Application of High Pressure Chopper Wave Feeding Speed ​​Regulation in Liaocheng Power Plant

Foreword

With the rapid development of the power industry, the commercialization of the power system, and the implementation of bidding for the Internet, it is important for power generation companies to tap their internal potential and save energy and reduce consumption. It is a common problem that the excess capacity of auxiliary equipments for power generation enterprises is large. In addition, the power supply is saturated, and the peaking tasks of the generator set are gradually increased. Therefore, it is imperative to implement speed regulation and energy saving for auxiliary motors. The motor speed regulation can not only save energy and reduce consumption, but also avoid the frequent start and stop of the motor during peak adjustment, reduce the motor failure rate and prolong the service life of the motor, and bring huge economic benefits to the enterprise.

Shandong Liaocheng Thermal Power Co., Ltd. (formerly Liaocheng Power Plant) was the first company to adopt chopper wave feed-forward AC speed regulation in the national power industry, following the successful operation of the #2 furnace B blower (300KW/4P-6KV) products in 1997 , It has adopted chopper wave feed-in speed regulation on other auxiliary machines. After a long period of practical operation, product reliability and performance have been tested, and remarkable energy saving (35-52%) and economic benefits have been received. The application of chopped wave feed-in speed regulation in our factory's auxiliary machine is shown in Table 1.

Table 1 Application List of Chopper Wave-feeding Speed ​​Regulation (6KV)

No.

Device name

Capacity KW

Number of poles

Speed ​​range

Maximum energy saving%

1

Blower

300

4

800-1450

43%

2

Induced draft fan

630

6

507-985

42%

3

Blower

710

8

421-745

34%

4

Circulating pump

1250

12

320-485

55%

5

Circulating pump

1250

12

320-485

57%

1.1 The composition of speed control device;

(1) The speed control device model is KRH-2;

(2) Starter cabinets, chopper cabinets, inverter cabinets

(3) With local control: start, stop, speed, full speed switching; with remote control;

(4) DCS automatic control interface, speed command signal 4-20mA, speed output signal 4-20mA, automatic / manual, speed control ID signal.

1.2 Chopper-infeed speed-regulating motor

The installation size of the internal-fed speed-regulating motor is the same as that of the original motor, and it is connected in parallel with the chopper control device. When the speed-governing control device accidentally fails, the automatic protection device can automatically switch the motor to a constant speed, which will not cause the motor to stop. Win, improve the reliability of the system.

The chopper-wave feed-forward speed regulation is a high-efficiency speed regulation technology with low voltage (usually about 200-500V) controlled high voltage (6KV-10KV), which is characterized by two high-tech “inside feed” and “chopper” Organically combined.

2.1 Internal Feeder Speed ​​Regulation and Its Power Control Principle

According to the theory of electrical machinery, the speed of the motor is related to the mechanical power and the electromagnetic torque as follows:

(1)

Where: Ω is the mechanical speed

PM is mechanical power

T is the electromagnetic torque

Also, according to energy conservation, there is

(2)

therefore (3)

Among them: Pem is electromagnetic power, p2 is rotor loss.

Formula (2) shows that the motor speed can be adjusted by electromagnetic power or loss power control. The electromagnetic power control changes the ideal no-load speed, the speed regulation is highly efficient, the loss power control increases the speed reduction, and the speed regulation is inefficient. All speed control methods belong to the principle of power control. This principle is the "power control theory of motor speed regulation" (ie, P theory) proposed by Qu Weiqian, the inventor of feed-in speed control.

Since the electromagnetic torque is in the steady state of speed regulation, depending on the magnitude of the load torque, when the load torque is determined by the objective operating conditions, the electromagnetic torque is then determined, therefore, the electromagnetic torque is not only Speed ​​control is irrelevant and cannot be changed at will. The effect of the dynamic torque on the speed is only reflected in the transition of the speed control. The change of the torque is the result of the power control and the speed response delay. Under a certain power control, the dynamic torque automatically decreases with the speed response until New load balancing is zero. Therefore, the motor speed can only be achieved through power control.

The feed-forward speed regulation is based on the rotor high-efficiency electromagnetic power control speed regulation. By shifting part of the power of the rotor (that is, power slip power), the net electromagnetic power of the rotor changes, so according to P theory, the motor speed is correspondingly obtained. control. In order to obtain high-performance speed control, the internal cause of the speed regulation of the motor is strengthened, and an internal feed-forward winding is additionally provided on the stator of the motor to receive the power slip power, and the active inverter makes the feed-in winding operate in the power generation state. The power is fed back to the motor stator via electromagnetic induction. The active power of the stator is basically balanced with the mechanical output power. Compared with variable frequency speed control, the chopper infeed speed control is only different from the control object. Both follow the same principle, so there is no essential difference.

Fig.1 Chopper power feed diagram and system diagram

2.2 The role and significance of chopping

The function of the chopper is equivalent to a high-speed switch that is periodically turned on and off at a certain frequency. By controlling the duty cycle of the chopping wave, it is possible to control the inverter current, that is, to control the current and power fed back to the internal feed-through winding so as to realize the speed regulation of the feed-in. Its significance lies in:

(1) The active power factor of the active inverter can be as high as 0.9 and constant.

(2) The harmonic effective value of the inverter current can be reduced to about 15% of the phase shift control. Stator current distortion of the feed-in motor is less than 5%.

(3) The rated capacity of the active inverter is only 14.8% of the motor capacity. With the simple triggering, the reliability is greatly improved.

(4) The additional power supply capacity is also 14.8% of the motor capacity. For an internally-fed adjustable-speed motor, the core space occupied by the feed-in winding can be greatly reduced, the process can be simplified, and the cost can be reduced.

Due to the requirement of the system speed range and operating characteristics, the frequency sensitive rheostat start-up and speed control stop modes are set.

(1) When starting, directly control the high-voltage switchgear. The motor can be started with frequency sensitivity to reduce the starting current and increase the starting torque.

(2) During the speed regulation operation, there is a large electromagnetic energy in the direct current loop. If the direct power failure occurs, overvoltage will be generated and the thyristor will be damaged. Therefore, when the speed is stopped, the set logic control will automatically go to full speed and then stop. The blackouts have power cuts and overvoltage protection to prevent equipment damage.

(3) The speed control device can self-check without stopping the machine. That is to say, the equipment can operate at low speed and low current when the equipment is running at full speed. This can detect whether the chopper and the inverter are normal without affecting the operation, which brings great convenience to maintenance.

(4) Realize remote operation in the centralized control room. This method is the same as the operation of this machine, and it is more convenient;

(5) DCS control method. The remote operation instruction realizes stable and smooth speed regulation under a given 4-20mA control signal, and can maintain the original given rotation speed when a wire breakage fault occurs, and at the same time, a wire breaking alarm signal is issued.

The reliability of a product generally refers to the product's continuous trouble-free operation time and automatic protection capability for suppressing faults. Mainly determined by:

1. Principle and design reliability; 2. Product device reliability; 3. Product process reliability

4.1 Design Principle Reliability

This is very important, especially the main circuit of speed control, to avoid the series and parallel power electronic devices, low voltage control of high pressure; control the main circuit to strive for simple, controllable power electronics as few as possible, to ensure maximum product reliability.

The chopper technology is used to make the control pulse of the active inverter no longer move, but locked at the minimum inverter angle. Therefore, a strong anti-jamming circuit such as a phase-locked loop can be used, so that the active inverter trigger pulse is very high. Reliable, basically solved a major technical problem of active inverter reliability.

4.2 Failure Compatibility

No control device can be 100% completely reliable, and the key to improving system reliability lies in improving the system's failure compatibility.

The chopper-wave feed-forward speed-regulating device and the constant-speed operating device of the speed-adjusting motor become a parallel relationship. When the speed-governing control device accidentally fails, the automatic protection device can automatically switch the motor to a constant speed operation so as not to cause the motor to stop operating. The motor can only be speed-adjusted, reducing the impact of the fault to a minimum.

