Design of LV Capacitor Banks
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Transcript of 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
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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
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Capacitor bank drawing
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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
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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
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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
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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
1.1.2.2.2.2 = 1+1+2+2+2+2 = 10 electrical steps with 6 outputs of the regulator used
1.2.4.4.4.4 = 1+2+4+4+4+4 = 19 electrical steps with 6 outputs of the regulator used
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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
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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
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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
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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
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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
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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
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Ventilation calculation
Standard and overrated types : example
• 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)
• system voltage : 400V 50Hz, IP=3X Q = 600 kvar Fan calculation (m3/h) = Q/2 => fan needed = 300 m3/h
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Ventilation calculation
detuned type
• 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 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)
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Ventilation calculation
Detuned type : example
• 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 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
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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
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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
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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
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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
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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
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Capacitor bank installation - Best practices
CT location Temperature Regulator setting CB