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What is numerical protection relay?

What is numerical protection relay?

Numerical relay is the relay in which the measured AC quantities are sequentially sampled and converted into numerical data that is mathematically and/or logically processed to make trip decisions.

Numerical relay is actually the digital relay as a unit for which manufacturers has developed standardized hardware, which can be used in conjunction with suitably developed software to meet variety of production requirements and applications.

Some Faults are unavoidable and beyond human control. So, the central electrical grid must run a real-time algorithm to detect such fault conditions and react quickly in order to minimize adverse impact. This monitoring function is typically managed by make-or-break contacts called switch-gears or relays. These relays are, in turn, controlled by a smart controlling unit that continually monitors the grid parameters (such as voltages, currents, temperature, and so forth) and switches the appropriate relays in case fault conditions occur. Most of the data processing happens in the digital domain; thus, these relays are often called Numerical Protection Relays. Numerical relays are based on the use of microprocessors.

Unlike Electromechanical relays the following tasks can be performed by Numerical relays.

  1. Numerical relay consists of many functions in one relay thus replace many traditional relays with one.
  2. One relay can be used in many ways. Users can configure relay according to their system requirement.
  3. Consists of no mechanical moving parts hence accurate operation.
  4. No maintenance is needed like electromechanical relays.
  5. Relays are compact in size and appearance is good.
  6. Many complicated functions can be achieved with developed logics using various Gates.
  7. Gives entire details of fault record including with the graphs.
  8. Some relays have different Setting groups. The advantage of setting groups is that user can change the entire settings of the relay by simply changing Group setting. Frequent configuration is not needed.
  9. The main advantage of Numerical relays is communication between relays and other equipment in the network is possible for doing automation of the system.

Common Features of Numerical Relays:

Any numerical relay usually consists of the following essential parts.

Numerical Relay Front Side:

Front side of any Numerical Relays usually have the following components.

  • LED Configuration Menu
  • LCD Display
  • Numerical Key pad
  • Led Reset Button
  • Menu Button
  • Control Button
  • Breaker ON/OFF buttons
  • Esc button
  • Run LED
  • Error LED

Numerical Relay Back Side:

Relay back side usually consist of different Terminal Blocks [TB] for giving the Digital and Analog inputs, outputs .

  • TB for Current Transformer inputs
  • TB for Potential Transformer inputs
  • TB for Binary Inputs
  • TB for Binary Outputs
  • TB for Relay Power Supply
  • TB for Live status contact
  • Slots for Communication Ports

Communication Protocols:

Relay communication is provided with the following protocols. These protocols helps to communicate relays among them and also with HMI through modem.

Following are the various protocols used.

Serial RS232; Modbus RS485; Ethernet TCP/IP:

These uncomplicated, serial & TCP protocols are mainly used in industry and by power supply corporations.

Numerical Relay Types:

The following are some of the various types of numerical relays

1. Over current/Earth fault Relays

2. Motor Protection Relays

3. Differential Relays

4. Line/Cable Differential Relays

5. Directional Over Current Relays

6. Under/Over Voltage Relays

7. Distance Relays

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