Well-designed DCS interface, all-digital circuit, with 256-bit digital-to-analog conversion, sudden increase given buffer, input short-circuit does not affect the speed operation and other functions. The system changes speed from full speed to full speed instead of returning to the starting state and then to full speed, but automatically accelerating smoothly on the basis of the current speed. When the speed approaches the rated value, it will automatically switch to full speed operation. Avoid conversion shocks.

4.3 Electronic devices

YQT-type chopper-wave feed-in variable-speed products use thyristors as the main power electronic device. Imported products are used for the main thyristors; vacuum contactors and imported relays are used for main electrical products; and programmable logic controllers are used for electronic devices to minimize the number of relays. Product reliability has been improved. All integrated circuit chips are imported devices.

4.4 Process aspects

Perfect testing equipment for power electronic devices; perfect production process and special facilities; accurate and reasonable structural layout, etc., all make the reliability of chopper-wave internal-vehicle speed-regulation products comparable to that of high-voltage frequency conversion and cascade speed control. Big advantage.

The following are the test data of the transformation of #3 circulating pump motor and #3 furnace fan of Shandong Liaocheng Thermal Power Co., Ltd.

5.1 3# B circulation pump motor

Motor technical parameters

Original motor: Nameplate: Y1250-12/1730 Voltage: 6KV Rated current: 153A

Power: 1250KW Rated Speed: 495 R/min

After the change of motor: Nameplate: YQT1250-12/1730 Voltage: 6KV Rated current: 148A

Power: 1250KW Rated Speed: 495-320 R/min

In December 2000, the unit was running at full capacity and the circulating pump was running experimental raw data.

Operating conditions

Circulation pump voltage (V)KV

Circulating pump current (I)A

Circulating pump speed (n) rev/min

Circulating pump power

Factor (cosφ)

Circulation pump consumption

Power (Pxh)Kw

I

6

88

380

0.537

491.08

II

6

112

460

0.716

833.335

Analysis of test results:

When the circulating pump operating speed is 380 rpm, the consumed power is 491.08kw; when the circulating pump operating speed is 460rpm, the consumed power is 833.355KW; when the circulating pump is at a low rotating speed, the power consumption is 342.27KW in one hour, ie When the unit is fully loaded, the motor speed is reduced by 17%, but the power consumption is reduced by 41%. If the motor is operated for 5,000 hours per year, about 1.71 million kwh can be saved. Calculated at 0.3 per kilowatt hour, it can save about 510,000 yuan. The cost of the renovation of the circulating pump motor is 1.12 million yuan. Therefore, the investment can be recovered in more than 2 years. If the peak load of the unit is considered, the power saving effect will be more obvious and the investment recovery period will be further shortened.

5.2 3# furnace fan

In May 2001, Shandong Liaocheng Thermal Power Co., Ltd. carried out an inward-feeding transformation of the B-blower and B-bender of the #3 unit (100MW) A and B four wind turbines. The test results for the B-send air blower are as follows:

Motor parameters: B induced fan motor: YQT2710-8 710KW voltage 6KV

B blower motor: YQT2630-6 630KW voltage 6KV

From the test data of the two fans, it can be seen that the energy saving effect of the fan is very obvious at low speed. Especially when the B blower is under low load, the power loss can be reduced by about 70% through reasonable adjustment of the baffle; since only the B blower and B blower are modified in our factory, the blower A and blower A are constant speed motors. A blower B blower share a wind tunnel, need to adjust the pressure balance through a reasonable adjustment of the baffle, if the A blower and B blower at the same time for speed adjustment, when the unit low load wind baffle opening (93%), B The blower also has great potential for energy conservation to be tapped.

Chopper wave feed-in speed regulation has been stable and reliable since our factory was successfully put into production. The energy-saving effect is 35%-52%. Practice has proved that the system is not only cheaper than the high-voltage frequency conversion speed control, but also the speed-adjusting efficiency. High, simple equipment structure, short investment recovery period. It is indeed a good method of speed control, with strong practicality and economy. Chopper wave feed-in speed regulation will be a strong competitor of high-voltage frequency conversion speed regulation.