Substation

Major Components in Electrical Substations and their Workings

The power system is a constituent of power generation, transmission and distribution systems. For all the power system operations, substations are required for their course of action. Substations are congregation of electrical equipment through which consumers get supply of electrical power from generating stations. By varying the voltage levels or frequency or any other aspects, the required electrical quantity can be altered in substations to provide quality power to consumers.

Based on the application of substations, they are classified into different types: Generation substation, Indoor substation, Outdoor substation, Pole mounted substation, Switching substation, Transmission substation, Converter substation and Distribution substation. In rare cases like wind farm power generation system, multiple hydroelectric and thermal power plants one can observe the collector substation which is used for transferring power from multiple turbines into one transmission unit.

Substation

The substation is an assembly of the following major electrical equipments:

• Electrical Power transformers
• Instrument transformers
• Conductors& Insulators
• Isolators
• Bus bars
• Lightning arresters
• Circuit breakers
• Relays
• Capacitor banks and miscellaneous equipment

Electrical Power Transformer

Electrical Power transformer

A static electrical machine used for transforming power from one circuit to another circuit without changing frequency is termed as Power transformer. The transformers are generally used to step down or step up the voltage levels of a system for transmission and generation purpose. These transformers are classified into different types based on their design, utilization purpose, installation methods, and so on.

Instrument Transformers:

Instrument transformers

The current and voltage transformers are together called as the Instrument transformers.

Current Transformer

Current transformer is used for the measurement of the alternating current by taking samples of the higher currents of the system. These reduced samples are in accurate proportions with the actual high currents of the system. These are used for installation and maintenance of the current relays in substations for protection purpose which are normally have low-current ratings for their operation.

Potential Transformer

Potential transformer is quite similar to the current transformer, but it is used for taking samples of high voltages of a system for providing low-voltage to the relays of protection system and also to the low-rating meters for voltage measurement. From this low-voltage measurement, the actual system’s high voltage can be calculated without measuring high voltages directly to avoid the cost of the measurement system.

Conductors

Conductors

The material or object that obeys the electrical property conductance (mostly made of metals such as aluminum and copper) and that allows the flow of electric charge is called conductor. Conductors permit free movement of the flow of electrons through them. These are used for the transmission of power or electrical energy from one place (generating station) to another place (consumer point where power is consumed by the loads) through substations. Conductors are of different types and mostly aluminum conductors are preferred in practical power systems.

 Insulators

Insulators

The metal which does not allow free movement of electrons or electric charge is called as an insulator. Hence, insulators resist electricity with their high resisting property. There are different types of insulators such as suspension type, strain type, stray type, shackle, pin type and so on. A few types of insulators are shown in the above figure. Insulators are used for insulation purpose while erecting electric poles with conductors to avoid short circuit and for other insulation requirements.

Isolators

Isolators

Isolator is a manually operated mechanical switch that isolates the faulty section or the section of a conductor or a part of a circuit of substation meant for repair from a healthy section in order to avoid occurrence of more severe faults. Hence, it is also called as a disconnector or disconnecting switch. There are different types of isolators used for different applications such as single-break isolator, double-break isolator, bus isolator, line isolator, etc.

Bus Bars

Bus bars

The conductor carrying current and having multiple numbers of incoming and outgoing line connections can be called as bus bar, which is commonly used in substations. These are classified into different types like single bus, double bus and ring bus.

Lightening Arresters

Lightening Arresters

The substation equipments such as conductors, transformers, etc., are always erected outdoor. Whenever light surges occur then, a high-voltage pass through these electrical components causing damage to them (either temporary or permanent damage based on the amount of voltage surge). Therefore, to avoid this difficulty, lightening arresters are placed to pass the entire lightening surges to earth. There are other arresters which are used to ground the switching surges called as surge arresters.

Circuit Breakers

Circuit Breakers

For the protection of substation and its components from the over currents or over load due to short circuit or any other fault the faulty section is disconnected from the healthy section either manually or automatically. If once the fault is rectified, then again the original circuit can be rebuilt by manually or automatically. Different types of circuit breakers are designed based on different criteria and usage. But in general mostly used circuit breakers are Oil circuit breaker, Air circuit breaker, SF6 circuit breaker, Vacuum Circuit Breaker, and so on.

Relays

Relays

Relays are used for disconnecting the circuits by manual or automatic operation. Relay consists of the coil which is excited or energized and such that making the contacts of relay closed activates the relay to break or make the circuit connection. There are different types of relays such as over current relays, definite time over current relays, voltage relays, auxiliary relays, reclosing relays, solid state relays, directional relays,inverse time over current relays, microcontroller relays, etc. The above figure shows some basic relays and their operation.

Capacitor banks

A Capacitor bank is a set of many identical capacitors connected in series or parallel within a enclosure and is used for the power factor correction and basic protection of substation.These capacitor banks are acts as a source of reactive power, and thus, the phase difference between voltage and current can be reduced by the capacitor banks. They will increase the ripple current capacity of the supply. It avoids undesirable characteristics in the power system. It is the most economical method for maintaining power factor and of correction of the power lag problems.

