Internship Report - Rizwan Asif

Electric System of a Fertilizer Plant With special reference to Fauji Fertilizer Company – Mirpur Mathelo

Rizwan Asif Electrical Engineering School of Electrical Engineering and Computer Science (SEECS), batch BEE-4 National University of Science and Technology (NUST)

Electrical System of a Fertilizer Plant

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Acknowledgments

I would like to express my sincere gratitude to Mr. Agha Kashif Haider,

Training Coordinator of Electrical and Instruments for his patient

guidance, enthusiastic encouragement and useful information regarding

the plant. I am particularly grateful for the assistance given by engineers

Mr. Ayaz Ali Jamali and Mr. Ali. They just didn’t train us regarding the

plant but also provided beneficial information regarding professional

interviews, jobs and other elements of practical life.

Assistance provided by other respectable engineers, namely Mr. Awais

and Mr. Jawad Hameed has also been a great help towards drafting this

report.

All in all, I would like to thank Fauji Fertilizer Company for giving an

opportunity to experience and learn about the plant site and its careful

maintenance.


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Table of Contents ABSTRACT ...................................................................................................................................................... 3

INTRODUCTION ............................................................................................................................................... 3

SAFETY WORKSHOP ......................................................................................................................................... 3

STUDY OF SINGLE LINE DIAGRAM, ITS COMPONENTS AND SWITCHGEAR. .................................................................... 3

SINGLE LINE DIAGRAM ................................................................................................................................. 4

GENERATORS ......................................................................................................................................... 4

TRANSFORMERS ..................................................................................................................................... 6

MOTORS .............................................................................................................................................. 9

RELAYS ............................................................................................................................................... 12

SIPROTECH ............................................................................................................................................... 14

CONCLUSION ................................................................................................................................................ 15


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Abstract

This paper will discuss the major electrical equipment

such as generators, protection replays, motor control

systems and transformers which are essential to the

working of an industry, specifically to a fertilizer plant.

Some latest equipment for example SIPROTEC relay

and its basic programming will also be discussed. This

paper is in reference to the final internship report of

the department of electrical engineering in Fauji

Fertilizer Company, Mirpur Mathelo (FFC-MM) Plant. A

single line diagram for this plant will be discussed in

detail for better understanding of industrial scale

electrical systems and their requirements.

Introduction

Any chemical plant has a basic requirement of optimum

pressures, temperatures and flow for carrying out their

chemical reactions. Therefore a large number of motors

are required to carry out the job of pumping and

compressing fluids. In order to power these motors we

require a power source (generator), distribution tools

(transformers), control equipment (relays) and safety

provisions (circuit breakers) etc. This results in a vast

and complex network of electrical systems which

require years of planning and training. Therefore a good

understanding of these systems is essential for keeping

the plant in a running state.

Fauji Fertilizer Company (FFC) arranges an internship

program for the benefit of university students to have a

scope of professional environment and knowledge of

industrial grade equipment and requirements. This year

(2015) the electrical engineering department covered

the following topics for the summer internship tenure:

Safety Workshop

Study of single line diagram, its components

and switchgear

Study of motor control center (MCC)

Observation of maintenance jobs in workshop

and substations

Study of SIPROTEC relays

These topics were conducted under proper supervision

through engineers of electrical department.

Safety Workshop

Safety is a major concern in industrial plants like FFC.

Safety precautions along with knowledge of dealing

with emergency situations is important.

FFC maintains a safety department to tackle with

uncanny circumstances. First aid, fire brigade and other

necessary facilities are available. This department

introduced the safety precautions for the plant.

Precautions:

1) Always wear a helmet and noise reduction ear

plugs in plant area.

2) Wear safety googles while in workshop

3) Always wear safety shoes

4) Always keep a breathing mask with you

5) Listen for the siren:

a. Repeated siren means there is an

emergency. Go to ammonia shelters or

assembly points. While wearing breathing

masks.

b. Continuous siren for 10 seconds indicate

that the emergency has been taken care

of.

