JP2013148401A - Insulation monitoring apparatus and monitoring method of direct current non-grounded circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To always monitor an insulation state between an electrical circuit in a direct current non-grounded circuit and ground by calculating an insulation resistance value obtained before operating a ground relay.SOLUTION: An electrical circuit voltage is detected by electrical circuit voltage detection means 41; a division ratio of voltage division resistors in a positive pole side electrical circuit and a negative pole side electrical circuit is changed by switching means 42; contacts are alternately switched at a predetermined time interval by switching control means 48 to forcedly generate a potential difference between an insulation resistor side and a voltage division resistor side; and respective currents allowed to flow on the positive pole side and negative pole side are detected by current detection means 43. Insulation resistance values between the positive pole side and the ground and between the negative pole side and the ground are calculated by arithmetic means 47 from the respective detected currents and electric circuit voltage and numerically displayed on measurement display means 49 to monitor the values.

Description

  The present invention relates to a technique for monitoring insulation between an electric circuit and a ground in a direct current ungrounded electric circuit, and more particularly to a technique for monitoring an insulation state before a ground fault relay operates.

In recent years, the use of natural energy has been reconsidered due to power generation that does not emit CO _{2 or} accidents in nuclear power generation, and development of power generation using natural energy has been promoted. Solar power generation using sunlight, power generation using wind power and geothermal heat, and other fuel cells using chemical reactions. When all of the electric power generated by these is generally used as DC power, it is converted into AC power by an inverter or the like.

  Construction of a large-scale power generation system, such as a mega solar power plant, requires a large installation area and is installed in a place away from the city, and is then transmitted to a substation away from the city by a DC circuit. Often done.

  In direct current power transmission, as in the case of alternating current power transmission, the insulation resistance between the transmission line and the ground may deteriorate, and a ground fault may occur, so a direct current ground fault relay is installed. When the ground fault relay operates, the electric circuit is cut off, causing a great deal of damage to the consumer.

  The purpose of the present invention is to constantly monitor the change in insulation resistance between the DC circuit and the ground before this ground fault relay is activated, and to take precautions before the circuit breaker is shut off. It is what.

  Conventionally, an insulation monitoring method of this type is shown in FIG. FIG. 5 is an equivalent circuit diagram of a conventional insulation monitoring method. In the figure, 10 is a DC power source, 11 and 12 are a positive-side electric circuit (hereinafter abbreviated as a positive-electrode circuit) and a negative-electrode side for transmitting power from the DC power source 10. An electric circuit (hereinafter abbreviated as a negative circuit), R1 and R3 are voltage dividing resistors that divide the voltage between the electric circuits, and R2 and R4 are a positive electrode and a negative electrode that are generated between the positive electrode 11 and the ground E and between the negative electrode 12 and the ground E. A side insulation resistance, R5, indicates a detection resistor provided between the voltage dividing point E ′ and the ground E. When the insulation resistance between the positive electrode circuit or the negative electrode circuit and the ground changes, the voltage dividing resistance low bodies R1, R3 and Since the current flowing into the detection resistor R5 changes depending on the ratio of the insulation resistances R2 and R4, the amount of change in the current is detected (for example, Patent Document 1).

Japanese Patent Application Laid-Open No. 2004-271285.

  In the conventional method shown in FIG. 5, the insulation resistance value cannot be obtained only by knowing the amount of change in the current flowing through the detection resistor. Further, when the ratio of the positive-side insulation resistance R2 and the negative-side insulation resistance R4 of the current flowing into the detection resistor due to the change in the insulation resistance and the resistance ratio of the voltage dividing resistors R1 and R3 are the same, the detection resistor The current I5 flowing through the body R5 is zero. That is, the potentials of the ground E and the voltage dividing point E ′ are the same, and no voltage is generated in the detection resistor R5, so that the insulation resistance cannot be detected.

  Further, when the insulation resistances R2 and R4 on the positive electrode side and the negative electrode side deteriorate at the same time, the current Igp flowing in R2-R5-R3 and the current Ign flowing in R1-R5-R4 interact with each other, and the deteriorated insulation resistance The current flowing through R2 and R4 cannot be accurately detected by the detection resistor R5. Therefore, there is a problem that an accurate insulation resistance value cannot be detected.

