Duval triangle using C₂H₂, C₂H₄ and CH₄

The ratio of these 3 gases can be drawn into a triangle. The area of that classifies the sort of transformer failure.

Failures can be:

• - PD => Partial discharge
• - D1 => Discharge of low energy
• - D2 => Discharge of high energy
• - T1 => Thermal fault; t<300°C
• - T2 => Thermal fault; 300°C< t<700°C
• - T3 => Thermal fault; t>700°C
• - DT => Indeterminate, mix of thermal fault and electrical discharge

IEC 60599:1999 definition:

Doernenburg ratio using C₂H₂, C₂H₄, C₂H₆, H₂ and CH₄

The Doernenburg Ratio Method to determine the quality of Transformer Insulating Liquid uses 4 ratios of Dissolved Gases to detect if a fault is present. These ratios are Methane divided by Hydrogen (CH₄/H₂), Acetylene divided by Ethylene (C₂H₂/C₂H₄), Acetylene divided by Methane (C₂H₂/CH₄), and Ethane divided by Acetylene (C₂H₆/C₂H₂). All four of these ratios must be within the ranges provided for the Suggested Fault Diagnosis to be accepted.

The following table outlines the 3 possible cases for a successful Doernenburg Ratio Method comparison.

For successful comparison, certain limits of gas concentration and ratio must be exceeded.

Roger's Ratio Method

The Roger's Ratio Method to determine the quality of Transformer Insulating Liquid uses 3 ratios of Dissolved Gases to detect if a fault is present. These ratios are Acetylene divided by Ethylene (C₂H₂/C₂H₄), Methane divided by Hydrogen (CH₄/H₂), and Ethylene divided by Ethane (C₂H₄/C₂H₆). All three of these ratios must be within the ranges provided for the Suggested Fault Diagnosis to be accepted.

There are 6 possible cases for a successful Roger's Ratio Method comparison.

Communication interfaces ETHERNET 10/100 Mbit/s (copper-wired or fibre-optical) and RS 485 to support proprietary communication protocols and to be open / prepared for substation communication protocols IEC 61850, MODBUS, DNP 3.

HYDROCAL 1005 and HYDROCAL 1008 have been designed in such a way to be free of re-calibration during its life time. However a DGA adjustment function allows adjustment of the HYDROCAL measurements in line with laboratory results.

HYDROCAL 1005 and HYDROCAL 1008 have been tested and approved according to the following Standards:

• - EC Low Voltage Directive 2006/96/E.C.
• - EC EMC Directive 2004/108/E.C.
• - EN 61326
• - EN 61010-1

HYDROCAL 1005 and HYDROCAL 1008 uses a head space principle for gas extraction. An oil sample in a vial is stirred around. During the process temperature and pressure is controlled. After approximately 5 minutes there is a quasi equilibrium between the gas-in-oil and the gas-in-air (headspace of the vial). The physical effect is called Henry’s law.

After reaching the equilibrium state the gas phase is pressed by natural oil force into the gas chamber for analysis.

Note: HYDROCAL 1005 and HYDROCAL 1008 have been designed with miniaturized head-space method with patent oil sampling system (EP 1 950 560 B1)

In HYDROCAL 1005 and HYDROCAL 1008 NIR: (Near Infrared Spectroscopy) is used for gas-in-gas analyzing. The wave length of near infrared is between 760 nm – 5 mm. It can measure the gas content of nearly all gases except H₂. When using normal air in the measurement chamber (instead of any carrier gas), H₂ spectrum is too close to oxygen and nitrogen and therefore cannot be filtered.

NIR measurement principle is based on the physical effect that gases absorb the energy of the light of specific wave-length. The reduction of the energy in light can be measured and is directly proportional to the content of gas.

The measurement is done with a photo-sensitive resistor. The selection of gas specific wavelength is realized with an optical filter.

The average time for all gases for HYDROCAL 1005 and HYDROCAL 1008 is 4 hours with a raise / fall filter of 500 ppm/day.

The following considerations have to be taken into account when an installation is made:

• Valve with full opening (full bore valve) or a ball valve with an internal thread of 1½” (DIN ISO 228: G 1½).

The HYDROCAL 1005 and HYDROCAL 1008 has a DIN ISO G 1½ thread.

As an option a valve with NPT 1½ standard can also be used.

• A good oil flux exists on the mounting location. If necessary, use a reduction piece (adapter).
• In order to have a sufficient oil flux/oil exchange, the diameter of the valve should be not less than 25 mm. For optimal working conditions, the valve diameter should not be more than 76 mm. The valve must be on earth potential.
• It is recommended to mount the HYDROCAL 1005 and HYDROCAL 1008 unit to a valve with an union- or sleeve nut. In this case the device has not to be rotated fix during the installation. An O-ring should be used as sealing.
• To ensure the correct function of the HYDROCAL1005 and HYDROCAL 1008 the location of mounting is very important. For a typical transformer, three places are possible:

Pos. 1: On return side of cooling circuit:

Please install the unit on a straight piece of tube on the cooler output between the cooler and the main oil tank. In order to avoid negative pressure, the unit must absolutely be mounted on the downstream side (after the bend) of the oil circulation pump.

