WO2013081310A1

WO2013081310A1 - A detection device of insulation resistance for non-interruption of electric power and hot-line

Info

Publication number: WO2013081310A1
Application number: PCT/KR2012/009277
Authority: WO
Inventors: Hyo Sung Kim
Original assignee: Kongju National University Industry-University Cooperation Foundation
Priority date: 2011-11-30
Filing date: 2012-11-06
Publication date: 2013-06-06
Also published as: KR101303597B1; KR20130060715A

Abstract

A device for measuring an insulation resistance in order to monitor the insulation state of electrical facilities. An insulation resistance R_ins is calculated from a voltage V^T that is measured by a voltage sensor in a hot line state in which a power distribution system is operating, using the discrete Fourier transformation (DFT). The insulation resistance R_ins is displayed depending on individual levels so that accidents depending on the levels can be rapidly coped with.

Description

A DETECTION DEVICE OF INSULATION RESISTANCE FOR NON-INTERRUPTION OF ELECTRIC POWER AND HOT-LINE

The present invention relates to a device for measuring an insulation resistance which is intended to monitor the insulation state of electrical facilities in an insulation terra (IT) grounding system.

FIG. 1 is a conceptual view of a distribution network in an IT grounding system. In the IT grounding, no terminals of a power line are grounded, but only a chassis of equipment is grounded. The main reason of using the IT grounding is that there is a time to locate a malfunctioning portion without stopping the power system at an accident in which one portion of the power line is earthed. This can consequently guarantee continued operation of the system. In order to realize advantages of such grounding, it is required to continuously monitor the state of the power line while the system is operating. For such monitoring, IEC61557 standards regulate that "an active device for measuring a hot-line insulation resistance" must be provided.

The present invention has been made to solve the foregoing problems with the prior art, and therefore an object of the present invention is to provide a device which can measure the insulation resistance of a power distribution system, in a hot line state in which the measuring device is operating and display the insulation resistance depending on levels in order to prevent a short circuit accident due to a decrease in insulation resistance or an electrical connection from occurring while enabling accidents to be coped with depending on their levels.

According to an aspect of the present invention, provided is a device for measuring a hot-line insulation resistance in order to monitor an insulation state of electrical facilities in an IT grounding system. The device comprises a measuring detector constantly connected to a distribution system that is to be measured; a sine wave generator connected to the measuring detector, the sine wave generator outputting a sine wave voltage having a predetermined phase, frequency and amplitude; a voltage sensor disposed in series between the measuring detector and the sine wave generator, the voltage sensor detecting a sine wave voltage component; a voltage amplifier connected to the voltage sensor, the voltage amplifier amplifying a voltage that is detected by the voltage sensor; an insulation amplifier connected to an output point of the voltage amplifier, the insulation amplifier signal-insulating the voltage that is amplified by the voltage amplifier; a signal processor connected to an output point of the insulation amplifier, the signal processor calculating an insulation resistance using a predetermined algorithm; and a display connected to the signal processor, the display displaying a result that is calculated by the signal processor.

In an exemplary embodiment, the distribution system may include a first power line and a second power line, and the measuring detector may include a first detector resistor which is connected to the first power line via a first detection point and a second detector resistor which is connected to the second power line via a second detection point, the first and second detector resistors being connected to the voltage sensor via a first node.

In an exemplary embodiment, the distribution system may be a direct current power generating system which outputs a first direct voltage via the first power line and a second direct voltage via the second power line.

In an exemplary embodiment, the voltage amplifier may be connected to the first node and to the second node which is between the sine wave generator and the voltage sensor.

In an exemplary embodiment, the device may further include a filter inductor disposed in series between a first node and the voltage sensor and a filter capacitor having one end which is connected between the filter inductor and the voltage sensor and the other end which is connected to a ground.

In an exemplary embodiment, the signal processor may calculate the insulation resistance from a sine wave voltage that is applied to a measurement circuit and a voltage that is measured by the voltage sensor, using the discrete Fourier transformation (DFT).

