TRANSFORMER%20OIL%20PROCESSING

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• TRANSFORMER OIL PROCESSING
• Paul J. HodgsonB.Sc (Hons) (Wales), M.Sc
  (Edinburgh)Executive Vice-President, Redragon
  Oil Gas Systems International Inc., Cambridge,
  Ontario, Canada
• Introduction
• Techniques in Processing Electrical Oils
• Processing on Energised Transformers
• Regeneration of Used Electrical Oil
• PCB Dechlorination
• Tests

2
Introduction

• Electricity is transmitted at very high voltages
  to minimise losses
• High voltages are not practical for everyday use
• Voltages are transformed to lower, safer levels
  in a number of steps
• - Power, transmission and distribution
  transformers

Transmission transformer- Incoming (primary)
voltage 150,000 V, 121 A Outgoing (secondary)
voltage 20,000 V, 909 A
3
Function of oil

• Insulation very high voltage
• differences between different parts of the
  transformer
• Cooling conversion from one voltage to another
  is not 100 efficient. There are losses caused
  by the transformation process that are
  manifested as heat

4
1. Techniques in Processing Electrical Oils
5

• Impurities in transformer oil are unavoidable
• Primary impurities are moisture and dissolved
  gases and usually accompanied by solids
• Secondary impurities consist of solids
  (colloidal), acidity, gas and moisture (product
  of oxidation)

6
Moisture

• Sources of moisture in transformer oil are
• - residual moisture of new transformer oil
• - residual moisture in insulation
• - moisture adsorbed from surrounding atmosphere
• - moisture as a by-product of oxidation
• Major transformer manufacturers recommend
  insulation dryness be below 0.5 and oil dryness
  below 10 ppm of water
• When transformer paper temperature increases,
  some of its moisture is released and absorbed by
  oil until equilibrium is reached

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Moisture (cont)
8
Moisture (cont)
9
Moisture (cont)
10
Moisture (cont)
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Air Gas

• Individual components of air are found in oil in
  the following composition
• Non-fault gases
• - nitrogen approximately 70
• - oxygen approximately 30
• Oil solubility at static equilibrium at
• 760 mm Hg and 25oC
• - hydrogen 7 by volume
• - nitrogen 8.6
• - oxygen 16
• - methane 30
• - acetylene 400
• - carbon dioxide 1200
• - butane 2000
• Transformer oils normally are stored under dry
  air or dry nitrogen atmospheres. The advantage
  of nitrogen blanketing is that in the absence of
  oxygen transformer oil cannot deteriorate

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Air Gas
(Fault gases)
From DiGiorgio, NTT, 2005
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Solids - Noncolloidal

• Mechanical particles gt0.1 micron are considered
  non-colloidal
• Solid particle contamination in transformer oil
  influences the dielectric strength
• Two main sources of solids contamination
• - cellulose insulation
• - dust during transformer manufacture

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Solids Non-colloidal
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Solids - Colloidal

• Solid particles lt0.1 micron are considered
  colloidal. These particles are small enough to
  be kept in suspension indefinitely
• Aging process of the oil is the main source of
  colloidal contamination
• Flocculation process creates colloidal particles
• In flocculation, particles of a few Angstroms in
  diameter unite into larger complexes of a max.
  diameter of 0.05 to 0.1 micron

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Acidity

• Aging of transformer oil is accelerated by
  temperature and the presence of oxygen and
  moisture
• Process of aging starts from oxidation of oil by
  dissolved oxygen
• Initial products of oxidation include organic
  acids of low molecular weight, peroxides,
  alcohols and ketones
• Later polymerization of unsaturated hydrocarbons
  precipitates into a sludge

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Acidity (cont)

• Sludge depositions and a increase in oil
  viscosity are the main factors in insulation
  overheating and the formation of colloidal carbon
• Acidity increases the affinity of oil for
  moisture and accelerates the process of
  flocculation
• The acceptable acidity limit of transformer oil
  in operation is 0.3 mg KOH/mg oil. New
  transformer oil acidity should be below 0.03 mg
  KOH/mg oil

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Acidity increase with time
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Definition of terms

