What Is a Voltage Relay?
A voltage relay is a device that detects voltage changes in an electric circuit and transmits them to another circuit or device.
Its main purpose is to detect voltage fluctuations and abnormalities in power and control systems, controlling and protecting systems accordingly. Voltage relays typically transmit signals through electrically isolated circuits to enhance electrical safety and ensure insulation between different circuits.
These devices are crucial in high-voltage environments due to their high measurement accuracy and reliable operation. Their design allows for precise detection and response to specific voltage values.
Uses of Voltage Relays
Voltage relays are employed in various applications, particularly in power transmission, distribution, power generation, and substations.
1. Power Systems
In power systems, voltage relays protect against abnormal voltages by detecting overvoltage or undervoltage situations and either shutting down electricity or monitoring power quality.
2. Transformers
Transformers use voltage relays to maintain proper voltage levels. Some transformers, equipped with tap-switchers, adjust output voltage automatically in response to supply voltage variations and power demand, as detected by voltage relays.
3. Generators
For generator safety and proper operation, voltage relays detect fluctuations or abnormalities, regulating voltage or interrupting circuits as needed. They are essential for controlling synchronous equipment and preventing overvoltage, undervoltage, and reverse power issues.
Principle of Voltage Relays
Voltage relays measure voltage through instrument transformers or similar devices. The input electrical signal is processed by a transformer circuit or similar device, which amplifies or modulates the signal to an appropriate level, adjusting its strength and range.
The processed signal is then converted to an analog or digital output, used for control or signaling purposes. In some designs, voltage relays are isolated between input and output circuits, using insulating materials and transformers for safety and circuit independence.
Types of Voltage Relays
Various types of voltage relays exist, each serving specific functions:
1. Overvoltage Relay
An overvoltage relay activates when the voltage in a power system exceeds a specified range, generating a control signal to shut down the circuit or alert the controller, preventing equipment damage and overloads.
2. Undervoltage Relay
An undervoltage relay operates when the voltage drops below a set level, triggering a control signal to interrupt the circuit or signal a controller. It is crucial for preventing issues caused by undervoltage in power systems and ensuring the activation of backup power supplies.
3. Ground Fault Overvoltage Relay
A ground fault overvoltage relay responds to ground faults in a power system, detecting overvoltage due to ground faults and preventing equipment damage and electrical accidents. However, it’s often used alongside ground fault direction relays and overcurrent overcurrent relays for comprehensive protection.