Topic 1 Plant Planning and Power Demand

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BEF 44903 Topic 1

BEF 44903 Industrial Power Systems Topic 1

Outlines

1.1 Plant Distribution Systems

1.2 Voltage and Frequency Considerations

1.3 Types of Plant Distribution Networks

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1.4 Power Demand and Load Estimation

1.5 Transformer Sizing

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1.1 Overview of Electric Power Systems

Generation System13.8 kV 15.6 kV

Distribution System11 kV 66 kV

Transmission System132 kV 500 kV

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1.1 Example of Plant Distribution System

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Panelboard Feeding240/415V

Harmonic Loads

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1.1 Planning Distribution Systems

Power system concept: Analysis Selection of the networkconfiguration Type of connection to ground Technical features

Network calculation: Load flow Short-circuit calculation Energy balance

Rating: Transformers Cables Protective/ switching devices Provisions for redundant supply

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Power system planning



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Source: Siemens

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An optimum network configuration should particularly meet the following requirements:

Favorable and flexible expansionoptions

1 Simple structure

2 High reliability of supply

3 Low losses

4 Favorable and flexible expansionoptions

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optionsoptions



Example of Industrial Power Networks

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A distribution system deals with the distribution of electrical energy to its specific loads.

The main purposes of planning are:To make the system economical (cost effective).To minimise power losses and maintain regulation

within permissible limits. Load survey and load forecasting of the area are

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necessary.



Load survey of a particular area is carried out to find out the present load requirement as well as the expected load gro th o er a period of 5 to 15 ears The follo ingload growth over a period of 5 to 15 years. The following basic data should be collected for starting this work:

A detailed map of the area showing important features. The existing number of houses, population and new construction

anticipated in the area. The expected number of shops post offices rural health centres

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The expected number of shops, post offices, rural health centres, etc.

The type of industry and number of industries possible in the area.

Development programmes implemented in the area.

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For the purpose of forecasting load, the prospective consumers may be categorized as under:

1 D ti i id ti l h1. Domestic consumers, i.e. residential houses.2. Commercial consumers, i.e. shops, schools, hospitals, hotels,

and other commercial establishments.3. Industrial consumers:

a. Small industriesb. Medium industriesc. Large industries

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d. Municipal consumers (i.e. street lighting, water works, parks, etc.)e. Agricultural consumersf. Mining industries


1.1 Layout of Distribution Systems

Sub-transmission Line (66kV 33kV)

132kV/66kV 66kV/11kV

11kV Feeder

11kV Feeder

11kV/415V

3 Phase Consumers

(415V)

Single Phase Consumers

Secondary Substation

Distribution Substation

Primary Substation

66kV Feeder

(66kV or 33kV)

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11kV Feeder

Industrial Consumer

Consumers (240V)

66kV Feeder

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1.1 Layout of Distribution Systems

The high voltage from transmission line (132 kV) is step-down at the Primary Substation to 66 kV or 33 kV.

From this primary substation power at 66 kV or 33kV is From this primary substation, power at 66 kV or 33kV is carried through sub-transmission lines to different load centres. The length of a sub-transmission line is about 50 km and they carry about 50 MW of power.

It has been found that sending power through sub-transmission lines at 33 kV or 66 kV is economical in terms of losses (i.e. I2R) and the capital cost (i.e. cost of

d i l d )

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conductor, insulators and supports). Most domestic, commercial and small-scale industrial

consumers receive power at low voltage, i.e. 240V or 415V. Large-scale consumers having load in excess of 100 kW buy bulk power at 11 kV and above.


1.1 Planning for Connection

Supplies at Low Voltages of 240V and 415V Maximum power requirements in kVA Types and number of equipment and its

corresponding connected capacity in kVA Shunt connected reactors and capacitors in kVAr For single-phase 240V motors with rating of greater

than 6kVA and/or three-phase 415V motors with rating greater than 75kVA:rating greater than 75kVA: (i) Rating in HP or KVA, (ii) Types of control equipment, (iii)

Methods of starting and starting current, (iv) Frequency of starting (number/hour), and (v) Rated power factor;

Voltage sensitive loads (indicating sensitivity)

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Supplies at 275kV, 132kV, 33kV, 22 kV, 11kV and 6.6kV For all types of loads:

Maximum Active Power consumption in kW; Maximum Reactive Power consumption in kVAR.

For motor loads: Types of control equipment; Methods of starting;g; Magnitude and duration of the starting current; Frequency of starting (number/hour); Under voltage setting and time; Negative phase sequence protection; Sub-transient and/or locked rotor reactance of the motor.

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For nonlinear loads with harmonic current injections: Harmonic current spectrum including harmonic number and

the corresponding maximum currentthe corresponding maximum current.

For fluctuating loads: The rates of change of Active Power and Reactive Power

consumption in kW/minute and kVAR/minute ,respectively, both increasing and decreasing;

The shortest repetitive time interval between fluctuations for Active Power and Reactive Power in minutes; and

The magnitude of the largest step changes in Active Power and Reactive Power in kW and kVAR respectively, both increasing and decreasing.

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For voltage sensitive loads: steady-state voltage tolerance limits of the equipment in

percentage of the nominal voltage;percentage of the nominal voltage; intrinsic immunity limits to short duration voltage variation; transient voltage tolerance limits of the equipment in

percentage of the nominal voltage and the corresponding duration;

harmonic current emission limit for equipment. For Shunt Connected Reactors and Capacitors:p

configuration and sizes of individual banks; types of switching and control equipment; and types of harmonic filtering reactors.

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Voltage Criteria Steady-State Voltage Fluctuation (Normal Condition):

Steady-State Voltage Fluctuation (Contingency Condition)

Voltage level % variation415V and 240V -10% & +5%6.6kV, 11 kV, 22kV,33kV +/- 5%132kV and 275kV -5% & +10

Steady-State Voltage Fluctuation (Contingency Condition)

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Voltage level % variation415V and 240V +/- 10%6.6kV, 11 kV, 22kV,33kV +10 & -10%132kV and 275kV +/- 10%

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1.2 Supply Voltage Options

Low Voltage: Single-phase, two-wire, 240V, up to 12 kVA maximum

demand Three-phase, four-wire, 415V, up to 45 kVA maximum

demand Three-phase, four-wire, C.T. metered, 415V, up to

1,000 kVA maximum demand

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1.2 Supply Voltage Options

Medium and High Voltages: Three-phase, three-wire and 11 kV for load of 1,000

kVA maximum demand and above Three-phase, three-wire, 22kV or 33kV for load of

5,000 kVA maximum demand and above Three-phase, three-wire, 66kV, 132kV and 275kV for

exceptionally large load of above 25 MVA maximum demand

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Frequency Criteria The supply frequency is 50 Hz 1%

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1.3 Classification of Distribution Systems

The distribution systems may be classified in the following ways:

1 A di t t f t ti1. According to nature of constructiona. Overhead distribution system (cheaper)b. Underground distribution system (in crowded area)

2. According to nature of currenta. DC distribution systemb. AC distribution system

3. According to number of wires2-wire DC system 3-wire DC system 1-phase 2-wire AC system

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2 wire DC system, 3 wire DC system, 1 phase 2 wire AC system,3-phase 3-wire AC system, 3-phase 4-wire AC system

4. According to the scheme of connections(a) Radial system(b) Ring system(c) Inter-connected system

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1.3 Primary Distribution Lines (Feeders)

The 33/11 kV secondary substation is established where the load requirement is approximately 5 MVA. Since normall a primar distrib tion line is designed to carr anormally a primary distribution line is designed to carry a load of 1-2 MVA, the number of primary distribution lines emanating from a 33/11 kV secondary substation is about 4.

When the load requirement increases and crosses about 8 MVA, the losses in the 33 kV sub-transmission line become large Thus power must fed from a 66 kV sub

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become large. Thus, power must fed from a 66 kV sub-transmission line. The number of primary distribution lines emanating from a 66/11 kV secondary substation is six to ten.



There are 3 different ways in which the primary distribution lines can be laid:1. The radial primary circuit2. The loop primary circuit3. The ring main system (or primary network)

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Radial Primary CircuitsWhen each circuit coming out of a substation is separate from the other circuits and has no inter-connection with any other circuit, it is called a radial circuit.

Factory having load of 1 MW at 11 kV

Circuit 1 for Factory

Circuit 2 feeding Substation in the city

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Circuit 3 for Rural Areas



Advantages of Radial Feeders:i. A heavy load very near the secondary substation.ii I l t d l dii. Isolated loads.iii. An area of low load density such as a village.

