WO2003005049A1

WO2003005049A1 - Apparatus and method for testing insulation of power cables in multiple manners

Info

Publication number: WO2003005049A1
Application number: PCT/KR2002/001276
Authority: WO
Inventors: Dong-Young Lee
Original assignee: Woori Technology Inc.
Priority date: 2001-07-05
Filing date: 2002-07-05
Publication date: 2003-01-16
Also published as: KR100418195B1; KR20030004510A

Abstract

A multiple insulation tester of a power cable comprises: a power unit for suppying a voltage for charging the power cable; a high voltega switch including a switch for supplying the voltage to the cable and stopping it, and a switch for discharging the voltage charged to the cable; a resistor including a very high resistance unit for measuring a deterioration time constant, a discharging resistor for discharging residual charges in the cable, a charging serial resistor, and a current measuring input resistor; a signal measurer for measuring the current and the voltage at the resistor; an input for selecting insulation diagnosis modes for diagnosing the cable's deterioration; and a controller including an operation controller for operating the high voltage switch and the resistor according to the insulation diagnosis mode, a signal processor for processing the measured data, and a deterioration determination unit for determining the cable's deterioration.

Description

Apparatus and Method for Testing Insulation of Power Cables in

Multiple Manners

CROSS REFERENCE TO RELATED APPLICATION

This application is based on Korea Patent Application No. 2001- 40013 filed on July 5, 2001 in the Korean Intellectual Property Office, the content of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

(a) Field of the Invention

The present invention relates to an apparatus and method for diagnosing insulation of power cables in multiple manners. More specifically, the present invention relates to an insulation diagnosing apparatus and method in multiple manners for increasing reliability of deterioration determination of power cables.

(b) Description of the Related Art

In general, since a user cannot visually check deterioration states of power cables laid underground, the user supplies a high DC voltage to the cables and measures a corresponding leakage current flowing in a skin layer of the cable to determine the cable's deterioration state.

However, since a pointer of a measuring device may tremble in the

above-noted method, accurate measuring values may not be obtained, and errors of the measured values may vary greatly according to a length of the underground power cable. Additionally, a high voltage is supplied to the cable for a long period of time, so it is very probable that the insulation of the cable may be destroyed during a diagnosis. In an attempt to rectify this problem, a high voltage is temporarily supplied to the cable to charge the cable, the voltage supply circuit is broken, the cable is discharged to measure the current that flows through high resistance, and the cable's deterioration is determined using a voltage attenuation method for calculating an attenuation degree of a discharge voltage through the measured data.

However, the conventional one-way diagnosing method relying on a single diagnostic method problematically includes probability of erroneous determination, and it is impossible to apply an on-line diagnostic method but an off-line diagnostic method to a domestic multi grounded system, and accordingly, loss eventually caused by a power cut because of the off-line diagnostic method must also be considered.

Further, a device for increasing field applicability through improvements of stableness of the apparatus, easy portability, and manipulation is required so as to efficiently manage cable laid underground.

SUMMARY OF THE INVENTION

It is an object of the present invention to improve reliability of insulation diagnosis for determining deterioration of cable laid underground,

and also to improve a device's field applicability.

In one aspect of the present invention, a multiple insulation tester for diagnosing insulation states of a power cable comprises a power unit for supplying a voltage for charging a power cable; a high-voltage switch including a switch for performing power supply and power stoppage for supplying a voltage to the cable, and a switch for discharging the voltage charged to the cable; a resistor including a very high resistance unit for measuring a deterioration time constant, a charging serial resistor applicable to all diagnosis methods, a current-measuring input resistor for measuring a polarization index, an absorption current, an isothermal relaxation current, and a discharging resistor for discharging residual charges in the cable; a signal measurer for measuring a current and a voltage optionally flowing through the resistor according to an operation of the high-voltage switch when the cable is charged; an input unit for selecting a plurality of insulation diagnosis modes for diagnosing the cable's deterioration state; and a controller including an operation controller for selectively operating the respective units of the high voltage switch and those of the resistor according to the insulation diagnosis mode set through the input unit, a signal processor for processing the data measured by the signal measurer into an appropriate format, and a deterioration determination unit for determining the cable's deterioration state on the basis of the processed data. The high voltage switch comprises a plurality of switches for

respectively supplying the power to a first phase, a second phase, and a

third phase of the cable, stopping the power, and performing a discharging

process.

