Operation Management-ICAI-Inter-Pumps, Motors, Transformers, Electrical Drivers

1.4 Pumps, Motors, Transformers, Electrical Drivers
Pumps
A pump is a device used to move liquids. A pump moves liquids from lower pressure to higher pressure,
and overcomes this difference in pressure by adding energy to the system (such as a water system). A gas
pump is generally called a compressor, except in very low pressure-rise applications, such as in heating,
ventilating, and air-conditioning, where the operative equipment consists of fans or blowers.
Pumps work by using mechanical forces to push the material, either by physically lifting, or by the force of
compression.
Pumps fall into two major groups: Rotodynamic pumps and positive displacement pumps. Their names
describe the method for moving a fluid. Rotodynamic pumps are based on bladed impellers which rotate
within the fluid to impart a tangential acceleration to the fluid and a consequent increase in the energy of
the fluid. The purpose of the pump is to convert this energy into pressure energy of the fluid to be used in
the associated piping system. A positive displacement pump causes a liquid or gas to move by trapping a
fixed amount of fluid or gas and then forcing (displacing) that trapped volume into the discharge pipe.
Positive displacement pumps can be further classified as either rotary-type (for example the rotary vane)
or lobe pumps similar to oil pumps used in car engines. Another common type is the helical twisted Roots
pump. The low pulsation rate and gentle performance of this Roots-type positive displacement pump is
achieved due to a combination of its two 90° helical twisted rotors, and a triangular shaped sealing line
configuration, both at the point of suction and at the point of discharge. This design produces a continuous
and non-verticals flow with equal volume. High capacity industrial “air compressors” have been designed
to employ this principle as well as most “superchargers” used on internal combustion engines.
Reciprocating-type pumps use a piston and cylinder arrangement with suction and discharge valves
integrated into the pump. Pumps in this category range from having “simplex” one cylinder; to in some
cases “quad” four cylinders or more. Most reciprocating-type pumps are “duplex” (two) or “triplex” (three)
cylinder. Furthermore, they are either “single acting” independent suction and discharge strokes or “double
acting” suction and discharge in both directions. The pumps can be powered by air, steam or through a
belt drive from an engine or motor. This type of pump was used extensively in the early days of steam
propulsion (19th century) as boiler feed water pumps. Though still used today, reciprocating pumps are
typically used for pumping highly viscous fluids including concrete and heavy oils.
Another modern application of positive displacement pumps are compressed air-powered doublediaphragm
pumps, commonly called Sandpiper or Wilden Pumps after their major manufacturers. They
are relatively inexpensive, and are used extensively for pumping water out of bunds, or pumping low
volumes of reactants out of storage drums.
Centrifugal pumps are Rotodynamic pumps which convert Mechanical energy into Hydraulic energy by
centripetal force on the liquid. Typically, a rotating impeller increases the velocity of the fluid. The casing,
or volute, of the pump then acts to convert this increased velocity into an increase in pressure. So if the
mechanical energy is converted into a pressure head by centripetal force, the pump is classified as centrifugal.
Such pumps are found in virtually every industry, and in domestic service in developed countries for
washing machines, dishwashers, swimming pools, and water supply.
After motors, centrifugal pumps are arguably the most common machine, and they are a significant user
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of energy. Given design margins, it is not unusual for a pump to be found to be over-sized, having been
selected poorly for its intended duty. Running a constant speed pump throttled causes energy waste. A
condition monitoring test can detect this condition and help size a smaller impeller, either new, or by
machining the initial one, to achieve great energy reduction.
Pumps also wear internally, at a rate varying with the liquid pumped, materials of construction and operating
regime. Again, condition monitoring can be applied to detect and quantify the extent and rate of wear and
also help decide when overhaul is justified on an energy-saving basis.
Kinetic Pumps: The features are:-
• Continuous energy addition
• Conversion of added energy to increase in kinetic energy (increase in velocity)
• Conversion increased velocity to increase in pressure
• Conversion of Kinetic head to Pressure Head
• Meet all heads like Kinetic, Potential, and Pressure
Motors:
An electric motor uses electrical energy to produce mechanical energy. The reverse process that of using
mechanical energy to produce electrical energy is accomplished by a generator or dynamo. Traction motors
used on locomotives often perform both tasks if the locomotive is equipped with dynamic brakes. Electric
motors are found in household appliances such as fans, refrigerators, washing machines, pool pumps,
floor vacuums, and fan-forced ovens. Most electric motors work by electromagnetism.
The classic division of electric motors has been that of DC types and AC types.
Transformers:
A transformer is a device that transfers electrical energy from one circuit to another through inductively
coupled wires. A changing current in the first circuit (the primary) creates a changing magnetic field; in
turn, this magnetic field induces a changing voltage in the second circuit (the secondary). By adding a load
to the secondary circuit, one can make current flow in the transformer, thus transferring energy from one
circuit to the other.
A key application of transformers is to reduce the current before transmitting electrical energy over long
distances through wires. Most wires have resistance and so dissipate electrical energy at a rate proportional
to the square of the current through the wire. By transforming electrical power to a high-voltage, and
therefore low-current form for transmission and back again afterwards, transformers enable the economic
transmission of power over long distances. Consequently, transformers have shaped the electricity supply
industry, permitting generation to be located remotely from points of demand. Transformers are some of
the most efficient electrical ‘machines’, with some large units able to transfer 99.75% of their input power
to their output.
Overview of Production Process
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Figure of Transformer
It is defined as a stationary induction apparatus for transforming electrical energy in AC system from one
circuit to another by changing voltage but without changing frequency. In its simplest form it consists of
two insulated coils wound over a common magnetic core of soft iron lamination as shown in figure. The
winding which receives power from the source is called “primary winding” and the winding which delivers
electric power to the load is known as “secondary winding”. The main purpose of transformer is to change
voltage between the two windings.
The operating principle is very simple. When an AC is fed to primary winding, current flows in the winding
which produces a magnetic flux within the core known as “mutual flux” which is proportional to the
number of winding and the frequency of AC supply. This flux links up the secondary winding to produce
an induced emf proportional to the number of turns of secondary winding. Thus if
E1 = voltage of primary winding
N1 = number of turns in primary coil
E2 = voltage of secondary winding
N2 = number of turns in secondary coil.
Then, 1
2
E
E = 1
2
N
N
If E2 is greater than E1 it is called a “step up” transformer as it increases the voltage and if E2 is less than E1,
it is known as “step down” transformer. Since the ampere turns of primary and secondary winding remains
the same and if I1 and I2 be the primary and secondary currents, then,
N1I1= N2I2
1 1 2
2 2 1
∴ = = E N I
E N I
or,
2
1
N
N
=
1
2
I
I
or, E1I1=E2I2
Auto Transformer: For a very small variation in output and input voltage “double wound” transformer as
explained becomes expensive and “Auto wound transformer” becomes cheaper. Auto transformer has a
single winding and the secondary voltage is tapped from that winding as shown in figure.
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Electrical Drivers:
A Driver is an electronic component used to control another electronic component, such as a high power
transistor. A transistor is a semiconductor device, commonly used as an amplifier or an electrically controlled
switch. The transistor is the fundamental building block of the circuitry in computers, cellular phones, and
all other modern electronic devices.
Because of its fast response and accuracy, the transistor is used in a wide variety of digital and analog
functions, including amplification, switching, regulation, signal modulation, and oscillators.