Limitations of Radial Feeders:i. When the load demand on the radial feeder increases, the

length of the feeder has to be extended. This results in a greater voltage drop which may cause the voltage towards the tail-end

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voltage drop which may cause the voltage towards the tail end to reach a value below the permissible limit.

ii. When a fault occurs at any point along the length of the feeder, supply to all the consumers beyond this point towards the tail-end gets interrupted.

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Loop Primary CircuitsTo overcome the limitations of the radial feeders, the ,loop primary circuit is taken to use.


Distribution Substation 2


CB4 CB5

11 kV 11 kV

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Substation 2 Substation 3

CB1CB2

CB3 CB6

A



Two 11 kV feeders emanate from the secondary substation.

In this system, every distribution substation receives supply from two sides.

In case of fault, say at point A, the circuit breaker 1 at distribution substation 1 and circuit breaker 6 at distribution substation 3 will open, thus isolating the faulty section. The supply to the substation 1 and 3 is still

i d d i b i d f h

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uninterrupted and continues to be received from another side.

This system is generally used in towns and cities.

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The reliability of supply in this system has improved in comparison with that in the radial system as it has an alternati e s ppl in case one side failsalternative supply, in case one side fails.

However, it must be realized that the source of supply for the whole loop system is a single secondary substation. If a fault occur in the secondary substation causing a failure of the 11 kV supply source, the whole of the system will suffer power interruption.

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Ring Main or Network SystemA more reliable system is the ring main system.y g y

Secondary Substation A



CB4 CB511 kV 11 kV

Secondary Substation B

CB7 CB8 CB9 CB10

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Substation 2 Substation 3

CB1CB2

CB3 CB6

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In the ring main system, there are two different sourcesof supply which are indicated as secondary substation Aand Band B.

The ring system has the added advantage from loop system is that should one of the sources of supply fail, say A, the whole system continues to get supply from the other source B.

The ring main system is by far the most reliable for i i f l I i b l l i

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continuity of supply. It gives a better voltage regulationand less feeder losses.

Circuit breakers are used instead of fuses for protecting the transformer in ring main system due to heavier loads.


1.3 Secondary Distribution Lines (Distributors)

Distribution substations are a link between feeders and distributors.

The standard voltage transformation at a distribution substation is 11 kV/415V. The declared consumer voltage as per Malaysian

Distribution Substations

11 kV Feeders 415 V Distributors

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declared consumer voltage as per Malaysian Nasional Grid is 415 V between phases and 240 V between phase and neutral with a permissible voltage variation of 5%.

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A consumer at the near-end of the distribution substation may have a voltage as high as 436 V(3-phase) and 252 V (single-phase) during light load hours whereas a consumer at the far-endmay have a voltage as low as 395 kV (3-phase) and 228 V (single-phase) at peak load hours.

The circuits for the secondary distribution

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system are essentially the same as those for primary distribution except that they are on a smaller scale.



When power is supplied to the consumers through the secondary distribution system, one of the following arrangements is used:1. Radial system2. Looped system3. Network system (Banked secondary system)

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Radial SystemIn this system, the LV distribution lines radiate out from the distribution substation.

I thi t th l i f i l 11 kV f d

11 kV Line220 kVA 11

kV/415V

LV CBRadial Line 1

Radial Line 2

Switch-cum Fuse Units

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In this system, the supply is from a single 11 kV feeder. A fault in the feeder will cause the interruption of supply to all consumers. Circuit breaker and switch-cum fuseunits are used for protection purpose.


1.3 Expanded Radial Scheme

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Looped SystemIn this case, the reliability of supply is better than in the radial system. In the case of fault on one line, the load can be fed from the other by connecting switch S.

11 kV Line220 kVA 11

kV/415V

CBS

415/240 V

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However, a fault in the 11 kV feeder will cause the interruption of supply to all consumers. Circuit breaker and the fuse unit provide a protection for the transformer and line respectively.

415/240 V


Primary Selective Scheme

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Banked Secondary SystemWhen radial secondary circuits are supplied by a single transformer, high starting currents of motors may cause objectionable voltage drops. One of the most effectiveand economical means of controlling such a voltage drop is the banking of distribution transformers.

11 kV Primary Distribution Line

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415/240 V Secondary Distribution Line

T1 T2 T3 Fuse



Transformers are said to be banked when two or more supplied from the same primary circuit are paralleled to feed into the same secondar mainsfeed into the same secondary mains.

By this arrangement more than one path is provided over which high currents can flow. This results in lowering the extent to which the voltage fluctuates on the line.