In an exemplary embodiment, the insulation resistance R_ins may be calculated by a formula:

. In this formula,

,

the sine wave voltage (V^S) is defined by

,

the voltage (V^T) that is measured by the voltage sensor is defined by

, and

R_t is a sum of a resistance of the first detector, a resistance of the second detector, and a resistance of the voltage sensor.

In an exemplary embodiment, the display may further include a display window which displays the measured insulation resistance.

In an exemplary embodiment, the device may further include an input which sets first and second reference values, so that a first-level alarm is generated when the insulation resistance is between the first and second reference values and a second-level alarm is generated when the insulation resistance is above the second reference value.

In an exemplary embodiment, the input may be a button type input or a dial type input.

In an exemplary embodiment, the device may further include at least one relay which operates depending on an individual step when the measured insulation resistance is within an individual range of the reference values that are set by the input; and a light-emitting diode and sound output which includes at least one light-emitting diode and sound equipment, and is operated by the relay.

As set forth above, the device for measuring a hot-line insulation resistance according to the invention can guarantee reliability in power supply by checking insulation trend on electrical facilities, and measure the insulation resistance of a power distribution system, such as a photovoltaic power generation system, in a hot line state in which the system is operating and display the insulation resistance depending on levels so that accidents can be coped with depending on their levels. This can consequently prevent a short circuit accident due to a decrease in insulation resistance or an electrical connection from occurring.

FIG. 1 is a conceptual view of an IT grounding system;

FIG. 2 is an example view of a photovoltaic power generation system;

FIG. 3a is a conceptual view of a device for measuring a hot-line insulation resistance according to an embodiment of the invention;

FIG. 3b is a conceptual view of a device for measuring a hot-line insulation resistance according to another embodiment of the invention;

FIG. 4 is a simple equivalent circuit of a device for measuring a hot-line insulation resistance according to an embodiment of the invention;

FIG. 5 is an impedance trace depending on frequency impedances;

FIG. 6 is a result depicting the result of measuring the trace of frequency impedances; and

FIG. 7 is a conceptual view of an algorithm for measuring an insulation resistance.

Exemplary embodiments of a device for measuring a hot-line insulation resistance according to the present invention will now be described more fully hereinafter with reference to the accompanying drawings.

FIG. 1 is a conceptual view of an IT grounding system, FIG. 2 is an example view of a photovoltaic power generation system, FIG. 3a is a conceptual view of a device for measuring a hot-line insulation resistance according to an embodiment of the invention, FIG. 3b is a conceptual view of a device for measuring a hot-line insulation resistance according to another embodiment of the invention, FIG. 4 is a simple equivalent circuit of a device for measuring a hot-line insulation resistance according to an embodiment of the invention, FIG. 5 is an impedance trace depending on frequency impedances, FIG. 6 is a result depicting the result of measuring the trace of frequency impedances, and FIG. 7 is a conceptual view of an algorithm for measuring an insulation resistance.

FIG. 2 shows the photovoltaic power generation system an example view of an IT grounding system. In the photovoltaic power generation system, impedance that is formed between a PV cell and the ground is expressed by equalizing with an insulation resistor Re and a distribution parasitic capacitance Ce. When the insulation resistance Re in that system is reduced owing to moisture or dust or a conductor line of the PV cell abuts the ground, the photovoltaic power generation system is subjected to a danger of an accident such as an electric shock or a short circuit. Owing to such problems, it is possible to prevent an accident by measuring a hot-line insulation resistance of a distribution system using the device for measuring a hot-line insulation resistance according to the present invention.

As shown in FIG. 3a, in the device for measuring the insulation state of electrical facilities in an IT grounding system, the device for measuring a hot-line insulation resistance according to the present invention includes a measuring detector 100, a sine wave generator 200, a voltage sensor 300, a voltage amplifier 400, an insulation amplifier 500, a signal processor 600 and a display 700.

