The invention generally relates to a traction transformer suitable for GTO/IGBT-based electric locomotives. In particular, the invention relates to traction transformer for 3-phase drive Electric Locomotives with increased hotel load capacity and a method for manufacturing the same.
Background of invention:-
An electric locomotive is a locomotive powered by electricity from overhead lines, a third rail or an on-board energy storage such as battery /fuel cells. The electricity is used to drive the motors which gives the driving thrust to the locomotives wheels.
Electric locomotives with on-board fuelled prime movers, such as diesel engines or gas turbines coupled to an electric generator, are classified as diesel-electric or gas turbine- electric locomotives because the electric generator/motor combination serves as a power transmission system.
A traction transformer is an integral part of an electric locomotive. Complete traction power as well as auxiliary power flows to different circuits through the traction transformer. A 25 kV-overhead supply is stepped down through the traction transformer to the desired levels and is fed to various systems through different controllers.
Conventional locomotives are based on DC drives. The DC drive system includes traction transformer, tap changer, rectifier etc to feed controlled DC supply to the traction motors. However, owing to the high maintenance requirements, DC drives are less favoured. In the existing art, 3-phase AC drive systems has increased in application due to their low maintenance requirements and increased energy

efficiency. The 3-phase AC drive system includes traction transformer and electronic converters to convert single phase AC supply to controlled 3-phase supply –which is fed to 3-phase induction motors.
The 3-phase drive systems requires transformer with high winding impedances to limit the system fault currents to safeguard the electronic converters. The 3-phase drive systems also require transformer with a high degree of magnetic de-coupling between different secondary windings to avoid problems of circulating currents between the different converters. The 3-phase drive systems also require transformer with high over-load capacity to take care of intermittent overloads during train starting and train braking due to higher acceleration and regenerative electrical braking method.
The traction transformers deployed at present in 3-phase drive 25kV 6000 HP Electric Locomotives has 01 primary winding, 04 traction windings, 01 auxiliary winding, 01 filter winding and 01 hotel load winding. The transformer also houses 02 series resonant chokes and 03 auxiliary converter doubles chokes. The locomotives do not use hotel load windings due to its inadequate rating and instead two DG set cars are attached to the trains to cater to the hotel load (generally air-conditioning and pantry load) requirements.
To do away with the DG set cars which consumes costly fuel (diesel) and also pollutes the environment, a new traction transformer having 01 primary winding, 04 traction windings , 01 auxiliary winding, 01 filter winding - same as that of the existing transformer and plurality of uprated and split hotel load windings- keeping the transformer weight/layout/dimensions/total losses same as that of the existing transformers for ease of interchangeability with the existing locomotives. The choke units also remain same as in the existing transformer.

Object of the invention:-
It is therefore an object of the invention is to provide a transformer for 3-phase drive locomotives having provision of uprated and split hotel load windings to cater to the train pantry car and air conditioning loads (hotel load).
Another object of the invention is to provide a transformer for 3-phase drive locomotives having provision of uprated and split hotel load windings utilizing core type construction and sandwich windings to achieve high winding impedances.
Another object of the invention is to provide a transformer for 3-phase drive locomotives having provision of uprated and split hotel load windings utilizing core type construction and sandwich windings to achieve high magnetic de-coupling between different windings.
Another object of the invention is to provide transformer for 3-phase drive locomotives having provision of plurality of uprated and split hotel load windings utilizing core type construction and sandwich windings restricting total transformer losses same as that of the existing transformer to keep the cooling system unchanged.
Another object of the invention is to provide a transformer for 3-phase drive locomotives having provision of uprated and split hotel load windings utilizing core type construction and sandwich windings to achieve uprated hotel load maintaining same tank profile as of the existing transformer-for ease of interchangeability.
Another object of the invention is to provide a transformer for 3-phase drive locomotives having provision of uprated and split hotel load windings utilizing core

type construction and sandwich windings is to achieve uprated hotel load maintaining the weight limitations of the existing transformer.
Brief description of accompanying drawing:-
Some embodiments of system or methods in accordance with embodiments of the present subject matter are now described by way of example, and with reference to the accompanying figures, in which:
Figure 1 shows a schematic illustration of the windings arrangement as described in the prior art.
Figure 2 shows the windings arrangement as described in the prior art.
Figure 3 shows a schematic illustration of the windings arrangement in accordance to the instant invention.
Figure 4 shows winding arrangement of the traction transformer in accordance to the invention.
Figure 5 shows tank cover of the traction transformer as described in prior art.
Figure 6 shows tank cover of the traction transformer as disclosed in accordance to the invention.
The figures depict embodiments of the present subject matter for the purposes of illustration only. A person skilled in the art will easily recognize from the following description that alternative embodiments of the structures and methods illustrated herein may be employed without departing from the principles of the disclosure described herein.

