Transformer Oil Flow Indicator

Sudden Pressure Relay / Oil Surge Relay for Oil-Immersed Transformers

Model:  DLF – 100   2   (TH)

1. Product Introduction

The oil flow indicator (also known as a sudden pressure relay or oil surge relay) is a passive, rapid-acting protective device installed in the connecting pipe between the transformer tank and the conservator (oil storage tank). It is widely used on oil-immersed power transformers, distribution transformers, and other oil-filled electrical equipment.

Under normal operation, the transformer oil flows slowly through the relay without actuating the contacts. When an internal fault (such as an arc or short circuit) causes a sudden pressure surge and rapid oil flow, the relay responds within milliseconds, operating its micro switch to trigger an alarm and trip signal, thereby protecting the transformer from further damage.

Working Principle

The indicator mainly consists of a housing, a flap (flow vane) mounted on a pivot, a return spring, a set of sealed electrical contacts, and an adjustable setpoint mechanism. The flap is positioned in the oil flow path inside the connecting pipe.

Under normal, steady oil flow the flap remains in its resting position under spring tension and the contacts stay open. When a fault generates a sudden pressure wave and high-velocity oil surge, the dynamic pressure acting on the flap overcomes the spring force, causing the flap to rotate rapidly. This movement directly drives the micro switch, closing (or opening) the sealed contacts to issue an instantaneous alarm / trip signal.

Because the device is entirely self-powered (passive), it requires no external supply and operates reliably even when the station auxiliary power is lost. After the fault is cleared, the flap automatically resets to its original position, ready for the next operation.

2. Model, Specification, Structure & Features

2.1 Model Designation

DLF  –  100    2    (TH)

Code	Meaning
DLF	Oil Flow Indicator (sudden pressure / oil surge relay) series
100	Nominal pipe / connection size (e.g. DN100); denotes the flange bore
2	Number of contacts / switches (2 groups: alarm + trip)
(TH)	Three-defense (salt fog / humidity / fungus) requirement, optional

2.2 Construction & Working Principle

• Flap assembly: (flow vane) pivoted in the oil stream, balanced by a calibrated return spring.
• Sealed contacts: contacts housed in a sealed chamber, isolated from the transformer oil.
• Adjustable setpoint: mechanism to set the oil-flow (pressure) trip threshold on site.
• Visual indicator: window on the cover for visual indication of the flap position / alarm state.
• Mounting: flanges to the transformer-conservator connecting pipe; orientation as marked.

3. Technical Data

Parameter	Specification
Product type	Oil Flow Indicator / Sudden Pressure Relay (oil surge relay)
Application	Oil-immersed power & distribution transformers
Installation position	Connecting pipe between tank and conservator
Rated pressure	As per transformer design (customizable)
Flow / pressure setpoint	Adjustable on site (typical 0.8–1.2 m/s oil velocity)
Response time	≤ 10 ms (rapid acting)
Number of contacts	2 groups (alarm + trip), SPDT
Contact capacity	AC 250 V / 5 A (resistive, typical)
Reset	Automatic (spring return) / manual reset optional
Connection (flange)	DN50 – DN150 (customizable)
Mounting orientation	As indicated on nameplate (arrow in oil-flow direction)
Enclosure protection	IP65 / IP66 (typical)
Body material	Cast aluminum alloy / stainless steel (optional)
Reference standard	IEC 60076-1, GB/T 6451

4. Key Features

• Fast protection: response to internal faults, minimizing transformer damage.
• Self-powered: (spring-loaded flap); no external power supply required.
• Hermetically sealed: electrical contacts completely isolated from oil for long service life.
• Adjustable: trip threshold to suit different transformer ratings and pipe layouts.
• Reliable & maintenance-free: design with visual position indicator; minimal maintenance required.
• Clear observation: indicator window for at-a-glance status check.

5. Applications

• Internal-fault protection of large oil-immersed power transformers.
• Rapid pressure / oil-surge alarm and trip for distribution transformers.
• Protection of reactors, converter transformers, and other oil-filled equipment.
• Integration with transformer comprehensive protection and SCADA systems.

6. Why Choose Us

• Customizable: mounting and setpoint options for different transformer ratings.
• Quality assured: 100% pressure / flow and contact-operation tested before shipment.
• Field proven: performance under outdoor and harsh (coastal, high-humidity) conditions.
• Fast response: quotation and technical proposal with drawing within 24 hours.

7. Ordering Information

To select the correct oil flow indicator, please specify the following information when requesting a quotation:

No.	Required Information	Example
1	Transformer rated power / voltage	220 kV, 180 MVA
2	Connection pipe size (DN)	DN100
3	Flow / pressure setpoint	1.0 m/s (adjustable)
4	Number & type of contacts	2 groups, SPDT (alarm + trip)
5	Mounting flange / special requirements	As per attached drawing

Send us your transformer / conservator connection drawing (DWG / DXF / PDF) and we will provide a free technical proposal within 24 hours.