Circuit-breaker timing and motion tests are diagnostic fingerprints of the complete release, latch, linkage, contact and damping system. They should not be reduced to one opening-time number: pole spread, auxiliary contacts, coil current, travel, velocity, contact wipe, overtravel, rebound and operating voltage explain whether a “fast” result is healthy or mechanically unsafe.
This FAT guide aligns timing definitions with IEC 62271-100 and shows how to use systems such as OMICRON CIBANO 500 without turning a test-set template into the acceptance authority. It covers test boundaries, contact channels, coil initiation, transducers, trace interpretation, tolerances, low-voltage nuance, operation sequences, restoration and records.
Executive conclusions
- Use IEC definitions and the breaker manufacturer’s model-specific limits; there is no universal acceptable opening/closing time for all MV breakers.
- Define time zero precisely—normally the electrical command at the specified coil terminals/test system—and identify main-contact state criteria.
- Measure all poles simultaneously with the same reference to calculate pole simultaneity/spread.
- Record actual DC voltage at the coil during operation and coil-current waveform; source setpoint alone is insufficient.
- Timing at nominal auxiliary voltage and minimum-pickup/operation testing answer different questions.
- IEC operation at a minimum specified voltage does not automatically guarantee the nominal timing window at that voltage unless the standard/contract/manufacturer explicitly states it.
- Faster is not automatically better: incorrect latch release, excessive velocity, insufficient wipe, overtravel/rebound and mechanism stress can accompany an abnormally short time.
- Opening time is not total fault-clearing time; protection time and arcing time/current zero are separate.
- Motion-sensor geometry and calculation point must be manufacturer-defined; an attractive curve from a poorly mounted transducer is invalid.
- Use test-set libraries as controlled templates and reporting aids, then verify every limit, wiring and calculation against approved source data.
1. Definitions that must not be mixed
| Quantity | Practical meaning | Typical boundary |
|---|---|---|
| Opening time | From opening release energisation to contact separation as defined | Coil command → main contact transition |
| Closing time | From closing device energisation to contact touch as defined | Close command → main contact transition |
| Break time | Opening time plus arcing interval to current interruption | Trip release → final current interruption |
| Arcing time | Contact separation to current interruption | Depends on current waveform/current zero |
| Clearing time | Protection/logic/output + breaker break time | Fault inception → interruption |
| Pole spread | Latest minus earliest pole transition for same operation | All main-contact channels, common time base |
Offline contact timing detects the change of electrical contact state; it does not reproduce arcing current or calculate the actual system current-zero interruption interval.
2. Acceptance sources
- contracted IEC 62271-100 edition/amendment and relevant definitions;
- breaker nameplate/data sheet and manufacturer routine/FAT procedure;
- model/mechanism-specific nominal values and tolerances;
- type-test/routine-test report or factory baseline for the exact serial/type;
- rated operating sequence and auxiliary-voltage range;
- travel/velocity/wipe/overtravel measurement method and transducer geometry;
- project protection-clearing study where system performance is being assessed;
- approved test-set template revision and engineering review.
IEC defines requirements and test methods, but acceptance of an individual breaker’s measured milliseconds is often tied to declared/manufacturer characteristics. Never import a 45 ms limit from another mechanism merely because both are 12 kV vacuum breakers.
3. Test equipment and channels
- simultaneous main-contact timing channels for all poles;
- auxiliary-contact dry/wet channels for 52a, 52b and mechanism switches;
- controlled trip/close coil supply or monitored station DC;
- coil-current and coil-terminal-voltage recording;
- linear/rotary motion transducer with approved fixture/scale;
- motor current/charging time channel where required;
- test software/template with defined trigger, thresholds and sample rate;
- calibration/functional verification for timing, voltage, current and motion channels;
- safety warning/exclusion and safe discharge arrangements.
OMICRON’s official CIBANO 500 information describes a combined micro-ohmmeter, timing analyser and AC/DC coil/motor supply. Its CB TN3 accessory acquires linear/rotary motion data, and IOB1 expands synchronous auxiliary-contact and coil/motor channels. These capabilities support the method; approved IEC/manufacturer limits remain the acceptance source.
4. Safety and breaker state
- Primary circuit de-energised, isolated, discharged and earthed under approved procedure.
- Breaker removed/test position or connected test configuration explicitly defined.
- Stored spring/hydraulic/pneumatic energy and moving-part exclusion controlled.
- No person or sensor cable in linkage/pinch zones.
- Remote/local sources prevented from unexpected operation.
- Coil/motor supply current and polarity suitable; suppression circuits understood.
- Test leads cannot obstruct racking, shutters or mechanism.