Detailed description of the preferred embodiment:-
Fig. 1 and 2 shows a schematic representation of a winding arrangement in a transformer to find application in a GTO/IGBT based 3 phase drive electric locomotive type with single hotel load (HL) winding .
In particular, Fig. 2 shows winding 19, 20 and 21 in a single hotel load winding traction transformer.
Fig. 3 shows the traction transformer has a provision of uprated and split hotel load winding to cater to the hotel load requirements of the trains by modifying the winding arrangement. Core type construction and sandwich methodology is implemented to achieve high winding impedances with high magnetic de-coupling between the different windings. CTC conductors have been used to minimize the eddy losses so as to limit the transformer total loss with uprated rating-within the limit specified for existing transformer to ensure compatibility with existing cooling system. Nomex insulated copper has been used to achieve high over-load withstand capability. Modified winding arrangement keeps the transformer overall dimensions and weight same as that of the existing transformer to ensure interchangeability.
Winding coil no. 19, 20 and 21 (single hotel load winding -945 KVA) of prior art transformer have been replaced by winding coil no. 19, 20, 21, 22, 23 and 24(higher rating and spilt hotel windings of 622.5 KVA each) in the new transformer. New coils are designed and placed in the same space which was released by coil nos. 19, 20, 21 of the prior art transformer. Winding copper, insulation blocks, oil ducts, winding configuration were selected to achieve the required parameters including inductance requirements of the hotel load convertors and at the same time complying with the specified electrical and mechanical constraints including transformer losses, transformer profile and transformer weight. Windings

placement was analysed using state of the art 3-D modelling tools to study the impact of aluminium tank material (non-conventional material) on various parameters including impedances and losses. Bushing plate of 7475 KVA transformer was re-designed by re-locating the thermometer sensor pocket (item-35 marked on drg) to a suitable location on the other side and releasing space for additional hotel load bushings.
The traction transformer for GTO/IGBT-based 3-phase drive 25kV 6000 HP Electric Locomotives type WAP-5/WAP-7 with increased hotel load capacity of lower fault currents due to high winding impedances-for the safety of convertors. Circulating currents between different convertors are eliminated due to high degree of magnetic de-coupling between secondary windings. Interchangeability with existing transformer by maintaining the total losses, overall dimensions and weight same as that of the existing transformer. Environment friendly as the new transformer would cater to the train hotel load and would eliminate the DG set cars. Clean electrical energy from transformer would replace the electricity generated by DG set cars associated with noise and smoke emissions. Increased passenger/parcel carrying capacity as the released DG set cars would be replaced by passenger/parcel cars.

We claim:-
1. A modified traction transformer for a GTO/IGBT based 3phase drive electric
locomotive that comprises of a primary winding, an auxiliary winding, a filter
winding, plurality of traction winding and plurality of split hotel load winding
wherein an additional hotel load winding are disposed within a winding housing of
the said transformer.
2. The modified traction transformer for a GTO/IGBT based 3phase drive electric
locomotive as claimed in claim 1, wherein the transformer specification are
configured to adapt the additional hotel load winding .
3. The modified traction transformer for a GTO/IGBT based 3phase drive electric locomotive as claimed in claim 1 and 2, wherein the transformer specification includes, insulation block, oil ducts, etc.
4. The modified traction transformer for a GTO/IGBT based 3phase drive electric locomotive as claimed in claim 1, wherein a thermometer sensor pocket is installed to release space for the additional hotel windings.
5. The modified traction transformer for a GTO/IGBT based 3phase drive electric locomotive as claimed in claim 1 wherein as illustrated in the accompanying drawings.