1. DESIGN OF A 400kV TRANSMISSION NETWORK
AND IT’S PROTECTION RELAY
(CASE STUDY OF KARUMA TO TORORO LINE)
BY
OWITI COLLINCE MANUKU BELE
MUYINZA ISAAC BELE
2. Project background
The Energy Policy for Uganda (2002)
It was put in place by the Government. Its main policy goal is “to
meet the energy needs of the Ugandan population for social and
economic development in an environmentally sustainable manner”.
One of UETCL Specific strategies to achieve this is by Increasing
the transmission voltage from 66kV and 132kV to 220kV and
400kV
3. Problem statement
Uganda is introducing a 400 kV network to its existing grid.
This high transmission voltage is going to result into more
severe faults and without appropriate design and protection it
can be hazardous to both personnel and equipment.
4. Objectives
Main Objective:
To design 400kV Transmission line from Karuma to Tororo and
come up with its Protection Relay system .
Specific Objectives:
To design a Transmission power system network from Karuma to
Tororo.
To design a protection relay system for transmission lines, busbars
and transformers.
5. Methodology
Step 1: Literature review
Studied relays and the different protection schemes.
Step 2: Data collection
Collected parameters required to calculate the settings.
Step 3: Data analysis (calculation)
Calculated the relay settings for 400 kV.
Used DigiSilent simulation software.
Step 4: Results
Came up with a design and settings to be used for proposed 400kV
transmission network.
6. Generator specifications
Substation Power
(MVA)
Voltage
(kV)
Active
power
(MW)
Reactive
Power (Mvar)
Power factor
Karuma 150 17 120 90 0.8
Source- Uganda Electricity Transmission Company Limited
Substation Number of
transformers
Power (MVA) Voltage(kV) Power factor
Karuma 2 500 17/400 0.8
Lira 2 320 400/33 0.8
Opuyo 2 320 400/33 0.8
Mbale 1 320 400/11 0.8
Tororo 2 320 400/220 0.8
Transformer specifications
Design Stage
7. Line ratings
Transmission
Line
Conductor
Type
Voltage
(kV)
Zero phase
sequence
Impedance(Ω)
Positive phase
sequence
impedance(Ω)
Line
length(KM)
Cable
cross
section
(mm2)
Karuma To
Lira
ACSR 400 0.2587 + j1.1740 0.03293 + j0.3184 80 520
Lira to opuyo ACSR 400 0.2587 + j1.1740 0.03293 + j0.3184 116 520
Opuyo to
Mbale
ACSR 400 0.2587 + j1.1740 0.03293 + j0.3184 102 520
Mbale to
Tororo
ACSR 400 0.2587 + j1.1740 0.03293 + j0.3184 40 520
Source- Uganda Electricity Transmission Company Limited
8. Power Grid
The grid was divided into two parts . The first part is from
Karuma to Opuyo and the second part is from Mbale to
Tororo.
12. Distance relay protection
Tripping Times
= Operating time of zone one+ CB operation + Distance relay
reset time + Errors of distance relay internal times+ safety margin
Zone reach
• =(line impedance per km*line length* percentage
reach)
13. Table of results
Zone Impedance
Magnitude ( Ω)
Operational time (s)
Karuma foward
Zone one 20.488 < 84.1 0.02
Zone two 30.732 < 84.1 0.14
Zone three 38.415< 84.1 0.26
Lira forward
Zone one 29.7 < 84.1 0.02
Zone two 53.455 < 84.1 0.14
Zone three 76.18 < 84.1 0.26
Lira reverse
Zone one 20.488 < 84.1 0.02
Zone two 30.732 < 84.1 0.14
Zone three 38.415< 84.1 0.26
14. Table of results(cont)
Opuyo forward
Zone one 26.11 < 84.1 0.02
Zone two 39.04 < 84.1 0.14
Zone three 48 < 84.1 0.26
Opuyo reverse
Zone one 29.696 < 84.1 0.02
Zone two 49.92 < 84.1 0.14
Zone three 67.84 < 84.1 0.26
Mbale forward
Zone one 10.24 < 84.1 0.02
Zone two 15.36 < 84.1 0.14
Zone three 19.2 < 84.1 0.26
Mbale reverse
Zone one 26.112 < 84.1 0.02
Zone two 51.2 < 84.1 0.14
Zone three 82.56 <84.1 0.26
Tororo reverse
Zone one 10.24 < 84.1 0.02
Zone two 29.12 < 84.1 0.14
Zone three 64 < 84.1 0.26
17. Overcurrent Relay
The Pick up current is determined in such a manner that the relay
does not trip under normal currents.
