Basic concepts of relay protection
1. Electricity systems
An overall system of power generation, transmission, transformation, distribution and use, which connects power plants, transformers and electricity users at various levels of voltage, is called the power system。
2. Electrical failure
The electrical system is operating with the possibility of faults, such as short circuits, short circuits and cut-off lines, of which short circuits of all types are most common and most dangerous. In case of short circuits, the heat and power effects of the current will cause damage to the malfunctioning equipment and the non-facing equipment through which the short-circuit currents pass, rendering the heavy man inoperable, accelerating the insulation of the light man and reducing the useful life of the equipment。
3. Irregular functioning
The normal operation of electrical components in the electrical system was disrupted, but no malfunctions occurred, and this was an abnormal state of operation, which could cause the quality of the electricity to deteriorate. For example, overload, reduced frequency, etc。
4. Relay protection
Relay protection is an automatic device capable of responding to failure or abnormal operation of the electrical system and equipment, acting on a breaker jump or signal。
Basic tasks of relay protection
1. Selectively remove faulty elements from the electrical system quickly and automatically to minimize the damage and ensure the continued operation of other non-facility parts of the system。
2. Reflects the abnormal working state of the system, generally alerting duty officers by sending warning signals. In the absence of a man on duty, a relay protection device is capable of absorbing the equipment and is designed to reduce load or jump。
The rationale for relay protection
The failure of the power system is usually accompanied by increased currents, reduced voltage and alternation between currents and voltage. Thus, the difference between these basic parameters in the event of failure and normal operation could constitute a relay protection of different principles. Overflow protection, for example, can be reflected in the increase in currents and actions; low voltage protection can be reflected in the decrease in voltage; distance protection can be reflected in the distance between short-circuit points and protected installation sites。
Basic requirements for relay protection
Reliability of relay protection
Reliability means that in the event of a malfunction within its protection, the movement should be acted upon reliably and should not be refused; in the case of normal operations or actions that it should not have, it should act reliably and should not be mistakenly。
2. Selective nature of relay protection
Selective means that when the power system fails, the relay protection action only removes the failure element so that the power outage is as small as possible to ensure that the non-facility component continues. If the protection or breaker refuses to move, the failure shall be removed by backup protection。
3. Rapidness of relay protection
Speed means that the protective device should be able to remove the malfunction as quickly as possible. Fast protection moves, shorter break-out times, less damage to malfunctioning elements, more stability in the operation of the electrical system and less further disruption。
Fault removal time = relay protection action time + breaker jump time. Protects the minimum action time = 0. 02 ~ 0. 03 seconds. The minimum action time of the breaker = 0. 05~0. 06 seconds。
4. Sensitivity of relay protection
Sensitivity means the ability to react to a malfunction or abnormal state of operation within its protection. Sensitivity is usually measured by the sensitivity factor k. Overflow protection with composite voltage locks can increase protection sensitivity。
Composition of relay protective devices
Enter a signal signal to measure the logical part of the signal to jump or signal the operative part。
Measurement component
The protection should be activated by measuring the relevant signals entered by the protected object and comparing them with the total values given。
Ii. Logical segment
Depending on the size, nature, order of occurrence or combination of the components, the protective device works according to a certain logical procedure and finally moves the operative part。
Executive
Finalize the tasks of the protective device based on the signals transmitted by the logical component. If the failure occurs when the jump is made; if the abnormally run signal is sent; if the normal run is not, etc。
