What is a Distribution Transformer?
Distribution Transformer is an electrical isolation transformer which convert high-voltage electricity to lower voltage levels acceptable for use in homes and business. A distribution transformer’s function is straightforward: to step down the voltage and provide isolation between primary and secondary. Electrical energy is passed through distribution transformers to reduce high-distribution voltage levels down to end-use levels. Nearly all energy passes through at least one distribution transformer before being consumed by an end-use appliance, motor, or other piece of equipment. Distribution Transformers are found in all sectors of the economy: residential, commercial, and industrial.
Distribution transformers are generally categorized in several ways:
- type of insulation: liquid-immersed or dry-type
- number of phases: single-phase or three-phase
- voltage level (for dry-type): low or medium
General Purpose Distribution Transformers.
They are generally used for supply appliance, lighting, motorized machine and power loads from electrical distribution systems. They are either ventilated or totally enclosed, and are available with either aluminum or copper windings in standard ratings from 50VA up to 750 kVA.
Since small distribution transformers do not generate much heat, a higher proportion of theses tend to be dry-type. Dry-types are less flammable, and are therefore often selected for use when they must be located in confined spaces on a customer’s premises. Distribution transformers are used in electric power systems. The final part of the distribution system at medium voltage are the distribution transformers. Due to the low impedance voltage, this type of power distribution transformer will not substantially limit the short circuit current in the case of a fault on its secondary side. It is therefore common practice that power distribution transformers have to be type tested to their ultimate short-circuit conditions. Power distribution transformers may be oil filled or dry-filled. Distribution Transformers consist of two primary components: Core and Coil. Coil is a conductor, or winding, typically made of a low resistance material such as aluminum or copper. Copper or aluminum conductors are wound around a magnetic core to transform current from one voltage to another. Liquid insulation material or air (dry-type) surrounds the transformer core and conductors to cool and electrically insulate the transformer.
A core made of magnetically permeable material like grain oriented steel.
Distribution transformers are either mounted on an overhead pole or on a concrete pad at ground level. There is some evidence to suggest that pole mounted transformers dissipate heat more easily than pad mounted units and may therefore be more fully loaded.
What is Switchgear? Features, components and classifications
Switchgear plays a vital role in the overall power distribution and consumption system. Generally speaking, switchboards are the term one uses to designate low voltage switching whereas switchgear connotes HT usage scenarios.
The switchgear system
The term “switch” brings to mind a device that makes or breaks an electrical contact. In the industrial and LT/HT context switchgear is more complex as switchgear dealers will tell you. Switchgear is typically classified into categories like low voltage/low tension switchgear, medium voltage switchgear and high voltage-high tension switchgear. A typical system has the power components and control system with a variety of safety and monitoring features. One of the best names in the switchgear business is Larsen & Toubro. L&T Switchgears are the first choice of industries and power distribution companies for their total reliability and faultless performance.
The term switchgear refers to a collection of various devices such as:
- Fuses
- Circuit breakers
- Isolators
- Relays, coils
- Disconnect switches
- Current transformers for sensing and monitoring as well as protection
All these components of switchgear may be contained in a suitable metal cabinet that is usually earthed for safety reasons. However, HT distribution systems with large circuit breakers and switchgear are usually housed in a building.
Apart from switching on and off electricity supply, switchgear must also control power to the load, detect overload conditions and have features to automatically trip, such as circuit breakers. This protects the equipment that consumes power and it also keeps cables and switchgear protected. Switchgear may also have multiple sources of supply and automatically switch load in case one source fails.
Switchgear and protection may be automated or manually operated though the former is preferable since the automated system detects overloads and short-circuits and immediately disconnects supply thus preventing a major hazard.
Some more features of switchgear:
The household switch you are familiar with usually has air as the isolating medium since air is an insulator. However, when it comes to HT/LT applications where voltages and currents may be quite high then the circuit breakers may be oil immersed, gas or even vacuum insulated. Some switchgear makes use of the hybrid model incorporating air and gas technologies. The main reason for using gas, air or vacuum is to quench the arc caused at the time of pulling contacts apart. For instance, medium voltage switchgear operates at around 40000 volts and this high a voltage can cause quite a spark. Vacuum circuit breakers are usually employed here.
Switchgear may be classified according to voltage and current rating, by the choice of insulating medium and the interrupting rating or the short circuit current that the device can handle. Then there are further sub-classifications possible such as manual/motorized or solenoid operated as well as the transmission and distribution system. Switchgear may be purposed for isolation purposes, as load break switches and as grounding switches too in high voltage switchgear, medium voltage and low voltage switchgear.