JPS645943B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a high-voltage power source for a two-stage electrostatic precipitator that is divided into a charging section and a dust collecting section.

In general, an electrostatic precipitator collects particles of a charged substance using an electric field, and therefore includes a dust collecting section in which high voltage electrodes and earth electrodes alternately face each other with a slight gap between them. It is generally accepted that the electric field strength of a rationally designed electrostatic precipitator will occasionally generate interpolar sparks during actual operation, and substances that can ignite due to the spark energy are subject to electrostatic precipitators. removed from However, apart from this, due to insufficient maintenance of the electrostatic precipitator, dust adhering to the electrode plate can straddle the gap between the high voltage electrode and the ground electrode, and leakage current through the dust can cause the dust to heat up and catch fire. In some cases, it is necessary to solve this problem as it is unique to the dust collector.

However, in conventional electrostatic precipitators, it is not recognized that it is important for safety to suppress leakage current due to dust that adheres between the electrode plates.
Although a control means is provided to simply detect a short circuit between the electrodes and turn off the power, it is possible that the waste may be heated and ignited before the short circuit occurs between the electrodes. In other words, the leakage current between the electrode plates due to dust may be close to the corona discharge current for charging the dust-collecting material, whereas in conventional devices, even if a corona discharge current is supplied, the high-voltage power supply and voltage linearity are A smoothing capacitor is included in the high voltage rectifier circuit to supply a sufficiently large current without damaging the circuit. Therefore, although a small amount of leakage current occurs between the electrode plates due to dust, unless it is sufficiently larger than the corona discharge current, it is impossible to distinguish between abnormality and normality between the electrode plates, resulting in the problem of dust ignition.

This invention was made in view of the above-mentioned circumstances, and by detecting leakage current equivalent to corona discharge current due to dust without error, heat generation due to dust can be eliminated.
The purpose of the present invention is to provide a high-voltage power supply for an electrostatic precipitator that can reliably prevent ignition.

The electrostatic precipitator according to the present invention has a two-stage type in which a charging part that charges the collected particles and a dust collecting part that collects the charged particles are separated, and the output terminal of the high voltage power transformer is connected to the charging part and the collecting part that collects the charged particles. A separate power supply is drawn out for the dust collection section, and the dust collection rectifier circuit does not have a smoothing capacitor or has a capacitance below a specified value, and changes in the rectified voltage waveform when leakage current occurs between poles in the dust collection section. The present invention is characterized in that it is a control device that determines leakage current due to dust from the aspects described above and performs ignition prevention control such as power supply voltage adjustment.

Hereinafter, one embodiment of the present invention will be described in detail.

Figure 1 shows the electrode configuration of an electrostatic precipitator, which has a two-stage structure with a charging section 1 provided at the front stage in the feeding direction of the precipitated material (indicated by the arrow) and a dust collecting section 2 located at the rear stage. be done. In the charging section 1, a high voltage is supplied between the wire electrode A and the common electrode C to generate corona discharge, and in the dust collecting section 2, a high voltage is supplied between the plate electrode B and the common electrode C to compensate for charged particles. collect. A power supply circuit for supplying power to these electrodes has the configuration shown in FIG.

In Figure 2, the AC line power supply 3 turns on and off.
Power is supplied to a leakage transformer 5 for high voltage generation through a thyristor 4 that controls the supply voltage by controlling the off ratio and firing angle. Unlike ordinary transformers, the leakage transformer 5 has a half-wave rectifier circuit on the secondary side, but it prevents abnormal current due to biased magnetization from flowing into the primary side, and further suppresses the increase in primary side current even in the event of a short circuit on the secondary side. It has the characteristic that the load voltage/current characteristics become a drooping curve and the corona current can be self-controlled.
The secondary winding of the leakage transformer 5 is a tapped winding from which an output terminal D for supplying power to the charging section 1 and an output terminal E for supplying power to the dust collecting section 2 are respectively drawn out. The AC high voltage generated between the output terminal D and the common terminal F is rectified by the rectifying element 6, and is supplied between the electrodes A and C through the current limiting resistor 7. Similarly, the high voltage generated between output terminal E and terminal F is rectified by rectifying element 8 and supplied between electrodes B and C through current limiting resistor 9.

Here, a smoothing circuit consisting of a smoothing capacitor 10 and a current limiting resistor 11 is provided in the rectifier circuit that supplies power between the charging section electrodes A and C, and causes a high DC voltage drop in response to the corona discharge generated in the charging section 1. The power supply impedance is configured to be low to prevent On the other hand, the rectifier circuit that supplies power between the dust collector electrodes B and C is directly connected between the electrodes B and C without providing a smoothing capacitor. In addition, the power consumption of the dust collecting section 2 is almost zero during normal operation, and even without a smoothing capacitor, the floating capacity of the electrodes B and C itself, for example in a small dust collector, is 10 ^-8 to ^{10 -9} F. Since it has capacity, it has sufficient smoothness characteristics. However, it is permissible to add a smoothing capacitor to the extent that it does not interfere with the determination of leakage current in the dust collection section by a control device, which will be described later.

