WO2018004443A1

WO2018004443A1 - Method and system for analyzing high voltage circuit breakers

Info

Publication number: WO2018004443A1
Application number: PCT/SE2017/050729
Authority: WO
Inventors: Stig RUDHOLM; Zoran Stanisic
Original assignee: Megger Sweden Ab
Priority date: 2016-06-29
Filing date: 2017-06-29
Publication date: 2018-01-04
Also published as: SE1650932A1

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 ANALYZING

HIGH 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 by means of an apparatus for analyzing high voltage circuit breakers, a plurality of circuit breaker parameters may be monitored to facilitate determining that the circuit breaker is operating as designed. One such parameter may be a circuit breaker contact arrangement status, which may indicate whether contacts comprised 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 an environment with high electrical fields, derived from nearby live wires, which may carry several kilo hundred volts. Since there is capacitance - though small - between the circuit breaker under test and nearby live wires there will be a current flow, which in worst case may be up to 25 imA. This current is lethal if a person, working on the circuit breaker, should be exposed to it. For this reason it is a rule to 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 out with 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 an apparatus for analyzing a circuit breaker phase comprising a first contact arrangement and a second contact arrangement electrically coupled in series which is reliable and safe. [0005] According to a first aspect of the invention a method for analyzing a circuit breaker phase comprising a first contact arrangement and a second contact arrangement electrically coupled in series is provided, wherein the method comprises the following steps: a) electrically coupling the first and second contact arrangements 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.

[0006] In a preferred embodiment, each of the steps c) and d) has duration of between 5 - 50 με, more preferably of between 10 - 20 με, and most preferably of 12.5 με.

[0007] In a preferred embodiment, the method comprises detecting the output voltage and the current and determining the ratio between the voltage and the current, which corresponds to the presently monitored contact arrangement impedance.

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

[0009] In a preferred embodiment, the first sense unit is connectable to a measuring point on a line side of the first contact arrangement, the second sense unit is connectable to a measuring point between the first contact arrangement and 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] In a preferred embodiment, the first, second, and third sense units are provided as separate units connected to the testing unit by means of cables, preferably shielded cables.

[001 1 ] In a preferred embodiment, the sense units are adapted to sense voltage and current.

[0012] In a preferred embodiment, the sense units each comprises a relay provided between an output connectable to the circuit breaker phase and the testing unit and being adapted to connect one side of a contact arrangement to another side in order to get a known state when tuning the generator block and calibrating the measurement block.

[0013] In a preferred embodiment, the generator block comprises a generator adapted to generate a signal, preferably a sinus signal, where the controller is adapted to set the frequency to suit the impedance 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.

[0014] By means of the inventive method and system for analyzing high voltage circuit 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 electrical signals to distinguish between relatively low impedance in closed circuit breaker contacts and relatively high impedance in grounding wires. [0016] In the cases where short grounding connections are at place it might be needed 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 parallel contacts having series resistance.

Brief description of drawings

[0018] The invention is now described, by way of example, with reference to the accompanying 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 phase with 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 a contact 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 to test a circuit breaker that is represented by the equivalent circuit shown in Figure 5;

Fig. 7 is a schematic illustration of the generator block that is represented in Figure 6;

Fig. 8 is a schematic illustration of the output transformer and filter block that is represented in Figure 7; Fig. 9 is a schematic illustration of a Circuit Breaker sense circuitry block in Figure 6;

Fig. 10 is schematic illustration of the Measurement block in Figure 6;

Fig. 1 1 is schematic of connections for monitoring a circuit breaker in a three phase 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] In the following, a detailed description of methods and systems for analyzing circuit breaker contacts will be given. Although the herein described methods are described with regard to circuit breaker contacts, it is contemplated that the benefits of the invention accrue to non-circuit breaker contacts such as those contacts typically employed in, for example, but not limited to, relays or switches, with one or two series connected contact arrangements.

