MV design guide - Schneider Electric
MV design guide - Schneider Electric
MV design guide - Schneider Electric
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Presentation<br />
Metal-enclosed,<br />
factory-built equipment<br />
Current<br />
Rated normal current: Ir (A)<br />
This is the rms. value of current that equipment can withstand when<br />
closed, without exceeding the temperature rise allowed in standards.<br />
The table below gives the temperature rises authorised by the IEC<br />
according to the type of contacts.<br />
Rated normal current:<br />
Type of mechanism Max. values<br />
of material<br />
Max. temperature Max. temp. rise<br />
of conductor (°C) = t°. max. - 40 °C<br />
contacts in air<br />
bare copper or copper alloy 75 35<br />
silver or nickel plated 105 65<br />
tin-plated 90 50<br />
bolted connections or equivalent devices<br />
bare copper, bare copper alloy<br />
or aluminium alloy 90 50<br />
silver or nickel plated 115 75<br />
tin-plated 105 65<br />
N.B.: rated currents usually used by Merlin Gerin are:<br />
400, 630, 1 250, 2 500 and 3 150 A.<br />
Examples:<br />
c For a switchboard with a 630 kW motor<br />
feeder and a 1 250 kVA transformer feeder<br />
at 5.5 kV operating voltage.<br />
v calculating the operating current<br />
of the transformer feeder:<br />
Apparent power:<br />
S = UIe<br />
Operating current: I (A)<br />
This is calculated from the consumption of the devices connected to the<br />
circuit in question. It is the current that really passes through the<br />
equipment.<br />
If we do not have the information to calculate it, the customer has to<br />
provide us with its value. The operating current can be calculated when<br />
we know the power of the current consumers.<br />
S 1 250<br />
I = = = 130 A<br />
Ue 5,5 • 1,732<br />
v calculating the operating current<br />
of the motor feeder:<br />
cosϕ = power factor = 0.9<br />
η = motor efficiency = 0.9<br />
P 630<br />
I = = = 82 A<br />
Uecosϕη 5.5 • 1.732 • 0.9 • 0.9<br />
8 Merlin Gerin <strong>MV</strong> <strong>design</strong> <strong>guide</strong> <strong>Schneider</strong> <strong>Electric</strong>