6. System modeling

The simulation of line differential protection is presented in Simulink/MatLab environment, as shown in Figure 8.

It simulates three-phase, the system components are a transmission line with PV arrays (800 kW), Wind farm (9 MW), Resistive load (45 kW, 100 kW), 25 kV distribution Bus, and the utility grid. The proposed settings of the protection scheme for transmission lines from Bus-Bar 7 to Bus-Bar 9, and the information corresponding to the lines are listed in Table 2, where is the rated secondary current. In this study, is taken to be 1 Amp. According to the value of, the following constants are:

where In is the current rating of the secondary current transformer; Io is the differential current at zero bias current; Ibias is the bias current when the relay characteristic starts to change; and K1, K<sup>2</sup> is the percentage biases. These constants can be obtained from the relay characteristic, which is used in relay operations. The differential protection operating region is above the slope of the characteristic, and the restraining of the region is below the slope of the characteristic. The dual slope bias technique is used to improve stability through fault and external fault CT saturation to provide further security. To achieve the appropriate setting, the characteristics of the relay to be applied must be considered. Three adjustable values

Innovative Differential Protection Scheme for Microgrids Based on RC Current Sensor

DOI: http://dx.doi.org/10.5772/intechopen.85473

The block consists of a relay that is divided into two units, as shown in Figure 9.

Differential protection between the two circuit breaker CBs, are known the local side (CB1) and far side (CB2), the Current Sensors RCA and RCB are installed at the Bus-Bar (7 and 9), to measure the current and voltage per phase. The current and voltage of each phase of the analog signal are converted into digital data using an analog-to-digital converter (ADC). The local side is directly connected to the relay, whereas the far side is connected through the delay block. Channel time delay is set at 27 ms, the output of the differential relay block is binary (0, 1). When disturbances happen in the protected zone, a current difference between the two CBs (local and remote) exists. Thus, the relay sends a signal tripping to isolate the defective zone from the rest of the protection scheme. In this study, we propose that the fault will occur in the middle of the transmission line, starting at 0.3 ms. In the fault parameter block, the fault type is simulated separately using MATLAB. This

Five cases have been tracked: Case 1, single line to ground fault (SLGF); Case 2, line-to-line fault (LLF); Case 3, double line to ground fault (2LGF); Case 4, threeline fault (3LF); and Case 5, three line to ground fault (3LGF). The main principle of the differential relay should be compared for both ends of the protected area. Modeling for each case is similar through comparison of the current at both ends. All used case results are indicated in Figures 10–24. Three diagrams, namely, remote, local, and differential, are presented in every figure. Remote and local measurements are conducted separately; each colour in this diagram represents one

(from the relay manual) are recommended as follows.

section investigates the cases of faults (internal and external).

7. Simulation results and discussion

Figure 9.

123

Flowchart for decision block.

$$I\_O = 0.3, \quad I\_{S2} = 0.2, \quad K\_1 = 0.35, \quad K\_2 = 1.25$$

Figure 8. Simulation representation of the differential protection scheme.


Table 2. Relay setting ranges. Innovative Differential Protection Scheme for Microgrids Based on RC Current Sensor DOI: http://dx.doi.org/10.5772/intechopen.85473

Figure 9. Flowchart for decision block.

interconnected and can be communicated to the central IED, which is implemented in the substation. On the other hand, IEDs can also monitor and update the electric flow of real-time status and can be used to manage and control the network. Figure 7 shows the monitoring and control by supervisory control and data acqui-

The simulation of line differential protection is presented in Simulink/MatLab

It simulates three-phase, the system components are a transmission line with PV

arrays (800 kW), Wind farm (9 MW), Resistive load (45 kW, 100 kW), 25 kV distribution Bus, and the utility grid. The proposed settings of the protection scheme for transmission lines from Bus-Bar 7 to Bus-Bar 9, and the information corresponding to the lines are listed in Table 2, where is the rated secondary current. In this study, is taken to be 1 Amp. According to the value of, the following

IO ¼ 0:3, IS<sup>2</sup> ¼ 0:2, K<sup>1</sup> ¼ 0:35, K<sup>2</sup> ¼ 1:2;

Relay setting Range Differential current setting (0.2–2.0 In) Bias current threshold setting (1–30) Lower percentage bias setting (0.3–1.5) Higher percentage bias setting (0.2–2.0 In)

sition system for smart grid technology.

Micro-Grids - Applications, Operation, Control and Protection

environment, as shown in Figure 8.

6. System modeling

constants are:

Figure 8.

Table 2.

122

Relay setting ranges.

Simulation representation of the differential protection scheme.

where In is the current rating of the secondary current transformer; Io is the differential current at zero bias current; Ibias is the bias current when the relay characteristic starts to change; and K1, K<sup>2</sup> is the percentage biases. These constants can be obtained from the relay characteristic, which is used in relay operations. The differential protection operating region is above the slope of the characteristic, and the restraining of the region is below the slope of the characteristic. The dual slope bias technique is used to improve stability through fault and external fault CT saturation to provide further security. To achieve the appropriate setting, the characteristics of the relay to be applied must be considered. Three adjustable values (from the relay manual) are recommended as follows.

