WHAT IS AN OVERCURRENT RELAY?

The overcurrent relay is a protection relay connected to the current transformers of the devices. The overcurrent relay continuously measures the current phases of the connected devices. If any fault is detected, what is expected from the overcurrent relay is to warn the circuit breaker relay according to the application scenario created on it, to activate the alarms connected to it and to record the moment of failure and events. The protection functions on the overcurrent relay are expected to be independent of each other and to record data with their own setting groups. An overcurrent relay using conventional current transformer measurement provides protection functions in this way.

When the protection is activated, it implements the protection stages through the operation of a matrix in which start and trip signals are sent to the output contacts.

The overcurrent relay must have a regulated overcurrent unit and a circuit breaker fault protection unit. The relay, which is set to be high and low, protects the device to which it is connected in both ways. Relays are expected to have a fault recording module and an HMI screen where this module can be managed. In this way, management both remotely and from the side of the device becomes possible. Start signals should be made in milliseconds (ms). Although the speed here varies according to the manufacturer, the expected response value is around fifty (50) ms at low current and thirty (30) ms at high current.

In the overcurrent relay, the recording process moves according to the sampled frequency range. RMS curves of the instantaneously measured signals and/or values are created and comparisons are made here. The energy supply of the relay that will provide this level of protection must be redundant. If possible, both card and source redundancy should be provided by feeding from different sources.

Although overcurrent relays have a protection scenario that works on its own, there should be a system that controls the software and electronic components of the relay. This system is expected to monitor the light (LEDs, power inputs, alarm lights, etc.) on the relay and record the failures that will occur here, and inform the relevant places according to the scenario created for this.

The overcurrent relay can provide data communication with different communication protocols. With this structure, it offers monitoring and control from different systems.