The controller operates a plurality of switches of the power supplying

and breaking switch to supply the voltage to the cable's first through third

phases during a predetermined voltage boosting time and a voltage supplying time when a three-phase multiple concurrent insulation diagnosis mode is set through the input unit, opens the power supplying and breaking switch to concurrently measure the deterioration time constants of the first through third phases on the basis of the signals flowing through the very high resistance unit of the resistor, and determines the cable's deterioration state

on the basis of the measured data.

The controller operates one of the switches of the power supplying and breaking switch to supply the voltage to one of the cable's phases

during a predetermined voltage boosting time and a voltage supplying time when a single-phase multiple insulation diagnosis mode is set through the

input unit, measures the signals flowing through the charging serial resistor

and the current measuring input resistor of the resistor to measure current

variations according to time and voltage variations according to time, opens

the switch to measure a deterioration time constant on the basis of the

cable's discharging current flowing through the very high resistance unit of the resistor, and subsequently determines two other phases' deterioration

states on the basis of the data measured through the diagnosis process.

The controller operates the discharging switch so that the residual charges in the cable may be discharged through the discharging resistor of the resistor before supplying the power for measuring the cable's deterioration state and after finishing each diagnosis.

The power unit comprises a battery including a battery cell, a charger for charging and discharging the battery cell, a breaking switch for stopping overcurrents caused by overcharging the battery cell, and a voltage detector for detecting a charging voltage of the battery cell.

In another aspect of the present invention, a multiple insulation diagnosing method of a power cable comprises: (a) selecting one of a plurality of diagnosis modes including a cable's three-phase concurrent diagnosis mode and a single-phase multiple diagnosis mode for sequentially measuring the respective single phases of the cable; (b) setting measurement variables including a diagnosis voltage and a measuring frequency according to the selected diagnosis mode; (c) charging the cable; (d) stopping the power supply to the cable when a predetermined time passes, and measuring the signals flowing through a resistor coupled to the cable according to the selected diagnosis mode; (e) operating a discharging switch and discharging the residual charges in the cable when the signal measurement is finished; and (f) processing the measured data into deterioration determination data, and determining the cable's deterioration

state on the basis of the processed deterioration determination data.

When the three-phase multiple concurrent diagnosis mode is selected in (a), power is supplied to the cable's three phases, deterioration

time constants of the first through third phases are concurrently measured on the basis of the signals flowing through a very high resistance unit of the resistor coupled to the cable, and the cable's deterioration state is determined on the basis of the measured deterioration time constants.

When the single-phase multiple insulation diagnosis mode is selected in (a), power is supplied to one of the three phases of the cable; current (the current flows to the cable) variations according to time and voltage variations according to time are measured to output diagnosing variables that represent a polarization index, an absorption current, and a current feature for each voltage step; the cable's power supplying circuit is broken; a deterioration time constant is measured on the basis of the signals flowing according to the cable's discharging; and the cable's deterioration state is determined on the basis of the diagnosing variables and the deterioration time constants.