The block consists of a relay that is divided into two units, as shown in Figure 9.

#### 7. Simulation results and discussion

Differential protection between the two circuit breaker CBs, are known the local side (CB1) and far side (CB2), the Current Sensors RCA and RCB are installed at the Bus-Bar (7 and 9), to measure the current and voltage per phase. The current and voltage of each phase of the analog signal are converted into digital data using an analog-to-digital converter (ADC). The local side is directly connected to the relay, whereas the far side is connected through the delay block. Channel time delay is set at 27 ms, the output of the differential relay block is binary (0, 1). When disturbances happen in the protected zone, a current difference between the two CBs (local and remote) exists. Thus, the relay sends a signal tripping to isolate the defective zone from the rest of the protection scheme. In this study, we propose that the fault will occur in the middle of the transmission line, starting at 0.3 ms. In the fault parameter block, the fault type is simulated separately using MATLAB. This section investigates the cases of faults (internal and external).

Five cases have been tracked: Case 1, single line to ground fault (SLGF); Case 2, line-to-line fault (LLF); Case 3, double line to ground fault (2LGF); Case 4, threeline fault (3LF); and Case 5, three line to ground fault (3LGF). The main principle of the differential relay should be compared for both ends of the protected area. Modeling for each case is similar through comparison of the current at both ends.

All used case results are indicated in Figures 10–24. Three diagrams, namely, remote, local, and differential, are presented in every figure. Remote and local measurements are conducted separately; each colour in this diagram represents one

Figure 13.

Figure 14.

Figure 15.

125

SLGF (A) voltage waveform.

SLGF (A) current waveform.

2LGF voltage waveform.

Innovative Differential Protection Scheme for Microgrids Based on RC Current Sensor

DOI: http://dx.doi.org/10.5772/intechopen.85473

Figure 10. SLGF current waveform.

Figure 11. SLGF voltage waveform.

Figure 12. 2LGF current waveform.

Innovative Differential Protection Scheme for Microgrids Based on RC Current Sensor DOI: http://dx.doi.org/10.5772/intechopen.85473

Figure 13.

Figure 10.

Figure 11.

Figure 12.

124

2LGF current waveform.

SLGF voltage waveform.

SLGF current waveform.

Micro-Grids - Applications, Operation, Control and Protection

Figure 14. SLGF (A) current waveform.

Figure 15. SLGF (A) voltage waveform.

Figure 19.

Figure 20.

Figure 21.

127

3LF voltage waveform.

3LF current waveform.

2LGF (B and C) voltage waveform.

DOI: http://dx.doi.org/10.5772/intechopen.85473

Innovative Differential Protection Scheme for Microgrids Based on RC Current Sensor

Figure 16.

Double-line (A and B) fault current waveform.

Figure 17. Double-line (A and B) fault voltage waveform.

Figure 18. 2LGF (B and C) current waveform.

Innovative Differential Protection Scheme for Microgrids Based on RC Current Sensor DOI: http://dx.doi.org/10.5772/intechopen.85473

Figure 19.

Figure 16.

Figure 17.

Figure 18.

126

2LGF (B and C) current waveform.

Double-line (A and B) fault current waveform.

Micro-Grids - Applications, Operation, Control and Protection

Double-line (A and B) fault voltage waveform.

2LGF (B and C) voltage waveform.

Figure 20. 3LF current waveform.

Figure 21. 3LF voltage waveform.

Figure 22.

3LGF current waveform.

Figure 24 shows the time differences between the moment of a fault and signal of the breaker during and after the occurrence of the fault (Table 3). Displays the output of our proposed relay measurements; compared with the traditional behaviour in normal operation, the speed of our proposed scheme is less than one cycle.

Decision speed Less than one cycle

Measurements Zone relay Relay output Trip or no trip The threshold of operation t = 0.3 ms

Innovative Differential Protection Scheme for Microgrids Based on RC Current Sensor

DOI: http://dx.doi.org/10.5772/intechopen.85473

The reliability of the relay protection system can be described in two respects: dependability and security. The reliability of the relay protection system detects and disconnects all faults in the protection zone. The safety of the relay protection system is capable of rejecting all events and transients that are not faulty so that the healthy part of the power system is not unnecessarily disconnected. Differential protection is the preferred solution for widespread use; fault protection for multiterminal systems becomes very difficult, and fast fault detection of systems becomes very important. This result provides different solutions for transmission line protection. This method is better than distance protection because differential

The performance of this algorithm is more efficient than distance relay protection. The disadvantages of the distance on the transmission line and the directional

1. If a fault occurs at the end of the line, the relay cannot be disconnected

protection requires fewer input data and reduces computation time.

8. Summary

129

Figure 24.

Table 3.

Specifications of the proposed relay.

over-current relay are as follows:

immediately at both ends of the line.

The difference between the occurrence of a fault and a breaker signal.

Figure 23. 3LGF voltage waveform.

phase, namely, red, green, and blue for phases A, B, and C, respectively. The signal to Trip is represented as a binary (0, 1) measurement depending on the difference between the signals of the two ends for sending the signal to the circuit breaker. In Figures 10–23, two types of status are shown: for current differential and the voltage differential, with the fault occurring at t = 0.3 ms.
