Operation, timing and mechanism
Circuit breaker timing and travel analysis records when each pole's contacts part or touch and how the moving contact travels during opening and closing. It reveals slow or sticky mechanisms, pole disagreement, excessive bounce and worn linkages that insulation and resistance tests cannot see.
Timing and travel analysis is a mechanical performance test for circuit breakers. A timing instrument connects across each pole's main contacts and, usually, to a motion transducer on the operating mechanism, and it records the sequence of events during an operation. For a close operation it captures the moment the control signal is applied, the moment each pole's contacts touch, and any bounce afterward. For an open operation it captures the moment each pole's contacts part. A travel transducer adds a curve of contact position against time, from which speed, overtravel, rebound, contact wipe and total stroke can be derived. Combined operations, such as close-open, open-close and open-close-open reclosing duties, are recorded where the breaker is built for them. The test applies to medium-voltage and high-voltage air, oil, vacuum and SF6 breakers, to circuit switchers and reclosers, and, in a closely related form, to the transfer time of automatic transfer switches. Low-voltage molded-case breakers have no practical travel access and are not tested this way.
A breaker has to open and close within a narrow window of time and speed to do its job. If it is too slow to interrupt, the arc lasts longer than the interrupter was designed for, which can damage contacts, overheat the medium or lead to a failure to clear. If the poles do not move together, a three-phase system sees unbalanced conditions during switching, and a closing pole that lags can cause damaging overvoltages or fail in a synchronized switching scheme. Weak springs, hardened lubricant, worn latches, a loose linkage or a sticking dashpot show up in a travel curve long before they cause a failure to operate. Because mechanisms are the most common cause of breaker failures, a trending timing record is one of the most useful pieces of maintenance evidence an owner can hold. The test also finds problems that follow reassembly or an overhaul, such as incorrect adjustment of linkages, contact wipe or the stroke, before the breaker is returned to service.
Contacts act as switches in the timing circuit. While the contacts are closed, the circuit through the pole is complete, and when they part it opens, so the instrument detects the instant of change as a time stamp relative to the initiating command. Where a pole has several interrupters or resistors in series, the instrument may see more than one event and can separate them. Travel is measured by a transducer, either a linear or a rotary type, coupled to the moving part so that position is sampled continuously. Plotting position against time gives a curve whose slope is speed. Features on the curve tell their own stories: a flat start suggests a delay or lash in the linkage, a slow middle suggests friction or a weak driving force, a sharp end suggests the dashpot or damper, and oscillation near the end suggests rebound or bounce. The time of each event is meaningful only in relation to the control signal that began the operation and to the control voltage supplied, because coils and motors respond more slowly at lower voltage. This is why the conditions of the test are recorded together with the traces.
The breaker is taken out of service, isolated, grounded as the owner's procedures require, and its stored energy is handled safely, since springs and hydraulic or pneumatic systems can operate without warning. The instrument leads are connected across the main contacts of each pole in a way that provides a dependable, low-noise circuit, and ground connections are arranged so that the test does not depend on the system ground. For a travel curve, the transducer is mounted to the manufacturer's recommended point and calibrated for the stroke, so that the measured length and the breaker's own markings agree. Control power is supplied at the voltage the manufacturer specifies for the control circuit, because coil and motor behavior depend on it. The breaker is then operated from its control circuit, from a close or a trip initiation from the test instrument, and the traces for each operation are captured. Typical sequences are close, open, close-open and, when the breaker is rated for it, open-close-open. Each operation is repeated so that the traces confirm repeatability. For breakers with a close resistor or a pre-insertion element, the extra contacts are measured too. Between operations, the breaker is allowed to recharge its springs or pressure, and the operation counter is read before and after.
The record holds the timing results for each pole and type of operation, the quantities derived from them, and, where travel was measured, the motion curves themselves. It identifies the breaker and its mechanism, the control supply used, the transducer and its calibration, the instrument, and the conditions of the mechanism at the time. The as-found state, including any recent operation, lubrication or adjustment, is noted. These details let a later reader tell a real change in the breaker from a change in the test setup, which is the whole value of keeping timing results for comparison over the life of the equipment.
Results are judged by comparison, and this page gives no time or speed values. The first comparison is with the manufacturer's published operating times and travel curve for the breaker type, which are the primary reference. The second is the spread between poles for the same operation, where closing or opening of the three poles is expected to occur close together, and the allowed spread is set by the published criteria and by the application. The third is the comparison of the new trace with the baseline recorded at acceptance and with earlier maintenance traces, where a trend toward longer times, lower speed or more bounce matters even when each value is still in range. The fourth is repeatability between operations of the same type. ANSI/NETA ATS-2025 and ANSI/NETA MTS-2023 list timing and motion analysis among the tests for breakers, and the published manufacturer data govern the values. Reviewers read the shape of the curve as well as the numbers. For the actual figures, refer to your own licensed copies of the standards and the manufacturer's instructions.
At acceptance the test establishes the baseline curve and confirms that adjustments from the factory survived shipping and installation. In maintenance, it checks the mechanism against that baseline and is often repeated after an overhaul or a trip on fault. Equipment class changes the practice. Vacuum breakers are checked for contact travel and overtravel, because wipe is a measure of contact wear that cannot be seen from outside. Oil and SF6 breakers with several interrupters per pole may show multiple events per pole. Air breakers with spring-charged mechanisms are tested at the specified control voltage and, where required, at reduced voltage to check coil margin. High-voltage breakers may be tested with the instrument in a way that includes the closing resistor stage. Automatic transfer switches are timed for transfer and retransfer duration in a related form of the test, and reclosers are timed over their reclosing sequence. Some designs offer no practical access for a travel transducer, so only contact timing is done.
The equipment classes and standard sections that call for this test, and the UltraDb forms that carry it.
Timing records when each pole's contacts part or touch relative to the command. Travel analysis adds a position curve from a transducer on the mechanism, which gives speed, overtravel, bounce and stroke. Timing alone can show pole disagreement, while travel curves reveal friction and mechanism wear.
A three-phase system is designed for balanced switching. If one pole lags, the circuit sees unbalanced conditions, which can cause overvoltages or stress equipment, and some schemes depend on precise closing instants. Published criteria set the allowed difference for each application.
Yes. Trip and close coils and charging motors respond more slowly at lower voltage, so the test is run at the specified control voltage and the voltage is recorded. Reduced-voltage operation is a separate check of the coil margin, covered by the minimum pickup test.
The interval depends on the breaker type, duty, history and the owner's maintenance program, and published maintenance guidance in ANSI/NETA MTS-2023 and the manufacturer's recommendations apply. Testing after an overhaul or a fault operation is common practice, and a trend of results is more useful than any single test.
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