To perform experiment on Distance protection Relay.

Experiment No.: – 04

Objective: –

To study the distance protection scheme for the transmission line with a numerical distance relay.

Theory: –

The fault study of the transmission line is to be carried out prototype low voltage transmission line modeling, which represents the 125 km long, 230 kV transmission line. The per-unit impedance of 125km long, 230 kV transmission line is typically 0.3 p.u on 100 MVA base. The prototype transmission line model is made with base of 230 V, 1 kVA. It consists of series resistance, series inductor, and shunt admittance (capacitor) to represent the line parameters as shown in figure 1. However, the shunt admittance is used for load flow study and disconnected for fault study (as shown in figure 2). The two sections of 125 km long transmission line model are used for fault study and distance relay study.

Transmission line model:

The transmission line parameters of each section are given as follows:

Z₁ = 0.3 pu; Z₂ = 0.3 pu; Z₀ = 3* Z₁; Z_n = 0.15 pu; Z_F=0;

Base voltage (𝐾V_b) = 0. 400 kV (400 V);

Base MVA (𝐾VA_b) = 1*10^-3 (1 kVA);

\[\color\green{Base\;current\;(I_b)}\color\red{=\;\dfrac{MVA_b*1000}{\sqrt3*KV_b}}\] \[\color\red{=\;\dfrac{1*10^{-3}*1000}{\sqrt3*0.4}\;=\;1.44\;A}\] \[\color\green{Base\;impedance\;(Z_b)}\color\red{=\;\dfrac{KV_b^2}{MVA_b}}\] \[\color\red{=\;\dfrac{0.4^2}{1*10^-3}\;=\;160\;{\Omega}}\]

Actual impedance of the 0.3pu transmission line = 0.3 * 160 = 48 Ώ

Circuit Diagram: –

***Figure 3. Power system modeling for fault study and distance protection***

The symmetrical (LLL/LLLG) and unsymmetrical faults (LG, LL, and LLG) can be simulated at
each section of the transmission line. The faults are simulated by activating the contactor C₆, C₇, C₁₀, C₁₆, C₁₇, and C₂₀ as shown in Figure 3.

The fault current magnitude of each fault can be calculated theoretically as follows:

Symmetrical fault:

\[\color\red{I_F\; =\; \dfrac{E}{Z_1}}\;\color\green{…………..(1)}\]

Unsymmetrical fault:

\[LG\;(AG)\;\] \[I_{a1} = \left\{\dfrac{E}{Z_1+Z_2+Z_0+3(Z_F+Z_n)}\right\};\] \[I_{F,a} = 3*I_{a1}………..(2.1)\]

\[LL\;(BC)\] \[ I_{a1} = \left\{\dfrac{E}{(Z_1+Z_2+Z_F)}\right\}\] \[I_{F,b} = -j*\sqrt3*I_{a1}\]

\[LLG\;(BCG)\] \[I_{a1} = \left[\dfrac{E}{Z_1+\left\{\dfrac{Z_2*(Z_0+3(Z_F+Z_n))}{Z_2+(Z_0+3(Z_F+Z_n))}\right\}}\right]\]

\[I_{a2} = -I_{a1}*\left\{\dfrac{Z_0+3(Z_F+Z_n)}{Z_2+(Z_0+(3(Z_F+Z_n))}\right\}\]

\[I_{a0} = -I_{a1}* \left\{\dfrac{Z_2}{Z_2+(Z_0+3(Z_F+Z_n))}\right\}\]

\[I_{F,b} = \alpha^2I_{a1}+\alpha I_{a1}+I_{a0}\]

Also, the voltage during fault is calculated using the symmetrical voltage components.
The transmission line parameters of each section are given as follows:
Z₁ = 0.3 pu; Z₂ = 0.3 pu; Z₀ = 3* Z₁; Zn = 0.15 pu;

Distance protection (MiCOM P442):

A numerical (digital) MiCOM P442 relay is used for transmission line protection. It is connected with the power system network through CT and PT. The ratio of CT and PT are 5/5 and 400/110, respectively. The MiCOM P442 uses the quadrilateral characteristics for phase and earth distance protection. It also has some additional functions like directional/non-directional overcurrent, under-voltage, over-voltage, etc. However, only the distance function is enabled in the relay used in the lab to avoid the overlapping between distance and other functions. The MiCOM P442 relay is also provided with the measurement, control, monitoring, post fault analysis, and self-diagnostic functions. The post fault analysis can be with the help of the fault recorder, which records all fault and disturbance with waveforms. The settings and functions of the MiCOM protection relay can be accessed both from the front panel keypad and LCD, and via the front and rear communication ports. Model no.: MiCOM P442911B2M0550K. The zone 1 setting is
set for 125 km long transmission line section modeling. The zone 2 setting is set for 250 km long transmission line sections modeling.

The distance relay measures the positive sequence impedance to detect the fault as follows:

\[ For\; phase \;fault,\; \;Z_1 = \left\{\dfrac{(V_b-V_c)}{(I_b-I_c)}\right\}…..(3)\]

\[ For\; ground \;fault,\] \[Z_1 = \left[\dfrac{V_a}{I_a+\left\{\dfrac{(Z_0-Z_1)}{3Z_1}\right\}I_{res}}\right]\]

PROCEDURE:

Switch on MCB on EMT1 panel.
Put forward/reverse switch SW1 on EMT4A at OFF position.
Remove the connections EMT54 (7) – EMT38 (28) and connect inductor in grid of
transmission line i.e., EMT42A (25) – EMT54 (7) and EMT42A (29) – EMT38 (28).
Screen control: Open ‘Distance Protection’ menu on SCADA screen in PC.
Press ‘ON’ button to make ‘CB19 ON’ on the SCADA screen.
Select ‘short TL’ button on the SCADA screen.
Select minimum load (225 Ώ)
Apply the different fault by selecting the appropriate fault selection push button on the
SCADA screen.
View the fault recorder in SCADA screen by clicking on ‘Dist. Relay EMT 53’ which
will open the popup measurement screen. Note down the records.

Observation Table: PRACTICAL OBSERVATION-

Type of Fault at 125km	Started phase	Trip Zone	Fault location	V_R	V_Y	V_B	I_R	I_Y	I_B
LG (AG)
LL (AB)
LLG (ABG)
LLL (ABC)
LLLG (ABCG)

Table No.4.1

Type of Fault at 250km	Started phase	Trip Zone	Fault location	V_R	V_Y	V_B	I_R	I_Y	I_B
LG (AG)
LL (AB)
LLG (ABG)
LLL (ABC)
LLLG (ABCG)

Table No.4.2

THEORETICAL CALCULATION:

Type of Fault at 125km	V_R	V_Y	V_B	I_R	I_Y	I_B	Z_1T
LG (AG)
LL (AB)
LLG (ABG)
LLL (ABC)
LLLG (ABCG)

Table No.4.3

Type of Fault at 250km	V_R	V_Y	V_B	I_R	I_Y	I_B	Z_1T
LG (AG)
LL (AB)
LLG (ABG)
LLL (ABC)
LLLG (ABCG)

Table No.4.4

Note: (i) Z_1T – Theoretically calculated positive sequence impedance using (3);
(ii) Calculate the Z_1T using the measured voltage and current obtained in the fault study.

Calculation:

Conclusion: –

To be written by student.

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