FIELD OF THE INVENTION
The invention relates to an improved Power transformer with Vacuum type on load tap changers (OLTC) working at an oil head of more than ten meter height.
BACKGROUND OF THE INVENTION
It is known that a power transformer increases or lowers the voltage of an AC circuit in an unsurprising way reliant on the ratio connecting the windings. For instance, a 100:1 ratio power transformer, 100 amps flowing through the primary transformer winding will effect in a power of 1 amp throughout the secondary winding.
A power transformer normally comprises of a primary and secondary coils of wire enfolded around a core, as a rule completed with steel or a nickel alloy. Transformer windings are electrically shielded from every other arid as of from the core. The winding linked to the power supply is termed as the primary winding. The transformer winding in which power is put in is termed as the secondary winding.
The power transformer additionally comprises an oil tank and a Tap Changing equipment (called as tap changer), placed inside the oil tank. The tank is completely filled with oil all the time. To cater for the expansion and contracting ' of the volume of oil in the tank owing to variation in temperature (due to ambient temperature and working temperature), a separate small oil reservoir tank, known as Conservator is provided, which is placed above the tank. The volume of the conservator is normally less than 10% of that of the transformer tank.

An on-load tap changer (OLTC) is used to change the tapping connection of the transformer winding while the transformer is energized. The tap changer is available for single and three-phase applications with one common neutral point. Depending on the three-phase rating, it might require three separate units, each having its own insulated phases. Tap changers can be located either inside the transfer main tank or outside in its own compartment
Switching from one position to another is performed through an impedance to avoid a short circuit between two steps of the regulating winding. The transition impedance can be either a resistor or a reactor.
Generally, the conservator is placed at an height of 1 to 2 meter above the tank. Accordingly, the pressure difference due to oil head (height of oil column above ground) between the conservator and the tank is in the tune of 0.1 kg/sq. cm to 0.2 kg per sq. cm.
Vacuum type on-load tap changer is also known, and contains a diverter switch and a tap selector. It adopts vacuum switching technology in the transition circuit of the diverter switch. And the tap selector is of a reliable structure continuously useful in long term operation. This tap changer is applicable to power transformers or industrial transformer.
The vacuum on-load tap changer generally has three voltage regulating modes: linear, reversing and coarse-fine.
Almost all the power transformers are provided with an On Load Tap changer (OLTC). The function of the OLTC is to change the output voltage of the transformer, while the transformer is in service. Conventional OLTC as stated

herein above, comprises a set of moving contacts placed in an oil filled compartment. The Vacuum type Tap changers (OLTC), have the contacts placed inside a vacuum bottle. These vacuum bottles are subjected to a pressure corresponding to the pressure difference of the conservator and the tank. In a conventional transformer, this pressure difference due to the oil head is around 0.1 to 0.2 kg/sq. cm. The Vacuum type OLTC are preferred over conventional OLTC owing to less wear and tear of the contacts, lesser oil contamination, lesser maintenance and higher longevity.
For some specific applications, the conservator is placed at an height even more than 30 to 40 meters above the tank (for example, if the transformer is placed at the basement of a multi storied building, the conservator is placed at the roof of the top most floor). In such a case, the pressure difference between the conservator and the tank is around 3.5 kg/sq. cm (corresponding to the difference in the height of conservator), and the Vacuum type On Load Tap changer (OLTC) becomes inoperable.
Vacuum type On Load Tap Changers can only work up to a pressure difference of 1kg / sq. cm.
OBJECTS OF THE INVENTION
It is therefore an object of the invention to propose an improved Power transformer with Vacuum type on load tap changers (OLTC) operable at an oil head of more than ten meter height.
Another object of the present invention is to propose an improved Power transformer with Vacuum type on load tap changers (OLTC) working at an oil head of more than ten meter height, where the transformer is placed for

example, at the basement of a multi storied building and the conservator is placed at the roof of the top most floor.
A still another object of the invention is to propose an improved Power transformer with Vacuum type on load tap changers (OLTC) operable at an oil head of more than ten meter height, which can be installed adjacent to a load centre without interrupting other activities.
A further object of the invention is to propose an improved Power transformer with Vacuum type on load tap changers (OLTC) operable at an oil head of more than ten meter height, which eliminates networking problems and reduces energy loss in transmission of power from the transformer to load point.
A still further object of the invention is to propose an improved Power transformer with Vacuum type on load tap changers (OLTC) operable at an oil head of more than ten meter height, which enhances applicability of known Vacuum type On Load Tap Changer (OLTC) up to oil head of 10 meters.
SUMMARY OF THE INVENTION
Accordingly, there is provided an improved power transformer with vacuum type on load tap changer (OLTC) operable at an oil-head exceeding ten meters, comprising a magnetic core, a high-voltage (HV) winding, a set of low-voltage (LV) winding, a transformer tank, and a vacuum type on load tap changer (OLTC); and a conservator (C) disposed at a height exceeding ten meters above the transformer. The transformer tank is configured into two halves, the first half accommodating the magnetic core-coil assembly, the second half housing the vacuum OLTC, the two halves being separated by a steel wall (W) having a plurality of cut-outs. The cut-outs are provided with insulated terminal

