Availability of reliable and quality power is essential for industries to be able to conduct their operations. Electrical energy savings have a direct impact on the bottom line of industrial plants and commercial businesses. Additional factors that have gained significance over the last few years are minimized and ease in maintenance, enhanced safety and technology for educed footprint on the environment.
Evolution in Substation Primary System and Equipment
Substations are the cornerstone of a transmission and distribution system, the focal point where electricity is controlled from. Over the last few decades evolution in the design of substations and the equipment installed in them has addressed issues of size, reliability, speed and automation while limiting maintenance. Some of these technology developments led to the launch in 1960s of gas Insulated Switchgear.
These smaller and compact switchgears educe the dimensions of conventional air insulated switchgear by 70 to 80 percent. Located indoors with all live parts encapsulated in insulating gas also greatly increases the reliability as the risk of primary failures, due to animals and atmosphere or industrial pollutions significantly reduced. The concept of GIS substations is kicking up in India and one example in the heart of Delhi is PGCIL's 400/220kV substation located in Maharani Bagh where 400kV and 220kV GIS solutions have been installed.
The latest trends are for pre-engineered, prefabricated and modularized substations which are available in various AIS, GIS and hybrid configurations, enabling short delivery times and a high quality of installation. In fact today in many cities across the world entire substations are being placed inside buildings and have therefore become invisible.
In India the concept of Unitized or Compact Secondary Substations at 12kV and 36kV is picking up and these have been installed in several cities. Comprising of an enclosed, fully compartmentalized assembly with HV switchgear, a distribution transformer and LV switchgear in a modular design the CSS saves space, ensures safety while preserving the aesthetics of the site.
Today's HV circuit breakers require less maintenance than their predecessors. In fact, SF6 circuit breakers have a maintenance interval (where the primary components need to be taken out of service) of 15 years. Even though disconnecting switches or rather a disconnecting function, their maintenance requirements are relatively higher.
A number of innovative switchgear concepts for air Insulated Substations (AIS) have effectively made the traditional open-air disconnecting switch redundant with the disconnecting function built onto or integrated into the breaker. This not only increases the availability of the substation but helps to reduce the space by 50%.
The conventional Instrument transformers that pass on information about primary current and voltages to the secondary equipment for protection, control and metering are large apparatus composed of insulation materials, copper and CARGO steel. The latest technology trend which is evolving is to replace these by fiber optic sensors. The information from these sensors is converted into digital fiber-optic signals, which are fed to the secondary equipment. This further reduces switchgear space while enhancing flexibility and security.
Evolution in Substation Secondary System and Equipment
The secondary system in a modern substation is used for:
Primary system protection and supervision
Local and remote access to power system apparatus
Communication links within the secondary system and interfacing to network management systems.
All these functions are performed by a Substation automation system which contains programmable secondary device, known as Intelligent Electronic Devices (IEDs) for control, monitoring, protection and automation. An IED can perform high-speed calculations in real time and trigger a trip signal, if necessary, in the event of an abnormal condition in the network.
Modern substations are generally remotely operated, and communication between the substation and the remote control centre is via a wide area network. Nowadays, new overhead lines or power cable connections are equipped with optical-fiber to enable protective system communication.
Future substation power handling equipment will be even more integrated and compact, while measuring functions and all of the secondary functions will be done using fiber-optics.
Building Intelligence in Reactive Power Compensation.
Reactive power is that component of power which increases losses in power transmission and distribution lines as well as at the point of energy usage. Where as, reactive power is generated in T&D lines, it is also generated by certain loads. Improving the power factor and voltage profile of power by reactive power compensation has been known to mitigate reactive power and hence improve energy efficiency for a long time; however its benefits are yet to be realized in India.
In T&D lines shunt compensation is done by using shunt capacitors in parallel to the system mainly for power factor improvement. Series compensation is done by connecting capacitors in series to transmission lines and used for boosting receiving end voltage. Both the above result in reduced line losses thus saving energy. in addition, series compensation also enhances transmission capacity of the lines, thus reducing to that extent, requirement of new transmission lines infrastructure.
In industries, greater requirement of quality power, increased awareness of loses due to reactive power as well as government penalties are increasing requirements to control power factor and reduce harmonics of industrial and electrical equipment.. The fact is that in many industrial processes, presence of loads which generate reactive power and non-linear loads which generate harmonics cannot be avoided. To overcome this, fixed compensation of reactive power is done by breaker controlled capacitors that feed fixed reactive power into the system. This is useful for systems that have constant loads or loads having a set pattern of operation.
Dynamic compensation involves feeding reactive power to the system which is dynamic varying in nature and is used with fluctuating loads e.g. arc furnace loads. This is done by devices such as thyristor controlled capacitors, thyristor controlled reactors with fixed capacitors or a combination of both. The latest devices for dynamic reactive power Electronic Devices that generate capacitive and inductive power as required by the system for total reactive power compensation without the usage of passive devices.
Due to the sensitive nature of the equipment used today in several industries, clean power without distortions or harmonics has become a pre-requisite. Sensitive components in computers and servers can crash causing massive loss of data due to poor quality of power. Passive or fixed harmonic filters are used to remove fixed harmonics from the system.
Active Filters, a more recent technology is an intelligent electronic device
which generates reverse harmonics relative to the harmonics present in the
system, thereby providing clean power.