IEC 44 : Part 1 : Specificationfor current transformers.
IEC 255: Electrical relays.
IEC 269: LV fuses.
IEC 289: Reactors.
IEC 529: Degrees of protection provided by enclosures (IP Code).
IEC 831: Shunt power capacitors of the self healing type for a.c. systems having rated voltage up to and including1 kV.
IEC 947 : Low-voltage Switchgear and control gear
BS 381C : Specification for colors for identification, coding& special purposes.
BS 1361 : Specification for cartridge fuses for a.c. circuitsin domestic and similar premises.
BS 3382 : Specification for electroplated coatings on threaded components.
BS 3692 : Specification for ISO metric precisionhexagon bolts, screws and nuts.Metric units. (ISO272)
BS 6231 : Specification for PVC-insulated cables for switchgear and control gear wiring.
BS EN 22063 :Specificationfor sprayed metal coatings.
ISO 1461: Hot dip galvanized coatings on fabricated ferrous products.
1. General system design data
Nominal system voltage
System earthing: 0.4 Kv
a. Impulse withstand voltage at 1.2/50 µs
b. One minute power frequency withstand
Maximum site ambient temperature
Minimum site ambient temperature
Maximum site relative humidity at 30 Cº
Maximum site solar radiation
Site pollution conditions (IEC 815):
2. Design data for LV capacitors.
Capacitor Bank kvar ratings
specified in schedule A
Enclosures doors with the door closed
Rated nominal voltage Un
0.4 kV ±10%
Insulation level for 1 min
Dry, self healing.
Short circuit level for 1 second
8h over voltage (in any 24 h period.)
30 min over voltage (in any 24 h period.)
5 min over voltage (in any 24 h period.)
1 min over voltage
Continuous over-current .
1.3 times normal rated current.
to suit primary current rating.
Fuses & un-balance protection
Incoming cable entry
From two sides and bottom
(1) Capacitor Bank arrangement.
The capacitor equipment, unless being supplied in the LV distribution section of a Package Substation, It is mounted in a free standing enclosure designed for indoor/outdoor use. The scope of supply include, but not be limited to, the following:
a) Capacitor units, comprising several capacitor elements connected in a three phase arrangement enclosed in aluminum case, with their terminals brought out.
c) Switching devices to connect the capacitor sub-banks to the supply. The switching of the capacitors is in response to the changing reactive load.
d) Reactive power regulator and controller and associated cabling.
e) Protectionequipment and all associated cabling.
f) All CT’s required to implement the scheme.
g) All primary and secondary cabling.
(2 ) Capacitor Elements
The capacitors elements preferably are wound from a metallized polypropylene film dielectric to produce a dry type cell. The wound dielectric/electrode coil is contained within a suitable case with wired out connections. The case shall be flexible to accommodate changes in the internal pressure.
(3 ) Capacitor Units.
The single capacitor elements are assembled into delta connected groups of 3, as many groups of 3 capacitors being connected to achieve the required capacitance of the capacitor unit. The assemble group of capacitor elements is contained within aluminumcase with the terminals brought out through bushings. The bushings are of well processed porcelain or cast resin, approved for outdoor use at continuous voltage, and hermetically sealed to the aluminum case. The terminals are heavily tinned and are suitable for standard copper conductors. All capacitor units are provided with an insulating terminal cover.
v The clearance between two capacitor units is not less than 5 cm.
Discharge resistors are connected across the external terminals, which suitably rated to drain the residual voltage to 50 volts within 60 seconds after the capacitor is disconnected from the supply. The containers shall be of aluminumsteel.
(4) Capacitor Sub-Banks
The capacitor bank is made up of a number of subbanks which can be switched onto the network to vary the amount of capacitance connected to it . The sub-bank is made up of one or a number of capacitor unitsas required making the required capacitance or kVA rating of the sub bank.
The total capacitance of the capacitor bank is such as to produce the kvar rating . The capacitor sub-banks have ratings of (10+15+20+25+25+25+40+40+40+40+40+40) kvar for capacitor banks rated at 360 kvar ,
(5) Internal protection.
Self-healing dielectric: this is a result of the characteristics of the metal deposit which forms the electrode and the nature of the insulating support (polypropylene film).
