Case Studies and Mini-Projects
CHAPTER 6
Applied case studies across industry, system integration, and the capstone mini-project
Electrical Control of Industrial Mechanisms
Master 1, Semester 3 · 2025–2026 · Prof. Z. TIR — University of El Oued
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What you will be able to do
CHAPTER 6 · LEARNING OUTCOMES
1
Recognise the principles of Chapters 1–5 in other industries
2
Size a regenerative supply, an inching drive and a winder drive
3
Check an installation against IEEE 519, cable overvoltage and availability
4
Write a testable specification and a control philosophy
5
Size, simulate and defend a complete design
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Electrical Control of Industrial Mechanisms · Prof. Z. TIR — University of El Oued
Chapter 6 · 2
Cross-sector industrial case studies
6.1
Five questions read any machine: load, quadrants, loop, sizing quantity, failure.
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Electrical Control of Industrial Mechanisms · Prof. Z. TIR — University of El Oued
Chapter 6 · 3
Five questions for every machine
6.1 · METHOD
✓
Load character: constant torque, quadratic, constant power or active? (Ch. 1)
✓
Quadrants, and where does the braking energy go? (Ch. 3, 4)
✓
Which quantity is controlled, and by which loop? (Ch. 2, 5)
✓
Which single number sizes the equipment?
✓
What happens when the drive fails — is that acceptable?
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Electrical Control of Industrial Mechanisms · Prof. Z. TIR — University of El Oued
Chapter 6 · 4
The reversing rolling mill
6.1 · METALLURGY
Lectures, Fig. 6.1
Electrical Control of Industrial Mechanisms · Prof. Z. TIR — University of El Oued
Chapter 6 · 5
Regenerated energy and power per mill reversal
6.1 · WORKED EXAMPLE
GIVEN
Jeq = 4200 kg·m² referred to the motor; constant-torque braking from +60 rad/s to rest in 2.5 s
FIND
The energy returned, and the mean and peak power the supply converter must accept
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SOLUTION
✓
Check. 100.8 kN·m × 60 rad/s = 6.05 MW: the same peak. The regenerative front end is rated on 6 MW, not 3.
Electrical Control of Industrial Mechanisms · Prof. Z. TIR — University of El Oued
Chapter 6 · 6
The cement kiln must never stop while hot
6.1 · PROCESS INDUSTRIES
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Lectures, Fig. 6.2
→
An independent inching drive, through an overrunning clutch and on its own supply, keeps the shell turning when the main drive fails
Electrical Control of Industrial Mechanisms · Prof. Z. TIR — University of El Oued
Chapter 6 · 7
Sizing a kiln inching drive
6.1 · WORKED EXAMPLE
GIVEN
Shell at 2.5 rpm; main motor 450 kW at 1490 rpm; inching at 0.1 rpm with a 1470 rpm motor on the main gearbox input
FIND
Shell torque, inching power, ratio of the auxiliary gearbox
SOLUTION
✓
Check. At constant torque power scales with speed: 450 × 0.1/2.5 = 18 kW. Full torque, 4 % of the power.
Electrical Control of Industrial Mechanisms · Prof. Z. TIR — University of El Oued
Chapter 6 · 8
The winder: constant power with a tension loop
6.1 · PAPER AND FILM
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Lectures, Fig. 6.3
→
Constant tension F at constant surface speed v: T = F·r, ω = v/r, so T·ω = F·v stays constant
Electrical Control of Industrial Mechanisms · Prof. Z. TIR — University of El Oued
Chapter 6 · 9
Torque and speed range of a winder
6.1 · WORKED EXAMPLE
GIVEN
Rewind roll grows from a 0.15 m core to 0.75 m full diameter; web tension F = 600 N at v = 8 m/s
FIND
The torque, speed and power range of the winder drive
SOLUTION
✓
Check. 45 × 107 ≈ 225 × 21 ≈ 4.8 kW = 600 × 8: torque times speed equals tension times surface speed.
Electrical Control of Industrial Mechanisms · Prof. Z. TIR — University of El Oued
Chapter 6 · 10
What the build-up ratio and the roll inertia cost
6.1 · PAPER AND FILM
Lectures, Fig. 6.3
Electrical Control of Industrial Mechanisms · Prof. Z. TIR — University of El Oued
Chapter 6 · 11
Six machines, one method
6.1 · SYNTHESIS
Machine | Load character | Quadrants | Sizing quantity |
Rolling mill | high inertia, fast reversal | I–IV | peak regenerated power |
Arc furnace | fast electrode position | I, III | loop bandwidth; flicker |
Cement kiln | constant torque, uninterruptible | I | shell torque at inching speed |
Draw-works | active (hoist) | I–IV | hook load × speed; braking |
Pipeline pump | quadratic (centrifugal) | I | duty point, static head |
Winder | constant power, tension loop | I, II | full-roll torque; build-up ratio |
!
