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Transformer Tap Changers

tap changers

Power transformers convert one voltage to another without changing frequency. The main parameter of transformer is transformation ratio, i.e. the ratio between primary and secondary coil voltages or the number of turns in the windings. To change transformation ratio, a tap changer is used, which changes the number of turns engaged at a given moment. Such devices allow keeping nominal voltage in the coils, if the primary or secondary voltage deviates from the setting. Tap changers operate with the transformer under load.

Tap changer oil system

There are two design types of tap changers depending on the oil system features. In the first case, the contactor of the changer is located in a separate tank on a insulator, while in the second case, the assembly is submerged, when the device is installed either inside the transformer tank or in a separate tank. The oil functions as an arc extinguisher; arcing may occur when the contactor is engaged.

For normal tap changer operation the temperature of the upper oil layers must not drop below -20 ⁰С. If the tank is separate, a special heating system is used to maintain the required oil temperature.

Frequent arcs degrade the oil’s quality. Heating of contactors, which occurs when transit resistance increases, further aggravates the problem. For best performance of the tap changer oil, its dielectric strength must be at least 30-40 kV with moisture content below 0.003%. Other tap changer oil parameters (color, acidity, carbon content) are of less importance and do not influence usability of the liquid in the contactor tank. Moisture content and dielectric strength are measured in oil samples taken every 5000 switches, but at least once a year.

The level of oil in the tank can be seen in the oil indicator. If the level is not maintained, arc burning time increases significantly, which should be avoided.

When selecting tap changer oil, viscosity must also be considered. If the oi lis too thick, the contactor must overcome higher mechanical resistance during switching, which may lead to failure in the long run.

Tap changer oil service life extension

If the analysis indicates that at least one of the parameters is out of specifications (moisture content or dielectric strength), the oil in the tap changer tank must be changed. However, frequent oil changes is not viable economically, which makes oil processing to dehydrate it and increase dielectric strength for oil reuse a reasonable alternative. This task is handled well by GlobeCore CMM-0.6 unit, which performs degassing and dehydration of tap changer oil with the processing rate of 600 liters per hour. This capacity is quite sufficient for servicing of the oil system.

The СММ-0.6 offers the following advantages:

  • increasing dielectric strength to 60 kV;
  • reduction of moisture content to below 10 ppm;
  • a special system to prevent foaming, which is highly probable when processing oil with high moisture content;
  • oil leak sensor. If a leak occurs, the unit automatically stops and notifies the operator;
  • silent operation;
  • powered by a regular power socket.

Spain. CMM-2R transformer oil regeneration plant was commissioned

August 16, 2017 in Seville (Spain) all works under the contract for the supply and commissioning of the regeneration plant CMM-2R were successfully completed.

This equipment is ideal for enterprises and organizations of the electric power industry, that do not require insulating oil processing capacity more than 0.3 m3 / h.

The plant’s components are optimised and provide a complete restoration of transformer oil properties (filters, regeneration columns, pumps, tanks, control cabinet, etc.).

The equipment can perform automatic regeneration of transformer oil, together with an external degassing unit and sorbent reactivation. It is also possible to introduce special antioxidant additives into the oil after the regeneration process is completed.

Commissioning in Saudi Arabia

August 5 – 8, 2017, in Jizan, our company engineering team carried out the commissioning and start up of the CMM-2,2 unit.

This unit added to the list of equipment already provided and commissioned for the electricity industry of Saudi Arabia by GlobeCore. The CMM-2,2 unit operates is several modes, and can be used for cleaning insulating oils from mechanical impurities, water and gases, and heating electric devices with hot oil, as well as vacuum drying of power transformers. In drying and filtration mode, the unit’s capacity is 2.2 m3 / h, and in degassing – 1.5 m3 / h.

Multiple passage of oil  through a CMM-2,2 unit provides oil parameters of:  total gas content below 0.5% (at the initial 10.5%) and mass moisture content below 10 g / t (at the initial 50 g / t).

The equipment s containerized and is mounted on a single axle trailer, which enables movement between transformers and electrical substations.

To receive consultation and to order a СММ-2,2 unit , please contact our managers on contacts link.

We invite you to participate in the seminar on industrial oils purification and regeneration

GlobeCore GmbH invites specialists of the power industry and everyone interested in innovations in electrical power industry to take part in our seminar on “Purification and regeneration of industrial oils”.