• Filtration particle removal
• Dehydration water removal
• Degasification removal of gas
• Purification all of the above
• Regeneration acidity, colour
• Desludging sludge dissolution
• Anti-oxidant DBPC blend-back

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Oil Processing Techniques

• Maintenance of transformer oils falls into two
  categories
• - preventative maintenance
• - restorative maintenance
• Regular preventative maintenance includes regular
  care for desiccant breathers, nitrogen blanketing
  systems and monitoring of proper additives level
• Restorative maintenance represents an attempt to
  return the contaminated oil and insulation to its
  original or as-new quality

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Filtration

• Main purpose to remove solids from transformer
  oil
• Cartridge type filters most popular
• Surface type filter cartridges with ratings of
  0.5 to 15 microns most practical for transformer
  oil applications
• Pleated paper design gives very large filtration
  area in a limited amount of space

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Processing of Oils with Fullers Earth

• The term Fullers Earth is applied to any clay
  which has an adequate decolorizing and purifying
  capacity
• Attapulgus clay deposits found in Georgia and
  Florida possess superior decolorizing and
  adsorption powers
• Activated Fullers Earth structure is highly
  porous and its active structure reaches more than
  100 m2/gram

23
Processing of Oils with Fullers Earth (cont)

• The order of sorbtivity of various substances by
  Fullers Earth
• - water
• - alcohols
• - acids
• - aldehydes
• - ketones
• - n-olefins
• - neutral esters
• - aromatics
• - cycloparaffins
• - paraffins

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Processing of Oils with Fullers Earth (cont)

• Purification of oils by Fullers Earth includes
  the following actions
• - filtration
• - adsorption
• - catalytic activity
• Different methods of Fullers Earth purification
• - contact method
• - fixed bed method
• - throwaway cartridges
• - re-fillable canisters or bags

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Fullers Earth Flow Schematic
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Fullers Earth equipment
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Thermo-Vacuum Treatment of Transformer Oils

• Most economical method in the removal of
  dissolved water and gases in EHV transformers
• Water present in oil in excess of the soluble
  water could be removed by heating oil to 120oC
• With the use of vacuum, water can be boiled out
  of oil at room temperature
• This vacuum process prevents overheating and
  oxidation of the oil
• Removal of air and other gases from oil is an
  added benefit of vacuum treatment

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Thermo-Vacuum Flow Schematic
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Thermo-Vacuum Treatment of Transformer Oils (cont)

• The maximum oil surface exposure to the effect of
  vacuum for a certain length of time is the most
  important factor in effective removal of
  dissolved water and gas
• Methods to expose oil to vacuum
• - spray nozzle (high surface tension of oil
  droplets causes problems)

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Thermo-Vacuum Treatment of Transformer Oils (cont)

• Raschig rings (adhesion of oil to surface of
  rings causes problems)
• - fibreglass coalescing (vacuum depth penetration
  an issue)
• - centrifuge bowl spray (not very effective)

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Mobile Transformer Oil Treatment Plant

• Most newer transformers are designed for full
  vacuum therefore suited for dry-out by vacuum
  technique
• Typical single pass performance 100 ppm to lt10
  ppm
• 12 to lt0.25
• Mobile transformer oil treatment plant can
  consist of the following
• - Thermo-vacuum unit
• - Fullers Earth filtration system
• - Extra capacity vacuum pump
• - Extra capacity oil heater
• - Additive (DBPC) injection package
• - Electric cables, oil and vacuum hoses
• - Instrumentation for continuous automatic
  monitoring of oil quality (e.g. hygrometer,
  vacuum controller, BDV, etc.)

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Mobile Transformer Oil Treatment Plant
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• Primary contamination in transformers is water,
  gas and solid particles
• Secondary contamination (aging of oil) develops
  under electrical stress in the presence of
  primary contamination
• Complete removal of primary contamination can
  only be accomplished by the thermo-vacuum
  technique

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• Adsorption treatment by Fullers Earth treatment
  removes products of aging
• Designed concept of packed columns of Fullers
  Earth cost effective
• Thermo-vacuum process along with Fullers Earth
  treatment reconditions oil as well as facilitates
  transformer dry-out

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Summary of effects of treatment on a transformer
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Section end
37
2. Processing on Energised Transformers
38
WARNING! WARNING!
It can be extremely dangerous to work on live
transformers Utmost care must be taken Use
experienced personnel only Fatal injury could
occur
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Grounding

• Ensure that the oil processing system is earthed
• Dangerous voltages can, under exceptional
  circumstances, be transmitted from the
  transformer to the oil processing system,
  resulting in the oil processing system floating
  up to these voltages. The system must be
  properly earthed. At the very least the grounding
  rod should be made from 10mm diameter galvanised
  steel and connected to the system with suitable
  copper braided flex.
• A connection to the transformer grounding cable
  should also be made.
• It is also advisable to ensure that any earth
  cable brought into the system for the purpose of
  supplying power is firmly connected at both ends
• Use wire braided hoses

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GroundingHotstick/Barehand clearances
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Grounding
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Grounding
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Before starting (1)

• Ensure that the oil processing system is filled
  with oil to
• just below the High Oil Level point in the
  vacuum
• chamber.
• It is imperative that when the system is first
  switched on and oil flow begins that there is no
  net loss of oil into the system as this runs the
  risk of draining the conservator and exposing the
  bushings in the transformer.

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Chamber oil level
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Before starting (2)

• Ensure that both the inlet and outlet oil hoses
  are filled with
• oil.
• For the same reason, there must not be a net loss
  of oil from
• the transformer and the possibility of
  introducing air into the
• transformer must be minimised
• (This can be easily accomplished with the TOLMS)

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Before starting (3)

• Ensure that top up oil is available and close to
  hand.
• Under certain conditions, where the transformer
  is very wet, there will be settling out of
  free water at the bottom of the transformer. It
  is advisable to drain as much of this free water
  as possible before connecting to the oil
  processing
• equipment. This must be done slowly. It is
  critical to observe
• the transformer oil level when draining
  water as the fluid level will drop.

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Before starting (4)

• Under no circumstances must the fluid level drop
  below the
• minimum level indicated on the conservator
  tank, as there is a
• risk that the bushings will become exposed,
  resulting in a
• flashover.
• If a great deal of water is being drained it is
  advisable to
• top-up the transformer from the top-up oil
  supply via the oil
• processing plant. Recirculate oil within the
  oil processing
• system to heat it and degasify it and then
  slowly top-up the
• transformer. Repeat until all the free water
  has been drained
• from the transformer.

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Operating procedure (1)
If using the TOLMS, attach the level sensor and
inlet solenoid valve assembly to outlet
connection on the bottom of the
transformer. The level sensor is a pressure
sensor that will operate on transformers that are
up to 20m high. The absolute sensor output is not
critical, the concern is only for changes to the
reading. It is important to allow the sensor
reading to stabilise for 30 minutes prior to
using the automatic shut-off system. Changes in
the level of the oil in the transformer will
produce changes in the output of the sensor. If
the sensor reading moves too much the plant will
close the inlet solenoid valve and shutdown as it
assumes that there is a leak of oil out of the
system. Small changes in the oil level in the
transformer are permitted, as they are not
critical and will happen as the oil processing
system cycles between high and low level
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Operating procedure (2)
Attach a one-way (check) valve on the far end of
the outlet hose, ensuring flow is from the oil
processing system into the conservator. This
valve will prevent any possibility of the vacuum
level in the oil processing system from draining
the conservator. If the TOLMS is available then
this step is not required see flow schematic
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Operating procedure (3)
Connect the oil hoses to the transformer Make
sure the hoses are filled with oil! This
requires great care and is potentially one of the
most dangerous aspects, especially connecting the
outlet hose from the oil processing system to the
top of the transformer or conservator tank if
flange on body is not available. It is highly
recommended that the transformer should be
switched off to make these connections Great
care is needed to avoid approaching the live
terminals too closely. (10kV will jump 3cm)
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Visualization
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TOLMS
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TOLMS
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TOLMS
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TOLMS
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TOLMS
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Start slowly!
Prior to opening the valves on the transformer it
is advisable to prepare the oil processing system
by internally recirculating oil that is in the
system i.e. having bypass open and inlet and
outlet closed. If the TOLMS is used then the
oil should be circulated around with V-203, V-204
open and V-201, V-202 closed. Once this oil has
reached temperature, processing of the
transformer can begin.
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Start slowly!
Monitor the conservator oil level at all times at
this early stage. Slowly open the inlet valve
and outlet valve on the oil processing system and
also any manual valve on the inlet and outlet
from the bottom of the transformer. Slowly close
the recirculating valve. Oil is now flowing
through the system and the level will be
monitored automatically
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Start slowly!
Important note If the transformer is relatively
small compared to the oil processing equipment
then do not process on full flow. Throttle the
inlet and outlet valves down or partially open
the internal recirculation valve. As a rule of
thumb, do not exceed 10 of the oil volume,
expressed as a flow rate e.g. 10,000 litres of
oil maximum flow rate 1,000 litres per hour
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During processing. (1)

