52883WA Advanced Diploma of Applied Electrical Engineering

The guiding principle for designing an electrical power distribution network are:

1. Functions of the structure of the power distribution for the future and present time.

2. There will be the proper determination of the location of service of the entrance of the power supply.

3. There is the determination of the source of the power that will include normal mode, standby mode and also emergency mode.

4. There will be proper management of the efficiency of the energy and also the management of the resources (Kirschen & Strbac 2018)

The responsibilities of the power consumers are

1. there will be the proper mechanism of the energy efficiency of the power with the proper management of the resources.

2. The consumer has the right to inform all the characteristics and the policies regarding power consumption with the safety policies (Kirschen & Strbac 2018).

a)      415 V ac

b)      1100 V ac

c)      22000 V ac

d)      132000 V ac

a)         415 V ac- Medium Voltage (MV)

b)         1100 V ac- High Voltage (HV)

c)         22000 V ac- High Voltage (HV)

d)         132000 V ac- Extra High Voltage (EHV)

a)      Expand:

i.            SAIFI, and

ii.             SAIDI.

b)      What are these values used for?

I.            SAIFI: The System Average Interruption Frequency Index

This is the average number of interruption that is faced by the customers in the connected feeders.

SAIFI= (Total no. of customers interrupted)/ (Total no. of Customers Served)

II.            SAIDI: System Average Interruption Duration Index

This is the average duration of the power interruption that is faced by the customers in a year (Kornatka 2017)

b) these values are used for the measurement of the index of the power interruption that is faced by the customers in the power supply.

a)      Ratio of maximum demand to connected load is ______.

b)      Ratio of average load to peak demand is _______.

a) Ratio of maximum demand to connected load is Demand Factor.

b) Ratio of average load to peak demand is the Load Factor.

The two benefits of choosing the correct rating and location of power transformers in an electrical network are

1. The correct rating of the power transformer helps in better regulation of voltage in a home with proper efficiency and accuracy (Kornatka 2017).

2. The location of the power transformer helps in making the wires and connection in smaller length and also there is lowering the cost of the electricity.

The total cost of the ownership is the cost of the total assets made by the owner in purchasing the electrical equipment like for the connection. This is at the individual or at the level of the business or any firm, the cost of total wiring, and other electrical items that are needed for the connection of the power and also the cost of the transformers that is needed for the power.

The four important ratings of the 11kV circuit breaker

1. Rated Short circuit breaking current

2. Rated short circuit making current

3. Rated short time current

4. Rated operating sequence of the circuit breaker (Chen et al.,2017).

a)      For an insulator string which of these values will be higher: Creepage or clearance?

b)      What type of failures does creepage protect against?

a) The value of the creepage of the insulator string must be high so that there is more insulation in the string.

b) The creepage protects the person or power system from the electrical operating voltage in case of any malfunction of any electrical equipment.

a)      For cables

b)      For overhead line conductors

a) the PVC cables of the electrical cables it is important to withstand the high temperature in case of a short circuit and this feature of long-lasting in the temperature there is less of the electrical hazards the temperature should be 250 ° C.

b) For the overhead line conductor temperature is more important because they are exposed to the environment and heat and this high wearing capacity of temperature helps in the long-lasting the conductors (Chen et al.,2017).

1. HV switchgear has high voltage which can burn any substance which is around the switchgear and this cause the fire risk of the transformer and leads to power failures in the electricity.

2. Clearance around the Switchgear should be cleaned at a regular period so that any hazard can be prevented (Renforth et al., 2018).

1. Shor circuit study was used to determine the fault in the current at each point of the system and this will help engineers in the required interrupting capacity.

2. this also helps in identifying the correct ways to solve the problem of the short circuit in the design of cables and this helps in making proper stress of the insulators and use of the insulating material for the cables and bus bars (Renforth et al., 2018)

a)      Stability study

b)      Voltage profile study

b)  Pulling out of induction motors on voltage sags can be studied using Voltage Profile Study.