This manufacturing techniqueavoids blowing the capacitor due to over voltages. The dielectric is perforated when over voltage occurs, causing discharges which vaporize the metal aroundthe short circuit and instantaneously restore electrical insulation.
Over pressure disconnecting device: if an electrical fault cannotbe overcome by the self- healing dielectric. Gas is emitted, deforming a membrane and taking the defectivecoil out of the circuit.
(6) External Fuses.
Each capacitor sub bank will be protected by fuses located externally to the capacitor units.
External fuses are in accordance with IEC 269 and protect the sub bank against faults not clear by the internal fuses such as faults on the bushings of capacitor units.
The fuse is capable of withstandingthe inrush current, as may be modified by any inrush current limiting devices provided on the sub bank, and also withstand the surge current from capacitors due to an external fault.
(7) Moulded case circuit breakers.(MCCB)
If a Moulded Case Circuit Breakers (MCCB) is used as the mains supply isolator to the capacitor bank then it’s circuit breaker mechanisms are of the trip free pattern to prevent closing the breaker onto a faulty circuit, and are engraved to indicate ‘ON/OFF’ position and rated current.
The MCCB ensure protection against circuit overloads and against short circuits bymeans of electronic protection thermal and instantaneous magnetic trips.
All MCCB can be adjustable to rated current of capacitor bank thermal protection.
Adjustment range (0.5 ÷1 ) In
magnetic protection adjustment range (2 ÷ ≥10) In .
The MCCB has the feature to limit the fault current to the rating of the MCCB.
for capacitor banks rated at 360kvar, the rated current for MCCB 800A, ICU ≥ 65KA
ICS ≥ 50% ICU for all MCCB.
(8) AC Magnetic Contactors.
Contactors used for power factor correction including limiting resistor to avoid inrush current
Contactors used for switching the capacitor sub-banks are designed to withstand the surge currents associated with capacitive switching. Provided to prevent manual operationof the contactor. Terminals and contacts are shrouded to prevent inadvertent finger contact.
All switchgear and protective devices and their connections are capable of carrying continuously 1.5 times the rated capacity of the capacitor unit to which they are connected, inaccordance with IEC 831 section6.
Operating voltage for coil of contactors 220 v ± 10% .
(9) Current Transformers : 5A with output 5 VA .
(10) Reactive Power Regulator.
The capacitor bank is equipped with reactive power controller which will detect and measure the reactive power on the LV network and initiate a control unit to switch the appropriate number of capacitor sub banks in or out. There has a manual on/off push button provided which will take control of the sub bank to allow switching to be under operator control. Indication and push buttons for manual operationof each sub bank are provided. The controller selects the sub bank to be switched in and means provided to vary the duty cycle to ensure a reasonable distributionof switching operations between different sub banks.
The system is designed to minimize disturbance on the system and to avoid hunting. The controller is automatically switch off the capacitor bank in the event of loss of the 20 kV supply and be capable of restarting the capacitor bank automatically on restoration of thesupply.
v The regulator measure and display the following ( active,reactive power, current, voltage, harmonies, power factor, frequency, capacitive load, number of stage in service………..).
v The regulator must protect the capacitor bank if the harmonies is equal or more than( 15 %).
v The regulator select the suitable capacitor unit to put it in service with regardingto ( work's hours and the required reactive power).
v The dimension of all the regulators are the same.
v Operating voltage 380 V with suitable protection.
v Regulator can be adjustment automatic and manual.
v C/k automatic no need program.
v Adjustment range (0.8….1 inductive, 0.9…..1 capacitive) acc. to IEC 61010-1 .
v Adjustment for time operation for range (5 …. ≥ 240 sec)
v Regulator can put the stages in operationafter select the power factor( no need
v Power consumption from voltage circuit ≤15 VA .
v Starting current ≤ 20 mA
(11) Capacitor Bank Enclosure
Each enclosure is to be fully complete with front hinged and lockable access doors and have side mounted cable entry chamber for dry type cable entry from below.
The enclosure is to comprise folded steel panels appropriately welded to ensure a rigid design is provided. If the enclosure is constructed of panels bolted to a weled steel frame, the frame must be hot dip galvanized to ISO 1461 to ensure long maintenance free life.