Why do I need a maximum current relay?
Purpose and principle of operation
This device is designed to monitor the magnitude of the current on a specific section of the network. If the set value is exceeded, the PMT switches, giving a signal to the actuator, which will de-energize the circuit section or turn on the alarm panel.
Each element: relay protection, starters, controllers, motors, transformers in the electrical network, has its own maximum permissible current. The use of a maximum current relay instead of circuit breakers or fuses has its advantage due to selectivity. In this case, it is an opportunity to disconnect a certain part of the circuit without affecting others.
The design of the current relay is represented by the following elements:
You can find out how the overcurrent relay works and how to configure it from the video:
Classification
In turn, devices are divided into several types of measurement: primary and secondary. The first type is connected to the device directly with its findings. Such a connection is common in networks up to 1000 volts.
The second type of PMT (in the photo below) is connected via a current transformer, measuring the secondary current, which is directly proportional to the primary and an order of magnitude smaller than in the measured circuit. Apply this type of connection in high voltage networks.
In turn, the secondary current relays are divided into induction and electromagnetic, differential, electronic. The principle of operation of the differential type of execution is to compare the current strength to and after the consumer. Under normal conditions, this value should be the same. If the parameters are different (for example, during a short circuit), РМТ closes the contacts, as a result of which the damaged line is disconnected from the network.
An example of a differential relay is residual current device, which is widely used both in everyday life and in production.
Note
The choice of the maximum current relay is due to the technical specifications, the required parameters, the maximum load threshold of the controlled mechanism. Modern current relays are small and can be directly installed in the control cabinet. RMT have a huge range of settings and settings, a variable operation algorithm, as well as the ability to display the actual value on a digital display.
In the end, we recommend watching another useful video on the topic:
So we examined what a maximum current relay is, what its purpose, device and principle of operation are.We hope the information provided was useful and interesting for you!
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