[0020] Referring to Fig. 1 , there is shown a sketch of a three phase high voltage circuit 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 arrangements 108, alternatively labeled CB1 and CB2. Each contact arrangement of a high voltage circuit breaker phase may include a pre-insertion resistor (PIR) 102 and a moving resistor contact 104 electrically coupled in parallel with a moving main contact 106. Thus, in the exemplary embodiment, circuit breaker phase 100 includes 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] In operation, when a circuit breaker phase 100 of a circuit breaker receives a command to close from an open position, linkages within the contact arrangement 108 cause movable portions of contacts 104 and 106 to shift towards engaging respective non-movable portions of contacts 104 and 106. During a testing sequence, movement of the movable portion of contacts 104 and 106 may initiate a timer. After a predetermined distance of travel of the movable portions of contacts 104 and 106 has lapsed, the movable portion of pre-insertion resistor contact 104 engages the non-movable portion of contact 104, causing current to flow through contact 104 and pre-insertion resistor 102. A current surge through contact 104 may be limited by pre-insertion resistor 102. After a predetermined time delay, the movable portion of contact 106 engages the non-movable portion of main contact 106. Since the resistance of main contact 106 may be

substantially less than the resistance of pre-insertion resistor 102, substantially all current flowing through the circuit breaker flows through main contact 106. During testing, the resistance values of contacts 104 and 106 may be determined, in addition to the resistance value of pre-insertion resistor 102 and the timing of circuit breaker contacts 104 and 106. More specifically, the resistances are measured dynamically and the value of pre-insertion resistor 102 is measured in a time period elapsed between the closing of resistor contact 104 and the closing of main contact 106. Based on the measured resistance values, known threshold values are used to determine when main contact 106 and resistor contact 104 are each considered to be open and/or closed, such that the contact timing may be calculated. In one embodiment no pre-insertion resistor 102 is included in the circuit 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] In Fig. 3 there is shown an exemplary equivalent circuit of a pair of contact arrangements 108 that may be used in the circuit breaker phase shown in Fig. 2. In this figure, L1 and L2 represent the lead inductances from the circuit breaker contact arrangements 108 to the connection points on the line side and the load side, respectively. Lead resistances R1 and R2, for a main contact 106 are in the range of a few 10th of micro ohms. CB represents the variable capacitance of a circuit breaker phase 100. [0025] The equivalent circuit shown in Fig. 3 may be simplified, see Fig. 4, to impedances 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 mainly capacitive, or a closed stated, wherein the contact arrangements essentially operate as a short circuit.

[0026] Fig. 5 is a schematic illustration of an exemplary equivalent circuit of the circuit 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 main contact and a pre-insertion resistor. In Fig. 5, both the line side and the load side are grounded and inductances added in the ground wires. The pre-insertion resistors labeled R_PIR1 and R_PIR2, respectively, may be detected in the range of 10 Ω to 3 kQ.

[0027] As shown in Fig. 5, the contact arrangements CB1 and CB2 may be connected through ground connections, which mainly are inductive, in the figure represented by L_Gnd_1 and L_Gnd_2. In some circuit breakers, these ground connections are relatively short. In those cases the ground connection inductance might need to be increased, in order to separate between a breaker contact and its ground connection, while monitoring contact state. Thus, in one embodiment each ground connector has an additional inductance, added by ferrite cores, here represented by L_Gnd_1 x and L_Gnd_2x, labelled 109 in Fig. 2.

[0028] Fig. 6 is a schematic illustration of an exemplary testing unit, generally designated 200, that is adapted to test a circuit breaker phase 100 that is represented by the equivalent circuit shown in Figure 5, i.e., a dual ground circuit breaker phase. In the figure L_Gnd_1 and L_Gnd_1 x are represented by the impedance Z_Gnd_1 . Likewise L_Gnd_2 and L_Gnd_2x are represented by the impedance 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 measurement signals received from the circuit breaker phase 100. Correspondingly, a plurality of outputs is provided for outputting test signals, generated by a control circuit generator. The testing unit 200 also has a power and communication interface that will be described in detail below with reference to Fig. 10.