The event will take place in Oldenburg (Germany) on September 27 at Edewechter Landstrasse, 173. The program of the seminar covers the problems of industrial oil aging and importance of oil regeneration. In the practical part of the seminar our engineer will demonstrate transformer oil regeneration on CMM-R unit.

If you would like to participate, you need to apply before September 1, 2017, by sending an email to [email protected].

SILICONE OIL RECYCLING UNIT CMM-1.0

We are all used to associating power transformers with transformer oil. But in the modern world, electrical companies widely utilize silicone oil as an alternative to mineral based fluids. This is not surprising, considering silicone oil benefits and advantages:

Silicone Fluid (or Polydimethylsiloxane silicone oil) features:

  •  higher dielectric strength and temperature stability,
  • low toxicity, low vapor pressure, low viscosity change
  •  higher resistance to oxidation and chemical inertness

The above make silicone transformer fluid much safer environmentally as well.

On the other hand, operating conditions and power transformer lifecycle can cause some issues:

  1. When arc discharges occur, silicone oil may release harmful gases under the influence of high temperature
  2. High oil viscosity may have a negative impact on transformer heat exchange, reducing circulation of the oil.
  3. Silicone oil is harder to dispose of, combustion of silicone oil causes release of harmful gases.

GlobeCore engineers insist that one process can address the issues above — Silicone Oil Recycling.

Our team has developed a new machine for Silicone Dielectric Oil Regeneration.

Its great advantages are compact size and efficiency.

Silicone Oil Recycler Specifications

Parameter Value
1 Processing capacity, m3/h:

– drying mode

– pumping mode

1.0

1.0

2 Maximum oil output temperature in heating mode, °С 60
  3* Treated oil parameters (at initial moisture content of no more than 50 ppm):

– maximum moisture content by weight , ppm

– filtration fineness, micron

10.0

5

4 Oil output head, m 20
5 Input pressure, MPa, no more than 0.1
6 Oil heater power, kW, 25,2
7 Oil heater mean surface power, kW/cm2, no more than 1.1
8 Nominal power consumption, kW 28
9 Three-phase AC @ 50 Hz, V 380
10 Maximum dimensions, mm

– length (without trailer)

– width (without trailer)

– height (without trailer)

3800 (1300)

2100 (800)

2100 (1550)

11 Maximum weight (without trailer), kg 860 (540)

Note   * With initial oil parameters as follows:

– moisture content by weight – no more than 0.005% (50 ppm)

– oil heating temperature up to +60±5 oС within 30 minutes of heating;

– gas content – no more than 10%

– dimensions may vary

The unit is used during installation, maintenance and operation of oil-filled high voltage equipment (power transformers, high-voltage switchgear, etc.).

The station is assembled in a frame structure with closing doors. Its components are: a vacuum column (VC), a control panel (CP), pumps (P1 and P2), vacuum pump (VP), pre-filter, coarse (F1) and fine filter (F2), piping with valves.

General view of the station is shown in figure 1.

Figure 1 – CMM-1 general view.

Mesh filter MF (figure 2) is installed at the input of the unit to remove mechanical impurities from the oil. Filtration rating of the filter is defined by 200 micron brass mesh, installed in the casing. For filter element cleaning, extract the filter from the input manifold and wash it in clean transformer oil.

Pumps Р1 and Р2 (Fig.1) facilitate input and output of transformer oil. The pumps are controlled from the control panel. P1 and P2 pumps are equipped with by-pass line and valves MV7 and MV8.

Cartridge filters F1 and F2 (figure 1) filter the oil with 25 and 5 micron filtration fineness respectively.

Principle of operation

Flow diagram

Figure 2 shows the unit’s flow diagram.

Figure 2. Flow diagram

The unit can operate in two modes:

1. Pumping and filtration (Flt);

2. Thermovacuum drying (Dry).

Call today+493021788825 or e-mail us to [email protected]

Zimbabwe. Annual presentations of GlobeCore equipment

June 8, this year a number of presentations on GlobeCore equipment was held in Bulawayo (Zimbabwe).