All the necessary equipment as well as guidance was

provided by technical training center and safety

workshop at FFC.

Study of Single Line Diagram, its

Components and Switchgear.

Massive electrical power networks are composed of

numerous discreet and non-discreet components which

work together to power other large systems like FFC.

Definitions:

Single line diagram is a simplified notation for three

phase systems. In which a three phase transmission is

represented by a single line.

Switchgear is a combination of discreet electrical

components usually implemented on a circuit board.

Figure 1 – Single line diagram of FFC Mirpur Mathelo Plant


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Single Line Diagram

The electrical system of FFC-MM at a macro level

consists of eight substations which provides direct

control of motors and other payloads. These substations

are powered by three generators, stepped down by a

number of transformers. These supplies are passed

through a number of protection relays. As shown in the

single line diagram figure 1.

Figure 1 – Original Single Line Diagram of FFC-MM (Curtsy of electrical workshop FFC-MM

also provided in Appendix A)

Feeders:

One important aspect of the single line diagram is to

know the proper representation of feeders. Feeders are

the output terminals from any module or switchgear.

Figure 2 – Feeders feeding to a motor control centr. Taken from single line diagram (figure 1)

In figure 2 we see that the feeder is shown in the form

of downward arrow while the payloads or further

subsystems it is feeding are mentioned beside it in a

block.

Bus Bars:

In a single line diagram, the 3-phase lines having same

potential are knows as bus bars.

For example in figure 3 the line separated by a relay

witch and connecting SWG1D-1 with SWG1E-1 is called

a bus-bar.

Figure 3 - Bus-bars. Taken from single line diagram (figure 1)

We shall discuss the following components in detail in

this paper.

Generators

Transformers

Motors & MCC

Relays

Generators

A generator converts mechanical power to electrical

power. Both AC and DC generators produce electrical

power, based on the fundamental principle of Faraday’s

Law of Electromagnetic Induction and Lenz’s Law i.e.

when a conductor is placed in a changing electrical field

then an emf is induced in the conductor. This emf will

cause a current to flow if the conductor circuit is closed.

Types:

There are two types of AC generators, namely

synchronous and asynchronous or induction generators.

Synchronous generators:

They convert mechanical energy into alternating

energy. The waveform of generated voltage is

synchronized with the rotor speed. Alternators

supply active and reactive power to load. Separate


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DC excitation system is required in an alternator

and brushes to supply DC voltage to rotor for

excitation.

Induction generators

In these type of generators the output voltage

frequency is regulated by power system to which

it’s connected. Meaning, it takes reactive power

from power system for field excitation and supplies

active power. If this generator is meant to supply a

standalone system, a capacitor bank needs to be

connected to supply a reactive power. Induction

generators do not require brushes or slip rings.

Starting a Synchronous Generator:

Asynchronous generators don’t require much effort to

start. A mechanical rotational force on the rotor, which

brings it to a speed more than the synchronous speed,

is enough to produce electrical energy. While in the

case of synchronous generators it is different.

We know that any generator will be synchronous it both

rotor and stator magnetic fields are aligned with zero

slip. Hence in to achieve this functionality we must

provide external help to the rotor for rotating it at

synchronous speed. To achieve this we use a separate

DC motor on the shaft, before attaching the main

mechanical load, which rotates the rotor until it

achieves synchronous speed. Once synchronous speed

is obtained, the DC motor is removed, the main

mechanical load is attached to the shaft and electrical

load is attached to the stator. This way synchronous

generation is achieved.

Brushless Generator:

Generators can also be classified on the base of carbon

brushes. Carbon brushes are the contacts which join the

rotor to external DC supply in order to provide voltage

for rotor magnetic field generation. The drawback of

using carbon brushes is that they wore out after

sometime and have to be replaced. This situation can be

avoided by using special type of generators called

brushless generators.