Electrical diagnosis results according to the diagnosis mode are generated into a database through the cable database management and diagnosing result analysis unit, and are managed, and final deterioration determination results may be output according to a cable history and environmental data.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and

constitute a part of the specification, illustrate an embodiment of the

invention, and, together with the description, serve to explain the principles of

the invention:

FIG. 1 shows a schematic diagram of a multiple insulation tester according to a preferred embodiment of the present invention; FIG. 2 shows a detailed configuration of the multiple insulation tester, and a connection state of a cable database manager to a diagnosis analyzer;

FIG. 3 shows a configuration of a battery of a power unit according to a preferred embodiment of the present invention;

FIG. 4 shows a configuration of a resistor according to a preferred

embodiment of the present invention;

FIG. 5 shows a detailed configuration of a controller and a memory

of the multiple insulation tester according to a preferred embodiment of the

present invention;

FIG. 6 shows an operation flow chart of a multiple diagnosing

method according to a preferred embodiment of the present invention; and

FIG. 7 shows a criterion for determining deterioration states

according to a preferred embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the following detailed description, only the preferred embodiment of the invention has been shown and described, simply by way of illustration of the best mode contemplated by the inventor(s) of carrying out the invention. As will be realized, the invention is capable of modification in various obvious respects, all without departing from the invention. Accordingly, the drawings and description are to be regarded as illustrative in nature, and not restrictive.

In a multiple insulation diagnosing method according to a preferred embodiment of the present invention, multiple diagnosis, single phase diagnosis, or three-phase concurrent diagnosis may be selected rather than relying on a single diagnostic method that is used for conventional insulation diagnosing. The multiple insulation diagnosing method generates an accident history and an installation year of a target cable, a cable history of cable environments, and environmental data, and provides weighting values to them to output final diagnosing results.

In detail, a principle of multiple or concurrent diagnosis is classified into DC component current measuring and DC component voltage measuring. In order to measure various diagnosing variables for respective measuring variables, insulation diagnosing methods including a polarization index method, a step-voltage current featuring method, an absorption current method, and a cable time constant method are concurrently or selectively applied, and hence, the reliability of diagnosing of the insulation states is greatly increased.

Also, the single-phase diagnosis or the three-phase concurrent diagnosis may be selected according to environmental and economical conditions of a measuring target, wherein various categories of data are made into variables by using a cable database management and diagnosing result analysis program, weighting values are applied to them, and the data with the weighting values applied are combined with electrical diagnosing results to output final diagnosing results. Among the insulation diagnosing methods, the polarization index method indexes variations of the current depending on time (e.g., the method indexes the variations of the current of one minute after supplying the power, and the current of ten minutes after supplying the power), and the method determines that the insulation state worsens as the trend of the index increases.

The step-voltage current featuring method increases a diagnosis voltage step by step, measures a current value of a predetermined point for each voltage step, and determines deterioration according to nonlinear degrees of a current-voltage characteristic. The diagnosis determines that the insulation state worsens as the degree of digression from linearity become greater.

The absorption current method removes charging current components and leakage current components, and determines deterioration

caused by processing signals of the absorption current components. The

method determines that the insulation state worsens as the polarization time

of the current component becomes greater.

The cable deterioration time-constant measuring method removes power, equivalently opens a cable RC equivalent circuit, and measures a

voltage signal to calculate and determine a deterioration time constant. The method determines that the insulation state worsens as the deterioration time constant becomes greater. The user applies these insulation diagnosing methods concurrently or alternately, or selectively applies a predetermined diagnosing method, and sets one of a three-phase concurrent diagnosis and a single-phase diagnosis to select various modes such as the three-phase concurrent diagnosis mode and the single-phase multiple diagnosis mode. Also, it is required to modify diagnosis conditions including a diagnosis voltage and a pressure-applying condition to an optimized

condition according to field conditions and accumulated diagnosis results,

and the preferred embodiment of the present invention may modify the

diagnosis conditions.

Further, in order to determine whether to change the cable, and a

corresponding range, it is required to determine a cable history including an

accident history, an installation year, and a cable environment, as well as to establish environmental data in addition to insulation diagnosing and

deterioration determination according to the above-described various electrical insulation diagnosis methods, and to provide weighting values to them and combine the data with the weighting values provided with electrical diagnosing results to output final diagnosing results. Accordingly, in the preferred embodiment, cable diagnosing results are generated into a database, and the cable history including the accident history, the installation year, the cable environment, and environmental data are analyzed together to thereby reliably determine whether to change the cable. A detailed device and method for realizing multiple insulation diagnosing according to the preferred embodiment of the present invention will now be described.

FIG. 1 shows a schematic diagram of a multiple insulation tester for a power cable according to a preferred embodiment of the present invention, and FIG. 2 shows a detailed configuration of respective units of the multiple insulation tester.

As shown in FIG. 1 , the multiple insulation tester comprises a power unit 100, a high-voltage switch 200, a terminal leakage remover 300, a resistor 400, a signal measurer 500, a controller 600, a memory 700, an I/O (input/output) communication unit 800, a data input unit 900, and a display

1000. The multiple insulation tester is coupled to a cable database management and diagnosing result analysis unit 1100. The power unit 100 comprises an AC-DC power supply 1 10 for

converting AC voltages into DC voltages and supplying the DC voltages, a

DC-DC power supply 140 for converting the DC voltages into predetermined

DC voltages and supplying them, a battery 130 for supplying an additional

DC voltage, and a power controller 120 for controlling operations of the

respective units to selectively supply voltages to the respective units. The

battery 130 is used to remove noise interference caused by AC input power when supplying the power and measuring the current in the field, where it is difficult to obtain the power. FIG. 3 shows a detailed configuration of the battery 130. As shown, the battery 130 comprises a battery cell 131 , an FET 132 for charging and discharging the battery cell 131 , a control IC 133 for controlling the FET 132 to control charging and discharging of the battery cell 131 , a breaking switch 134 for stopping overcurrents caused by overcharging the battery cell 131 , and a voltage detector 135 for detecting a charging voltage of the battery cell

131. In this instance, the battery cell 131 includes a Lithium-Ion battery cell,

and the control IC 133 controls charging and discharging of the battery cell

131 on the basis of the voltage output by the voltage detector 135 so as to

charge to an adequate voltage and supply the same to the respective circuits.

The high-voltage switch 200 comprises switches 211 , 212, and 213

for supplying and breaking power, and discharging switches 221 , 222, and

223 for obtaining the device's stability and improving measurement reliability. The terminal leakage remover 300, made of plastics such as Teflon, prevents external noise caused by terminal leakage at the time of measuring signals.

The resistor 400 comprises a very high resistance unit 410 for measuring an attenuation voltage and a deterioration time constant; a charging serial resistor 420 applicable to all types of diagnosis methods; a current measuring input resistor 430 for measuring a polarization index, an absorption current, and an isothermal relaxation current; and a discharging resistor 440 for discharging residual charges in the cable at the time of starting a mode diagnosis or terminating each diagnosis.

FIG. 4 shows a configuration of the resistor 400. In the preferred embodiment of the present invention, the resistor 400 includes a Teflon cell in which the very high resistance unit 410, of substantially 1 through 10TΩ ,

is installed. The very high resistance unit 410 is required to have a final equivalent resistance of at least 102 times greater than a cable equivalent resistance so as to obtain measurement reliability. The charging serial resistor 420 controls the charging current in response to variations of the capacitive component depending on the cable's length. The current

measuring input resistor 430 prevents noise interference caused by measuring micro-currents.

The signal measurer 500 measures a leakage current measured through the resistor 400 to determine the cable's deterioration state, and it comprises a current/voltage converter for converting the measured leakage

current into a corresponding voltage; an amplifier for amplifying the voltage;

a sample-and-hold circuit for sampling the amplified voltage; a clock signal

generator for generating clock signals; a frequency divider for dividing

outputs of the clock signal generator; a second controller for controlling a

signal converting operation according to the clock signals; and an A/D converter, operable in synchronization with outputs of the frequency divider,

for converting the sampled signals provided by the sample-and-hold circuit into digital data, and outputting the digital data to the second controller. Since the respective components of the signal measurer 500 are well-known to a skilled person, no further detailed description will be provided.

