chapter 1 plant planning and power demand.pdf

7/28/2019 Chapter 1 PLANT PLANNING AND POWER DEMAND.pdf

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BEF 44903 Chapter 1

BEF 44903 Industrial Power Systems Chapter 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 System

13.8 kV 15.6 kV

Distribution System

11 kV 66 kV

Transmission System

132 kV 500 kV

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1.1 Example of Plant Distribution System

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PanelboardFeeding

240/415V

Harmonic Loads


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1.1 Planning Distribution Systems

A distribution system deals with the distribution

ofelectrical 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

w v y . w

basic data should be collected for starting this work:

9A detailed map of the area showing important features.

9 The existing numberof houses, population and new construction

anticipated in the area.

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, , ,

etc.

9 The type of industry and numberof industries possible in the

area.

9 Development programmes implemented in the area.


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For the purpose offorecasting load, the prospective

consumers may be categorized as under:

. omest c consumers, .e. res ent a ouses.

2. Commercial consumers, i.e. shops, schools, hospitals, hotels,

and other commercial establishments.

3. Industrial consumers:

a. Small industries (up to 20 kW)

b. Medium industries (up to 100 kW)

c. Large industries (above 100 kW)

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

f. Mining industries


1.1 Layout of Distribution Systems

Sub-transmission Line

132kV/66kV 66kV/11kV

11kV Feeder

11kV/415V

3 PhaseConsumers

(415V)

Single Phase

Secondary

Substation

Distribution

SubstationPrimary

Substation

(66kV or 33kV)

8

ee er

Industrial

Consumer

(240V)


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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.

,carried through sub-transmission lines to different loadcentres. The length of a sub-transmission line is about 50km 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 interms oflosses (i.e. I2R) and the capital cost (i.e. cost of

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

consumers receive power at low voltage, i.e. 240V or415V. Large-scale consumers having load in excess of100 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

(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

} Forall typesall types of loads:

Maximum Active Power consumption in kW;

Maximum Reactive Power consumption in kVAR.

} Formotor loadsmotor loads:

Types of control equipment;

Methods of startin

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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} Fornonlinear loadsnonlinear loads with harmonic current injections:

Harmonic current spectrum including harmonic number and

.

} Forfluctuating loadsfluctuating 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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} Forvoltage sensitive loadsvoltage sensitive loads:

steady-state voltage tolerance limits of the equipment in

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.

} ForShunt Connected Reactors and CapacitorsShunt Connected Reactors and Capacitors:

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):

-

Voltage level % variation

415V and 240V -10% & +5%

6.6kV, 11 kV, 22kV,33kV +/- 5%132kV and 275kV -5% & +10

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Voltage level % variation

415V 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:. ccor ng o na ure o cons ruc on

a. Overhead distribution system (cheaper)

b. Underground distribution system (in crowded area)

2. According to nature of currenta. DC distribution system

b. AC distribution system

3. According to number of wires

- - - -

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, , ,

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

y y u y

load of1-2 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

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. , -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 circuit

2. The loop primary circuit

3. The ring main system (or primary network)

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Radial Primary Circuits

When 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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Secondary

Substation

Circuit 3 for Rural Areas



Advantages of Radial Feeders:

i. A heavy load very near the secondary substation.

. so ate oa s.

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

-

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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 Circuits

To overcome the limitations of the radial feeders, the

loop primary circuit is taken to use.

Secondary

Substation

Distribution Distribution

CB4 CB5

11 kV 11 kV

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Distribution

Substation 1

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 atdistribution 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

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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

v u y, .

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 System

A more reliable s stem is the rin main s stem.

SecondarySubstation A

Distribution Distribution

CB4 CB5

11 kV 11 kV

SecondarySubstation B

CB7 CB8 CB9 CB10

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Distribution

Substation 1

CB1CB2

CB3 CB6


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In the ring main system, there are two different sources

of supply which are indicated as secondary substationA

.

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

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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 transformerin 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 volta e as er Mala sian

Distribution

Substations11 kV Feeders 415 V Distributors

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Nasional Grid is 415 V between phases and 240

V between phase and neutral with a permissible

voltage variation of5%.


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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-end

may 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 forprimary 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 system

2. Looped system3. Network system (Banked secondary system)

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Radial System

In this system, the LV distribution lines radiate out from

the distribution substation.

