SE1650932A1 - Method and system for analyzing high voltage circuit breakers - Google Patents

Abstract

A method for analyzing a circuit breaker phase (100) comprising a first contact arrangement (108) and a second contact arrangement (108) electrically coupled in series comprises the following steps: a) electrically coupling the first and second contact arrangements (108) to electrical ground; b) triggering a contact operation timer at a start of a test; c) applying a test voltage across the first contact arrangement while the first and second contact arrangements remain electrically coupled to electrical ground and the second contact arrangement is short circuited; d) applying a test voltage across the second contact arrangement while the first and second contact arrangements remain electrically coupled to electrical ground and the first contact arrangement is short circuited; and repeating steps c) and d) while detecting at least one of a first closure of the two contact arrangements and a first opening of the two contact arrangements using the test voltage and determining the timing of the contact arrangements based upon the operation of the contact operation timer. A method which is reliable and safe is thereby provided. A system for implementing the method is also provided.

Description

METHOD AND SYSTEM FOR ANALYZINGHIGH VOLTAGE CIRCUIT BREAKERS Technical field

[0001] The present invention relates generally to high voltage circuit breakers,and more specifically to methods and systems for analyzing circuit breaker contacts.

Background art

[0002] During testing of at least some known high voltage circuit breakers bymeans of an apparatus for analyzing high voltage circuit breakers, a plurality ofcircuit breaker parameters may be monitored to facilitate determining that thecircuit breaker is operating as designed. One such parameter may be a circuitbreaker contact arrangement status, which may indicate whether contactscomprised in contact arrangements are opened or closed, and an analog position of the circuit breaker contacts.

[0003] However, a high voltage circuit breaker might be located in anenvironment with high electrical fields, derived from nearby live wires, which maycarry several kilo hundred volts. Since there is capacitance -though small-between the circuit breaker under test and nearby live wires there will be a currentflow, which in worst case may be up to 25 mA. This current is lethal if a person,working on the circuit breaker, should be exposed to it. For this reason it is a ruleto connect both sides of a high voltage circuit breaker being serviced to ground,i.e., protective earth, to lead away any induced current. Tests may be carried outwith exception from this rule - with only one side grounded, but the preferred case is to be able to test a circuit breaker with both sides grounded.

Summary of invention

[0004] An object of the present invention is to provide a method and anapparatus for analyzing a circuit breaker phase comprising a first contactarrangement and a second contact arrangement electrically coupled in series which is reliable and safe. 70549

[0005] According to a first aspect of the invention a method for analyzing acircuit breaker phase comprising a first contact arrangement and a second contactarrangement electrically coupled in series is provided, wherein the methodcomprises the following steps: a) electrically coupiing the first and second contactarrangements to electrical ground; b) triggering a contact operation timer at a startof a test; c) applying a test voltage across the first contact arrangement while thefirst and second contact arrangements remain electrically coupled to electricalground and the second contact arrangement is short circuited; d) applying a testvoltage across the second contact arrangement while the first and second contactarrangements remain electrically coupled to electrical ground and the first contactarrangement is short circuited; and repeating steps c) and d) while detecting atleast one of a first closure of the two contact arrangements and a first opening ofthe two contact arrangements using the test voltage and determining the timing ofthe contact arrangements based upon the operation of the contact operation timer.

[0006] ln a preferred embodiment, each of the steps c) and d) has duration ofbetween 5 - 50 us, more preferably of between 10 - 20 us, and most preferably of12.5 us.

[0007] ln a preferred embodiment, the method comprises detecting the outputvoltage and the current and determining the ratio between the voltage and thecurrent, which corresponds to the presently monitored contact arrangementimpedance.

[0008] According to a second aspect of the invention, a system for analyzing acircuit breaker phase comprising a first contact arrangement and a second contactarrangement electrically coupled in series is provided, the system comprising atesting unit comprising a generator block and a measurement block, the systembeing characterized by a first sense unit, a second sense unit, and a third senseunit connected to the testing unit and connectable to a circuit breaker phase, thesense units being adapted to sense operating parameters for the testing of thecircuit breaker phase, and a controller connected to the generator block and the 70549 measurement block and adapted to execute the method according to the invenfion.

