Medium Voltage Application Guide
Medium Voltage Application Guide
Medium Voltage Application Guide
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SWITCHGEAR<br />
ANSI-defined switchgear<br />
ANSI defined switchgear is equivalent to IEC classification LSC2B-PM, with the following characteristics:<br />
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the main switching device is withdrawable, with disconnecting auxiliary control circuits<br />
separate compartments are provided for voltage transformers and control power transformers<br />
busbar compartments are divided between adjacent enclosures<br />
metal barriers isolate the withdrawable compartment, when the main switching device is drawn-out into<br />
test position<br />
main circuit busbars and connections are covered with fire resistant insulating material<br />
mechanical interlocking prevents stored energy discharge of withdrawable parts<br />
a locking method prevents the withdrawable switching device from being moved into service position<br />
low voltage control parts are segregated from medium voltage apparatus<br />
all voltage transformers must have primary circuit current limiting fuses<br />
Switchgear Ratings<br />
Switchgear is rated according to IEC 62271-1. When choosing switchgear, its rating must be sufficient for the<br />
electrical characteristics at the point of installation, the environmental conditions it needs to operate under, and the<br />
safety requirements. Future expansion of the switchgear distribution system needs to be considered, as this may<br />
affect initial rating requirements.<br />
Switchgear selection is determined by considerations including:<br />
Electrical conditions<br />
System operating voltage (U)<br />
System operating frequency (f)<br />
Nominal operating current (I)<br />
Short circuit current levels at point of installation (I SC , I dyn , etc)<br />
Horizontal busbar arrangement<br />
Environmental conditions<br />
Ambient temperature<br />
Altitude<br />
Pollution degree<br />
Indoor or outdoor installation<br />
Personnel safety considerations<br />
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Internal Arc Classification (IAC)<br />
Interlocking of access areas and switchgear apparatus<br />
Access method (eg tools, keys, process, etc)<br />
Withdrawable switchgear apparatus<br />
Switchgear information for enquiries or ordering<br />
When enquiring about, or ordering switchgear, the supplier should at minimum provide the following information.<br />
When enquiring, advise the supplier of any unusual operating condition requirements (eg altitude 1800 metres).<br />
System characteristics<br />
nominal system voltage and frequency<br />
expected highest voltage<br />
type of neutral earthing system<br />
Service conditions<br />
any non-standard service requirements which differ from normal routine<br />
Installation specifics<br />
indoor or outdoor installation<br />
number of phases<br />
busbar arrangement details<br />
rated voltage (U r )<br />
rated frequency (f r )<br />
Page 72 <strong>Medium</strong> <strong>Voltage</strong> <strong>Application</strong> <strong>Guide</strong> 710-12280-00A
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