Protection relay (Protection Relay) is a device that detects electrical abnormalities. Whether it is voltage, current, resistance or any other electrical quantity. that occurred in the electrical system and when abnormalities occur in the system At which point the protection relay is set. The protection relay will work. to change the state of the contactor and cut off any equipment quickly, which works quickly It provides protection for valuable equipment. and is important to be efficient and there was no serious damage to those devices.

photo Protection relay

that protection relay It has been widely used both in the past and in the present. which has been developed continuously ever since Make it in the present Protection relays are complex. Able to work efficiently and is highly reliable which is used for each type of protection It will depend on that. Device or system that needs protection How important is it? If it is very important, the price is high, such as a large electrical transformer. or generator These devices must use effective protective relays. Has a variety of functions Covers all aspects of abnormalities that will occur with that device. In order not to damage the equipment at all. Because whenever severe damage occurs to these devices There will be a large impact. For example, if there is severe damage to a large power transformer, it will cause a power outage in a wide area. or if there is severe damage to the generator It will cause the machine to be stopped in order to find the cause and make repairs. Unable to produce electricity for a long period of time It has an impact on the organization's income. and in other respects which is absolutely not worth it Moreover, If it cannot be repaired and fixed This means that the entire piece of valuable equipment must be replaced. This will be many times more expensive.

Circuit of protective relay and components [1]

that protection relay It will work together with instrument transformers (Instrument Transformer) such as voltage transformers (Voltage Transformer) and current transformers (Current Transformer) to make these instrument transformers. Serves to measure electrical quantities in the system. and forwarded to the protective relay to process and command the circuit breaker to release the circuit (Open Circuit or Trip). Therefore, if we compare the electrical system to a human being. Protection relay It acts like the human brain. Voltage transformer and current transformer It acts like a human's sense organ, such as the ears, eyes, or nose. And when the organ senses an abnormality The brain then commands the organs for movement to work, such as the arms and legs, which is like a circuit breaker to cut off the electrical circuit. Therefore, in the circuit of the protective relay It will consist of the following equipment.

  1. No. 1 Circuit Breaker (Circuit Breaker) Originally, it performed the function of Close (Open Circuit) or Close Circuit (Close Circuit), but when working with relays Circuit breakers will work only when in the Closed circuit state. It will close the circuit immediately. that receives a trip command from the protection relay Through the work of the trip coil (Shunt Trip Coil)
  2. No. 2 Protection Relay (Protection Relay) is a device that receives signals from signal measuring devices and processes them to decide whether Is the quantity received in accordance with the specified conditions? If an abnormality occurs, the circuit must be connected. to have direct current electricity Flows through the shunt trip coil of the circuit breaker to allow the circuit breaker to cut off the power output.
  3. No. 3 Circuit breaker control circuit (Actuator) in circuit breaker There will be equipment for controlling the closing of electrical circuits. which is used to work with protection relays When the protection relay works It will make the trip cycle complete. There will be direct current flowing through the circuit into the circuit breaker control device. Make the trigger control device break this circuit. Push the trigger to cut off the circuit breaker. Therefore causing the circuit breaker to close the circuit quickly. This device is a trip coil (Shunt Trip Coil).
  4. No. 4 Direct current circuit (DC Circuit) in the operation of the protection system They are mostly used as direct current circuits. Because it has higher stability and reliability than AC circuits. which if a power outage occurs The protection system can still function normally. Because it uses direct current electricity from batteries in the power station. In addition, most trip coils and equipment in circuit breakers use direct current as well.
  5. Number 5 Battery (Battery) In that protection system need credibility and very high stability If using an AC power source to operate When there is a power outage The protection system will not be able to work. Makes it happen when the protection relay detects an abnormality. But cannot order to cut off the circuit breaker. Because there is no supply source to feed the trip coil of the circuit breaker. This may cause more severe damage. In most protection systems It uses a battery voltage of 110 volts.
  6. Numbers 7 and 8 Signal Measuring Device (Sensing Device) They are a current transformer (Current Transformer) and a voltage transformer (Voltage Transformer). Their duties are to change the size of the current and voltage. If the voltage is very high, reduce it to a size suitable for the protective relay coil. Normally, the current is 1 ampere or 5 amperes and the voltage is 110 volts or 120 volts.

How many types of protective relays are there? [1]

From the previous topic It will make many readers He had doubts that If the equipment used for protection has many types And how many types of protection relays are there? It will work precisely. Are all types equally effective? And if we want to use protective relays What type of protection relay should I choose? Therefore it will be suitable for our system. The following are the types of protection relays. which is divided according to structural characteristics which can be divided into 4 types as follows

  1. Attractive type relay

It is a protective relay that relies on magnetic attraction. It is divided into 5 types:

  1. Plunger relay It is a relay that uses magnetic attraction between the coil and the iron core. Has a structure as shown.
  1. Hinged armature relay It is a relay that uses gravity from an iron core. which has a coil wrapped around it acting on the rocker beam or armature This type of relay can be used with direct current. But if used with alternating current, it must have a shaded ring coil or separate the magnetic circuit into two parts. (Split-magnetic circuit) in order to eliminate vibrations from the suction force caused by alternating current so that the relay is completely suctioned.
  1. Rotor armature relay This type of relay relies on a magnetic field. Makes the armature rotate and the moving contact connect to the circuit as shown.
  1. Balance beam relay The operation of this type of relay depends on two currents: current I1 (Operating Current) and I2 (Restraining Current). If current I1 > I2, the attraction force on I1 will be greater than I2, causing the direction of rotation to be positive. The relay will work so that the contacts (Trip Contact) can be connected to each other. On the other hand, if the current I2 > I1 causes the direction of rotation to be negative. The relay will not contact. For graphs showing areas where relays work and don't work. which depends on the value of current I1 and I2 as shown in the next image

photo Structure of a cantilever relay

  1. Directional relay of electromagnetic attraction type From the picture below If the current flowing into the moving armature (Movable armature) is current Ia1, it will cause the armature magnetic field to be N1 and S1, creating an attraction-repulsion force. go in the same direction causing the contact surfaces to not connect to each other It is considered that the relay is not working. But if the current flowing is current Ia2 as shown in the picture, N2 and S2 will cause the beam to rotate in the direction that the contacts meet each other.

photo Directional gravity relay

  1. Electromagnetic induction relay (Electromagnetic induction) 

This type of relay is used with alternating current only. If direct current is used, it will not be able to induce the turntable to rotate. The work uses the principle of a split phase induction motor to induce current in the rotor or rotating disk when high current flows through it. There will be a rotational force to rotate the moving contacts to connect with the stationary contacts of the relay together. Electromagnetic induction relay They can also be divided according to their structural characteristics as follows: