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.

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.

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 capabilities of the EGIL200 are easily extended by adding software and accessories. Popular examples of additional features are DualGround™, SDRM, and First Trip.

With DRM measurements the arcing contact length in SF6 breakers can be reliably estimated without disassembling the circuit breaker. In SF6 breakers the arcing contact is commonly made of Wolfram (tungsten). This contact burns off and becomes shorter for each interruption of load current. (*)