[0009] ln a preferred embodiment, the first sense unit is connectable to ameasuring point on a line side of the first contact arrangement, the second senseunit is connectable to a measuring point between the first contact arrangementand the second contact arrangement, and the third sense unit is connectable to a measuring point on a load side of the second contact arrangement.

[0010] ln a preferred embodiment, the first, second, and third sense units areprovided as separate units connected to the testing unit by means of cables, preferably shie|ded cables.

[0011] ln a preferred embodiment, the sense units are adapted to sense voltage and current.

[0012] ln a preferred embodiment, the sense units each comprises a relayprovided between an output connectable to the circuit breaker phase and adaptedto connect one side of a contact arrangement to another side in order to get aknown state when tuning the generator block and calibrating the measurementblock.

[0013] ln a preferred embodiment, the generator block comprises a generatoradapted to generate a signal, preferably a sinus signal, where the controller isadapted to set the frequency to suit the impedance of the network formed by thecircuit breaker phase and its connections, in order to achieve largest possiblerecorded ratio of impedance change from open to closed circuit breaker.

[0014] By means of the inventive method and system for analyzing high voltagecircuit breakers timing of a three phase circuit breaker can be performed with both sides grounded.

[0015] The system according to the invention uses high frequency electricalsignals to distinguish between relatively low impedance in closed circuit breaker contacts and relatively high impedance in grounding wires. 70549

[0016] ln the cases where short grounding connections are at place it might beneeded to increase the inductance in the ground connections by adding ferrite cores around the grounding wires.

[0017] Furthermore they can distinguish between main contacts and parallelcontacts having series resistance.

Brief description of drawinqs

[0018] The invention is now described, by way of example, with reference to theaccompanying drawings, in which: Fig. 1 is an example sketch of a three phase high voltage circuit; Fig. 2 is a schematic illustration of an exemplary high voltage circuit breaker phasewith both sides grounded; Fig. 3 is a schematic illustration of an exemplary equivalent circuit of a contact pair that may be used in the circuit breaker phase shown in Figure 2; Fig. 4 is a simplified schematic illustration of the exemplary equivalent circuit of acontact pair that may be used in the circuit breaker phase shown in Figure 2; Fig. 5 is a schematic illustration of an exemplary equivalent circuit of the circuit breaker phase with both sides grounded, shown in Figure 2; Fig. 6 is a schematic illustration of an exemplary testing unit that may be used totest a circuit breaker that is represented by the equivalent circuit shown in Figure Fig. 7 is a schematic illustration of the generator block that is represented in Figure6; Fig. 8 is a schematic illustration of the output transformer and filter block that isrepresented in Figure 7; 70549 Fig. 9 is a schematic illustration of a Circuit Breaker sense circuitry block in Figure6; Fig. 10 is schematic illustration of the Measurement block in Figure 6; Fig. 11 is schematic of connections for monitoring a circuit breaker in a threephase system; and Fig. 12 is an oscilloscope picture of the measured signals from a system for analyzing circuit breaker contacts according to the invention.

Description of embodiments

[0019] ln the following, a detailed description of methods and systems foranalyzing circuit breaker contacts will be given. Although the herein describedmethods are described with regard to circuit breaker contacts, it is contemplatedthat the benefits of the invention accrue to non-circuit breaker contacts such asthose contacts typically employed in, for example, but not limited to, relays orswitches, with one or two series connected contact arrangements.

[0020] Referring to Fig. 1, there is shown a sketch of a three phase high voltagecircuit breaker, each phase 100 with two contact pairs in series, each with parallel Pre-lnsertion Resistors and contact pairs, in its environment during service or test.

[0021] Fig. 2 is a schematic illustration of a high voltage circuit breaker phase,generally designated 100, shown in Fig. 1, comprising two contact arrangements108, alternatively labeled CB1 and CB2. Each contact arrangement of a highvoltage circuit breaker phase may include a pre-insertion resistor (PIR) 102 and amoving resistor contact 104 electrically coupled in parallel with a moving maincontact 106. Thus, in the exemplary embodiment, circuit breaker phase 100includes two contact arrangements 108 that each includes a pre-insertion resistor,of which only one is shown in Fig. 2. Also, each of the two contacts 104, 106 comprises a movable portion and a non-movable portion.

