LOW VOLTAGE POWER FACTOR CORRECTION EQUIPMENT

1 ) GENERAL

This articles specifies the requirements for the design , manufacture , testing of low voltage power factor corrections sets with all necessary ancillary equipment.
Three phase automatic power factor correction sets shall be installed indoor. Installation will be carried out by others and all relative information to enable the installation to be carried out efficiently shall be provided.

2 ) APPLICABLE STANDARDS

The design of the low voltage capacitor bank and accessories shall comply with the requirements of the latest current edition of following standards and with the specific requirements of this specification.

IEC60831 : Part 1&2- Shunt power capacitors of the self healing type for a.c systems having rated voltage up to and including 1 kV.

IEC 60439-1 : Low Voltage Switchgear and Controlgear Assemblies.

IEC 60947 : Low Voltage Switchgear
Part 2 : Circuit Breakers
Part 4 : Controlgear for voltages up to and including 1000 V a.c .

IEC 60269 : LV fuses.

IEC 60289 : Reactors

IEC 60529 : Degree of protection provided by enclosures ( IP code ).

3 ) DESIGN CONDITIONS

3-1 ) Ambient temperature

The LV capacitor banks shall be designed for the following ambient temperature inside the electrical room :
Maximum : 40°C
Average over 24 hours : 35°C
Annual average : 25°C .
Minimum : -5°C

In case of higher temperature, the components must be overrated.
With overrated components ( capacitors, reactors, fans ), the LV capacitor banks are able to withstand the following ambient temperature inside the electrical room :
Maximum : 50°C
Average over 24 hours : 45°C
Annual average : 35°C
Minimum : - 5°C

3-2 ) Altitude

The LV capacitor bank shall be designed to be installed at a maximum of
2000 m.

3-3 ) Humidity

The humidity withstand by the equipment shall be according to IEC 60439-1.

3-4 ) Site pollution conditions

The site pollution conditions shall be maximum class 3 according to IEC 60815

4 ) ELECTRICAL SYSTEM CHARACTERISTICS

4-1 ) Low voltage network system

Nominal system voltage : 400 or 415 V
Voltage tolerance ( 400 V ) : +/-10 %
Rated frequency : 60 Hz

4-2 ) Harmonic pollution

The capacitor bank shall be designed to withstand harmonic pollution and avoid harmonic amplification.
The following rules shall be taken into account.
Capacitor rated 400/415 V ( for 400 V network ) shall be used if the power of harmonic generator in kVA is lower or equal than 15 % of the power of the transformer.
Capacitor rated 470 V ( for 400 V network ) shall be used if the power of harmonic generator is between 15 and 25 % of the power of the transformer.
Capacitor rated 470 V with detuned reactors shall be used if the power of harmonic generator in kVA is between 25 and 50 % of the power of transformer.

5 ) POWER SUPPLIES

Power supplies for LV capacitor bank shall be :
400/415 V 3 phases , 60 Hz, 3 wire .
230 V single phase 60 Hz for control circuits, fans and anti-condensation heaters ( if there are ).

6 ) INSPECTION AND TESTING

Tests shall be performed at the manufacturer’s works in accordance with the relevant IEC standards .
The tests shall include :

Routine tests for capacitor bank :
Inspection for conformity with the specifications
Dielectric test on power circuit : 2,5 KV
Dielectric test on control circuit : 1 KV
The routine test for complete capacitor banks shall be carried out on an automatic. assembly line.
During inspection, routine test shall be carried out only on some samples ( 2 or 3 capacitor banks ).

Routine tests for capacitor :
Voltage withstand test between terminals ( 2 s )
Capacitance measurement
Loss angle measurement on similar capacitor
During inspection, routine test shall not be performed again.

Type tests for capacitor :
Type testing shall be only supplied for loose capacitors on similar capacitor. Type test certificate shall be issued by an independent test station of international repute.

Type tests for power factor controller and contactors.
Type test shall be supplied for power factor controller and contactors. Type test certificate shall be issued by an independent test station of international repute.


7 ) CAPACITORS

The capacitors shall be low-losses units, tested in accordance with IEC60831 part 1&2. Each element is to be of a dry self healing metallised polypropylene film and to be housed in an individual case.
A protection system shall be fitted to each element which shall comprise an HRC cartridge, an integral discharge resistor and an overpressure disconnect device.
Each element forming the three phase capacitor shall be fitted with an internal discharge resistor to ensure that the capacitor is discharged to a voltage not exceeding 50 V measured at the capacitors terminals, one minute after disconnection from the power supply.
The use of polychlorinated biphenols ( PCB ) and oil as capacitor impregnation is not acceptable.

The capacitor looses in Watts shall not exceed 0.7 W/kvar discharge resistor included.

7-1 ) Enclosure and connection

The group of element forming a three phase capacitor unit shall be installed in a plastic enclosure.
The capacitor shall be indoor type.
Each capacitor shall be provided with three terminal pads and shall not required earth connection.
7-2 ) Certification

The three phase capacitor shall be designed and manufactured in a ISO 9001 and ISO 14000 certified plant.

