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MODULE TITLE : ELECTRICAL SUPPLY AND DISTRIBUTION SYSTEMS

TOPIC TITLE : SUPPLY SYSTEMS AND LOAD VOLTAGE LEVELS

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ESD - 3 - TMA (v1)

THIS BOX MUST BE COMPLETED

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Published by Teesside University Open Learning (Engineering)

School of Science & Engineering

Teesside University

Tees Valley, UK

TS1 3BA

+44 (0)1642 342740

retrieval system, or transmitted, in any form or by any means, electronic, mechanical,

photocopying, recording or otherwise without the prior permission

of the Copyright owner.

This book is sold subject to the condition that it shall not, by way of trade or

otherwise, be lent, re-sold, hired out or otherwise circulated without the publisher's

prior consent in any form of binding or cover other than that in which it is

published and without a similar condition including this

condition being imposed on the subsequent purchaser.

IMPORTANT

Before you start please read the following instructions carefully.

1. This assignment forms part of the formal assessment for this module. If

you fail to reach the required standard for the assignment then you will be

allowed to resubmit but a resubmission will only be eligible for a Pass

grade, not a Merit or Distinction.

You should therefore not submit the assignment until you are reasonably

sure that you have completed it successfully. Seek your tutor's advice if

unsure.

2. Ensure that you indicate the number of the question you are answering.

3. Make a copy of your answers before submitting the assignment.

4. Complete all details on the front page of this TMA and return it with

the completed assignment including supporting calculations where

appropriate. The preferred submission is via your TUOL(E) Blackboard

account:

https://eat.tees.ac.uk

5. Your tutor’s comments on the assignment will be posted on Blackboard.

Teesside University Open Learning (Engineering)

1. (i) State briefly how the equivalent circuit of a generator is similar to

that of a short transmission line.

(ii) On what assumptions is the representation of the following simple

load supply system (FIGURE 1) based?

FIG. 1

(iii) In what way does it differ from the radial supply system shown in

FIGURE 2?

FIG. 2

(iv) In FIGURE 1, the first transformer steps up the voltage and the

second steps down the voltage. State the reason or reasons why you

think this is done.

Load

Teesside University Open Learning (Engineering)

2. For the following distribution feeder systems shown in FIGURES 3(i), (ii)

and (iii) determine the load voltage levels.

FIG. 3

(i)

(ii)

(iii)

11kV j4.6Ω

3.2MVA @ 0.8 pf lag

1.8MVA @ 0.6 pf lead

11kV j4.6Ω 3.2MVA

@ 0.8 pf lag

1.8MVA @ 0.6 pf leadj2.7Ω

11kV j4.6Ω 3.2MVA

@ 0.8 pf lag

1.8MVA @ 0.6 pf lead

j5.4Ωj2.7Ω

Teesside University Open Learning (Engineering)

3. (a) A short 3-phase 11 kV line delivers a load of 4.1 MW, 2.6 MVAr lag.

If the series impedance of the line is (7.2 + j12.1) Ω/ph, calculate the sending end voltage and load angle.

(b) Develop the receiving end performance chart for the above line and

load to a 3-phase power scale. (Use a scale of 10 mm = 1000 V and

30 mm = 4.1 MW.)

4. Using the chart you produced in Question 3, determine:

(a) the real and reactive power when

(i) the transmission angle remains unaltered and the sending end

voltage is increased by 28%

(ii) the original sending-end voltage is reduced by 15% and the

transmission angle increased by 9°. (Use the same scale as that

for Question 3 (b))

(b) the real power limit for the sending voltage in (ii) above (i.e. when

reduced by 15%).

Teesside University Open Learning (Engineering)

5. The following phase schematic diagram (FIGURE 4) shows an 11 kV,

50 Hz, 3-phase, short line feeding a load. By calculation or constructing

the phasor diagram (use a scale of 1 mm = 2 A) for the load current with

VR as reference, determine the capacitive current and

• calculate the capacitive reactance/ph such that the load power factor

is increased to 0.98 lag

• calculate the percentage reduction in line current with this value of

capacitive reactance in circuit.

FIG. 4

6. Compare FIGURES 2 and 4 from lesson ESD - 2 - 2 (reproduced here)

with those of FIGURES 1 and 8 from lesson ESD - 3 - 2 (also reprodued)

and state briefly why they are similar.

FIG. 2 from ESD - 2 - 2 (reproduced)

R I

IZS

IXS IR

VR = 11kV

Total load 3.2 MW

1.9 MVAr lag

R + jX

√3

Teesside University Open Learning (Engineering)

FIG. 4 from ESD - 2 - 2 (reproduced)

FIG. 1 from ESD - 3 - 2 (reproduced)

R + jX

Z ∠ ψ

NS NR

VR ZR ∠ φ

ψ φ

ZS –

VE ZS VI

∝ E since is constant

V ZS

Teesside University Open Learning (Engineering)

FIG. 8 from ESD - 3 - 2 (reproduced)

Real power

Reactive power lead

Reactive power lag

Real power limit ba

Constant p.f.

Constant Q

Constant P

VRI

VSVR Z

(VR) 2

Teesside University Open Learning (Engineering)

Question No.

Teesside University Open Learning (Engineering)

Question No.

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