DGA is the study of dissolved gases in transformer insulating fluids.

It is a highly sensitive and reliable technique which can reveal abnormal behaviour developing inside a transformer. At a minimum, the dissolved hydrogen concentration serves as an indicator of any fault type. By measuring multiple "fault gases" and their evolution over time, DGA can serve as an advanced tool to diagnose the health of a transformer, and a key element of a comprehensive preventive maintenance program.

Since the 1960s, many utilities have drawn oil syringe samples annually or semi-annually from each of their critical transformers and sent them to DGA laboratories for analysis. This practice remains the foundation of DGA today. Increasingly though, portable DGA analyzers and on-line DGA monitors are now taking their place in the industry, providing more timely DGA data in more automated ways.

Transformer oil is a petroleum distillate mineral oil used as a cooling fluid and as a dielectric insulator in high-voltage high-power transformers. It generally contains a number of additives which extend the service life.

Transformer oil is the most common member of a larger class of dielectric insulating fluids used in transformers. Other types include silicone-based fluids and fluids made of natural esters.

The dielectric fluid circulates among the key internal components of the transformer, and often through cooling radiators as well. If it exposed to extreme conditions of thermal or electrical stress, it will degrade and generate dissolved "fault gases" as products of the degradation. Dissolved fault gases can also be formed if the cellulose insulation (also called solid insulation) of the transformer begins to degrade.

In a properly functioning transformer, small amounts of fault gases will develop through slow aging of fluid and solid insulation. At the other extreme, severe sudden faults which generate large amounts of fault gases can lead to catastrophic transformer failure.

The Morgan Schaffer network of distributors is constantly growing and now covers most areas of the world. See our "Contact Us" directory for the most up-to-date information.

Our technical support specialists are standing by to answer all of your questions about Calisto. Request assistance via our Tech Support Hub or call us at 1-514-739-1967 (Eastern Time, GMT-5).

Yes. All Calisto monitors are sold with a PC-based user interface software which can be used to configure the equipment to suit your communication and alarm preferences. While Calisto Access has traditionally been used with Calisto and Calisto 2 units, the new Calisto Manager interface will be introduced to support the entire family of Calistos.

The entire Calisto family can communicate via Modbus with SCADA systems. Modbus can be connected directly on the RS-485 port, or using a TCP/IP to RS-485 Modbus converter.

The Calisto family supports the following communication protocols:

• Modbus on RS-485
• DNP3/ASCII on RS-485 and DNP3/TCP on Ethernet
• IEC61850 on Ethernet (option)
• Morgan Schaffer System Protocol on all ports

Calisto can communicate directly or remotely with SCADA systems using the isolated RS-232 port (1500V) channel, the RS-485 (1500V) port, the Ethernet port, the analog outputs, or the dry-contact relays.

Each member of the Calisto family has calibrated 4-20mA analog outputs which can be configured to suit your preferences. Also provided are 4-20mA inputs which can be used to provide transformer oil temperature signals to the Calisto.

Calisto 5 and Calisto 9 can operate at ambient temperatures in the range -50C to +55C. Calisto and Calisto 2 can operate at ambient temperatures in the range -40C to +55C, and this can be extended to -50C with the optional cold conditions kit.

All Calisto instruments are independently tested for conformity with IEC/EN 61326. All permanently connected ports are rated for 5kV impulse, 2.6kVac

Please see the specification sheet for each model.

The following must be taken into account during an installation:

• Minimum valve diameter of 1/2 inch.
• The inlet and outlet valves must not be close to an oil pump.
• The outlet or return oil line must not exceed 9m (30 feet).
• The inlet oil line must be longer than three (3) feet for ease of installation.
• The distance between the two transformer valves must be at least 3 feet.
• The Calisto inlet should ideally connect to the lower of the two selected transformer valves.
• The inlet valve must be at least 18 inches above the main tank bottom. Include one loop or bend in the oil line to allow for expansion and contraction. Do not straighten the lines between the transformer tank and the Calisto.
• In very hot conditions, it is strongly recommended not to insulate the oil lines. Use the enclosed insulation at possible chafing points only.
• In very cold conditions, it is strongly recommended to insulate the oil lines.

Our premium oil lines are made from stainless steel flexible hose. We recommend these lines, or solid stainless steel tubing for new installations of Calisto 5 and Calisto 9.

If cost is an issue, Copper lines can be used for any Calisto installation.

No, Calisto requires two separate valves. This ensures that the monitor is continuously exposed to representative oil from the inside of the transformer. It is important that the monitor inlet and outlet be physically separated to prevent oil recirculation. Valves with a minimum diameter of 1/2", located near the monitor, are the most appropriate.