- Operation count, duty cycle and mechanism cooling/recharge limits controlled.
- Test ends with breaker in the agreed transport/as-left state.
5. Wiring and time zero
- Connect each main-contact channel to the designated pole terminals.
- Confirm contact-channel test voltage/current is suitable and does not pass through VTs/arresters/electronics.
- Use the actual trip/close coil circuit or clearly state if mechanism is directly driven by the test set.
- Define time zero as the test-set output, coil-terminal voltage threshold or other approved reference.
- If interposing relay/control wiring is excluded, the measured time will not include its delay.
- If the full panel control circuit is included, record that boundary and DC voltage drop.
- Verify dry/wet auxiliary inputs and polarity.
- Perform a stationary channel sanity test before operating the breaker.
Two test teams can report different “opening time” for the same breaker if one starts at PLC command and another at trip-coil energisation. The boundary must appear in the report title/diagram.
6. Main-contact timing
- Verify initial contact state and mechanism charged/ready.
- Set/measure coil supply at the required test condition.
- Arm simultaneous contact, voltage/current and auxiliary channels.
- Issue one open or close command.
- Record each pole transition and calculate spread.
- Repeat the manufacturer-specified number of operations, respecting duty.
- Preserve each valid result; do not report only the fastest/best.
- Compare individual operations, pole consistency and declared limits.
- Investigate drift, scatter, double transitions or contact bounce.
7. Pole simultaneity
For one operation:
Δtpoles = max(tL1, tL2, tL3) − min(tL1, tL2, tL3)
- Use simultaneous channels/common trigger.
- Check instrument threshold and contact wetting are equal.
- Compare opening and closing spread separately.
- Correlate an outlier with linkage adjustment, pole travel, damping and contact resistance.
- Do not average the three pole times and hide spread.
- Use manufacturer/IEC-declared tolerance, not a generic project habit.
8. Auxiliary contact timing
- Record 52a/52b make/break relative to main-contact transition.
- Verify break-before-make or make-before-break behaviour required by design.
- Check TCS, anti-pumping, motor control and position logic windows.
- Identify chatter/bounce that can create multiple SOE or logic transitions.
- Confirm physical auxiliary switch adjustment and full mechanism stroke.
- Test panel/SCADA indication end to end after mechanical timing.
An auxiliary contact is not the main contact. It can indicate early/late or be misadjusted while the interrupter operates correctly; measure both when sequence matters.
9. Coil-current and voltage signatures
A DC coil current trace reflects electrical and mechanical stages: inductive current rise, armature motion, latch release, plunger stop and circuit interruption. Interpretation is model-specific.
- Record voltage at coil terminals throughout the operation.
- Record current peak, shape, key transition times and total energisation.
- Compare phases only if separate coils and identical circuits exist.
- Compare with manufacturer/factory baseline at the same voltage/temperature.
- Low voltage, high wiring resistance or current-limited source can lengthen time.
- Changed signature can indicate sticky latch, plunger friction, shorted turns, wrong coil or suppression diode.
- Do not diagnose exact mechanical fault from one waveform without model reference/inspection.
10. Motion transducer setup
- Use manufacturer-approved access point and fixture.
- Identify linear/rotary ratio between measured shaft and contact travel.
- Set direction, zero, scale and mechanical limits before operation.
- Ensure sensor/fixture cannot detach or obstruct full stroke.
- Use adequate sample rate/filter without smoothing away bounce.
- Record transducer type, range, serial, attachment photo and calculation method.
- Validate final travel against physical mechanism/reference where possible.
- Remove fixture and restore covers/seals after test.
11. Motion quantities
| Quantity | What it can reveal | Caution |
|---|---|---|
| Total travel | Stroke/adjustment/linkage | Sensor ratio and reference point |
| Contact wipe/insertion | Contact pressure reserve | Model-specific derivation |
| Velocity in defined window | Energy transfer/interruption performance | Window must be manufacturer-defined |
| Overtravel | Motion beyond final rest position | Excess can stress mechanism |
| Rebound | Return after overtravel | Damper/latch condition |
| Contact bounce | Repeated make/break near transition | Electrical threshold affects detection |
| Timing scatter | Repeatability/friction/latch variation | Keep voltage/temperature/state equal |
12. Velocity calculation
Average velocity over a defined window is:
vavg = (x2 − x1) / (t2 − t1)
Results depend strongly on window selection. “Maximum velocity,” “average around contact separation” and “average over full stroke” are different quantities. Use the manufacturer’s specified points; do not adjust the window after seeing the curve to obtain a passing value.
