АНГ 2 Relay protection / Individual_Task_1

1) What is the operation principle of relay?

2) What requirements for protections do you know?

3) Why do we need protection?

4) How to select the pickup value of a relay?

5) How to set the operating time of a relay?

6) What the selectivity is?

7) How relays are connected in the power system?

8) What is Relay Time?

9) What are the fundamental elements of relay?

Answers

1) Relays quickly detect a fault and turn off circuit breakers that shut off the flow of current into the faulty component, thereby isolating it, which gives the advantages of rapid isolation.

2) There are four main requirements: Selectivity, speed, sensitivity and reliability.

Selective is a protection action in which it turns off only the damaged element by means of its circuit breakers.

Sensitivity – the ability of the relay protection device to respond to the minimum values of emergency parameters.

Reliability – the ability of the protection device to perform specified protection functions for a specified time under specified operating conditions.

3) The purpose of protection is to disconnect the damaged element or section of the power system from its undamaged parts as soon as possible.

Consider an example. The relay is working properly, and the circuit breaker cannot eliminate the malfunction due to any malfunction. The fault remains in the system until any other means are used to eliminate it. In this case, the main or backup relay starts the timer after the fault is detected, after which the timer turns off by timeout and sends a shutdown signal to all switches that can power the faulty switch.

4) The relay should allow normal load as well as a certain degree of overload to be supplied. So the pickup value of the relay should be more than maximum load. At the same time, the relay should be sensitive enough to respond to the smallest fault. So, pickup value should be less than the smallest fault current.

5) For anchor time relays, operation is ensured by a spring mechanism, wound by hand or automatically, when voltage is applied to the device. With the help of a mechanical superstructure scale, set the values ​​​​on it, set the time and period for switching on and interrupting the current line for the consumer.

To adjust the operating time of an electronic relay, it is necessary with the help of regulators, for example, in the form of slots for screwdrivers, or handles that control the resistance parameters of resistors in the circuit, increasing the resistance of the capacitor will take longer to charge, thereby increasing the time delay of power failure.

Logic relays, which use microcircuits in their composition, are programmed due to the presence of digital displays and many keys.

6) Selectivity consists in the possibility of disabling a minimum number of circuit breakers to eliminate the malfunction. Selective is a protection action in which it turns off only the damaged element by means of its circuit breakers.

7) The relay is connected to the power system in the general case with three connectors: input, adjustment and output. Inputs: The relay needs information from the system to make a decision. This data can be collected in various ways. In some cases, wires in the field can be connected directly to the relay. Other applications require additional devices to convert the measured parameters into a format that the relay can process. These additional devices can be current transformers, potential transformers. Settings: Many protection relays have adjustable settings. User program settings (reception levels) that allow the repeater to make a decision. The relay compares the input signals to these settings and responds accordingly. Outputs: The relay has several ways to signal that a decision has been made. Typically, a relay will operate a switch (relay contact) to indicate that an input has exceeded a set value, or a relay may provide notification via visual feedback such as a counter or LED. One of the advantages of electronic or microprocessor relays is the ability to communicate with a network or PLC. An example is a thermostat. The measured input is the temperature, and the input device of the protection relay is the temperature sensor. The user sets the desired temperature setting (selection level). The relay measures the existing air temperature and compares it with the set one. The outputs can be used to provide control (on or off the air conditioner or oven) and visual indication on the thermostat display.

The picture below shows a good diagram of connecting the relay to the network and load. A phase is connected to one of the power contacts, a load is connected to the second, and zero is connected to the second output of the load.

8) The relay time is the time from detecting a fault to sending a trip signal to all switches that can power the faulty switch.

9) Basic fundamental elements of the relay are: • Sensing element: It is the measuring element measures the actuating quantity. Actuating quantity is change in current in case of over current relay • Comparing element: It compares the actuating quantity with the relay pre-settingof the relay • Control element: On pick up of the relay control element carryout the final switching operations such as closing the circuit to operate circuit breaker

An electromagnetic relay consists of a coil, an armature and a set of contacts.