Figure 4 - Brushless generator diagram. (Curtesy of Graig Pearen – Brushless Alternators)

Brushless generators work on same principle as simple

as simple generators. The difference is that apart from

the main alternator having a rotating field and

stationary armature, there is an exciter with rotating

armature and stationary field. Both exciter’s rotating

armature and main alternator’s rotating field are on the

same shaft, making a common rotor but their stators

are different.

Once the shaft starts rotating the exciter circuit starts

producing AC in the rotating armature. This AC is

directed to a bridge rectifier which converts this AC to

DC. Now this DC, hence produced, is used to magnetize

the rotor. Therefore producing rotor magnetic field.

Now that the rotor is magnetized we can use it to

generate power through the main alternator, and no

brushes were required during the process. Figure 4

provides a simple diagram of brushless AC generator.

Automatic voltage regulator (AVR) controls the current

flow in the exciter armature and hence the output

power produced.

Synchronization:

Synchronization is the phenomena in which more than

one generator are connected in a common system. Two

generators can be synchronized by fulfilling the

following conditions.

Both have same frequency of output voltage

Both have same magnitude of output voltage


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Both generators must have same phase

sequence. That is, their phases must be

synchronized with time.

If any of these conditions are not met then one of the

generator will start acting as a motor.

FFC:

FFC –MM has deployed a total of four generators as

shown in figure. Three of these are being used all the

time where as one is for emergency purposes. All

generators operate at 50Hz frequency with 6.3 kV

output voltage for synchronization.

Figure 5 – Single line diagram of generators in FFC-MM, taken from figure 1 (also provided in Appendix A)

Steam: TG-701-A & TG-701-B

701-A supplies power to Bus ‘A’ and 701-B to Bus

‘B’ and these both are synchronized via Bus ‘C’.

They are producing 10,000 kVA each.

Gas: GT-703

703 supplies to Bus ‘D’ and is connected to Bus ‘B’

through a pyro breaker. This generator is producing

17,000 kVA.

Diesel: MG-702

This is a Standby Diesel generator which is available

for emergency cases i.e. for Bus ‘E’. If any of the 2

steam generators fails, the plant keeps working. If

both of the steam turbines fail or the gas turbine

alone fails, then the diesel turbine is turned on as

an alternative source of power. It has the capacity

to produce 19,000 kVA.

Transformers

Certain loads or devices require relatively lower or

higher voltage or current than the available supply. For

example we have a 220V supply at our homes but many

devices like mobile phone chargers require lesser

amount than that, hence transformers are required to

perform this conversion. Hence, transformers are

electrical devices which use the phenomena of

electromagnetic induction to increase or decrease

voltage.

Basic Construction:

A transformer consists of a soft iron laminated frame

called core, with two insulated coils wounded around its

legs. As shown in figure 6, one of the coils is called

primary coils while the other is called secondary coil.

Input voltage is taken at the primary side and output at

secondary side.

Figure 6 - Transformer basic construction (Curtesy of S.J Chapman – Electrical Machinery Fundamentals)

The amount to which a transformer increases or

decreases output voltage is determined by the ratio of

number of turns at primary side ‘Np’ and number of

turns at secondary side ‘Ns’, called transformer ratio.

𝑇𝑟𝑎𝑛𝑠𝑓𝑜𝑟𝑚𝑒𝑟 𝑅𝑎𝑡𝑖𝑜 = 𝑁𝑠

𝑁𝑝

Types:

Here are some types of transformers on the basis of

laminated core type.

Core-type


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Windings are cylindrical former wound, mounted

on the core limbs. The cylindrical coils have

different layers and each layer is insulated from

each other. Low voltage windings are placed nearer

to the core, as they are easier to insulate. Figure

7(a) shows a three phase core type transformer

winding.

Shell-type

The coils are former wound and mounted in layers

stacked with insulation between them. A shell type

transformer may have simple rectangular form, or

it may have a distributed form. Figure 7(b) shows a

three phase shell type transformer winding.

Figure 7 - (a) Core Type (b) Shell Type Transformer

Kinds:

The following kinds of transformer are found in general.

Power transformer

Used in transmission network, high rating.

