Voltage control relays

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Voltage monitoring relays

Relays are one of the most widely used automation components with many applications. First of all, electromagnetic relays are known, although voltage control relays can also be used. They are also called monitoring relays.

Voltage control relays: characteristics

Voltage monitoring relays have many applications. Among them, the main one is three-phase electrical installation protection which is effective. They are considered universal because they are used in all types of devices. They are found, for example, in high HV and medium MV switchgears. Voltage relays can be used in power protection automatics systems. They prevent the grounding of the live distribution bay. Then each contactor works as it should. Relays of this type can also be found in low-voltage switchgear and control devices. Most often, relays have three operating modes:

  • undervoltage with or without error memory,

  • overvoltage with or without error memory,

  • in band with or without error memory.

Then they can also work as single-phase receiver protection detecting voltage drop immediately. Regardless of the operating mode, phase failure and phase rotation are also monitored. The selection of the operating modes and the range of permissible voltages is made through switches and regulators located on the front panel of the relay. Thanks to the Umin and Umaks regulators it is possible to set the thresholds for the overvoltage and undervoltage release. This in turn translates into flawless Umin supervision and Umaks supervision, based on the best parameters. Voltage monitoring relays are excellent at supervising network parameters that support three-phase machines. It is possible to, for example, supervise the motor overload, supervise the pump overload, or state a condition such as incorrect phase sequence - always quickly detected and preventing the negative effects of possible failures. Signals from all relays inform about faults in the network, which allows, for example, to stop the production line in a timely manner or alert employees in a given plant about irregularities.

Voltage monitoring relays: important parameters

When analyzing voltage control relays, important parameters should be taken into account: type of electrical connection, 1-phase undervoltage control, 1-phase overvoltage control, 1-phase hysteresis function, DC undervoltage control, DC hysteresis function, control voltage type, number of break contacts, number of changeover contacts, depth, rated control voltage, operating voltage setting value from, maximum allowed time delay when energizing, use of detachable terminals, 3-phase undervoltage control, 3-phase overvoltage control, 3-phase hysteresis function, DC overvoltage control, type of measured voltage, maximum allowable time delay at power failure, number of make contacts, height, setting value of make voltage to, width. It is on this basis that the appropriate relays are selected for the intended use. Certainly, mains voltage asymmetry as well as other errors will be immediately indicated.

Voltage relays are used to disconnect the load of a single-phase installation in the event of voltage fluctuations in the network and to automatically reconnect after restoring the appropriate parameters. In four independent modes, the voltage relays additionally play the role of: minimum voltage control relay, maximum voltage control relay and time relay with activation delay.

By familiarizing yourself with the individual options, you will be able to match the right device without much problem.