In the high voltage generation circuit having such a configuration, high-resistance foreign matter such as dust extending between the electrode plates of the dust collecting section 2 is detected by using the detection voltage of the voltage dividing resistor 12 of the voltage dividing resistors 12 and 13 for high voltage detection. control device 14
Based on this determination, the thyristor 4 etc. are controlled to prevent ignition.

Now, if we take out only the electric circuit of the dust collecting section 2, we get the equivalent circuit shown in FIG. Here, 15 is the self-capacity of the dust collection electrode, and 16 is a high-resistance foreign substance. When the resistance value of the foreign object 16 is infinite, that is, when the foreign object does not straddle electrodes B and C, the voltage waveform between electrodes B and C becomes a perfect direct current. on the other hand,
If a foreign object straddles the electrodes and leakage current occurs between them, the resistance value of the foreign object 16 becomes a finite value, so the voltage between electrodes B and C will include ripples. It is known that this ripple content has the characteristics shown in FIG.

Therefore, by monitoring the voltage between electrodes B and C using the detection output of the voltage dividing circuit 12, ripples can be generated.
In other words, it is possible to know that a leakage current has occurred in the dust collecting part electrode, and by determining that this leakage current is caused by a foreign object, measures such as turning off the power can be taken before the danger of the foreign object igniting occurs. be able to. The control device 14 performs foreign object determination and ignition prevention control based on the leakage current detection.

The control device 14 takes in the detected voltages from the voltage dividing circuits 12 and 13 as a digital signal through an analog-digital converter, and controls the firing phase of the thyristor 4 through digital processing using a microcomputer or the like. In addition to controlling the voltage of the dust collecting section 2, the thyristor 4 is controlled by determining the leakage current of the dust collecting section due to foreign matter from the detection system signal of the voltage dividing circuit 12. This control device 14
Of course, the function is not limited to the above-mentioned digital method, but can also be provided with an analog method.

The control device 14 determines leakage current due to foreign matter by the following operation.

First, if a spark occurs in the charged part of the dust collecting part or in the dust collecting part, this is not a safety problem, but since there is no smoothing capacitor between the electrodes of the dust collecting part or the capacitance is small, the voltage waveform will be different. Disturbance occurs. In addition, fluctuations in the power supply voltage sometimes cause voltage disturbances between the electrodes of the dust collection section. In order not to misidentify these disturbances as the occurrence of ripples due to foreign matter, the control device 14 repeatedly tests for the occurrence of ripples without immediately identifying the occurrence of an abnormality even if the control device 14 recognizes the occurrence of ripples. In this test, voltage disturbances caused by sparks and power supply voltage disturbances end in an extremely short time, whereas ripples caused by foreign objects continue for a relatively long time. Therefore, the control device 14 determines that ripples have occurred due to foreign objects only when the ripples are determined to have occurred in all tests conducted over a period sufficiently longer than the time during which ripples occur due to voltage disturbances caused by sparks or power fluctuations.

In addition, the total capacitance C between the electrodes of the dust collection part that is permissible in order to determine that the ripple is caused by foreign matter is
is obtained from the following formula.

However, is the power supply frequency, V is the dust collection section voltage, and i
is the value of the leakage current to be detected, and n is the number of bits of digital data that provides the resolution of the detected voltage in the control device 14.

As described above, in the present invention, in a two-stage electrostatic precipitator in which the charged part and the dust collecting part are separated, voltage is applied to the charged part and the dust collecting part from terminals drawn out individually from the transformer, and the collecting part is A smoothing capacitor is not installed in the dust collecting part, or a capacitor with an extremely small capacity is used, and the duration of the ripple voltage generated by a small leakage current in the dust collecting part is used to distinguish between the occurrence of leakage current due to sparks, etc. It is possible to easily identify and prevent fire accidents.

[Brief explanation of drawings]

Fig. 1 is an electrode configuration diagram of a two-stage electrostatic precipitator, Fig. 2 is a high-voltage power supply circuit diagram showing an embodiment of the present invention, Fig. 3 is an equivalent circuit diagram of the dust collection section in Fig. 2, FIG. 4 is a ripple voltage characteristic diagram in FIG. 3. 1; Charge part, 2; Dust collection part, 5; Leakage transformer, 10; Smoothing capacitor, 12, 13;
Voltage dividing circuit, 14; control device, 15; dust collector self-capacity, 16; leakage impedance.

Claims (1)

[Claims] 1 In a two-stage electrostatic precipitator in which the charging section and the dust collection section are separated, the output terminals of the high voltage generation transformer are dedicated to the charging section and the dust collection section, respectively, and the high voltage rectification for the dust collection section is The circuit does not include a smoothing capacitor or is equipped with a high-voltage power supply circuit whose total capacitance including the self-capacity of the dust collection part does not exceed a predetermined value. A high-voltage power source for an electrostatic precipitator, characterized in that it is provided with a control device that detects from waveform fluctuations, determines that leakage current has occurred due to foreign matter, and controls the high-voltage power supply voltage when this detection continues for a predetermined period of time.