Distribution transformer

Used in distribution network, comparatively lower

rating than that of power transformers.

Instrument transformer

Used in relays and measuring purpose in different

instruments. They are of two types

Current transformer (CT)

This transformer converts high current input to

low current output so that it can be measured

to a standard without damaging the

instrument. Its construction is shown in figure

8.

Figure 8 - Current Transformer (CT). (Curtsy of electricaleasy.com)

Potential transformer (PT)

This transformer converts high voltage inputs

to low voltage outputs for measurement

purposes. Its construction is shown in figure 9.

Figure 9 – Potential Transformer (PT). (Curtsy of electricaleasy.com)


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Multi-tapped Transformer

These transformers have more than one primary or

more than one secondary coil. They can be used to

change the transformer ratio and hence the rate to

which we can change the output level of that

transformer.

Auto Transformer

Common winding for input and output so there is

no isolation between them.

Unit Transformer

Most switchgear assemblies are configured as unit

substations. They follow the system concept of

locating transformers as close as practicable to

areas of load concentration at utilization voltages,

thus minimizing the lengths of secondary

distribution cables and buses.

Isolation Transformer

Used to transfer electrical power from a source of

AC power to some equipment or device while

isolating the powered device from the power

source, usually for safety reasons.

Transformer Tests:

The following two transformer tests are performed in

order to determine its complete characteristics.

Open Circuit Test

Relative meters connected on low voltage side

and voltage is varied using autotransformer

High voltage side kept open

No-load current is small, hence ignored

Input power consists of core losses in

transformer during no-load condition

Used to calculate IRON CORE losses

Short Circuit Test

Meters connected on high voltage side of

transformer

Low voltage side is short-circuited

Voltage slowly increased until ammeter gives

reading equal to rated

Voltage applied for full load current is small,

hence ignored

Used to calculate COPPER losses

Cooling System and Methods:

The following terminologies are used to identify the

cooling system in transformers.

ONAN(Oil Natural Air Natural)

ONAF(Oil Natural Air Forced)

OFAF(Oil Forced Air Forced)

OFWF(Oil Forced Water Forced)

ODAF(Oil Directed Air Forced)

ODWF(Oil Directed Water Forced)

Maintenance:

The following parts and maintenance techniques are

used to test the transformer’s performance and safety.

Cable and Winding

Cables and windings of a transformer might get

damaged insulation with time and hence produce

hotspots which cause leakage currents. To test the

insulation a method called meggaring is used. In

meggaring we pass an increasing current through

an open circuited wire (coil) and observe how much

leakage current is produced. On that basis we

determine if the wire is capable of further used or

should be replaced.

Note that leakage current is produced is produced

in an open circuit because it represents the current

which passes to the damaged insulation.

Contacts

The electric contacts at of the transformer are

tested to be tight.

Oil Testing

Transformer oil is used as cooling agent as well as

an insulator between core and the body. It is

necessary that it remains in good shape hence a

number of tests are conducted on it like acidity

test, moisture test and conductivity test.


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Security Relay Check (Buchholz Relay)

It is a safety device mounted on oil-filled power

transformers and reactors, equipped with an

external overhead oil reservoir called a

"conservator".

Trips at 75-80 °C(depending on the ratings

60°C in northern areas

Detects rise in temperature if turns short circuited

Pressure Relieve Device(PRD)

This device is used to keep a check on the

transformer oil pressure. If the pressure exceeds a

certain threshold then this device allows

atmospheric pressure to balance the growing

temperature.

Silica gel

This gel is used to absorb moisture from the

transformer oil. We can check its reusability by

observing its color. If it’s blue then good otherwise

if pink, then it needs to be replaced or recycled.

Motors

Motors are devices which use faraday’s law of

electromagnetic induction to produce mechanical work

from electrical energy.

Motors can be DC and AC depending on the type of

input electrical energy they take. For the sake of a

fertilizer plant we shall discuss 3-phase AC motors only.

Figure 10 - A 3-phase AC motor

In the single line diagram shown in figure 1, motors are

not shown but instead written in the feeder description.

