Eps Assign 1

8/13/2019 Eps Assign 1

http://slidepdf.com/reader/full/eps-assign-1 1/11

Electrical Power System Assignment 1

MOHAMMAD ZAIN(4234685)

Electrical Power Systems

Assignment 1 (Substation Visit)

Name : MOHAMMAD ZAIN

Student ID : 4234685

Subject: Electrical Power Systems

Subject Code : HET326

Lecturer : IR Jimmy Lo





Abstract

An inspection to the facilities of a public utility is directed. Students are to learn the components

of equipment that the power system includes and to make a report of how the system and its

components are working.

Introduction(Working of Substation)

A substation is a part of an electrical generation, transmission, and distribution system where

voltage is transformed from high to low or low to high by using transformers. A substation

contains a number of components such as the transformer, the consumer incoming high voltage

supply and associated switchgears and housed in a purpose – built enclosure. The substation

normally is found in the town area. By having a substation, the engineers can check and repair

the flawed occurs in the substation. Substation can be considered as distribution substations,

transmission substations, switching substations or any combination of them. In this report, we

will emphasis on the distribution substation in the urban area. The overall report will be

discussed on the components of equipment at the distribution substation and how the

components are connected to make the power system works.

Distribution substation

A distribution substation transfer power from the transmission system to the distribution system

of an area by reducing the voltage to suitable voltage value for the local distribution. The

incoming for a distribution substation is normally 2 transmission lines. The incoming voltages to

the distribution substation are typically medium voltage which is 33kV. Larger incoming

voltages are depending on the areas to be supplied and the practices of local function. Besides

the substation is changing the voltage, it is also use to isolate faults in either the transmission

substation or the distribution system.

Components of equipment at distribution substation

There are two parts in a substation system, primary and secondary system auxiliaries. The

primary system is the main system for transmission to operate, consisting of transformers,capacitor banks and switch gears. The secondary system emphasizes on protection and backup of

the transmission system power if any accidents occur.





A distribution substation consists of the following equipment:

Switch Gear(Carrying Primary Current)

In the substation there was a Switchgear placed beside the Capacitor bank carrying the primarycurrent. It is a combination of electrical disconnect switches, fuses, or circuit breakers used to

control, protect and isolate electrical equipment. The switches can be operated manually to break

a circuit for maintenance and can also break the circuit automatically in fault conditions, thereby

protecting the system.

Functions of Switch Gear

Carrying the normal load current

Making or breaking the normal load current

Clearing the fault current (for which sensing devices like CT, PT,and various relays are employed)

Component of Switch Gear

1. Circuit Breaker2. Current Transformer (CT)

3. Potential Transformer (PT)

4. Protective Relays

5. Measuring Instruments6. Switches

7. Fuses

8. Surge Arresters9. Isolators

10. Miniature Circuit Breakers(MCB)

Some of the component which have been used in the Distribution Substation(Switch Gear) which

we visited are explained below.

Isolator

Isolator is a mechanical switching device that used for isolating a circuit or equipment from the

source of power, in case the circuit is being shorted for example, if there is lighting and some

other source of load disturbing flow. The circuit is automatically broken through switches.It also

used to carry load current continuously.





Circuit Breaker

A circuit breaker is an equipment which can open or close a circuit under normal as well as fault

conditions. The circuit breaker is connected to the capacitor bank. This circuit breaker is used to

switch on and isolate the power supply. It is designed to break a circuit which is carrying current

at the time. Where large currents and/or voltages are present, the opening of the circuit may

induce dangerous arcing, so means such as air blast must be used to "blow out" the arc. Air

breakers are being phased out and replaced with vacuum. An isolator is only designed to isolate a

circuit or other component after the current has already ceased, so it doesn't need to have any

means to stop the arc. Thus in high voltage/high current installations such as in power stations or

grid switching stations, the initial operation to isolate the circuit, whether planned or as a result

of a fault, is by the circuit breaker, the isolator is then used to isolate the circuit breaker for

maintenance or repair.

