ELECTRONIC MOTOR PROTECTION RELAY ( EMPR )
It is controlled electronically by picmicrocontroller .
Following are its main parts :
Ac to dc converter
Following is its circuit , this circuit can be modified according to requirements and outputs .
Function of PIC microcontroller
Its functions are some of following
Analogue to digital conversion of DC signal
Control the multiplexer inputs and thus the channel selection
Compare with the reference voltage level
Perform the function of comparator
Control the output contacts/relays
Speed depends on parallel prcessing of signals. Usually speed of pic is too fast , so
we don’t need parallel processing . In some cases speed might be important .
Three Phase Induction Motor
It has a squirrel cage
rotor with copper
at both ends.
HIGH VOLTAGE MOTORS
This is microprocessor based
device which monitors all the
activities in motor supply and in
case of any faults it trips the
motor . Its functions are also to
start and stop the motor .
Over Temperature Protection .
RTD are present in
motors . Output of RTDs
is fed to SHIMAX MAC5B ,
which gives digital output
to controlling circuitary
for tripping and reset of
motors at high
Temperature limits for
output can be adjusted in
10 times of rated primary current injected means 5
percent of composite error is created .
5 - composite error .
10- accuracy limiting factor
5P10,Means 5%(5P) Of Ration Error Even if 10 Times
fo Rated current pass through the primary of CT
these r the standard ALF list - 5 , 10 , 15 ,20 ,30
composite error is related to harmonics
Class PS is an abbreviatioin for Protection-Special
Class of CT's. These are used generally for Differential
For grounding system, ZCT is used with
Ground Relay for ground fault detection.
Cable and earth cable also should be
placed through window .
Various Industry Motor Applications
Thermal Stress Causes Motor Failure
•Most of the motor failure contributors and failed motor components are related
to motor overheating.
•Thermal stress potentially can cause the failure of all the major motor parts:
Stator, Rotor, Bearings, Shaft and Frame.
•The overall result of an overvoltage condition is a decrease in
load current and poor power factor.
•Although old motors had robust design, new motors are designed
close to saturation point for better utilization of core materials and
increasing the V/Hz ratio cause saturation of air gap flux leading
to motor heating.
•The overvoltage element should be set to 110% of the motors
nameplate unless otherwise started in the data sheets.
•The overall result of an undervoltage condition is an increase in current and motor
heating and a reduction in overall motor performance.
•The undervoltage protection element can be thought of as backup protection
for the thermal overload element. In some cases, if an undervoltage condition
exists it may be desirable to trip the motor faster than thermal overload
•The undervoltage trip should be set to 80-90% of nameplate unless otherwise
stated on the motor data sheets.
•Motors that are connected to the same source/bus may experience a
temporary undervoltage, when one of motors starts. To override this temporary
voltage sags, a time delay setpoint should be set greater than the motor starting
•Indication of unbalance Î negative sequence current / voltage
•Unbalance causes motor stress and temperature rise
•Current unbalance in a motor is result of unequal line voltages
•Unbalanced supply, blown fuse, single-phasing
•Current unbalance can also be present due to:
•Loose or bad connections
•Incorrect phase rotation connection
•Stator turn-to-turn faults
•For a typical three-phase induction motor:
•1% voltage unbalance (V2) relates to 6% current unbalance (I2)
•For small and medium sized motors, only current transformers (CTs) are available and no voltage
transformers (VTs). Measure current unbalance and protect motor.
•The heating effect caused by current unbalance will be protected by enabling the unbalance
input to the thermal model
•For example, a setting of 10-15% x FLA for the current unbalance alarm with a delay of 5-10
seconds and a trip level setting of 20-25% x FLA for the current unbalance trip with a delay of
2-5 seconds would be appropriate.
Ground Fault Protection
•A ground fault is a fault that creates a path for current
to flow from one of the phases directly to the neutral
through the earth bypassing the load
•Ground faults in a motor occur:
•When its phase conductor’s insulation is damaged for example
due to voltage stress, moisture or internal fault occurs between
the conductor and ground
•To limit the level of the ground fault current connect an
impedance between the supplies neutral and ground.
This impedance can be in the form of a resistor or
grounding transformer sized to ensure maximum ground
fault current is limited.
Ground Fault Protection
Zero Sequence CT Connection
•Most sensitive & inherent noise immunity
•All phase conductors are passed through the window of the same CT referred to as the
zero sequence CT
•Under normal circumstances, the three phase currents will sum to zero resulting in an output
of zero from the Zero Sequence CT’s secondary.