See figure 2 for more details.

Motors are important for a fertilizer plant like FFC-MM

because certain chemical processes require specific

amount of pressure and flow rate of fluids. Hence

motors are essential for driving pumps and compressors

throughout the plant. Motors are controlled through

motor control centers “MCC”, which will be discussed

later in this section.

Basic Construction:

A motor mainly consists of a rotating part called the

rotor and a stationary part called stator.

The rotor might be of squirrel cage or wound rotor. The

rotor is supplied with DC voltage in case of a

synchronous motor to produce a magnetic field,

otherwise in case of induction motor the rotor magnetic

field is produced on the expense of reactive power

drawn by the stator (we shall discuss type of motors

later).

The stator consists of copper winding through which

input AC voltage is passed. This input voltage produces

a rotating magnetic field which interacts with the

magnetic field of the rotor to produce mechanical work.

Types of motors:

Motors are of two types namely synchronous and

asynchronous or induction motors.

To understand the difference we must understand the

concept of rotating magnetic field. In an AC motor the

stator windings are such that one phase follows the

other e.g if 1, 2 and 3 represent input phases then the

winding is like 123123123. This creates alternating

magnetic poles along the winding. Since magnetic field

flows from North to South Pole, and the poles are

consistently changing or moving along the stator hence

we obtain a rotating magnetic field. Now the magnetic

field of rotor tries to align with this rotating magnetic

field and hence mechanical work is obtained.

Now in the case of a synchronous motor the rotor and

stator magnetic field are aligned together and hence the

rotor rotates with a speed equal to the inverse of input

voltage frequency. This relationship is shown by the

equation:


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𝑛𝑠 = 120𝑓

𝑃

Where ‘f’ is the frequency, ‘P’ are the number of poles

produced and ‘ns’ is the speed of rotor. In case of

synchronous motor it is called synchronous speed.

On the other hand asynchronous motors don’t have an

aligned magnetic field and the stator or rotor magnetic

field cross each other at certain points. We can say that

we call a motor asynchronous when it’s rotor is

operating at a speed other than synchronous speed. The

difference between rotor and stator magnetic field in

terms of speed is called slip. Which can be found by the

equation.

𝑆 = 𝑛𝑠 − 𝑛𝑠𝑦𝑛𝑐

Where ‘ns’ is the speed of rotor and ‘nsync’ is the

synchronous speed.

In FFC-MM has both synchronous as well as

asynchronous motors.

Starting a motor:

Motors require more energy to start but once they

gather speed, relatively less energy is consumed. Hence

a starting circuit consisting of wye-connection is used

which provides more current and after that the input 3-

phase is converted to a delta connection.

Moreover in case of a synchronous motor apart from

the wye-delta starter circuit, we need to do some extra

effort to get it started. To make the motor achieve

synchronous speed we rotate the rotor through a DC

motor. Once it gets synchronous speed then we turn on

the power in stator.

Motor Nameplate:

Every motor comes with a nameplate which describes

its important features and required conditions for

proper operation.

Here we will provide some important fields mentioned

on a SIEMENS Motor.

Phase & Input type

This is to describe the input power. For example it

could be a 3-phase AC motor or a DC motor.

Type

This field describes the physical type of motor.

There are 14 such type of motors which are

provided with specific codes. ‘B’ is a known code

for motors which have a horizontal shaft (shaft is

also called rotor), while ‘V’ stands for motors with

vertical shafts.

For example ‘B3’ indicates a motor with horizontal

shaft and a foot mounted body.

Serial No.

This is a production number for the company use.

Rated Voltage and Connection Type

Rated voltage is the amount of voltage at which

certain tests are conducted on the motor. These

tests include rated speed, rated power

consumption etc. While the connection type

indicates weather a wye or delta connection was

used.

Power Output

This the power in kilo-watts that the motor delivers

at rated voltage.

Rated Load Amperes

The average current consumed by motor at rated

voltage.

