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FIELD OF INVENTION :
The invention relates to an improved brushless synchronous alternator for oil rig
application.
BACKGROUND OF INVENTION :
In the recent years, oil sectors require high rated brushless synchronous
alternator to cater various load conditions of drilling operation of oil well during
critical drilling, deep drilling and angular drilling. The alternator is used for
providing rated power supply on continuous basis at site conditions i.e. operating
condition of temp range of -5 deg to 55 deg C, limits of noise, vibration, heat &
exhaust gases. It has also been noticed that due to very low power factor of the
alternator during above conditions high reactive power is required. The users
further require that the THF should be within limits of the International
standards. As the oil rig wells are normally located at very remote places, hence
the alternators for such purpose should be self-starting without any field flushing
of the alternator. The existing alternators used for oil rig application are upto
1215 kVA, 1000 RPM. However, it has been noticed that the residual voltage
generated by the alternator is insufficient for self starting of alternator at site.
OBJECTS OF INVENTION :
It is therefore an object of invention to propose an improved brushless
synchronous alternator for oil rig application.

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A still another object of the invention is to propose an improved brushless
synchronous alternator for oil rig application which is enabled to possess a self
start characteristic including a lower THF to meet the limits of international
standards.
A further object of this invention is to propose an improved brushless
synchronous alternator for oil rig application which is mountable on the existing
power pack in operation.
A still further object of the invention is to propose an improved brushless
synchronous alternator for oil rig application, which is designed with a capacity
of 1430 kVA, 600V, 1000 RMP, 50 Hz.
SUMMARY OF THE INVENTION :
Accordingly, there is provided an improved brushless synchronous alternator, in
particular for oil rig application which is applicable under load conditions of
drilling operation of oil well during critical drilling, deep drilling and angular
drilling, self start characteristic and low power factor condition. The frame of the
alternator is of tubular construction, sturdy and light in weight. The newly
designed frame, pedestal plates and end-shields enable an easy assembly and
dismantling of the alternator. Lifting lugs are installed on the frame for lifting
the alternator with a conventional overhead hoist. A removable drip-proof,
louvered cover in two halves encloses the exciter and diode wheel of the
alternator. The alternator has been designed to improve the telephonic harmonic
factor (THF) of the existing machines. THF of the new alternator during testing
has been found to be much lower as compared to the limits specified by National
/ International Standards.

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The brushless synchronous alternator of the invention is having a high power to
weight ratio, and is suitable for coupling and aligning with diesel engine. A
capsule type wound stator is provided for the alternator. The alternators having
self start and many more features. The features have been achieved by
designing and reviewing the electrical parameters and a newly designed exciter
introduced to cater magnetic field requirement of the alternator through pre-
assessment of the open circuit and short circuit characteristics.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Fig 1 illustrates an open circuit and a short circuit characteristic in a graphical
representation of a synchronous alternator according to the invention.
Fig. 2 illustrates a sectional diagram of the brushless synchronous alternator
according to the invention.
Fig. 3 illustrates an outline diagram of the brushless synchronous alternator
displaying mounting of the alternator according to the invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
As illustrated in Fig 2, a stator core (3), made of one-piece low loss steel
laminations (2), are stacked together to form a complete stator construction. The
stator coils (1) are class 'H' insulated, and inserted in stator slots.

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Stator coils (1) of insulated copper performer which are placed inside the slots in
core and joined together in the form of a 3-phase winding. The stator coils (1),
which have multiple number of turns, are consolidated together before insertion
in to the slots.
The 3- phase electrical connection of the stator winding are brought out for
supply by connection rings (9).
The rotor of the alternator has a shaft (14) including a set of rim punching
assembly (15) with at least one dovetail groove. A pole and coil assembly (17) is
fitted in this dovetail groove. The pole and coil assembly (17) includes pole
assembly made of sheet steel punching which are retained from both ends by
end plates. Field coils are assembled on the pole assembly (17). The pole and
coil assembly (17) is locked in the dovetail of the rim punching assembly (15) by
means of tapered keys. All field coils are connected in series with copper
connectors joined by bolting. Damper bars (22) are inserted in the pole assembly
(15) which are shorted by SC (21) rings at both ends.
Exciter armature core (18) is made of sheet steel lamination (2) stacked together
and armature coils of enameled copper are placed inside the slots in the core
and joined together in the form of 3-phase winding.
Exciter stator core (12) made of sheet steel lamination (2), with pole type
configuration, are stacked together and field coils are placed on the poles. The
field coils are joined together in series by brazing the leads.
Rotating rectifier bridge assembly (19). is mounted on the rotor shaft (14) and
the rotating rectifier assembly (18) which consists of a full wave rectifier bridge
made of six semi-conductor devices mounted on aluminum heat sinks (20) and
are retained in the heat-sink assemblies with retaining nuts & washers.

