Design of LV Capacitor Banks

Guide for the design and production of LV compensation cubicles

Rectiphase/REC11EN-08/99 2

Design rules and critical parameters

In addition to the general design rules applicable for electrical panels, specific recommendations have to be followed for capacitor assembling and installation

capacitor units installation power factor relay settings contactor specification reactors characteristics and location air cooling system efficiency capacitor bank protection capacitor bank - routine test preventive - corrective - maintenance


Capacitor units installation

• wrong position • correct position

The capacitor units must be installed in a position so that natural air cooling is efficient. In addition, a minimum 25mm distance is required between two capacitor units


Capacitor bank drawing


Varplus and temperature class The capacitor units are designed in order to withstand ambient

temperatures according to IEC 831 standard

(1) Ambient air temperature : temperature around capacitor only (not in the electrical room)

Assembling can modify the temperature category of the capacitor units

Symbol Maximum24 hours 1 year

A 40 30 20B 45 35 25C 50 40 30D 55 45 35

Highest average over all periods ofAmbient air temperature °C (1)

temperature class max

24 hours 1 year 230/240V 400/415V 440/470V 480/525V 550/590V 600/690V-25/D 55 45 35 up to 40 up to 65 up to 76 up to 85 up to 100 up to 100-25/C 50 40 30 41 to 50 67.5 to 90 77 to 100 86 to 100-25/B 45 35 25 51 to 60 92.5 to 100

ambient air temperature (°C) reactive power (kvar)highest average over all periods of


Power factor relay setting

The power factor relay supplies automatic settings

• insensitive to CT direction

• insensitive to phase rotation polarities

• automatic search of C/K The power factor relay requires several settings

• time delay : 50 sec minimum (compulsory)

• sequence : n, CA, CB, S

• CK : depends on the power of the smallest step and CT ratio

• cos phi targeted

Rectiphase OFFER2EN.PPT/01.99 7

Physical steps - Electrical steps : Explanations

Due to the switching programs of the regulator ( 1.1.1 , 1.1.2 , 1.2.2 , 1.2.4 ...... ) the number of electrical steps may be higher than the apparent number of capacitors

CA : All the steps have the same power (1.1.1) CB : Steps 2, 3 ..6 power = Twice step 1 power (1.2.2) n : Step 2 power = Step 1 power (1.1.2)

all others steps = Twice step 1 power n : Step 2 power = Twice step 1 power (1.2.4)

all others steps = Four time step 1 power


How to find the number of electrical steps ?

1.1.1.1.1.1 = 1+1+1+1+1+1 = 6 electrical steps with 6 outputs of the regulator used

1.2.2.2.2.2 =1+2+2+2+2+2 = 11 electrical steps with 6 outputs of the regulator used



Rectiphase OFFER2EN.PPT/01.99 9

Physical steps - Electrical steps : example

Rectimat 2 : 105 kvar

• electrical steps : 7*15 kvar

• physical steps : 15+30+60 kvar

• switching programs : 1.2.4= 1+2+4 = 7 electrical steps

Output powerkvar 15 kvar 30 kvar 60 kvar15 1 0 030 0 1 045 1 1 060 0 0 175 1 0 190 0 1 1

105 1 1 1

Physical steps


Contactor specification

Capacitor switching is followed by transient phenomena resulting from capacitor charging

Télémécanique LC1-D.K contactors have been designed for capacitor switching

Peak closing current

Oscillation frequency

Network voltage

Capacitor current

Capacitor voltage


Contactor solution

Standard contactor

• Inrush current > 200 In main contacts damagedcapacitor destruction

Télémécanique LC1-D.K contactor

• pre-insertion block (inrush current reduction)long life : 300 000 switching cycles -400V


Reactors characteristics and location

detuned type capacitor bank :overrated capacitor unit + detuned reactorstandard tuning level 215 Hz or 5.4%

As the detuned reactors generates heat, particular attention must be paid to :