The four causes of insulation failure in solid insulation are:

1. harmonic distortion in solid insulators

2. Excessive current draw in the solid insulator

3. overheating of the solid insulator

4. Winding Contamination of the insulators

The problems of high impedance arc faults

1. Conductors are found broken and also touch the ground

2. there is a chance of the fire risk (Telford et al., 2016)

3. chances of the electric shock that can be a danger

4. may lead to the Three-phase ground fault (LLLGF)

a)      Lightning flash

b)      Insulator failure

c)      Transformer winding insulation failure

d)      Underground cable fault

d) underground cable fault is most successful for choosing the auto-reclosing of an overhead line because this will avoid the unwanted digging of the underground cable and take them out for the repairing work.

a)      System with high resistance and low reactance

b)      System with low resistance and high reactance

a) System with high resistance and low reactance has a short circuit with a high DC offset.

The two examples of unbalance faults are:

1. Single line-to-ground fault (SLG)

2. Line-to-line fault (L-L)

a)      Phase to earth (star connected system)

b)      3-phases faults

a) the wires of the electrical equipment that can be short-circuited with the done with the high flow of the electricity then there is a chance of the short circuit but extra current flows through the wire and earth absorb the current in this way current can be limited (Telford et al., 2016).

b) this will be limited by the impedance of the generator and the impedance of the line at the generation that can be managed through the symmetrical faults.

a)      Electric shock

b)      Arc hazard

a) For the safety against the electric shock of the networks there is the use of the protective shield and also there is the use of the insulating material for the wires and system so that there will be no chance of getting electric shocks.

b) there will be proper distance and minimum recommended distance among the energised conductors so that there is less of arc flash in the circuit.

The short circuit will 12.5 kA

a)      What will be the fault kVA for a 3-phase 1500 kVA transformer with 0.06 pu impedance?

b)      What is the secondary short circuit (line) current if the secondary line voltage is 440V?

a) I_(fault) = S_(kVA) x 100 / (1.732 x V_(V) x %Z)

I_(fault) = 1500 x 100 / (1.732 x 440 x 6)

= 32.80 kA

b) 32.78 kA

Impedance= 0.66

The two causes of failures in electrical distribution systems are:

1. There may be chances of the poor design of electrical distribution systems which may result in failures.

2. There may be chances of the failure of the transformers which leads to the failure of the electrical distribution system (Sallam & Malik 2018).

The two effects of power interruptions are:

1. The power failures lead to the data loss of productivity which results in a huge impact on the individual or any organisation.

2. The power interruption leads to the disruption of communications which has a great impact on the community (Sallam & Malik 2018).

a)      Direct, and

b)      Indirect losses due to power outage.

a) If there is a cyclone that strikes the town and the transformer of the building is blown away in this case there is a direct power outage.

b) If there is power loss in a particular room of the building or any particular floor of the building due to a short circuit then this is an example of an indirect power outage.

a)      Gas turbine

b)      Steam turbine

c)      Diesel Engine

c) For the generating system diesel Engine can be used as the black start source this can be used as the power supply for the big generator that can help for the start of the big generator (Oruc & Dincer 2021).

a)      RTU

b)      IED

a) RTU: Remote Terminal Unit

This is used to connect different hardware for the distribution of the power supply

b) IED: Intelligent Electric Device

this is used as an added device to the industrial Control system to make advanced power automation (Oruc & Dincer 2021).

1. the recording that is related to the incident can be recorded at the end of the circuit of the electrical power with the involved circuit (Kermani et al., 2021).

2. indirectly related to the incident that occurs during sustaining the circuit reading with the proper recording of the circuit that is not directly involved in a specific incident.