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Further advantages of this system:i. More reliable, have alternative supply from other transformer.ii. Better load distribution on each transformer.iii. The voltage drop in the system is reduced.

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This system is mostly used in areas of low load densities, where a multiple primary and secondary net ork is not j stifiednetwork is not justified.

If a fault occurs within one of the transformers, it will be automatically disconnected from the line by blowing the two secondary line fuses and the primary transformer fuse without interrupting service to any consumer.

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1.3 Secondary Selective Scheme

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1.3 Sparing Transformer Scheme

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1.4 Load Data

Typical range of Industrial Loads: Light Industry 50 kVA to 7000 kVA Heavy Industry 1,000 kVA to 200,000 kVA

Typical Industrial Loads: HVAC Process equipment, pumps, compressors and fans Industrial services such as boiler, water treatment Workshop and laboratory equipment Motor control centre

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1.4 Initial Maximum Demand Estimation

2 methods to estimate the maximum power demand in feasibility/ conceptual design stage: VA/m2 or W/ ft2 This is normally apply to commercial

building where the typical loads are lighting, general power, and HVAC. Example: 50 100 VA/m2 for non-retail buildings, 60 150 VA/m2 for retail buildings. 0.9 W/ft2 for lighting and 4.7 W/ft2 for Air Condition.

Maximum demand of a similar building/ industry g yApplicable for residential, commercial, and industrial buildings. Example: Plant A having maximum demand of 2 MVA then this figure can be used for a plant of similar capacity.

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1.4 Detailed Load Estimation

Comprehensive load estimate based on actual load information.

Can be calculated either in kVA or amperes. If the output is given in kW, the kVA can be obtained using following formula:

Future load should be considered as given in)( PFkWkVA

Future load should be considered as given in spare circuits for future use.

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1.4 Diversity Factor (DF)

For better load estimation, a proper diversity factor should be considered as not all

Types of load/ circuit Recommended DF

equipment/ load operate simultaneously. Definition of diversity factor:

Typical diversity factor values:Load ConnectedDemand Max.DF

Types of load/ circuit Recommended DFLighting load 100%General purpose power circuit 40% - 50%Main switchboard 80% - 90%Intermittent duty loads 50%

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1.4 Example: Max. Loading for MCC (SB)Load

description3/

1

DutyN or

S

Motorrating(kW)

Ope-ratingmotor power (kW)

PF x = K

Motor input power

Heater 3 load (kVA)

1load

R phase (kVA)

1load

Y phase (kVA)

1load

B phase (kVA)

Cooling tower 1 fan 3 N 15 12 0.7 17.1 17.1

Cooling tower 2 fan 3 S 15 12 0.7 17.1 -

Heater 3 N 5 - - - 5 5

Fan coil 1 N 1.5 1.3 0.6 2.2 2.2

Water pump 3 N 11 9 0.68 13.2 13.2

Extract fan 1 N 1 0.8 0.6 1.3 1.3

Compressor 1 N 1.5 1 0.6 1.6 1.6

Future pump 3 N 5.5 4 0.6 6.7 6.7

Total load 42.0 2.2 1.3 1.6

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Total load on the MCC = 47.1 kVA

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1.4 Example: Max. Loading for LV Switchboard

Load description

Duty (N/ S) Connected (kW)

Operating load (kW)

K kVA

DB 1 - - - - 30

DB 2 - - - - 78

MCC 1 - - - - 47.1

MCC 2 - - - - 50

Packaging machine - 37 31 0.7 44.3

CO2compressor N 75 68 0.765 88.9

W t 1Water pump 1 N 30 25 0.68 36.8

Water pump 2 S 30 25 0.68 -

Welder N 18 - 0.5 36

Future 50

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Total load on LV Switchboard = 461.1 kVA


1.4 Old Supply Schemes for various M.D

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1.4 New Supply Schemes for various M.D

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1.4 In-Class Practise (1)

A small industrial plant has the following loads: Twenty (20), 200HP motors (only half of them are

running at any given time). Ten (10), 50 HP motors (8 motors are running at the

same time). 500 kW of heating and process loads. Two (2), 50 kVA lighting transformers, and

100 HP of small (mostly fractional HP) motors 100 HP of small (mostly fractional HP) motors.

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TASKSDecide the proper supply voltage (from local utility)

TASKSDecide the proper supply voltage (from local utility)

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1.5 Common Connection for Transformer

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1.5 Why Delta Grounded Star

Delta at primary Free of 3rd harmonics of the magnetizing currents and

any possible homopolar current are free to circulatethrough the sides of the delta, without flowing into thenetwork; thus, the magnetic fluxes remain sinusoidalat the secondary.

