**5. Implementation of the digital differential protection using matlab**

This implementation is done using Matlab/Simulink environment. Figure 7 shows the simulated power system built in Matlab/Simulink environment. In which a three phase, 250MVA, 60Hz, (735/315) kV, Y/ power transformer is used in this system. The contents of each designed block are illustrated in separate figs. 8 to 12.

There are some coefficients are kept hidden for the reader to find them. These coefficients can change the behavior of the design.

**Figure 7.** Matlab/Simulink Model of the proposed system

**Figure 8.** The differential relay block contents

logic (1) takes place, which indicates a detection of an internal or external fault.

detection of an internal fault. Then a trip signal is released to stop the simulation.

back to step two to start the calculation again for the next sample.

each designed block are illustrated in separate figs. 8 to 12.

**Figure 7.** Matlab/Simulink Model of the proposed system

scope 3

scope 5

scope 4

i + i + i + -

can change the behavior of the design.

Discrete, Ts = 5e-005 s.

> A B C

a b c CB1

A B C a b c

Iabc\_B2 Iabc\_B3

N A B C

**Step 3.** Taking the final decision:

In the meantime, the harmonic calculation is performed. If the percentage value of the second harmonic amplitude is in the range of (0.3 to 0.6) of the fundamental component amplitude, then the logic (0) occurs, that means recognition of inrush current. Otherwise, the

If the logic cases received from both cases (a & b) in step two are both (1), that indicates a

For the other logic options of (0,1) means an external fault, (1,0) means an inrush current, or (0,0) indicate an occurrence of an inrush current or an external fault, and the simulation goes

This implementation is done using Matlab/Simulink environment. Figure 7 shows the simulated power system built in Matlab/Simulink environment. In which a three phase, 250MVA, 60Hz, (735/315) kV, Y/ power transformer is used in this system. The contents of

There are some coefficients are kept hidden for the reader to find them. These coefficients

Power Transformer CTs CTs

Trip

I4

I5

I3

a b c

fault

A B C

i + i + i + -

A

a

A1

A

a

A1

a1

A

a

A1

a1

a1

I6

scope 2

scope 1

A B C a b c

A B C

a b c CB2

A B C 45 kW

Diff. Relay

I2

I1

AA1

AA1

AA1

aa1

aa1

aa1

A B C

**5. Implementation of the digital differential protection using matlab** 

**Figure 9.** The comparator block contents

**Figure 10.** The amplitude comparator block contents

**Figure 11.** The harmonic comparator block contents

**Figure 12.** The ratio block contents