[0030] Sense units 21 Oa, 21 Ob, 21 Oc are located close to the circuit breaker connections. These sense units are adapted to sense the different parameters needed for the testing of the circuit breaker phase 100, such as voltage and current. In this example, the first sense unit 210a is connected to a measuring point on the line side of the first contact arrangement CB1 , the second sense unit 210b is connected to a measuring point between the first contact arrangement CB1 and the second contact arrangement CB2, and the third sense unit 210c is connected to a measuring point on the load side of the second contact

arrangement CB2.

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

[0032] Figure 7 is a schematic illustration of a generator block 202 of the testing unit 200 that is represented in Fig. 6. The generator block includes generator, switch, output and protection circuitry sub-blocks wherein the generator sub-block 202a comprises a generator V1 that generates a sinus signal HF, where the frequency is set by a microcontroller in the measurement block described below with reference to Fig. 10 through an input signal F. The frequency is set to suit the impedance of the network formed by the circuit breaker phase and its connections, to achieve largest possible recorded ratio of impedance change from open to closed circuit breaker. A limitation resistor RJJmit is a resistor adapted to limit the output 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 202b comprising a first switch SW1 and a second switch SW2 that are controlled by the microcontroller through signals Sel_Output_1 and Sel_Output_2, respectively. The first and second switches SW1 and SW2 connect the sinus signal HF of the generator V1 either to an output sub-block 202c and more specifically to a first output transformer and filter circuit, labeled Output transformer & filter 1 , or to a second output transformer and filter circuit, labeled Output transformer & filter 2, or to 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 and filter circuits to the generator V1 they connect the output transformer and filter circuits to 0V, which is a negative signal potential from the generator V1 . Then the corresponding output is shorted, one at a time. This is to get a known contact breaker 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 of the circuit breaker phase or to the load side HF2 of the circuit breaker phase. A signal 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] In case of monitoring a circuit breaker phase having only one contact arrangement, the HFmid need not to be connected. In this mode both of the switches SW1 and SW2 connect the generator, through the output transformer and filter blocks. The signal polarity is then set to get the HF2 - HF1 voltage amplitude twice as large as HFmid - HF1 amplitude (or HF2 - HFmid).

[0037] The protection sub-block 202d of the generator block comprises inductors L6 - L1 1 having inductances with high impedance for the signal frequency being generated by the generator V1 and with low impedance for 50/60 Hz that connect any induced current to ground. This is for safety in case of poor connection of the protective grounding wires or if the ungrounded midpoint of the circuit 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 filter circuits 202c shown in Fig. 7. Each of the output transformer and filter circuits comprises a transformer T3 that isolates the generator V1 from its OV potential enabling connection of several outputs in series. A first end of the primary winding of the transformer T3 is connected to the input of the output transformer and filter circuit. A capacitor C3 provided between a second end of the primary winding of the transformer T3 and OV blocks any dc offset voltage from the generator V1 and/or output switch to prevent saturation of transformer T3. Finally, inductors L3 and L4 provided between the secondary winding of the transformer T3 and outputs HF- and HF+ attenuate common mode and differential mode high frequency noise from the generator V1 .

[0039] Fig. 9 is a schematic illustration of the sense units 210a, 210b, 210c in Figure 6, labeled 210 in Fig. 9. Input HF is adapted to be connected to one side of the output of the generator block 202 described with reference to Fig. 7. Output V is adapted to be connected to one side of a voltage measurement circuitry described below with reference to Fig. 10. A sense unit 210 comprises a resistor R1 that provides high impedance to limit the load of the input HF signal. In parallel with resistor R1 a capacitor C1 is provided that compensates for the capacitance in the voltage measurement cable between the signal lead and its surrounding shield. The sense unit 210 also comprises a current transformer T1 that

transforms the current flowing from the generator block to the circuit breaker phase 100 and its ground connection. Input HF is connected to one end of a first side of current transformer T1 . Also, resistor R1 and capacitor C1 are provided between this first side of the current transformer T1 and output V. A shunt resistor R2 is provided across a second side of current transformer T1 to limit the measurement output voltage of the current transformer T1 in case of interruption of the signal cables to the Measurement Input circuitry described below. The shunt resistor preferably has a low value, such as 33 Ohms. A voltage across this shunt resistor R2 corresponds to the measured current and is provided as a differential voltage at the outputs l+, I-.

[0040] The current transformer T1 is connected between a voltage

measurement point where R1 and C1 connects to T1 and the circuit breaker connection CB not to measure any current flowing to the voltage measurement cable. The impedance across the primary side of the current transformer T1 is reasonably 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 to another side in order to get a known state when tuning the generator and calibrating the measurement circuitry. This is described below with reference to Fig. 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 units separate from the testing unit 200 is that cable lengths from the sensing components to the measuring point on the circuit breaker can be minimized. This results 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 200 are optimized in the following way: The connector cable to the sense unit 210b provided at the midpoint between the contact arrangements is as short as possible, such as 0.5 meter. The connector cables to the line side and to the load side sense units 210a, 210c are, together, long enough to reach the connection points 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 the testing unit 200 in Figure 6. The measurement block 204 has voltage

measurement inputs that are differential inputs for voltage measurement and for current measurement that are used to get attenuation of common mode disturbances. The voltage measurement inputs measure the voltage differences between the following points of the circuit breaker phase when measuring on two serially connected contact arrangements, such as illustrated in Fig. 6:

Line side vs. midpoint, "V1 " = "V1 +" - "V-" Load side vs. midpoint, "V2" = "V2+" - "V-"

Line side vs. load side, "V1 -2" = "V1 " - "V2"

[0045] Current measurement inputs measure current flowing into the circuit breaker at the:

Line side: "11 " = "R1 " x ("11 +" - "11 -") is a voltage representing current flow at the line side.

Load side: "I2" = "R2" x ("I2+" - Ί2-") is a voltage representing current flow at the load side.

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

[0047] Input selectors (voltage and current sense) select, depending of mode setting (one contact pair or two contact pairs in series) select either:

'V' = "V1 " and T = "H "

'V = "V2" and T = "I2"

'V = "V1 -2" and T equals either "11 " or "I2".

[0048] A Magnitude & Phase Detector takes the 'V and 'I' signals to detect the 'V7T ratio ("V/l") and also the phase difference ("0(V) - 0(!)").

[0049] The calibration relays RE1 of the sense circuitry, described above with reference to Fig. 9, are activated to short the circuit breaker contacts to achieve a known circuit breaker contact state while tuning the measurement frequency and recording 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:

• Control the HF generator frequency • Schedule input and output switching

• Control calibration relays

• Record the output of the Magnitude and Phase detector

• Evaluate the recorded values of the detector and outputs to find circuit breaker state

• Communicate circuit breaker state data to a main unit

• Receive and execute commands from the main unit

[0051 ] Figure 1 1 is an illustrative schematic of connections for monitoring a circuit breaker in a three phase system. A cable unit comprised of three sense units 210a, 210b, 210c, i.e., with attached voltage sense, current sense and calibration circuitry is connected across each pair of contact arrangements of a circuit breaker phase with two contact arrangements in series.

[0052] A respective testing unit 200 contains the HF generation, calibration circuitry, measurement input, control circuitry, output and input switches and protection 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 main unit 230 also supplies power to the three cable units. State for the circuit breaker is monitored by a circuit breaker analyzer 240, which is a computer connected to the main unit 230. The circuit breaker analyzer 240 connects to the main unit 230 to record contact state. It also controls the circuit breaker operation and records the timing of the contact state changes during a preset measurement time.

