Support for the TM1700 circuit breaker analysers
Connect the Ethernet cable between the instrument and the PC, then switch on the TM1700 unit and the PC. In CABA Local, select the “System settings” tab then “Versions”. The IP address of the unit is shown at the bottom of the screen. In some cases, you have to scroll down a little to be able to see the address. If the address appears as 0.0.0.0, wait two minutes to let the PC and the TM1700 establish communication. You can also check the TM1700 to see if it has a sticker with the TM1700 IP address.
In CABA Win, select “Options”, then “System settings”, then the “Communication” tab. Make sure the Ethernet setting is selected. Click on “Scan network”, and a TM host name along with MAC address and IP address should appear in the popup window. Highlight the TM unit and click “OK”. The IP address should automatically appear. If the scan network does not find the TM1700 unit, manually enter the IP address of the TM1700 instrument in the IP address field and make sure the “Port No.” is set to 6000.
Note: CABA Win only connects to the TM1700 unit when it is in measuring mode. You must select a breaker and then a test occurrence. Once “New recording” is clicked, a CABA remote box will appear that connects to the TM1700 unit. For further details, view the CABA Win software run-through video above.
The internal computer battery is faulty, but you can still run a test. Please get in touch with Megger technical support for battery replacement instructions or send the instrument to a service centre at your earliest convenience.
First, press Ctrl+Alt+Del and select “Task Manager”; then, under the “Processes” tab, locate and highlight “HMI.exe” in the drop-down list. Click the button “End Process” in the lower right corner. The desktop will then be displayed, and you’ll need to click “Start” and then “Shut Down”.
The Megger Display mode is disabled. Connect a USB keyboard to the TM1700 instrument. Switch on the TM1700, and as soon as the first text appears on the screen, press the DEL button repeatedly to enter the BIOS setup. The password is “energy”. Navigate to the advanced tab and change the “Megger Display mode” parameter to “Enabled”. Select “Save and Exit” and then click “OK.”
A button under the screen on the lower left turns the touch screen on and off; toggle this button.
Please ensure the proper drivers are installed in the instrument and are created for use with Windows XP. Please refer to “Optional software” in the instrument’s User Guide.
If the circuit breaker has AC coils, the control section can’t detect the auxiliary contacts. If you have a Timing Aux section, set up your breaker in “Breaker view” to measure more than 1 auxiliary contact per mechanism. The Timing Aux section will then measure the auxiliary contact when you connect it to the ‘a’ and ‘b’ contacts. You can also create a test plan with the Test Plan Editor to use the Aux module.
The instrument senses the position of the circuit breaker via the control section, i.e., the operating mechanism position. Therefore, if a common operating mechanism is selected, only one LED indicates the position of the whole breaker. If the circuit breaker has three operating mechanisms, you must hook up control wiring to each mechanism separately to have a position indication of each of the three phases. Additionally, you must turn on “Auto detect” in the settings.
The parameter list is adjustable. If the parameter is not present in the list, you can add it within the Test Plan Editor for your breaker setup. To make the changes in the test plan editor effective, mark the breaker and select “New test” using the CABA Win main program. The subsequent measurements will now contain the added parameters.
If the template in question is defined as the default, you will not be able to delete it. Change the default setting to another template, and then you can delete the template in question.
Go to the “Connection” screen when attaching your transducer and select your motion channel. Here you can check the position of the transducer in monitor mode. Make sure the motion transducer is set at approximately 50 % (40 to 60 %.) Most circuit breaker mechanisms do not move more than 90 to 100 degrees, so this will allow plenty of travel in either direction.
Note: if using a digital angular transducer, there is no need to check this since it can rotate multiple times.
Many circuit breakers (CBs), especially IEEE-designed CBs, have an X-Y relay scheme for an anti-pump circuit. This circuit is designed to protect the interrupter/resistor in the case where two control signals are applied at the same time for an extended period. The close time is measured from the close coil energisation to the first metal-on-metal contact touch. If there is an X relay in the control circuitry, the time to energise the X relay must be subtracted from the overall close time. Note: you can use the Auxiliary contact (Timing Aux) to measure the X relay.
Check all connections on the timing leads, both to the breaker and the analyser. If there is any oxidation or grease at the connection point, try to polish the area where the clamps connect. Check the spring pressure of timing clamps.
This is either an issue with the operating voltage, coil, or latch system. First, check the operating voltage during the operation to verify that it is near the nominal value. If the operating voltage is correct, service the latch system by cleaning and lubricating as needed, or the coil will need to be replaced. See the results interpretation section for further details on measuring coil current.
Redo the measurement with nominal voltage. Measure the voltage throughout the test to verify an adequate voltage source.
Interpreting test results
Time and travel analysis verifies the correct operation of a circuit breaker. It assures that the breaker will be able to clear a fault in a matter of a few cycles. If the circuit breaker has been sitting for months or even years, it must be able to operate at a moment's notice. The best way to evaluate timing results is to compare the measured values against the manufacturer's specifications. The specifications should be in the circuit breaker's manual or on a commissioning checklist. Factory test reports are often delivered with the circuit breaker; they will have specifications or a baseline against which to compare.
If the manufacturer's specifications or baseline results are not available:
- an initial detailed measurement must be performed to generate a baseline. When a network has several of the same breakers, you can generate nominal values and a targeted range of specifications to compare against, adjusting any outliers as needed.
- the information below can be used as a general guideline but by no means applies to all circuit breakers.
Contact times are measured in milliseconds in modern circuit breakers. On older circuit breakers, they may be specified in cycles. The contacts that one evaluates include main contacts, resistor contacts, and auxiliary contacts. Five different operations or sequences are performed while timing: Close, Open, Close-Open, Open-Close, and Open-Close-Open.
The main contacts are responsible for carrying the current when the circuit breaker is closed and, most importantly, extinguishing the arc and preventing a restrike when the circuit breaker opens to clear a fault. Pre-insertion resistor contacts dissipate any overvoltages that can occur upon closing higher voltage breakers attached to long transmission lines. Post-insertion resistors are used on older air blast circuit breakers to protect the main contacts during the opening operation. Both pre-insertion and post-insertion resistors are commonly referred to by the acronym PIR. The auxiliary contacts (AUX) are contacts within the control circuitry that tell the circuit breaker what state it is in and help control its operation.
The circuit breaker is rated in cycles, and this specifies how long the breaker will take to clear a fault. The open contact times will be less than the rated time of the circuit breaker because the open contact time is when the contacts actually part. In operation, once the contacts part, there is still an arc bridging the gap across the contacts that needs to be extinguished. The open contact time should be less than one-half to two-thirds of the rated interruption time of the circuit breaker, and the closing times are generally longer than the open times. The time difference between the three phases, known as pole spread or simultaneity between phases, should be less than 1/6 of a cycle for opening operations and less than 1/4 of a cycle for closing operations, according to both IEC62271-100 and IEEE C37.09. If the circuit breaker has multiple breaks within one phase, these should all operate almost simultaneously. If one contact operates faster than the others, then one break will have a significantly higher voltage on it compared to the others, causing a fault. A tolerance of less than 1/8 of a cycle is required by IEC, whereas IEEE allows 1/6 of a cycle for this intra-pole spread. Even with the limits specified by IEEE and IEC, the simultaneity of most circuit breakers is often specified at 2 ms or less. Contact bounce is also measured with the timing channels. Contact bounce is measured in time (ms) and can often appear on closing operations. Excessive bounce indicates that the spring pressure in the contacts is weakening.
Pre-insertion resistors (PIR) are used in conjunction with the main contacts on closing. The resistor is inserted first to dissipate overvoltages, and then the main contacts follow; afterward, the resistor contact is either shorted out or removed from the circuit. The main parameter to evaluate here is the resistor insertion time; this is how long the resistor contact is in the circuit before the main contacts close. Typical resistor insertion times are between half a cycle and a full cycle. If the main contact is faster than the resistor contact, the breaker is not functioning correctly.
Auxiliary (AUX) contacts are used to control the circuit breaker and let it know its state. The A contacts follow the state of the main contacts, i.e., if the breaker is open, the A contact is open, and if the breaker is closed, the A contact is closed. The B contacts follow the opposite state of the breaker, i.e., the B contact is closed when the breaker is open and vice versa. There are no generalised time limits for the difference between AUX contact and main contact operation. However, it is still important to understand and check their operation and compare them to previous results. The AUX contacts prevent the close and open coils from being energised for too long and burning out. AUX contacts can also control the contact dwell time, i.e., the amount of time the main contacts are closed on a Close-Open operation.