• If the TOLMS is not used then a great deal of
  vigilance is required!
• The conservator level must be monitored at all
  times !
• The condition of the hoses must be monitored at
  all times!
• The flow rate must be monitored at all times

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During processing. (2)
Oil volume in a transformer changes with
temperature The volume of oil in the transformer
changes significantly between day time and night
time. It may be necessary to temporarily top-up
the oil during night time operation, especially
if the TOLMS is being used. This oil can be
drained during the day time shift. Take care
when introducing oil into the unit, minimise the
chance of air getting into the system.
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Shutdown
Normal Shutdown Switch off the heaters, wait 30
minutes. Open the recirculating valve on the
degasifier. Close the outlet valve at the bottom
of the transformer and the inlet valve on the oil
processing system. Continual running oil out of
the degasifier until the oil level is at the
desired level in the transformer. Control this
via the recirculating valve and the outlet valve.
Remember that this level will drop when the
transformer cools down. Close the inlet valve on
the transformer. The transformer is now isolated
(deep breath!)
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Shutdown (continued)
Switch off the inlet pump. Close the outlet valve
and switch off the outlet pump. Close the
recirculating valve. If possible shutdown the
transformer for 5 minutes. If not possible then
carefully remove the hoses from the transformer
and remove the oil level sensor and inlet
solenoid valve assembly.
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Shutdown
EMERGENCY Once the oil level in the conservator
reaches the Minimum oil level, it is crucial to
prevent any further drop in oil level. CLOSE
THE OUTLET VALVE AT THE BOTTOM OF THE TRANSFORMER
FIRST and worry about the oil processing system
last! Once the outlet valve of the transformer is
closed no more oil will leave the transformer and
there is time for an orderly evaluation of the
problem that caused the oil level to drop
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What Can Go Wrong?

• Tripping of the Bucholtz relay the relay will
  not trip on a small or infrequent
  release of bubbles but will if the amount of
  introduced air is large. Proper design of the
  degasifier will minimise this possibility.
• Oil leakage from burst hoses the TOLMS will
  minimise the risk of the transformer flashing
  over internally through lack of oil.
• Float-up of the degasifier proper grounding
  and wire-braided hoses will minimise this.
• Flash-over of the transformer through dumping
  of contaminants into the transformer e.g. sludge,
  free water. Correct operational procedure will
  minimise this risk

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Remember.

• Not every transformer can be processed energised
  if the oil test shows poor results, process
  off-line! It is not worth getting killed to
  process online.

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Heads Up! Oil parameters..

• Free water where possible do not process
  on-line where free water exists. If it must be
  processed on-line, drain as much free water as
  possible from the transformer, taking all
  precautions to maintain the correct oil-level in
  the transformer. Free water introduced into the
  degasifier will destroy the vacuum level.
• Dissolved water a limit of 50 PPM should be
  observed. Over this value, consider off-line
  processing.
• Acidity if higher than 0.2 mg KOH/mg, check
  for physical appearance of sludge. If present,
  consider off-line processing.

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Section end
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3. Regeneration of Used Electrical Oil
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WHAT IS REGENERATION ?