Current Transformer and Voltage Transformer

Instrument transformers means current transformer & voltage transformer are used in

electrical for stepping down currents and voltages of the system for metering and protection

purpose. Actually relays and meters used for protection and metering, are not designed for high

currents and voltages.

Figure 1: Switch Gear

Control and Protection Panel

In this room, there are a lot of panels which represents the particular substation. Control and protection panel consist of typically a switchgear. As in substations switchgear is located on both

the high voltage and the low voltage side of large power transformers. The switchgear on the low

http://www.electrical4u.com/electrical-transformer/potential-voltage-transformer.php

http://en.wikipedia.org/wiki/Electrical_substation

http://en.wikipedia.org/wiki/Transformer

http://en.wikipedia.org/wiki/Transformer

http://en.wikipedia.org/wiki/Electrical_substation

http://www.electrical4u.com/electrical-transformer/potential-voltage-transformer.php





voltage side of the transformers is located in a building, with medium-voltage circuit breakers for

distribution circuits, along with metering, control, and protection equipment. Protection relays in

the switchgear are the brain that controls the Circuit Breaker We saw how the protection relays

in the switchgear is the brain that controls the Circuit Breaker in case there is a requirement tocreate isolation. The Protection and Control Panel provides alarms that indicate which part of the

transmission system is faulty so that problems can be minimized and avoided. It also indicatesthe tap position on the transformer. It helps in changing the tap position so that even though theinput voltage fluctuates, the output remains steady.

Figure 2:Control Panel

Some of the component which have been used in the switch gear in the control and protection

panel section are explained below.

Protective Relay

A protective relay is an electromechanical apparatus, often with more than one coil, designed to

calculate operating conditions on an electrical circuit and trip circuit breakers when a fault is

detected.

Miniature Circuit Breakers

we use more commonly Miniature Circuit Breaker or MCB in low voltage electrical network

instead of fuse. It automatically switches off the electrical circuit during abnormal condition of

http://www.electrical4u.com/electrical-fuse-hrc-fuse-high-rupturing-capacity/

http://www.electrical4u.com/electrical-fuse-hrc-fuse-high-rupturing-capacity/





the network means in over load condition as well as faulty condition. The fuse does not sense

but Miniature Circuit Breaker does it in more reliable way. MCB is much more sensitive to over

current than fuse.

Transformer

Transformer is a vital link in a power system which has made possible the power generated atlow voltages to be stepped up to extra high voltages for transmission over long distances and

then transformed to low voltages for utilization at proper load centers. With this tool in hands it

has become possible to harness the energy resources at far off places from the load centers andconnect the same through long extra high voltage transmission lines working on high

efficiencies. At that, it may be said to be the simplest equipment with no motive parts.

Figure 3: Transformer

It consists of two parts which are the primary winding and secondary winding. The varying

current at the primary winding creates magnetic flux in the transformer’s core and through thesecondary winding. This magnetic flux induces electromotive force (EMF) or known as

secondary winding voltage. If a load is connected to the secondary side, this current will flow

where the electrical energy will be transported from the primary to the secondary side.





where Vp,Np and Vs,Ns are voltages and number of turns in the primary and secondary siderespectively.

The type of transformer used in substation is a step down transformer. It steps down voltage

form 33kV to desired 11.5kV.

Figure 4: Transformer Nameplate

Functions

In our visiting site, the substation has use a 3Ф (3-phase) transformer to step down the voltage

primary 33kV to 11.5kV voltage secondary.

Rating

Referring to the transformer plate the rating is shown below.