The motion curve gives you more information than any other measurement when performing time and travel analysis. It is vital to understand whether or not your circuit breaker is operating correctly. To measure motion, you connect a travel transducer to the circuit breaker, which measures the position of the mechanism or contacts as a function of time. The transducer will measure either an angular or linear distance. The angular measurements are often converted to a linear distance with a conversion constant or conversion table. A linear measurement can also be converted with a ratio as well. The goal is to translate the motion of the transducer into the actual motion of the contacts and determine the stroke of the main contacts. From the stroke, you can calculate various parameters. If no conversion constant or table is available, the stroke and related parameters can still be evaluated as is but may not match manufacturer specifications.
Velocity or speed is measured on both the opening and closing operations. The most critical parameter to measure on the circuit breaker is the velocity of the opening contacts. A high voltage breaker is designed to interrupt a specific short circuit current; this requires operating at a specific speed to build up an adequate cooling stream of air, oil, or gas, depending on the breaker type. This stream cools the electric arc sufficiently to interrupt the current at the next zero crossover. The velocity is calculated between two points on the motion curve. There are various ways to choose these speed calculation points, the most common being contact touch/separation and a time before/after or at distances below closed or open positions.
The travel curve above represents a Close-Open operation. The stroke of the contacts is measured from the ‘resting open’ position to the ‘resting closed’ position. When the circuit breaker closes, the contacts travel past the closed position; this is referred to as overtravel. After overtravel, the contacts may travel past the resting closed position (towards open); this is the rebound parameter. These parameters (i.e., stroke, overtravel, and rebound) are also measured on the Open operation but are referenced to the ‘resting open’ position as opposed to the closed position.
The opening operation on the graph above shows both overtravel and rebound. The graph indicates where the contacts touch and separate. The distance from contact touch/separation to the resting closed position is referred to as wipe or penetration. The distance through which the breaker’s electric arc is extinguished is called the arcing zone. This is the position on the curve where you want to calculate the trip velocity referenced above. Since the open operations occur at high speeds, a dashpot is often employed to slow the mechanism down toward the end of the travel. The position where the dashpot is in effect is referred to as the damping zone. In many breakers, you can measure damping from the travel curve. Some breakers, however, may require a separate transducer hooked up to measure damping. You can measure damping on both Open and Close operations. Damping can have distance or time parameters associated with the curve.
The stroke of the circuit breaker is very small for vacuum circuit breakers, approximately 10 to 20 mm, and increases in the 100 to 200 mm range for SF6 circuit breakers, with longer strokes required for higher voltages. Older bulk oil circuit breakers can have stroke lengths above 500 mm. If comparing the stroke of two different circuit breakers, they should be within a few mm of each other as long as they are of the same type and use the same mechanism. If you can find no limits, you can compare the overtravel and rebound to the stroke of the breaker; they should be below about 5 % of the total stroke. Any excessive rebound or overtravel should be investigated to prevent further damage to the contacts and operating mechanism; a faulty dashpot is often the cause.
Measuring the operating voltage and coil current on a routine basis can help detect potential mechanical and/or electrical problems in the actuating coils well in advance of their emergence as actual faults. The main analysis focuses on the coil current trace; the control voltage trace will mirror the current curve in operation. The primary parameter for evaluating the voltage is the minimum voltage reached during the operation. The coil’s maximum current (if permitted to reach its highest value) is a direct function of the coil’s resistance and actuating voltage.
When you apply a voltage across a coil, the current curve first shows a straight transition whose rate of rise depends on the coil’s electrical characteristics and the supply voltage (points 1 to 2). When the coil armature (which actuates the latch on the operating mechanism’s energy package) starts to move, the electrical relationship changes, and the coil current drops (points 3 to 5). From this point on, the coil and latch system has completed its function to release the stored energy in the mechanism. When the armature hits its mechanical end position, the coil current rises to the current proportional to the coil voltage (points 5 to 8). The auxiliary contact then opens the circuit, and the coil current drops to zero with a current decay caused by the inductance in the circuit (points 8 to 9).
The peak value of the first lower current peak is related to the fully saturated coil current (max current), and this relationship gives an indication of the spread to the lowest tripping voltage. If the coil were to reach its maximum current before the armature and latch start to move, the breaker would not be tripped. If this peak changes with respect to previous measurements, the first thing to check is the control voltage and to what minimum value it reaches during operation. However, it is important to note that the relationship between the two current peaks varies, particularly with temperature. This also applies to the lowest tripping voltage. If the time between points 3 to 5 increases or the curve shifts up or down in this region, this indicates a faulty latch or a faulty coil. The most common cause is a lack of lubrication in the latch system; cleaning and lubricating the latch is advised.
