generators, generator types, generator function, generator instillation, working principle of generator starter circuit, relationship between KW,KVA and KVAR auto voltage regulation (AVR), speed monitoring circuit.

1. Generators
By NS Wickramasinghe BSc(E&E Eng)

2. Basic Classification of Generators
DC Generator AC Generator

3. Major Component of Large Generator
Fly Wheel Connecting Shaft
Auto Voltage Regulator (AVR)
Stator
Rotor
Current Rectifier
Exciter
Output Terminal

4. Stator
The stator core is a hollow cylinder formed by stacks of laminated, cold rolled silicon steel plates
The laminations are clamped by insulated bolts. The core has ventilation ducts that allow coolant air to
flow through them.
Full-length longitudinal slots, designed to accommodate the winding conductors, are provided on the
inner periphery of the core.
The stator core is supported within the frame by using a flexible mounting.
This arrangement prevents the high level of vibration - usual in a 2-pole machine due to the magnetic
forces - to be transferred to the frame and the foundation.

5. Rotor
Slots are cut along the full length of the rotor body to accommodate the field windings.
The exciter side of the shaft has center bores, which allow the field winding leads to pass
through them for connection with the rotating rectifier (RR) of the brushless excitation system.
Two axial blowers are mounted on the two ends of the generator rotor shaft.
A fan guide is clamped to the stator which directs the air to flow into the blower.
Retaining rings made of non-magnetic material are fitted with the winding end turns to support
and protect the turns from being damaged by centrifugal forces which develop on a running
generator.
This also allows axial thermal expansion of the rotor winding.
The generator field windings are connected with the RR of brushless excitation system by using
two insulated conductors that pass through the hollow center bore of the rotor shaft.

6. Output Terminal
Generally located at the upper part of the stator frame, and on the opposite side of the
prime mover, is the CT Trunk for making electrical output connections.
The CT trunk houses the three leads for the generator three line terminals and the
bushing CTs.
The adaptor box connects the generator line terminals with the IPB to deliver the power.
Three terminal leads are shorted after passing the bushing CT’s to form the neutral
terminal and are connected to the generator neutral grounding equipment.

7. Type of Field Excitation
Types Of Generators
Method of Field Excitation
Rotor Construction
Slip Ring Type
Brushless Type
Cylindrical
Rotor Type
Salient Pole
Type
Self Excited
Type
Externally
Excited Type

8. Slip Ring Type
For these types of generators, slip
rings are used for feeding excitation
supply to the field windings.
Slip ring rotates with the rotor.
Excitation
supply is fed through carbon brushes.
These brushes touch the slip rings
and are fixed.
As the slip rings rotate, sparking takes
place near the brushes.
Distance of the carbon brushes is
adjusted in such way that minimum
sparking takes place.
Automatic Voltage
Regulator
AVR Sensing Signal
Generator Output
Negative
Biased Field Main Field
Stabilizing
Feedback Supply
Stator
Rotating Field
PM Magnet

9. Brushless Type
These generators use the principle of rotating
rectifier for excitation purpose. There are no
rubbing parts in these types of generator.
Most of the large generators used to provide AC to
ships' electrical systems are of the brushless type.
Brushless generator, following units are
fitted/coupled to the generator rotor:
(a) HF generator field winding, which is
permanent magnet and is coupled to the
generator rotor.
(b) Three phase wounded Armature of AC
exciter
(c) Rotating rectifier unit, which rectifies
output of AC exciter. The rectified output
serves as feed to the main generator field
winding.
Exciter AC
Diode bridge and
Surge Suppression Resistor
Diode Failure unit
Exciter Field
Stator
Generator Field
PM Generator
Automatic
Voltage Regulator

10. Self Excited Type
AVR Sensing Signal
Static rectifier Supply
Stator
Rectifier Control
Signal
Auto Voltage
regulator
Generator Output
Rotating
Field
Alternators, excitation to the field winding is
given from the generator output itself.
Output of the generator is rectified and
controlled by the Auto Voltage Regulator and
then fed to the field winding either by slip
rings or brush-less arrangement.

11. Externally Excited Type
In these types of generators, excitation to the field winding is given through external means. For this
purpose, a battery or a separate DC generator may be used.
Cylindrical Rotor Type
It is generally used for steam turbine driven alternators, which run at very high speed. The rotor
consists of smooth solid forged steel cylinder, having a number of slots milled out at intervals along the outer
periphery for accommodating field coils.
Salient Pole Type
It is used in low and medium speed alternators. It has a large number of projecting (salient) poles having
their cores bolted on to a heavy metallic wheel of cast iron. Their large diameters and short axial length
characterize such alternators.