  The present invention has been made to solve such a problem, and forcibly changing the voltage dividing ratio of the voltage dividing resistor during measurement, so that the insulation resistance value can be accurately determined even under the above-mentioned conditions that could not be detected conventionally. It makes it possible to detect.

  In the present invention, means for solving the above-mentioned problems are circuit voltage detecting means for detecting the circuit voltage of the DC non-grounded circuit, voltage dividing resistors R1 and R3 for dividing the circuit voltage, and voltage dividing A switching means for changing the voltage dividing ratio by alternately switching the auxiliary resistor between the positive electrode side and the negative electrode side, and a current provided between the switching means and the ground E to detect a current flowing between the ground and the electric circuit; Current detection means for detecting a current between the earth, a detection signal detected by the current detection means and a voltage signal detected by the electric circuit voltage detection means, and a current signal between the electric circuit and the earth when switched to the positive side And a calculation means for calculating an insulation resistance from a current signal between the electric circuit and the ground when switched to the negative electrode side, and a measurement display means and / or an alarm means for displaying the insulation resistance value calculated by the calculation means. Resistance R2, negative side Calculating the insulation resistance values of R2 and R4 when the resistance was and R4 so as to monitor changes in insulation resistance value between the DC Nonreferenced path and ground and calculated by the following arithmetic expression.

R2 = (V4a−V4b) × V / (V4b × I5a−V4a × I5b)
R4 = (V2b−V2a) × V / (V2b × I5a−V2a × I5b)
However, R1 and R3 are voltage dividing resistors, R6 is an auxiliary voltage dividing resistor, and R5 is a detection resistor included in the current detecting means, and these values are known. V is a voltage, the voltage of the numerical resistor attached thereto, I is the current, and the current flowing through the numerical resistor attached thereto. a and b indicate switching-on contacts in the switching means.

  V4a can be obtained by V3a-V5a, V4b can be obtained by V3b-V5b, V2a can be obtained by V1a + V5a, and V2b can be obtained by V1b + V5b.

  In addition, the monitoring method includes a switching unit that divides the voltage of the DC ungrounded circuit with a voltage dividing resistor, and switches and changes the voltage dividing ratio between the voltage dividing point of the voltage dividing resistor and the ground. In addition to providing a detecting means for detecting the current flowing between the voltage dividing point and the ground, the switching means alters the voltage dividing ratio by alternately connecting auxiliary voltage dividing resistors to the voltage dividing resistors on the positive electrode side and the negative electrode side. The current flowing when the current is changed is detected by the current detection means, and the insulation resistance values between the positive circuit and the ground and the negative circuit and the ground are calculated by the calculation means from the detected current and the circuit voltage. The measurement display means for displaying the value based on the value and / or the insulation resistance between the DC non-grounded electric circuit and the ground is monitored so that an alarm is issued when the insulation resistance value becomes a predetermined value or less.

  The above-described calculation of the insulation resistance value can be obtained by the following arithmetic expression when the insulation resistance between the positive electrode circuit and the ground is R2 and the insulation resistance between the negative electrode circuit and the ground is R4.

R2 = (V4a−V4b) × V / (V4b × I5a−V4a × I5b)
R4 = (V2b−V2a) × V / (V2b × I5a−V2a × I5b)
However, R1 and R3 are voltage dividing resistors, R6 is an auxiliary voltage dividing resistor, and R5 is a detection resistor included in the current detecting means, and these values are known. V is a voltage, the voltage of the numerical resistor attached thereto, I is the current, and the current flowing through the numerical resistor attached thereto. a and b indicate switching-on contacts in the switching means.

  V4a can be obtained by V3a-V5a, V4b can be obtained by V3b-V5b, V2a can be obtained by V1a + V5a, and V2b can be obtained by V1b + V5b.

  (1) In the conventional method, when the positive-side insulation resistance R2 and the negative-side insulation resistance R4 have the same value or the same ratio as the voltage dividing resistors R1 and R3, the potential becomes the same potential and no resistance voltage to be measured is generated. Although the insulation resistance could not be measured, in the present invention, by switching the value of the voltage dividing resistor using the voltage dividing ratio switching means, a potential difference occurs between the insulation resistance side and the voltage dividing resistance side, even under conditions that could not be achieved in the past. The insulation resistance value can be detected.

  (2) The insulation resistances on the positive electrode side and the negative electrode side can be obtained by alternately switching on and off by the voltage division ratio switching means.