WARNING: Follow the circuit breaker's safety protocols when performing any maintenance. At a minimum, the control power to the breaker must be off, and the mechanism energy needs to be discharged or blocked before maintenance.
If the latch system is lubricated correctly, the next step is to verify the resistance of the close and open coils to make sure they are correct and replace them as necessary.
The charts below indicate typical failure modes associated with time and travel measurements on high voltage circuit breakers and possible solutions to the problem.
WARNING: Follow the circuit breaker's safety protocols when performing any maintenance. At a minimum, the control power to the breaker must be off, and the mechanism energy needs to be discharged or blocked before maintenance.
|Close time||Open time||Damping time||Charging motor||Possible cause of failure condition|
|Faster / Slower||Normal||Normal||Normal||Change in characteristic of the closing system. Latching system is binding.|
|Faster||Normal||Normal||Normal||Spring charging system used for closing is defective.|
|Slower||Normal||Normal||Normal||Spring charging system used for closing is defective.|
|Normal||Slower||Normal||Normal||Change in characteristic of the closing system. Latching system is binding.|
|Faster||Slower||Normal / Slower||Normal / Slower||Reduced force exerted by opening strings. One of the opening strings is broken.|
|Slower||Slower||Normal / Slower||Normal / Slower||Increased friction throughout the entire breaker caused by (for example) corrosion in the linkage system.|
|Normal||Faster||Normal||Normal||Malfunctioning puffer system or extremely low SF6- pressure.|
|Normal||Normal||Faster||Faster||Damaged opening damper. Not enough oil in the dashpot.|
|Normal||Normal||Slower||Slower||Damaged opening damper. Increased friction in the dashpot.|
|Coil current||Varies with coil resistance and control voltage.|
|Control voltage||Increased voltage drop indicates resistance of the coil supply cables. Must be measured in order to obtain traceability of coil current measurements and timing measurements.|
|Coil resistance||A change could indicate a burned coil or a short circuit between winding turns. Can be calculated from control voltage and peak current.|
|Armature stop time||Increased time indicates increased mechanical resistance in latch system or coil armature.|
|Armature start current||Increased current indicates increased mechanical resistance in coil armature. Gives an indication of the lowest operation voltage (coil pick up).|
|Max motor current||Varies with winding resistance, supplied voltage and applied force. Start current not considered.|
|Motor voltage||Increased voltage drop indicates increased resistance in the motor supply cables.|
|Spring charge motor start time||Closing time of auxiliary contact for the sprint charge motor.|
|Spring charge motor stop time||Increased time shows e.g. higher mechanical friction.|
Micro-ohm measurements, also commonly referred to as static resistance measurements (SRM) or as digital low resistance ohmmeter (DLRO) tests (sometimes also called Ducter™ tests), are performed on the circuit breaker while the contacts are closed to detect possible degradation or damage in the main contacts. If the resistance of the main contacts is too high, there will be excessive heating that can cause damage to the circuit breaker. Typical values are below 50 μΩ on distribution and transmission circuit breakers, whereas generator circuit breaker values are often below 10 μΩ. If the value is abnormally high, repeating the test several times or applying the current for 30 to 45 seconds may be needed to “burn in” the contacts; this will help to push through any oxidation or grease that may be on the contacts. The micro-ohm test results for all three phases should be within 50 % of each other, and any outlier should be examined. Always verify good connections and retest when values are high. IEC requires a test current of 50 A or greater, whereas IEEE requires 100 A or greater.
The DRM test method was developed as a diagnostic test to evaluate the arcing contact wear in SF6 circuit breakers. The test is conducted by injecting a DC current, approximately 200 A or higher, through the breaker and measuring the voltage drop and current while the breaker is operated. A DRM test should not be confused with a static resistance measurement (micro-ohm measurement), which measures contact resistance when a breaker is closed.
The breaker analyser then calculates and plots resistance as a function of time, along with motion, if you use a suitable transducer. When contact movement is recorded simultaneously, you can read the resistance at each point of contact. Since there is a significant difference in resistance between the main contact and the arcing contact, the resistance graph and the motion graph will indicate the length of the arcing contact. In some cases, circuit breaker manufacturers can supply reference curves for the type of contact in question.