Capacitor banks

Emerging trends in technological development have created advancement in the substation installation and maintenance. For example, SCADA, supervisory control and data acquisition technique made it possible to control a substation automatically from a remote location. For more data regarding miscellaneous components and technologies in substations, post your queries in the comments section below.

The Transistor

The transistor is one of two most important inventions of the last century. Without the transistor’s invention, most of the electronic devices on which you’re so hopelessly dependent would not exist. The modern age rely on the transistor – personal computers, televisions, smartphones, tablets, phablets, laptops, routers and foot massagers suffused with billions of them.
Transistors are to electronic devices what cells are to our bodies.

TRANSISTORS

   

    Diodes are made up from two pieces of semiconductor material, either silicon or germanium to form a simple PN-junction and we also learnt about their properties and characteristics. If we now join together two individual signal diodes back-to-back, this will give us two PN-junctions connected together in series that share a common P or N terminal. The fusion of these two diodes produces a three layer, two junctions, and three terminal devices forming the basis of a Bipolar Junction
Transistor, or BJT for short.

Transistors are three terminal active devices made from different semiconductor materials
that can act as either an insulator or a conductor by the application of a small signal voltage.
The transistor's ability to change between these two states enables it to have two basic
functions: "switching" (digital electronics) or "amplification" (analogue electronics). Then
bipolar transistors have the ability to operate within three different regions:

1.Active Region - the transistor operates as an amplifier and Ic = β.Ib
2.Saturation - the transistor is "fully-ON" operating as a switch and Ic = I(saturation)
3.Cut-off - the transistor is "fully-OFF" operating as a switch and Ic = 0

Transistors (MOSFET , BJT or JFET) has two major applications

1. use it as a switch
2. use it as an amplifier (to amplify current or voltage)

we will now talk about using it as a switch.

why do we use transistor as a switch ? why not any other device ?

So here’s the answer

Its because of the property of base terminal to control the current from collector to emitter. (in case of BJT)

The input voltage is always applied to “base” of the transistor and the output voltage is taken out from the “collector” terminal to the ground (in case of a common emitter BJT)

Now,

There are two conditions,

• If I don’t apply any voltage to the base terminal, the base current (Ib) will be zero and the transistor will remain in cutoff region since collector current (Ic) will be zero and the output voltage (Vout) will be equal to Vcc(+5 volts) and transistor will act as open switch. i.e (logic 1)

• If I apply input voltage (Vin) to the base terminal, the base current (Ib) will flow. But if I apply “specifically very high input voltage” (very high Vin) , to the base terminal, the base current will increase and thus the collector current current will increase. This increase in collector current will be very high (Ic will be very high) thus the transistor will go in saturation region.

since collector current (Ic) is very high and output voltage (Vout) will be zero

transistor now will act as closed switch.

So basically, the conceptual meaning is that the base acts as a controller and it allows the transistor to be open or close.

Base controls the flow of current from collector to emitter terminal.

That is a property of a “switch” hence transistor proves that it can be used as a switch.

what I wrote here is for your conceptual understanding of why transistor is used as a switch. I didn’t explained it in detail as you can find many websites explaining the working of transistor.

Analog vs Digital انالوګ او ډيجيټل

#Analogue Versus #Digital

        There are two basic ways of representing the numerical values of the various physical quantities withwhich we constantly deal in our day-to-day lives. One of the ways, referred to as analogue, is to
express the numerical value of the quantity as a continuous range of values between the two expected
extreme values. For example, the temperature of an oven settable anywhere from 0 to 100 C may be
measured to be 65 C or 64.96 C or 64.958 C or even 64.9579 C and so on, depending upon the
accuracy of the measuring instrument. 

Similarly, voltage across a certain component in an electronic circuit may be measured as 6.5 V or 6.49 V or 6.487 V or 6.4869 V. The underlying concept in this mode of representation is that variation in the numerical value of the quantity is continuous and could have any of the infinite theoretically possible values between the two extremes.

The other possible way, referred to as digital, represents the numerical value of the quantity in steps
of discrete values. The numerical values are mostly represented using binary numbers. For example,
the temperature of the oven may be represented in steps of 1C as 64 C, 65 C, 66 C and so on.
To summarize, while an analogue representation gives a continuous output, a digital representation
produces a discrete output. Analogue systems contain devices that process or work on various physical quantities represented in analogue form. 

Digital systems contain devices that process the physical quantities represented in digital form.

