MESSKO MSAFE — gas relay (Buchholz relay) for transformers

Description

The MESSKO MSAFE is a gas relay, or Buchholz relay, and serves as the main protection of oil transformers and reactors with a conservator. It is installed in the pipe between the tank and the conservator, and for an OLTC also between the tap changer head and its own conservator. The relay responds to internal faults. Weak partial discharges, creeping currents and local overheating gradually decompose the liquid and solid insulation with the formation of gases, while with an arc or a heavy flashover gas is released violently. The relay therefore detects both early, barely noticeable defects and emergency situations.

Inside there are 2 floats and 1 flap. The upper float drops when gas accumulates under the relay cover and gives a warning signal. The lower float responds to loss of oil. The flap operates on a sudden oil surge towards the conservator, and the operating velocity is selected from the series 0.65 m/s, 1 m/s, 1.5 m/s, 2 m/s, 2.5 m/s or 3 m/s with a tolerance of ±15%. The floats are solid, not hollow, so even if damaged they will not take in oil and lose buoyancy. MESSKO has long used this float type in its MTO oil level indicators.

Signals are generated by magnetic reed switches, up to 4 in NC, NO or changeover design, 2 per function, potential-free. The relay is fitted with 1–2 contacts, up to 4 NC, NO or changeover in total. The reed switches are separated from the oil by an immersion tube, so a switch can be replaced from the terminal box side without opening the oil circuit. Insulation is tested at 2.7 kV AC for 2 s between contacts and housing and 1 kV AC across open contacts. Cable entry is via M25x1.5 for a diameter of 13...20 mm or via a 1/2 NPT thread. Vibration resistance is confirmed to IEC 60068-2-6. The relay can be checked remotely by supplying compressed air through a tube.

The housing is cast aluminium with RAL 7033 or 7038 powder coating, and 95% of the mechanical parts are made of stainless steel. Connection DN25, DN50, DN80 or G1 1/2 thread, degree of protection IP66, corrosion resistance class CX, operating oil temperature −40…+115 °C. There is an offshore version with seawater-resistant coating. Each relay undergoes a helium leak test and a test on an oil test bench, and the result is recorded in a test report.

For maintenance there are a gas sampling device, a test pump and a gas quick test. The sampling device draws off the gas accumulated in the relay so it can be sent for analysis or vented. A hand or foot pump is used to check operation, and the quick test gives a first idea of the nature of the gas right at the substation. A protective cover can be fitted over the gas inspection window. With systematic monitoring, power transformers operate for 30 years and longer, and the gas relay remains one of the first devices to report an incipient defect.

Technical specifications

Customs codes

Codes are for reference: the final code is determined at declaration for the specific model.

Questions and answers