The four types of maintenance approaches normally practised are:

1. Corrective maintenance

2. Preventive Maintenance

3. Risk-based Maintenance

4. Condition-based maintenance

a)      What is meant by embedded generation? (1 mark)

b)      List any two sources used for such generation. (1 mark)

c)      List any three major advantages of embedded generation compared to centralized power plants. (3 marks)

a) This is the process of the generation of electricity at a particular location and then providing the electricity to the main supply for the distribution of the electricity network.

b). The two sources of the embedded generation are:

i. Hydroelectric power plant

ii. Nuclear Power plan (Ohijeagbon & Ajayi 2015)

c) The three major advantages of embedded generation compared to centralized power plants are:

i. There is a reduction in the loss of the transmission of the electricity to the electric systems of the power supply.

ii. The embedded generation leads to generating clean and green energy which reduces the environmental concern for the generation of electricity and supply of the electricity.

iii. The embedded generation of the electricity will help in avoiding the electric hazard with the continuous monitoring of the power supply to the electric grid this will help in reducing the load on the cables of the electric and also reduce the electric hazards due to the overload of the electricity (Kennedy & Agalgaonkar 2016).

The different types of power distribution approaches that are adopted by the utilities and industries are:

1. AC distribution System:

In this system, the consumption of power is in the form of AC. The electricity that is needed and transmitted in the form of the AC Power and this current can be easily stepped up and stepped down by the transformers. According to the voltage level of the AC Power, there are also two types of system (Jenkins & Pérez-Arriaga 2017)

i. Primary distribution system: In this system, the use of the voltage level is slightly higher than the utilization voltage. In this case, there is a 3-phase system and the range of the voltage is 3.3kV, 6.6kV & 11kV

ii. Secondary Distribution System: In this system, the power supply of the voltage is low 11kV to 415V and this is used for small consumers like household workers.

2. Radial System: this system has a separate feeder for the power in each area and the direction of the power in only one direction only and there is less cost and their low reliability of this system.

3. Ring main System: this system has its name with the connection in the loop with the single transformer supply to all the distributors and this is connected with the substation of the electrical power plant (Jenkins & Pérez-Arriaga 2017).

What will be the fault of MVA if there is a short circuit on the 22 kV bus?

All other impedances in the system can be neglected. Perform the calculation using a base MVA of 200MVA.

Show that the fault level of the parallel combination obtained in this method is the same as the sum of the fault MVA of the two transformers when operating alone.

for the transformer1 the fault will be

I_(fault) = S_(kVA) x 100 / (1.732 x V_(V) x %Z)

I_(fault) = 15 x 100 / (1.732 x 440 x8)

= 0.246kA

For transformer 2 the fault will be

I_(fault) = S_(kVA) x 100 / (1.732 x V_(V) x %Z)

I_(fault) = 30 x 100 / (1.732 x 440 x 16)

= 0.246 kA

In the parallel combination of the transformer fault

T1+T2= 0.246+0.246

= 0.492kA

When impendence = 0

MVA rating = 200MVA

Then the fault will be = S_(kVA) x 100 / (1.732 x V_(V) x %Z)

And when neglected the impedance hence the impedance will be 0 then there Is an infinite fault in the system.

Hence from the above calculation of the combination of the transformers in the parallel circuits and the sum of the faults MVA is equal when they are operating alone with the transformer1 and transformer2.

a)      Differentiate between Planned preventive maintenance and condition-based maintenance.

b)      List the condition monitoring tests used for:

i.            Circuit breakers

ii.             Transformers

iii.            Cables, and

iv.            Busbars

(need two examples for each category).

a).

b)

I.            Circuit Breaker:  The condition monitoring test that is used is

1.      Off-line Monitoring

2.      Continuous Monitoring

3.      Real-time Monitoring

II.            Transformers: the condition monitoring test that is used are:

1.      Tan delta on winding monitoring test

2.      Monitoring test for the test of the Polarization

3.      Monitoring test of the Furan Analysis of the transformers

III.            Cables:  the condition monitoring test that is used are

1.      The test of the withstand testing of cable

2.      There is also a testing of the partial discharge of cable current

3.      There is the testing of the tan delta of the cable

IV.            Busbars: the condition monitoring test that is used are

1.      Use of the Yokogawa DTSX innovative temperature for the overheating sensors of the temperatures

2.      The maintenance can be done in the condition of the blackout

3.      There is always the maintenance of the switchboards and also emergency generators for keeping better solutions of the monitoring.