Build Daily

Machines, Rc Ds, Meters

August 12, 2017 18:07

What is relaying , and what is it for ?

In accordance with the rules of technical operation of electrical installations (abbreviated PTE) of electric power equipment, substations and power plants themselves must always be protected against short circuit and normal operation failures.As a special protection devices are used, the main element of which is a relay.Actually, so they are called - relaying device and the PLC (RPA).Today there are many devices that can in the shortest possible time to prevent the accident at the power service area or at least alert people about the violation of the working mode.In this article, we will consider the appointment of relay protection, as well as its type and device.

  • What is it for?
  • Basic requirements for protective devices
  • Classification relay
  • RZA design

What is it for?

First of all tell you about why you need to use the RPA.The fact that there is such a danger as the occurrence of fault current on the circuit.As a result, short circuit very quickly destroyed conductive parts, insulators, and the equipment itself, which entails not only the occurrence of an accident, but an accident at work.

Protective devices in the substation

voltage, current leakage can occur addition to short-circuit, the evolution of gas from the decomposition of the oil inside the transformer, etc.In order to timely detect the danger and prevent it, use special relays that signal (if the failure of the equipment does not pose a threat) or immediately cut off power to the defective area.This is the primary purpose of relay protection and automation.

Basic requirements for protective devices

So, in relation to the RPA following requirements:

  1. selectivity.In the event of an emergency must be switched off only the portion in which an abnormal operation is detected.The rest of electrical equipment should work.
  2. sensitivity.Relay protection must respond to even the most minimal value alarm parameters (setpoint operation).
  3. speed.No less important requirement to RZA, becausethe faster the relay operates, the less chance of damage to the electrical equipment, as well as a hazard.
  4. reliability.Needless devices must fulfill their protective function to the specified operating conditions.

simple words the appointment of relay protection and the requirements for it, lie in the fact that the device must monitor the performance of electrical equipment, to respond promptly to changes in the operating mode, immediately turn off the damaged part of the network and alert the staff about the accident.

Classification relay

In examining this topic it is impossible not to dwell on the kinds of relay protection.Classification of the relay as follows:

  • Connection: primary (included in the equipment chain direct) and secondary (connection through transformers).
  • Option: electromechanical (the system disengages the movable contacts circuit) and electronic (tripping occurs electronically).
  • Purpose: measurement (performed metering voltage, current, temperature and other parameters) and logical (transmit commands to other devices, exercise endurance time, etc.).
  • method of exposure: direct exposure to the protection relay (connected mechanically with the tripping device) and indirect effects (exercise control circuit of the electromagnet, which turns off the power).

As for the types of relay protection and automation, a lot of them.Immediately take a look at what are the kinds of relays and what they are used.

  1. overcurrent protection (MTZ) is triggered if the current setpoint reaches the manufacturer.
  2. Directional overcurrent protection, in addition to setting the direction of the power control is carried out.
  3. Gas Protection (PP) is used to turn off the power transformer as a result of the gas discharge.
  4. Differential, scope - protection of busbars, transformers, and generators due to the comparison currents entering and leaving.If the difference is greater than a predetermined set point, relay protection is triggered.
  5. Remote (RS), turn off power if it detects a decrease in the resistance in the circuit, which occurs if there is a short-circuit current.
  6. Distance protection with high-frequency lock, is used to turn off the overhead line when it detects a short-circuit.
  7. remotely lock on the optical channel, a more robust version of the execution of the previous type of protection, becauseeffects of electrical noise on the optical channel is not as significant.
  8. Logical busbar protection (LZSH), is also used to detect short-circuit, but in this case, the tire and feeders (feeder lines extending from the substation bus).
  9. Arc.Purpose - protection of the complete switchgear (KRU) and complete transformer substations (CTS) from the fire.The principle of operation is based on triggering of the optical sensor due to an increase of illumination, and the pressure sensor when the pressure increases.
  10. Differential-phase (DFZ).Are used to control the phase at the two ends of the supply line.If the current exceeds the set point, the relay is activated.

We would like to also consider the types of PLC, the purpose of which, in contrast to relaying the contrary turn on the power again.So, in modern automation RZA use the following form:

  1. Automatic entry reserve (AVR).This automation is often used to connect the generator to the network as a backup power source.
  2. Autoreclosing (APV).Scope - Power transmission voltage of 1 kV and above, as well as the busbar substations, electric motors and transformers.
  3. Automatic load shedding, which disables third-party devices at lower frequencies in the network.

addition, there are the following types of automation:

Variety of automation

Here we examined the purpose and scope of the protection relay.The last thing I would like to tell - what it consists of RZA.


Design The relay is a diagram of the following parts:

  1. Starting bodies - voltage relays, current, power.Designed to control the mode of operation of electrical equipment, as well as the detection of irregularities in the chain.
  2. Measuring bodies - may also be in the starting organs (current relays, voltage).The main purpose - running other devices, the supply of the signal resulting from the detection of abnormal operating mode and instantaneous tripping devices or with a time delay.
  3. logical part.Presented timers, as well as intermediate and index relay.
  4. executive part.Directly responsible for the shutdown or the inclusion of switching devices.
  5. transmitting part.It can be used in phase-differential protection.

Scheme of work

Finally we recommend you to view helpful videos on the topic:

RZA in the energy sector for beginners
YouTube Preview

That's all we wanted to tell you about the appointment of relay protection and requirements for it.Hopefully, now you know what the RPA, what her scope and what it is made.

will be helpful to read:

  • What are the time switch?
  • response Reasons
  • breaker How to identify a short circuit in the network