•If one of the motors phases were to shorted to ground, the sum of the phase currents
would no longer equal zero causing a current to flow in the secondary of the zero
sequence. This current would be detected by the motor relay as a ground fault.
•Differential protection may be considered the first line of protection
for internal phase-to-phase or phase-to-ground faults. In the event
of such faults, the quick response of the differential element may
limit the damage that may have otherwise occurred to the motor.
Core balance method:
•Two sets of CT’s, one at the beginning of the
motor feeder, and the other at the neutral point
•Alternatively, one set of three core-balance
CTs can also be used
•The differential element subtracts the current
coming out of each phase from the current
going into each phase and compares the result
or difference with the differential pickup level.
Summation method with six CTs:
•If six CTs are used in a summing configuration, during
motor starting, the values from the two CTs on each
phase may not be equal as the CTs are not perfectly
identical and asymmetrical currents may cause the CTs
on each phase to have different outputs.
•To prevent nuisance tripping in this configuration, the
differential level may have to be set less sensitive, or
the differential time delay may have to be extended to
ride through the problem period during motor starting.
•The running differential delay can then be fine tuned to
an application such that it responds very fast and is
sensitive to low differential current levels.
Short Circuit Protection
The short circuit element provides protection for
excessively high overcurrent faults
Phase-to-phase and phase-to-ground faults are
common types of short circuits
When a motor starts, the starting current (which
is typically 6 times the Full Load Current) has
asymmetrical components . These asymmetrical
currents may cause one phase to see as much as
1.7 times the RMS starting current.
To avoid nuisance tripping during starting, set
the the short circuit protection pick up to a value at
least 1.7 times the maximum expected symmetrical
starting current of motor.
The breaker or contactor must have an interrupting
capacity equal to or greater then the maximum
available fault current or let an upstream protective
device interrupt fault current.
Stator RTD Protection
•A simple method to determine the heating within the
motor is to monitor the stator with RTDs.
•Stator RTD trip level should be set at or below the
maximum temperature rating of the insulation.
•For example, a motor with class F insulation that has
a temperature rating of 155°C could have the Stator
RTD Trip level be set between 140°C to 145°C, with
145° C being the maximum (155°C - 10°C hot spot)
The stator RTD alarm level could be set to a level to
provide a warning that the motor temperature is rising
OVER CURRENT PROTECTION
EARTH FAULT PROTECTION
Over Temperature Protection
Remote Area or
On – Off Control Loops
Proportional Control Loops
Types of Pneumatic Fittings
• Push-In Fittings, very quick
joint with the tube
• Cap tight Fittings, neat,
quick joint using a finger
• Compression Fittings
Flank Angle and Taper Angle
Crest and Root
Pitch is sometimes written as the number of
threads within threads in one inch distance
If the pressure in the
volume with the output
port exceeds the set
value, the diaphragm
shuts off the input port
and then opens the
exhaust ports to
relieve the excess
Pressure Regulators working
The set screw
tension in the
off the push
rod off its seat.
The push rod
shuts off the
exhaust port in
Pneumatic Control Valve Actuator
Actuators are of many different types.
The positioner is working on
the basis of force balance
The input signal to positioner
and stroke of the actuator are
following a relation which is
determined by the contour of
the cam disc
This positioner can control
single as well as double acting
Electro Pneumatic Converter or
I / P Converter
An I / P Converter is used for converting
standard current signals to standard
Like converting 4 – 20 mA current signal to 3 –
15 psi pressure
Essential building block of pneumatic valve
positioners and many other pneumatic
This converter is necessary for completing
the control loops because controllers
receive and transmit their signals in the
form of current .
Reactor is basically an inductor .
It adds impedance to the motor
circuit , thus limiting the current
After short period of starting
rector is bypassed by another
contactor in parallel .
Two timers are used if one fails
other dectects it failure and
indicates its failure by tripping the
motor as it can be quite dangerous
if keeps running wrong.
It also protects the motor
and indicates if fault occurs.
Phase shift control for soft start
or dimming effect
Variable Frequency Drives
Types of AC ASD's
There are three different types of ASD's on
the market that primarily differ in the type
of rectification they use to convert AC to
DC and back to AC.
