For many industries that rely on mission critical power, a constant flow of electricity is essential to not just keeping the basic functions of the business running; oftentimes it can mean the difference between life and death.
A proactive approach is the best way to defend against downtime or outages. Condition based maintenance or monitoring is a complete program that takes preventative measures and testing to ensure a constant flow of power. Breaker settings, cleaning, testing and calibration is a big part of this program.
Typically, every breaker consists of the following:
- trip units and/or relays
- breaker assembly
- arc chutes or vacuum bottles
- control panels
- operating mechanism
Testing, Settings and Calibrating the Circuit Breaker Trip Units and Relays
The overcurrent relay is the most commonly used relay to protect the power distribution system. Its function is to sense the overcurrent in a system and provides the circuit breaker tripping operation.
According to the construction type relay and trip units can be categorized as one of the following main categories:
- solid state
The relay operating characteristic is displayed as a logarithm function of operating current and time. The curves typically use log-log scales to cover a wide range of current and time. Curves that are similar appear for overcurrent relays with different time-delay characteristics. Adjusting the operating time of relays is possible. Breaker settings is when the operating time and current value is adjusted by an engineer’s coordination study.
Main kinds of trip settings for standard breaker configuration include:
- Overload protection
- L (LT: long-time delay)
- Short-circuit protection, delayed
- S (ST: Short-time delay)
- Short-circuit protection, instantaneous
- I (inst: instantaneous)
- Earth-fault protection
- G (GF: ground fault)
Once the right setting is found, the next step is breaker testing and the calibration of the relays/ trip units. This will ensure the acting relay or trip unit for a predetermined value. Relay calibration involves complex testing performed on the relay or trip unit to confirm and adjust its trip characteristic. It should be within the limits suggested by the manufacturer. Every relay manufacturer has standard test and service procedures for the wide array of relays offered.
Calibration/Testing of Trip Units
Low-Voltage calibration/testing involves primary injection testing, testing for all the types of trip settings (L,S,I,G) the breaker has and then a round of final testing. The manufacturer’s instructions should be the major guide throughout all testing and procedures. Secondary testing I also an option, but it is only testing the secondary side of the trip unit and will leave out the current-transformers of the testing procedure.
Calibration/Testing of Relays
To test relays, the minimum operating current test and time curve calibration. Time curve calibration / testing ensures that the relay operating time for specific values of current will be as shown on the time current curves. Should the operating time not be within the tolerance for the values of the applied current, the relay should be adjusted to the point that the operating time is correct. Should the operating time not be within the tolerance of the high values of the applied current.
Test results can vary due to conditions and types of instrumentation used, so it should never be assumed that the accuracy of the test equipment is a given. The accuracy can change depending on the frequency with which the tools are used and recalibration. Keeping the data recorded is essential to the accuracy of the entire procedure overall.
A trusted advanced electrical solutions company will be able to take care of all of these procedures to keep your power system running at its best. At Rinzler, our seasoned experts can ensure the constant flow of power to your business, handling all condition-based monitoring including setting, testing and recalibrating of unlimited kinds of breakers, trip units and relays.