The controller 600 determines the cable's deterioration state on the

basis of the data output from the signal measurer 500, and it comprises a microprocessor with a built-in program for diagnosing the cable's states. In

particular, the controller 600 comprises an operation controller 610 for setting

a mode for diagnosing the cable's deterioration state according to the user's

selection, and selectively operating the respective components of one of the

resistor 400 and the high voltage switch 200 so that the cable's deterioration

state may be measured; a signal processor 620 for processing the data

measured by the signal measurer 500 into a predetermined format; and a

deterioration determination unit 630 for determining the cable's deterioration

state on the basis of the processed data. FIG. 5 shows an exemplified controller.

The memory 700 stores the cable's deterioration measured results

and a deterioration diagnosing program, and the memory 700 comprises a

ROM, a RAM, and a flash memory.

The data input unit 900 comprises a keypad, and the display 1000

comprises an LCD. In the preferred embodiment of the present invention, the

user may more conveniently diagnose the cable's deterioration state through

a simply configured data input unit or a display without using a personal computer, and since the size of the data input unit 900 may be minimized, the user may easily diagnose the cable's deterioration state anywhere.

The I/O communication unit 800 communicates desired data with the cable database management and diagnosing result analysis unit 1 100 according to a predetermined communication method including the USB, the RS232, and the Ethernet. As shown in FIG. 2, the cable database management and diagnosing result analysis unit 1 100 comprises a communication interface

1110 for communicating with the multiple insulation tester, a cable database

1 120 for storing information on the deterioration state of the cable diagnosed

by the multiple insulation tester, a database manager 1130 for managing

data inputs and outputs to the cable database 1120, and a data analyzer

1140 for analyzing cable deterioration diagnosing results on the basis of

various data stored in the cable database 1120. The cable database management and diagnosing result analysis unit 1100 may be installed and realized in a personal computer.

A detailed multiple insulation diagnosis method on the basis of the above-configured device according to the preferred embodiment of the present invention will now be described.

FIG. 6 shows an operation flowchart of the multiple insulation diagnosis method according to the preferred embodiment of the present invention.

As explained, the respective components of the multiple insulation tester are connected to a target cable, the deterioration state of which will be diagnosed. That is, the high voltage switch 200 and the resistor 400 are connected to both measuring ends of the target cable to thereby supply a high voltage for the diagnosis and provide signals to the resistor 400 for measuring various diagnosing variables in step S100. One of the three-phase concurrent diagnosis mode, the single-phase multiple diagnosis mode, and various modes generated by selectively and alternately applying the above modes is input, and diagnosis variables including applying voltage, boosting voltage, and frequency of repetition are input through the data input unit 900 in step S110. The operation controller 610 controls the operation of the high voltage switch 200 and the power unit 100 according to the selection of the mode input to the data input unit 900 and the diagnosis variables (e.g., applying voltage, boosting voltage, and frequency of repetition) to thereby

charge the cable in step S120.

When a predetermined time elapses, the power supplying and

breaking switches 211 , 212, and 213 of the high voltage switch 200 are

opened, and the signal measurer 500 measures the signals flowing through

the very high resistance unit 410, the charging serial resistor 420, or the current-measuring input resistor 430 of the resistor 400 according to the

insulation diagnosis mode selected from the data input unit 900 in step S130.

When the signal measurer 500 performs measuring for a predetermined time, the operation controller 610 operates the discharging switches 221 , 222, and 223 to thereby discharge the residual charges in the three-phase cable through the discharging resistor 440 of the resistor 400 for a predetermined time in step S140.

The signal processor 620 processes the data measured for the predetermined time period into an appropriate format according to the

deterioration determination data in step S150. The deterioration

determination unit 630 determines an insulation state according to

predetermined data processing steps and criterion on the basis of the

processed data, and displays corresponding results through the display 1000

in step S160.

When all the diagnosing is finished, the diagnosing result data are

stored in the memory 700, and if needed, the I/O communication unit 800 transmits the diagnosing result data to an external personal computer to

store the data therein, and the cable database management and diagnosing

result analysis unit 1 100 makes the target cable's cable history and

environmental data into variables, provides weighting values to the variables,

and outputs final diagnosing results in step S170.

