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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

Photo: Dylan Moore, CC BY-SA 2.0, Wikimedia Commons

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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

Photo: FFC1966, CC BY-SA 4.0, Wikimedia Commons

Electrical Control of Industrial Mechanisms · Prof. Z. TIR — University of El Oued

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Cross-sector industrial case studies

6.1

Five questions read any machine: load, quadrants, loop, sizing quantity, failure.

Photo: Unknown author, Public domain, Wikimedia Commons

Electrical Control of Industrial Mechanisms · Prof. Z. TIR — University of El Oued

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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

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The reversing rolling mill

6.1 · METALLURGY

  • The slab passes back and forth; the drive reverses at full torque many times a minute
  • Four quadrants at tens of MW, energy recovered in every deceleration
  • Constant-torque braking: power falls linearly to zero
  • So the peak regenerated power is twice the mean

Lectures, Fig. 6.1

Electrical Control of Industrial Mechanisms · Prof. Z. TIR — University of El Oued

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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

Photo: Unknown author, Public domain, Wikimedia Commons

SOLUTION

  1. Erev = ½ × 4200 × 60² = 7.56 MJ
  2. Mean power 7.56 / 2.5 ≈ 3.0 MW
  3. Braking torque 4200 × 60 / 2.5 = 100.8 kN·m
  4. Peak 2 × 7.56 / 2.5 ≈ 6.0 MW, at the start of braking

✓

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

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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

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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

  1. ωs = 2.5 × 2π/60 = 0.262 rad/s → T = 450 000/0.262 ≈ 1.72 MN·m
  2. Constant torque at 0.1 rpm (0.0105 rad/s): P ≈ 18 kW
  3. Main train 1490/2.5 = 596 → its input turns at 59.6 rpm
  4. Auxiliary gearbox 1470/59.6 ≈ 25

✓

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

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The winder: constant power with a tension loop

6.1 · PAPER AND FILM

Photo: FFC1966, CC BY-SA 4.0, Wikimedia Commons

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

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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

  1. Tcore = 600 × 0.075 = 45 N·m; Tfull = 600 × 0.375 = 225 N·m
  2. ωcore = 8/0.075 ≈ 107 rad/s; ωfull = 8/0.375 ≈ 21 rad/s
  3. Torque ×5 while speed ÷5: power F·v = 4.8 kW throughout
  4. The drive needs a 5:1 constant-power range

✓

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

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What the build-up ratio and the roll inertia cost

6.1 · PAPER AND FILM

  • Field weakening covers only 2:1 to 3:1: a 2:1 motor for the 5:1 roll is rated 12 kW for 4.8 kW
  • Roll inertia grows as r⁴: every line ramp needs extra torque
  • Full roll, 0.5 m/s²: +33 N·m, 15 % — else tension sags 88 N
  • Diameter computed as r = v/ω; held at standstill

Lectures, Fig. 6.3

Electrical Control of Industrial Mechanisms · Prof. Z. TIR — University of El Oued

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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

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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

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Six-pulse rectifiers inject harmonics

6.2 · POWER QUALITY

  • The DC-link capacitor charges only near the voltage peaks: pulsed line current
  • Orders 6k ± 1: 5th, 7th, 11th, 13th… amplitudes falling about 1/h
  • Current THD 80–120 %; simulated 81 %, 37 % with a 3 % line reactor
  • Extra heating in transformers and cables: K-factor derating

Lectures, Fig. 6.4

Electrical Control of Industrial Mechanisms · Prof. Z. TIR — University of El Oued

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IEEE 519 judges the TDD at the PCC

6.2 · POWER QUALITY

  • Limit on total demand distortion at the point of common coupling
  • TDD = drive THD × the drives' share of the plant demand
  • Isc/IL 20–50: TDD 8 %, each harmonic below the 11th 7 %
  • Harmonic voltage: vh ≈ h·xs·ih

Lectures, Fig. 6.5

Electrical Control of Industrial Mechanisms · Prof. Z. TIR — University of El Oued

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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

  1. Isc = 1443/0.06 = 24.1 kA → Isc/IL = 24: limit 8 %
  2. I1 = 250 000/(√3 × 400 × 0.95) = 380 A
  3. TDD: bridge 30.9 %, reactor 14.2 %, 12-pulse 3.8 %, AFE 1.5 %
  4. Reactor complies only up to I1 = 214 A: about 140 kW

✓

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

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Long motor cables: reflections and bearing currents

6.2 · MOTOR CABLES

  • PWM edges on a cable reflect: up to 2·VDC, about 1130 V on a 400 V supply
  • 400 ns edges tolerate 30 m; 50 ns edges reach full reflection under 4 m
  • Remedies: dv/dt or sine filter, inverter-duty motors
  • Common-mode voltage drives bearing currents: insulated bearing, shaft earthing

Lectures, Fig. 6.6

Electrical Control of Industrial Mechanisms · Prof. Z. TIR — University of El Oued

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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

  1. Without filter: Lc = 50 ns × 1.5 × 10⁸/2 = 3.75 m
  2. 25 m is almost 7 × longer: Vm,pk ≈ 2 × 566 ≈ 1130 V
  3. With filter: Lc = 75 m
  4. Vm,pk ≈ 566 × (1 + 25/75) ≈ 755 V

