capacitors

Low Voltage CapacitorsLow Voltage Capacitors

2

LV Capacitors Training

Product:

Varplus, Varlogic, Functional Plates...

Application

Power, Compensation, Harmonics...

To introduce the concept of power and power factor correction

To present the Schneider offer

4

Power - Definitions

Power Factor

Compensation and power factor correction

Compensation techniques

Sizing a capacitor bank

Harmonics

5

Real power is the power dissipated in the resistance of a circuit. This component of power produces useful mechanical work and heat

Reactive power is the power used to energise the inductive elements of a circuit (eg. Motors). This component of power does not produce any useful work

6

There are three types of Power: Real power P (kW)

Reactive power Q (kVAr)

Apparent power S (kVA)

Real + Reactive = Apparent

P

SQ

7

The apparent power consumed by a system is given by

S = apparent power S = U x I U = rms voltage I = rms current

Real power is given by P = U Icos

= S cos

Reactive power is given by Q = U Isin

= S sin

= VA= kVA

= W= kW

= VAr= kVAr

8

The electrical efficiency of the installation is measured by the power factor:

PF =

P

SQ

active power apparent power = = cos

P (kW) S (kVA)

The apparent power (S) is greater (for a given value of P) as cos is smaller. This is why some electricity supply authorities penalise by

- imposing a kVA demand charge

or

- low power factor charge

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S cos P

Apparent power

Power factor

Real power

The real power is directly proportional to the apparent power.

Ideally, the target power factor is

10

Low power factor is caused by a high demand in reactive power from such equipment as:

Fluorescent and gas discharge lights

Transformers and motors

Arc furnaces

Low power factor results in:

Increased kVA and increased costs

Increased current, voltage drops and losses

Reduced efficiency

11

To compensate for a low power factor, and to maintain the real power P for the load, more reactive power is required in the user network

user networkuser network

loadload

active energy reactive energy

power supply authority


12

This extra reactive power can be provided by the power supply authority


loadload




Disadvantage:

Ongoing penalty costs incurred from power supply authority

13

Or it can be provided by a bank of capacitors


loadload




capacitor bank

capacitor bank

Advantage

One off cost, pays for itself in the long run

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S cos P

Apparent power

Power factor

Real power

Capacitor bank

This is the principle of power factor correction:

using a capacitor bank to provide reactive power which increases the power factor of the network.

15

Q2(kVAr)

By installing capacitors (Pc), the kVA (S2) taken from the supply authority is reduced (for the same amount of kW) as shown:

P(kW)

S1Q1(kVAr)

1

2

S2

Pc

16

Global: Connection on the main busbar

M M MM

Comments

reduces kVA demand on transformer

all downstream cables still carry reactive current

17

By SectorConnection on the busbars of local distribution board

M M MM

Comments

reactive current still present in downstream cables

size and losses of cables to DB reduced

18

Individual Connection directly upstream of individual circuits

M M MM

Comments

upstream cables carry less current & kW (due to reduced losses)

significant reactive current eliminated

self excitation

20

using tables

doing your own calculations

using the Schneider Selection guide

using the guide for fixed compensation at motor

21

Say we had a 200kW installation running at a power factor of 0.67. We want to increase the power factor to 0.91. How do we calculate the size of the capacitor bank required?

Using tables

22

For P=200kW, Q= 0.652 x 200 = 130.4kVAr

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From Calculations

To achieve a power factor of 0.91 from 0.67, we will require to multiply the real power consumed by a coefficient given by

(tan1- tan 2) tan1 = 1.108tan 2= 0.455(tan1- tan 2) = 1.108 - 0.455

For P=200kW, Q= 0.653 x 200

= 0.653

= 130.6kVAr

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Using the Schneider Selection Guide

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Fixed compensation for direct connection to motors

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M

Qc

Risk of self excitation

To avoid self excitation, Use the following formula:

Qc 0.9 x I0 x Un 3

I0 is the no load current

Un is the 3-ph supply voltage


27

M Qc

No risk of self excitation

Capacitor connected in parallel with separate switchgear


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What are harmonics

Harmonic distortion

Effects of harmonics

Solutions

29

Any periodic signal having a certain frequency f, can be represented as the sum of

a sinusoidal signal of the same frequency f - fundamental

and

sinusoidal components with frequencies which are multiples of the fundamental (2f, 3f, 4f…) - harmonics

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-1.5

-1

-0.5

0

0.5

1

1.5

Fundamental-1.5

-1

-0.5

0

0.5

1

1.5

Harmonic-1.5

-1

-0.5

0

0.5

1

1.5

Resulting waveform

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Harmonics occur in the presence of non--linear loads.

U

I

U

I

Linear Non linear

Current waveshape is same as voltage - linear

Current waveshape different from voltage - non- linear

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Harmonic generators include:

variable-speed drivesthyristor controlled equipmentstatic converters (UPS)arc furnaceswelding machinesfluorescent lightingsaturated reactors (transformers)

33

HV

~=

~=

M

TransformerHV / LVIharmonics

Harmonic generators

34

Identifying the level of harmonic pollution in a network.

