Contact Resistance Meter
What is a circuit breaker?
A circuit breaker is a switching device that interrupts the abnormal or fault current. It is a mechanical device that disturbs the flow of high magnitude (fault) current and in additions performs the function of a switch. The circuit breaker is mainly designed for closing or opening of an electrical circuit, thus protects the electrical system from damage.
There are many types of circuit breakers on the basis of the medium of arc extinction such as Oil circuit breakers, Minimum circuit breakers, Air blast circuit breakers, Sulphur hexafluoride circuit breakers, Vacuum circuit breakers, Air break circuit breakers.
Why Circuit Breaker Contact resistance measuring is Important?
The contact resistance test measures the resistance of electrical contacts of circuit breaker, isolators& bus bar. The contacts in the circuit breaker needs to be checked periodically to ensure that the breaker is healthy and functional. Poorly maintained or damaged contacts can cause arcing, loosing phase, and even fire. It measures the resistance at the micro- or milli-ohm level and is used primarily to verify that electrical connections are proper. It helps to detect loose connections, eroded contact surfaces, contaminated or corroded contacts. It is important for contacts that carry large amounts of current as higher contact resistance leads to higher losses I2R and lower current carrying capacity.
How Testing Done
The two common checks conducted on the contacts of a circuit breaker are the visual inspection check and the contact resistance check.
- The Visual inspection check involves examining the contacts of the circuit breaker for any pitting marks due to arcing and worn or deformed contacts.
- The second check is the contact resistance measurement. This involves injecting a fixed current, usually around 100A, 200A and 300 A through the contacts and measuring the voltage drop across it. This test is done with a special contact resistance measuring instrument. Then, using Ohm’s law, the resistance value is calculated. The resistance value needs to be compared with the value given by the manufacturer. The value should also be compared with previous records.
Both these tests need to be done together. As there are cases of contacts having good contact resistance yet being in a damaged condition. Thus, for a contact to be certified healthy, it needs to have a good contact resistance and should clear the visual inspection test.
MVT by Crest (Millivolt Drop Tester)
The Millivolt Drop Tester is a powerful, digital millivolt drop-cum-contact resistance meter consisting of a 20×4 line LCD, an in-built continuous DC source of up to 200A, no ON-OFF duty cycle, and ability to measure contact resistances of a variety of test objects like circuit breakers, isolators, bus-bars. Thus MVT is an ideal preventive maintenance tool for measuring critical resistances. New PLC controlled smart MVT with an ability to program tests through HMI and store results on a flash drive.
- Continuous current injection of up to 200A DC and direct display of micro-ohm value.
- Selectable continuous current injection of 20, 50, 100 & 200A DC for testing wide range of objects with lower current ratings and higher resistances and vice versa.
- Single LCD to display current and resistance/ millivolt-drop value.
- Resistance ranges of 5 micro-ohm to 10 milli-ohm @200A , 10 micro-ohm to 20 milli-ohm @100A & from 10 milli-ohm to 100 milli-ohm @20A.
- Resistance Auto-Ranging facility for certain models.
- No need for lead resistance compensation as Kelvin's four-wire measurement method is used.
- Easy to operate instrument supplied in DIN standard enclosure or in a carrying case. A movable trolley can also be provided as an option.
- Supplied with 15 meter long, factory-calibrated test lead set with specially designed Ck/Crocodile clamp suitable for EHV class test objects.