• Regeneration is the procedure followed if oil
  purification is insufficient to return the oil to
  an acceptable condition
• Regeneration is the restoration of the oil to, or
  better than, virgin oil specifications

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HISTORY OF REGENERATION

• 1940 Burmah-Castrol in UK
• 1975 Castrol South Africa
• 1980 Fluidex (SA), Filtervac (Canada)
• 1994 Enviroil (SA)
• 1998 Enervac (Canada)
• 2004 Redragon (Canada)

74
WHEN TO REGENERATE ?
75
WHEN TO REGENERATE

• Usually, but not exclusively, determined by
  acidity level of oil

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IFT vs. NN
Courtesy TMI
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OIL PROPERTIES
Courtesy TMI
78
Why is NN important

• Acidity dissolves transformer components
• Leads to build-up of sludge
• Reduces cooling effects of oil
• Transformer overheats, leading to more rapid
  build-up

79
When to regenerate (2)

• Critical Neut Number is around 0.2, above this
  point increase in acidity is exponential
• Many utilities will consider regenerating oil as
  low as 0.05
• Generally, the larger the transformer the lower
  the NN

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Two methods of regeneration
81
Two methods of regeneration (cont)
82
Two methods of regeneration (cont)
83
Operational oil parameters
84
Typical Before and After
by Rondar. Results are per Rondar test reports T
2003-0565 and T 2003-0566 on oil scrapped by GE
Burlington
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Overview
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A panacea? No..
89
Waste streams - 2,000,000 litres of oil recovered

• Gaseous none
• (clean air)
• Liquid 8,000 litres
• (acidic oil)
• Solid 850 kg
• (spent activated carbon can be regenerated)

90
Other applications

• Polishing stage of used engine oil recycling
  plant
• Replacement of disposable Fullers Earth in palm
  oil refining

91
Used engine oil recycling

• Polishing stage of thin film vacuum distillation
  plant that produces as new N100 and N300 cuts
  (and asphalt filler) from used crankcase oil

Courtesy PESCO
92
PROS' CONS' OF REGENERATION ?

• LIFE EXTENSION OF A LIMITED RESOURCE
• It is environmentally criminal not to recycle and
  reuse a limited resource.
• Regeneration technology has a long history which
  shows that recycled oil is as good as, if not
  better than new. The same oil that has been aged,
  regenerated, aged and regenerated 6 times shows
  no decrease in efficiency showing an effective
  lifetime for oil-in-use of over 100 years.
• Modern waste stream technologies and management
  minimise the environmental loading from the
  reactivation technique to a fraction of
  replacement oil and traditional non-reactivation
  technique loading.

From work by George Hodgson and ESKOM, South
Africa, 2001
93
PROS' CONS' OF REGENERATION ?

• ECONOMICALLY ADVANTAGEOUS
• The price of purchasing regenerated oil is
  typically less than 80 of new oil and can be as
  low as 50.
• Ancillary savings increment when considering
  there is no downtime when reclaiming on energised
  equipment. Replacement with new oil and hot oil
  flush requires equipment switch off.

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PROS' CONS' OF REGENERATION ?

• CONTROL OF ASSET RETAINED
• Oil in use is an asset.
• Use of regeneration technology removes dependence
  on oil companies to deliver replacement supplies
  and isolates from wildly fluctuating external
  market prices.
• Large organisations with their own reclamation
  systems are further insulated.

95
PROS' CONS' OF REGENERATION ?

• PCB contamination is not removed
• Level of the contaminant is only negligibly
  affected.
• Virgin oil does not contain PCB. PCBs can be
  removed from regenerated oil through chemical
  treatment of the oil at an added cost.

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PROS' CONS' OF REGENERATION ?

• Initial equipment capital cost could be high
• Minimum oil quotas are required to offset the
  capital cost.
• New system costs typically start around
• US 400,000

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MOBILE CONFIGURATION
98
MOBILE CONFIGURATION
99
MOBILE CONFIGURATION
100
SEMI-MOBILE CONFIGURATION
101
STATIC CONFIGURATION
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STATIC CONFIGURATION
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Summary of effects of treatment on a transformer
106
WHAT ITS ALL ABOUT!
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Section end
108
4. PCB Dechlorination
109
The PCB Story

• Polychlorinated biphenyls were first synthesized
  in 1881
• Excellent properties fire-resistant, very
  stable, insulating, low volatility
• Generic name Askarel (40 to 70 PCB)
• Brand names Aroclor (US) Kanechlor (Japan)
  Pyranol (US) Santotherm (Japan) Pyroclor (US)
  Fenchlor (Italy) Phenoclor (France) Apirolio
  (Italy) Pyralene (France) Clophen (Germany)
  Sovol (USSR) Elaol (Germany)