User guides and documents
Software and firmware updates
CABA Win circuit breaker analysis software simplifies testing and ensures the quality of the test procedure, and it can be used with Megger circuit breaker testers TM1800, TM1700, TM1600/MA61, and EGIL.
CABA Local – Internal software for TM1700 and TM1800
CABA Local is applicable for installation on below Circuit breaker anlaysers
Yes, you will need an external power source to operate the circuit breaker’s coils or charge its spring motors. If station power is available, you can connect it to the Control module to operate the breaker. You will need a separate power supply if there is no station power. Megger manufactures a power supply called the B10E.
Megger has various leads, accessories, and transducer mounting kits to help make your circuit breaker testing easier. Check out the circuit breaker accessories guide for a complete list of our circuit breaker accessories.
The internal battery of the instrument is a low-power battery for keeping the date and time in the instrument; the TM1700 must be connected to an AC supply.
Yes, if your printer is supported by the Windows XP operating system. Many manufacturers offer drivers for Windows XP for free on their websites. Please consult the manufacturer of the printer before attempting to install the printer.
Yes, the PIR resistance will be measured automatically by the Timing M/R section if the PIR value is between 10 Ω and 10 kΩ. The main and the resistor contacts are measured with the same connection. Note: when using the DCM DualGround™ accessory, you cannot record resistor times and values.
Yes, you can use any incremental transducer with the instrument. Check Appendix A of the User Guide for pin configuration and the type of connector you need.
Yes, connect the slider wire to pin 3 on the analogue channel and the other two wires to pins 1 and 2, respectively. If you have the XLR to banana cable, GA-00040, the slider is connected to the white wire, and the two ends of the transducer are connected to the brown and green wires, respectively.
Connect the current clamp’s negative terminal to analogue channel pin 1 and its positive terminal to analogue pin 3. If you have the XLR to banana cable, GA-00040, the negative terminal is connected to the brown wire and the positive to the white wire.
The licence key for CABA Win is printed on the manual that comes with your analyser and is also printed on your CD or flash drive that contains the software. It is an alphanumeric key that starts with CABA.
The default password is “energy”.
Yes, CABA Local can use the setup with a test plan from CABA Win. You will need to import the circuit breaker into the TM1700. CABA Local will automatically convert the test plan for compatibility. To import a breaker, click on the “Circuit Breakers” folder under the “Breaker List” tab. An “Import Breaker” button will appear to the left of the breaker list. Please refer to the “import a breaker” section in the instrument’s User Guide for further details.
Creating new templates using the Test Plan Editor (TPE) within the CABA Win program is best. Open CABA Win and click on “File”, followed by “Test Plan Editor”. Click on “Edit” and then “New breaker”. Follow the TPE wizard to create a new circuit breaker. Once you have created a breaker, highlight the breaker in the TPE and click on “Edit”, followed by “Create template from selected breaker”. See the “Using Your Product” videos above concerning the TPE for further details.
Open up CABA Win and click on “File”, followed by “Test Plan Editor”. Click on the “Templates” tab and navigate the file tree to find the circuit breaker template. Highlight the breaker type in the tree, then select the template you want in the window to the right. Once you have highlighted the template, click “Edit”, followed by “Create breaker from selected template”.
Note: you should verify the circuit breaker parameters and pass/fail values against the circuit breaker manual or commissioning checklist.
Often it is beneficial to have multiple breaker lists within CABA Win to organise the breakers. To change the breaker list, click “File”, then “Open”, then “Breaker list”. From here, select the appropriate folder.
Timing ensures that the three phases are synchronised and that the contacts are opening at the correct time. Still, travel measurements provide much more information on how the contacts perform. Travel verifies the stroke of the circuit breaker, as well as the velocity of the contacts. The circuit breaker times can be out of specification, but as long as the velocity of the interrupter is correct, it will still be able to clear the fault. Additionally, travel will reveal mechanical issues such as overtravel and over-damping. To simplify transducer connections, Megger provides a variety of transducers and connection adapters that fit multiple circuit breakers.
Yes, the motion of the circuit breaker is measured independently of the timing using a travel transducer. Connect the transducer as you would normally.