Every industrial drive is a combination of the loads of Chapters 1–5
Electrical Control of Industrial Mechanisms · Prof. Z. TIR — University of El Oued
Chapter 6 · 12
System integration: what surrounds the drive
6.2
A correctly chosen drive still fails in service if the system around it is inconsistent with it.
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Electrical Control of Industrial Mechanisms · Prof. Z. TIR — University of El Oued
Chapter 6 · 13
Six-pulse rectifiers inject harmonics
6.2 · POWER QUALITY
Lectures, Fig. 6.4
Electrical Control of Industrial Mechanisms · Prof. Z. TIR — University of El Oued
Chapter 6 · 14
IEEE 519 judges the TDD at the PCC
6.2 · POWER QUALITY
Lectures, Fig. 6.5
Electrical Control of Industrial Mechanisms · Prof. Z. TIR — University of El Oued
Chapter 6 · 15
IEEE 519 compliance of a drive installation
6.2 · WORKED EXAMPLE
GIVEN
1000 kVA, 6 %, 400 V transformer; LV bus is the PCC; IL = 1000 A; 250 kW of six-pulse drives, PF 0.95
FIND
The TDD for each front end, and the drive power a line reactor can serve
SOLUTION
✓
Check. Bare bridge: I5 = 256 A is 26 % of IL (limit 7 %), and v5 = 5 × 0.06 × 256/1443 = 5.3 % (limit 5 %).
Electrical Control of Industrial Mechanisms · Prof. Z. TIR — University of El Oued
Chapter 6 · 16
Long motor cables: reflections and bearing currents
6.2 · MOTOR CABLES
Lectures, Fig. 6.6
Electrical Control of Industrial Mechanisms · Prof. Z. TIR — University of El Oued
Chapter 6 · 17
Is a dv/dt filter needed?
6.2 · WORKED EXAMPLE
GIVEN
400 V supply, VDC = 566 V; 50 ns IGBT edges; 25 m of motor cable; vp = 1.5 × 10⁸ m/s; filter stretches edges to 1 µs
FIND
The peak motor terminal voltage without and with the filter
SOLUTION
✓
Check. The filter does not remove the reflection; it lengthens the edge until the cable is electrically short.
Electrical Control of Industrial Mechanisms · Prof. Z. TIR — University of El Oued
Chapter 6 · 18
Protecting a variable-speed drive
6.2 · PROTECTION
Lectures, Fig. 6.7
Electrical Control of Industrial Mechanisms · Prof. Z. TIR — University of El Oued
Chapter 6 · 19
Availability: units in series, units in redundancy
6.2 · AVAILABILITY
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Electrical Control of Industrial Mechanisms · Prof. Z. TIR — University of El Oued
Chapter 6 · 20
Value of an N+1 pump set
6.2 · WORKED EXAMPLE
GIVEN
A pumping station needs three pump sets; each set MTBF = 8000 h, MTTR = 8 h
FIND
The station availability with three sets, and with a fourth (N+1)
SOLUTION
✓
Check. Two simultaneous failures needed: 1 − A3/4 ≈ 6 q² = 6 × (0.001)² = 6 × 10⁻⁶ — the same result.
Electrical Control of Industrial Mechanisms · Prof. Z. TIR — University of El Oued
Chapter 6 · 21
Commissioning has a fixed order
6.2 · COMMISSIONING
Lectures, Fig. 6.8
→
FAT → install → loop checks → drive (nameplate, auto-tune, direction, encoder, speed loop, outer loop) → SAT → safety validation
Electrical Control of Industrial Mechanisms · Prof. Z. TIR — University of El Oued
Chapter 6 · 22
The mini-project: a capstone design
6.3
From analysing a given mechanism to conceiving, specifying and defending your own.
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Electrical Control of Industrial Mechanisms · Prof. Z. TIR — University of El Oued
Chapter 6 · 23
From specification to defended design
6.3 · METHODOLOGY
Lectures, Fig. 6.9
Electrical Control of Industrial Mechanisms · Prof. Z. TIR — University of El Oued
Chapter 6 · 24
Each stage ends with a deliverable and a test
6.3 · DELIVERABLES
Stage | Deliverable | Accepted when |
Specification | numbered requirements; loads, duty, environment | every requirement is measurable and testable |
Philosophy | axis table; safety functions; GRAFCET | every hazard has a safety function |
Sizing | calculation sheets; assumption register | every choice traced to a calculation and a datasheet |
Simulation | model and results | each result names the requirement it verifies |
Defence | report and presentation | the design answers the specification point by point |
!
