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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
2
1.4 Power Demand and Load Estimation
1.5 Transformer Sizing
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BEF 44903 Industrial Power Systems Chapter 1
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
3
BEF 44903 Industrial Power Systems Chapter 1
1.1 Example of Plant Distribution System
4
PanelboardFeeding
240/415V
Harmonic Loads
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BEF 44903 Industrial Power Systems Chapter 1
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
5
necessary.
BEF 44903 Industrial Power Systems Chapter 1
1.1 Planning Distribution Systems
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.
6
, , ,
etc.
9 The type of industry and numberof industries possible in the
area.
9 Development programmes implemented in the area.
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BEF 44903 Industrial Power Systems Chapter 1
1.1 Planning Distribution Systems
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)
7
d. Municipal consumers (i.e. street lighting, water works, parks, etc.)e. Agricultural consumers
f. Mining industries
BEF 44903 Industrial Power Systems Chapter 1
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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BEF 44903 Industrial Power Systems Chapter 1
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
9
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.
BEF 44903 Industrial Power Systems Chapter 1
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)
10
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BEF 44903 Industrial Power Systems Chapter 1
1.1 Planning for Connection
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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BEF 44903 Industrial Power Systems Chapter 1
1.1 Planning for Connection
} 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.
12
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BEF 44903 Industrial Power Systems Chapter 1
1.1 Planning for Connection
} 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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BEF 44903 Industrial Power Systems Chapter 1
1.2 Voltage and Frequency Considerations
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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BEF 44903 Industrial Power Systems Chapter 1
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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BEF 44903 Industrial Power Systems Chapter 1
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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BEF 44903 Industrial Power Systems Chapter 1
1.2 Voltage and Frequency Considerations
Frequency Criteria
} The supply frequency is 50 Hz 1%
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BEF 44903 Industrial Power Systems Chapter 1
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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BEF 44903 Industrial Power Systems Chapter 1
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
19
. , -transmission line. The number of primary distribution
lines emanating from a 66/11 kV secondary substation is
six to ten.
BEF 44903 Industrial Power Systems Chapter 1
1.3 Primary Distribution Lines (Feeders)
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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BEF 44903 Industrial Power Systems Chapter 1
1.3 Primary Distribution Lines (Feeders)
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
21
Secondary
Substation
Circuit 3 for Rural Areas
BEF 44903 Industrial Power Systems Chapter 1
1.3 Primary Distribution Lines (Feeders)
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
-
22
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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BEF 44903 Industrial Power Systems Chapter 1
1.3 Primary Distribution Lines (Feeders)
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
23
Distribution
Substation 1
CB1CB2
CB3 CB6
A
BEF 44903 Industrial Power Systems Chapter 1
1.3 Primary Distribution Lines (Feeders)
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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BEF 44903 Industrial Power Systems Chapter 1
1.3 Primary Distribution Lines (Feeders)
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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BEF 44903 Industrial Power Systems Chapter 1
1.3 Primary Distribution Lines (Feeders)
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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BEF 44903 Industrial Power Systems Chapter 1
1.3 Primary Distribution Lines (Feeders)
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
27
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.
BEF 44903 Industrial Power Systems Chapter 1
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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BEF 44903 Industrial Power Systems Chapter 1
1.3 Secondary Distribution Lines (Distributors)
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
29
system are essentially the same as those forprimary distribution except that they are on a
smaller scale.
BEF 44903 Industrial Power Systems Chapter 1
1.3 Secondary Distribution Lines (Distributors)
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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BEF 44903 Industrial Power Systems Chapter 1
1.3 Secondary Distribution Lines (Distributors)
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.
BEF 44903 Industrial Power Systems Chapter 1
1.3 Expanded Radial Scheme
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BEF 44903 Industrial Power Systems Chapter 1
1.3 Secondary Distribution Lines (Distributors)
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
33
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
BEF 44903 Industrial Power Systems Chapter 1
Primary Selective Scheme
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BEF 44903 Industrial Power Systems Chapter 1
1.3 Secondary Distribution Lines (Distributors)
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
35
415/240 V Secondary Distribution Line
T1 T2 T3 Fuse
BEF 44903 Industrial Power Systems Chapter 1
1.3 Secondary Distribution Lines (Distributors)
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.
36
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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BEF 44903 Industrial Power Systems Chapter 1
1.3 Secondary Distribution Lines (Distributors)
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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BEF 44903 Industrial Power Systems Chapter 1
1.3 Secondary Selective Scheme
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BEF 44903 Industrial Power Systems Chapter 1
1.3 Sparing Transformer Scheme
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BEF 44903 Industrial Power Systems Chapter 1
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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BEF 44903 Industrial Power Systems Chapter 1
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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BEF 44903 Industrial Power Systems Chapter 1
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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BEF 44903 Industrial Power Systems Chapter 1
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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BEF 44903 Industrial Power Systems Chapter 1
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
44
Total load on the MCC = 47.1 kVA
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BEF 44903 Industrial Power Systems Chapter 1
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
45
Total load on LV Switchboard = 461.1 kVA
BEF 44903 Industrial Power Systems Chapter 1
1.4 Old Supply Schemes for various M.D
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BEF 44903 Industrial Power Systems Chapter 1
1.4 New Supply Schemes for various M.D
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BEF 44903 Industrial Power Systems Chapter 1
1.5 Common Connection for Transformer
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BEF 44903 Industrial Power Systems Chapter 1
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.
49
BEF 44903 Industrial Power Systems Chapter 1
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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BEF 44903 Industrial Power Systems Chapter 1
1.5 Basic Installation of Industrial Plant
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BEF 44903 Industrial Power Systems Chapter 1
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
52
isolated.
Installation of the SMVswitching and isolationdevice positionedimmediately to the supplyside of the transformer.
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BEF 44903 Industrial Power Systems Chapter 1
1.5 Methods of Transformer Installation
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
53
ncom ng ne GMV , sadvisable to provide aswitching, isolation andprotection device on theindividual MV risers of thetwo transformers (IMV1 andIMV2) as well.
BEF 44903 Industrial Power Systems Chapter 1
1.5 Methods of Transformer Installation
MethodMethod 33 Substation with two transformers
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
54
.
When coordinating theprotections, the fact thatthe overcurrent on the LVside is divided between thetwo transformers must betaken into consideration.
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BEF 44903 Industrial Power Systems Chapter 1
1.5 Methods of Transformer Installation
MethodMethod 44 Substation with two transformers
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
55
.
This managementmethod allows a lowervalue of the short-circuitcurrent on the busbar.
BEF 44903 Industrial Power Systems Chapter 1
1.5 Transformer Sizing
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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BEF 44903 Industrial Power Systems Chapter 1
1.5 Transformer Sizing
Short circuit capacity with infinite source
What is %Z?
ISCmax = ?
kVASC = ?
1000 kVA
11kV 415 V
Infinite source
57
%Z = 5%kVASC = ?
BEF 44903 Industrial Power Systems Chapter 1
1.5 Transformer Sizing
Short circuit capacity with finite source
SC(TX)
MVASC(SEC) = ?
ISCmax = ?
1000 kVA
11kV 415 V
500 MVASC
58
%Z = 5%
kVASC = ?
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BEF 44903 Industrial Power Systems Chapter 1
1.5 Transformer Sizing
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?
59
M 80% Full loadInrush current = 6 times
Recommended