  (3) By always detecting the circuit voltage, an accurate insulation resistance value can be obtained even when the circuit voltage fluctuates.

  (4) By setting the resistance value of the auxiliary voltage dividing resistor R6 when the auxiliary resistor is used for changing the voltage dividing ratio to R1 >> R6 and R3 >> R6, voltage fluctuation between the electric circuit and the ground is suppressed to be small. And the influence of noise on the load equipment can be reduced.

The block diagram of embodiment of this invention. The equivalent circuit diagram of FIG. FIG. 3 is an equivalent circuit diagram when the a-side contact is on and the b-side contact is off in FIG. 2. FIG. 3 is an equivalent circuit diagram when the b-side contact is on and the a-side contact is off in FIG. 2. Explanatory drawing of a prior art.

  Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram for explaining the present invention, wherein 1 is a DC power source, 2 and 3 are positive and negative side positive and negative electrode circuits connected to the DC power source 1, and 4 is an insulation monitoring device. The insulation monitoring device 4 assists the circuit voltage detection means 41 that takes in the circuit voltage V and detects the circuit voltage, the voltage dividing resistors R1 and R3 that divide the circuit voltage, and the voltage dividing ratio of the voltage dividing resistors R1 and R3. A voltage dividing ratio switching means 42 for switching and changing the voltage dividing resistor R6 is provided.

  Reference numeral 43 denotes current detection means comprising a detection resistor, which is connected between the voltage dividing ratio switching means 42 and the ground E via a ground line 44 and detects a current flowing between the voltage dividing resistor and the ground E. 45 is an amplifier circuit for amplifying the detection signal of the current detection means 43, 46 is inputted with the output signal of the amplification circuit 45 and the circuit voltage signal detected by the circuit voltage detection means 41, and these input signals are converted into an A / D converter 46. The digital signal is converted into a digital signal and input to the calculation means 47.

  48 is a switching control means of the voltage dividing ratio switching means 42, and switches the contacts in the voltage dividing ratio switching means 42 according to a command from the calculating means 47. This switching is performed when the contact connected to the voltage dividing resistor R1 on the positive electrode circuit 2 side is the a side contact, the contact connected to the voltage dividing resistor R3 on the negative electrode circuit 3 side is the b side contact, and one is on The other is turned off and is alternately turned on and off at predetermined time intervals. R6 is an auxiliary voltage dividing resistor, which is inserted in series on the voltage dividing resistor R3 side when the a-side contact is on, and the voltage dividing ratio becomes R1 / (R3 + R6), and the voltage dividing ratio is changed. The same applies when the b-side contact is on.

  R2 is a positive electrode side insulation resistance between the positive electrode circuit and the ground to be detected and monitored by the present invention, and R4 is a negative electrode side insulation resistance between the negative electrode circuit and the ground. The positive-side and negative-side insulation resistances R2 and R4 are close to infinity in the normal state of the electric circuit, and appear and change due to deterioration of the insulation between the electric circuit and the ground.

  Now, when the insulation between the positive electrode circuit 2 and the ground deteriorates and the positive electrode side insulation resistance R2 is generated, the voltage dividing resistor R3 when the contact of the voltage dividing ratio switching means 42 is in the a side on and the b side off. Is added to the auxiliary voltage dividing resistor R6, the voltage dividing ratio becomes R1 / (R3 + R6), and the divided current flows from the current detecting means 43 to the ground E. When the b-side is on and the a-side is off, the voltage division ratio is (R1 + R6) / R3, and flows from the current detection means 43 to the ground E by the divided current.

  The current detection means 43 inputs detection signals, each of which detects the current that flows when the voltage dividing ratio is switched by the switching means 42, to the calculation means 47 via the amplifier circuit 45 and the A / D converter 46. The calculation means 47 calculates the positive and negative side insulation resistances R2 and R4 based on the respective input signals and the voltage signal from the circuit voltage detection means 41. 48 is a switching control means for controlling the switching contact of the voltage dividing ratio switching means 42, and switches the contacts alternately at predetermined time intervals. 49 is a measurement display means, and displays the result calculated by the calculation means 47 in a visible state as a number or a graph. Reference numeral 50 denotes an alarm means that issues an alarm by sound or light when the insulation resistance value falls below a preset value.