110
The PCB Story (cont)

• However found to be toxic and by-products fatal
• Production banned in North America in 1977
• /- 635,000,000 kg produced in North America
• Used in transformers, capacitors plus other
  non-electrical applications

111
The PCB Story (cont)

• Most countries have a maximum allowable limit of
  50 PPM but this is coming down (2 PPM?)
• Even developed countries have problems (UK,
  Spain)
• Two main treatment options
• Incineration (gt1200C, O2 rich, gt2s)
• Chemical treatment (Na, K)

112
The PCB Story (cont)

• Polychlorinated biphenyls, commonly known as
  chlorobiphenyls or PCBs, are a group of
  halogenated aromatic hydrocarbons (arenes)
  characterized by the biphenyl structure (two
  phenyl rings (C6H5)2) and at least one chlorine
  atom substituted for hydrogen. The chlorine
  atoms can be attached at any of the ten available
  sites. In theory there are 209 congeners but
  only approximately 130 congeners have actually
  been used in chemical formulations (Holoubek,
  2000). Typically 40-60 of the 10 possible
  substitution sites are occupied with chlorine
  atoms (four to six chlorine atoms) (Environment
  Canada, 1988). Some regulatory agencies only
  regulate those congeners that have at least two
  chlorine atoms attached. They are virtually
  insoluble in water and very resistant to thermal
  and biological degradation.
• Source Basel Convention, September 2002

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Chemical Treatment

• Continuous

114
Chemical Treatment

• Batch

115
Frequently Asked Questions

• Who developed the process
• In which countries has the technology been
  used.
• How long has the process been in successful
  operation
• Detailed description of the process and
  technology
• Total waste from 1500 litres at 50 PPM PCB
• What are the waste products
• What is the operational cost of the unit
• What is the cost to buy the unit

116
Who developed the process

• The process was developed in Canada by
  Ontario Hydro and BC Hydro. The process was
  developed in 1982. Both utilities have been
  operating units since the mid-1980s and have
  current Canadian Ministry of Environment
  approval.
• The process was independently developed in the
  US around the same time.

117
In which countries has the technology been
used.

• Canada, United States, Mexico, Japan, United
  Kingdom, France, Spain and Australia are
  countries that have used or use this technology.

118
How long has the process been in successful
operation

• For approximately 20 years. The first Ontario
  Hydro unit was delivered in 1982.
• By 2001, BC Hydro had reclaimed 15,000,000
  litres of contaminated oil for re-use.

119
Detailed description of the process and
technology

• General
•  
• A PCB treatment system comprises of several steps
  and the unit is comprised of several modules to
  achieve this end-
•  
• A degassification module primary function is to
  remove any water in the oil down to a known level
  of around 10 PPM
• A sodium dispersion system this module controls
  the amount of sodium introduced into the mixing
  tanks
• The mixing tanks this is the section of the
  system where the PCB contaminated oil is mixed
  with the sodium dispersion and the PCBs are
  converted to harmless by-products

120
Detailed, comprehensive description of the
process and technology

• The nitrogen purge system this module controls
  the nitrogen blanket above the mixed volume and
  also in the sodium module
• The chiller package is used to take out any
  remaining condensables in the treated oil and
  reduce the temperature of the oil prior to
  treatment in the (optional) centrifuge module
• The centrifuge module this option is used to
  accelerate the return of treated oil back into
  service. If a tank farm principle is used then
  this is not required.

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Total waste from 1500 litres at 50 PPM PCB

• Total waste will be approximately 7 kilograms
  based on above parameters.

123
What are the waste products

• 49.8 filterable oil   
• 30.9 sodium chloride   
• 10.0 un-saponifiables   
• 5.4 NaOH   
• 0.8 Fatty acid esters   
• 0.8 sodium carbonate   
• 1.3 sodium soap   
• 0.1 asphalt and tar   
• Non-detectable PCB, dioxin and di-benzo furane   
     
• 60 of sludge is water soluble. SG 0.95, flash
  point gt100C, pH between 12 - 14

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What is the operational cost of the unit

• This is dependent on local labour rates but in
  a study performed by Ontario Hydro, based on two
  operators, shows the cost to recover 1 litre of
  oil contaminated at 200 PPM PCB is US 20 cents,
  excluding capital financing costs.

