USE OF IED(Intelligent Electronic Device) IN MODERN ELECTRICAL INDUSTRY

Protection devices are an important part of the power supply system. They have evolved from simple microprocessors in 1985 to the advanced numerical relays of the current era. The numerical relays are a focal point of interest in the account that can be programmed. Protection devices using numeric protection relays are advantageous in the account as they provide better protection, reliability, troubleshooting and fault information.

Over the period of time, electrical engineering has evolved from static to dynamic studies. Now there are advances such as the digital signal processor and the computational hardware that improves the efficiency of the numerical relays in the protection of the devices. The current protection devices of the power system present the user with integrated functions. The numerical power system protection devices can perform multiple tasks on attributes such as protection, control, monitoring and measurement. In addition to this, the communication capability of these relays provides remote control and data transfer in real time.Now the conventional system of electromechanical and static relays is generally restricted to the single-function protection strategy. This shows the tactical dexterity of a digital relay system.

Auxiliary power supply: Older protection relays and voltage regulators may not need auxiliary supply, but IEDs always require an auxiliary power supply. Most IEDs accept an extended range, e.g. 24 – 250 V DC /110 – 240 V AC. 
Analog inputs: Protection relays and voltage regulators are always provided with current and voltage transformer inputs. Besides that, devices may be provided with sensor inputs (e.g. temperature sensors) and/or 4..20 mA inputs. Note that for some IEDs rated secondary current (1 A or 5 A) and frequency (50 or 60 Hz) must be specified before ordering. Note also that the correct phase of the sensing voltages and currents, and the right direction of the currents are important.
Digital inputs: Some IEDs require potential-free contacts for digital (logic) inputs, while others recognize the positive power supply voltage (source) or negative power supply voltage (sink) as a logical 1. Digital inputs may be commands or as status information.
Analog outputs: Some IEDs are provided with transducer outputs, e.g. 4..20 mA or 0..10 V. Mostly these outputs are programmable. These outputs can be active type or passive type outputs. The passive type requires external power supply.
Digital outputs: Digital outputs can be potential free normally open, normally close or change-over contacts or solid state contacts. It is important to check switching capability of the output contacts, because differences can be significant. Digital outputs may be commands or status information.
Serial communication ports: There are several ports possible for serial communication like RS 485, ethernet (RJ45), optical, etc.. IEDs are mostly also provided with an RS 232 or USB port for local communication with a laptop or PC.
  

Functionality

The extended functionality of an IED can be separated into the following groups: protection, control, monitoring, metering and communication.
Protection: This functionality covers all protection functions to protect a generator, motor, transformer or feeder.
Control functions and logics: These elements may be control loops in voltage regulators, control logics in circuit breakers, etc.
Monitoring: Each IED should have internal self-supervision and aux. supply monitoring. A “watch-dog” or “healthy” output contact will close if the IED is operating well. Monitoring may also include loss of analog sensing inputs (e.g. loss of voltage, current, temperature sensors), trip circuit supervision, event recording, etc.
Metering: Most IEDs contain metering values including line voltages (V), phase currents (A) and voltages (V), neutral current (A), residual voltage (V), frequency (Hz), power (MW, MVAr, MVA) and energy (kWh, KVArh), harmonics, disturbance recording, temperaturs and analog channels. Some IEDs are also provided with programmable transducer outputs.
Serial communication: IEDs could support protocols like Modbus RTU, Modbus TCP, Profibus, etc.. In order to enable interoperation of IEDs from different vendors, IEC created the modern IEC 61850 standard.

Advantages

1.      Compact Size:

While numerical relay is in compact size and use indication on LCD for relay activation.Digital protection can be physically smaller, and almost always requires less panel wiring than equivalent functions implemented using analog technology.

2.      Flexibility:

A variety of protection functions can be accomplished with suitable modifications in the software only either with the same hardware or with slight modifications in the hardware.

3.      Reliability

A significant improvement in the relay reliability is obtained because the use of fewer components results in less interconnections and reduced component failures.

4.      Multi Function Capability

Traditional electromechanical and static protection relays offers single-function and single characteristics. Range of operation of electromechanical relays is narrow as compared to numerical relay.

5.      Different types of relay characteristics

It is possible to provide better matching of protection characteristics since these characteristics are stored in the memory of the microprocessor.

6.      Digital communication capabilities

The microprocessor based relay furnishes easy interface with digital communication equipment. Fiber optical communication with substation LAN. Helpful in using IEC 61850 

7.      Modular frame

The relay hardware consists of standard modules resulting in ease of service.

8.      Low burden

The microprocessor based relays have minimum burden on the instrument transformers.

9.      Sensitivity

Greater sensitivity and high pickup ratio.

10.  Speed

With static relays, tripping time of ½ cycle or even less can be obtained.

11.  Fast Resetting

Resetting is less.

12.  Data History

Availability of fault data and disturbance record. Helps analysis of faults by recording details of:
  1. Nature of fault,
  2. Magnitude of fault level,
  3. Breaker problem,
  4. T. saturation,
  5. Duration of fault.

13.  Auto Resetting and Self Diagnosis

Electromechanical relay do not have the ability to detect whether the normal condition has been attained once it is activated thus auto resetting is not possible and it has to be done by the operating personnel, while in numerical relay auto resetting is possible.

14.  Other Advantages

  • By combining several functions in one case, numerical relays also save capital cost and maintenance cost over electromechanical relays
  • Separate connection is not required, zero sequence voltages and currents can be derived inside the processor
  • Basic hardware is shared between multiple functions, the cost of individual protection functions can be reduced significantly.
  • Loss of voltage feature helps block the relay in case of momentary/permanent loss of voltage.

Comments

Post a Comment