  FIG. 2 shows an equivalent circuit diagram for explaining the calculation by the calculation means 47. In the figure, the same or corresponding parts as those in FIG. 3 shows an equivalent circuit when the a-side contact is on and the b-side contact is off, and FIG. 4 shows an equivalent circuit when the a-side contact is off and the b-side contact is on. Calculation of the resistance values of the insulation resistances R2 and R4 by the circuit will be described.

  In the following formulas, the symbols a and b indicate that the a-side contact and the b-side contact are on, respectively, and I1 to I5 and V1 to V5 are voltage dividing resistors, detection resistors, The current flowing through the insulation resistances R1 to R5 and the voltage between the resistances are shown. R5 shows a detection resistor in the current detection means 43. R3a shows R3 + R6, and R1b shows R1 + R6.

  The positive electrode side insulation resistance R2 and the negative electrode side insulation resistance R4 are obtained as follows.

<When a side contact is on, b side contact is off>
First, the circuit voltage V and the voltage V5a of the detection resistor R5 are measured. The current I5a flowing therethrough from V5a is obtained by V5a / R5.

Next, the current I1a flowing through the resistor R1 is obtained.
I1a = (V + R3a × I5a) / (R1 + R3a) (1)
The voltage V1a of the resistor R1 is obtained by V1a = I1a × R1.

  Next, the current I3a flowing through the resistor R3a is obtained by I3a = I1a−I5a, and the voltage V3a is obtained by I3a × R3a.

  Next, the voltage V2a of the resistor R2 is obtained by V2a = V1a + V5a, and the voltage V4a of the resistor R4 is obtained by V3a−V5a.

The current I2a flowing through the resistor R2 is
I2a = (V−R4 × I5a) / (R2 + R4) = V2a / R2 (2)
From this equation, R2 = V2a * (R2 + R4) / (V-R4 * I5a) (3).

<When b side contact is on, a side contact is off>
First, the circuit voltage V and the voltage V5b of the detection resistor R5 are measured. From this V5b, I5b is obtained by V5b / R5.

Next, the current I1b flowing through the resistor R1b is obtained.
I1b = (V + R3 × I5b) / (R1b + R3) (4)
The voltage V1b of the resistor R1b is obtained by V1b = I1b × R1b.

  Next, the current I3b flowing through the resistor R3 is obtained by I3b = I1b−I5b, and the voltage V3b is obtained by I3b × R3.

  Next, the voltage V2b of the resistor R2 is obtained by V2b = V1b + V5b, and the voltage V4b of the resistor R4 is obtained by V3b−V5b.

The current I2b flowing through the resistor R2 is
I2b = (V−R4 × I5b) / (R2 + R4) = V2b / R2 (5)
From this equation, R2 = V2b × (R2 + R4) / (V−R4 × I5b) (6)
From the calculation results of both equations (3) and (6),
V2a * (R2 + R4) / (V-R4 * I5a) = V2b * (R2 + R4) / (V-R4 * I5b) (7)
From this, the negative side insulation resistance R4 is
R4 = (V2b−V2a) × V / (V2b × I5a−V2a × I5b) (8)
Is obtained.

Similarly, I4a = (V + R2 × I5a) / (R2 + R4) = V4a / R4 (9)
R4 = V4a × (R2 + R4) / (V + R4 × I5a) (10)
Similarly, I4b = (V + R2 × I5b) / (R2 + R4) = V4b / R4 (11)
R4 = V4b × (R2 + R4) / (V + R4 × I5b) (12)
From the calculation results of both formulas (10) and (12), V4a × (R2 + R4) / (V + R2 × I5a) = V4b × (R2 + R4) / (V + R2 × I5b)
From this, the positive-side insulation resistance R2 is
R2 = (V4a−V4b) × V / (V4b × I5a−V4a × I5b) (13)
Is obtained.

  Although the case where two contacts are used in the voltage dividing switching means 42 has been described, the contact does not necessarily mean a contact, and may be a logic circuit (element), a transistor, or the like. By changing, the current flowing through the detection resistor changes, and the insulation resistance value can be obtained similarly.

  Further, according to the present invention, the voltage and current of each resistor is obtained from the detected current before changing the voltage dividing ratio, the detected current after changing the voltage, and the electric circuit voltage, and the value of the insulation resistance is obtained from the difference. Therefore, as long as the values of the voltage dividing resistors (including the auxiliary voltage dividing resistors) and the current detecting resistors are known, the resistance values may be arbitrary values, and the ratios may be arbitrary.

