency of the sample measured by the water pump 1 is certain, when the flow is required to be adjusted to decrease, the speed n can decrease proportionally, and at this time, the shaft output power P decreases in a cubic relationship. That is, the power consumption of the pump motor is approximately proportional to the speed. For example, the power of a water pump motor is 55kW. When the speed drops to 4/5 of the original speed, its power consumption is 28.16kw, saving 48.8%. When the speed drops to 1/2 of the original speed, its power consumption is 6.875kw, saving 87.5%. Frequency converter is an electric energy control device that uses power semiconductor devices to convert power frequency power supply into another frequency. It first converts power frequency AC power supply into DC power supply through rectifier, and then converts DC power supply into AC power supply with controllable frequency and voltage to supply motor. Controllable frequency means controllable motor speed, so as to achieve the purpose of energy saving

G × 36No. The rated current of 17F primary air fan is 260a. When the generator operates under the rated load of 600MW, the maximum current of the primary air fan is 186.5a, only 71.7% of the rated current. When the generator operates under low load, the minimum current is about 133a, which is about 51.2% of the rated current. Therefore, the primary air fan has a lot of energy-saving space. After many arguments, the company decided to change the pressure control of primary air main pipe from throttling control to speed control, so as to reduce energy consumption and improve the overall economic benefits of the unit

2.1 transformation scheme

Panshan Power Generation Company used the opportunity of unit minor repair to carry out frequency conversion transformation for four primary air fan motors of two units in 2003 and 2004 respectively. Rockwell's abpowerflex7000 series double PWM (Pulsewidthmodulation) current type variable frequency speed regulation device without input isolation transformer is adopted, which belongs to the "one driven one" manual bypass mode. The inverter is connected to the original electrical circuit, as shown in Figure 2

the whole transformation plan includes three parts:

1) installation and access of frequency converter a special frequency conversion room is set up locally beside the fan, in which the main equipment installed includes the main cabinet of frequency converter, dual control power supply switching box, UPS (AC uninterruptible) power cabinet of frequency converter and cabinet air conditioner of frequency conversion room, All local operations of the frequency converter and the inspection and setting of operating parameters and alarm parameters are completed in the frequency conversion room

2) transformation of electrical switch part 6kV high-voltage switch is equipped with frequency converter protection circuit and "power frequency/frequency conversion working mode" switching handle to cooperate with the switching of frequency conversion operation and power frequency of primary fan. In addition, the power supply transformation of frequency converter control power supply and operation power supply is completed from 380V low-voltage AC auxiliary bus section and 220V DC bus section

3) transformation of thermal logic and DCS operation screen after the transformation of primary air fan frequency converter, the main working mode selection and frequency converter startup allowable program control logic scheme are as follows

add a reminder of the working mode of the primary air fan on the original primary air fan system screen of DCS (as shown in Figure 1). The frequency converter start button is no longer added to the primary air fan system screen, and the same button is still used to start the primary air fan under different working modes. In the power frequency mode, the screen prompts that the primary air fan is in the power frequency mode. Press the original operation button to start, then close the 6kV switch, and adjust the opening of the moving blade at the fan inlet during the fan operation to maintain the air pressure of the main pipe at the set value. In the frequency conversion mode, the screen prompts that the primary air fan is in the frequency conversion mode, and still press the original button to start. The starting sequence of 6kV switch and frequency converter under the frequency conversion mode of primary air fan is as follows: when the operator presses the start button, first close the 6kV switch of primary air fan, wait for 30s (charging time of inverter reactor), detect the presence of frequency converter ready signal, and start the frequency converter. At this time, the inlet moving blades of the operating fan remain fully open, and the fan output is changed by adjusting the motor speed to maintain the main pipe pressure at the set value

2.2 control mode of primary air fan under frequency conversion mode

1) retain the original primary air fan baffle regulating station and another set of frequency conversion regulating station. When the primary air fan operates in the frequency conversion mode, the inlet adjusting baffle shall be fully opened, and the motor speed shall be changed through the frequency converter to adjust the pressure of the main pipe at the outlet of the fan

2) when the primary air fan operates in power frequency mode, the frequency conversion regulating station is forced to operate manually; During the operation in frequency conversion mode, the baffle regulating station is forced to be manual