board (TB) with corresponding numbers of terminal bushings (B) allowing connection between the coils and the OLTC. The second half of the transformer tank is smaller in size than the first half and provided with an auxiliary conservator (AC) leading to maintaining of oil-head pressure on the vacuum OLTC in the range of 0.1 kg/sq.cm which is equivalent to 1 meter oil head.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Figure 1 - Shows a prior art arrangement of a transformer and a conservator.
Figure 2 - Shows a prior art arrangement where the transformer is placed at basement and the conservator at the roof top of a multi-storied building.
Figure 3 - Shows an arrangement according to the invention, in which the tank of the transformer is configured with two halves, and an auxiliary conservator.
Figure 4 - Shows the arrangement of figure-3 in which the second half of the tank accommodating the auxiliary conservator, and the first half is connected to the main conservator.
DETAIL DESCRIPTION OF THE INVENTION
According to the prior art, the conservator (c) is mounted as a separate load above the transformer tank (TT) (as shown in Figure-1).
As per specific applications, the prior art conservator (c) is mounted at an height

of above 30 meter above the tank (TT) (as shown in Figure-2).
In the inventive system, the tank (TT) is internally bifurcated into two separate chambers (1,2). The two chambers (1,2) are isolated totally from each other by a metallic wall W (as shown in Figures-3).
The bigger chamber (1) accommodates the core - coil assembly of the transformer. The second chamber (2) is much smaller in size, and it houses the vacuum Tap changer (OLTC). The two chambers (1,2) are separated by a wall (W) made of steel plate, in which cut outs (openings) are provided. Insulated terminal board (TB) are mounted on these cut outs. A plurality of termination bushings (B) are mounted on the terminal board (TB). Connection from the coils to the OLTC (are done through these bushings (B) on the terminal board (TB) (as shown in Figure-3).
The main conservator (C) is connected to the first Chamber (1) (which houses the core-coil) assembly to maintain it's oil level. The second chamber (2) (that houses the OLTC) has a small conservator (AC) (due to smaller volume of oil in the second chamber) that is mounted locally above the tanks, as shown in Figure-4). As a result, the oil head (pressure) appearing on the Vacuum OLTC in the range of 0.1 kg / sq. cm (equivalent to 1 mtr oil head), even when the main conservator is placed at 30 meter above the tank.
ADVANTAGES OF THE INVENTION
1. This invention provides an improved Power transformer using Vacuum type tap changer operable at any amount of oil head (pressure), and deriving all the advantages of Vacuum OLTYC viz. practically maintenance free OLTC.

2. According to the invention, the transformer is placed at the basement of a multi storied building and the conservator is placed at the roof of the top most floor. This ensures requirement of much less space for installation of the transformer; which is always a constraint in the vicinity of multi-storied buildings.
3. The present invention enables enhancement of operational range of existing Vacuum type Tape changer suitable up to a maximum oil head of 10 meter only.
4. There is no need to develop a Vacuum type OLTC for higher oil head (pressure). With this inventive arrangement, any Vacuum type OLTC can be used in any power transformer irrespective of the location of conservator.
5. Installing of an improved power transformer with Vacuum type OLTC closer to the Load centre, there by resulting reduction in networking problems and reduction in energy loss in transmission of power from transformer to load point.
6. The improved power transformer requires much lesser installation space as well as saving the energy thereby increasing the efficiency of the system. With the innovative arrangement the range of application of the Vacuum type OLTC in Transformer is increased.
2.
WE CLAIM
1. An improved power transformer with vacuum type on load tap changer (OLTC) operable at an oil-head exceeding ten meters, comprising:
- a magnetic core, a high-voltage (HV) winding, a set of a low-voltage (LV) winding, a transformer tank, and a vacuum type on load tap changer (OLTC); and
- a conservator (C) disposed at a height exceeding ten meters above the transformer tank,
characterized in that the transformer tank is configured into two halves, the first half accommodating the magnetic core-coil assembly and the second half housing the vacuum OLTC, the two halves being separated by a steel wall (W) having a plurality of cut-outs, the cut-outs provided with insulated terminal board (TB) with corresponding numbers of terminal bushings (B) allowing connection between the coils and the OLTC, and in that the second half is smaller in size than the first half and provided with an auxiliary conservator (AC) leading to maintaining of oil-head pressure on the vacuum OLTC is the range of 0.1 kg/sq.cm which is equivalent to 1 meter oil head.

ABSTRACT

The invention relates to an improved power transformer with vacuum type on load tap changer (OLTC) operable at an oil-head exceeding ten meters, comprising a magnetic core, a high-voltage (HV) winding, a set of a low-voltage (LV) winding, a transformer tank, and a vacuum type on load tap changer (OLTC); and a conservator (C) disposed at a height exceeding ten meters above the transformer tank, the transformer tank is configured into two halves, the first half accommodating the magnetic core-coil assembly and the second half housing the vacuum OLTC, the two halves being separated by a steel wall (W) having a plurality of cut-outs, the cut-outs provided with insulated terminal board (TB) with corresponding numbers of terminal bushings (B) allowing connection between the coils and the OLTC, and in that the second half is smaller in size than the first half and provided with an auxiliary conservator (AC) leading to maintaining of oil-head pressure on the vacuum OLTC is the range of 0.1 kg/sq.cm which is equivalent to 1 meter oil head.