There are circumstances when the magnetising inrush current of a transformer can require the system designer to focus special attention on methods to mitigate the effect of the magnetising current on the system operation. For example, in island
operation when a single generator is used to energise a transformer with an MVA
rating significantly greater than the rating of the generator.
The magnetising inrush current occurs at the instant the transformer is switched on. There is an inrush current in the primary winding that is significantly greater than the full load current. If the secondary winding is not connected then there may be no secondary current. Furthermore, the characteristics of the phase currents, phase voltages and kVAR reactive load may vary from phase to phase and from one switching event to the next, even with the same source generator.
If there are multiple transformers, the phenomena of resonance between the transformers may be observed.
In such instances, the effect of the magnetising current may vary from a number of cycles to many seconds.
The situation may be more complex if one transformer is already connected and loaded at the time of switching on another transformer. In this case, the most important factors are the kW load with respect to the capacity of the generator and the power factor of the load.
One tool available to the designer, as an aid to mitigation, is the configuration of the generator control and protection systems. The modelling of the power system during the design may helpful in understanding the transient response of the system and the effect of remedial measures. This can reduce the risk of an unsatisfactory outcome during commissioning.
Each system should be evaluated on a case-by-case basis. More information on transformer resonance is given in the references below.
1. M. Martinez Duro, R. Denis, Electricite’ de France, France, “Parameter uncertainty assessment in
the calculation of the overvoltages due to transformer energisation in resonant networks” CIGRE C4-204 2012
2. [B17] Lin, C. E., Cheng, C. L., Huang, C. L., and Yeh, J. C., “Investigation of magnetizing inrush current in
transformers—Part II: Harmonic analysis,” IEEE PES Winter Power Meeting, New York, 92 WM 246-9 PWRD,
Jan. 26–30, 1992
The State coroner in Queensland has delivered his findings into the accidental electrocution of three young men installing insulation in the rooves of residential homes in 2009 and 2010. The coroner’s findings have been reported in the Courier Mail.
The Master Electricians Australia association recommends that all circuits in all homes be retrofitted safety switches. The deaths of these young men is tragic, but future deaths may be prevented if this recommendation is followed.
CIGRE Internation Colloquium and Workshop on Managing Substations in the Power System of the Future.
Cigre Australia is hosting the International Colloquium and Workshop on Managing Substations in the Power System of the Future in Brisbane, from 8 to 11 September 2013.
The colloquium is being held in conjunction with Cigre Study Committees B3 (Substations) and D1 (Materials and Emerging Test Techniques) and their Working Groups.
The meetings of these Study Committees and Working Groups brings together international and national experts to provide a unique opportunity to hear and learn from leaders in the industry, and will provide great value to
participants and their organisations.
The theme of the colloquium has been designed to align with Cigre’s major strategic focus on Power Systems of the Future, and is aimed at bringing together managers, engineers, researchers and practitioners from electrical utilities, consultants, designers, and service providers in the electrical power industry, and universities to learn of new developments and practices and to update their knowledge and understanding of:
· Trends in technology;
· Latest developments and trends in substation design;
· Trends and impact of modern materials and testing techniques on substation equipment, and
· Life cycle management, diagnostics, and maintenance trends.
Crompton Instrument Integra 1630
Multifunction meters provide digital displays of electrical parameters. A wide range of meters is available from many manufacturers. Multifunction meters have been used since the early 1980’s. Their use has increased over time because of the advantages offered by multifunction meters compared with traditional analogue meters. The application for multifunction meters covers a wide range, from low voltage switchboards to HV substations.
Advantages can include:
· A large range of electrical parameters measured with a single device
· Power quality parameters can be measured
· Digital display
· Compact display
· Network connectivity options for remote monitoring, trending and data logging
In the selection of the meter, care should be exercised to identify both the functions and electrical parameters necessary for the particular application. For example, the application may require the total harmonic distortion (THD) and the harmonic voltages / currents to a certain order e.g. to the 25th harmonic.
The configuration of the meter will be done by the user and the method will vary according to the manufacturer.
Some meters are configured from the front face of the meter, using a keypad. Others are configured using
software provided by the manufacturer. If the meter is connected to a data network, there will be additional
configuration to get the meter working as part of the network and then testing to prove the data interface.
An important factor to consider is the location of the meter. It is difficult to place the meters in an outdoor location without additional protection. This is because of the IP rating of the meter and whether or not the meter can be easily read in sunlight. An ideal location would be inside an air conditioned switch-room.
Other features to be checked before selecting a meter include:
· The range voltage and current phases e.g. single-phase, 3-phase 3-wire, 3-phase 4-wire
· The programmable ranges for the voltage transformer (VT) input
· The maximum measurement ranges for kW, kVA, kVAR
· The requirement for demand measurements e.g. current 15-minute maximum demand
· The programmable units for pulse outputs
· The network connection e.g. Modbus RS485, Modbus TCP/IP, Lonworks, Ethernet/IP, etc.
· Internal bridging of current transformer (CT) secondaries within the meter, which could limit the
connection of other devices in the CT loop
· DC auxiliary supply voltage, so that communication to the device is maintained if the AC circuits are not