• the location of these reactors separate compartments if possible (1)

• and the air cooling system a forced air cooling system is required

(1) If not, the reactors must be fitted above the capacitors


Air cooling system efficiency

Typical heating

• loose capacitors : 0.7 W/kvar

• standard and overrated range : 2.5 W/kvar

• detuning range : 7 W/kvar Joule losses for reactors

• DR : 12.5 kvar = 80 W

• DR : 25 kvar = 160 W

• DR : 50 kvar = 300 W

• DR : 100 kvar = 400 W


Ventilation calculation

Standard and overrated types

• maximum temperature : 40°C

• average temperature over 24 hours (electrical room) : 35°C

• average annual temperature : 25°C

• cubicle dimension : 2000 (H) x 400 (D) x 800 (L)

• system voltage : 400V 50Hz, IP=3X

(1) air inlet : Xcm² => air outlet = X x 1.1 cm²example : air inlet : 200 cm² => air outlet : 220cm²

Q ventilation air inlet(kvar) type air flow

90 natural 200 cm²180 natural 300 cm²210 natural 400 cm²

> 210 forced fan (m3/h)=Q/2



Standard and overrated types : example




• cubicle dimension : 2000 (H) x 400 (D)

• system voltage : 400V 50Hz, IP=3X Q = 600 kvar Fan calculation (m3/h) = Q/2 => fan needed = 300 m3/h



detuned type





• system voltage : 400V 50Hz, IP=3X detuned capacitor bank must be ventilated reactors have to be located either separate compartment or other

cubicle ventilation of capacitor cubicle : same rules as “standard and

overrated type ventilation of reactor cubicle

• air flow calculation => AF = 0,3 x DP

• DP : dissipated power (W)



Detuned type : example





• system voltage : 400V 50Hz, IP=3X Q = 300 kvar (50+50+2x100 kvar)

• ventilation of capacitor cubicle : 150 m3/h

• ventilation of reactor cubicle

– AF= 0.3 x DP

– DP = (300x2) + (450x2) = 1500 W

– AF= 450 m3/h


Capacitor bank protection

IN = Q/3/UIN = 60 kvar/3/400V = 86.6 A

When set of fuses protects two steps => coefficient : 1.41IN

Ith : 10IN

1.6 IN

1.6 IN

1.5 IN

Standard type

Overrated type

DR type (6.9%)tuning 3.8

DR typetuning 4.3 (5.4%)

1.36 IN

1.5 IN

1.19 IN

1.31 IN

Circuit breaker rating Fuse HRC rating


Capacitor bank - Routine test

Dielectric test : 2500V 50Hz 1minTest done between 3 phases short circuit and earth (insulation measurement can be done under 500V with R>1000 ohms/V

Conformity (drawing, list of components)Visual aspect (wiring, IP, panels…)

Control wiring test (eventually) test report


Preventive / Corrective - Maintenance

General information

• activity of the plant

• capacitor bank description and pictures/drawing Ambient conditions

• temperature (room and capacitor bank)

• harmonic pollution Power factor relay checking

• time delay

• C/K contactors used (specifics, loop of cables…) auto/ON/OFF selector


Harmonic pollution - Assessment and solutions

GH : total power (kvar) of harmonic generator

SN : nominal power of the transformer (kvar)

S : apparent power consumed during measurement

calculation measurement

Standard rangeGH

------ 15%SN

SThd (A) x ------- < 5%

SN

Overrated rangeGH

15% < ----- 25%SN

S5% < Thd (A) x------ 10%

SN

Detuned rangeGH

25% < ------ 60%SN

S10% < Thd (A) x----- < 20%

SN


Capacitor bank assembling - Best practices

Respect of discharge of capacitor (fix and automatic) Temperature (capacitor, electrical room) Reactors and capacitor location Harmonic pollution Capacitor switching


Capacitor bank installation - Best practices

CT location Temperature Regulator setting CB

Documents

Design of LV Capacitor Banks