[0022] ln operation, when a circuit breaker phase 100 of a circuit breakerreceives a command to close from an open position, linkages within the contact 70549 arrangement 108 cause movable portions of contacts 104 and 106 to shift towardsengaging respective non-movable portions of contacts 104 and 106. During atesting sequence, movement of the movable portion of contacts 104 and 106 mayinitiate a timer. After a predetermined distance of travel of the movable portions ofcontacts 104 and 106 has Iapsed, the movable portion of pre-insertion resistorcontact 104 engages the non-movable portion of contact 104, causing current toflow through contact 104 and pre-insertion resistor 102. A current surge throughcontact 104 may be limited by pre-insertion resistor 102. After a predeterminedtime delay, the movable portion of contact 106 engages the non-movable portionof main contact 106. Since the resistance of main contact 106 may besubstantially less than the resistance of pre-insertion resistor 102, substantially allcurrent flowing through the circuit breaker flows through main contact 106. Duringtesting, the resistance values of contacts 104 and 106 may be determined, inaddition to the resistance value of pre-insertion resistor 102 and the timing ofcircuit breaker contacts 104 and 106. More specifically, the resistances aremeasured dynamically and the value of pre-insertion resistor 102 is measured in atime period elapsed between the closing of resistor contact 104 and the closing ofmain contact 106. Based on the measured resistance values, known thresholdvalues are used to determine when main contact 106 and resistor contact 104 areeach considered to be open and/or closed, such that the contact timing may becalculated. ln one embodiment no pre-insertion resistor 102 is included in thecircuit breaker, and only the timing of main contact is determined.

[0023] Optionally, there are provided added inductances in the grounding wires,in the figure shown as ferrite cores 109.

[0024] ln Fig. 3 there is shown an exemplary equivalent circuit of a pair ofcontact arrangements 108 that may be used in the circuit breaker phase shown inFig. 2. ln this figure, L1 and L2 represent the lead inductances from the circuitbreaker contact arrangements 108 to the connection points on the line side andthe load side, respectively. Lead resistances R1 and R2, for a main contact 106are in the range of a few 10th of micro ohms. CB represents the variablecapacitance of a circuit breaker phase 100. 70549

[0025] The equivalent circuit shown in Fig. 3 may be simplified, see Fig. 4, toimpedances Z1 and Z2 and a circuit breaker CB of a pair of contact arrangements,which may be in an open state, wherein the contact arrangements are mainlycapacitive, or a closed stated, wherein the contact arrangements essentiallyoperate as a short circuit.

[0026] Fig. 5 is a schematic illustration of an exemplary equivalent circuit of thecircuit breaker phase 100 shown in Fig. 2 with two contact arrangements in series,labeled CB1 and CB2, respectively, each with a parallel contact pair with a maincontact and a pre-insertion resistor. ln Fig. 5, both the line side and the load sideare grounded and inductances added in the ground wires. The pre-insertionresistors labeled R_PlR1 and R_PlR2, respectively, may be detected in the rangeof 10 Q to 3 kQ.

[0027] As shown in Fig. 5, the contact arrangements CB1 and CB2 may beconnected through ground connections, which mainly are inductive, in the figurerepresented by L_Gnd_1 and L_Gnd_2. ln some circuit breakers, these groundconnections are relatively short. ln those cases the ground connection inductancemight need to be increased, in order to separate between a breaker contact and itsground connection, while monitoring contact state. Thus, in one embodiment eachground connector has an additional inductance, added by ferrite cores, hererepresented by L_Gnd_1x and L_Gnd_2x, labelled 109 in Fig. 2.

[0028] Fig. 6 is a schematic illustration of an exemplary testing unit, generallydesignated 200, that is adapted to test a circuit breaker phase 100 that isrepresented by the equivalent circuit shown in Figure 5, i.e., a dual ground circuitbreaker phase. ln the figure L_Gnd_1 and L_Gnd_1x are represented by theimpedance Z_Gnd_1. Likewise L_Gnd_2 and L_Gnd_2x are represented by theimpedance Z_Gnd_2. The circuit breaker phase model is described above with reference to Fig. 5.

