Support for EGIL200 circuit breaker analyser
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. Ensure that 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 you’re using a digital angular transducer, there is no need to check this since it can rotate multiple times.
The first time you measure, e.g., a close operation, you select the operation sequence with the “Sequence” button in the lower right of the screen. When you want to make a second recording of the same sequence (i.e., close), you mark the “Tmg Cls” label in the menu to the left of the graph window and then turn the “Operate/Measure” rotary switch.
The printer has an LED status light that indicates several situations.
- The green status light is on: Normal conditions
- Yellow light flashing with:
- 2 Flashes: the printer is overheating; let it cool and try again
- 3 Flashes: out of paper; replace with a new printer roll
- 4 Flashes: paper is jammed; open the lid and clear the jam
To replace the paper roll, gently press the green button upwards. Doing so will open the lid. Remove the old roll and replace it with a new one, making sure to feed a few centimetres of paper through the paper slot.
Note: the paper has a front side and a backside. If, when printing results, the paper comes out blank, open the lid and rotate the paper roll so the paper feeds in the opposite direction. Try printing again.
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. When there is an X relay in the control circuitry, you must subtract the time to energise the X relay 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.
A slow operation with a correct velocity 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
A 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 (reclose), 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 1/2 to 2/3 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 that's 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 springs. One of the opening springs 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 increased 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, supply 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 spring 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.
User guides and documents
Software and firmware updates
Under the main menu, select the “Breaker” list, choose the breaker you want to test, and create a “New test”.
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 circuit breaker accessories.
On the “Test" tab, the “Phase” selection setting allows you to cycle between individual phases and all three phases at once.
On the “Test” tab, turn on the “Motion measurement” under the “Timing measurement”. From here, you can select “analogue” or “digital” for motion measurement type. Select the appropriate transducer settings, i.e., linear, rotary, conversion table (if needed), and speed calculation points. View the “Connections" screen for how to connect the transducer to the EGIL200. You will need one or three transducers depending on whether the circuit breaker has a common operating mechanism for all three phases or individual mechanisms for each phase.
The EGIL200 can measure wet or dry AUX contacts. Dry contacts are contacts that do not have any voltage present on them. Wet contacts are contacts with a voltage present when they are closed. The max voltage the AUX contact can be connected to is 250 V AC and +/- 300 V DC. To turn on AUX contact measurements, select “AUX” under the measurement section on the “Test” tab. The EGIL200 will automatically sense if the contact is wet or dry.
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.
Yes. You need an external power source to operate a circuit breaker’s coils or to 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.
The licence key for CABA Win is printed on the manual that comes with your analyser and on your CD or flash drive containing the software. It is an alphanumeric key that starts with “CABA.”
If available, follow the circuit breaker manufacturer’s recommendations. You can often obtain this information in the circuit breaker manual or by consulting the manufacturer. If unable to secure the manufacturer’s recommendations, the general guidance is to find a convenient place to attach the transducer. If possible, attach a linear transducer directly to the contacts or to 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 the most convenient. When the transducer is 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 you select a transducer and determine a mounting method, you should use the same transducer type and mounting location for future testing to compare results.
Megger provides multiple transducers and transducer mounting kits for both rotary and linear transducers. Some are breaker specific, while others can be used on various circuit breakers. You should connect one transducer per each mechanism. Generally, a rotary transducer is used for live tank breakers. In contrast, 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 measuring the motion of VCBs. Megger has an accessories data sheet with a complete list of available transducers. If unsure about which types of circuit breakers you may encounter, the rotary mounting kit and an SF6 dead tank kit will cover most high voltage SF6 circuit breakers. The 50 mm transducer and bulk oil transducer kit will cover most VCBs and bulk oil breakers if needed.
The circuit breaker manufacturer typically provides speed calculation points. These should be on 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 your circuit breaker manufacturer.
- 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 to 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. Also, you can 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 the 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. When performing an open-close (reclose) operation, you must 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.
Basic testing for all breakers is the same. You want to record coil current, station voltage, contact resistance, contact times, and travel and, from there, calculate specific parameters. The main difference between a vacuum circuit breaker and an SF6 or OCB is that the stroke will be much shorter.
NETA recommendations for motion tests depend on the type of circuit breaker. According to NETA ATS and MTS, time and travel analysis is recommended but not required for medium vacuum circuit breakers. For oil circuit breakers and SF6 circuit breakers, NETA requires a time and travel analysis.
On the “Test” tab, turn on coil current measurements, select clamp, and click on individual measurement. You will need three current clamps connected to the analogue channels, as shown on the “Connections” screen. Connect the clamps around the individual control wires supplying the coils. You can choose either the positive or negative wire; verify that the polarity of the clamp aligns with the current flow.