Pick up currents (4A,5A,6A,7A,8A)
Select the intentional delay indicated by the Time Multiplier
Setting (TMS).
Choosing The lowest Time Multiplier Setting to ensure fastest
operation
TMS for Relay at bus bar 1 = 0.5
18. Table of results for overcurrent relay settings
Maximum short circuit current
400kV Bus bar Time Multiplier
Setting
Pick up current (A) Operating Time
(Seconds)
Tororo 0.5 4 0.11
Mbale 1 5 0.51
Opuyo 2 6 0.91
Lira 3 7 1.31
Karuma 4 8 1.71
21. For 400/33 kV transformers
Current That flows into the line
From Power = 3 *Current*Line voltage
Current(I) =
Power
𝑉𝑜𝑙𝑡𝑎𝑔𝑒 3
On the HV side
Ip =
320∗106
400∗103∗ 3
= 462A
CT Ratio of 500/5
On the LV side
Is =
320∗106
33∗103∗ 3
= 5600A
CT Ratio of 6000/5 on the LV side
22. DIFFERENTIAL RELAY
Output current from the CTs
HV side
462∗5
500
= 4.62 A
Ratio correction factor;
5
4.62
=1.08
LV side
5600∗5
6000
= 4.67 A
Ratio correction factor;
5
4.67
=1.07
Calculation (Cont’)
23. Table of results for Differential relay settings for
transformers
Substation Power
rating
(MVA)
Voltage
(kV)
Current (A) CT ratio CT output (A) Ratio
correction
factor
HV LV HV LV HV LV LV HV
Step Down Transformers
Lira, Opuyo 320 400/33 462 5600 500/5 6000/5 4.62 4.67 1.08 1.07
Mbale 320 400/11 462 16800 500/5 17000/5 4.62 4.92 1.08 1.01
Tororo 320 400/220 462 840 500/5 900/5 4.62 4.67 1.08 1.01
Step Up Transformer
Karuma 500 18.5/400 722 15604 800/5 16000/5 4.51 4.88 1.11 1.02
24. Table of results for Differential relay settings for
busbars
Sustation Power rating
(MVA)
Voltage (kV) CT ratio Current (A) CT output (A) Ratio
correction
factor
Karuma 500 400 800/5 722 4.51 1.11
Opuyo Lira,
Mbale Tororo
320 400 500/5 462 4.62 1.08
Opuyo, Lira ,
Tororo
320 33 6000/5 5600 4.67 1.07
Mbale 320 11 17000/5 16800 4.92 1.01
Karuma 500 18.5 16000/5 15604 4.88 1.03
25. Challenges
In the process of coming up with the design and relay
settings, we faced many challenges and these included:
Uganda Transmission Company Limited(UETCL)
provided less information from that we had requested.
It was difficult to schedule meetings with the engineers of
UETCL, sometimes they were in the field and when they
returned they where very tied or had other meetings and
this made it difficult.
26. Recommendation
This project only covered 400kV transmission line from
Karuma to Tororo, therefore other studies on the line
should be done for example the generator protection at
Karuma substation.
College of Engineering ,Design, Art and Technology
should set up a protection lab where relay settings can be
simulated for protection relay setting studies. This is
because it is difficult to get access to the relays being
used.
27. conclusion
This study has resulted in a number of conclusions which
can be summarized as follows:
The power grid has been designed within the DigSILENT
power factory which can calculate the worst case scenario
of short-circuit current.
The transmission voltage level has been selected to be
400kV being stepped down to 11kV, 33kV and 220kV.
The main objective was accomplished from the results and
simulations obtained for the network.