[0029] The testing unit 200 comprises a plurality of inputs for measurementsignals received from the circuit breaker phase 100. Correspondingly, a plurality ofoutputs is provided for outputting test signals, generated by a control circuit 70549 generator. The testing unit 200 also has a power and communication interface thatwill be described in detail below with reference to Fig. 10.

[0030] Sense units 210a, 210b, 210c are located close to the circuit breakerconnections. These sense units are adapted to sense the different parametersneeded for the testing of the circuit breaker phase 100, such as voltage andcurrent. ln this example, the first sense unit 210a is connected to a measuringpoint on the line side of the first contact arrangement CB1, the second sense unit210b is connected to a measuring point between the first contact arrangementCB1 and the second contact arrangement CB2, and the third sense unit 210c isconnected to a measuring point on the load side of the second contact arrangement CB2.

[0031] Shielded cables 220 are provided to connect HF generation andmeasurement blocks, voltage and current and calibration circuitry blocks of thetesting unit 200 to the circuit breaker 100 through the sense units 210a, 210b,210c. HF generation and measurement blocks, voltage and current and calibrationcircuitry blocks are described below.

[0032] Figure 7 is a schematic illustration of a generator block 202 of the testingunit 200 that is represented in Fig. 6. The generator block includes generator,switch, output and protection circuitry sub-blocks wherein the generator sub-block202a comprises a generator V1 that generates a sinus signal HF, where thefrequency is set by a microcontroller in the measurement block described belowwith reference to Fig. 10 through an input signal F. The frequency is set to suit theimpedance of the network formed by the circuit breaker phase and its connections,to achieve largest possible recorded ratio of impedance change from open toclosed circuit breaker. A limitation resistor R_Limit is a resistor adapted to limit theoutput current from the generator V1 in case of a shorted output.

[0033] The sinus signal HF acts as input signals to a switch sub-block 202bcomprising a first switch SW1 and a second switch SW2 that are controlled by themicrocontroller through signals Sel_Output_1 and Sel_Output_2, respectively. Thefirst and second switches SW1 and SW2 connect the sinus signal HF of the 70549 generator V1 either to an output sub-block 202c and more specifically to a firstoutput transformer and filter circuit, labeled Output transformer & filter 1, or to asecond output transformer and filter circuit, labeled Output transformer & filter 2, orto both the first and second output transformer and filter circuits at the same time.The output transformer and filter circuits are described below.

[0034] When switches SW1 or SW2 do not connect the output transformer andfilter circuits to the generator V1 they connect the output transformer and filtercircuits to OV, which is a negative signal potential from the generator V1. Then thecorresponding output is shorted, one at a time. This is to get a known contactbreaker state to the measurement circuitry while measuring on either circuit breaker contact arrangement.

[0035] The output transformer and filter circuits connect to the line side HF1 ofthe circuit breaker phase or to the load side HF2 of the circuit breaker phase. Asignal HFmid having the opposite output polarity of the generator V1 connects to the midpoint of a circuit breaker phase having two contact arrangements in series.

[0036] ln case of monitoring a circuit breaker phase having only one contactarrangement, the HFmid need not to be connected. ln this mode both of theswitches SW1 and SW2 connect the generator, through the output transformerand filter blocks. The signal polarity is then set to get the HF2 - HF1 voltageamplitude twice as large as HFmid - HF1 amplitude (or HF2 - HFmid).

[0037] The protection sub-block 202d of the generator block comprisesinductors L6 - L11 having inductances with high impedance for the signalfrequency being generated by the generator V1 and with low impedance for 50/60Hz that connect any induced current to ground. This is for safety in case of poorconnection of the protective grounding wires or if the ungrounded midpoint of thecircuit breaker phase receives large induced current from nearby live high voltage wires.

[0038] Fig. 8 is a schematic illustration of one of the output transformer and filtercircuits 202c shown in Fig. 7. Each of the output transformer and filter circuits 70549 comprises a transformer T3 that isolates the generator V1 from its OV potentialenabling connection of several outputs in series. A first end of the primary windingof the transformer T3 is connected to the input of the output transformer and filtercircuit. A capacitor C3 provided between a second end of the primary winding ofthe transformer T3 and OV blocks any dc offset voltage from the generator V1and/or output switch to prevent saturation of transformer T3. Finally, inductors L3and L4 provided between the secondary winding of the transformer T3 and outputsHF- and HF+ attenuate common mode and differential mode high frequency noisefrom the generator V1.