12. Generator Protection
Various kinds of generators, based on prime mover design, for power generation onboard ships. A
few of these generators are as follows
(a) Diesel Alternators
(b) Gas Turbine Generators
(c ) Steam Alternators.
Various protections incorporated in a generator is specific to the type of generator. Whenever any of
the protections operate, fuel/steam supply to the generator is stopped, causing stoppage of the engine. A few
protections common to most of the generators can be listed as below
(a) Over speed protection
(b) Low oil pressure protection
(c) High exhaust gas temperature protection
(d) High bearing temperature protection
(e) Over voltage protection
(f) Under voltage protection
(g) Overload or overcurrent protection

13. Over Speed Protection
Normally there are two types of over speed tripping mechanisms
a) Mechanical over speed trip
b) Electronic over speed trip
However in the modern world it use only electronic over speed trip
Electronic Over Speed Trip
To understand the electronic over speed trip, a normal lay out of the system is described below. The electronic
over speed trip consists of
a) Fly wheel mounted speed sensor
Magnetic speed sensor (Magnetic pickup) is preferred in generator engines. Due to the
discontinuity of actuator surface (gear tooth of flywheel) voltage is excited in the pick off coil of sensor,
producing an electric analog wave. This cyclic wave created by the flywheel is read by the sensor.

14. Over Speed Protection
b) Signal condition unit
This unit act as a receiver to the speed sensor. Basic function of
the signal conditioner is to convert one type of electronic signal which may
be difficult to read into another type into a more easily read format. This can
be achieved by amplification, excitation and linearization of an electrical
signal.
c) Detection and Comparison unit
There is a set value which is normally 10 % above the rated speed
and acts as base value for this unit. Signal condition unit output is
continuously detected and compared with the set value.
d) Trip signal unit
If the difference between the set value and detected value is
above the limit, then this unit gives a trip signal which in turn shuts down
the generator.
Power Supply
Signal
Condition
unit
Trip Signal
unit
Stop Valve
Prime mover
Fuel
Inlet

15. Low Oil pressure protection
Oil pressure loss while operating at full power is likely to result in severe
engine damage. Reduction of engine speed and load, or stopping the engine can
minimize damage. Engine oil pressure must be monitored. Two operating
conditions require alarms and shutdowns. • Low oil pressure at low engine
speed (idle conditions) • Low oil pressure at high engine speed and/or load.

16. High exhaust gas temperature protection
Changes from normal exhaust stack temperatures give useful information concerning
air filter restriction, after cooler restriction, valve problems, turbocharger fouling and engine
speed and load. Excessive temperatures indicate a variety of impending engine problems.

17. Over voltage protection
Generator over voltage may occur during a load rejection or excitation control failure.
In the case of hydroelectric or gas turbine driven generators, upon load rejection, the generator may speed
up and the voltage can reach high levels without necessarily exceeding the generator’s V/Hz limit.
The voltage regulating equipment often provides this protection. If it is not, it should be provided by an AC
overvoltage relay.
This relay should have a time delay unit with pickup at about 110% of the rated voltage. It should also have
an instantaneous unit with pickup at about 130% to 150% of the rated voltage.
It is not generally required with large generators

18. Under voltage protection
An under voltage condition is a decrease in the rms AC voltage, to less than 90% at the power frequency
for a duration, longer than 1 minute.
The term "brownout" is often used to describe sustained periods of under voltage initiated by the utility to
reduce power demand. Under voltages result from events which are the reverse of those causing over
voltages.

19. Exciter Error Voltage Loop
feedback
Main Error Voltage Loop
Generator Voltage
Out
Automatic Voltage Regulator
In case of any voltage difference
between that of generator and the
reference, the amplified voltage
difference is used to control the
output of meta dyne generator
The auto voltage regulator (AVR) consists of a voltage
comparator which compares a stabilized reference voltage
and the mean three phase r.m.s. line voltage of the
generator
AVR. which supplies the field current of main generator exciter so as to control the line voltage of the generator
itself.

20. Speed Monitoring and Stop Circuit
Speed monitoring - When the engine achieve initial set rpm
the LSR relay Activated. When the engine achieve 800 rpm and
HSR relay pick up along with the TD3 Relay. The electronic
speed switch connected to a signal generator mounted on the
engine that feeds the engine’s speed (RPM). Many of the
speed switches also have a tachometer out put to a meter on
the engine gauge panel or in the control room so that operator
can be Monitor the engine speed.
Emergency
Shutdown
Emergency
Shutdown
SDR
5
ESS
Normal
Shutdown
ESS
5A
Techo
Generator
Tachometer
5
Electronic Speed Switch
Fuse
Fuse
Emergency Shutdown - it is consist of a push button than can be
use to stop the engine at any time whether there is an emergency
start signal present or not. Emergency switches are in series such
that both must be initiate to stop The engine. This switches pick
up the ‘L’ and ‘L1’ relays. The ‘L’ is an instantaneous relay which
pick up the SDS shutdown solenoid. This solenoid is part of the
Governor or part of engine control sys. Activation of SDS relay
reduce the fuel supply to the engine and engine will stop.