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The dimensions of holes for mounting of the alternator has been kept same as
by modifying the stator frame so that it can be fitted in same power pack.
The alternator stator core (3) is built up of one-piece low loss steel laminations
(2). The steel laminations (2) are assembled under pressure to form the stator
core (3). The stator core (3) is rigidly fixed on to a frame (4) by means of a key.
Stator coil (1) leads are brought out to four connection rings (9) (three phases
and one neutral ring). Bus-bars (13) are bolted to these rings and brought out in
the terminal box.
The rotor core is made from rim punching, stacked together under pressure and
fitted on the rotor shaft (14) with a key. The pole punching, of salient pole
construction, is stacked together to form a pole assembly. The "pole and coil
assembly" (17) is locked in the dovetail of the rim punching assembly (15) by
means of tapered keys. Damper windings (22) are made of heavy copper bars
embedded in poles and rigidly brazed to end rings.
The exciter consists of two basic component assemblies, the stationary field
assembly (12) and the rotor comprising of the rotating exciter armature (18) and
rotating rectifier bridge assembly (19). In the exciter field assembly (12), there
are twelve poles consisting of pole punching stacked together and welded to
form a stator core (3). It is assembled along-with their field coils and are bolted
to the NDE end-shield (11).
The exciter armature (18) and rotating rectifier bridge assembly (18) are sleeve
mounted on the shaft (14) of the main alternator. The rotating rectifier
assembly (18) consists of a full wave rectifier bridge made of six semi-conductor
devices mounted on aluminum heat sinks (20).

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The present invention proposes a synchronization of the parameters to achieve
the desired load of the oil rig during normal running condition, deep drilling
condition, critical drilling condition and angular drilling condition.
This invention constitutes synchronizing of these parameters which have been
developed to achieve the desired power required in service for use on oil rig as
illustrated in Fig 1.

Brushless Synchronous alternator part details
Item No. Part Description
1 Stator coil
2 Stator laminations
3 Stator core
4 Magnet Frame
5 Clamping Plate
6 End Shield DE
7 End Shield NDE
8 Lifting Lug
9 Connection Rings R, Y, B and N
10 Bearing Assembly. DE
11 Bearing Assembly. NDE
12 Exciter Stator Assembly.
13 Bus Bars R, Y and B
14 Rotor Shaft
15 Rim punching assembly
17 Pole and Coil Assembly.
16 Fan

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18 Exciter Armature Assembly.
19 Rotating rectifier bridge assembly
20 Space Heater
21 Support ring
22 Damper Bars
23 Coupling Hub
24 End Cover

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WE CLAIM
1. An improved brushless synchronous alternator adaptable to oil rigs, in
particular for dip, critical and angular drillings, comprising:
- a stator core (3) built-up of one-piece low loss steel laminations (2)
rigidly fixed on to a frame (4), leads of the stator core (3) being
brought out for supply by a plurality of connection rings (9), the
connection rings (9) bolted to a plurality of bus bars (13);
- a rotor core fitted on a rotor shaft (14);
the rotor core formed out of rim punching and stacked under
pressure; a pole and coil assembly (15) locked on the dovetail of
the rim punching assembly (15); a plurality of damper windings
(22) embedded in the poles and brazed to end rings; and
- an exciter device comprising a stationary field assembly (12), an
exciter armature assembly (18), and a rotating rectifier bridge
assembly (19), the exciter armature assembly (12) and the rotating
rectifier bridge assembly (18) being sleeve-mounted on the shaft
(14) of the main alternator.
2. The alternator as claimed in claim 1, wherein the rotating rectifier bridge
assembly (18) comprises a full-wave rectifier bridge made of six semi
conductor devices mounted on aluminum heat sinks (20).
3. The alternator as claimed in claim 1, which has a rating of 1430kVA,
600V, 1000 RPM.

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4. An improved Brushless Synchronous Alternator adaptable to oil rigs, in
particular for dip drilling and critical drilling conditions as substantially
described and illustrated herein with reference to the accompanying
drawings.

Accordingly, there is provided an improved brushless synchronous alternator, in
particular for oil rig application which is applicable under load conditions of
drilling operation of oil well during critical drilling, deep drilling and angular
drilling, self start characteristic and low power factor condition. The frame of the
alternator is of tubular construction, sturdy and light in weight. The newly
designed frame, pedestal plates and end-shields enable an easy assembly and
dismantling of the alternator. Lifting lugs are installed on the frame for lifting
the alternator with a conventional overhead hoist. A removable drip-proof,
louvered cover in two halves encloses the exciter and diode wheel of the
alternator. The alternator has been designed to improve the telephonic harmonic
factor (THF) of the existing machines. THF of the new alternator during testing
has been found to be much lower as compared to the limits specified by National
/ International Standards.
The brushless synchronous alternator of the invention is having a high power to
weight ratio, and is suitable for coupling and aligning with diesel engine. A
capsule type wound stator is provided for the alternator. The alternators having
self start and many more features. The features have been achieved by
designing and reviewing the electrical parameters and a newly designed exciter
introduced to cater magnetic field requirement of the alternator through preassessment of the open circuit and short circuit characteristics.