7-3 ) Technical data

Tolerance on capacitance value : 0, + 10 %.
Insulation level :
60 Hz , 1 minute withstand voltage : 6 kV
1.2 / 50 µs : 11 kV
Temperature class : - 25 / D

Surrounding temperature :
Maximum : 55 °C
Average over 24 hours : 45°C
Annual average : 35°C
Admissible current overloads : 30 %

Admissible voltage overloads :
8 h in any 24 h period : 10 %
30 min in any 24 h period : 15 %
5 min in any 24 h period : 20 %
1 min in any 24 h period : 30 %

8 ) POWER FACTOR CONTROLLER

The power factor controller shall be of the electronic type capable of switching capacitor contactors in 12 steps.
The technical specification should be as follows :
Connection type : Line to line or Line to neutral .
Connection features : Insensitive to CT direction / Insensitive to phase rotation polarity
Voltage input : 220 / 240 V
Voltage measurement :
Frequency : 60 Hz ( +/- 1 Hz )
Current input : CT …../ 5 A class 1 .
Step output contacts : 12,volt free contacts
Alarm output contact : 1 ,volt free contact
Momentary no voltage function : Disconnection of all steps after voltage greater than 15 ms, automatic reconnection
Step configuration programming : Fixed / Auto / Not used .

Information provide :
Cosine phi
Connected steps
Period before switching
Step output status ( capacitance loos survey )
Load and reactive current
Total voltage harmonic distortion
Voltage , temperature, Power ( S,P,Q)
Voltage harmonic spectrum ( 3,5,7,11,13 )

Alarms and warning :
Low power cosine phi
Hunting
Abnormal cosine phi
Overcompensation
Frequency not detected
Over current
Under voltage
Over voltage
Over temperature
Total voltage harmonic distortion
Capacitor overload
Power factor setting : Digital , 0.8 ind to 0.9 cap
C/K setting : Automatic search or manual setting
Accuracy class : 1.5 %
Display : 7 segments + l.e.d
Temperature : Working state 0 to 50°C

9 ) CONTACTORS

Contactors shall be used to switch capacitors in or out of service. They shall comply with IEC 60947 and shall have a rating suitable for the service required. The contactors should be provide with inrush limitation to reduce the magnitude of transient overvoltage to a safe level.
The contactors shall be LC1-D.K range or similar.
The pre-insertion resistances to limit the inrush current shall only be switched into circuit during the contactor closing and opening cycle. When the main contacts are closed, the resistances shall be disconnected. This limit the time the resistances are in circuit and the heat produced to give a long working life.
The electrical durability at nominal load shall be 300 000 operation cycles.

10 ) FUSES

The steps of the capacitor bank shall be protected by fuses. One set of fuses could be used to protect one or 2 steps maximum. Fuses shall be of the HRC cartridge approved type to IEC 60269. Fuse shall be correctly sized according the type offered.

11 ) REACTORS

Detuned reactors shall be used in case of harmonic pollution ( see chapter n°3 )
The detuned reactor shall be three phase iron core with aluminium or cooper winding.
The reactor shall comply with IEC 60289.

Tolerance : +/- 5 %
Tolerance between phase : Lmax/Lmin < 1.07
Tuning order : 4.3 ( relative impedance : 5.4 % )
Harmonic current spectrum for tuning order 4.3 :
I3 = 2 % I1
I5 = 69 % I1
I7 = 19 % I1
I11 = 6 % I1
Permissible overload fundamental current : 1.1 time the nominal current ( I1 ).
Insulation level : 1.1 kV according to IEC 6076
Test voltage ( coil to core ) : 3 kV 1 minute
Distance between terminals and earth : 20 mm
12 ) TRANSFORMER 400/230 V 60 HZ

A voltage transformer 400/230 V shall be used to feed the auxiliary supply.

13 ) CURRENT TRANSFORMER

The current transformer shall comply with IEC 6044 and shall be of 5 A output, class 1, 5 VA minimum.
The current transformer will be supplied by the contractor.

14 ) CABLES

13-1 ) Control cables

Small wiring shall be carried out in PVC insulated 750 V conductor and with core ferruled.
The cross section shall be minimum 1mm² .
The colours used shall be red, black, white, Yellow/Green .
Plastic clips shall be fitted at the end of the conductor to identify it.

13-2 ) Power cable

The power cable used shall be black PVC insulated 1000V , 1000V2K type.
No identification of each cable shall be done.

15 ) DESIGN FEATURES

The equipment shall be housed in a metal enclosure with an IP 31 protection degree.
The capacitor bank shall have a protection against direct contact when door is opened.
According to the reactive power and the ambient temperature the capacitor bank should be forced cooling.
The fan shall be controlled by a thermal probe.
The capacitor bank shall be made of compensation modules . Each modules are manufactured with capacitors, contactors and fuses. The modules shall be fully tested before being fitted inside the cubicle.
Each panel shall be fitted with an earth terminal in the form of a 10 mm diameter threaded bolt and fitted with two nuts and washers.

14-1 ) Design data

IEC standard : 60439-1

Protection degree : IP 21D, Indoor type.

Insulation level : 0,66 kV

Withstand 60 HZ , 1 minute : 2.5 kV

Short circuit level for 1 second : 25 kA

Gland plates : Un-drilled

Incoming cable entry : Bottom .
14-2 ) Enclosure thickness

The thickness of the metal sheet of the enclosure shall be 1.5 mm.
However some metal parts and devices inside the enclosure may have a lower thickness.

14-3 ) Surface treatment / Painting

14-3-1 )Surface treatment :
The metalic parts of the enclosure shall be :
washed at 40°C minimum to take of grease.
Rinsed in water.

14-3-2 ) Painting :
A power Epoxy/Polyester shall be applied with a minimum thickness of 30 microns.
Epoxy protects against chemical attack and polyester protects against mechanical attack.
The painting shall be polymerised into an oven.
Without any specific information or requirement the colour shall be the standard of the supplier.

14-4 ) Rating plate

Self-stick shall be fitted inside the cubicle with the following information :
Reactive power
Nominal voltage
Frequency
IEC 60439 standard compliance
14-5 ) Components identification.

Self-stick shall be used to identify each components fitted in the capacitor banks ( capacitors, contactors, power factor controller, fuses, reactors ( if there are ) ) .