THD : Total Harmonic Distortion

Ratio between the rms value of the harmonic voltages and the fundamental

%100...

21

224

23

22 x

v

vvvvTHD n

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Capacitors do not generate harmonics. They only amplify them.

The impedance of capacitors decreases as frequency increases

Therefore, at higher frequencies, the capacitors draw a lot more current.

f (Hz)0

Z

zC C f

1 1

2 zC C f

1 1

2

36

With capacitors in the network, resonance may occur.

f (Hz)0

Z

zC C f

1 1

2 zC C f

1 1

2

If the natural frequency of the capacitor + network is close to a harmonic frequency, that harmonic current will be considerably amplified.

37

The increase in current will cause

Capacitors to overheat

Additional losses to appear throughout network

Cables and equipment to overheat

Harmonic voltages can affect electronic equipment

Interference on communication and control circuits

38

z

f (Hz)

Network + caps

Network + caps + reactors

fr

Manipulate the resonant frequency so that it is far from a harmonic frequency

What is the solution to harmonics?

Network alone

39

Two solutions :

Use detuning reactors in series with the capacitors to

Design a passive filter suited to the polluted network. In principle, a filter is installed for each harmonic to be absorbed.

LCf r 2

1

protect them.

Where L is the inductance of the reactor

40

To determine the best solution, use the following table (for transformer power Sn 2MVA):

Gh 0.15 Sn 0.15 Sn Gh 0.25 Sn Gh > 0.60 Sn

Use standard capacitors Use 470V capacitors

Use 470V capacitors &

anti harmonic reactors

Where Gh is the sum of the kVA rating of the harmonic generators on the network.

0.25 Sn Gh 0.60 Sn

required

Harmonic filter

41

Or, as a rough rule of thumb:

if THD(voltage) < 3% , use 470V capacitors

if THD(voltage) 3% - 8%, use detuning reactors + 470V rated capacitors

if THD(voltage) > 8%, passive filters are required

42

HV

~=

~=

M


Connect detuning reactors in series with capacitors

Effect of harmonic currents on capacitors reduced

43

Filters :

filters are used when it is necessary to reduce the harmonic distortion rate

passive filters are made up of an LC branch with a frequency of tuned to the frequency of the

voltage harmonic to be eliminated

in principle, a filter is installed for each harmonic to be eliminated

the filter presents a low impedance at frequency fr and absorbs nearly all of this current

LCf r 2

1

44

5 7

HV

~=

~=

M


Connect detuning reactors in series with capacitors

Harmonic currents absorbed by filters

Harmonic filters

45

Capacitor banks also need to be designed to block high frequency signals transmitted by the supply authorities for load control.

Most common frequencies are

750Hz

1050Hz

To prevent the capacitors from ‘absorbing’ the signal, a blocking circuit is required.

46

Rejector coils are the most common method. They are connected in parallel with capacitors, as shown, to create a parallel resonant circuit at signal frequency.

L

L

L

C

C

CCC

C

47

Summary

A network with harmonics has distorted waveforms

Capacitors amplify harmonics

Reactors are used to alter the impedance of capacitor banks

Use rejector coils for signal frequencies

Use detuning reactors for polluted networks

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Varplus Capacitors

Functional Plates

Varlogic Control Relays

CAPS

49

Main characteristics:Main characteristics:

• 5 to 100kVAr - 230V to 690V5 to 100kVAr - 230V to 690V• Self HealingSelf Healing• Safety - EACH element fitted with 2 part Safety - EACH element fitted with 2 part

protection. Double insulationprotection. Double insulation• Tamper proof discharge resistors fitted to Tamper proof discharge resistors fitted to

each elementeach element• Low watts lossesLow watts losses• Designed and tested to IEC831 parts 1 & 2Designed and tested to IEC831 parts 1 & 2

Main characteristics:Main characteristics:

• 5 to 100kVAr - 230V to 690V5 to 100kVAr - 230V to 690V• Self HealingSelf Healing• Safety - EACH element fitted with 2 part Safety - EACH element fitted with 2 part

protection. Double insulationprotection. Double insulation• Tamper proof discharge resistors fitted to Tamper proof discharge resistors fitted to

each elementeach element• Low watts lossesLow watts losses• Designed and tested to IEC831 parts 1 & 2Designed and tested to IEC831 parts 1 & 2

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1978-1987 : dry metallised film (polypropylene) - external protection

Up to 1978 : Polychlorinated biphenyl (PCB)

Various materials used:

1987- : polypropylene - internal protection, thermo setting resin case

52

terminalsinternal fuse

• the fuse protects against the fuse protects against high current faults If > I fusehigh current faults If > I fuse

NOTE : OPERATES ONLY FOR NOTE : OPERATES ONLY FOR HIGH CURRENT SHORT TIME HIGH CURRENT SHORT TIME FAULTS (EFFECTIVE Isc)FAULTS (EFFECTIVE Isc)

53

terminalsOpen circuit

54


discharge resistor

• resistor reduces voltage resistor reduces voltage to less than 50 V in 1 to less than 50 V in 1 minuteminute