11 kV Line220 kVA 11

kV/415V

LV CBRadial Line 1

Radial Line 2

Switch-cum

Fuse Units

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n s sys em, e supp y s rom a s n g e ee er.A fault in the feeder will cause the interruption of supply

to all consumers. Circuit breakerand switch-cum fuse

units are used for protection purpose.


1.3 Expanded Radial Scheme

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Looped System

In 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

CB

S

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 System

When radial secondary circuits are supplied by a single

transformer, high starting currents of motors may cause

objectionable voltage drops. One of the most effective

and 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

y .

By this arrangement more than one path is providedover 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 oflow load

densities, where a multiple primary and secondary

w u .

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 buildin / industr

Applicable for residential, commercial, and industrialbuildings. 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 iven in

)( = PFkWkVA

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

equipment/ load operate simultaneously.

Definition of diversity factor:

Typical diversity factor values:

LoadConnectedDemandMax.DF =

Lighting 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

description

3

/

1

Duty

N or

S

Motor

rating

(kW)

Ope-

rating

motor

power

(kW)

PF x

= K

Motor

input

power

Heater 3

load

(kVA)

1

load

R

phase

(kVA)

1

load

Y

phase

(kVA)

1

load

B

phase

(kVA)

Cooling

tower 1 fan3 N 15 12 0.7 17.1 17.1

Cooling

tower 2 fan3 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 l oad 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

Du ty (N/ S) Connec ted

(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

ater pumpN 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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1.5 Common Connection for Transformer

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1.5 Why Delta Grounded Star

Delta at pr imaryDelta at pr imary

} Free of 3rd harmonics of the magnetizing currents and

any possible homopolar current are free to circulate

through the sides of the delta, without flowing into the

network; thus, the magnetic fluxes remain sinusoidal

at the secondary.

} in case of unbalanced loads at the secondary

winding, the reaction current absorbed by the primary

flows only through the corresponding winding (asshown in the figure) without affecting the other two.

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1.5 Why Delta Grounded Star

GroundedGrounded StarStar atat secondarysecondary

} 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 the

secondary remains close to the phase value, thusguaranteeing higher safety for people and maintaining

the insulation.

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1.5 Basic Installation of Industrial Plant

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1.5 Methods of Transformer Installation

MethodMethod 11 Substation with a single transformer

In the case where theprotection device alsocarries out switching and

isolation functions, aninterlock must be providedwhich allows access to thetransformer only when thepower supply line of the

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isolated.

Installation of the SMVswitching and isolationdevice positionedimmediately to the supplyside of the transformer.


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MethodMethod 22 Substation with two transformers

with one as a spare for the other

The circuit-breakers on theLV side must be connectedwith an I interlock whosefunction is to prevent thetransformers from operatingin parallel.

Apart from the switching andisolation device on the

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ncom ng ne GMV , sadvisable to provide aswitching, isolation andprotection device on theindividual MV risers of thetwo transformers (IMV1 andIMV2) as well.




which operate in parallel on the same busbar

Possible to use twotransformers with lowerrated power.

Operation in parallel of thetransformers could causegreater problems inmanagement of the

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.

When coordinating theprotections, the fact thatthe overcurrent on the LVside is divided between thetwo transformers must betaken into consideration.


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which operate simultaneously on two separate

half-busbars

Providing a CLV bus-tieand an I interlockwhich prevents the bus-tie from being closedwhen both the incomingcircuit-breakers from the

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.

This managementmethod allows a lowervalue of the short-circuitcurrent on the busbar.



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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Short circuit capacity with infinite source

What is %Z?

ISCmax = ?

kVASC = ?

1000 kVA

11kV 415 V

Infinite source

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%Z = 5%kVASC = ?



Short circuit capacity with finite source

SC(TX)

MVASC(SEC) = ?

ISCmax = ?

1000 kVA

11kV 415 V

500 MVASC

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%Z = 5%

kVASC = ?


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Simple transformer-load connection

1000 kVA

11kV 415 V

%Z = 5.0%

kVASC = ?

ISCmax = ?

kVASC = ?

Is the given size (1000kVA) suitable to servethe motor load?

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M 80% Full loadInrush current = 6 times

chapter 1 plant planning and power demand.pdf

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