The measuring detector 100 is connected to both a first detection point 110 and a second detection point of the distribution system in order to measure a voltage. The measuring detector 100 includes a first detector resistor 111 which has one end connected to the first detection point 110 and the other end connected to a first node and a second detector resistor 112 which has one end connected to the second detection point 120 and the other end connected to the first node. The measuring detector 100 diverges at the first node so as to be connected to both ends of the distribution system, and thus measures the voltage of the distribution system in order to measure an insulation resistance.

The sine wave generator 200 is connected at one end thereof to the first node, and outputs a sine wave voltage that has a predetermined phase, frequency and amplitude to the measuring detector 100.

The voltage sensor 300 is disposed in series between the first node and the sine wave generator 200, and detects a sine wave component that is applied to a resistor of the voltage sensor 300.

The voltage amplifier 400 is connected to the first node and the second node between the sine wave generator 200 and the voltage sensor 300, and receives and amplifies the sine wave voltage component that is applied to the resistor of the voltage sensor 300.

The insulation amplifier 500 is connected to an output point of the voltage amplifier 400. The insulation amplifier 500 receives a voltage that is amplified by the voltage amplifier 400, and insulates signals in order to prevent a danger of an electric shock and transfers signals in an insulated state.

The signal processor 600 is connected to the output point of the voltage amplifier 400, and calculates an insulation resistance using a predetermined algorithm and determines a phase, frequency and amplitude of the sine wave generator 200.

The display 700 is connected to the signal processor 600, and displays a result that is calculated in the signal processor 600. The display 700 further includes a display window 730 which displays a measured insulation resistance. The display 700 outputs a message such as an insulation resistance and state information, and provides an interface environment that a user can easily watch. The display 700 can be implemented as a liquid crystal display (LCD) or a light-emitting diode (LED).

As shown in FIG. 3b, a device for measuring a hot-line insulation resistance 1000' according to another embodiment of the invention includes a measuring detector 100' a sine wave generator 200' a voltage sensor 300' a voltage amplifier 400' an insulation amplifier 500' a signal processor 600' and a display 700'.

The measuring detector 100' includes a first detector resistor 111' which is connected to a first power line L1 through a first detection point 110' and a second detector resistor 112' which is connected to a second power line L2 via a second detection point 120'.

The sine wave generator 200' is connected at one end thereof to the first node, and outputs a sine wave voltage having a predetermined phase, frequency and amplitude to the measuring detector 100'.

The voltage sensor 300' includes a first voltage sensor 300a which is connected in series between the first detector resistor 111' and the first node and detects a sine wave voltage component that is applied from the sine wave generator 200' and a second voltage sensor 300b which is connected in series between a second detector resistor 112' and the first node and detects a sine wave voltage component that is applied from the sine wave generator 200'.

The voltage amplifier 400' includes a first voltage amplifier 400a which is connected to both ends of the first voltage sensor 300a and receives and amplifiers a sine wave voltage component that is applied to a resistor of the first voltage sensor 300a and a second voltage amplifier 400b which is connected to both ends of the second voltage sensor 300b and receives and amplifies a sine wave voltage component that is applied to a resistor of the second voltage sensor 300b.

The insulation amplifier 500' includes a first insulation amplifier 500a which is connected to an output point of the first voltage amplifier 400a and insulates signals and a second insulation amplifier 500b which is connected to an output point of the second voltage amplifier 400b and insulates signals.

The signal processor 600' is connected to each output point of the first and

second insulation amplifiers

500a and 500b, and calculates an insulation resistance using a predetermined algorithm and determines a phase, frequency and amplitude of the sine wave generator 200'.

A description will be given below of the operation of the device for measuring a hot-line insulation resistance according to the invention. In FIG. 3a, L1 and L2 indicate power lines of a distribution system. Although the insulation resistor Re and the distribution parasitic capacitance Ce (see FIG. 2) are not shown in this figure, they refer to impedance that occurs between the L1/L2 power lines and the ground. Since the measuring detector 100 is constantly connected to the distribution system, it is easy to measure an insulation resistance and it is possible to reliably supply electricity by finding insulation trend. A voltage that is applied to both ends of the voltage sensor 300 using a sine wave that is generated by the sine wave generator 200 is detected and amplified using the voltage amplifier 400, is signal-insulated using the insulation amplifier 500, and is then transferred to the signal processor 600. The signal processor 600 calculates an insulation resistance using a proposed algorithm. The measured insulation resistance is alarmed using an LED and sound depending on respective predetermined stages, and the measure insulation resistance and its state are displayed on the display 700 so that they can be checked.

