11 EMERGENCY LIGHTING
14 POWER FACTOR CORRECTION
14.1 General
14.1.1 Cross References General
Comply with the General Services Requirements section.
Related sections
Refer to the LV Switchboards section.
14.1.2 Standards
IEC 60831 (1-2) Power factor correction capacitors IEC 60664 and Power factor regulator
IEC 1010-1 General Safety Requirements for Electrical Equipment for Measurement, Control, Laboratory Use.
IEC 600070 Capacitor switching contractors
IEC 60831 Shunt power capacitors of the self-healing type for a.c. systems having a rated voltage up to and including 1000V
IEC 60871 Shunt power capacitors for a.c. systems having a rated voltage up to and including 1000V
IEC 60289 Detuned reactors IEC 60076 Power Transformers
IEC 61921 Low voltage power factor correction banks BS 88 Cartridge fuses for voltage up to 1000 V ac
BS 1650 Capacitors for connection to power frequency system BS EN 60947 Control gear for voltage up to 100V ac
Local Supply Authority specifications for Power Factor Correction
14.2 General Requirements
The power factor of every installation shall be controlled to between 0.95 lagging and unity.
The power factor correction capacitors shall be installed as close to the load as possible.
Power factor correction capacitors shall be provided with a means of prompt discharge on disconnection of the supply voltage. The discharge circuit shall be permanently or automatically connected to the capacitor. Manual means of switching or connecting the discharge circuit shall not be permitted.
For automatically regulated group compensation capacitor banks, the rating each capacitor step shall be such that the initial steps shall have less kVAr rating and the rating of subsequent steps shall be increased progressively to the desired maximum kVAr.
For induction motors the capacitor rating may not exceed 90% of the no load reactive power of the motor.
The occurrence of harmonics in circuit can lead to disturbance in the system and may cause capacitor failure. In order to eliminate or reduce these risk harmonic filters should be employed in series with capacitors.Capacitor shall be able to withstand up to 30 times In caused by harmonics.
Contactors shall be designed for capacitive switching and shall be able to withstand switching surges.Contactors shall be rated for 1.5 to 1.8 times the normal rated current of the capacitor and shall isolate all three phases on switch off.
Each capacitor step shall be protected by means of HRC fuses (current limiting type).
Capacitor shall not be a part of the motor control centre, main LV Panel or submain panel; it hall be accommodated in a separate cubical.
The capacitor panel must be provided with a suitably rated main incomer isolating switch. This shall be a three-pole isolator or MCCB. The handle of the incomer isolator shall be interlocked with the door to ensure that the capacitor bank is de-energized when the door is open.14.3 System Parameters
Rated phase to phase voltage: 400V +10% -10%
Number of phases: three System connection: delta Rated insulation voltage: 500V Rated frequency: 50Hz
Maximum prospective fault level and terminals: 50kA for 1 second Maximum step size: 50kVAr
Maximum cubicle rating: 300kVAr
Capacitor operating losses: Not exceeding 0.5W/kVAr
14.4 Components
14.4.1 Capacitors
Each capacitor bank: reactive power as specified.
Provide individual capacitor units in robust, sealed metal containers of adequate strength to successfully contain an internal electrical disturbance with minimal damage to adjacent units.
Fix insulator bushings to the container such that the unit is able to satisfactorily withstand system disturbances to the fault level specified.
Provide capacitor units comprising only materials which do not present a fire or health hazard under normal operating or fault conditions.
Provide discharge resistors to ensure the safe discharge of each capacitor unit and ensure that the discharge to earth does not cause operation of earth fault protection systems.
Self-healing design with non PCB type.
Capacitor compartment designed so that there is sufficient heat dissipation at the specified ambient temperature to ensure that the hottest element temperature is insufficient to reduce capacitor life.
Connect all the capacitor unit casings together and to the earth bar.
14.4.2 Capacitor Protection
Protect each capacitor bank against short-circuits by fuses.
For all fault currents above the short-circuit rating of the contactor use the fuses to provide the protection.
Co-ordination between the contactor and fuses: type C.
Discriminate with the fuses at the supply disconnect device.
Include with the fuses devices to automatically open all three phases when a fuse blows on any one phase.
Provide fuses and other equipment with sufficient thermal capacity to cope with the transient overcurrent when the capacitors are switched.
Over current relay to be provided in capacitor bank.
14.4.3 Reactors and Harmonic Filters
Provide power factor correction equipment able to accommodate the levels of harmonics that are likely to exist at the site in particular the levels of non-linear loads.
Comply with IEC 61000 for the maximum harmonic loads resulting from the application of the capacitors.
Provide detuning reactors for each capacitor bank to reduce switching inrush and provide suitable filter circuits for suppression of harmonic voltages and currents in the installation to avoid excessive overloading of the capacitors. Incorporate detuning reactors in an adjacent cubicle with separate ventilation system.
Detuning reactors shall be selected and installed based on the load characteristics of the installation.
As follows:
They shall be made from high conductivity copper windings with a high quality grain oriented steel core.
The construction shall be secure to minimise the noise generated even in the presence of harmonics.
The reactors shall be rated at 160% continuous at 40oC. Class f insulation is preferred.
The flux density at rated current shall be less than 0.8 tesla.
The reactors shall be of low loss design with a Q factor greater than 10.Provide blocking inductors for Local Supply Authority ripple control signalling to the requirements of the Local Supply Authority.
14.4.4 Reactive Power Control Relay
The reactive power control relay shall be suitable for control of the specified capacitor banks including those for the future without hunting.
The relay shall provide the following features:
Microprocessor control.
Built-in cos ø control digital display.
Cyclic operation to provide uniform working duty for all capacitor stages.
Programmable stage ratios for all standard capacitor stages.
Characteristics of power factor correction such that cos ø is programmed as a limit value in the upper load range while over-correction is avoided in the light load range.
Phase sequence display for three-phase connection.
Five different switching time delays.
Unoccupied stages cannot be switched on or off.
LED's on the front panel to show deviations from the set control characteristic.
Foil keyboard insensitive to contamination.
Approved safety feature to prevent inadvertent or unauthorised reprogramming.
All preset values are safely stored by a non-volatile EEPROM memory for mains failure.
Fault signal contacts.14.4.5 Display Modes
A built in digital display shall, as selected, show:
Number of stages connected
Actual power factor
Active current
Reactive current14.4.6 Manual Operation
The reactive power control relay shall be capable of manual operation to enable the correct switching and current draw of each capacitor bank to be checked.
14.4.7 Terminal Strips
All secondary wiring connections which run externally to the power factor correction cubicle shall be brought to a terminal strip to facilitate easy connection. Terminals for alarm monitoring by the BMCS are to be coloured blue.
14.4.8 Alarms and Indication
Provide an alarm in the form of a lamp, easily visible from the front of the cubicle, for each of the following: