Power System Safety and Protection

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Master of Engineering
(Electrical Systems)

Unit code MEE512
Unit name Power System Safety and Protection
Assessment # 3
Paper # B
Version # 1
Created by Naser Hashemnia Date 17 Aug 2022
Reviewed by Yuanyuan Fan
Naser Hashemnia
Date 18 Aug 2022
27 Jan 2023

Master of Engineering (Electrical Systems) 2
MEE512_Assessment3_PaperB_v1
Assessment Instructions:
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understand your requirements and responsibilities as a student of EIT.
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Master of Engineering (Electrical Systems) 3

Unit code and name: MEE512: Power System Safety and Protection
Assessment #: 3B
Assessment type: Practical
Weighting: 25%
Total marks: 100 marks

Please complete your answers on the assessment cover page document available on Moodle.
Clearly label your question numbers (there is no need to copy the full question over). Include all working
out.
Part 1:
A radial distribution system is supplied from 22 kV network shown in Figure 1. The details of the
load impedances and equipment are indicated on the single line diagram and Table 1.
Use the given information in Figure 1 and Table 1 to solve Question 1.

Master of Engineering (Electrical Systems) 4
MEE512_Assessment3_PaperB_v1
Figure 1
Table 1

CTs Transformer Cable Motor Bus
CT_1= 200/1
CT_2= 50/1
CT_3 = 750/1
CT_4=650/1
1.5 MVA
Δ / Y
Z =6.2%
XLPE CU 11 KV from
OLEX
95 mm^2 CU
20 meter
Z=0.05 Ohms
220 kW
Running PF=1
Start current 1 kA
Bus _1= 22 kV
Bus_2= 0.415 kV

Question 1: (50 marks)
a) Use ETAP software to build the model of the network and run the short circuit simulation:
(25 marks)
i. determine the 3-phase fault level current (kA) at Bus 22 kV.

Master of Engineering (Electrical Systems) 5
ii. determine the 3-phase fault level current (kA) at Bus 0.415 kV.
iii. determine the fault level at the motor terminal.
Assumptions:
Relay selection: using the ETAP library, select a protection manufacturer (for example ABB,
Schneider, Schweitzer, etc.) and select the relevant over current protection relays.
Consider the coordination time between relays is 0.25 seconds.
TMS selection is based on the range and steps available on the selected relay.
The assumption from the utility for Relay 1:
TSM = 0.6 p.u.
Pick-up (sec) = 1 p.u.
CT RATIO = 200/1
b) Use time delayed and instantaneous over current relays to perform proper discrimination
and coordination settings to protect the network. (A screenshot of the ETAP modeling must
be included in the report). (25 marks)
Part 2

Question 2: (50 marks)
a) Using standard IDMT relays, calculate the relay settings of the relays R1, R2 and R3 for the
system shown in Figure 2 below. Plug setting and TMS of the relay
R4 is 100% of CT
secondary rating and 0.1, respectively. (25 marks)

Figure 2
Master of Engineering (Electrical Systems) 6
MEE512_Assessment3_PaperB_v1
b) Figure 3 shows a single-line diagram of a portion of a power station. Considering an
adequate discrimination margin, determine the relay settings of phase overcurrent relays of
IDMT type used therein. Assume that the minimum operating time of relays beyond a PSM
equal to 20 is constant at 2.3 seconds at a TMS of 1.0. The fault level at the 6.6 kV bus is 45
kA and that at the 415 V bus is 42 kA. (25 marks)
Figure 3
END OF ASSESSMENT