The device for measuring a hot-line insulation resistance may include an inductor and a capacitor in order to remove noises. Specifically, the device for measuring a hot-line insulation resistance 1000 according to the invention can remove noises that would otherwise give unnecessary influence on the measured insulation resistance by further including a filter inductor 130 which is provided in series between the first node and the voltage sensor 300 and a filter capacitor 140 which is connected at one portion thereof between the filter inductor 130 and the voltage sensor 300 and at the other portion thereof to a ground.

The signal processor 600 calculates an insulation resistance R_ins from a voltage V^S that is applied to a measurement circuit and a voltage V^T that is measured by the voltage sensor, using the discrete Fourier transformation (DFT).

..... (1)

..... (2)

Then, a current that flows through the total impedance is calculated as in the following formula (3).

.....(3)

The total impedance becomes the following formula (4).

..... (4)

When a sine wave that is applied to the measuring circuit is

, actual and imaginary numbers can be calculated as in the following formula (5).

..... (5)

In addition, when only a real number component is present at

, the value of the total impedance can be calculated more simply as the following formula (6).

..... (6)

FIG. 4 is a simple equivalent circuit of a device for measuring a hot-line insulation resistance according to an embodiment of the invention. The sine wave generator 200 generates a sine wave having a size V^S. L is a sum of a parasitic inductance of a measuring system and a low pass filter inductance. R_ins and C_ins are an insulation resistance and a parasitic capacitance which are distributed in the distribution network, and are generally formed by parallel synthesis. The total impedance is calculated as in the following formula (7).

..... (7)

That is, the impedance component is considered in complex notation. When the impedance component is expressed on a complex plane, an impedance trace depending on frequencies has a semicircular shape, as shown in FIG. 5. The major characteristics of the impedance trace are as follows:

①

at

..... (8)

②

at

..... (9)

③

at

..... (10)

FIG. 6 shows the result of measuring an impedance trace depending on frequencies at an assumption R_t=1MΩ and R_ins=3MΩ It can be appreciated that a point of intersection of a real number axis is located correctly at R_t=1MΩ and (R_ins+R_t)=3MΩ and that the radius of a semicircle is correctly (R_ins/2)=1.5MΩ as predicted in the formula.

When regarding the impedance trace, a triangle that is inscribed in the semicircle is a right-angled triangle. Thus, an actual number component and an imaginary number component of complex impedance at a frequency that is present on the semicircle have the following relationships (11) to (13).

..... (11)

..... (12)

..... (13)

Therefore, an algorithm for measuring an insulation resistance as shown in FIG. 7 is proposed. Referring to the impedance trace shown in FIG. 5, the value of R_t is known by measuring the actual number component Z_re and the imaginary number component Z_im of the complex impedance obtained from a semicircular frequency. Therefore, the insulation resistance R_ins is obtained by calculating the above-described formulae.

The device for measuring a hot-line insulation resistance 1000 according to the invention can set individual danger levels and have alarms depending on the individual danger levels in order to prevent a danger of an accident in a distribution system by measuring an insulation resistance and detecting a danger of an electric shock or a short circuit. For more efficient operation, it is possible to set a first reference value and a second reference value, and generate a first-level alarm signal when an insulation resistance is between the first and second reference values and a second-level alarm signal when the insulation resistance is above the second reference value. Since it is necessary to set the configuration different depending on environments, a configuration that enables the reference values to be set is required. Accordingly, the device for measuring a hot-line insulation resistance 1000 according to the invention further includes an input 800 with which the reference values are set, such that the individual danger levels can be effectively coped with.