If available, follow the circuit breaker manufacturer’s recommendations; you can often find this in the circuit breaker manual or by consulting the manufacturer. If unable to secure the manufacturer’s information, the general recommendation is to find a convenient place to attach the transducer. If possible, attach a linear transducer directly to the contacts or the actuating arm of the contacts; this negates the need for a conversion table or factor. Often this is not practical, so the next best option is to connect to a point as close to the contacts as possible with minimal linkages between the connection point and the contacts. A rotary or a linear transducer may be used depending on what is most convenient. If not connected directly to the contacts, you will need a conversion factor or table to measure correct stroke parameters and contact velocity. Caution: ensure that neither the transducer nor its mounting components are in the path of any moving parts of the mechanism or linkages. Once a transducer and mounting method are determined, you should use them for future testing to compare results.
Megger provides multiple transducers and transducer mounting kits for rotary and linear transducers; some are breaker specific, while others can be used on various circuit breakers. One transducer should be connected per each mechanism. Generally, a rotary transducer is used for live tank breakers, whereas linear transducers are used for dead tank breakers and bulk oil circuit breakers. Vacuum circuit breakers (VCBs) have a short stroke, so often, a small linear transducer, 50 mm or less, is used for the motion of VCBs. Megger has an accessories data sheet with a complete list of available transducers. If you’re unsure of what types of circuit breaker you may encounter, the rotary mounting kit and an SF6 dead tank kit will cover the majority of high voltage SF6 circuit breakers. Additionally, the 50 mm transducer and Bulk Oil transducer kit will cover most VCBs and bulk oil breakers if needed.
The circuit breaker manufacturer often provides the speed calculation points, typically in the commissioning checklist, factory test report, or manual. If no speed calculation points are provided, then the recommended points are Contact Touch and 10 ms before contact touch for the close, and Contact Separation and 10 ms after contact separation for the open. These points provide the velocity of the contacts in the arcing zone of the interrupter.
There are three main ways to do this:
- Contact the manufacturer of your circuit breaker.
- Find the geometric transfer function between the point of transducer attachment and the moving contact and create your own table.
- Make a reference measurement with one transducer attached to the moving contact and one in the desired transducer attachment point. From the result of the reference measurement, you can create a table.
First, make a reference measurement (footprint) of the circuit breaker when it is new and use this to compare future tests. Use the default settings for speed calculation points. Alternatively, if the circuit breaker is older, check to see if several breakers of the same type are available to test. Compare results with other circuit breakers of the same kind; these should be from the same manufacturer and model type, not just the same rated voltage and current. You can also make some checks within the test. For most breakers, all three phases should be within 1 to 2 ms of each other, but occasionally a 3 to 5 ms difference may occur for some older breakers. When the breaker has multiple breaks per phase, the difference between contacts in the same phase should be approximately 2 ms or less. On modern circuit breakers, the trip times should be between 20 to 45 ms, with close times taking longer but generally less than 60 ms.
The control pulse must energise the trip or close coil long enough to release the corresponding latch. As long as the pulses are applied to the control circuitry with working auxiliary contacts, the AUX contacts will interrupt the current, preventing coil burnout. A typical pulse of 100 to 200 ms is sufficient to operate the coil but not long enough to burn out the coil. For a Close-Open operation, a short delay of 10 ms is sufficient from when the close pulse starts to when the open pulse is applied. The open pulse must be applied before the contact physically opens to test the correct Close-Open time. You must take care when performing an Open-Close (Reclose) operation to avoid “pumping” the circuit breaker. A pulse delay of 300 ms is typical to protect the circuit breaker from mechanical damage.
The two predominant standards are:
- IEEE C37.09 IEEE Standard Test Procedure for AC High-Voltage Circuit Breakers Rated on a Symmetrical Current Basis.
- IEC 62271-100 High-voltage switchgear and controlgear – Part 100: Alternating-current circuit breakers.
NETA also has acceptance testing (NETA ATS) and maintenance testing (NETA MTS) specifications that cover a broad range of electrical equipment, including circuit breakers.
DRM entails measuring the resistance of the circuit breaker contacts throughout the opening and closing operations and then plotting the resistance against time. The plot obtained during the opening operation is particularly informative. It will show a step change in resistance as the main contacts open since, at this point, the arcing contacts will carry all of the test current. A short time later, the resistance will increase almost to infinity as the arcing contacts open. By noting the time and/or distance between the operation of the main contacts and the arcing contacts, it is possible to deduce the remaining length of the arcing contacts – something that could otherwise only be determined by dismantling the breaker. This technique does, of course, rely on the availability of dependable information about the motion of the breaker contacts during operation. Still, Megger circuit breaker test sets like the TM1700 series and the TM1800 series provide facilities for accurate motion analysis and DRM and support for dual ground testing.