125
Federal discharge criteria
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Section end
127
5. Tests
128
Significance of tests

• Aniline Point (D 611) The aniline point is the
  temperature at which a mixture of aniline and oil
  separates. It provides a rough indication of the
  total aromatic content, and relates to the
  solvency of the oil for materials which are in
  contact with the oil. The lower the aniline
  point, the greater the solvency effect.
• Carbon Type Composition (D 2140) The carbon type
  composition characterizes an insulating oil in
  terms of the percentage of aromatic, naphthenic,
  and paraffinic carbons. It can be used to detect
  changes in oil composition and to relate certain
  phenomena that have been demonstrated to be
  related to oil composition.
• Color (D 1500) The color of a new oil is
  generally accepted as an index of the degree of
  refinement. For oils in service, an increasing or
  high color number is an indication of
  contamination, deterioration, or both.

From Doble Engineering, 2005
129
Significance of tests

• Corrosive Sulfur (D 1275) This test detects the
  presence of objectionable quantities of elemental
  and thermally unstable sulfur-bearing compounds
  in an oil. When present, these compounds can
  cause corrosion of certain transformer metals
  such as copper and silver.
• Dielectric Breakdown (D 877, D 1816) The
  dielectric breakdown is the minimum voltage at
  which electrical flashover occurs in an oil. It
  is a measure of the ability of an oil to
  withstand electrical stress at power frequencies
  without failure. A low value for the
  dielectric-breakdown voltage generally serves to
  indicate the presence of contaminants such as
  water, dirt, or other conducting particles in the
  oil. Method D 1816 is more sensitive than Method
  D 877 to contaminants that lower the
  dielectric-breakdown voltage and is the preferred
  method for assessing the intrinsic breakdown
  strength of an oil.

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Significance of tests

• Water Content (D 1533) A low water content is
  necessary to obtain and maintain acceptable
  electrical strength and low dielectric losses in
  insulation systems.
• Flash Point (D 92) The flash point is the minimum
  temperature at which heated oil gives off
  sufficient vapor to form a flammable mixture with
  air. It is an indicator of the volatility of the
  oil.
• Furanic Compounds (D 5837) Furanic compounds are
  generated as byproducts of the degradation of
  cellulosic materials such as insulating paper,
  pressboard, and wood. These compounds serve as
  indicators of insulation degradations. Because
  they are dissolved in the oil, furanic compounds
  can readily be sampled and tested by high
  performance liquid chromatography (HPLC). No
  significant quantity should be detected in new
  oils.

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Significance of tests

• Impulse Breakdown Voltage (D 3300) The impulse
  breakdown voltage is the voltage at which
  electrical flashover occurs in an oil under
  impulse conditions. It indicates the ability of
  an oil to resist transient voltage stresses such
  as those caused by nearby lightning strokes and
  high-voltage switching surges. The results are
  dependent on electrode geometry, spacing, and
  polarity.
• Interfacial Tension (D 971) The interfacial
  tension of an oil is the force in dynes per
  centimeter required to rupture the oil film
  existing at an oil-water interface. When certain
  contaminants such as soaps, paints, varnishes,
  and oxidation products are present in the oil,
  the film strength of the oil is weakened, thus
  requiring less force to rupture. For oils in
  service, a decreasing value indicates the
  accumulation of contaminants, oxidation products,
  or both. It is a precursor of objectionable
  oxidation products which may attack the
  insulation and interfere with the cooling of
  transformer windings.

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Significance of tests

• Neutralization Number (D 974) The neutralization
  number of an oil is a measure of the amount of
  acidic or alkaline materials present. As oils age
  in service, the acidity and therefore the
  neutralization number increases. A used oil
  having a high neutralization number indicates
  that the oil is either oxidized or contaminated
  with materials such as varnish, paint, or other
  foreign matter. (A basic neutralization number
  results from an alkaline contaminant in the oil.)
  
