HTP070 Purifier for Dielectric Fluids

Description

HTP070 PURIFIER FOR DIELECTRIC FLUIDS

The HTP070 purifier permits treatment of the oil in a power transformer, while on-line and on-load.

APPLICATION AREAS

• The ‘PALL’ HTP070 oil purifier removes water, solid particles, air and other gases
  present in the dielectric fluids.
• The operation of the HTP070 purifier is based on the principle of vacuum
  dehydration combined with fine filtration to remove particulate contamination.
• The purifier is designed to treat power transformers while on load. It is an integrated
  unit consisting of a mobile purifier unit mounted on wheels, and incorporates an
  isolation system and has connection accessories.
• In addition to on-load treatment of transformer oil, the purifier can be used for the
  treatment of bulk fluid.

THE NATURE AND DETRIMENTAL EFFECTS OF CONTAMINATION IN POWER TRANSFORMERS

• Excessive contamination is detrimental to the optimal performance of power transformers.
• This contamination, whether liquid or solid, degrades the dielectric performance of
  the transformer insulating materials.
• Figure 1, below, shows the damaging and costly effects on breakdown voltage of
  excessive water content, combined with high particle contamination, chiefly
  composed of cellulose fibres originating from paper and pressboard.
• In addition, the water, which is a product of the decomposition of the cellulose
  insulation under thermal stress, is also a factor in accelerated ageing of the
  insulation paper

HTP070 PURIFIER FOR DIELECTRIC FLUIDS TECHNICAL INFORMATION

water content at 20°C………………………………………….. < 10 ppm

Particle count according to ISO 4406……………… < 12/10

Particle count according to NAS 1638…………….  < 4

Dielectric strength…………………………………………………….. > 75 kV

It is absolutely essential to keep the overall contamination level of the transformer oil in service at low levels to ensure the dielectric strength of the oil and to minimise the risk of transformer breakdown.

The table above shows typical values for a new transformer.

They must be adapted to suit the type of transformer, its age, and technology.

A NEW APPROACH TO THE TREATMENT OF TRANSFORMERS

A new method of treating transformers while on-load has been developed by Pall and EDF, working in partnership and departing from conventional technology.

This process is the subject of an agreement between Pall and EDF which covers the treatment of power transformers under load using the HTP070 purifier, a specially designed unit for this application.

The HTP070 purifier permits extremely high
performances to be reached, without manual supervision except during connecting and disconnecting operations.

The development of this type of treatment offers the following advantages:

• A substantial reduction in direct and indirect treatment costs.
• Better control of the water content in both the transformer oil and the paper insulation.

The process allows treatments lasting several weeks and can therefore be much more efficient. Since such treatments do not require the transformer to be taken out of service, a major cost factor has been eliminated.

Remote monitoring package:

The HTP 070 can be equipped with a remote monitoring package. The system involves the use of a Global Satellite Modem (GSM) or landline connected to the purifier PLC together with all necessary pressure transducers and moisture sensors.

This allows the operator:

• access to the system data from the ‘Home Base’
• Allows the operator to down-load system history from base
• The monitor will ‘Ring Home’ in the event of a system alarm and indicate the nature of the alarm
• It can also be used to flag service points.

This option has proved its value as the HTP 070 has to operate in remote ares for long periods.

OPERATING PRINCIPLES OF PURIFIERS

The fluid is pumped into the vacuum chamber (1) through the inlet strainer (2) by the inlet pump (7).

A spray nozzle at the top of the chamber produces a cone of fluid with a thin film and a large surface area.
The vacuum chamber is maintained at approximately 10 mbar absolute by the vacuum pump (4). Air entering the chamber passes through an air breather (5), removing airborne contamination to avoid adding dirt to the system. The air
expands rapidly through a restriction (3) to approximately 100 times its ambient volume which decreases the relative humidity inside the chamber to a fraction of the ambient level.
Gases and water vapour are transferred from the fluid surface to the upward flowing air thereby drying and degassing the fluid. The wet air is then exhausted via the oil mist separator (7) and vacuum pump (4) to atmosphere.
The purified fluid collects at the bottom of the chamber and is returned to the transformer or reservoir via the discharge pump (8) through the ß5(c)≥1000 high Beta performance ‘Ultipor III’ filter element (9). When the discharge filter element reaches the pre-set differential pressure a warning beacon is illuminated.
The fluid level in the vacuum chamber is maintained by a level sensor (10) which allows some of the fluid to circulate back to the chamber.
A sight glass is fitted to give visual confirmation of the fluid level in the chamber. Downstream of the discharge filter (9) is a second vessel and associated valving (not shown) for the detection and removal of air bubbles in the transformer oil.