Short Circuit شارټي

"Make sure you don't short the battery, otherwise it will burn" Language is important. If you know what "short" means, you can easily make sure the battery don't burn. If you don't know... ..well, you will have no idea if what you are doing will cause the battery to burn or not. To "short" something means to create a short circuit. A short circuit is a connection that was not meant to be there. For example, if you accidentally connect the plus to the minus of a battery, you'll have a short circuit between plus and minus of the battery. Which is not good because some batteries can actually explode if you short them. What Causes A Short Circuit? If you built the circuit, the most probable is that YOU caused the short circuit. I know that's hard to accept. I never accept it. ...until I find the error and I realize there's no way I can blame this on someone else. It's usually because I made one of these errors: * Connected something the wrong way * Added too much solder to a pad so that it flowed over to a neighbouring pad and created a solder bridge * Clipped of a component leg that landed on my circuit * Placed my circuit on top of something made of metal Also, if a component in your circuit is damaged, it can create a short circuit. What do you need to do to create less short circuits? And to find the short circuits you do create? Practice. Build many circuits.

د بریښنا انتقال او ویش Transmission and Distribution Lines

Transmission and Distribution Lines

       The power plants typically produce 50 cycle/second (Hertz), alternating-current (AC) electricity with voltages between 11kV and 33kV. At the power plant site, the 3-phase voltage is stepped up to a higher voltage for transmission on cables strung on cross-country towers. High voltage (HV) and extra high voltage (EHV) transmission is the next stage from power plant to transport A.C. power over long distances at voltages like; 220 kV & 400 kV. Where transmission is over 1000 kM, high voltage direct current transmission is also favoured to minimize the losses.

Sub-transmission network at 132 kV, 110 kV, 66 kV or 33 kV constitutes the next link towards the end user. Distribution at 11 kV / 6.6 kV / 3.3 kV constitutes the last link to the consumer, who is connected directly or through transformers depending upon the drawl level of service. The transmission and distribution network include sub-stations, lines and distribution transformers. High voltage transmission is used so that smaller, more economical wire sizes can be employed to carry the lower current and to reduce losses. Sub-stations, containing step-down transformers, reduce the voltage for distribution to industrial users. The voltage is further reduced for commercial facilities. Electricity must be generated, as and when it is needed since electricity cannot be stored virtually in the system.

There is no difference between a transmission line and a distribution line except for the voltage

level and power handling capability. Transmission lines are usually capable of transmitting large quantities of electric energy over great distances. They operate at high voltages.

Distribution lines carry limited quantities of power over shorter distances.

Voltage drops in line are in relation to the resistance and reactance of line, length and the current drawn. For the same quantity of power handled, lower the voltage, higher the current drawn and higher the voltage drop. The current drawn is inversely proportional to the voltage level for the same quantity of power handled. The power loss in line is proportional to resistance and square of current. (i.e. PLOSS=I2R). Higher voltage transmission and distribution thus would help to minimize line voltage drop in the ratio of voltages, and the line power loss in the ratio of square of voltages. For instance, if distribution of power is raised from 11 kV to 33 kV, the voltage drop would be lower by a factor 1/3 and the line loss would be lower by a factor (1/3)2 i.e., 1/9. Lower voltage transmission and distribution also calls for bigger size conductor on account of current handling capacity needed.

FERRANTI EFFECT

A long transmission line can be considered to compose a considerably high amount of capacitance and inductance distributed across the entire length of the line. Ferranti Effect occurs when current drawn by the distributed capacitance of the line itself is greater than the current associated with the load at the receiving end of the line(during light or no load). This capacitor charging current leads to voltage drop across the line inductor of the transmission system which is in phase with the sending end voltages. This voltage drop keeps on increasing additively as we move towards the load end of the line and subsequently the receiving end voltage tends to get larger than applied voltage leading to the phenomena called Ferranti effect in power system. It is illustrated with the help of a phasor diagram below.
Thus both the capacitance and inductor effect of transmission line are equally responsible for this particular phenomena to occur, and hence Ferranti effect is negligible in case of a short transmission line as the inductor of such a line is practically considered to be nearing zero. In general for a 300 Km line operating at a frequency of 50 Hz, the no load receiving end voltage has been found to be 5% higher than the sending end voltage.
Now for analysis of Ferranti effect let us consider the phasor diagrams shown above.
Here, Vr is considered to be the reference phasor, represented by OA.

This is represented by the phasor OC.

Now in case of a long transmission line, it has been practically observed that the line electrical resistance is negligibly small compared to the line reactance, hence we can assume the length of the phasor Ic R = 0, we can consider the rise in the voltage is only due to OA - OC = reactive drop in the line.

Now if we consider c0 and L0 are the values of capacitance and inductor per km of the transmission line, where l is the length of the line.

Since, in case of a long transmission line, the capacitance is distributed throughout its length, the average current flowing is,

Thus the rise in voltage due to line inductor is given by,

From the above equation it is absolutely evident, that the rise in voltage at the receiving end is directly proportional to the square of the line length, and hence in case of a long transmission line it keeps increasing with length and even goes beyond the applied sending end voltage at times, leading to the phenomena called Ferranti effect in power system.