A stage is finished when its test is passed, not when its time has run out
Electrical Control of Industrial Mechanisms · Prof. Z. TIR — University of El Oued
Chapter 6 · 25
Testable requirements, fixed sizing order
6.3 · METHOD
Lectures, Fig. 6.9
Electrical Control of Industrial Mechanisms · Prof. Z. TIR — University of El Oued
Chapter 6 · 26
How the mini-project is assessed
6.3 · ASSESSMENT
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Electrical Control of Industrial Mechanisms · Prof. Z. TIR — University of El Oued
Chapter 6 · 27
Common mistakes in system design
WATCH OUT
✗
MYTH
“The safety function can be implemented in the PLC program.”
✓
WHAT IS TRUE
A standard PLC can fail silently. Safety functions need certified safety hardware at the required PL (ISO 13849-1) or SIL (IEC 62061), independent of the control program.
✗
MYTH
“Selecting the drive is the design; the rest is wiring.”
✓
WHAT IS TRUE
Transformer, cables, protection, harmonics, cable length and dv/dt, earthing and EMC, braking path: any inconsistency makes a correct drive fail in service.
Electrical Control of Industrial Mechanisms · Prof. Z. TIR — University of El Oued
Chapter 6 · 28
Two traps in the numbers
WATCH OUT
✗
MYTH
“The datasheet quotes 37 % THD, so the plant meets IEEE 519.”
✓
WHAT IS TRUE
The limit is on the TDD at the PCC, referred to the whole plant's demand. The same drive complies in a large plant and violates in a small one.
✗
MYTH
“With N+1 drives the process cannot stop.”
✓
WHAT IS TRUE
The calculation assumes independent failures. Units on one switchboard, one control supply or one parameter set fail together.
Electrical Control of Industrial Mechanisms · Prof. Z. TIR — University of El Oued
Chapter 6 · 29
Two more traps
WATCH OUT
✗
MYTH
“An energy saving at rated conditions is the annual saving.”
✓
WHAT IS TRUE
Annual energy depends on the load duration curve. Weight each operating point by its real hours; rated saving × 8760 h overstates it.
✗
MYTH
“A design is complete when it works.”
✓
WHAT IS TRUE
A defensible design states its assumptions, justifies components against standards, quantifies margins and identifies failure modes.
Electrical Control of Industrial Mechanisms · Prof. Z. TIR — University of El Oued
Chapter 6 · 30
Quick check — try before you look
SELF-CHECK 6.1–6.6
6.1
Jeq = 4200 kg·m², constant-torque braking from 50 rad/s to rest in 2 s: energy and peak power?
6.2
Winder 10 m/s, 500 N, 0.2 → 1.0 m roll: torque range, power, motor rating with 2:1 field weakening?
6.3
I1 = 200 A at 37 % THD; IL = 800 A, Isc = 20 kA. Does it meet the IEEE 519 TDD limit?
6.4
100 ns edges, 400 V supply, 20 m cable: critical length and peak terminal voltage?
6.5
Why no overload relay between drive and motor, and what protects the motor at low speed?
6.6
Two pump sets of A = 0.999, one needed: station availability? Both needed?
Electrical Control of Industrial Mechanisms · Prof. Z. TIR — University of El Oued
Chapter 6 · 31
Summary
CHAPTER 6 · SUMMARY
KEY EQUATIONS
Electrical Control of Industrial Mechanisms · Prof. Z. TIR — University of El Oued
Chapter 6 · 32
Practise this
CHAPTER 6 · NEXT STEPS
TD
Exercises 6.1–6.7
Mill supply, kiln inching drive, winder, IEEE 519, cable filter, N+1 economics, and a model mini-project.
MP
Mini-project
Choose a mechanism, write the specification and control philosophy, size, simulate and defend.
TP
Lab works
TP 6 — PLC integration project: from a written specification to a commissioned, fault-tested program.
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Electrical Control of Industrial Mechanisms · Prof. Z. TIR — University of El Oued
Chapter 6 · 33
Image credits
CHAPTER 6 · SOURCES
Electrical Control of Industrial Mechanisms · Prof. Z. TIR — University of El Oued
Chapter 6 · 34