General Design Guidelines
1.1 Ratings
1.1.1 The capacitor bank should be rated for three-phase service for power factor correction at the voltage level specified on the electrical single-line diagram.
1.1.2 Power capacitor banks should be designed to withstand the specified voltage rating, electrical short circuit rating, and continuous current rating mentioned on the electrical one-line diagram and/or data sheet.
1.1.3 The ratings of the bank and associated switchgear, switching devices, capacitors, fuses, and all other applicable components should meet the required specifications.
1.1.4 The temperature limits for insulation materials should be as required.
1.1.5 Total Harmonic Distortion (THD) should comply with IEC 61000-2-4.
1.2 Enclosures, Bus Works, and Arrangement
1.2.1 The enclosure should be a freestanding type, utilizing a modular design with provisions for expansion. The capacitor cells, contactor, controller, and related equipment should be mounted in the same enclosure to minimize field installation.
A capacitor bank should have a single compartmentalized enclosure construction that houses all components, including fuses, capacitors, and unbalance detection circuits.
1.2.2 The enclosure should have an IP42 rating for indoor use. Standalone enclosures for capacitor banks should include the following:
a. The enclosure should comply with Impact Code IK 07 as per IEC 60529.
b. All ventilation louvers should be located on the front of the enclosure and backed with a stainless steel mesh.
c. The enclosure should have front access with removable side and back panels.
d. The internal space should be sufficient for maintenance.
e. The required number of removable lifting eyes should be mounted on top of the enclosure to properly support the equipment during lifting and installation.
1.2.3 Buses should be designed with sufficient current density, tin-plated copper, and insulated for continuous rating.
1.2.4 All flexible power cables should have stranded copper conductors and should be installed in accordance with IEC 61936-1 and IEC 60364 (series).
1.2.5 A door-mounted on/off switch should be provided to de-energize control power to all door-mounted control devices and indicating lights.
1.2.6 The main fuse or circuit breaker compartments and capacitor compartments should be equipped with wide-view windows. These windows should be constructed of impact-UV-resistant material to facilitate checking the mains, capacitors, and capacitor fuses without opening doors or de-energizing the bank, and for infrared (IR) monitoring using an infrared camera.
1.2.7 The base of the enclosure should be equipped with structural steel channels.
1.2.8 All bus insulators and bus bar inserts should utilize either wet-process glazed porcelain or cycloaliphatic epoxy material. Furthermore, the bus insulation, except at the joints, should be bonded to the bus bar and should be either liquid dipped or fluidized bed epoxy. The insulating materials for buses and connections should be flame-retardant, non-hygroscopic, and track-resistant throughout.
1.2.9 All bolted power bus connections should be secured with corrosion-resistant, silicon-bronze hardware, including bolts, locking washers, nuts, or jam nuts. Connections should be made with a minimum of two bolts.
1.3 Capacitor Cells
1.3.1 Capacitor elements rated up to 1000 Volts should be constructed with a polypropylene film dielectric system with self-healing metallized electrodes.
For automatic capacitor banks rated above 1000 volts, all-film, low-loss, double-bushing capacitors should be provided. Capacitors rated above 1000 volts should be designed, manufactured, and tested in accordance with all applicable IEC standards.
1.3.2 Capacitor cells should be furnished with a Pressure Sensitive Interrupter (PSI).
1.3.3 Each capacitor unit and/or bank should be provided with a means to discharge each unit in 3 minutes to 75 V or less, from an initial peak voltage of √2 times the rated voltage (UN) for capacitors rated up to and including 1000 Volts. Refer to IEC 60832-1 for more details.
Each capacitor unit should be provided with means to discharge to 75 V or less from an initial peak voltage of √2 times the rated voltage (UN). The maximum discharge time for capacitors rated 1000 Volts and above is 10 minutes. Refer to IEC 60871-1 for more details.
1.3.4 The capacitor cells should be impregnated with a biodegradable material. The capacitor dielectric fluid should have superior electrical and chemical characteristics with at least 5 years of proven field experience.
1.3.5 The capacitor cells should be designed to withstand the duties described in IEC 60831-1, IEC 60871-1, and IEC 60931-1.
1.4 Controls and Protection
1.4.1 All controls and protection devices should be installed indoors.
1.4.2 The capacitor cells, fuses, and switching contactor or vacuum switches or vacuum circuit breakers (VCBs) for each step of the capacitor bank should be mounted on a removable tray for ease of removal and replacement. The contactor switching duty should comply with IEC 60831-1 and 60931-1.
1.4.2 Vacuum switches or VCBs can be used for switching the Medium Voltage Capacitor Banks, complying with IEC 608771-3.
1.4.3 When required, a door-mounted, solid-state, multi-step, and adjustable power factor controller should be provided. This controller should automatically switch the steps in and out to provide power factor correction to a desired set point. As a minimum, the following features should be included with the door-mounted controller:
a. Manual/Automatic selector switch.
b. Microprocessor-based adjustable control.
c. Adjustable target power factor setting from 0.8 inductive (lagging) to 0.95 capacitive (leading).
d. Adjustable switching time delay from 10 to 60 seconds.
e. Fault signaling output relay if the target power factor is not reached.
f. Continuous front panel displays indicating which steps are on.
g. Digital display of actual power factor.
h. No volt release of all output contacts when the supply voltage has been interrupted for 35 milliseconds. This serves to protect the capacitors after the power has been restored.
i. Rotational switching programs to ensure that the steps are used equally. The first step turned on should be the first step turned off.
1.4.4 Current limiting fuses should be provided on all three phases of each step, complying with IEC 60931-3 or IEC 60871-4, as applicable.
1.4.5 Contactors should be IEC-rated in accordance with IEC 60831-1 or 60871-2.
1.4.6 A voltage transformer of suitable rating should be provided for control power and voltage sensing. Protection should be provided with two primary current limiting fuses and one secondary current limiting fuse.
1.4.7 Automatically switched capacitor banks to improve power factor should meet the requirements of the applicable standards.
1.4.8 The automatic capacitor bank should be provided with