The method for diagnosing the cable's deterioration in multiple

manners will now be described according to respective setting modes.

When the user selects the three-phase concurrent diagnosis mode so as to reduce a power cut time at the time of the off-line diagnostic method in the previous step S110, the operation controller 610 receives the diagnosis variables including the applying voltage, the boosting voltage, and the frequency of repetition for performing the three-phase concurrent diagnosis mode through the data input unit 900, and drives the power unit 100 to boost the supplied voltage for a predetermined time according to the length of the target cable so that the voltage may reach a predetermined

diagnosis voltage.

When the voltage reaches the predetermined diagnosis voltage, the

operation controller 610 operates the power supplying and breaking switches

21 1 , 212, and 213 so as to concurrently supply the boosted voltage to the

three-phase mode for a predetermined time, and when a predetermined time

elapses, it operates the power supplying and breaking switches 21 1 , 212,

and 213 to stop the voltage supply to the three-phase mode. Next, the signal measurer 500 measures the current flowing through the very high resistance unit 410 of the resistor 400 to perform three-phase concurrent measurement of the deterioration time constant. In this instance, results of power supply and measurement are displayed to the display 1000 in real-time. When the signal measurer 500 finishes measuring the deterioration time constant, the operation controller 610 operates the discharging switches 221 , 222, and 223 to discharge the residual charges in the three-phase cable through the discharging resistor 440 of the resistor 400 for a predetermined time. The operation controller 610 repeatedly charges the cable and measures the signals according to the frequency of repetition selected by the data input unit 900, and when the signals are measured according to the frequency of repetition, the signal processor 620 processes the measured data into an appropriate format, and the deterioration determination unit 630 processes the processed data according to predetermined data processing steps and criterion to determine the cable's insulation state, and displays determination results on the display 1000.

When a single-phase multiple diagnosis mode for applying various insulation diagnosing methods in the multiple manner, and sequentially measuring the three-phase cables for each single phase to maximize the reliability in the previous step S110, the operation controller 610 receives the diagnosis variables including the applying voltage, the boosting voltage, and the frequency of repetition for performing the single-phase multiple diagnosis mode through the data input unit 900.

Next, the operation controller 610 boosts the voltage supplied by the power unit 100 for a predetermined time to reach a predetermined diagnosis voltage. In this instance, the operation controller 610 boosts the voltage from

0 to 5kV by 1kV steps to repeat the diagnosis voltage's supplying, stopping,

and discharging.

The power supplying and breaking switches 212 and 213 of phases B and C are opened so as not to supply the voltage to the cable's phases B and C, and the power supplying and breaking switch 211 of phase A is controlled to supply the voltage controlled to a predetermined first diagnosis voltage by the power unit 100 to the cable's phase A. The signal measurer 500 measures the currents and the voltages for predetermined voltage steps for a predetermined voltage supplying time to supply them to the controller 600, and the controller 600 outputs current vs. time and voltage vs. time feature data for a predetermined time. When the measuring is finished, the power supplying and breaking switch 211 of phase A is opened to stop the power and measure the deterioration time constant.

The current vs. time and voltage vs. time feature data measured after the power is supplied are respectively applied to the polarization index method, the absorption current method, and the step-voltage current featuring method. In this instance, the data of the power supplying, the current vs. time and voltage vs. time features, and the deterioration time constant measuring, are displayed on the screen through the display 1000 in real-time.

When the measurement is finished, the operation controller 610 operates the power supplying and breaking switch 211 of phase A to discharge the residual charges in the cable through the discharging resistor 440 of the resistor 400 for a predetermined time.