VVI - Variable Voltage Input
CSI - Current Source Input
PWM - Pulse Width Modulated
Variable Frequency Drives
Basic Principle of Operation
The electronic VFD can be used to vary the
speed of an AC motor and at the same time
retain its torque producing capability. The main
power source provides a fixed voltage, fixed
frequency supply that is converted into a
variable voltage, variable frequency output in
such a way that in most of the operating speed
range, the V/f ratio is maintained constant.
This of course is achieved though sophisticated
microprocessor based control electronics.
A VFD consists of an input rectifier (which
converts AC to DC) followed by an inverter
(that inverts DC to AC) connected through a DC
intermediate voltage link.
Energy Savings through Speed Control
The power consumption of a blower or pump
follows the "Cube Law", which means that by
reducing the speed to 80% of the maximum
value the power consumption will be reduced
to about 50%.
Improved Power Factor
A Variable Frequency Drive offers a
fundamental power factor of near unity at all
loads and speeds and hence no Power Factor
Correction (PFC) capacitors are required.
Added to that is the advantage of substantial
restriction on the Reactive Power drawing thus
avoiding penalties from the electric supply
Affinity Laws governing fluid flow
The characteristics of centrifugal equipment such as blowers and pumps vis-à-vis flow can
be explained by the following basic equations:
Flow is proportional to speed (F α N)
Pressure is proportional to square of speed (P α N2)
Therefore Power = F × P α N3
From the above equations it can be very easily concluded that while at the maximum flow
with 100% speed the power consumption is 100%, at 50% flow with corresponding speed
of 50% the power consumed is just 12.5%. A small reduction in speed therefore produces
a very significant reduction in power consumption.
Reduction in mechanical wear and tear
When a HVAC installation no longer runs at full speed additional benefits apart from those
related to energy savings are available:
• Increased lifetime of belt drive on fans.
• With soft start/stop there is less wear and tear on bearings.
• Some VFDs have automatic belt monitoring, which increases intervals between maintenance
• No more jammed guide vanes/dampers.
• Lower noise levels.
• On pumps, fitting a VFD will result in eliminating water hammer during start/stop situations.
Increased Comfort Level
As a byproduct of the energy savings from reducing fan speeds, acoustic air movement
noise from the fan is also reduced.
Noise from fans in a quiet environment can be very annoying. If a fan sized for full
occupancy is supplying a partly occupied room, the acoustic noise level can be as high as
70 dbA. The noise level will vary depending on the throttling with dampers or guide
vanes. More the throttling, greater is the noise.
Line and Load Reactors
Essentially a reactor is an inductor.
Use a reactor:
To add Line Impedance.
To provide some voltage buffering against
low magnitude line spikes.
To reducing Harmonics (When no link choke
To compensating for a low inductance
Only as part of a filter for reflected wave
PLC (programable logic controller)
PLC Systems are designed to replace relay
based logic controls .
PLC (programable logic controller)
Processor module (used
for conversion between
e.g to convert ethernet
to RS485 protocol
diagram shows a very oversimplified
diagram of the structure
HMI (human machine interfaces)
SIMENS WinCC Flexible was
used to program the HMIs .
It has a Touch Screen to get the inputs and states
for running the machine .
It also shows outputs of different digital and
analogue sensors for giving feedback status to the
DCS (distributed control system)
Due to large system and
huge no of analogue inputs
and outputs , it uses DCS
System , which is very user
friendly and Aids a lot to
process engineers .
DCS System have CPUs ,
Aspect Servers , Domain
Vaccum Circuit Breaker
This is 11kV circuit breaker which
has motorised (for charging) spring
for making contacts and breaker has
mechanical latching system for
keeping the contacts closed after
once contacted till the reset .
My Opinion Over All
• Different than I thought
• Lots of hands on
• Learnt a lot
• Figuring out I can be more
good at some things than I
• Getting better at many
skills I considered myself to
Aditional Skills I’ve Improved:
• Multi-tasking skills
• Time management
• Computer skills
(Word, Power point)
• Social media skills
• Note taking
First venture in Electronics , surely not the
This was a landmark experience within a
young, dynamic and ambitious firm
I learnt a lot on team-working and gained
confidence throughout these 2 months.
I pride myself on having worked on high profile
+ Living at guest house helped me during my stint
Thank you to the whole team @Century
A Special Thank you
General Manager (Mr. Nadeem ullah )
Assistant Manager (Mr. Tahir )
Mr . Habib ur Rehman , Mr. Azhar , Mr.Imran , Mr. Talha ,
Mr . Faizan and to the whole team @ pm7
For so much kind help in all aspects .