The input 800 may be configured as a button type, a dial type or a combination thereof. In the case of the button type, it is preferred that the input be configured such that it is possible, for example, to enter a reference value-setting mode, move a cursor in an insulation resistance-setting mode, increase or decrease the set values, initialize the set values, complete setting of the set values, or start measurement by manipulating the input. In the case of the dial type, the input may be configured such that it can be manipulated to increase or decrease set values.

Also provided is at least one relay 710 which operates depending on an individual step when a measured insulation resistance is within the range of an individual reference value that is set in the input 800. Also provided is a light-emitting diode (LED) and sound output 720 which includes at least one LED and sound equipment, and is operated by the relay. Consequently, an alarming signal and an intuitive LED indication and sound regarding a dangerous situation can be generated so that the situation can be rapidly checked and accidents depending on respective levels can be rapidly coped with.

The present invention is not limited to the foregoing embodiments but can be applied to a variety of fields. It is to be understood that obviously many modifications and variations are possible without departing from the concept of the present invention.

Claims

A device for measuring a hot-line insulation resistance in order to monitor an insulation state of electrical facilities in an IT grounding system, comprising:

a measuring detector (100) constantly connected to a distribution system that is to be measured;

a sine wave generator (200) connected to the measuring detector, the sine wave generator outputting a sine wave voltage having a predetermined phase, frequency and amplitude;

a voltage sensor (300) disposed in series between the measuring detector and the sine wave generator, the voltage sensor detecting a sine wave voltage component;

a voltage amplifier (400) connected to the voltage sensor, the voltage amplifier amplifying a voltage that is detected by the voltage sensor;

an insulation amplifier (500) connected to an output point of the voltage amplifier, the insulation amplifier signal-insulating the voltage that is amplified by the voltage amplifier;

a signal processor (600) connected to an output point of the insulation amplifier, the signal processor calculating an insulation resistance using a predetermined algorithm; and

a display (700) connected to the signal processor, the display displaying a result that is calculated by the signal processor.
The device of claim 1, wherein

the distribution system comprises a first power line (L1) and a second power line (L2), and

the measuring detector comprises a first detector resistor (111) which is connected to the first power line via a first detection point and a second detector resistor (112) which has is connected to the second power line via a second detection point, the first and second detector resistors being connected to the voltage sensor via a first node.
The device of claim 2, wherein the distribution system comprises a direct current power generating system which outputs a first direct voltage via the first power line and a second direct voltage via the second power line.
The device of claim 2, wherein the voltage amplifier is connected to the first node and to a second node which is between the sine wave generator and the voltage sensor.
The device of claim 1, further comprising:

a filter inductor (130) disposed in series between the first node and the voltage sensor; and

a filter capacitor (140) having one end which is connected between the filter inductor and the voltage sensor and the other end which is connected to a ground.
The device of claim 1, wherein the signal processor calculates the insulation resistance (R_ins) from a sine wave voltage (V^S) that is applied to a measurement circuit and a voltage (V^T) that is measured by the voltage sensor, using discrete Fourier transformation.
The device of claim 6, wherein

the insulation resistance (R_ins) is calculated by a formula:

, where

,

,

the sine wave voltage (V^S) is defined by
,

the voltage (V^T) that is measured by the voltage sensor is defined by
, and

R_t is a sum of a resistance of the first detector resistor(111), a resistance of the second detector resistor(121), and a resistance of the voltage sensor(300).
The device of claim 1, wherein the display further comprises a display window (730) which displays the measured insulation resistance.
The device of claim 1, further comprising an input (800) which sets first and second reference values, so that a first-level alarm is generated when the insulation resistance is between the first and second reference values and a second-level alarm is generated when the insulation resistance is above the second reference value.
The device of claim 9, wherein the input comprises a button type input or a dial type input.
The device of claim 9, further comprising:

at least one relay (710) which operates depending on an individual step when the measured insulation resistance is within an individual range of the reference values that are set by the input; and

a light-emitting diode and sound output (720) which includes at least one light-emitting diode and sound equipment, and is operated by the relay.