industrial power systems topic 1

PLANT PLANNING

AND

POWER DEMAND

Industrial Power Systems

Topic 1

BEF 44903

BEF 44903 – Industrial Power Systems – Topic 1

2

Outlines

1.1 Plant Distribution Systems

1.2 Voltage and Frequency Considerations

1.3 Types of Plant Distribution Networks

1.4 Power Demand and Load Estimation

1.5 Transformer Sizing


3

1.1 Overview of Electric Power Systems

Distribution System

11 kV – 66 kV

Transmission System

132 kV – 500 kV

Generation System

13.8 kV – 15.6 kV


1.1 Example of Plant Distribution System

4

Panelboard Feeding

240/415V

Harmonic Loads


1.1 Planning Distribution Systems

Power system concept:

– Analysis

– Selection of the network

configuration

– 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

5

Power system planning



6

Source: Siemens



An optimum network configuration should

particularly meet the following requirements:

7

1

Simple structure

2

High reliability of supply

3

Low losses

4

Favorable and flexible expansion

options



8


9


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 necessary.


10


For the purpose of forecasting load, the prospective consumers may be categorised as follows:

• Domestic consumers, i.e. residential houses.

• Commercial consumers, i.e. shops, schools, hospitals, hotels, and other commercial establishments.

• Industrial consumers:

• Small industries

• Medium industries

• Large industries

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

• Agricultural consumers

• Mining industries


11

1.1 Layout of Distribution Systems

132kV/66kV 66kV/11kV

11kV Feeder

11kV Feeder

11kV/415V

Industrial

Consumer

3 Phase

Consumers

(415V)

Single Phase

Consumers

(240V)

Secondary

Substation

Distribution

SubstationPrimary

Substation

66kV Feeder

Sub-transmission Line

(66kV or 33kV)


12

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 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 conductor, insulators and supports).

Most domestic, commercial and small-scale industrialconsumers 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:

(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)

13



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;

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.

14



For nonlinear loads with harmonic current injections:

Harmonic current spectrum including harmonic number and

the 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.

15



For voltage sensitive loads:

steady-state voltage tolerance limits of the equipment in

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:

configuration and sizes of individual banks;

types of switching and control equipment; and

types of harmonic filtering reactors.

16


1.2 World Voltage and Frequencies Standards

17


1.2 IEC Voltage Standards (IEC 60038 Edition 7.0 2009-06)

18



Voltage Criteria

Steady-State Voltage Fluctuation (Normal Condition):

Steady-State Voltage Fluctuation (Contingency Condition)

19

Voltage level % variation

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

6.6 kV, 11 kV, 22 kV,33 kV +/- 5%

132 kV and 275 kV -5% & +10

Voltage level % variation

415 V and 240 V +/- 10%

6.6 kV, 11 kV, 22 kV,33 kV +10 & -10%

132 kV and 275 kV +/- 10%


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

20


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, 22 kV or 33 kV for load of

5,000 kVA maximum demand and above

Three-phase, three-wire, 66 kV, 132 kV and 275 kV

for exceptionally large load of above 25 MVA

maximum demand

21



Frequency Criteria

The variation of the supply frequency is 50 Hz ± 1%

(European Standard) and 60 Hz ± 1% (US Standard)

22


23

1.3 Classification of Distribution Systems

The distribution systems may be classified in

the following ways:1. According to nature of construction

a. Overhead distribution system (cheaper)

b. Underground distribution system (in crowded area)

2. According to nature of current

a. DC distribution system

b. AC distribution system

3. According to number of wires

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


24

1.3 Primary Distribution Lines (Feeders)

The 33/11 kV secondary substation is established where

the load requirement is approximately 5 MVA. Since

normally 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-

transmission line. The number of primary distribution

lines emanating from a 66/11 kV secondary substation is

six to ten.


25


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)


26


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.

Secondary

Substation

Factory having load

of 1 MW at 11 kV

Circuit 1 for Factory

Circuit 2 feeding Substation in the city

Circuit 3 for Rural Areas


27


Advantages of Radial Feeders:

i. A heavy load very near the secondary substation.

ii. 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

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.


28


Loop Primary Circuits

To overcome the limitations of the radial feeders, the

loop primary circuit is taken to use.

Secondary

Substation

Distribution

Substation 1

Distribution

Substation 2

Distribution

Substation 3

CB1CB2

CB3

CB4

CB6

CB5

A

11 kV 11 kV


29


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

uninterrupted and continues to be received from another

side.

This system is generally used in towns and cities.


30


The reliability of supply in this system has improved in

comparison with that in the radial system as it has an

alternative supply, in case one side fails.

However, it must be realised 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.


31


Ring Main or Network System

A more reliable system is the ring main system.

Secondary

Substation A

Distribution

Substation 1

Distribution

Substation 2

Distribution

Substation 3

CB1CB2

CB3

CB4

CB6

CB5

11 kV 11 kV

Secondary

Substation B

CB7 CB8 CB9 CB10


32


In the ring main system, there are two different sources

of supply which are indicated as secondary substation A

and 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

continuity of supply. It gives a better voltage regulation

and less feeder losses.