Yes. For static resistance measurements (SRM/micro-ohm/DLRO), you must measure the current flowing through the ground circuit and subtract this from the total current that the test set provides. You can accomplish this with a current clamp connected to the analogue module using the SDRM module with the TM1700. Megger also has a Mjölner and DLRO100 that allow DualGround™ testing of contact resistance. See the FAQ on GIS and micro-ohm for special considerations when testing GIS.
Dynamic resistance measurements (DRM) can also be measured with both sides of the breaker grounded. Since the key to this measurement is looking at the difference in resistance between the arcing and main contacts, an absolute value of resistance is not needed, only relative resistance.
The first trip test uses small clamp-on current transformers that connect to the coil circuit and the load or protection transformers on the circuit breaker while the breaker is still in service. The breaker is then tripped, and the coil current is measured along with the voltage drop. The current extinction times of the three phases are also measured. The coil current trace and other parameters can be compared to previous measurements to see if the breaker is operating normally. This test ensures that no operation is left unmeasured and gives a picture of ‘real life’ conditions and how the circuit breaker performs after remaining closed for months or even years.
Because the first trip is relatively easy and quick, some people have tried to replace traditional timing tests with first trip testing. However, it is important to remember that first trip testing complements but does not replace off-line time and travel analysis. With first trip, you are comparing previous measurements and trending. In contrast, a time and travel analysis allows you to compare and trend results and verify that the circuit breaker is operating within manufacturer and IEEE/IEC specifications.
If the switchgear has a VDS (voltage detection system) outlet, you can measure timing using any Megger TM1800 or TM1700 circuit breaker analyser in conjunction with a VDS adapter. Connect the adapter to the VDS outlet on the circuit breaker and measure the timing by monitoring the presence of voltage in the primary circuit. The VDS outlet is a low voltage outlet fed from a capacitive voltage transformer inside the switchgear, so you carry out the measurements with the circuit breaker on-line. No disconnections or additional ground connections are needed or possible. You can control the circuit breaker analyser outside the switch room for extra safety.
It will probably be possible to do this by taking advantage of the DualGround™ functionality offered by the TM1700 and TM1800 circuit breaker analysers. You’ll also need the accessory ferrite kit as this lets you temporarily increase the impedance of the ground loop, making it easier for the instrument to achieve accurate results. Most GIS circuit breaker types can be measured by grounding both sides and making connections at the switchgear grounding point. We can give you more detailed guidance if you tell us the details of your switchgear.
Measuring static resistance in GIS switchgear is possible, but you will probably have to do this with both sides of the switchgear grounded. You’ll need to remember that you are only interested in the current that passes through the circuit breaker rather than the total current supplied by the current injector. In GIS switchgear, the ground loop resistance is very low, so this is where most of the injected current will flow. With the TM1700 series and the TM1800 series, you can measure the total current supplied, and with a current clamp, you can also measure the current in the ground loop.
Note: it can be challenging to fit the current clamp with some types of switchgear.
If you have suitable access points, this may be possible. A common issue is that you can only access both sides of the circuit breaker by using DualGround™ measuring techniques. In these cases, it is impossible to carry out DRM tests on GIS switchgear because the ground loop resistance is so low that the opening and closing of the arcing contact in parallel with it produces no measurable change in the overall resistance. The resistance of the ground loop can be less than 100 micro-ohms. In contrast, the resistance of the arcing contact can be up to a couple of milliohms.
The most common method is to connect a rotary transducer to the mechanism. With some ABB circuit breakers, the mechanism is in a box at the top of the breaker, while with some Siemens models, it is at the front. A few models have built-in transducers, but this is rare. You’ll need analogue or incremental (digital) channels in your analyser, a compatible transducer, and a mounting kit to measure motion. The switchgear manufacturer should be able to supply the reference data for motion measurements. According to the IEC, stroke and distance should be measured directly rather than converted. The switchgear manufacturer can advise where the transducer should be attached, which is important as space is often minimal. Different types and sizes of transducers are available, so it should be possible to find one that fits your switchgear.
The instrument is not rated for DC inlet supply. However, several types of DC to AC converters are available on the market. Please get in touch with us for more information.