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:
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 the 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 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 Application of Electrical Vehicle Supply Equipment (EVSE) - Impact on the Electrical Power Infrastructure for Parking Stations
Plug-in electric vehicles (PEVs) are now available for the driving public. General Motors has released the Chevrolet Volt and Nissan has released the Nissan Leaf. These vehicles are manufactured in USA and Japan. Over time, the penetrations of PEVs into the market is forecast to increase.
PEVs have two classes of charging methods. These methods have been defined by SAE J1772-2010.
The first charge method is AC Level 1, which has a rating of 120 Vac, single phase at the maximum current of 12 A. The second charge method is AC Level 2, which has a rating of 208-240 Vac, single phase at a maximum current of 80 A.
The charging method which is likely to be applicable in Australia is the second charge method. A typical charging station is the GE DuraStation.
This station provides fast level 2 charging in 4-8 hours for a full cycle charge. The most commonly available models have a maximum continuous current rating of 30 A. This represents a continuous load of 7.2 kVA at 240 Vac.
This means that the station will need to be supplied by a dedicated circuit, protected by a 40 A circuit breaker. In the USA, the NEC does recognise that any diversity should be included in determining the maximum demand.
The impact of the addition of EVSE to parking stations is that a relatively significant load will have to be serviced in areas that are traditionally have very minimal loads.
For instance, a multilevel car park in the city will have a typical load of lighting and perhaps a lift. If 300 charging stations were to be installed, the total installed capacity would be 2,160 kVA. It is likely to require a complete overhaul of the LV electrical installation.
The installation of EVSE may also impact the electrical load for houses and car parks such as:
There will also be an impact on the distribution network, which will have to support the additional load. The additional load at the point of connection may require the distribution company to upgrade the consumer mains and install additional transformers.
Furthermore, there will be an impact of the load profile. For example, the cars used to commuting will be charge overnight and during the day.
Unexcited synchronization is used where multiple generators are required to black start and energise a load comprising transformers, where the rating of the transformers is many times the rating of the multiple generators.
It allows comparatively large transformers to be energised by multiple generators, without subjecting the generators to the usual inrush current of the transformers.
(Reference: Case Study - Unloaded Transformers Energised by a Generator at 11 kV; Effect of Magnetising Inrush)
It allows a smaller generation capacity to be installed, instead of a capacity which could withstand the inrush of the transformers at rated voltage. Unexcited synchronization also reduces the mechanical stress on the transformers through the ramped excitation of the transformer.
Unexcited synchronization may be the either the primary or secondary means of synchronization for the generators.