Distance Protection knowledge

Line distance protection is to determine the fault location by measuring the distance (or impedance) between the fault point and the protection installation site, and take corresponding protection measures. Its core component is impedance relay, which can calculate according to the ratio of current and voltage Measure the impedance to determine the distance of the fault point. 

 
Configuration of line distance protection 

Line distance protection mainly consists of the following parts: 

1. Starting component: instantaneous starting protection device when a short circuit fault occurs. 

2. Directional component: Determine the direction of short-circuit fault and ensure the directionality of protection action. 

3. Measuring component: Measure the distance (or impedance) from the short circuit point to the protection installation. 

4. Time element: acts according to the predetermined time limit characteristics to ensure the selectivity of protection actions. 

5. Actuator: acts to trip the circuit breaker and cut off the faulty circuit. 

Principle of line distance protection 

The length of the transmission line is constant, and its impedance is basically constant. When a transmission line fails, the fault point to the protection installation.The impedance at will change. Line distance protection determines whether the fault occurs in the protection range by measuring this impedance change Within the enclosure. When the measured impedance is less than the set impedance, the protection device will send out an action signal to cut off the faulty line and ensure that the power system.

Safe and stable operation of the system. 

By measuring the change of impedance, we can judge whether the fault occurs in the protection zone, and take corresponding protective measures. 

Time-limited characteristics of distance protection 

The relationship between the action time (t) of distance protection and the distance (1) from the protection installation point to the short circuit point t = f (1) is called distance protection 

Time limit characteristic. This feature is similar to three-stage current protection and is divided into three action ranges: 

1. Paragraph I: Instantaneous action, the protection range is 80 ~ 85% of the total length of the line. 

2. Paragraph II: Time-limited action, the protection range should not exceed the protection range of the next line distance from Section I, with a higher 

A time limit of t to ensure the selectivity of action. 

3. Paragraph III: Overcurrent protection is similar, its starting impedance is selected according to the load parameters during normal operation, and the action time limit .One At higher than the maximum action time limit of other protections within the protection range. 

The importance of distance protection 

Distance protection plays an important role in power systems, mainly reflected in the following aspects: 

1. Improve the selectivity of protection: Through the time limit characteristic, ensure that only the faulty line is cut off without affecting other normal operation lines .

2. Improve the quick action of protection: Section I acts instantaneously to quickly remove faults and reduce equipment damage and system impact. 

3. Improve the sensitivity of protection: it can reliably reflect various short-circuit faults, regardless of the location and type of the fault point, it is sure the safe and stable operation of the power system.