Rating Voltage: 33/11.5 kVRating Power: 15/20 MVA

No. of Phases: 3

Rated Frequency: 50 Hz

Capacitor Rating (Capacitor Bank): 5MVar





Voltage of Windings

High Voltage Side(Primary) = 33kVLow Voltage Side(Secondary) = 11.5kV

Turns Ration = 2.9 approximately

Number of Winding

No. of Windings =

Vector Group

Vector group is a standard way of categorizing the primary and secondary winding

configurations of three-phase transformers. Vector group for the substation transformer isDyn1. It means that the primary side is having a Delta winding while the secondary side is

having a Y winding with Neutral Point in voltage phase 30 degree.

Winding Earth

The winding earth usually connected to neutral line which is to be grounded. The earth wire

current is calculated below.

Type of Cooling

One characteristic of all transformers is that when they are energized they create losses in the

circuit. Due to power loss in the transformer, heat is generated and this is mainly due to copper

loss. So the transformers are designed to dissipate excess heat and therefore ensure longer

insulation life. The current cooling method for the transformer in the substation is ONAN, but





the information plate on it says that it will be upgraded to ONAF in future. Both cooling systems

can be summarized as below.

ONAN is a mode of operation in which oil circulates by convection. Air is passed

through cooling tubes by natural passage.

ONAF uses a fan to increase the air flow and cooling which therefore increases the ratingof the transformer.

Voltage Impedance

Voltage impedance is the amount of voltage applied to the primary side to produce full load

current in the secondary side. As expressed in the nameplate the Voltage impedance is as

follow.

Side Voltage Tap Position Current Percentage

Impedance, Xs

Primary 33 kV 9t

262 A 10.8 %

(Based on 15MVA at 75°c)

P.U impedance under 100MVA base

It can be calculated using the formula

Voltage Impedance x

x (

)

2

For the rating power

15 MVA, P.U impedance = 72%

Capacitor Bank

In a transmission line, the flow of reactive power in the line decides the receiving end voltage.

Managing Voltage level at the receiving end is very important as higher voltage can damage the

consumers equipment and there will be a great loss. In many cases, we see sudden voltage rise or

fall due to lightning or due to any fault on the healthy phases and in any case damage to the

equipment occurs.

As already discussed, excess of reactive power as well as its scarcity should be monitored. Forthis purpose, compensation is done by using various devices. Here the reactor absorbs excess

reactive power whereas the capacitor supplies for makeup of reactive power in cases of high

demand.

For low power factor loads, the reactive power demand is very high. Therefore, we need to

increase the power factor using capacitor bank. This reduces the var demand by supplying the

appropriate amount of reactive power to the load.





Figure 5 :Power Factor

In simple words capacitor bank is an array of capacitors connected into a circuit. They are used

to control the voltage that is supplied to the customer by eliminating the voltage drop in the

system caused by inductive reactive loads.

To improve the power factor, capacitor bank is used. It reduced the reactive losses by reducing

the power factor. The capacitor bank used in the substation was 5MVAr.

Figure 6: Capacitor Bank





Single Line Diagram

A single line diagram has been attached at the end of this assignment. The diagram shows theconnection of the components of the power system in distribution substation. The 33kV

incoming voltage is going to the capacitor banks through feeder and it is also going into a step

down transformer. Both the circuit breaker and transformer have switch gears which includescircuit breaker, current transformer, isolator etc. The stepped down voltage in another bus bar is

been seen to sent to different feeding lines for distribution purposes.

Conclusion

This trip helped in gaining knowledge and understanding about the factors considered for

transmitting power. The working principle of the transformer is studied and analyzed. The

transformer acts as medium to increase or decrease the transmission voltage and deliver it to the

load with the help of the cables. We learned how a Capacitor bank is used to improve power

factor in power distribution. Moreover I gained knowledge about a switch gear that how muchimportant it is in power distribution and the equipments included in switch gear like circuit

breaker, isolator etc. Also we studied about the safety requirements and safety measures taken to

minimize damage caused to both human life and system in case of any emergency condition. We

have realized that a proper understanding of concepts can only be established when exposed to

practical field.

Eps Assign 1

Documents

Transcript of Eps Assign 1