In the preferred embodiment, the above-described diagnosing process is repeated for each voltage step input according to setting of the single-phase multiple insulation diagnosis mode, and the signal processor

620 processes the data measured by the signal measurer 500 according to the repetition into an appropriate format, while the deterioration determination unit 630 determines the cable's insulation state on the basis of the data processed according to a predetermined data processing step and criterion, and the corresponding results are then displayed through the display 1000.

The above-noted method is sequentially performed with respect to the cable of phases B and C, and in this instance, the states of the high voltage switch 200 of other phases except the phase of the target cable are opened.

The deterioration determination unit 630 determines the cable's

insulation state on the basis of the data processed according to the above- set insulation diagnosis mode, and FIG. 7 shows a graph for representing a deterioration determination criterion according to the preferred embodiment of the present invention.

As shown, the deterioration determination unit 630 determines a deterioration index to determine the cable's deterioration states as the three

categories of good, marginal, and bad.

In the case of the three-phase concurrent diagnosis mode, the deterioration determination unit 630 determines the cable's deterioration states as the three categories of good, marginal, and bad according to a predetermined determination criterion for each phase, and determines the cable's final determination results and whether to change the cable according to whether determination results are matched for each phase. When the three phases are matched, the deterioration determination unit 630 determines that the cable's deterioration state is one of good, marginal, and bad.

In the case of the single-phase multiple diagnosis mode, weighting values are provided to the respective diagnosing methods (including the polarization index method, the absorption current method, and the step- voltage current featuring method), the respective determination results are summed to determine final results, and the final results are determined according to whether the determination results of the respective diagnosing methods are matched. That is, when more than three of the results of the respective diagnosing method are matched, the cable's deterioration state is

determined to be one of good, marginal, and bad.

An algorithm built into the controller 600 executes the above-noted deterioration determination methods, and the determination results are provided to a diagnosing person through the display 1000. Also, the determination results and data are stored in the memory 700, and when necessary, they are transmitted to the cable database management and diagnosing result analysis unit 1100 installed in a personal computer, through the I/O communication unit 800, and generated into a database and then managed. The cable database management and diagnosing result analysis unit 1100 combines data obtained by generating the cable history including the accident history, the installation year, and the cable environments, and the environmental data with the electrical diagnosing results measured through the device of the present invention to output final diagnosing results.

As described above, the insulation diagnosis modes may be selected in various ways according to the single method for applying a single insulation diagnosing method for determining the cable's deterioration state,

the multiple method for applying at least two insulation diagnosing methods, and states of whether to perform a cable's single-phase diagnosing or a

three-phase concurrent diagnosing.

Voltages for determining the cable's deterioration states for the respective modes may be set according to predetermined steps, and frequencies for repeatedly performing the measurement operation for each voltage may be established.

Therefore, the user may selectively apply a plurality of modes according to diagnosis requirements or environments to determine the cable's deterioration state, and may selectively apply measurement variables

(voltages for respective steps, and repeated frequencies of measurements) of respective modes to improve reliability of the insulation diagnosing.

According to the present invention, the multiple insulation diagnosing device and method reduces power cut time and increases reliability of insulation diagnosing through setting of various diagnosing modes.

Further, the present invention unifies the device's components, installs a terminal leakage remover and a battery, automates the total diagnosing process, and reduces its weight and size according to the cable's environments to improve the device's security, portability, and manipulation

degrees.

While this invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the

appended claims.

Claims

WHAT IS CLAIMED IS:

1. A multiple insulation tester of a power cable, comprising: a power unit for supplying a voltage for charging the power cable; a high voltage switch including a switch for supplying the voltage provided by the power unit to the cable and stopping the same; and a switch for discharging the voltage charged to the cable; a resistor coupled to the cable, including a very high resistance unit for measuring a deterioration time constant, a discharging resistor for discharging residual charges in the cable, a charging serial resistor, and a current measuring input resistor; a signal measurer for measuring the current and the voltage selectively flowing through the resistor according to an operation by the high voltage switch when the cable is charged; an input unit for selecting a plurality of insulation diagnosis modes for diagnosing the cable's deterioration state; and a controller including an operation controller for selectively operating the respective units of the high voltage switch and those of the resistor according to the insulation diagnosis mode set through the input unit, a signal processor for processing the data measured by the signal measurer into an appropriate format, and a deterioration determination unit for determining the cable's deterioration state on the basis of the processed

data.

