Technical information
Adequate protection
This page describes the various types of electrical transformers and how a DGPT2 protection device can be mounted on each of them.
Types of transformers
Dry (air-cooled) transformers
The live parts are coated with a protective resin (often epoxides) and are mounted on a support chassis in free air. This type of transformer needs to be well ventilated, as well as the room where it is housed. It is also preferable to filter the air to eliminate dust.
We will not deal with fitting protection devices on air-cooled transformers.
Liquid-cooled transformers
The live parts of liquid-cooled transformers are contained in a tank filled with a dielectric liquid:
- PCB (e.g. Askarel™, Pyralene™). These products were banned in Europe in 1987 (for new equipments)
- Ugilec™. This replacement fluid for Pyralene was banned in Europe in 1994 (for new equipments)
- Oil (mineral oil, silicone oil, etc.)
The role of the dielectric fluid is to protect the live parts from atmospheric humidity and to dissipate operating heat.
Oil-filled sealed-tank transformers
These transformers are airtight. The tank is flexible with corrugations, allowing for variations in the volume of the dielectric fluid caused by temperature variations.
The tank cover usually has a 60 mm (2.36 inch) diameter hole in it, sealed with an 85 mm (3.35 inch) diameter solid flange attached by means of 3 or 4 hooks (French standard NF C 52-107). This hole is primarily used as the filling hole.
The DGPT2 is easily mounted in place of the sealing flange.
Expansion transformers
These transformers have a so-called conservator on them which acts as a reservoir and expansion tank (for the variations in the dielectric’s volume). It is often equipped with a visible level, a dryer and a drain valve.
Depending on when the transformer was manufactured, the tank cover may have either a 60 mm (2.36 inch) diameter hole or another type of filling system (a tube with a stopper for example).
The transformer can be adequately protected, but the DGPT2 must be fitted with the IB adaptation to mount it in place of the Buchholz device, in order for it to be connected to the expansion tank.
If the cover has a 60 mm diameter hole, the DGPT2 can be mounted with no additional modification. If another filling system is used, the DGPT2 must be replaced by a DGP without a mounting flange (SB option) and with a tapped body at the base. An adapter will be made (at the customer’s charge) for the connection between the existing filling system and the DGP. Additionally, the DGP must be fitted with the IB option as previously mentioned. If the temperature function is needed, a TDC can be mounted on the tank well; the DGPT2 is thus made of two independent parts : DGP-IB/SB + TDC = DGPT2
Gas cushion transformers
The rigidity of the airtight tank is compensated by a neutral gas cushion which handles the variation of the dielectric volume by compression. In general, the tank cover has only one filling point.
The protection functions cannot be all be ensured with this type of transformer, and modifications must be undertaken, by removing the buffer gas, fitting an expansion tank to compensate for the dielectric fluid’s volume variations, and adding dielectric fluid.
As with expansion transformers, the DGPT2 must be fitted with the IB adapter for mounting in place of the Buccholtz device in order to connect it to the expansion tank. If the transformer’s lid has a 60 mm diameter filling hole, the DGPT2 can be fitted directly. If not (other filling system), refer to the corresponding paragraph of ‘Expansion transformers’.
Breathing transformers
In breathing transformers, the tank is rigid but the transformer is kept at the atmospheric pressure. The live parts are immersed in dielectric fluid, the level of which varies according to the operating temperature (volume expansion due to heating).
On the tank cover, there is generally a hooked breather often with a dryer containing silica gel (blue crystals which absorb the humidity from the ambient air).
Fitting a DGPT2 on breathing transformers raises the same issues as with gas cushion transformers.
Summary of fitting solutions
Device and options according to transformer type
| Type of transformer | 60 mm (2.36”) hole? | Device | Options |
|---|---|---|---|
| Oil-filled sealed tank |  |
DGPT2 | – |
 |
DGP | SB | |
| Expansion | |
DGPT2 | IB |
| |
DGP | IB/SB | |
| Gas cushion | |
DGPT2 | IB |
| |
DGP | IB/SB | |
| Breathing | |
DGPT2 | IB |
| |
DGP | IB/SB |
Required modifications according to transformer type
| Type of transformer | 60 mm (2.36”) hole? | Add a conservator? | Modification needed? | TDC |
|---|---|---|---|---|
| Oil-filled sealed tank | |
- | - | - |
| |
- | Yes | Yes | |
| Expansion | |
- | - | - |
| |
- | Yes | Yes | |
| Gas cushion | |
Yes | - | - |
| |
Yes | Yes | Yes | |
| Breathing | |
Yes | - | - |
| |
Yes | Yes | Yes |