JPS5924374Y2 - electrostatic precipitator - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement of an electrostatic precipitator, and in particular, an object of the present invention is to provide a spark discharge detection device for an electrostatic precipitator that can detect spark discharge extremely reliably and accurately.

Electrostatic precipitators utilize a corona discharge phenomenon in gas, and the dust collection efficiency increases as the corona discharge force increases, that is, as the charge voltage applied to and supplied to the dust collection electrode increases.

Therefore, in an electrostatic precipitator, it is desirable to apply as high a charge voltage as possible between the electrodes; however, when the charge voltage increases, the corona discharge flow increases significantly, and spark discharge is likely to occur. If this occurs frequently and large spark discharges occur, it becomes easy to transition to a self-sustaining discharge such as an arc or glow discharge.

Most of these spark discharges, arc discharges, and glow discharges are in a short-circuit state, so they do not contribute to the dust collection function at all.

In particular, once arc discharge and glow discharge occur, they will not disappear unless charging is stopped, which will significantly reduce dust collection efficiency, and will also have an extremely negative effect on dust collectors and power supplies, so their occurrence should be avoided. We must prevent this as much as possible.

Therefore, in order to obtain high dust collection efficiency in an electrostatic precipitator, it is desirable to control the charging voltage as high as possible by paying attention to the state of spark discharge generation. , it is essential to detect them quickly.

First, such a conventional spark detection method will be explained with reference to FIGS. 1 and 2.

In Fig. 1, 1 is an AC power supply terminal, 2 is a thyristor type control unit consisting of a main control thyristor connected in anti-parallel, 3 is a current limiting reactor, and 4 is a DC high voltage consisting of a step-up transformer T and a high voltage rectifier Rec. Converter, 5 indicates the dust collection part, ■1 and I.

are the currents flowing through the input side and the output side of the DC high voltage converter 4, respectively, and Eo is the charge voltage.

There are various methods for detecting spark discharge in an electrostatic precipitator having such a very general configuration, and the following three methods, which are also commonly used, will be sequentially explained below.

■ A method that focuses on the magnitude of the primary current 11 or secondary current of the transformer.

In this method, as shown in FIG. 2, when a spark occurs at time t, a current of 11 or I is generated.

Focusing on the fact that the value increases and the peak value also increases accordingly,
This is a method of obtaining a spark detection signal vs at a point where the peak value exceeds a certain level VC.

Although this method has a simple circuit configuration, relatively small sparks cannot be detected.

In addition, the impedance of the current limiting reactor 3 shown in Figure 1 is often large depending on its purpose, so there is often no noticeable difference in the peak current value between sparks and normal times, resulting in low spark detection accuracy. .

■ A method that focuses on the drop in charge voltage.

In this method, as shown in FIG. 2, when a spark occurs at time t, the charge voltage E.

decreases immediately and almost reaches zero.

In this case, the charge voltage E. A method of determining when ve has become below a certain level ve, and the charge voltage E at time t.

There is a method based on the differentiation of the falling edge of .

The former is a simple circuit, but the charge voltage E.

is difficult to detect. Generally, charged voltage is transmitted to the control circuit by dividing it with a resistor and insulating it with a photocoupler, etc. However, the linearity of the transmission is usually not very good, and division by the resistor also increases the detection impedance and causes noise effects. can no longer be ignored.

Therefore, setting ve in FIG. 2 becomes difficult.

On the other hand, the latter charge voltage E.

In addition to the above-mentioned transfer problem, the method using the falling differentiation of is also susceptible to noise.

■ The above current ■1 or I.

This method focuses on the fact that the waveform becomes two peaks when there is a spark.

In this method, when a spark is generated, the current increases from that point on, so a change occurs in the rise of the current, and a differential signal can be obtained.

This method focuses on the uniqueness of the spark current waveform and is an extremely sophisticated method that processes the signal using an electronic circuit, but since it ultimately uses the differentiation of the current, it is easily susceptible to the influence of noise. Adjustment becomes difficult due to the correlation between accuracy and noise margin.

Moreover, the characteristic of two peaks in the spark current waveform may become less noticeable depending on the type of load, etc., which may cause problems in practical use.

In view of the shortcomings of the conventional detection method, the present invention has been developed to prevent sparks from occurring when the impedance of the current limiting reactor provided on the input side of a high voltage DC converter is set to a larger value than the impedance of the step-up transformer T in the high voltage DC converter. Although current is flowing when a discharge occurs, the input voltage of the high-voltage DC converter rapidly drops to an extremely low voltage or almost zero voltage due to a large voltage drop due to the impedance of the current limiting reactor, which is unique to spark discharge. It is characterized by the fact that it uses this phenomenon to reliably and accurately detect spark discharge.