[0054] A time stamp is set when the circuit breaker analyzer activates the trip or close coils in the operation mechanism(s) of the circuit breaker. Times and circuit breaker state data are recorded during the circuit breaker operation and presented to the operator/test personnel. [0055] The method for analyzing a contact arrangement according to the invention will now be described in detail. The method is applied on a circuit breaker phase comprising a first contact arrangement CB1 and a second contact arrangement CB2 electrically coupled in series, wherein each of the contact arrangements preferably comprises a main contact and a pre-insertion contact connected in parallel, as described above with reference to Fig. 2.

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

[0057] A test voltage is applied 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. Then a test voltage is applied 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. These two steps are repeated 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.

[0058] Figure 12 is an oscilloscope picture of the measured signals from the sense units 210a, 210b, 210c when performing the method according to the invention. The signals include the voltage across the currently measured contact arrangement (V_ATT) , the current through the currently measured contact arrangement (l_ATT), the magnitude output from the detector, i.e., the ratio between the voltage and the current (V/l_RATIO) and a status signal CHAN_1 displaying which output/measurement channel is presently active. In the present case, the first contact arrangement CB1 is measured when the signal CHAN_1 is high and the second contact arrangement CB2 is measured when the signal CHAN_1 is low. Thus, the oscilloscope picture shows the signals present when the test device is set to switch or toggle between two contact arrangements in series. Switching or toggling takes place repeatedly preferably every 12.5 με, thus enabling each contact arrangement state to be sampled/monitored every 25 με; thus at a rate of 40 kilo samples per second, although other sampling rates are possible. Thus, the duration between each switching or toggling may be for example between 5 - 50 με or more preferably between 10 - 20 με. As seen from the figure the voltage measured across the open contact arrangement CB2 is higher while the current is lower compared to the voltage and current from the contract arrangement CB1 , which is in closed state.

[0059] The output voltage V/l_RATIO corresponds to the presently monitored contact arrangement impedance. This is sampled at the time of switching or toggling to the other channel. The oscilloscope picture shows for the first cycle at what point the first contact arrangement CB1 is sampled, designated "Sampling CB1 ", and at what point the second contact arrangement CB2 is sampled, designated "Sampling CB2". This sampling is repeated for every cycle. As can be seen from the picture, the first contact arrangement C1 is closed, i.e., the ratio has a low value corresponding to a low impedance, and the second contact

arrangement CB2 is open, corresponding to a high impedance. The ratio is evaluated and the contact states of the contact arrangements are presented to the circuit breaker analyzer 240.

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

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

Claims

1 . A method for analyzing a circuit breaker phase (100) comprising a first contact 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) 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 e) 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.

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

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

4. A system for analyzing a circuit breaker phase (100) comprising a first contact arrangement (CB1 ) and a second contact arrangement (CB2) electrically coupled in series, comprising:

- a testing unit (200) comprising a generator block (202) and a measurement block (204), c h a r a c t e r i z e d b y

- a first sense unit (210a), a second sense unit (21 Ob), and a third sense unit (210c) connected to the testing unit (200) and connectable to a circuit breaker phase (100), the sense units being adapted to sense operating parameters for the testing of the circuit breaker phase (100), and a controller connected to the generator block (202) and the measurement block (204) and adapted to execute the method according to claim 1 .

5. The system according to claim 4, wherein the first sense unit (210a) is connectable 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 between the 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 side of the second contact arrangement (CB2).

6. The system according to claim 4 or 5, wherein the first, second, and third sense units (210a, 210b, 210c) are provided as separate units connected to the 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 the testing unit (200) and being adapted to connect one side of a contact arrangement to another side in order to get a known state when tuning the generator block (202) and calibrating the measurement block (204).

9. The system according to any one of claims 4-8, wherein the generator block (202) comprises a generator (V1 ) adapted to generate a signal, preferably a sinus signal (HF), where the controller is adapted to set the frequency to suit the impedance 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.