Power Factor

Power factor is defined as the cosine of angle

between voltage and current in a vector diagram.

The magnitude of this factor shows the amount of

reactive voltage required to run the motor. If it is

close to 1 then it is assumed that no reactive power

is required.

Rated Speed and Direction

The output speed of the shaft at rated voltage and

weather the motor works clockwise or counter

clockwise.


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Locked and Rated Current ratio

The ratio of current at locked state and rated

voltage, also called service factor. By locked state

we mean when the rotating magnetic field

becomes so fast that the rotor magnetic field

doesn’t chase it anymore and there is not relative

motion between stator and rotor.

Protection Index

This index provides information about how much

the motor is resistant to water, dust and other

natural factors. A list of such factors is universally

known.

Rated Frequency

The frequency of input voltage at rated voltage.

Insulation Class

The class of insulation used. Knowledge of this

factor provides the maximum amount of heat the

winding insulation of motor can resist.

Safe Locked Rotor Time

The amount of time the rotor can safely operate at

locked state. This time is important because

maximum power is consumed by the motor in this

state which might damage the motor.

Test Date

Last date the motor was tested.

Rotor Class

The class of rotor being used. These are also

universal codes which are used frequently to

identify the type of rotor.

Ambient Temperature

The average temperature at which the motor can

run optimally without causing any damage.

Gross Weight

Total weight of the motor.

Motor Control Center (MCC):

Motors are to be controlled from MCC. Here motors can

be shut down but not started. The reason being safety

protection issues. MCC also provides all sorts of

electrical protection here at MCC. So that if there is any

electrical fault then the motor can be switched off

before it causes any damage, to itself or workers in the

working area.

Figure 11 - An MCC diagram for the operation of a motor (Also provided in appendix A)

Figure 11 shows a complete diagram of MCC operating

in FFC-MM. This diagram shows some isolators

(switches) which can be operated manually. Some

Magnetic contractors which are only turned on when

external voltage is supplied to some nearby coils.

Here we shall study the how we can start the motor and

how we can test it using this diagram.

The diagram is such that module enclosed by dotted

lines are the ones we can physically interact with in the

MCC while the rest is hidden from us. Once we power

the control circuit through a switch at the bottom left

corner of the diagram then a coil “LCN” is activated

which completes the circuit to the motor. Hence

starting it. Once the motor has started all the switches

labeled “LCN” will turn ON. This causes “LCNX” coil to

get excited. This LCNX coil then activates its related

switches and hence we can see that the power supply

we used for powering the motor is now taking a

completely different path. Now in case there is come

electrical issue like short circuiting then respective


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breakers on the MCC will trigger hence de-exciting the

“LCN” switch which causes the motor to stop.

In order to test the motor, the isolator at shown at the

bottom left side of the diagram is triggered to “test”

and the original circuit is turned off. Note that the state

of switches shown here are all in normal state when no

power is supplied to the circuit. Hence when we alter a

switch’s state, its corresponding state switches are

triggered in the same direction, while the switches in

the opposite state reverse their direction according to

the new state. Hence if we find that now when “LCN” is

excited the indicator switches are started but the motor

doesn’t start because its isolators have reversed their

state.

Note that the starting switch is not present in the MCC

but outside near the motor. This is to prevent accidents.

Relays

Relays are electrical devices which trigger switches in an

electrical network. Their basic functionality is to provide

protection and switching.

Relays consists of poles and throws. Poles are the input

terminals while throws are the output of the relay.

Three configurations exists for relays. For example a

relay with one pole and two throws will be called single

pole double throw (SPDT). Similarly SPST and DPST also

exists.

ANSI Numbers:

According to the IEEE standard C37.2-2008, different

types of relays have been assigned identical numbers.

These numbers are useful while indicating a particular

type of relay in a single line diagram.

Types of Relays:

Relays are usually of four types based on their

construction and the physical phenomena they obey.

Electromechanical Relays:

These type of relays are constructed on the base of

electromagnetism. An electromagnetic coil is

excited through the input supply, which in return

magnetizes and triggers a nearby switch. Hence

controlling the flow.