21. Starting Circuit
Generator starting module works as follow. The
circuit includes a relay CP1, which monitors
power on this portion of the circuit. There is a
similar relay (CP2 and CP3) in the circuits in
speed monitoring circuit and fault monitoring
circuit that monitor the power in those sections
of the circuits. A contact on each of these relays
goes to an annunciator window to alarm that
power has been lost. shows a switch on the
local control panel in the emergency generator
room used to select the control mode of operation
of the emergency generator. When the switch is in
the 'REMOTE‘ position (thrown to the left), the unit
can be started from the control room or other
remote location.
Maintenance
Local
Remote
Maintenance
Start
Engine
Reset
Local
Start
Remote
Start
HSR
LSR
SFR
ESS
Emergency
Start Signal
Fuse
Fuse
4
SFR
4
TD2
4

22. Starting Circuit
An ‘Emergency Start” contact in the control room
(or elsewhere) initiates a fast start by picking up the
ESS relay shown in Figure. Picking up the ESS relay
will in turn pick up the 4 relay. The 4 relay picks up
the Air Start Solenoid Valves (ASV), which cranks the
engine for starting. Note that the ESS relay will
cause a start whether the control switch is in the
‘Remote’ or ‘Local’ position, but not the
‘Maintenance’ position. Note also that a 4 contact in
series with the ESS contact latches in the 4 relay.
The TD2 relay is a timing relay set for 7 seconds. It is
in parallel with the 4 relay.
Maintenance
Local
Remote
Maintenance
Start
Engine
Reset
Local
Start
Remote
Start
HSR
LSR
SFR
ESS
Emergency
Start Signal
Fuse
Fuse
4
SFR
4
TD2
4
When the engine starts and accelerates, first the
LSR relay will pick up and then the HSR relay will
pick up at their respective speed set points. The 4
relay and the ASV solenoid will be de-energized to
complete the starting process.

23. Relationship Between KW, KVA, KVAR, and PF
There is a relationship between the KW, KVA, KVAR, and Power Factor that allows us to calculate any one,
knowing at least two others. That relationship is described by the following formulae:
𝐾𝑉𝐴2
= 𝐾𝑊2
+ 𝐾𝑉𝐴𝑅2 𝑃𝑜𝑤𝑒𝑟 𝐹𝑎𝑐𝑡𝑜𝑟(𝑃𝐹) =
𝐾𝑊
𝐾𝑉𝐴
Single Phase
𝐾𝑉𝐴 =
𝐼 × 𝑉
1000
Three Phase
𝐾𝑉𝐴 =
3 × 𝐼 × 𝑉
1000
𝐾𝑊 =
𝐼 × 𝑉 × 𝑃𝐹
1000
𝐾𝑊 =
3 × 𝐼 × 𝑉 × 𝑃𝐹
1000
𝐻𝑜𝑟𝑠𝑒𝑃𝑜𝑤𝑒𝑟(𝐻𝑃) =
𝐼 × 𝑉 × 𝑃𝐹 × %𝐸𝐹𝐹
746
𝐻𝑜𝑟𝑠𝑒𝑃𝑜𝑤𝑒𝑟(𝐻𝑃) =
3 × 𝐼 × 𝑉 × 𝑃𝐹 × %𝐸𝐹𝐹
746

24. Generator Installation Procedure
 After unpacking first conduct a thorough inspection to detect any damage that may have occurred during
shipment.
 Check whether the rated amperage / wattage capacity of the unit is similar as what you purchased from
tally plate.
 The unit should be placed outdoors in a protective enclosure, where sufficient air for cooling and ventilation
is available in an unobstructed manner.
 The generator should be placed on a level surface, which is non-combustible and non-conducting, a little
above ground level to prevent contact from rising water levels.
 The generator should be installed in close proximity to the location of the transfer switch and the fuel
supply, to reduce the required length of cabling and piping respectively.
 You may be required to seek a permit if you intend to store a large fuel tank. The fuel pipe sizing,
construction and layout must comply with world standards to minimize the hazards.

25. Generator Installation Procedure
 A grounding lug is usually provided for grounding the frame and external conducting parts of the
equipment. It is essential to consult a qualified electrician to determine grounding requirements and
follow procedures that meet local regulations.
 All batteries must be completely charged before they are inserted into the generator.
 Similar care must be ensured while unpacking and installing the transfer switch or change over switch.
The switch should be wall-mounted and all the points must be in level with each other to prevent
distortion of the switch.
 Installation of fire extinguishers are essential for the place where your generator located
 The exhaust system may need to be covered with insulated material to prevent fire resulting from
contact with combustible materials.

27. Reference
 SL Dockyard training manual
 Diesel Generator as emergency power source – USNRC HRTD
 http://www.electrical4u.com/protection-system-in-power-system
 http://www.animations.physics.unsw.edu.au
 http://www.mpoweruk.com/generators.htm
 http://electricalengineering-access.blogspot.com/2015/03/common-generator-problems-and-
its.htmlhttp://electricalengineering-access.blogspot.com/2015/03/common-generator-problems-and-
its.html
 http://www.generatorjoe.net/html/aboutgenerators.html