• protection against protection against direct contactdirect contact

55


overpressure bellow

metallic disk

discharge resistor

• Dielectric loses its self Dielectric loses its self healing propertyhealing property

Gas pressure increases Gas pressure increases slightly and reaches the slightly and reaches the bellowsbellows

• the bellows risethe bellows rise

• the metallic disc short the metallic disc short circuits the terminals across circuits the terminals across the fusethe fuse

• faulty element taken out of faulty element taken out of serviceservice

56

terminals

• the bellows risethe bellows rise

• the metallic disc short the metallic disc short circuits the terminals across circuits the terminals across the fusethe fuse

• faulty element taken out of faulty element taken out of serviceservice

57

terminals

overpressure bellow

plastic case

resin

gas release channel

internal fuse

coil

metallic disk

discharge resistor

58

2 physical sizes

Varplus M1 (1 row of capacitors)

Varplus M4 (4 rows of capacitors)

Up to 16 kVAr at 470V (12.5kVAr @ 415V)

60 kVAr at 470V (50kVAr @ 415V)

59

2 physical sizes

4 kVAr 16 kVAr 1 18 kVAr 1 1 111 kVAr 1 2 2

212.5 kVAr 2 1 2 250 kVAr

kVAr 15 22 25 26 30 31 33 75

ModularitykVAr ratings shown at 415V

1TotalMaximum total combination at 415V is 100kVAr

60

Easy connections total access to the terminals moulded terminal housings maintains phase separation between cables minimum connection length to the contactor Easy mounting same fixing locations for all range vertical mounting - optimum space efficiency - good heat dissipation - optimisation of cubicle space

61

Capacitors are usually affixed to a mounting plate before connection inside a switchboard.

62

Each functional plate unit consists of the following:

Fuses or circuit breakers

Fuse connections

Contactors

Capacitors

To switch the capacitor steps

To connect to main busbars

To protect the unit

63

Capacitors Fuses

Mounting plate

ContactorConnections

Circuit breaker

64

Selecting functional plate components:

• Equipment (cables, fuses and circuit breakers) rated to at least 1.5 times the full load current

• LC1D*K contactors are especially made for capacitor switching applications.

• fitted with a premake power block which includes damping resistors.

• inrush current is limited to a maximum of 80 times the nominal current .

65

R6 - 6 step relay

R12 / RC12 - 12 step relay

66

Functions of the control relay:

•Monitoring:voltage, current, power, power factor, connected steps, temperature, total harmonic distortion.

•Regulation:capacitor step switching

67

MERLIN GERINrectiphasevarlogic R6

+-

esc. ent.

0.99


+-

esc. ent.

0.994 -

C/K auto2 -

1 -

3 -

7 -

6 -

nº steps5 -

8 -

0,96+(2s)

manual stepping

-

+

-

+

1 - - 42 - 53 - 6

esc.

ent.

ent.

cos steps

4 -

C/K auto2 -

1 -

3 -

7 -

6 -

nº steps5 -

8 -

0,96+(2s)

manual stepping

-

+

-

+

1 - - 42 - 53 - 6

esc.

ent.

ent.

cos steps

A1

A2

A5

A4

A3

low power factor

hunting

abnormal cos fi

undervoltage

capacitive cos fi

A6

A7 overcurrent

A8 overvoltage

I.Lo low load current

I.Hi high load current

frequency not detected

A1

A2

A5

A4

A3

low power factor

hunting

abnormal cos fi

undervoltage

capacitive cos fi

A6

A7 overcurrent

A8 overvoltage

I.Lo low load current

I.Hi high load current

frequency not detected

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+-

esc. ent.

0.99


+-

esc. ent.

0.99

C/K auto

nº steps

0,96+(2s)

manual stepping

-

+

-

+

1 - - 42 - 53 - 6

esc.

ent.

ent.

cos steps

1

2

4

5

6

7

8

3

Set target cosC/K ratio auto searchC/K ratio manual inputManual steppingNumber of stepsStep programVoltage connectionDelay

69

nº salidas

-esc. + ent.

MERLIN GERINrectiphasevarlogic RC12

elección cos

1 2 3 4 5 6

7 8 9 10 11 12

+-

nº salidas

-esc. + ent.

MERLIN GERINrectiphasevarlogic RC12

elección cos

1 2 3 4 5 6

7 8 9 10 11 12

+-

• Measurement

• Commissioning

• Programming

• Alarm

• Maintenance

Available modes

70

Measurement Mode

Total harmonic distortion

Step status

Reactive current

Load current

71

Commissioning Mode

C/K auto

Interface language

C/K manual

CT ratio

Manual override

Target cos

72

Programming Mode

Connection type

Capacitor loss setup

Delay

Phase polarity detection

Input voltage

Step program

Number of steps

Step configuration

73

Alarm Mode

Activate and de-activate alarms

Maintenance mode

Settings - programming of alarm thresholds

Measurements

Bank test

capacitors

Documents

fuse faulty

power factor

reactive power

power factor

real power

apparent power

detuning reactors

bellows rise