DESCRIPTION OF SYMBOLS 1 ... DC power supply 2 ... Positive electrode side electric circuit 3 ... Negative electrode side electric circuit approval 4 ... Insulation monitoring device 41 ... Electric circuit voltage detection means 42 ... Voltage division ratio switching means 43 ... Current detection means 44 ... Ground line 45 ... Amplifying circuit 46 ... A / D converter 47 ... calculating means 48 ... switching control means 49 ... measurement display means 50 ... alarm means

Claims (3)

Circuit voltage detection means for detecting the circuit voltage of the DC ungrounded circuit, voltage dividing resistors R1 and R3 for dividing the circuit voltage, and the voltage dividing ratio of the voltage dividing resistor to the auxiliary voltage dividing resistor R6 on the positive side Switching means for alternately switching to the negative electrode side to change the voltage dividing ratio, current detection means for detecting a current flowing between the switching means and the ground, a detection signal detected by the current detection means, and the An operation to calculate the insulation resistance value from the current signal between the electric circuit and the ground when the detection signal detected by the electric circuit voltage detection means is switched to the positive side and the current signal between the electric circuit and the ground when the electric signal is switched to the negative side And a measurement display means and / or alarm means for displaying the insulation resistance value computed by the computing means, the insulation resistance value of R2 and R4 when the positive-side insulation resistance is R2 and the negative-side insulation resistance is R4. Calculation by calculation means is as follows DC and obtaining an arithmetic expression Nonreferenced path of the insulation monitoring device.
R2 = (V4a−V4b) × V / (V4b × I5a−V4a × I5b)
R4 = (V2b−V2a) × V / (V2b × I5a−V2a × I5b)
However, R1 and R3 are voltage dividing resistors, R6 is an auxiliary voltage dividing resistor, and R5 is a detection resistor included in the current detecting means, and these values are known. V is the voltage, the voltage of the numerical resistor attached thereto, I is the current, and the current flowing through the numerical resistor attached thereto. a and b indicate switching-on contacts in the switching means. V4a is obtained by V3a-V5a, V4b is obtained by V3b-V5b, V2a is obtained by V1a + V5a, and V2b is obtained by V1b + V5b.   A switching means is provided to divide the voltage of the DC ungrounded circuit with a voltage dividing resistor and switch the voltage dividing ratio between the voltage dividing point of the voltage dividing resistor and the ground, and the voltage dividing point between the switching means and the ground. Detecting means for detecting the current flowing between the ground and the ground, and the switching means alternately connects the auxiliary voltage dividing resistors to the voltage dividing resistors on the positive electrode side and the negative electrode side to change the voltage dividing ratio, A voltage difference is forcibly generated on the voltage dividing resistor side, and each current flowing when each is changed is detected by the current detection means, and between the detected current and the voltage between the electric circuits, the calculation means calculates the current between the positive circuit and the ground. An insulation monitoring method for a DC non-grounded circuit characterized in that an insulation resistance value between the negative electrode circuit and the ground is calculated and displayed on the measurement display means and / or alarmed by the alarm means based on the calculated value. The calculation of the insulation resistance value in claim 2 is performed by setting R1 and R3 as voltage dividing resistors, R5 as an auxiliary voltage dividing resistor R6, and R5 as a detection resistor, R2 as an insulation resistance between the positive circuit and the ground, and a negative circuit and the ground. 3. The DC non-grounded circuit insulation monitoring method according to claim 2, wherein the insulation resistance between the two is determined by the following operator equation when R4 is R4.
R2 = (V4a−V4b) × V / (V4b × I5a−V4a × I5b)
R4 = (V2b−V2a) × V / V2b × I5a−V2a × I5b
However, R1 and R3 are voltage dividing resistors, R6 is an auxiliary voltage dividing resistor, and R5 is a detection resistor included in the current detecting means, and these values are known. V is the voltage, the voltage of the numerical resistor attached thereto, I is the current, and the current flowing through the numerical resistor attached thereto. a and b indicate switching-on contacts in the switching means. V4a is obtained by V3a-V5a, V4b is obtained by V3b-V5b, V2a is obtained by V1a + V5a, and V2b is obtained by V1b + V5b.

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