[0039] Fig. 9 is a schematic illustration of the sense units 210a, 210b, 210c inFigure 6, labeled 210 in Fig. 9. lnput HF is adapted to be connected to one side ofthe output of the generator block 202 described with reference to Fig. 7. Output Vis adapted to be connected to one side of a voltage measurement circuitrydescribed below with reference to Fig. 10. A sense unit 210 comprises a resistorR1 that provides high impedance to limit the load of the input HF signal. ln parallelwith resistor R1 a capacitor C1 is provided that compensates for the capacitancein the voltage measurement cable between the signal lead and its surroundingshield. The sense unit 210 also comprises a current transformer T1 thattransforms the current flowing from the generator block to the circuit breakerphase 100 and its ground connection. lnput HF is connected to one end of a firstside of current transformer T1. Also, resistor R1 and capacitor C1 are providedbetween this first side of the current transformer T1 and output V. A shunt resistorR2 is provided across a second side of current transformer T1 to limit themeasurement output voltage of the current transformer T1 in case of interruptionof the signal cables to the Measurement lnput circuitry described below. The shuntresistor preferably has a low value, such as 33 Ohms. A voltage across this shuntresistor R2 corresponds to the measured current and is provided as a differentialvoltage at the outputs l+, l-.

[0040] The current transformer T1 is connected between a voltagemeasurement point where R1 and C1 connects to T1 and the circuit breaker connection CB not to measure any current flowing to the voltage measurement 705491 1 cable. The impedance across the primary side of the current transformer T1 isreasonably low, to give a low voltage drop, to minimize corruption of the voltage measurement.

[0041] A relay RE1 is provided between the output CB and input/output V_Cal,Cal and is thereby adapted to connect one side of a contact arrangement toanother side in order to get a known state when tuning the generator andcalibrating the measurement circuitry. This is described below with reference toFig. 10 where a calibration signal Cal connects to V_Cal_1, V_Cal_Mid or V Cal 2.

[0042] The thought behind providing these components in the sense unitsseparate from the testing unit 200 is that cable lengths from the sensingcomponents to the measuring point on the circuit breaker can be minimized. Thisresults in more accurate measurements allowing accurate values for both current and voltage.

[0043] The cables from the sense units 210a, 210b, 210c to the testing unit 200are optimized in the following way: The connector cable to the sense unit 210bprovided at the midpoint between the contact arrangements is as short aspossible, such as 0.5 meter. The connector cables to the line side and to the loadside sense units 210a, 210c are, together, long enough to reach the connectionpoints of a rather large circuit breaker, such as a “Dead Tank Circuit Breaker”,meaning cables with a length of 4-5 meters.

[0044] Figure 10 is a schematic illustration of the measurement block 204 of thetesting unit 200 in Figure 6. The measurement block 204 has voltagemeasurement inputs that are differential inputs for voltage measurement and forcurrent measurement that are used to get attenuation of common modedisturbances. The voltage measurement inputs measure the voltage differencesbetween the following points of the circuit breaker phase when measuring on twoserially connected contact arrangements, such as illustrated in Fig. 6: - Line side vs. midpoint, “v1” = “vi +” - 70549 12- Lead eide ve. midpeini, “v2” = “v2+” - - Line eide ve. ieed eide, “v1-2” = “v1"-“v2”

[0045] Current measurement inputs measure current flowing into the circuit breaker at the: - Line side: “l1” = “R1”x (“l1+”- “l1-“) is a voltage representing currentflow at the line side.

- Load side: “l2” = “R2” X (“|2+” - “l2-“) is a voltage representing currentflow at the load side.

[0046] The current inputs have shunts to convert the current signal to adifferential voltage.

[0047] lnput selectors (voltage and current sense) select, depending of modesetting (one contact pair or two contact pairs in series) select either: - *v'=“v1”end1'=“n”- *v'=“v2”end1'=“m”- 'v' = “v1-2” end 'r equeie either “i1” er “i2”.

[0048] A Magnitude & Phase Detector takes the 'V' and 'l' signals to detect the'V'/'l' ratio (“V/l”) and also the phase difference (“ø(V) - ø(l)”).

