Contact resistance meters – Sonel MMR-6500 and MMR-6700 micrometers

As a result of burning an electric arc, carbon deposits accumulate on the HV circuit breaker contacts. As a consequence, the actual conduction surface decreases, and the resistance and heating rise, which leads to a fall in the efficiency of the device. Therefore, the power substation may be completely disconnected. To avoid this type of failure, the contact resistance of the switches should be tested periodically. According to IEC 62271-100, this test should be performed with a current from 50 A up to the rated value of the device. The ANSI C37.09 standard indicates that this current should be at least 100 A. In practice, higher values, that more closely match the actual operating conditions of the switchgear, are used.

For such measurements SONEL S.A. has launched micrometers:

• Sonel MMR-6500 with a measuring current up to 100 A,
• Sonel MMR-6700 with a measuring current up to 200 A.

 

Wherever we want to measure small resistances

Many innovative solutions have been introduced to these meters, facilitating measurements as well as enabling tests in situations where it has been difficult or even impossible so far (amorphous transformers). High performance have been provided. The maximum current - 100 A or 200 A - and a resolution of 0.1 μΩ in combination with many measurement modes significantly reduces test time. This is of great importance with a large number of objects to check.

Sonel MMR-6500 and Sonel MMR-6700 microohmmeters can be used to measure all types of switch contacts, connectors and HV switches - including those grounded on both sides. In addition, they can be used to test bolted, welded, forged joints and other continuities, i.e. wherever we want to measure small resistances.

Measuring the winding resistance of transformers with an amorphous core

Testing of contacts, connectors, switches, etc. can be carried out without the need to disconnect them from the voltage (this applies to the same phase), using uni- or bidirectional current. Measuring inductive objects, such as motors, transformers or coils, is possible after selecting the function intended for this purpose. If we have doubts whether we are testing a purely resistive or inductive object, we can use the automatic mode. Particularly interesting is the ability to measure the winding resistance of transformers with an amorphous core, which until now caused a lot of trouble. The core demagnetization function has not been omitted.

Temperature monitoring

Checking the motor winding temperature is another specialized test. It takes place as a result of measuring the resistance of the coils in the cold state and after a period of operation, taking into account the temperature coefficient. The temperature can also be determined in a contacted way, using an optional probe.

Applications in technological processes

The possibility of setting the upper and lower limits for the measured quantities together with the automatic triggering opens up the entire spectrum of meter applications in continuous technological processes. An addition in this area is the recorder of resistance change over time.

Interface & memory

The large touchscreen provides a user interface that allows quick and intuitive access to all measurement and additional functions, as well as to the memory. The memory itself can be organized before measurements or on an ongoing basis. It has a tree structure, already known from the Sonel MMR-650 meter. We can save tens of thousands of measurements in it, according to our own preferences. The meters offer variety of communication modes with the computer, such as USB, Wi-Fi or LAN (option). Additional accessories, a 2D code reader and printer, help provide smooth work in situations of periodic measurement of many objects or control of serial products at the end of the technological process.

Durable housing

An additional advantage is the solid, hermetic casing. It perfectly protects against external conditions and prevents accidental damage.

Sonel MMR-6500 and Sonel MMR-6700 are the most modern and universal microohmmeters in their class. High quality, wide configuration flexibility and unique solutions of these devices guarantee both economic and technical proof of their sensational effectiveness when used wherever small resistances should be measured.