Note: Choose this place only in case of continuous oil flux through the cooler.

Pos. 2: Flange below on the transformer tank:

The flange must be at minimum height of 40 cm in order to allow installation and mounting of HYDROCAL1005 and HYDROCAL 1008 unit.

Pos. 3: Upper filling valve:

It is possible to mount the HYDROCAL 1005 and HYDROCAL 1008 unit on this position, if the filling level of the oil is min. 100 cm higher than the mounting position. This position is not recommended, because the filling process is influenced by the hydrostatic pressure of the oil and it may be difficult to operate and read the data of the unit.

Pos. 4:

Never install the HYDROCAL 1005 and HYDROCAL 1008 unit on top of the cooler or on the suction face of the pump. In this case, filling oil cannot be carried out the right way.

If the device must be installed at the bottom of the transformer, the distance between ground and installation valve must be at least 250 mm

• 4 stages safety concept have been implemented to HYDROCAL 1005 and HYDROCAL 1008 devices.
• Filling/Draining level sensor
• Filling/Draining flow meter
• Filling/Draining time control
• Flow meter timing observation

A software Watch Dog is also implemented on the Hydrocal devices

Usually no specific maintenance program is required for HYDROCAL 1005 and HYDROCAL 1008.

A service manual can be provided complementary to HYDROCAL 1005 and HYDROCAL 1008 Operation Manual. This is a guide for Service and Maintenance cases. A troubleshooting section detailing possible errors and problems is shown with hints how to fix them.

The measurement cell is calibrated in order that external gases have no effect on the measurement. A “0” measurement is also performed before all new measurement cycles.

Usually no, there is no specific port for oil sampling.

However a sampling tube is situated inside the unit, see operation manual (chapter 2.4: Installation of the HYDROCAL 1005 unit). Be careful using this sampling tube! The device has to be stopped first before HYDROCAL airing screw is opened. At the end of oil sampling, the device should be restarted manually.

No, there is no cross sensitivity to other gases. Accuracy specifications include cross sensitivities and it is the value related to gas-in-oil.

For instance to extend the current setting of 40 min up to 6 hours or 1 day in order to extend the life time of HYDROCAL 1005 and HYDROCAL 1008?

It is not possible to change measurement period/cycle due to the measurement concept itself.

No, there is no problem with so-called “dead oil loops”.

Natural oil convection exists in a transformer. Therefore, there is always oil flow / exchange inside a transformer. Additionally if there would be dead oil loops, the next measuring gas sample would have lower values, it is usually not the case, confirming good oil exchange.

Advantages of using one valve instead of using 2 outlets and 2 tubes in and out:

• Non availability of second one
• Easier installation
• Maintenance cost, external tubes may need regular maintenance due to weather conditions

Easier exchange (product migration) if customer requires other HYDROCAL type (HYDROCAL 1001-1002-1003, etc.)

Operation temperature (Ambient) for HYDROCAL 1005 and HYDROCAL 1008 is -55°C to +55°C

For information, a large number of HYDROCAL devices are installed in the Middle East, without display problems caused by sunlight.

The built-in webserver of the CheckMeter 2.3 genX serves to remote display the graphical user interface and to remote control the unit over a Wireless Local Area Network (WLAN) connection.

The webserver can be accessed with a standard web browser on a control unit, which can be a smartphone, a tablet, a computer or any device with web browser and WLAN access. No app or software must be installed. Thanks to the galvanic separation through the wireless connection, the CheckMeter 2.3 genX can be placed in the installation and be operated in safe distance from dangerous parts of the installation.

To use the webserver the control unit must be connected to the same wireless network WLAN and the device Name or IP address of the CheckMeter 2.3 genX must be known and be entered in the URL field of the web browser started on the control unit.

The necessary information can be found at:

  DB / Basic settings / Ethernet communication setup

There are two possibilities to connect the control unit to the WLAN:

(A) Connect to WLAN of CheckMeter 2.3 genX
Access point mode

(1) Connect control unit to: WLAN: CMgenX-57731 AP

(2) Enter in URL field of web browser
Name:

IP:

(B) Connect to the same existing WLAN
Access point mode

(1) Connect control unit to WLAN: MTE

(2) Enter in URL field of web browser

Name:

IP:

It may need some time to connect and to provide the IP address. The connection is OK, if you see the hook symbol behind the WLAN name and if the IP address is updated.

Note: In some browsers the entry of Name or IP alone will not work. In this case http:// or https://must be added in front.

For details how to setup the WLAN at the CheckMeter 2.3 genX in access point or connection mode see the operation manual.

Operation manual

The built-in operation manual can be accessed in the browser of the control unit as on the device. This allows parallel operation with view of the operation manual on the control unit during manual operation of the device.

Simple Meter Testing Guide