It was only last year in August that similar presentations were held in the capital of Zimbabwe- Harare. Then, not all the representatives from Zimbabwe electrical industry could be present at the presentations. This called for a new opportunity for more participants to attend.

Traditionally, GlobeCore presented its equipment for cleaning and regenerating different mineral oils, as well as equipment for vacuum treating and drying transformers. The most interest were  given to mobile and stationary regeneration plants. The presentation was supported with a practical demonstration of a laboratory UVR unit that cleaned the samples of contaminated industrial oils

GlobeCore is grateful to all participants for their interest and assistance in organizing the events, and is sure that these presentations will further constructive cooperation.

Equipment commissioning in Finland

May 31, our company technical team completed the works under the contract on production, delivery and commissioning of a CMM-4/7 unit in Finland (Helsinki).

This equipment is designed for businesses that repair and install high-voltage oil-filled equipment. The first transformer it services was a 400 MVA  transformer.

Operating modes of the unit

CMM-4/7 operates in three modes. Each  mode performs a certain set of functions:

  • “Degassing mode” consists of an automatic warm-up of the unit; heating oil to a set temperature, filtration and degassing ;
  • “Heating and filtration” consists of heating and filtration of oil without degassing in a vacuum column
  • “Manual mode” involves a diagnosis of good condition of units components, i.e.  valves, pumps, etc.

CMM-4/7 processing rate

The unit can treat any transformer oil with viscosity below 70 cSt at 50 ° C. The processing rate in degassing mode, is 4 m3 / h, and in heating and filtration mode  is 7 m3 / h.

Processed oil parameters:

  • Volumetric gas content – below 0.1%;
  • Moisture content by weight – below 10 g / t;
  • ISO 4406 industrial purity class   – / 14/12;
  • Mechanical impurities content – below 8 g / t;
  • Filtration fineness is 5 μm.

Additional Features

TSS (Transformer Security System). is provided to monitor the oil level in a transformer.   It protects a transformer from oil leaks or breaking of hoses.

Botswana. Commissioning of CMM-12R and CMM-4/7

In May, more of GlobeCore equipment was commissioned  in Gaborone (Botswana).

At this time two transformer oil regeneration plants CMM-12R and CMM-4/7 were installed and commissioned

In its design, CMM-12R is a multifunctional complex that carries out both processing of insulating oils and maintenance of transformers. The main distinguishing feature of this equipment is – that it recovers and regenerates oil by removing dissolved gases, solid particles, free and dissolved water, as well as oil decay products. It can recover oil directly in a transformer tank without switching a transformer off-line. CMM-12R also removes sludge from the windings; it heats a transformer and its active parts with hot oil, and performs a vacuum treatment.

CMM-4/7 is also a multifunctional equipment. It performs the following tasks:

  • Drying, degassing and cleaning of insulating oil from mechanical impurities;
  • Heating oil before filling electrical equipment with it;
  • Vacuum drying and evacuation of transformers.

The number of GlobeCore equipment is growing in Pakistan

May 13, 2017, the number of GlobeCore equipment in Pakistan increased by one unit.

A CMM-4/7 unit was commissioned by the company’s engineering team in Lahore. This equipment performs  heating of power transformers, as well as drying, cleaning, degassing and nitriding of insulating oil.

CMM-4/7 provides:

  • volumetric gas content below 0.1%;
  • moisture content by weight –below 5 g / t;
  • ISO 4406 cleanliness class  – / 14/12 .

Regular servicing of power transformers with CMM-4/7 allows  to prolong their service life and maintain the reliable operating life of the transformer.

ELECTRICAL TRANSFORMER REPAIR

ELECTRICAL TRANSFORMER ELECTRICAL TRANSFORMER

THE GLOBECORE PROCESS
TO MAINTAIN ELECTRICAL TRANSFORMER OIL IN GOOD CONDITION

Problem #1: Moisture in transformer oil

Nature of Problem: Transformer oil readily absorbs moisture from the air. This water decreases dielectric strength of the oil

GlobeCore Solution: CMM Oil Purification Plant is designed for thermo-vacuum drying, filtration and removal of solid impurities from dielectric insulating oils with a viscosity of no more than 70 cSt at 50°С.  The plant offers purification to class 9 from initial purity class 13 (contaminant content below 0.004%) in multiple passes of the product through the filter section. The Plant is available in different configurations and capacities.