[0049] The calibration relays RE1 of the sense circuitry, described above withreference to Fig. 9, are activated to short the circuit breaker contacts to achieve aknown circuit breaker contact state while tuning the measurement frequency andrecording initial signals from the Magnitude & Phase Detector.

[0050] The measurement block 204 also comprises the above mentioned microcontroller labeled Controller which is adapted to perform the following tasks: o Control the HF generator frequency 7054913o Schedule input and output switchingo Control calibration relayso Record the output of the Magnitude and Phase detector o Evaluate the recorded values of the detector and outputs to find circuit breakerstate o Communicate circuit breaker state data to a main unito Receive and execute commands from the main unit

[0051] Figure 11 is an illustrative schematic of connections for monitoring acircuit breaker in a three phase system. A cable unit comprised of three senseunits 210a, 210b, 210c, i.e., with attached voltage sense, current sense andcalibration circuitry is connected across each pair of contact arrangements of acircuit breaker phase with tvvo contact arrangements in series.

[0052] A respective testing unit 200 contains the HF generation, calibrationcircuitry, measurement input, control circuitry, output and input switches andprotection circuitry for each phase of a three phase circuit breaker test setup.

[0053] A main unit 230 communicates with the three testing units 200. The mainunit 230 also supplies power to the three cable units. State for the circuit breaker ismonitored by a circuit breaker analyzer 240, which is a computer connected to themain unit 230. The circuit breaker analyzer 240 connects to the main unit 230 torecord contact state. lt also controls the circuit breaker operation and records thetiming of the contact state changes during a preset measurement time.

[0054] A time stamp is set when the circuit breaker analyzer activates the trip orclose coils in the operation mechanism(s) of the circuit breaker. Times and circuitbreaker state data are recorded during the circuit breaker operation and presentedto the operator/test personnel. 7054914

[0055] The method for analyzing a contact arrangement according to theinvention will now be described in detail. The method is applied on a circuitbreaker phase comprising a first contact arrangement CB1 and a second contactarrangement CB2 electrically coupled in series, wherein each of the contactarrangements preferably comprises a main contact and a pre-insertion contactconnected in parallel, as described above with reference to Fig. 2.

[0056] First, the first and second contact arrangements are electrically coupledto electrical ground, as described above with reference to Fig. 5. Then a contactoperation timer is trigged at a start of a test.

[0057] A test voltage is applied across the first contact arrangement while thefirst and second contact arrangements remain electrically coupled to electricalground and the second contact arrangement is short circuited. Then a test voltageis applied across the second contact arrangement while the first and secondcontact arrangements remain electrically coupled to electrical ground and the firstcontact arrangement is short circuited. These two steps are repeated whiledetecting at least one of a first closure of the two contact arrangements and a firstopening of the two contact arrangements using the test voltage and determiningthe timing of the contact arrangements based upon the operation of the contact operation timer.

[0058] Figure 12 is an oscilloscope picture of the measured signals from thesense units 210a, 210b, 210c when performing the method according to theinvention. The signals include the voltage across the currently measured contactarrangement (V_ATT) , the current through the currently measured contactarrangement (l_ATT), the magnitude output from the detector, i.e., the ratiobetween the voltage and the current (V/l_RATlO) and a status signal CHAN_1displaying which output/measurement channel is presently active. ln the presentcase, the first contact arrangement CB1 is measured when the signal CHAN_1 ishigh and the second contact arrangement CB2 is measured when the signalCHAN_1 is low. Thus, the oscilloscope picture shows the signals present when thetest device is set to switch between two contact arrangements in series. Switching 70549 takes place repeatedly preferably every 12.5 ps, thus enabling each contactarrangement state to be sampled/monitored every 25 ps; thus at a rate of 40 kilosamples per second, although other sampling rates are possible. Thus, theduration between each switching may be for example between 5 - 50 ps or morepreferably between 10 - 20 ps. As seen from the figure the voltage measuredacross the open contact arrangement CB2 is higher while the current is lowercompared to the voltage and current from the contract arrangement CB1, which isin closed state.

