JP6411876B2 - Three-phase heater resistance detection method - Google Patents

Description

  The present invention relates to a resistance value detection method for a three-phase heater, and more particularly to a resistance value detection method useful for detecting disconnection or life of a heater.

  If the resistance value of the heater can be detected directly, the disconnection and life can be determined. However, in each heater heater, etc., each heater is installed in the furnace, so the resistance value of the heater is directly measured in a high-temperature atmosphere in real time. It is difficult to do. Therefore, for example, Patent Document 1 proposes a heater abnormality detection device that detects the disconnection and life of a three-phase heater from a line current that can be easily measured outside the furnace.

JP-A-8-180960

  However, the conventional heater abnormality detection device has a problem that although it is possible to detect the disconnection or the like in any of the three-phase heaters, it is not possible to specify which phase the heater is.

  Therefore, the present invention solves such a problem, and provides a resistance value detection method for a three-phase heater that can specify which phase the heater that has been disconnected or has reached the end of its life, etc., is provided. Objective.

  In order to achieve the above object, according to the first invention, when the three-phase heater is delta-connected, each line current (Ir, Is, It) and each line voltage of the three-phase heater (21 to 23). (Ers, Est, Etr) is detected, and an expected value (a) of the phase current (Irs) of one phase of the three phases is set, and the predicted value and two of the detected line currents are set. The remaining one-phase line current (Is ') is calculated based on the phase line current (Ir, It), and the difference between the calculated line current (Is') and the detected line current (Is) is allowed. When the difference is larger than the difference (e), the phase current expected value (a) is corrected to obtain a corrected phase current expected value (a ′) and the corrected phase current expected value (a ′). The remaining one-phase new line current (Is ′) is calculated based on the phase line current (Ir, It), and the calculated new line current (Is) and the detection are calculated. The calculation of a new line current is further repeated until the difference between the calculated line currents (Is ′) falls within the allowable error (e), and the calculated new line current (Is ′) and the detected line current are repeated. The expected value (a ′) of the corrected phase current when the difference of (Is) falls within the allowable error (e), the phase currents (b, c) of other phases calculated at this time, and the detection The resistance value (Rrs, Rst, Rtr) of each phase is calculated based on each line voltage (Ers, Est, Etr).

  According to the first aspect of the present invention, since the resistance value of each phase of the three-phase heater connected in delta connection can be calculated, disconnection, life, etc. can be reliably detected for each heater of each phase. In particular, the disconnection or the like is not detected indirectly from the line current, but is directly detected from the resistance value itself, so that handling is easy.

  In the second aspect of the invention, when the three-phase heater is star-connected, the resistance value of each phase is calculated according to the procedure according to claim 1, assuming that the three-phase heater is delta-connected, The calculated resistance value (Rrs, Rst, Rtr) of each phase is converted into the resistance value of each phase of the star-connected three-phase heater using the delta star conversion formula.

  According to the second invention, since the resistance value of each phase can be calculated even if the three-phase heater is star-connected, it is possible to reliably detect disconnection, life, etc. for each phase heater. it can.

  The reference numerals in the parentheses refer to the correspondence with specific means described in the embodiments described later.

  As described above, according to the resistance value detection method for a three-phase heater of the present invention, the resistance value can be detected for each phase of the three-phase heater. Can be reliably determined.

It is an energization circuit diagram of a heater energization device which enforces a method of the present invention. It is an electric circuit diagram of a three-phase heater. It is an electric current vector diagram of a three-phase heater. It is a flowchart which shows the calculation procedure of a heater resistance calculating apparatus.

  The embodiment described below is merely an example, and various design improvements made by those skilled in the art without departing from the gist of the present invention are also included in the scope of the present invention.

  FIG. 1 shows the configuration of a heater energizing apparatus for carrying out the method of the present invention. In FIG. 1, three-phase heaters 21, 22, and 23 provided in the furnace body 1 are delta-connected, and three feeder lines 41, 42, and 43 extend from the heaters 21 to 23 to the outside of the furnace to control power. It is connected to the output side of the device 3. The input side of the power control device 3 is connected to a three-phase AC power source 5. Current feed lines 41, 42, 43 are provided with current transformers 61-63, and their outputs are input to the line current detection device 6. Further, a transformer 71 is connected between the power supply lines 41 to 43, and an output thereof is input to the line voltage detection device 7.

  The line currents Ir, Is, It and the line voltages Ers, Est, Etr of the power supply lines 41 to 43 detected by the devices 6 and 7 are input to the heater resistance calculation device 8, and the calculated line resistance Rrs, Rst, and Rtr are displayed on the display 81 and input to the heater disconnection detector 82. When disconnection is detected, the disconnection display alarm 83 is activated. The heater resistance calculation device 8 has a built-in computer, and details of the calculation procedure will be described later.

  FIG. 2 shows an electrical circuit diagram of the heaters 21 to 23, in which Ir, Is, It are R-phase, S-phase, and T-phase line currents, Ers, Est, Etr are RS line voltages, ST, respectively. The line voltage and the TR line voltage. Irs, Ist, and Itr are RS phase current, ST phase current, and TR phase current, respectively. Each current and voltage is a vector quantity.