3) when the frequency conversion mode is started, the baffle is forced to be fully opened and the output of the frequency converter is the lowest speed. When the frequency converter is in operation, the control station tracks the speed feedback value to realize undisturbed switching

4) the conditions for switching frequency conversion automatic regulation to manual operation are as follows (any one is satisfied):

(1) the pressure signal of the main pipe at the outlet of the primary air fan is faulty

(2) primary air fan operates in power frequency mode

(3) when the deviation between speed regulation command and speed feedback is greater than 150r/min

2.3 problems in variable frequency operation of primary air fan

after variable frequency operation of primary air fan, some problems were also found, which threatened the operation safety of the fan and affected the energy-saving effect

2.3.1 high operating temperature

the frequency converter has a high calorific value during operation, and the designed heat dissipation device can not meet the needs. It has been improved after installing high-power cabinet air conditioner in the frequency conversion room, but the hidden danger of high operating temperature still exists, and the installation of high-power air conditioner increases power consumption. At present, the cooling system of the condensate pump frequency converter in our plant operates well. Therefore, the same forced water-cooled air circulating cooling system has been configured for the primary air fan frequency conversion system (the system layout is shown in Figure 3). The opportunity of unit maintenance will be used to connect the cooling system with the frequency converter. It is believed that the problem of high operating temperature can be completely solved

2.3.2 it is difficult to realize Rb (rapid return of load) protection function under fan frequency conversion mode

RB protection of primary air fan cannot be realized normally, which has both design problems and baffle quality problems. It is mainly manifested in that after a primary air fan trips intuitively and conveniently, due to the slow closing of the inlet and outlet baffles of the tripping fan, the primary air "returns", that is, part of the primary air returns to the atmosphere through the tripping fan. The rapid decline of the pressure of the primary air main pipe can not guarantee the normal delivery of pulverized coal in the operating pulverizing system, resulting in the accumulation of a large amount of pulverized coal, and at the same time, the other operating primary air fan is in danger of overcurrent tripping. In 2003, an accident of unit shutdown caused by the tripping of 1# primary air fan with variable frequency operation occurred in 3# unit. The main reason is that the closing time of the inlet and outlet baffles of the primary air fan is too long, which makes a large amount of primary air return through the tripping fan for a long time, resulting in a low primary air pressure, a large amount of pulverized coal accumulated in the operating pulverizing system and pulverized coal conveying pipeline. When the primary air pressure suddenly recovers, a large amount of accumulated pulverized coal enters the furnace for deflagration, and the water level of the steam drum rises sharply, As a result, the water level of the steam drum rises rapidly from the lowest water level of -200mm to +300mm within tens of seconds, causing the high III value protection action to trip and shut down

it can be said that the failure of Rb protection of primary air fan has little to do with frequency conversion transformation, and the same problem exists even under power frequency mode. Fortunately, the company has successfully realized the RB protection function of the primary air fan under the power frequency mode after 3 years of analysis of the causes of the failure of the primary air fan Rb, drawing lessons from the accident, and through the transformation of the inlet and outlet baffles and many tests and debugging. In order to realize RB protection under the next frequency conversion mode, ensure the long-term frequency conversion and energy-saving operation of primary air fan, and eliminate potential safety hazards

2.3.3 the fan/frequency conversion switch needs to be powered off manually.

the power frequency and frequency conversion working mode of the primary fan need to be switched off, and then the high-voltage switch needs to be powered off. Manually change the status of the inlet and outlet knife switches and bypass knife switches of the frequency converter, and then power on again to start the fan. At present, the feasibility of the automatic bypass system for undisturbed switching is being investigated to prepare for the further installation of the automatic bypass system for the frequency converter

3 effect of primary air fan after frequency conversion transformation

from the perspective of operation, the power consumption of primary air fan is only about 1000kW at rated load through frequency conversion transformation and operation optimization, while the power consumption before transformation is more than 1700kw, and the power saving rate is more than 40%. The power consumption rate after frequency conversion transformation of primary air fan is 0.47%, which is 0.17 percentage points lower than that before transformation. The average monthly power consumption is reduced by 650000 kW · h, and the annual power saving is more than 6 million KW · H. It can be recovered after three years of operation