• Pour Point (D 97) The pour point is the lowest
  temperature at which oil will just flow. A low
  pour point is important, particularly in cold
  climates, to ensure that the oil will circulate
  and serve its purpose as an insulating and
  cooling medium. It may be useful for identifying
  the type (naphthenic, paraffinic) of oils.

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Significance of tests

• Power Factor (D 924) The power factor of an
  insulating oil is the cosine of the phase angle
  between a sinusoidal potential applied to the oil
  and the resulting current. Power factor indicates
  the dielectric loss of an oil thus the
  dielectric heating. A high power factor is an
  indication of the presence of contamination or
  deterioration products such as moisture, carbon
  or other conducting matter, metal soaps and
  products of oxidation.
• Specific Gravity (D 1298) The specific gravity of
  an oil is the ratio of the weights of equal
  volumes of oil and water determined under
  specified conditions. In extremely cold climates,
  specific gravity has been used to determine
  whether ice, resulting from the freezing of water
  in oil-filled apparatus, will float on the oil
  and possibly result in flashover of conductors
  extending above the oil level. The specific
  gravity of mineral oil influences the heat
  transfer rates. Oils of different specific
  gravity may not readily mix when added to each
  other and precautions should be taken to ensure
  mixing.

From Doble Engineering, 2005
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Significance of tests

• Oxidation Inhibitor Content (D 2668, D 4760)
  These tests provide a method for the quantitative
  determination of the amount of oxidation
  inhibitor (2,6-ditertiary butyl-paracresol or 2,6
  ditertiary phenol) present in an inhibited oil.
  Control of the inhibitor content is an important
  factor in maintaining long service life of
  inhibited insulating oils.
• Power Factor Valued Oxidation (PFVO) This test,
  developed by the Doble Engineering Company,
  periodically measures the power factor of an oil
  while it is being aged at 95C in the presence of
  copper and air. Consequently, it indicates the
  dielectric-loss characteristics of insulating oil
  as a function of accelerated aging conditions.
  The resulting graph of power factor versus time
  characterizes a given oil. It is applicable as a
  continuity test, as well as a measure of oil
  quality. The test is run concurrently with the
  Doble Sludge-Free Life test which measures the
  time until the oil forms sludge.

From Doble Engineering, 2005
135
Significance of tests

• Oxidation Stability (acid/sludge) (D 2440) The
  acid/sludge test is a method of assessing the
  oxidation resistance of an oil by determining the
  amount of acid/sludge products formed when tested
  under certain prescribed conditions. Oils which
  meet or exceed the requirements tend to preserve
  insulation system life and ensure acceptable heat
  transfer. The test may also be used to check the
  performance consistency of this characteristic of
  production oils.
• Oxidation Stability (D 2112) This test is a rapid
  method for the evaluation of the oxidation
  stability of new insulating oils containing an
  oxidation inhibitor. It is used as a control test
  for evaluating the response characteristics of
  new oils to oxidation inhibitors. It may also be
  used to check the performance consistency of
  production oils. Good oxidation stability is a
  principal requirement for long service life of
  transformer oils.

From Doble Engineering, 2005
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Significance of tests

• Gassing Under Electrical Stress (D 2300) The
  gassing tendency is defined as the rate of gas
  evolved or absorbed by an insulating oil when
  subjected to electrical stress of sufficient
  intensity to cause ionization. The characteristic
  is positive if gas is evolved and negative if gas
  is absorbed. Correlation of results with
  equipment performance is limited at present.
• Polychlorinated Biphenyls (D 4059) Regulations
  prohibiting the commercial distribution of
  polychlorinated biphenyls (PCBs) mandate that
  insulating oils be examined for PCB contamination
  levels to assure that new products do not contain
  detectable amounts.
• Viscosity (D 445) Viscosity is the resistance of
  oil to flow under specified conditions. The
  viscosity of oil used as a coolant influences
  heat transfer rates and consequently the
  temperature rise of an apparatus. The viscosity
  of an oil also influences the speed of moving
  parts in tap changers and circuit breakers. High
  viscosity oils are less desirable, especially in
  cold climates. Standard viscosity curves can be
  generated using Method D 341 by measuring two or
  three data points and plotting the data on
  special chart paper. The resulting curve can be
  used to interpolate or extrapolate values at
  temperatures where the viscosity is not measured
  directly.

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Section end