The Application Of WIN-HV Inverter In Heat Supply Industry

The Application of WIN-HV Inverter in Heat Supply Industry

Abstract:

This essay explains the working principle of WINNER-branded medium-voltage inverter(hereafter refered as WIN-HV inverter) manufactured by Shenzhen Winner S&T Co Ltd, and application in two circulating water pumps and one induced draft fan in Shenyang Guohui Heat Supply Co Ltd.

Key word:

Win-HV inverter, energy-saving reformation

I Prolegomena

Environmental protection and energy-saving have become the most crucial fundamental conditions in the process of urbanization. Especilally in the metropolises, there is a large amount of high energy consumption equipments, led by high voltage high power pumps and fans in the water and heat supply system, with energy consumption accounting for 50%-70% of the total. The medium voltage frequency conversion speed control technique, the most advanced speed control technique in the current world, can meet users’ general-purpose requirements and provide them more convenience. What’s more, this technique can help secure 50%~75% energy, which is definitely regarded as the optimal energy saving choice during the period of energy shortage and price soaring.

II General Situation Introduction

With a registered capital of USD 8 million, Guohui Heat Supply is a listed clean energy supplier in China. Its main businesses include centralized heating and heat supply network construction, contributing up to 96.58% of the company’s total revenue. The company predominates a more than 30% market share in its located city-Shenyang, with a heating area of 270 million square meters. Guohui Heat Supply, actively responding to the government’s appeal of energy saving and environmental protection, persists in using environment-friendly fuel made from straw. And to enhance energy saving efficiency and operation security, it has purchased two sets of WIN-HV medium voltage inverter(hereafter refered as WIN-HV inverter) from Shenzhen Winner S&T Co after repeated visitation and investigation.

The heating boiler, the main heating equipment of Guohui Heat Supply, has two circulating water pumps and a induced draft fan which are all driven by medium voltage high power motors. The company previously controlled the water flow quantity by adjusting the valve opening, which wasted a large amount of power. In addition, vast power is wasted for the pumps and fan are incompatible with the pipe network system parameters.

In contrast, after strict scrutiny, Shenzhen Winner customized a perfect proposal for Guohui Heat Supply that is to refit the boiler’s water supply from valve regulation to frequency conversion speed control constant pressure water supply, and to add a manual bypass cabinet to control the fan. After the WIN-HV inverter is installed, the company realizes accurate flow quanlity control by regulating the motor speed on the pumps and fan, securing a mass of power previously wasted by the valve and by incompatibility of the pumps and fan with the pipe network system parameters. Accordingly Shenzhen Winner wins unanimous praise and recognition from Guohui Heat Supply for its prominent technical scheme, reliable product quality and professional after-service.

III Reconstruction project

1. To install one WIN-HV inverter to control the two circulating pumps, and adopt manual bypass system

2. Take 4~20mA current signal of the pressure transmitter from the pumping main as the feedback signal, and obtain the given frequency from the DCS system

3. The RUN signal and STOP signal are given by the DCS system

4. The status signal of the medium voltage inverter is sent from the control cabinet to the DCS system for the purpose of instantaneous detection

5. The pressure value of the pumping main can exceed the requested 6.8MPa after reconstruction

6. Shut down the bypass valve of each pump, and the appropriate flux can be produced by adjusting the speed of the motor through the inverter.

7. For the induced draft fan, adopt a WIN-HV inverter with manual bypass system, to realize motor speed control by regulating the frequency.

IV Working principle of WIN-HV inverter

WIN-HV inverter presents the unique topological structure through serial connection of several power units. Each unit provides constant low voltage level output, and achieve the requested medium voltage output by superposition to other units. Please refer to the diagram as following.

Take the 10kV inverter with nine serially-connected power units per phase as an example, each phase contains nine units with equivalent power, and phase voltage is 5773V. The effective output voltage Ve of each power unit is 641V. The manifold series structure not only enables the inverter to realize medium voltage output, but also helps to reduce pressure to the components and make the output waveform more perfect. And this structure can also prevent the grid from pollution and maintain the percent of input current harmonic distortion below the IEEE519-1992 standard of 4%. Output power factor is high, so there is no need to install the input noise filter and power factor compensation device; the output waveform is much close to sine wave, and no potential faults will occur such as motor overheat, torque fluctuation, noise interference, output dv/dt and common-mode voltage. What’s more, the inverter can be applied to asynchronous motors without an output filter.

V Reliable design

In order to prolong the service life of the inverter, the power units of WIN-HV inverter adopt redundancy design, with each phase made up of nine serially-connected power units. The inverter also adopts automatic bypass system to ensure reliability. When one power unit breaks down, the inverter will automatically bypass that unit. The bypass function can blank off on line the faulty unit and guarantee continuous operation of the inverter. Meanwhile, it can ensure output voltage and output current at each phase keep consistent, decreasing the forced outage rate to the maximum degree. In addition, the inverter has installed manual bypass device as well.

On condition that the inverter stops running as fault occurs, the motor can manually switch to the mains supply and continue operation. The power frequency bypass consists of three high voltage isolating switches K1, K2 and K3. When the motor runs with frequency conversion, K1 is connected and K2 lies in the frequency conversion place. When the motor runs with power frequency, K3 is connected while K1 and K2 are disconnected.

VI Application

During the trial run and commercial operation period, the inverters work moothly, with high accuracy and reliability, helping Guohui Heat Supply saving a lot of energy and money. Please refer to the table below:

 

Item

Power  (kW)

Motor current (A)

Power factor

Average power consumption per day   (kW.h)

Average power consumption per year (kW.h)

Annual power saving volume (kW.h)

Power fare (Yuan/degree)

Avera-ge saved cost

pumps

Before reform

355

26

0.84

9078

3268080

 

0.8

 

After reform

355

19

0.99

7818

2814480

453600

0.8

362880

fan

Before reform

315

23

0.82

7839

2822040

 

0.8

 

After reform

315

17

0.99

6995

2518200

303840

0.8

243072

From the table above, it is easy to draw a conclusion that the two sets of WINNER-HV inverters can help Guohui Heat Supply secure more than RMB600,000 per year. What’s more, the inverters help prolong the service life of the pumps and fan since they can suppress inrush current to the grid at start, bringing more benefits to the user.

VII Conclusion

Since the two sets of WIN-HV inverters were put into use, no fault has occurred. That proves the reliability of Winner-branded inverter. The introduction of WIN-HV inverters not only has brought Guohui Heat Supply economic benefits, but also enhanced the automation level of its heating supply system.