2. The tester of claim 1 , wherein the high voltage switch comprises a

plurality of switches for respectively supplying the power to a first phase, a

second phase, and a third phase of the cable, stopping the power, and

performing a discharging process.

3. The tester of claim 2, wherein the controller operates a plurality of

switches of the power supplying and breaking switch to supply the voltage to

the cable's first through third phases during a predetermined voltage

boosting time period and a voltage supplying time period when a three-phase multiple concurrent insulation diagnosis mode is set through the input unit, opens the power supplying and breaking switch to concurrently measure the deterioration time constants of the first through third phases on the basis of the signals flowing through the very high resistance unit of the resistor, and determines the cable's deterioration state on the basis of the measured data.

4. The tester of claim 2, wherein the controller operates one switch of the power supplying and breaking switch to supply the voltage to one of

the cable's phases during a predetermined voltage boosting time and a

voltage supplying time when a single-phase multiple insulation diagnosis

mode is set through the input unit, measures the signals flowing through the

charging serial resistor and the current measuring input resistor of the

resistor to measure current variations according to time and voltage

variations according to time, opens the switch to measure a deterioration

time constant on the basis of the cable's discharging current flowing through the very high resistance unit of the resistor, and subsequently determines two other phases' deterioration states on the basis of the data measured

through the diagnosis process.

5. The tester of one of claims 1 through 4, wherein the controller operates the discharging switch so that the residual charges in the cable may be discharged through the discharging resistor of the resistor before supplying the power for measuring the cable's deterioration state and after finishing each diagnosis.

6. The tester of claim 1 , wherein the power unit comprises a battery including a battery cell, a charger for charging and discharging the battery cell, a breaking switch for stopping overcurrents caused by overcharging the battery cell, and a voltage detector for detecting a charging voltage of the battery cell.

7. A multiple insulation diagnosing method of a power cable comprising:

(a) selecting one of a plurality of diagnosis modes including a cable's

three-phase concurrent diagnosis mode and a single-phase multiple

diagnosis mode for sequentially measuring respective single phases of the

cable;

(b) setting measurement variables including a diagnosis voltage and

a measuring frequency according to the selected diagnosis mode;

(c) charging the cable; (d) stopping the power supplying to the cable when a predetermined time passes, and measuring the signals flowing through a resistor coupled to the cable according to the selected diagnosis mode;

(e) operating a discharging switch and discharging the residual charges in the cable when the signal measurement is finished; and

(f) processing the measured data into deterioration determination data, and determining the cable's deterioration state on the basis of the processed deterioration determination data.

8. The method of claim 7, wherein when the three-phase multiple concurrent diagnosis mode is selected in (a), power is supplied to the cable's three phases, deterioration time constants of the first through third phases are concurrently measured on the basis of the signals flowing through a very high resistance unit of the resistor coupled to the cable, and the cable's deterioration state is determined on the basis of the measured deterioration time constants.

9. The method of claim 7, wherein when the single-phase multiple insulation diagnosis mode is selected in (a), power is supplied to one of the

three phases of the cable; current (the current flows to the cable) variations

according to time and voltage variations according to time are measured to

output diagnosing variables that represent a polarization index, an absorption

current, and a current feature for each voltage step; the cable's power

supplying circuit is broken; a deterioration time constant is measured on the basis of the signals flowing according to the cable's discharging; and the

cable's deterioration state is determined on the basis of the diagnosing

variables and the deterioration time constants.

10. The method of claims 8 and 9, further comprising: generating the cable's deterioration state determination results

according to the diagnosis mode into a database, and managing them; and finally determining the cable's deterioration state on the basis of the data stored in the database and additional data including the cable's cable history.