In case of unbalanced loads at the secondarywinding, the reaction current absorbed by the primaryflows only through the corresponding winding (asshown in the figure) without affecting the other two.

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1.5 Why Delta Grounded Star

Grounded Star at secondary To make line and phase voltages easily available. For safety reasons, since, in the event of a fault

between the MV and LV sides, the voltage at thesecondary remains close to the phase value, thusguaranteeing higher safety for people and maintainingthe insulation.

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1.5 Basic Installation of Industrial Plant

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1.5 Methods of Transformer Installation

Method 1 Substation with a single transformer

In the case where the protection device also carries out switching and isolation functions, an interlock must be provided which allows access to the transformer only when the power supply line of the substation has been

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substation has been isolated.

Installation of the SMV switching and isolation device positioned immediately to the supply side of the transformer.



Method 2 Substation with two transformerswith one as a spare for the other

The circuit-breakers on the LV side must be connected with an I interlock whose function is to prevent the transformers from operating in parallel.

Apart from the switching and isolation device on the i i MV li (I ) it i

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incoming MV line (IGMV), it is advisable to provide a switching, isolation and protection device on the individual MV risers of the two transformers (IMV1 and IMV2) as well.

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Method 3 Substation with two transformerswhich operate in parallel on the same busbar

Possible to use two transformers with lower rated power.

Operation in parallel of the transformers could cause greater problems in management of the network

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network. When coordinating the

protections, the fact that the overcurrent on the LV side is divided between the two transformers must be taken into consideration.



Method 4 Substation with two transformerswhich operate simultaneously on two separatehalf-busbars

Providing a CLV bus-tie and an I interlock which prevents the bus-tie from being closed when both the incoming circuit-breakers from the transformer are closed

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transformer are closed. This management

method allows a lower value of the short-circuit current on the busbar.

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1.5 In-Class Practise (2)

Refer again the problem given in In-Class Practise (1).

TASKDesign a simple power system (one-line diagram)

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Transformer sizing is generally based on: Total max. demand of individual/group consumer Installed voltage level (kV) Method of installation or arrangement Short circuit capacity

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1.5 In-Class Practise (3):Transformer Sizing

Lets calculate voltage drop in transformer 1000KVA, 11/0.480 kV, impedance 5.75% due to startingof 300 kW 460V 0 8 po er factor motor code Dof 300 kW, 460V, 0.8 power factor, motor code D(kVA/HP). Motor starts 2 times per hour and theallowable voltage drop at transformer secondary terminalis 10%. Is the transformer size suitable?

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Code Letter (KVA per HP) -Locked Rotor CurrentMotor Code Min Max

A 3.15 -B 3.16 3.55C 3 56 4C 3.56 4D 4.1 4.5E 4.6 5F 5.1 5.6G 5.7 6.3H 6.4 7.1J 7.2 8K 8.1 9L 9.1 10M 10.1 11.2

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M 10.1 11.2N 11.3 12.5P 12.6 14R 14.1 16S 16.1 18T 18.1 20U 20.1 22.4V 22.5 -

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If the previous motor load is changed to the following:

Total KW of Three Phase Motors: 300 kWTotal KW of Single Phase Motors: 10 kWVolt (L-L) : 460 VoltPower Factor: 0.8Locked Rotor Current: 450% (Max)

Analyse again the suitability of the transformer sizeused.

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Short circuit capacity with infinite source

FLA = ?What is %Z?ISCmax = ?kVASC = ?

1000 kVA11kV 415 V

Infinite source

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kVASC ?%Z = 5%kVASC = ?

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Short circuit capacity with finite source

MVASC(TX) = ?MVASC(SEC) = ?ISCmax = ?

1000 kVA11kV 415 V

500 MVASC

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%Z = 5%kVASC = ?



Simple transformer-load connection

1000 kVA11kV 415 V%Z = 5.0%kVASC = ?

FLA = ?ISCmax = ?kVASC = ?

Is the given size (1000 kVA) suitable to serve

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M 80% Full loadInrush current = 6 times

)the motor load?

Topic 1 Plant Planning and Power Demand

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