Medium Voltage Application Guide

ELECTRICAL SUPPLY
Glass fiber and plastic material shall withstand the operating temperatures and exposure to sunlight.
Appropriate measures shall be taken to prevent chemical deterioration of the contact surfaces.
MV SWITCHBOARD
1. The “metal enclosed” MV Switchboard under this contract shall comprise the panels as shown
on the drawings and / or schedules.
2. The switchboard shall comply with the latest issue of IEC 62271-1 and IEC 62271-200 and with
the nominated IP rating against the external environment
3. The switchboard shall be of the modular “metal enclosed” floor mounted, extensible type
equipped with circuit breakers, busbars. instruments. relays and all accessories as is described
in the specifications hereinafter and the Drawings.
4. All cubicles shall be of standard pattern and dimensions, robust in construction; dust and vermin
proof. and suitable for indoor use. The design of the cubicles and associated equipment shall be
such as to enable extensions to be made at either end.
5. The switchboard cubicles shall have separate compartments for the switchgear, busbars, cable
termination, relays and controls. The compartment shall restrict access to that area described
above only.
6. Pressure relief flaps shall be provided on the top of each HV cubicle to relief excess pressure
deeming an internal fault.
7. All circuit breakers or contactors shall be of the withdrawable isolating type. with the trucks
identical and interchangeable in every switchgear cubicle. A positive guide shall be provided for
the truck entry into the cubicle and clear indications given when the truck is at the engaged
position.
3.5 Busbar System
1. Busbars and electrical connections between pieces of apparatus shall be of electrolytic copper
and shall be sufficiently insulated from earth and from each other to withstand the specified high
voltage tests.
2. Busbars shall be air-insulated. All busbars shall be suitable for normal operations at rated
voltage, conditions and working environment without secondary insulation. The busbars,
connections and their insulated supports shall be of approved construction, mechanically strong,
and shall withstand all the stresses which may be imposed upon them due to fixing, vibration,
fluctuations in temperature, short circuits or other causes.
3. The busbars shall be so arranged that they may be extended in length without difficulty.
Connections shall be kept as short and straight as possible, and any joints shall not increase the
resistance of the connection. When dissimilar metals are connected, approved means shall be
provided to prevent electro-chemical corrosion.
4. The busbars and connections shall be so arranged and supported that under no circumstances,
including short circuit conditions, can the clearances from earthed metalwork or other conductors
be less than the distances required in the standards.
3.6 Circuit Breakers
1. CB’s shall be Vacuum type for new MV Switchboards. CB’s must comply with IEC 62271-100.
2. The CB breaking capacity shall be equal to, or greater than the busbar Isc.
3. The circuit breaker shall be of the trip free, vertical or horizontal isolation, horizontal drawout
carriage mounted type. The number of electrical and mechanical operations must be stated.
4. The various parts of the circuit breaker shall be of substantial construction, carefully fitted to
reduce mechanical shock during operation to a minimum and to prevent inadvertent operation
due to vibration or other causes.
5. The circuit breaker shall be arranged for trip free, independent manual operation.
6. The CB method of operation to be provided as part of the submission.
7. The circuit breakers shall have been subjected to impulse voltage tests for the rated voltage.
8. The circuit breaker shall be provided with automatic locking devices to lock the movable portion
of the unit in either the 'engaged' or fully 'isolated' position, The interlocking mechanisms shall be
provided to satisfy the following requirements:
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