Here, assuming that the respective phase currents Irs, Ist, Itr flow in the direction of the arrows in FIG. 2, the line currents Ir, Is, It are expressed by the following equations (1) to (3).
Ir = Irs−Itr (1)
Is = Ist−Irs (2)
It = Itr-Ist (3)

Therefore, assuming that the line voltages Ers, Est, Etr are in an equilibrium state, and the magnitudes (absolute values) of the phase currents Irs, Ist, Itr are a, b, c, respectively, the vector diagram of each current is shown in FIG. It becomes like 3. Here, if the values of a, b, and c are known, the resistance values Rrs, Rst, and Rtr of the heaters of the respective phases RS, ST, and TR can be calculated by the following equations (4) to (6). Here, E is the absolute value of the line voltages Ers, Est, Etr. When the line voltages Ers, Est, Etr are unbalanced, an error occurs in the calculated resistance value. However, if the line voltage is in the normal range, this error is about 5% and does not cause a problem.
Rrs = E / a (4)
Rst = E / b (5)
Rtr = E / c (6)

  In the present embodiment, a, b, and c are determined by the heater resistance calculation device 8 according to the procedure shown in the flowchart of FIG. First, in step 101, it is confirmed whether or not there is a measurement abnormality of the line currents Ir, Is, It. That is, when the measured values of the line currents Ir, Is, It are X, Y, Z, respectively, and the value of X is the largest, when θ obtained by the following equation (7) exceeds 120 ° Subsequent calculations are not performed on the assumption that the line currents Ir, Is, and It are abnormal. This is because one of the phase currents Irs, Ist, and Itr becomes a negative value when one of the internal angles of the triangle connecting the points O, P, and Q in FIG. 3 exceeds 120 °.

  In step 102, in FIG. 3 in which the direction of the phase current Irs coincides with the x-axis, the magnitude (a) of the phase current Irs is set equal to the line current Ir, and the coordinates (a, 0) of the point O are determined. In step 8), the magnitude c of the phase current Itr is calculated. In step 103, the X coordinate Px and the Y coordinate Py of the point P in FIG. 3 are calculated by the following equations (9) and (10). Note that Ir in the equation (8) indicates the magnitude (absolute value) of the line current.

  In the following step 104, the magnitude b of the phase current Ist is calculated by the following equation (11) using c calculated in step 102. In step 105, the X coordinate Qx and the Y coordinate Qy of the point Q in FIG. 3 are obtained from the following equations (12) and (13). In the equation (11), It represents the magnitude (absolute value) of the line current.

  In step 106, the length between points Q and O in FIG. 3 is calculated as Is ′ by the following equation (14). In the subsequent step 107, the length (magnitude) Is ′ is compared with the detected line current Is (hereinafter, the line current Is is also simply referred to as Is). Here, when Is ′ = Is, since c is 0 in the equation (8), a disconnection output is issued assuming that the TR phase is completely disconnected (step 111), and the calculation is terminated.

  If Is ′> Is or Is ′ <Is in step 107, it is checked in step 108 whether or not | Is−Is ′ | is equal to or smaller than a tolerance e (for example), and | Is−Is ′ | Otherwise, in step 109, the magnitude a of the phase current Irs is updated to a new value a ′ by the following equation (15) to determine the coordinates (a ′, 0) of the new O point (FIG. 3). Return to. Thereafter, steps 102 to 108 are repeated using a ′. Note that the gain Kp in the equation (15) is determined by design, but it may be set to about 0.1.

  If | Is−Is ′ | becomes equal to or smaller than the tolerance e in step 108, in step 110, using the magnitudes a ′, b, and c of the respective phase currents calculated at this time, The heater resistance values Rrs, Rst, Rtr of the respective phases RS, ST, TR are calculated according to 4) to (6) and displayed, and based on these resistance values, the disconnection of the heaters 21-23 of each phase ( An alarm is given by determining whether the resistance value is excessive), short-circuited (resistance value is too low) or life (resistance value gradually increases).

  In addition, when the three-phase heaters 21 to 23 are star-connected, the above calculation is performed assuming that the three-phase heaters 21 to 23 are connected, and the resistance value of each phase obtained is calculated using a known delta-star conversion formula. Convert to each phase resistance value in star connection.

  Further, when a transformer having a transformation ratio P is connected between the measurement point of the line current and the line voltage and the three-phase heater, the heater resistance value obtained by the above procedure is divided by the square of P.

  As described above, according to the resistance value detection method of the present embodiment, the heater resistance value of each phase of the three-phase heater is calculated, and based on this, the disconnection, short circuit, or life of the heater is detected. Is possible.

  DESCRIPTION OF SYMBOLS 1 ... Furnace body 21, 22, 23 ... Heater, 3 ... Electric power control apparatus, 8 ... Heater resistance calculation apparatus, Ers, Est, Etr ... Line voltage, Ir, Is, It ... Line current, Irs, Ist, Itr … Phase current, Rrs, Rst, Rtr… heater resistance value.

Claims (2)

When the three-phase heater is delta-connected, the line current and line voltage of the three-phase heater are detected, and the predicted value of the phase current of one of the three phases is set. And calculating the remaining one-phase line current based on the two-phase line current out of the detected line currents, and the difference between the calculated line current and the detected line current is larger than the tolerance The phase current predicted value is corrected to obtain a corrected phase current predicted value, and the remaining one-phase new line current is calculated based on the corrected phase current predicted value and the detected two-phase line current. The calculation of the new line current is repeated until the difference between the calculated new line current and the detected line current falls within the tolerance, and the calculated new line current and the detected line current are repeated. When the difference in phase is within the allowable error, the corrected phase current expected value and this time calculation Are other phase current of phases is, and the detected three-phase resistance value detection method of the heater of calculating the phase resistance value based on the line voltages. When the three-phase heater is star-connected, the resistance value of each phase is calculated according to the procedure of claim 1 assuming that the three-phase heater is delta-connected, and the calculated phase of each phase A method for detecting a resistance value of a three-phase heater, wherein the resistance value is converted into a resistance value of each phase of a three-phase heater star-connected using a delta star conversion formula.

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