An embodiment of the electrostatic precipitator of the present invention will be described below with reference to FIGS. 3 and 4.

First, in FIG. 3, the same reference numerals as in FIG. 1 indicate members corresponding to those in FIG.

Generally, in an electrostatic precipitator, as shown in FIG. 4a, the primary AC current 11 flowing through the power supply line flows with a delay from the power supply voltage 1.

This current 1 is detected by a current detector 6 such as a current transformer,
The detected current is obtained as a voltage signal V1 as shown in FIG. 4 via a current-voltage converter 7 and a full-wave rectifier circuit 8.

The comparator circuit 9 compares this signal 1 with the set voltage Vx from the adjustment circuit 10, and outputs a rectangular output signal V, (v,'0) in the region where the signal v1 is larger than the set voltage Vx. Figure 4C).

On the other hand, the voltage V□ in the power supply line between the current limiting reactor 3 and the step-up transformer T exhibits a remarkable change near the zero point of the current ■1 when the current ■1 is flowing, as shown in Figure 4d, and its waveform has an almost rectangular wave shape.

This voltage V
Although the impedance ZL of is larger than the impedance Z□ of the step-up transformer T in the high voltage DC converter 4, if each is set so that 2L>2□, the time t1
When a spark discharge occurs at , the current 11 continues to flow, but the voltage V
, immediately decreases sharply to almost zero.

That is, with the occurrence of spark discharge, the load side exhibits a state close to a short circuit, so in the case of ZL-Z□, the current-limiting reactor 3 bears most of the main circuit voltage, so that the voltage 1 becomes almost zero.

For example, a current limiting reactor 3 is used to suppress the value of current flowing during spark discharge, etc. to about three times the current value during steady state or less.
If the impedance ZL of the step-up transformer T is set to about 30% to 50% of the total impedance of the main circuit, the impedance Z□ of the step-up transformer T is usually a few percent to about 5.6%, so during spark discharge, ZL/Z □Becomes -6 to 10.

In particular, in order to suppress the output side voltage V of the current limiting reactor 3 to a sufficiently low value over the period when the spark discharge current is flowing, the impedance ZL>Z□, preferably Z, -/Z1
>5.

By selecting the impedance ratio in this manner, detection accuracy can be improved.

This voltage V is detected by a voltage detection circuit 11 such as a transformer, and is obtained as a detected voltage signal 1 as shown in FIG. 4e through a full-wave rectifier circuit 12.

This voltage signal V□ is compared with the set voltage vY from the adjustment circuit 13 in the comparator circuit 14, and the comparator circuit compares the voltage signal V□ with the set voltage vY from the adjustment circuit 13 only in the region where the signal ■ is higher than the level of the set voltage ■7, as shown in FIG.
It outputs rectangular voltage signals ■ and ′ as shown in .

Therefore, as can be seen from f in the same figure, during the period T1 during which spark discharge occurs, even though the current ■1 is flowing, the signal V□'
is at zero level (VT'-〇).

The logic circuit 15 receives the above signal V,'=0, signal v, /-1
4, only when the voltage V□ on the output side of the current limiting reactor 3 is at a very low level even though the current ■1 is sufficiently flowing through the current limiting reactor 3. A rectangular signal ■α as shown in g is output.

This rectangular signal may be used as a spark detection signal as it is, or it may be differentiated via a differentiating circuit 16 and converted into a differential signal 5 as shown in the fourth diagram, which is then sent from a terminal 20 and used as a spark detection signal.

Here, the set voltage VY of the adjustment circuit 14 is set to be larger than the value of the signal ■□ at the time of spark discharge, as shown in part A, and therefore the impedance Z□ of the step-up transformer and the impedance ZL of the current limiting reactor are Naturally, the level of the set voltage (1) can change depending on the magnitude of the voltage.

Next, another embodiment of the present invention will be described with reference to FIGS. 4 and 5.

As mentioned above, when a spark discharge occurs, the spark detection method as in the above embodiment is very effective when the voltage ■□ drops significantly or drops to a value close to zero, but the spark discharge occurs at time t2. As in the case of spark discharge, there are cases where the voltage V1 is inverted, that is, the voltage polarity is reversed (Fig. 4 d), and in this case, the detection signal of the voltage V1 is full-wave rectified as in the above embodiment. Then, as shown in part B of the signal ■□ shown in Figure 4e, the voltage becomes higher than the level of voltage VY, and even though spark discharge is actually occurring, in Figure 4g and h As shown by the dotted line, the spark detection signal that should originally be obtained cannot be obtained.