✓

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

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Protecting a variable-speed drive

6.2 · PROTECTION

Lectures, Fig. 6.7

  • Breaker Q1: short circuit and the supply cable
  • RCD type B only, with raised threshold: normal HF leakage is large
  • Semiconductor fuses (I²t) protect the rectifier
  • Drive's current limit and thermal model protect motor and cable — no overload relay
  • PTC / Pt100 in the winding: the only valid protection at low speed

Electrical Control of Industrial Mechanisms · Prof. Z. TIR — University of El Oued

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Availability: units in series, units in redundancy

6.2 · AVAILABILITY

  • Shorter repairs raise availability as much as fewer failures — and cost less
  • Process stops if any unit fails: availabilities multiply
  • N+1: k of n units needed — losing it takes two failures
  • Only if failures are independent: beware the common switchboard

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Electrical Control of Industrial Mechanisms · Prof. Z. TIR — University of El Oued

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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

  1. One set: A = 8000/8008 = 0.999001
  2. Three in series: A³ = 0.99701 → 26 h a year at reduced capacity
  3. Three of four: A⁴ + 4A³(1 − A) = 0.999994
  4. → about 3 minutes a year

✓

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

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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

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The mini-project: a capstone design

6.3

From analysing a given mechanism to conceiving, specifying and defending your own.

Photo: Mixabest, CC BY-SA 3.0, Wikimedia Commons

Electrical Control of Industrial Mechanisms · Prof. Z. TIR — University of El Oued

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From specification to defended design

6.3 · METHODOLOGY

Lectures, Fig. 6.9

  • Specification: motions, loads, duty cycle, performance targets, environment, safety
  • Control philosophy: axes, drive types, sensors, interlocks, operator interface
  • Sizing: every component justified by calculation and manufacturer data
  • Simulation tied to requirements; then the defence

Electrical Control of Industrial Mechanisms · Prof. Z. TIR — University of El Oued

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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

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Testable requirements, fixed sizing order

6.3 · METHOD

Lectures, Fig. 6.9

  • Not “the hoist shall be fast” but “1000 kg at 0.5 m/s, ±5 mm at each level”
  • State the environment: a summer ambient above 40 °C changes the frame size
  • Size in order: load → motor → drive → braking → supply → protection
  • Assumption register: every number the specification does not give

Electrical Control of Industrial Mechanisms · Prof. Z. TIR — University of El Oued

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How the mini-project is assessed

6.3 · ASSESSMENT

  • Specification (4 marks) and control philosophy (4)
  • Component sizing (5): correctness and justification
  • Safety and reliability (3)
  • Presentation and defence (4)
  • The reasoning is assessed, not only the result

Photo: Mixabest, CC BY-SA 3.0, Wikimedia Commons

Electrical Control of Industrial Mechanisms · Prof. Z. TIR — University of El Oued

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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

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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

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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

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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

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Summary

CHAPTER 6 · SUMMARY

  • Mill: rate the regenerative supply on the peak, twice the mean
  • Kiln: full torque at a few % power; winder: build-up ratio and inertia
  • Harmonics: TDD at the PCC, not the drive's THD
  • Long cables double the voltage beyond trvp/2
  • Availability: short repairs; N+1 only with independent failures
  • Testable spec → axis table → sizing in order → simulation → defence

KEY EQUATIONS

Electrical Control of Industrial Mechanisms · Prof. Z. TIR — University of El Oued

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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.

Photo: FFC1966, CC BY-SA 4.0, Wikimedia Commons

Electrical Control of Industrial Mechanisms · Prof. Z. TIR — University of El Oued

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Image credits

CHAPTER 6 · SOURCES

  • Figures and diagrams: Lectures booklet, Electrical Control of Industrial Mechanisms (computed in Python/Simscape or drawn in TikZ from the chapter's own equations).
  • Rotary kilns, Sundon cement plant - geograph.org.uk - 2421111 — Dylan Moore, CC BY-SA 2.0, Wikimedia Commons, https://commons.wikimedia.org/wiki/File:Rotary_kilns,_Sundon_cement_plant_-_geograph.org.uk_-_2421111.jpg
  • Burgos BOBINAS — FFC1966, CC BY-SA 4.0, Wikimedia Commons, https://commons.wikimedia.org/wiki/File:Burgos_BOBINAS.jpg
  • 2015.028.040 Final rolling mill action forming finished steel rails — Unknown author, Public domain, Wikimedia Commons, https://commons.wikimedia.org/wiki/File:2015.028.040_Final_rolling_mill_action_forming_finished_steel_rails.tif
  • Variable Frequency Drive (VFD) - 3 — Suyash.dwivedi, CC BY-SA 4.0, Wikimedia Commons, https://commons.wikimedia.org/wiki/File:Variable_Frequency_Drive_(VFD)_-_3.jpeg
  • MPI bus address setting — Mixabest, CC BY-SA 3.0, Wikimedia Commons, https://commons.wikimedia.org/wiki/File:MPI_bus_address_setting.JPG
  • Licence texts: creativecommons.org/licenses (CC BY, CC BY-SA); creativecommons.org/publicdomain/zero/1.0 (CC0). Photos are shown unmodified except for cropping and scaling.

Electrical Control of Industrial Mechanisms · Prof. Z. TIR — University of El Oued

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