Timing tests serve the purpose of determining the durations for operations such as opening (tripping), closing, close - opening, and reclosing. These time measurements are crucial for ensuring the safe and reliable operation of circuit breakers, thus being a key outcome of proper circuit breaker design.
The main contact times are verified after production, during commissioning, and while the circuit breaker is in - service as part of periodic maintenance. To conduct these tests, timing test devices need to be connected to both the coils and the main contacts of the circuit breaker.
Industry standards define the operation time as the interval from the moment the coil is energized until the main contacts open or close. A typical timing test device applies a voltage to the coils and utilizes an internal clock to measure the time elapsed until the state of the main contacts changes. Generally, there are two main methods employed to detect this state change:
- Voltage divider method: This method measures the change in voltage.
- Resistance threshold method: It measures the change in resistance.
However, these two methods are inapplicable when both sides of the circuit breaker are grounded, since the signal change becomes undetectable in such cases.
There are alternative test methods available:
- Dynamic capacitance measurement (DCM)
- Current sensor measurement (CSM)
The accompanying photo depicts a timing test connection to switchgear (on the left) and time curves (on the right).
