DNO & iDNO approved transformers

Oil Temperature Indicators are used to monitor the temperature of the insulating oil within the transformer's tank. It is crucial for observing overheating of the transformer's insulating oil. High oil temperatures can result from factors such as load variations, ambient temperature changes, and internal faults. Monitoring oil temperature helps manage the transformer's cooling system. Cooling mechanisms, such as fans, can be activated if the oil temperature exceeds safe limits. By monitoring oil temperature trends over time, maintenance personnel can identify potential issues and schedule maintenance activities proactively. Monitoring oil temperature also contributes to maintaining the quality of the insulating oil. Elevated temperatures can accelerate oil degradation, leading to reduced insulating properties.

This capillary-based, mechanical, remote-indicating thermometer features configurations for oil temperature measurement with up to 6 flexible switches for alarm, trip, and cooling system functions. Maintaining proper oil temperature ensures the optimal performance and reliability of the transformer in various operating conditions.

Winding Temperature Indicators are critical devices used in power and distribution transformers to monitor and indicate the temperature of the transformer windings, which are the major conductive components carrying current. Unlike oil temperature indicators, which monitor the oil surrounding the windings, WTIs measure the actual winding temperature, which tends to run hotter than the oil. This gives a more accurate picture of transformer load stress and its proximity to thermal limits.

Heat is generated during operation due to the flow of electrical current through a transformer's windings. Accurate temperature monitoring contributes to effective asset management by optimising maintenance schedules and extending transformer lifespans. Winding temperature indicators are designed to activate alarms or trips if temperatures exceed safe limits. They could provide input to cooling systems (like fans or pumps) to maintain safe operating temperatures, and some advanced models can record historical temperature data for trending and diagnostics.

The Ashridge 852 WTI & OTI provides an ultra-precise reading by continuously measuring the winding temperature and the oil temperature and displaying the data on a dual display. Top oil temperature measurements and the winding current are combined with Ashridge's algorithm, which is based on the IEC 354 standard, to provide accurate temperature readings. The extensive range includes alarm relay output, data logging, a wide range of CT inputs, dual display and an intelligent cooling control system with ‘deviation from normal’ alarms to ensure optimal asset life and protection for the transformer.

For accurate temperature readings and data logging, the Ashridge software provides a "compare settings with template" facility and downloads the settings for incorporation into documentation or archiving. Understanding the transformer lifespan and regularly examining the temperature increase the safety of the transformer and the personnel working on it. Proper temperature monitoring contributes to effective asset management by optimising maintenance schedules and extending the lifespan of transformers.

A bund, also known as a containment pit or catchment area, is a secondary containment system designed to contain and prevent the spread of oil in case of a leak, spill, or rupture of transformer radiators, main tank or other components. The bund is constructed around the transformer and is designed to hold 110% of the total liquid in the transformer, ensuring that any leaks or spills are prevented from reaching the surrounding environment.

The primary purpose of the bund is to contain oil leaks, preventing environmental contamination or hazards. Bunds are critical for preventing oil spills from reaching the soil and water, reducing the potential harm to ecosystems and groundwater. Compliance with environmental regulations and standards is a key application of bunds. Bund mitigates the financial and legal risks associated with environmental pollution resulting from oil leaks or spills.

Bund filters are designed to capture hydrocarbon pollutants while letting clean rainwater pass through and safely discharge into the environment. By stopping bunds from filling up and spilling over, they reduce the need for costly oil-water separators or vacuum tanker services.

Magnetic Oil Level Gauge is used to measure the level of insulating oil within the transformer tank. Specifically designed for use on power transformers, this device gives an analogue indication of the oil level inside the conservator by a graduated dial with arrow and one or more electric signals when the oil inside the conservator reaches the maximum or minimum level.

The primary purpose of the MOG is to monitor the oil level within the transformer tank. Adequate oil levels are crucial for proper cooling and insulation. Low oil levels can lead to overheating, reduced insulation effectiveness, and potential damage to the transformer. Consistent monitoring of oil levels over time can help predict potential maintenance needs. Significant changes in oil levels indicate leaks or other issues requiring attention. MOGs assist in maintaining the integrity of the transformer's containment system.

The conservator helps manage the expansion and contraction of insulating oil due to temperature changes. This is important for ensuring proper cooling and insulation properties of the transformer. Conservators prevent overpressure from building up inside the transformer, which could result in mechanical stress or damage to components.

As gases are generated within the transformer due to normal operation or faults, the conservator allows these gases to escape safely, preventing pressure build-up. The conservator reduces oil surface contact from surrounding air, thus minimising the ingress of moisture or contaminants. By providing space for oil expansion and contraction, the conservator minimises exposure to air, reducing the risk of oil oxidation.

