What is relay protection and what is it for?

What is it for?

First of all, we will talk about why you need to use RPA. The fact is that there is such a danger as short circuit current in the chain. As a result of the short circuit, conductive parts, insulators and the equipment itself are very quickly destroyed, which entails not only the occurrence of an accident, but also an industrial accident.

In addition to a short circuit, it may occur overvoltage, current leak, gas evolution during the decomposition of oil inside the transformer, etc. In order to detect a hazard in a timely manner and prevent it, special relays are used that signal (if a malfunction of the equipment does not pose a threat) or instantly turn off the power in the faulty area. This is the main purpose of relay protection and automation.

Basic requirements for protective devices

So, in relation to RPA the following requirements are presented:

1. Selectivity. In the event of an emergency, only that section in which an abnormal operating mode is detected should be turned off. All other electrical equipment should work.
2. Sensitivity. Relay protection must respond even to the smallest values ​​of the alarm parameters (set by the trip setting).
3. Performance. No less important requirement for relay protection, as the faster the relay operates, the less chance of damage to electrical equipment, as well as the occurrence of danger.
4. Reliability. Of course, the devices must perform their protective functions in the given operating conditions.

In simple words, the purpose of relay protection and the requirements for it are that the devices must monitor the operation of electrical equipment, respond in a timely manner to changes in the operating mode, instantly disconnect the damaged section of the network and signal personnel about the accident.

Relay classification

When considering this topic, one can not stop at the types of relay protection. The relay classification is as follows:

• Connection method: primary (connected directly to the equipment circuit) and secondary (connected via transformers).
• Variant of execution: electromechanical (the system of movable contacts disengages the circuit) and electronic (disconnection is done using electronics).
• Appointment: measuring (carry out measurements of voltage, current, temperature and other parameters) and logical (transmit commands to other devices, carry out time delay, etc.).
• Way of action: relay protection of direct action (mechanically connected to the disconnecting device) and indirect effect (control the circuit of the electromagnet, which turns off the power).

As for the types of RPA themselves, there are many. Immediately consider what types of relays are and what they are used for.

1. Overcurrent protection (MTZ), triggered if the current reaches the setpoint set by the manufacturer.
2. Directional overcurrent protection, in addition to the setting, the direction of power is monitored.
3. Gas protection (GZ), is used to turn off the power to the transformer as a result of gas evolution.
4. Differential, scope - protection of busbars, transformers, as well as generators by comparing the values ​​of currents at the input and output. If the difference is greater than the set point, the relay protection is activated.
5. Remote (DZ), turns off the power if it detects a decrease in resistance in the circuit, which occurs if a short-circuit current occurs.
6. Remote protection with high-frequency interlock, is used to turn off the overhead line when a short circuit is detected.
7. Remote with optical channel locking, a more reliable version of the previous type of protection, as the effect of electrical noise on the optical channel is not so significant.
8. Logical bus protection (LSS) is also used to detect short circuit, only in this case on the tires and feeders (supply lines extending from substation tires).
9. Arc. Purpose - protection of complete switchgears (switchgear) and complete transformer substations (KTP) from fire. The principle of operation is based on the operation of optical sensors as a result of increased illumination, as well as pressure sensors with increasing pressure.
10. Differential phase (DFZ). They are used for phase control at two ends of the supply line. If the current exceeds the setpoint, the relay trips.

Separately, I would also like to consider the types of electroautomatics, the purpose of which, in contrast to relay protection, on the contrary, is to turn on the power back. So, in modern relay protection and automation use the following type of automation:

1. Automatic reserve input (ABP). Such automation is often used when connecting the generator to the networkas a backup source of electricity.
2. Automatic reclosing (AR). Scope - power lines of 1 kV and above, as well as busbars of substations, electric motors and transformers.
3. Automatic frequency unloading, which turns off third-party devices when lowering the frequency in the network.

In addition, there are the following types of automation:

So we examined the purpose and scope of relay protection. The last thing I would like to talk about is what the RPA consists of.

Relay Design

The relay protection device is a diagram of the following parts:

1. Launchers - voltage relay, current, power. Designed to control the operation of electrical equipment, as well as detect violations in the circuit.
2. Measuring organs - can also be located in the starting organs (current, voltage relays). The main purpose is to start other devices, signaling as a result of detecting an abnormal operating mode, as well as instantly turning off the devices or with a time delay.
3. The logical part. Submitted by timers as well intermediate and indicator relays.
4. Executive part.Responsible directly for turning off or on switching devices.
5. The transmitting part. It can be used in differential phase protection.

Finally, we recommend that you watch a useful video on the topic:

That was all we wanted to tell you about the purpose of relay protection and the requirements for it. We hope that now you know what RZA is, what is its scope and what it consists of.

It will be useful to read:

• What are time relays?
• Reasons for tripping a circuit breaker
• How to detect a short circuit in the network