Circuit breakers are used instead of fuses for protecting

the transformer in ring main system due to heavier loads.


33

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

Nasional Grid is 415 V between phases and 240

V between phase and neutral with a permissible

voltage variation of 5%.

Distribution

Substations11 kV Feeders 415 V Distributors


34


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

system are essentially the same as those for

primary distribution except that they are on a

smaller scale.


35


When power is supplied to the consumers

through the secondary distribution system, one

of the following arrangements is used:

1. Radial system

2. Looped system

3. Network system (Banked secondary system)


36


Radial System

In this system, the LV distribution lines radiate out from

the distribution substation.

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 fuse

units are used for protection purpose.

11 kV Line220 kVA 11

kV/415V

LV CBRadial Line 1

Radial Line 2

Switch-cum

Fuse Units


1.3 Expanded Radial Scheme

37


38


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.

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.

11 kV Line220 kVA 11

kV/415V

CB

S

415/240 V

415/240 V


Primary Selective Scheme

39


40


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

415/240 V Secondary Distribution Line

T1 T2 T3 Fuse


41


Transformers are said to be banked when two or more

supplied from the same primary circuit are paralleled to

feed 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.

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.


42


This system is mostly used in areas of low load

densities, where a multiple primary and secondary

network 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.


1.3 Secondary Selective Scheme

43


1.3 Sparing Transformer Scheme

44


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

45


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 –

Applicable 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.

46


1.4 Initial Maximum Demand Estimation

When some or all of the load characteristics are

not known, the values shown below may be

used to give a very approximate estimate of VA

demands (Electrical Installation Guide 2016 – Schneider).

47


1.4 Detailed Load Estimation

It 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

spare circuits for future use.

For better load estimation, a proper utilisation

factor (ku) and diversity factor (ks) should be

considered as not all equipment/ load operate

simultaneously.

48

)( PFkWkVA


1.4 Utilisation Factor (ku)

In normal operating conditions, the power

consumption of a load is sometimes less than

that indicated as its nominal power rating, a fairly

common occurrence that justifies the application

of an utilisation factor (ku) in the estimation of

realistic values.

This factor must be applied to each individual

load, with particular attention to electric motors,

which are very rarely operated at full load.

In an industrial installation this factor may be

estimated on an average at 0.75 for motors.

49


1.4 Diversity Factor (ks)

Definition of diversity factor (IEC defined as coincidence factor)

Typical diversity factor values:

50

Load ConnectedDemand Max.k s

Types of load/ circuit Recommended DF

Lighting load 100%

General purpose power circuit (SSO) 40% - 50% (for industrial installation)

Main switchboard 80% - 90%

Intermittent duty loads ≤ 50%


1.4 Example: Max. Loading for MCC (SB)

Load

description

3ø

/

1ø

Duty

N or

S

Motor

rating

(kW)

Ope-

rating

motor

power

(kW)

PF x η

= K

Motor

input

power

Heater 3ø

load

(kVA)

1ø

load –

R

phase

(kVA)

1ø

load –

Y

phase

(kVA)

1ø

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 load 42.0 2.2 1.3 1.6

51

Total load on the MCC = 47.1 kVA


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

CO2

compressorN 75 68 0.765 88.9

Water 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

52

Total load on LV Switchboard = 461.1 kVA



Rated Diversity Factor for distribution

switchboards: the assumed loading of the

outgoing circuits of the assembly or group of

outgoing circuits may be based on the values:

53



Diversity factor according to circuit function:

54


1.4 Example of application of factors ku and ks

55


1.4 Old Supply Schemes for various M.D

56


1.4 New Supply Schemes for various M.D

57


1.5 Common Connection for Transformer

58


1.5 Why Delta – Grounded Star

Delta at primary

Free of 3rd harmonics of the magnetising 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 (as

shown in the figure) without affecting the other two.

59


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 the

secondary remains close to the phase value, thus

guaranteeing higher safety for people and maintaining

the insulation.

60


1.5 Basic Installation of Industrial Plant

61


1.5 Methods of Transformer Installation

Method 1 – Substation with a single transformer

62

• 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 isolated.

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



Method 2 – Substation with two transformers

with one as a spare for the other

63

• 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 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.




which operate in parallel on the same busbar

64

• Possible to use two transformers with lower rated power.

• Operation in parallel of the transformers could cause greater problems in management of the 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.




which operate simultaneously on two separate

half-busbars

65

• 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.

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


1.5 Transformer Sizing

• Total max. demand of individual/ group consumer

• Installed voltage level (kV)

• Method of installation or arrangement

• Short circuit capacity

Transformer sizing is generally based on:

• Voltage drop at secondary (TR) must less than 10%

• Motor full load current ≤ 65% of transformer full load current

• If motor start more than once/ hour, transformer size should be increased additional 20%

Criteria to be met:

66

industrial power systems topic 1

Documents