Electromechanical relays are of further two types

latching and non-latching. Latching relays return to

their non-excited state (Normally Open or Normally

Closed) when input supply is disconnected. This

functionality is achieved through the use of springs.

Whereas Non-Latching relays maintains its state

once changed. This is achieved with the help of

permanent magnets, which therefore is more

energy efficient. In order to alter the current state

an opposite current in the coil is required. Some

commercial relays utilize an external circuit for

reversing the state of the switch.

FFC mainly deploys non-latching electro-mechanical

relays in its subsystems. Specifically called

electromagnetic contractors.

Comparatively electromechanical relays are slower,

with an average time delay of 5~15 milli-seconds.

Magnetic contractors are an example of

electromechanical relays.

Reed Relays:

These type of relays use the same electro-magnetic

phenomena as of electromechanical relays. The

difference is in the construction. Reed relays use

two separated contacts in a cylindrical case

wrapped around by a solenoid. When current

passes through this solenoid then the contacts

meet due to magnetic force produced by the

solenoid and hence completing the circuit.

Reed relays are 10 times faster but are prone to arc

currents and burn out immediately. Hence reed

relays are not much reliable and used only with

circuits having less fluctuations.

Solid-State and FET Relays:

Solid-State and FET relays use silicon based diodes

and transistors for their functionality. Solid-State

relays use light emitting diodes and LDRs to sense

change in voltage in a conductor, while a CMOS

transistor reacts to the change in resistance, hence

allowing or stopping the current accordingly. While

FET is a single CMOS transistor which takes input at


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the gate and allows current to pass accordingly

though drain and source.

These relays are the fastest and generally deployed

in modern systems.

Microcontroller Based Relays:

Latest trend in relays is to use programmable relay

systems. These relays are useful for large

coordination systems. They provide a great deal of

complexity in their design.

SIPROTECH is an example of microcontroller relay,

which will be discussed in detail later.

Examples:

Some important industrial use relays are discussed

below along with their ANSI numbers in parenthesis:

Starting Circuit Breaker (6)

ANSI number 6. Its function is to connect a machine

to its source of starting voltage.

Distance Relay (21)

Indicates if the circuit admittance, impedance, or

reactance increases or decreases beyond

predetermined limits.

Synchronism Check Relay (25)

It is a device that operates when two a-c circuits are

within the desired limits of frequency, phase angle,

or voltage, to permit or to cause the paralleling of

these two circuits

Under voltage Relay (27)

It is a relay that functions on a given value of under-

voltage

Directional Power Relay (32)

is a device that functions on a desired value of

power flow in a given direction or upon reverse

power resulting from arc back in the anode or

cathode circuits of a power rectifier

Field Excitation Relay (40)

is a relay that functions on a given or abnormally

low value or failure of a machine field current, or

on excessive value of the reactive component of

armature current in an a-c machine indicating

abnormally low field excitation

Thermal Relay (49)

is a relay that functions when the temperature of a

machine armature

or other load-carrying winding or element of a

machine or the temperature of a power rectifier or

power

transformer (including a power rectifier

transformer) exceeds a predetermined value.

Instantaneous Overcurrent Relay (50)

is a relay that functions instantaneously on an

excessive value of current or on an excessive rate of

current rise, thus indicating a fault in the apparatus

or circuit being protected.

AC Time Overcurrent Relay (51)

is a relay with either a definite or inverse time

characteristic that functions when the current in an

a-c circuit exceed a predetermined value.