13. Is faster opening always better?
No. Protection studies need sufficiently fast clearing, but the breaker mechanism and interrupter are designed as a coordinated system. An abnormally fast measured operation can indicate:
- incorrect latch/linkage adjustment or reference definition;
- excessive mechanism energy/velocity;
- insufficient contact wipe or wrong sensor ratio;
- damper/buffer malfunction and excessive overtravel/rebound;
- high mechanical stress, bounce or reduced repeatability;
- timing boundary that excludes a control/interposing delay;
- test-voltage/source above the intended condition.
Interruption also requires dielectric recovery and current-zero behaviour; offline opening time alone does not prove short-circuit break performance. Accept the manufacturer/IEC declared window, travel and velocity together—neither “as fast as possible” nor arbitrary slowing is sound.
14. Operating sequences
- single O and C operations for baseline;
- CO, OC or O–t–CO sequence only as rated/required;
- autoreclose sequence with correct dead time and mechanism readiness;
- anti-pumping/trip-free sequence with overlapping commands;
- dual trip/close coil tests where supplied;
- minimum-voltage pickup/operation as a separate test;
- motor/spring recharge time before the next rated sequence.
OMICRON’s IOB1 official description notes synchronous control/recording of multiple coils and auxiliary contacts for complex CO sequences. The breaker’s rated sequence and manufacturer duty remain controlling.
15. Nominal versus minimum auxiliary voltage
Separate three questions:
- Does timing at rated/declared reference voltage meet the manufacturer window?
- Does the breaker operate reliably at the specified lower limit measured at the coil terminals?
- Does the contract/manufacturer also require a timing window at that lower limit?
The answer to question 2 does not automatically make question 3 “yes.” Coil force/current decreases with voltage and operating time may lengthen. Record the requirement accurately and do not fail a breaker against a timing tolerance that was never specified at minimum voltage.
16. Failure diagnosis
| Finding | Possible checks |
|---|---|
| All poles slow | Coil voltage/current, latch friction, mechanism energy, temperature, test boundary |
| One pole slow/spread high | Linkage/pole adjustment, damper, contact travel, sensor/channel |
| High operation scatter | Supply regulation, latch friction, mechanism readiness, trigger threshold |
| Excess overtravel/rebound | Damper/buffer, energy, linkage and sensor scaling |
| Aux contact early/late | Aux switch cam/adjustment and physical main-contact relation |
| Abnormal coil signature | Wrong coil, wiring drop, suppression, plunger/latch friction |
- Preserve first trace and exact test state.
- Verify wiring, threshold, voltage, channel and sensor geometry.
- Repeat only enough to establish reproducibility within operation limits.
- Open NCR and obtain manufacturer-approved inspection/adjustment.
- After correction, repeat timing, motion, coil current, resistance and functional/interlock tests affected.
- Retain before/after traces and update operation count.
17. FAT report
- breaker/panel serial, type, mechanism and operation count;
- standard/procedure/manufacturer limit source;
- test boundary/diagram and time-zero definition;
- coil rated/applied/terminal voltage and current trace;
- all pole open/close times and pole spread per operation;
- 52a/52b timing and sequence;
- transducer/fixture/ratio and travel/velocity/wipe/overtravel/rebound;
- test-set/template/software/firmware and calibration;
- ambient/mechanism state and operation sequence;
- raw traces, accepted results, NCR and retest;
- final settings, removed sensors/leads and as-left breaker state.
Common mistakes
- Reporting one average instead of each pole and spread.
- Not defining time zero/test boundary.
- Using supply setpoint instead of coil-terminal voltage.
- Selecting a generic template limit for the wrong breaker.
- Assuming fastest is best.
- Calling opening time total clearing time.
- Using an unverified motion ratio/window.
- Reporting only the best of repeated operations.
- Applying nominal timing tolerance at minimum voltage without a requirement.
- Adjusting mechanism without full regression and operation-count record.
Official standards and primary references
- IEC 62271-100:2021+AMD1:2024 — current AC circuit-breaker definitions, rated sequence and test requirements.
- IEC 62271-1:2017+AMD1:2021 — current common operating/control requirements.
- IEC 62271-200:2021+AMD1:2024 — current assembly integration/routine-test requirements.
- OMICRON CIBANO 500 official information — integrated timing, micro-ohm and coil/motor-supply capabilities.
- OMICRON CB TN3 official information — linear/rotary motion-acquisition accessory.
- OMICRON IOB1 official information — synchronous auxiliary-contact and coil/motor channel expansion.
Engineering note: A test set measures; it does not define the breaker’s acceptance limits. Always preserve the manufacturer-approved timing/motion method for the exact mechanism.