CMM 0.5

Processing rate 0.5 – m3/hour

CMM-2.2

Capacity 2.2  m3/hour

CMM-4.0

Capacity 4 m3/hour

 power transformer repair unit electricl transformer repair unit power transformer repair plant
Perfect solution for small electrical transformers
Conventional 220 electrical outlet power capability
The unit is compact, protected with metal doors, can be trailer mounted for on  field use Perfectly fit for heating electrical transformer and other equipment that contains dielectric insulating oil with hot oil

Problem #2: Moisture in Solid Insulation

Nature of Problem: Insulating paper absorbs and retains moisture due to higher affinity of water to paper than to oil. Moisture in oil-paper insulation can cause electrical transformer failures because (1) it decreases dielectric strength, (2) it accelerates cellulose aging (depolymerization) and (3) it causes emission of gas bubbles at high temperatures.

GlobeCore Solution: Vacuum Cold Trap is connected to Electrical Transformer and vacuum pumps bring the pressure down to 26 Pa. Cooling of the evaporator in the low temperature trap to minus 70oC, causes pressure difference of water vapor above the surface of the solid insulation in the transformer tank and in the body of the cold trap. This difference is the driving force of water evacuation.

The unit is available in stock.

Vacuum Cold Trap

Processing rate is 27×3=81  Pa, liters/second, min

solid isulation maintenance machine
The vacuum cold trap is designed for pulling vacuum and drying of solid insulation of power transformers with voltages 110-1150kV during installation, service and repair

Problem #3: Transformer Oil Oxidation

Nature of Problem: The reaction between unstable hydrocarbons in the oil, oxygen and other catalysts such as moisture, with additional factors such as heat, results in accumulation of decay products in the oil (oxidation by-products). Once oil oxidation starts, the oxidation products themselves act as catalysts to accelerate the oxidation reaction.

GlobeCore Solution: CMM-R and UVR units are designed for Complete Oil Restoration (of dielectric strength and chemical composition). The main operating principle of those units is percolation of oil through a stable sorbent layer. The CMM-R plant operates with Fuller’s earth and the UVR unit uses a special GlobeCore sorbent. All together, the systems remove acids, water and contaminants from insulating oil and insulating paper/windings of an electrical transformer. Those units are very Environmentally Friendly, as exhausted sorbent can be reactivated and used again in up to 300 cycles.

CMM-R2

Processing rate 100 – l/hour

CMM-R24

Capacity 6000  l/hour

UVR 450/16

Capacity 100-1000 l/hour

Transformer oil bleaching machine
The unique feature of the CMM-R unit is the capability to regenerate insulation oil directly in an electrical transformer ·                Energized transformer oil processing; and

·                Automatic Sorbent Reactivation

·                Trailer mounted

 

The unit successfully processes dielectric transformer oil, turbine oil, industrial oil, heavy fuel oil, and Diesel fuel

 

Problem #4: Dissolved gas and/or decay products

Nature of Problem: During its lifetime, the transformer generates decomposition gases, essentially from the organic insulation, under the influence of various stresses, both normal and abnormal, which could lead to failure if ignored.

GlobeCore Solution: The UVM unit is designed for degassing, drying, removal of solid particles and heating of transformer oil used in power transformers up to 1150V.
The unit can process mineral oils with the following properties:

Dynamic viscosity, mm2/sec, at 50 °С                    2…12;

Density at 20°С, kg/m3                                           800…950;

Moisture content, ppm, max                                    100;

Purity class ISO 4406, at least                                -/19/16

The UVM unit is available in different design configurations, Zeolite Filtration Section CP-260 is available as an option.

CMM-UVM 4/7

Processing rate 4 – m3/hour

CMM-UVM 10/15

Capacity 8 m3/hour

MCU ZEOLITE OIL DRYING UNIT

Capacity from 1.5 to 4.0 m3/hour

Transformer oil degassing unit Insulating oil degassing machine Zeolite drying system
The UVM unit is designed for:

·         Vacuumizing transformers;

·         Removal of solid particulate matter;

·         Removal of water;

·         Removal of gases

The unit is placed on a tandem axle trailer that is street legal and ready to be towed to any remote  location  This unit is designed to significantly reduce acid levels in used insulating oil