[0059] The output voltage V/l_RATlO corresponds to the presently monitoredcontact arrangement impedance. This is sampled at the time of switching to theother channel. The oscilloscope picture shows for the first cycle at what point thefirst contact arrangement CB1 is sampled, designated “Sampling CB1”, and atwhat point the second contact arrangement CB2 is sampled, designated“Sampling CB2”. This sampling is repeated for every cycle. As can be seen fromthe picture, the first contact arrangement C1 is closed, i.e., the ratio has a lowvalue corresponding to a low impedance, and the second contact arrangementCB2 is open, corresponding to a high impedance.The ratio is evaluated and thecontact states of the contact arrangements are presented to the circuit breaker analyzer 240.

[0060] Preferred embodiments of a method and a system according to theinvention have been described. lt will be appreciated that these can be variedwithin the scope of the appended claims without departing from the inventive idea.

[0061] ln the disclosed embodiments analyzing of a circuit breaker phase havingtwo serially connected contact arrangements has been shown and described. Theinventive system is also applicable to a circuit breaker phase having a singlecontact arrangement. ln this case, the middle sense unit 210b is omitted and thetwo other sense units 210a, 210c are connected to either side of the single contact arrangement.

Claims (9)

1. A method for analyzing a circuit breaker phase (100) comprising a firstcontact arrangement (CB1) and a second contact arrangement (CB2) electrically coupled in series, wherein the method comprises the following steps: a) electrically coupling the first and second contact arrangements (CB1, CB2) toelectrical ground; b) triggering a contact operation timer at a start of a test; c) applying a test voltage across the first contact arrangement while the first andsecond contact arrangements remain electrically coupled to electrical groundand the second contact arrangement is short circuited; d) applying a test voltage across the second contact arrangement while the firstand second contact arrangements remain electrically coupled to electricalground and the first contact arrangement is short circuited; and e) repeating steps c) and d) while detecting at least one of a first closure of the twocontact arrangements and a first opening of the two contact arrangements usingthe test voltage and determining the timing of the contact arrangements basedupon the operation of the contact operation timer.

2. The method according to claim 1, wherein each of the steps c) and d)has duration of between 5 - 50 us, more preferably of between 10 - 20 us, andmost preferably of 12.5 us.

3. The method according to claim 1 or 2, comprising detecting the outputvoltage (V) and the current (I) and determining the ratio (V/l_RATlO) between thevoltage and the current (V/l_RATlO), which corresponds to the presently monitored contact arrangement impedance. 7054917

4. A system for analyzing a circuit breaker phase (100) comprising a firstcontact arrangement (CB1) and a second contact arrangement (CB2) electrically coupled in series, comprising: - a testing unit (200) comprising a generator block (202) and a measurementblock (204), characterized by - a first sense unit (210a), a second sense unit (210b), and a third sense unit(210c) connected to the testing unit (200) and connectable to a circuitbreaker phase (100), the sense units being adapted to sense operatingparameters for the testing of the circuit breaker phase (100), and a controller connected to the generator block (202) and the measurementblock (204) and adapted to execute the method according to claim 1.

5. The system according to claim 4, wherein the first sense unit (210a) isconnectable to a measuring point on a line side of the first contact arrangement(CB1), the second sense unit (210b) is connectable to a measuring point betweenthe first contact arrangement (CB1) and the second contact arrangement (CB2),and the third sense unit (210c) is connectable to a measuring point on a load sideof the second contact arrangement (CB2).

6. The system according to claim 4 or 5, wherein the first, second, andthird sense units (210a, 210b, 210c) are provided as separate units connected tothe testing unit (200) by means of cables, preferably shielded cables (220).

7. The system according to any one of claims 4-6, wherein the sense units (210a, 210b, 210c) are adapted to sense voltage and current.

8. The system according to any one of claims 4-7, wherein the sense units(210a, 210b, 210c) each comprises a relay (RE1) provided between an output(CB) connectable to the circuit breaker phase and adapted to connect one side ofa contact arrangement to another side in order to get a known state when tuning the generator block (202) and calibrating the measurement block (204). 7054918

9. The system according to any one of claims 4-8, wherein the generatorblock (202) comprises a generator (V1) adapted to generate a signal, preferably asinus signal (HF), where the controller is adapted to set the frequency to suit theimpedance of the network formed by the circuit breaker phase and its connections,in order to achieve largest possible recorded ratio of impedance change from open to closed circuit breaker.