In other words, false detection will occur.

The cause of the polarity reversal of the voltage V□ is currently unknown, but in this embodiment, spark discharge can be detected reliably and accurately even if such a phenomenon occurs.

This method is basically the same as the above embodiment, and the current
1 and voltage ■□ are separated into positive and negative half waves so that their phases are synchronized, and then the phases of the respective detection signals are matched and compared.

In FIG. 5, the half-wave discrimination circuit 20 distributes the detection signal of the current 11 into positive and negative half-waves, and similarly the half-wave discrimination circuit 21
Also performs the function of distributing the detection signal of voltage V□ into positive and negative half waves.

Therefore, it can be considered that a half-wave of the signal V1 shown in FIG. 4 without the hatching appears on the output side a of the discrimination circuit 20, and a half-wave shown with the hatching appears on the output side a'.

Similarly, it can be considered that the half-wave of the signal V□ shown in FIG. 4e without the hatching appears on the output side of the discriminator circuit 21, and the half-wave shown with the hatching appears on the output side b'. .

In this case, a must be synchronized with the phase of the half-wave signals appearing at a' and b'.

Each signal of these half-wave parts is sent to the adjustment circuits 9 and 1 in the comparison circuits 10.10' and 14.14' as in the previous embodiment.
3 and its output is compared to the set voltage level of logic circuit 1.
5.15', the signal is processed in the same manner as described above, combined by diodes D1 and D2, and further differentiated by a differentiating circuit 16, and is obtained as a spark detection signal at a terminal 20.

By distributing each half wave in this way, the B part of signal 1 during the spark discharge shown in Figure 4e will be erased from the shaded part, so the spark discharge will occur at the output coupling point 18. A rectangular signal (fourth signal) with a width equal to the current flow period T2
It is easy to understand that the result (indicated by the dotted line in Figure g) appears.

As described above, this invention is based on the idea that if a current limiting reactor with an impedance larger than the impedance of the step-up transformer is provided on the primary side of the step-up transformer, when a spark discharge occurs, current flows through the primary and secondary sides of the step-up transformer. Although the current is flowing, the secondary side of the step-up transformer is short-circuited, so the current-limiting reactor bears most or almost all of the main circuit voltage, causing the current-limiting reactor to become the step-up transformer. The extremely unique condition that occurs with a spark discharge, in which the voltage between the two points drops significantly, is detected and used as a criterion for determining the occurrence of a spark discharge, making it possible to detect a spark discharge extremely reliably and accurately.

In the above embodiment, the current was detected on the primary side of the step-up transformer, but it may of course be detected on the secondary side.

Also, in the above embodiment, the voltage was detected between the current limiting reactor and the step-up transformer, but the voltage may also be detected on the secondary side in the same way as the current, and in this case, the voltage can be detected regardless of the impedance of the current limiting reactor. , especially effective for those with large ripple voltage.

[Brief explanation of the drawing]

1 and 2 are block diagrams and diagrams showing current and voltage waveforms of an electrostatic precipitator for explaining a conventional spark discharge detection method, respectively, and FIG. 3 is a diagram showing an electrostatic precipitator according to the present invention. FIG. 4 is a diagram showing voltage and current waveforms of various parts to explain the present invention. FIG. 5 is a diagram showing another embodiment of the spark detection device for an electrostatic precipitator according to the present invention. FIG. 1... AC power supply terminal, 2... Thyristor type control section, 3... Current limiting reactor, 4...
...High voltage DC converter, T...Step-up I~France 6...Current detector, 7...Current-
Voltage converter, 8, 12...Full wave rectifier circuit, 11
...Voltage detection circuit, 9, 13...Adjustment circuit, 10, 14...Comparison circuit, 15...
...Logic circuit, 16...Differential circuit, 20.21
...Half-wave discrimination circuit.

Claims (1)

[Scope of utility model registration request] A thyristor-type control unit is provided in the power supply path between the AC power source and the step-up transformer, and the impedance Z is such that the relationship between the impedance Z of the step-up transformer is ZL/Z1>.
A current detection circuit that detects a current flowing in a power supply path, and a voltage detection circuit that detects a voltage in a power supply path between the current limiting reactor and the primary winding of the step-up transformer. an adjustment circuit that provides respective set signal levels, a comparison circuit that compares each detection signal from the current detection circuit and the voltage detection circuit with the corresponding set signal level, and is operated by the output signals of these comparison circuits. and a logic circuit that generates a spark discharge generation signal when the current detection signal is higher than the set signal level and the voltage detection signal is lower than the set signal level. Electrostatic precipitator.