AC Circuit Breaker (52)

is a device that is used to close and interrupt an a-c

power circuit under normal conditions or to

interrupt this circuit under fault of emergency

conditions

Overvoltage Relay (59)

is a relay that functions on a given value of over-

voltage

AC Directional Overcurrent Relay (67)

is a relay that functions on a desired value of a-c

over-current flowing in a predetermined direction

Frequency Relay (81)

is a relay that functions on a predetermined value

of frequency (either under or over or on normal

system frequency) or rate of change of frequency

Lockout Relay (86)


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is an electrically operated hand, or electrically reset

relay or device that functions to shut down or hold

an equipment out of service, or both, upon the

occurrence of abnormal conditions

Differential Protective Relay (87)

is a protective relay that functions on a percentage

or phase angle or other quantitative difference of

two currents or of some other electrical quantities

Tripping or Trip-Free Relay (94)

is a relay that function to trip a circuit breaker,

contactor or equipment, or to permit immediate

tripping by other devices; or to prevent immediate

re -closure of a circuit interrupter if it should open

automatically even though its closing circuit is

maintained closed

Protection Coordination:

An important technique while discussing relays is of

protection coordination. Relays, in a power distribution

network, are placed in a hierarchy which prevents

complete disaster of a system in case one relays fails.

The relays placed at different hierarchy work in

coordination to protect the whole system. Such that if a

lower hierarchy relay fails then a relay from the upper

hierarchy is closed, this way the whole module or may

be system is shut down instead of allowing the fault to

continue damage. Hence we call it a protection

coordination system.

For example in figure 12, which is taken from the single

line diagram in figure 1, shows a basic protection

coordination in SS4 of FFC-MM.

Figure 12 - Protection Coordination. Taken from figure 1

Here we see a circuit breaker right after the transformer

and some fuses in the subsequent systems. Here if any

of the fuse fails to work then the circuit breaker below

the transformer opens. Hence saving the whole system

from damage.

There are several ways to achieve this functionality. One

is to time the fuses and breakers such that they act one

after the other. For example the fuse in the system is

selected such that it goes off after 0.25 seconds of short

current passes through it. In that case the circuit

breaker above will be chosen such that it switches off at

0.5 seconds of short circuit current. This way a suitable

protection coordination is achieved.

SIPROTEC

SIPROTEC relays are programmable relays,

manufactured by SIEMENS company, which can be

employed on electrical machines. Instead of placing

various different relays, a single SIPROTEC relay can be

placed to define the relative times of opening/closing of

circuits according to the provided parameters using the

panel.

FFC uses SIPROTECs in many of it’s electrical systems.

Figure 13 shows one in Sub-Station 1 (SS1) of FFC-MM.

Figure 13 - SIPROTECH in SS1 of FFC-MM

Basic Structure:

SIPROTEC takes current (IA, IB, IC and In/INs) as well as

voltage inputs (VA, VB and VC/3Vo) which pass through


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current and potential transformers in the measuring

inputs (MI) section, as shown in figure 14.

Figure 14 - SIPROTECH internal structure (Curtsy of SIPROTECH manual V4.4)

The inputs from MI after stepping down are amplified at

the input amplifier (IA) stage. Then a microcomputer

(µC) processes the information and performs actions at

the power supply (Uax), hence acting as relay.

Programming:

DIGSI is the programming software used to program

these relays by making logics using different gates,

placing them as inputs/outputs accordingly. A program

window of ‘CFC’ opens on startup of DIGSI where the

user can make logics.

SIPROTEC relays can be used for one particular

machine/device. Meaning, for 3 transformers, we will

connect 3 SIPROTEC relays for programming their

parameters.

An example of a motor MP-800E has been shown in

figure 15 with a logic performing XOR gate functionality:

Figure 15 - DIGISI implementing an XOR operation.

Conclusion

Industry is different than the classroom and it is true.

We have seen some equipment that we study all along

our undergraduate and graduate studies but the

parameters required by industry are different. For

example working at a fertilizer plant it is not important

that you know the equivalent circuit of a transformer

but you should be aware of its types, basic equations, its

oil requirements and testing techniques.

Working at a fertilizer plant made the author realize the

practical implementation and significance of electrical

machinery. The effect of changing parameters and

importance of safety when working with high voltage

levels.


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APPENDIX A

Single Line Diagram of FFC-MM 1


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Motor Control Center (MCC) of FFC-MM 1


Page 18

Single Line Diagram of Generator systems in FFC-MM

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