Oil- and gas-actuated protection relays are used on liquid-insulated transformers to provide protection from electrical faults occurring inside the transformer, accompanied by gas generation or oil surge onto the conservator. The Buchholz relay is primarily designed to detect the presence of gases generated due to electrical faults, such as short circuits or insulation breakdown, occurring within the transformer.

The primary application of a Buchholz relay is to detect internal faults within the transformer, such as short circuits between windings, inter-turn faults, or arcing. Rapid gas generation within the transformer's insulating oil can indicate insulation degradation, overheating, or other issues, providing early warning of potential problems. The presence of gas can indicate the occurrence of faults within the transformer. Buchholz relays help detect these conditions. Early detection of internal faults by the relay helps prevent major failures that could lead to costly downtime and extensive repairs. By analysing the composition of the gases collected by the Buchholz relay, maintenance personnel can gain insights into the nature of the fault and the transformer's condition.

The Buchholz relay's Gas Collecting Device is a small chamber with three functions: extracting gas from the Buchholz relay and venting it from the system, testing both the alarm and trip circuits of the Buchholz relay, and draining oil from the Buchholz relay.

Offering protection against high humidity, pressure variations, dielectric loss, and outgassing, the Brownell Transformer Breather absorbs moisture from the air, maintaining dryness. It features a shatterproof, UV-stabilised polycarbonate cylinder. The Envirogel Orange to Green colour-changing silica gel allows for visual recognition when the unit needs replacing or refilling.

The primary purpose of a transformer breather is to control the moisture levels in the conservator tank and the insulating oil. Moisture can lead to oxidation or degrade the oil's insulating properties and cause insulation breakdown. The breather's air filter prevents dust, dirt, and other contaminants from entering the tank and contaminating the oil. Transformer breathers ensure the tank remains at atmospheric pressure by allowing air movement. This prevents overpressure occurrences that could damage the transformer. Monitoring the colour indicator of the breather allows service personnel to schedule maintenance and desiccant replacement when needed.

Pressure and/or vacuum indicator for accurate representation of the pressure state inside the transformer, featuring a 3.5-inch (88.9 mm) dial with at least 180° of angular pointer deflection for easy reading at a glance and available in a wide variety of pressure ranges and scales for many applications.

PVGs play a vital role in assessing a transformer's overall health. Abnormal pressure or vacuum readings could indicate internal issues such as partial discharges, winding faults, or oil degradation. Monitoring pressure and vacuum levels helps prevent catastrophic failures. Overpressure situations could lead to oil leaks, insulation breakdown, or even explosions, while excessive vacuum could cause moisture and contaminants to enter the transformer.

By analysing pressure and vacuum trends over time, maintenance professionals can predict when a transformer might require maintenance. This approach can help avoid unplanned downtime and reduce operational costs. Pressure and vacuum monitoring contribute to the safety of the transformer and the personnel working around it. Early detection of abnormal conditions allows for timely actions. Maintaining proper pressure and vacuum levels ensures the transformer operates within its designed parameters, optimising its efficiency and lifespan.

Mechanical overpressure protection device provides pressure-relief on transformers during overpressure conditions, automatically resealing once pressure has subsided. PRDs are designed to release excess pressure in a controlled manner to avoid transformer tank rupture or other potential hazards.

The primary purpose of a PRD is to prevent the buildup of excessive pressure within the transformer tank. Excessive pressure can be caused by events such as internal electrical faults, short circuits, and rapid heating. By releasing pressure in a controlled manner, PRDs prevent the transformer tank from rupturing due to overpressure, which could result in oil spills, fires, or, in severe cases, explosions.

PRD helps avoid the ejection of insulating oil from the transformer tank, which can occur if pressure is not relieved properly. Oil ejection poses safety risks and can cause environmental damage. PRDs can be manually activated during maintenance or emergency situations to release pressure from the transformer.

Marshalling boxes serve as a central point for organising and connecting various electrical cables and wires associated with different components of the system. They play a crucial role in maintaining a clean and organised wiring arrangement, facilitating maintenance, and ensuring an organised arrangement to avoid errors.

Designed by our engineers and assembled in our "bungalow" in Leeds, marshalling boxes organise the wiring and connections between the transformer and the necessary monitoring and protection systems, including connections to temperature sensors, pressure sensors, and protection devices. In systems where multiple cables from different sources need to be interconnected, such as in complex transformer installations, marshalling boxes simplify the wiring arrangement, making it more manageable and efficient.