• Electrical India
  • May 5, 2015

Switch To Switcgears,And Circuit Breakers With Relays

The human progress is a continuous journey, so what is in vogue today becomes obsolete after some time. Still the journey is continuing... 

-P S Shah



We are living in e-era or electronic era, where many of our day to day transactions or activities are being done with the help of electronics. But the foundation stone as well as driving force behind this is electricity. The life of modern human being is dependent on electricity. If electricity goes for a few hours, the entire human activities get disturbed and go out of gear. With ever increasing use and usage of electricity, the complexity of electrical network is also increasing.
Electricity was invented about two decades back. Starting with its usage for illumination, it got penetrated in almost all spheres of human activities. The simplest means of control of light is switch. It can perform simple task of switching on and off a light or other low power consuming appliances with human intervention. To begin with, tumbler switches were popular, then sleek switches got entry and today modular switches are in vogue. 

Fig. 1: Domestic switch...  

With the usage of high power appliances in houses, the need for higher rating switches was felt – so switches with arc shields were also developed and they were used in what is called domestic power lines.
Porcelain Kitkat fuses were used as protective devices for short circuits, which later on were reformed to what is known as HRC (High Rupturing Capacity) fuses and were able to clear faults of higher currents. Then MCBs (Miniature Circuit Breakers) were developed with breaking capacity up to 6 to 9 kilo amperes, which are now popular in domestic segments as well as in lighting circuits in commercial and industrial sectors. Today with the use of smart sensors and remote control techniques, the remote controlled lights, fans and air conditioners are also being used in high-end dwellings.
With ever increasing usage of electrical energy, the need for higher capacity controlling devices was also felt. This lead to the development of high current carrying capacity control devices – and use of some mechanical devices like gears for rapid closing and opening of current interrupting devices, hence, the name switch gear got coined.

The use of power contactors with arc control devices – like arc chutes and magnetic blow out coils became popular for frequent opening and closing of high ampere circuits.
But only control is not enough, the additional need of safety and protection of power equipments led to the development of thermal release for operational overload and short circuit releases against short circuits in Modular Circuit Breakers (MCBs) as well as Moulded Case Circuit Breakers (MCCBs).

Fig. 2: Typical MCCB...

Low and medium voltage Air Circuit Breakers of breaking capacities in the range of few thousand kVA or MVA were also developed with built in releases.
The use of no-volt coil was yet another safety feature. The requirements of safety lead to development of relay contactors that were used to develop interlocking system.
The ever increasing demands for electrical energy led to the development of various protective relays. The relays are application specific, and are sentinel or watch dogs of electrical network. Relays with circuit breakers have played lion’s role in safe generation, transmission and distribution of electrical energy or power.

Fig. 3: Typical LV circuit breaker...

The major challenge for technocrats is the development of ability of high ampacity and high voltage controlling devices to carry normal operation currents, detect any abnormal condition, break the circuit and even make the circuit with very large values of currents. These requirements lead to the development of newer insulating materials as well as the media, which are able to extinguish the arc without losing their insulating property over and over again.
Starting with the air as medium, the journey continued with mineral oils (liquid), synthetic oils (liquid), gases, solid state power controlling device like Thyristors and vacuum. This is as far as main power system is concerned.
The development in relay technology also continued side by side and advanced from electro-mechanical relays to electromagnetic relays and then numeric relays.
Along with these, the technologies and techniques for continuous monitoring of devices as well as equipments and measurements of various parameters for electrical systems – and even individual devices were also developed.
The protective, monitoring, measuring and recording requirements are application or system-specific and form a special branch. For example the use of semiconductors like diodes and thyristors in power circuit lead to the development of special fuses for this segment – with total break time of a few cycles (mili seconds).
The relays used for large and HT motors have characteristics matching their needs, and those for power transformers have characteristics to suit their needs. While relays used in power generation plants for generators may have some functions quite different from those used for similar rating motors.
Some state-of-the-art technology products like circuit breakers have even integrated measuring functions, so that data – like current, voltage, energy values and system states can be recorded, and can be communicated to the higher level automation systems.
The human progress is a continuous journey, so what is in vogue today becomes obsolete after some time.
But the quest of human being in the field of electricity will continue for higher rating generating stations – presently known as Ultra Mega Power Plants (UMPP), newer and renewable sources of energies, higher quantum of transmission of electrical energy [what is known as Extra High Voltage (UHV) level], higher rating substations for distribution of electrical power, higher level of safety, control and comforts.
This perhaps is the reason from journey from switch to switch gear and circuit breaker with relays. (The title of this article). The use of software for better monitoring of electrical power system is yet another innovation.


The Author is Deputy General Manager,Surat Special Economic Zone.