Technical information
Options
Option IB: Buchholz relay-type fitting
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Devices concerned: DGPT2 & DGP.
The IB option concerns only rigid tank transformers that are protected with a device called Buchholz relay.
The Buchholz relay
In complete models of Buchholz relays, a first mercury contact detects gas discharge, and a second mecrury contact detects rapid flow of dielectric fluid from the transformer to the expansion tank. Transformer manufacturers usually mount Buchholz relays as standard equipment on expansion-tank transformers.
DGPT2 fitted in place of a Buchholz relay
Although our transformer-protection devices were primarily designed for completely-filled and flexible-tank transformers, they can be used with rigid-tank transformers equipped with expansion tanks.
Buccholz relay/DGPT2 comparison
- Gas discharge: The Buchholz relay detects gas bubbles, and so does the DGPT2. Since the device is mounted directly on the tank at its highest point and with no bends, gas bubbles are trapped in the device’s tubular body.
- Excess tank pressure: The Buchholz relay detects a rapid flow of dielectric fluid from the transformer’s tank to the expansion tank. With a DGPT2, since the entire circuit up to the expansion tank is under pressure, excess pressure will be detected. Furthermore, pressure detection is much more rapid (5 milliseconds) than flow detection.
- Temperature : Buchholz relays do not monitor temperature. With a DGPT2, the device’s well is completely immersed and temperature is constantly monitored.
Mouting caveats
- The bottom of the expansion tank must be at least 50 mm (2”) above the top of the device’s body.
- Ensure the expansion tank can be hermetically sealed (leakproof stopper in the filling hole).
- Flexible or rigid tubes can connect the device to the expansion tank, but ensure the material is compatible with the transformer’s dielectric fluid.
- Add the relative pressure due to the height of the dielectric column (see diagram) to the pressure switch’s reference value.
IB adapter
| Description | Ref. | Comments |
|---|---|---|
| IB adapter | CP108 | Nickel-plated brass |
| Seal | CP109 | O-ring Viton® seal, internal diam. 14 mm (.55”), torus diam. 2 mm (.08”) |
| Body protection plug | CP116 | — |
| IB adapter protection cap | CP117 | 3/8” |
The standard body is equipped with a 3/8” threaded journal protected by a smooth plug.
This plug can be removed (e.g. with a small screwdriver) to fit the adapter on the device.
The IB adapter is supplied free of charge and is protected by a cap.
Fitting the IB adapter
- Remove the grey plug from the body.
- Fit the O-ring seal in the groove at the end of the thread.
- Screw the adapter into the body using a no. 18 spanner.
- Remove the adapter’s red protection cap.
- Check that the O-ring seal is not excessively tightened.
In order for the device’s body to communicate with the expansion tank, the 4-mm (.16”) separation at the end of the thread must then be removed.
Drill through the separation with a 9-mm (.35”) drill (9.5 mm [.37”] maximum) using the adapter as a drilling guide, then remove the leftover plastic swarf.
The device is now ready to be mounted.
Mounting the DGPT2-IB
Contact the transformer’s manufacturer if it is still under guarantee.
The procedures described hereafter are provided for information only. The user is entirely responsible for carrying them out. These procedures only concern transformer updates (transformer manufacturers have their own installation procedures).
Mounting precautions
- The transformer must be powered off
- The procedure must be carried out on cooled down equipment (ideal ambient temperature of 20°C [68°F]).
- The expansion tank must be empty
- The dielectric fluid’s level must be slightly below the transformer’s cover.
- The hole the device is to be mounted on must be open
Mounting procedure
- Fit the transformer/device seal: either the flat Viton® seal supplied with the device (Ref. AC101) or any other system.
- Mount and fit the device: either with the 4 metal hooks supplied with the device (Ref. AC102) or any other system.
- Connect the IB adapter from the device to the expansion tank.
- Check the various connections thoroughly.
Filling the transformer with dielectric fluid follows one of two procedures according to whether the transfomer is equipped with a drain tap or not.
No drain tap
Before mounting the device, remove the DGPT2’s drain tap then the small float. This will make for quicker dielectric fluid filling.
Before filling, protect the device from accidental spills of dielectric fluid, especially between the electrical housing and the transparent body.
- Open the expansion tank’s filling hole.
- Fill the device slowly using a plastic funnel (1).
- Put the small float back into the device’s body.
- Screw the device’s drain tap back on.
- Top the dielectric fluid in the expansion tank back up to its original level (2).
- Seal the expansion tank’s filling hole tightly.
Drain tap
- Open the expansion tank’s filling hole.
- Fit a pump onto the drain tap (1).
- Remove the black cap from the device’s drain tap.
- Open the device’s drain tap by turning the nozzle anticlockwise (it will sink into the tap body).
- Fit a vinyl tube onto the end of the nozzle and place the other end of the tube in a recipient (2).
- Open the transformer’s drain tap.
- Activate the pump so as to fill the protective unit slowly, then the expansion tank.
- As soon as dielectric fluid starts running out of the device’s drain-tap nozzle, close it by turning it clockwise.
- Stop the pump as soon as the dielectric fluid reaches its original level in the expansion tank.
- Close the transformer’s drain tap.
- Seal the expansion tank’s filling hole tightly.
- Remove the pump, tube and recipient.
- Put the black plug back onto the device’s drain-tap nozzle.
Gas cushion and breathing transformers
Calculate the gas cushion’s volume
Breathing and gas cushion transformers must be equipped with a so-called conservator (expansion tank), the volume of which must match the volume of the gas cushion.
- V: gas-cushion volume
- L: Length of transformer’s tank
- l: width of transformer’s tank
- h: approximate height of gas cushion
- H: height of fluid in the transformer
- k: tank/fluid height ratio
k = (H + h) / H
V = (L × l × h) × k
Filling height
Mounting and filling procedures are identical to those of transformers with expansion tanks. However, the fluid must be filled up to the bottom of the expansion tank in order to respect the volume V calculated previously. The conservator thus acts as an expansion tank and replaces the gas cushion.
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